February 2019 Volume 25, Number 1

ENVIRONMENTAL & ENGINEERING GEOSCIENCE

Environmental & Engineering Geoscience FEBRUARY 2019

VOLUME XXV, NUMBER 1

Volume XXV, Number 1, February 2019

THE JOINT PUBLICATION OF THE ASSOCIATION OF ENVIRONMENTAL AND ENGINEERING GEOLOGISTS AND THE GEOLOGICAL SOCIETY OF AMERICA SERVING PROFESSIONALS IN ENGINEERING GEOLOGY, ENVIRONMENTAL GEOLOGY, AND HYDROGEOLOGY

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Environmental & Engineering Geoscience

Environmental & Engineering Geoscience

Volume 25, Number 1, February 2019

Volume 25, Number 1, February 2019

Table of Contents

Table of Contents

1

Geological and Geotechnical Characterization of the Terrateig Dam in Valencia, Spain Francisco Javier Torrijo, Santiago Alija, Julio Garzón-Roca, and Mário Quinta-Ferreira

1

Geological and Geotechnical Characterization of the Terrateig Dam in Valencia, Spain Francisco Javier Torrijo, Santiago Alija, Julio Garzón-Roca, and Mário Quinta-Ferreira

15

Selection of Suitable Dam Axis Location Considering Permeability and Grout Curtain Optimization Mustafa Can Canoğlu

15

Selection of Suitable Dam Axis Location Considering Permeability and Grout Curtain Optimization Mustafa Can Canoğlu

27

Engineering Geology, History and Geography of the Pittsburgh, Pennsylvania Area Richard E. Gray, Brian H. Greene, Ryan W. Fandray, and Robert J. Turka

27

Engineering Geology, History and Geography of the Pittsburgh, Pennsylvania Area Richard E. Gray, Brian H. Greene, Ryan W. Fandray, and Robert J. Turka

Geological and Geotechnical Characterization of the Terrateig Dam in Valencia, Spain

Geological and Geotechnical Characterization of the Terrateig Dam in Valencia, Spain

FRANCISCO JAVIER TORRIJO*

FRANCISCO JAVIER TORRIJO*

Department of Geotechnical Engineering, Universitat Politècnica de València, Camino de Vera s/n, 46022, Valencia, Spain

Department of Geotechnical Engineering, Universitat Politècnica de València, Camino de Vera s/n, 46022, Valencia, Spain

SANTIAGO ALIJA

SANTIAGO ALIJA

Department of Geotechnical Engineering, Universidad Internacional de La Rioja, Avenida Gran Vía Rey Juan Carlos I, 41 28002 Logroño, Spain

Department of Geotechnical Engineering, Universidad Internacional de La Rioja, Avenida Gran Vía Rey Juan Carlos I, 41 28002 Logroño, Spain

JULIO GARZÓN-ROCA

JULIO GARZÓN-ROCA

Department of Geotechnical Engineering, Universitat Politècnica de València, Camino de Vera s/n, 46022, Valencia, Spain

Department of Geotechnical Engineering, Universitat Politècnica de València, Camino de Vera s/n, 46022, Valencia, Spain

MÁRIO QUINTA-FERREIRA

MÁRIO QUINTA-FERREIRA

Department of Earth Sciences, Geosciences Center, University of Coimbra, 3000-272 Coimbra, Portugal

Department of Earth Sciences, Geosciences Center, University of Coimbra, 3000-272 Coimbra, Portugal

Key Terms: Dams, Rock Mechanics, Karstification, Modeling, Foundations ABSTRACT The Terrateig Dam is a clear example of the importance of preliminary geotechnical analysis in establishing appropriate foundation criteria. A solution for dam foundations in soluble terrains using grouting is proposed. The work shows that grouting could reduce the uplift pressure on the foundation base, diminish the flow rate, and reduce or even eliminate any internal erosion. This paper presents the difficulties detected during the planning and execution phase of the Terrateig Dam, founded on a soluble substrate. Because dams are among the most significant kinds of engineering projects with regard to the construction of a sound foundation, an extensive and thorough campaign of field and laboratory testing was undertaken. In situ tests on the rock masses enabled the detection of karstification processes.

A finite element analysis, using geotechnical parameters determined during the geological investigation, was conducted to assess the suitability of consolidation grouting for counteracting karstification.

*Corresponding author email: fratorec@trr.upv.es

INTRODUCTION The Serpis River is one of the most important coastal rivers in the Valencia Province in Spain. For centuries, it has suffered flooding caused by peak flows from one of its main tributaries, the Vernissa (Figure 1). To solve this problem, a flood-control dam was planned in the Terrateig municipality. The objective of the dam is to control and regulate the water flowing into the Serpis from the Vernissa. The retention provided by this dam is intended to attenuate peak flows and therefore mitigate any downstream damage.

The Terrateig Dam is a category A, straight gravity dam, according to the classification of Penas et al.

(1996). It is 400 m long and 3 m wide at the crest, and it reaches a maximum height over the foundation of 26.5 m. The structure was designed to be semipermeable to water (i.e., it is not a storage dam), and it has design features that avoid pore pressure both in the core of the dam and in its foundations (Sumi, 2008).

The dam and its foundations were designed to resist unusual and extreme loads, including earthquakes.

This paper sets out the main geological and geotechnical characteristics of the Terrateig Dam foundations.

A general description of the dam construction and the geological and geotechnical problems encountered is also provided. Because dams are among the most significant kinds of engineering projects with regard to the construction of sound foundations (González and Ferrer, 2011), an extensive and thorough campaign of field and laboratory testing was undertaken to describe and characterize the foundation materials

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

1

Key Terms: Dams, Rock Mechanics, Karstification, Modeling, Foundations ABSTRACT The Terrateig Dam is a clear example of the importance of preliminary geotechnical analysis in establishing appropriate foundation criteria. A solution for dam foundations in soluble terrains using grouting is proposed. The work shows that grouting could reduce the uplift pressure on the foundation base, diminish the flow rate, and reduce or even eliminate any internal erosion. This paper presents the difficulties detected during the planning and execution phase of the Terrateig Dam, founded on a soluble substrate. Because dams are among the most significant kinds of engineering projects with regard to the construction of a sound foundation, an extensive and thorough campaign of field and laboratory testing was undertaken. In situ tests on the rock masses enabled the detection of karstification processes.

A finite element analysis, using geotechnical parameters determined during the geological investigation, was conducted to assess the suitability of consolidation grouting for counteracting karstification.

*Corresponding author email: fratorec@trr.upv.es

INTRODUCTION The Serpis River is one of the most important coastal rivers in the Valencia Province in Spain. For centuries, it has suffered flooding caused by peak flows from one of its main tributaries, the Vernissa (Figure 1). To solve this problem, a flood-control dam was planned in the Terrateig municipality. The objective of the dam is to control and regulate the water flowing into the Serpis from the Vernissa. The retention provided by this dam is intended to attenuate peak flows and therefore mitigate any downstream damage.

The Terrateig Dam is a category A, straight gravity dam, according to the classification of Penas et al.

(1996). It is 400 m long and 3 m wide at the crest, and it reaches a maximum height over the foundation of 26.5 m. The structure was designed to be semipermeable to water (i.e., it is not a storage dam), and it has design features that avoid pore pressure both in the core of the dam and in its foundations (Sumi, 2008).

The dam and its foundations were designed to resist unusual and extreme loads, including earthquakes.

This paper sets out the main geological and geotechnical characteristics of the Terrateig Dam foundations.

A general description of the dam construction and the geological and geotechnical problems encountered is also provided. Because dams are among the most significant kinds of engineering projects with regard to the construction of sound foundations (González and Ferrer, 2011), an extensive and thorough campaign of field and laboratory testing was undertaken to describe and characterize the foundation materials

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

1

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Figure 1. Terrateig Dam location map. The dam is located in the southern part of the Valencia Province (Spain), in the upper area of the Vernissa River, in Terrateig municipality.

(Jembere and Yihdego, 2016). This information was used to determine the geotechnical parameters of the Cretaceous limestone and dolomite bedrock in the foundation material. The elastic moduli of the materials were obtained using both direct methods (dilatometers, uniaxial compression tests with strain measurements, and ultrasonics) and empirical correlations (Bieniawski, 1984; Galera et al., 2005).

Sub-surface exploration revealed karstification in the foundation bedrock. Many authors have highlighted the geotechnical and hydrogeological problems that may occur with karstic rock masses and dams (Mather, 2013; Li et al., 2013; Han et al., 2015; Jiang et al., 2015; Mozafari and Raeisi, 2016; and Sopaci and Akgün, 2016). Merritt (1995) studied the geotechnical aspects of dam design and construction in soluble rock masses; Schaefer (2009) evaluated the risk of dams on karstic foundations; Gutiérrez et al. (2015) studied La Loteta Dam (Spain), located in a karstic depression generated by inter-stratal salt dissolution; Mozafari and Raeisi (2015) performed a hydrogeological 2

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

analysis of karst leakage at Kowsar Dam (Iran); and Milanović (2004, 2015) studied engineering problems associated with karst. Obviously, the karstification of the Terrateig Dam foundation needed to be investigated and treated. Consolidation grouting was planned, and a finite element model of the dam was developed to assess the effect of grouting on the karstification problem. Consolidation grouting involves injecting a grouting material into the discontinuities within a rock mass, with the aim of reducing the hydraulic gradient. The grouting is not intended to create a barrier (Yihdego, 2016), but to improve the mechanical performance of the dam foundations.

This study shows the importance of preliminary geotechnical analysis in establishing the appropriate foundation design criteria. The work also shows that dam foundation grouting can reduce the uplift pressure on the foundation base, diminish the flow rate, and reduce or even eliminate internal erosion.

analysis of karst leakage at Kowsar Dam (Iran); and Milanović (2004, 2015) studied engineering problems associated with karst. Obviously, the karstification of the Terrateig Dam foundation needed to be investigated and treated. Consolidation grouting was planned, and a finite element model of the dam was developed to assess the effect of grouting on the karstification problem. Consolidation grouting involves injecting a grouting material into the discontinuities within a rock mass, with the aim of reducing the hydraulic gradient. The grouting is not intended to create a barrier (Yihdego, 2016), but to improve the mechanical performance of the dam foundations.

This study shows the importance of preliminary geotechnical analysis in establishing the appropriate foundation design criteria. The work also shows that dam foundation grouting can reduce the uplift pressure on the foundation base, diminish the flow rate, and reduce or even eliminate internal erosion.

GEOLOGICAL FRAMEWORK

GEOLOGICAL FRAMEWORK

The Terrateig Dam is located between two major regional geological units in the Iberian Peninsula, the Prebetic (Betic System) and Iberian (Iberian System).

The most significant geological features are NW-SE– oriented monoclines with axial planes dipping approximately 30° NE, in addition to gentle slopes with N-S–striking normal faults (IGME, 1979; Vera et al., 2004).

The Vernissa River is the main tributary of the Serpis River: It dominates the eastern side of the hydrographic network and empties directly into the Mediterranean. The materials exposed in the vicinity of the river (Figure 2) include Cretaceous marine carbonates and Quaternary fluvial soils (IGME, 1979).

The former are Upper Cretaceous limestones and dolomites with intense karstification dominated by limestone pavement features and sinkholes, where dissolution and erosion have impacted the surface of a pre-existing karst landscape. Dissolution and corrosion along sub-horizontal layers in the carbonate rock mass have resulted in various microforms oriented in the same direction as the faults and discontinuities in the zone (Senís, 1990).

The Terrateig Dam is located between two major regional geological units in the Iberian Peninsula, the Prebetic (Betic System) and Iberian (Iberian System).

The most significant geological features are NW-SE– oriented monoclines with axial planes dipping approximately 30° NE, in addition to gentle slopes with N-S–striking normal faults (IGME, 1979; Vera et al., 2004).

The Vernissa River is the main tributary of the Serpis River: It dominates the eastern side of the hydrographic network and empties directly into the Mediterranean. The materials exposed in the vicinity of the river (Figure 2) include Cretaceous marine carbonates and Quaternary fluvial soils (IGME, 1979).

The former are Upper Cretaceous limestones and dolomites with intense karstification dominated by limestone pavement features and sinkholes, where dissolution and erosion have impacted the surface of a pre-existing karst landscape. Dissolution and corrosion along sub-horizontal layers in the carbonate rock mass have resulted in various microforms oriented in the same direction as the faults and discontinuities in the zone (Senís, 1990).

METHOD Geological and Geotechnical Investigation The geological investigation of the site involved the drilling of 16 coreholes (82 mm in diameter) and the generation of 12 geophysical profiles; these were all located in the section corresponding to the dam foundation (cross section A-A in Figure 2) or in its

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Figure 1. Terrateig Dam location map. The dam is located in the southern part of the Valencia Province (Spain), in the upper area of the Vernissa River, in Terrateig municipality.

(Jembere and Yihdego, 2016). This information was used to determine the geotechnical parameters of the Cretaceous limestone and dolomite bedrock in the foundation material. The elastic moduli of the materials were obtained using both direct methods (dilatometers, uniaxial compression tests with strain measurements, and ultrasonics) and empirical correlations (Bieniawski, 1984; Galera et al., 2005).

Sub-surface exploration revealed karstification in the foundation bedrock. Many authors have highlighted the geotechnical and hydrogeological problems that may occur with karstic rock masses and dams (Mather, 2013; Li et al., 2013; Han et al., 2015; Jiang et al., 2015; Mozafari and Raeisi, 2016; and Sopaci and Akgün, 2016). Merritt (1995) studied the geotechnical aspects of dam design and construction in soluble rock masses; Schaefer (2009) evaluated the risk of dams on karstic foundations; Gutiérrez et al. (2015) studied La Loteta Dam (Spain), located in a karstic depression generated by inter-stratal salt dissolution; Mozafari and Raeisi (2015) performed a hydrogeological 2

METHOD Geological and Geotechnical Investigation The geological investigation of the site involved the drilling of 16 coreholes (82 mm in diameter) and the generation of 12 geophysical profiles; these were all located in the section corresponding to the dam foundation (cross section A-A in Figure 2) or in its

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Geological and Geotechnical Dam Study

Geological and Geotechnical Dam Study

Figure 2. Geological map and profile of the Terrateig Dam. The geological-geotechnical plane and cross section show the relationship of the construction with the underlying Quaternary and Cretaceous strata. Also presented are the geological parameters and the position of the on-site exploratory drilling.

Figure 2. Geological map and profile of the Terrateig Dam. The geological-geotechnical plane and cross section show the relationship of the construction with the underlying Quaternary and Cretaceous strata. Also presented are the geological parameters and the position of the on-site exploratory drilling.

surroundings, in order to thoroughly characterize the materials in the area. The average borehole depth was approximately 25 m. The maximum depth reached was around 60 m.

The geotechnical characterization was based on the interpretation and statistical analysis of numerous field and laboratory tests, including: boreholes, trial pits, dilatometer tests, geophysical surveys, cross-holes, and geomechanical field stations. Lugeon tests were carried out to determine the permeability of the rock masses (Yihdego, 2017), and permeameter tests were performed on the sandy silts. These laboratory and in situ tests were undertaken in accordance with the American Society for Testing and Materials (ASTM) and UNE-EN standards.

surroundings, in order to thoroughly characterize the materials in the area. The average borehole depth was approximately 25 m. The maximum depth reached was around 60 m.

The geotechnical characterization was based on the interpretation and statistical analysis of numerous field and laboratory tests, including: boreholes, trial pits, dilatometer tests, geophysical surveys, cross-holes, and geomechanical field stations. Lugeon tests were carried out to determine the permeability of the rock masses (Yihdego, 2017), and permeameter tests were performed on the sandy silts. These laboratory and in situ tests were undertaken in accordance with the American Society for Testing and Materials (ASTM) and UNE-EN standards.

Seismic hazards were assessed on the basis of catalogued events around the project area as well as with reference to the Spanish Seismic Construction Code (NCSE-02, 2002). The intensity values and corresponding seismic accelerations for 100, 500, 1,000, and 3,000–5,000 year recurrence intervals were calculated using the deterministic method, according to the seismic hazard in the Valencia region and an uncertainty assessment.

Determination of Geotechnical Parameters The physical parameters of the different rock materials, i.e., the moisture (w), dry density (γd ), and porosity (n), were obtained directly in the laboratory.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

3

Seismic hazards were assessed on the basis of catalogued events around the project area as well as with reference to the Spanish Seismic Construction Code (NCSE-02, 2002). The intensity values and corresponding seismic accelerations for 100, 500, 1,000, and 3,000–5,000 year recurrence intervals were calculated using the deterministic method, according to the seismic hazard in the Valencia region and an uncertainty assessment.

Determination of Geotechnical Parameters The physical parameters of the different rock materials, i.e., the moisture (w), dry density (γd ), and porosity (n), were obtained directly in the laboratory.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

3

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Figure 3. Photos illustrating the laboratory strength test.

Figure 3. Photos illustrating the laboratory strength test.

The strength parameters, i.e., the uniaxial compression strength (UCS or σc ) and tensile compression strength (σtb ), were determined in the laboratory by both direct methods, including (Figure 3) uniaxial compression and indirect tensile resistance tests, and indirect methods by correlating Schmidt rebound hammer results obtained at the field test stations (Miller, 1965).

The rock quality designation (RQD) index (Deere, 1963) was determined for all the rock formations in the area. Moreover, for the most significant formation studied, comprising alternating micritic and brecciated limestone (C3 ), which is present throughout almost the entire area where the dam is located, the rock mass rating (RMR) index was also computed (Bieniawski, 1989). Shear strength parameters, i.e., cohesion (c) and angle of friction (�), were determined through empirical correlations with the RQD (González and Ferrer, 2011) and the RMR (Bieniawski, 1989).

Estimation of the Elasticity Modulus of the Rock Mass Various methods were used to determine the elastic moduli of the rock formations. The most direct were in situ dilatometer tests of the rock mass, and laboratory tests, including a UCS test to measure strain, and ultrasonic tests. In the case of the dilatometer tests, the moduli were read from the corrected curve (equal to the slope of the linear section of the curve corresponding to the elastic or pseudo-elastic phase). For 4

the laboratory methods, values given by both static (uniaxial compression) and dynamic (ultrasonic) tests were “strain moduli” values, which were subsequently transformed into elastic moduli using the correlations of González and Ferrer (2011) and Jiménez Salas and De Justo Alpañes (1975). It is interesting to note that the relationship between the static and dynamic moduli is quite variable, and according to data from the U.S. Bureau of Reclamation (Coon and Merritt, 1970), the ratio Estat /Edyn may range between 0.85 and 2.9.

Other authors, such as Matthews et al. (2000), set the ratio for intact rocks from 0.85 to 4.2.

Additionally, indirect methods based on empirical correlations were used to estimate the elastic moduli of the rock mass. Based on the RQD (or alternatively, on indices for the velocity of seismic waves), correlations can be established with the strain modulus of the rock mass, resulting in the Bieniawski reduction factor (Bieniawski, 1984). That factor is the ratio between the static modulus of rock mass obtained in situ (Ein situ ) and the modulus of intact rock measured in the laboratory (Elab ). Furthermore, Bieniawski (1978) also established a correlation between the strain modulus and the RMR index (intended for foundations): Em = 2RMR − 100(GPa).

(1)

This formula is suitable for RMR 50. Bieniawski himself recommended “appropriate engineering judgement” when using this formula. Later, it was modified

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

The strength parameters, i.e., the uniaxial compression strength (UCS or σc ) and tensile compression strength (σtb ), were determined in the laboratory by both direct methods, including (Figure 3) uniaxial compression and indirect tensile resistance tests, and indirect methods by correlating Schmidt rebound hammer results obtained at the field test stations (Miller, 1965).

The rock quality designation (RQD) index (Deere, 1963) was determined for all the rock formations in the area. Moreover, for the most significant formation studied, comprising alternating micritic and brecciated limestone (C3 ), which is present throughout almost the entire area where the dam is located, the rock mass rating (RMR) index was also computed (Bieniawski, 1989). Shear strength parameters, i.e., cohesion (c) and angle of friction (�), were determined through empirical correlations with the RQD (González and Ferrer, 2011) and the RMR (Bieniawski, 1989).

Estimation of the Elasticity Modulus of the Rock Mass Various methods were used to determine the elastic moduli of the rock formations. The most direct were in situ dilatometer tests of the rock mass, and laboratory tests, including a UCS test to measure strain, and ultrasonic tests. In the case of the dilatometer tests, the moduli were read from the corrected curve (equal to the slope of the linear section of the curve corresponding to the elastic or pseudo-elastic phase). For 4

the laboratory methods, values given by both static (uniaxial compression) and dynamic (ultrasonic) tests were “strain moduli” values, which were subsequently transformed into elastic moduli using the correlations of González and Ferrer (2011) and Jiménez Salas and De Justo Alpañes (1975). It is interesting to note that the relationship between the static and dynamic moduli is quite variable, and according to data from the U.S. Bureau of Reclamation (Coon and Merritt, 1970), the ratio Estat /Edyn may range between 0.85 and 2.9.

Other authors, such as Matthews et al. (2000), set the ratio for intact rocks from 0.85 to 4.2.

Additionally, indirect methods based on empirical correlations were used to estimate the elastic moduli of the rock mass. Based on the RQD (or alternatively, on indices for the velocity of seismic waves), correlations can be established with the strain modulus of the rock mass, resulting in the Bieniawski reduction factor (Bieniawski, 1984). That factor is the ratio between the static modulus of rock mass obtained in situ (Ein situ ) and the modulus of intact rock measured in the laboratory (Elab ). Furthermore, Bieniawski (1978) also established a correlation between the strain modulus and the RMR index (intended for foundations): Em = 2RMR − 100(GPa).

(1)

This formula is suitable for RMR 50. Bieniawski himself recommended “appropriate engineering judgement” when using this formula. Later, it was modified

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Geological and Geotechnical Dam Study

by Serafim and Pereira (1983) for all RMR: Em = 10

RMR−10 40

(GPa).

(2)

According to the U.S. Federal Energy Regulatory Commission (1999), “where RMR > 58, use the Bieniawski formula; where RMR < 58, use the SerafimPereira one.” In this work, we followed these criteria.

As a general rule, the geological strength index (GSI) can be calculated as (Sonmez et al., 2003): GSI = RMR89,basic dry − 5,

Geological and Geotechnical Dam Study

Table 1. Mean values of the orientation of the strata (Eo ) and the three sets of discontinuities (J1, J2, and J3) obtained in field studies of the alternating formations of micritic and brecciated limestone (C3 ).

Joints E0 J1 J2 J3

Dip Direction

Dip

184° 307° 126° 254°

20° 81° 83° 82°

RESULTS

discontinuities were observed (Table 1). This limestone rock mass can be considered blastable, with a vp between 2,500 and 6,000 m/s (Contreras and Santamaria, 1998).

(4) The fourth formation is a formation of alluvial deposits (Quaternary, Q2 ), comprising sands and silts with rounded riverbed pebbles. These materials are excavatable and have a low load-bearing capacity.

(5) The fifth formation consists of anthropogenic fills (Quaternary, R), composed of clay, sand, gravel, and aggregation fill from human activity. These occur sporadically.

Stratigraphic Characterization From the data collected in the geological investigation, the following five formations were identified (1) The first formation is a gray dolomite formation (Cretaceous, C1 ), characterized by complete or partial replacement of calcite by dolomite with grade 4 strength and grade II weathering (ISRM, 1981). The in situ geophysical tests revealed that the material was blastable, with a propagation velocity (vp ) between 5,000 and 6,000 m/s (Contreras and Santamaria, 1998).

(2) The second formation is a continuous level of beige-ocher calcarenites with intercalated partially cemented and heavily carbonated sandy silts (Cretaceous, C2 ), with oxide-stained discontinuities that have been smoothed by groundwater flow. It varies in thickness between 2.8 and 5.0 m and has strength grade 2 with grade III weathering (ISRM, 1981). This rock mass is considered rippable, with a vp between 1,500 and 2,500 m/s (Contreras and Santamaria, 1998).

(3) The third formation is a formation of alternating micritic and brecciated limestone (Cretaceous, C3 ) with intercalated reddish clay levels that are very firm and have a medium plasticity. This formation shows the most evident signs of karstification in the form of limestone pavements and karrens, with grade 4 strength and grade II weathering (ISRM, 1981). It is exposed over the entire study area. Marked stratification and three families of

Em = 10

RMR−10 40

(GPa).

(2)

According to the U.S. Federal Energy Regulatory Commission (1999), “where RMR > 58, use the Bieniawski formula; where RMR < 58, use the SerafimPereira one.” In this work, we followed these criteria.

As a general rule, the geological strength index (GSI) can be calculated as (Sonmez et al., 2003): GSI = RMR89,basic dry − 5,

(3)

where RMR89, basic, dry is understood to be the RMRbasic value of Bieniawski (1989) for dry rock mass conditions (since there is a 15 point penalty for a wet rock mass). After obtaining the GSI, the strain modulus of the rock mass (E) can also be calculated using the following formula (Hoek and Brown, 1997): σ 0.5 GSI−10 c · 10 40 , (4) E= 100 where σc is the UCS (given in MPa).

by Serafim and Pereira (1983) for all RMR:

Table 1. Mean values of the orientation of the strata (Eo ) and the three sets of discontinuities (J1, J2, and J3) obtained in field studies of the alternating formations of micritic and brecciated limestone (C3 ).

Joints E0 J1 J2 J3

Dip Direction

Dip

184° 307° 126° 254°

20° 81° 83° 82°

(3)

where RMR89, basic, dry is understood to be the RMRbasic value of Bieniawski (1989) for dry rock mass conditions (since there is a 15 point penalty for a wet rock mass). After obtaining the GSI, the strain modulus of the rock mass (E) can also be calculated using the following formula (Hoek and Brown, 1997): σ 0.5 GSI−10 c · 10 40 , (4) E= 100 where σc is the UCS (given in MPa).

RESULTS

discontinuities were observed (Table 1). This limestone rock mass can be considered blastable, with a vp between 2,500 and 6,000 m/s (Contreras and Santamaria, 1998).

(4) The fourth formation is a formation of alluvial deposits (Quaternary, Q2 ), comprising sands and silts with rounded riverbed pebbles. These materials are excavatable and have a low load-bearing capacity.

(5) The fifth formation consists of anthropogenic fills (Quaternary, R), composed of clay, sand, gravel, and aggregation fill from human activity. These occur sporadically.

Stratigraphic Characterization Hydrogeology The Valencia region has a Mediterranean-type river system notable for its highly irregular flow, on occasion leading to violent flooding, which is worsened by the deforestation of the catchment areas. The area under study falls within the Marchuquera-Falconera Aquifer of the Prebetic System No. 50.1, ValenciaAlicante (IGME, 1988).

The water table detected during the in situ tests was located at 140 m above sea level (m.a.s.l.). The permeability of the rock mass is controlled by fissuring and karstification. The different permeability tests (Olalla and Sopeña, 1991; González and Ferrer, 2011) showed that the C1 formation is permeable, with a hydraulic conductivity of 7.4 × 10−6 m/s, whereas formations C2 and C3 are very permeable, with values of 1.13 × 10−5 m/s and 3.04 × 10−5 m/s, respectively.

Seismotectonics The historical data collected revealed the occurrence of major earthquakes in the area (Giner et al., 2003), with intensities between VII and VIII (Medvedev-Sponheuer-Karnik [MSK] scale), associated with thrusting from the Alcaraz-Xátiva Arc. To the west of the dam area, there is a major seismogenic zone, where earthquakes of intensity VII and VIII have been recorded (Giner and Molina, 2001).

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

5

From the data collected in the geological investigation, the following five formations were identified (1) The first formation is a gray dolomite formation (Cretaceous, C1 ), characterized by complete or partial replacement of calcite by dolomite with grade 4 strength and grade II weathering (ISRM, 1981). The in situ geophysical tests revealed that the material was blastable, with a propagation velocity (vp ) between 5,000 and 6,000 m/s (Contreras and Santamaria, 1998).

(2) The second formation is a continuous level of beige-ocher calcarenites with intercalated partially cemented and heavily carbonated sandy silts (Cretaceous, C2 ), with oxide-stained discontinuities that have been smoothed by groundwater flow. It varies in thickness between 2.8 and 5.0 m and has strength grade 2 with grade III weathering (ISRM, 1981). This rock mass is considered rippable, with a vp between 1,500 and 2,500 m/s (Contreras and Santamaria, 1998).

(3) The third formation is a formation of alternating micritic and brecciated limestone (Cretaceous, C3 ) with intercalated reddish clay levels that are very firm and have a medium plasticity. This formation shows the most evident signs of karstification in the form of limestone pavements and karrens, with grade 4 strength and grade II weathering (ISRM, 1981). It is exposed over the entire study area. Marked stratification and three families of

Hydrogeology The Valencia region has a Mediterranean-type river system notable for its highly irregular flow, on occasion leading to violent flooding, which is worsened by the deforestation of the catchment areas. The area under study falls within the Marchuquera-Falconera Aquifer of the Prebetic System No. 50.1, ValenciaAlicante (IGME, 1988).

The water table detected during the in situ tests was located at 140 m above sea level (m.a.s.l.). The permeability of the rock mass is controlled by fissuring and karstification. The different permeability tests (Olalla and Sopeña, 1991; González and Ferrer, 2011) showed that the C1 formation is permeable, with a hydraulic conductivity of 7.4 × 10−6 m/s, whereas formations C2 and C3 are very permeable, with values of 1.13 × 10−5 m/s and 3.04 × 10−5 m/s, respectively.

Seismotectonics The historical data collected revealed the occurrence of major earthquakes in the area (Giner et al., 2003), with intensities between VII and VIII (Medvedev-Sponheuer-Karnik [MSK] scale), associated with thrusting from the Alcaraz-Xátiva Arc. To the west of the dam area, there is a major seismogenic zone, where earthquakes of intensity VII and VIII have been recorded (Giner and Molina, 2001).

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

5

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Table 2. Intensity on the Medvedev-Sponheuer-Karnik (MSK) scale, seismic acceleration (ac ), coefficient of horizontal seismicity (CHS), and coefficient of vertical seismicity (CSV) for different periods of recurrence measured in the Valencia region.

Table 2. Intensity on the Medvedev-Sponheuer-Karnik (MSK) scale, seismic acceleration (ac ), coefficient of horizontal seismicity (CHS), and coefficient of vertical seismicity (CSV) for different periods of recurrence measured in the Valencia region.

Earthquake Major earthquake Project earthquake Usual earthquake Basic earthquake

Recurrence Intervals (years)

Intensity (MSK)

Seismic Acceleration (ac ), g

CSH, g

CSV, g

3,000–5,000 1,000 500 100

7.8 7.7 7.2 5.8

0.13 0.12 0.09 0.03

0.065 0.060 0.045 0.015

0.046 0.042 0.032 0.011

Table 2 shows the computed values of intensity and design acceleration for 100, 500, 1,000, and 3,000– 5,000 year recurrence intervals, values which are typically used when designing dams. Acceleration was computed considering the terrain type (rock mass) and the special importance of the dam construction, and based on the Spanish Seismic Construction Code (NCSE-02, 2002), which considers an average level of seismicity, with a basic seismic acceleration of 0.07·g (where g is acceleration of gravity). The coefficient of horizontal seismicity (CSH) was set as 50 percent of the design acceleration (Eurocode 8, 2004; ROM 0.5-05, 2005). The coefficient of vertical seismicity (CSV) was set as 70 percent of the CSH. Geotechnical Parameters Table 3 shows the mean values of the geotechnical parameters obtained through laboratory and in situ tests on the three rock formations under study. In addition to rock density, the table lists RQD, tensile strength, UCS, and deformability parameters (elastic modulus and Poisson’s ratio).

According to its RQD, the gray dolomite formation (C1 ) is a medium-quality formation, and it corresponds to a hard rock (ISRM, 1981). For this material, cohesion was estimated as being between 200 and 600 kPa, and the angle of friction was estimated between 25° and 35° (González and Ferrer, 2011).

The ocher calcarenite formation (C2 ) is a moderately hard rock (ISRM, 1981). Very scattered RQD values were logged in the drill cores, indicating fair to poor quality. Its cohesion was estimated as being between 50 and 400 kPa, and the angle of friction was estimated between 25° and 35° (González and Ferrer, 2011).

The alternating micritic and brecciated limestone (C3 ) is a good-quality, hard rock (ISRM, 1981). The RMR index was computed for this formation, giving an RMRbasic value of between 58 and 65, which designates these materials as “class III,” medium rock mass quality (Bieniawski, 1981). The RMRcorrected was calculated by factoring the orientation of the slope relative to the main structure of the rock mass, yielding a mean value of around 57. Accordingly, the in situ elastic modulus (Bieniawski, 1978) may be set to 14,000 6

MPa. In addition, the GSI was calculated (Sonmez et al., 2003), giving an average value of 57, and then correlated with the elastic modulus, resulting in a value of 9,700 MPa. Hence, the in situ elastic modulus was estimated at around 12,000 MPa (approximate average value of elastic modulus obtained by correlations with RMR and GSI). Cohesion parameters and the internal angle of friction of this formation were set to 270 kPa and 32°, respectively, based on the RMR ratio (Bieniawski, 1978).

The alluvial materials (Q2 ) have a higher proportion of gravel and pebbles and fewer fines. Sub-rounded gravel and cobbles varying in size between 1 and 15 cm predominate. These clasts are surrounded by a lowplasticity and very dense reddish-brown sandy silt matrix. The bearing capacity varies from low to very low.

Similarly, the anthropogenic fills (R) comprise reddishbrown sandy silts of medium-low plasticity and a moderately firm consistency, with a low bearing capacity.

The values adopted for the different formations studied and used subsequently for the numerical analyses are summarized in Table 4.

FINITE ELEMENT ANALYSIS During the characterization of the geological and geotechnical properties, a karstified area was observed on the left abutment, within the C3 brecciated limestone formation onto which the foundations of the structure were planned to rest. The aspect and extension of this karstification were also observed during excavation (Figure 4). This underlined the need to find a solution, given the serious risk to the stability of the structure.

If karstification cavities or openings appear in foundation areas, the most common treatment is consolidation grouting, which can also improve the watertightness of the foundations, reduce seepage pressures, decrease uplift, and reduce the requirements needed to stabilize the dam (Weaver and Bruce, 2007).

To establish the suitability of using consolidation grouting in the dam, a numerical analysis was developed by using the finite element software Plaxis, version 2016.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Earthquake Major earthquake Project earthquake Usual earthquake Basic earthquake

Recurrence Intervals (years)

Intensity (MSK)

Seismic Acceleration (ac ), g

CSH, g

CSV, g

3,000–5,000 1,000 500 100

7.8 7.7 7.2 5.8

0.13 0.12 0.09 0.03

0.065 0.060 0.045 0.015

0.046 0.042 0.032 0.011

Table 2 shows the computed values of intensity and design acceleration for 100, 500, 1,000, and 3,000– 5,000 year recurrence intervals, values which are typically used when designing dams. Acceleration was computed considering the terrain type (rock mass) and the special importance of the dam construction, and based on the Spanish Seismic Construction Code (NCSE-02, 2002), which considers an average level of seismicity, with a basic seismic acceleration of 0.07·g (where g is acceleration of gravity). The coefficient of horizontal seismicity (CSH) was set as 50 percent of the design acceleration (Eurocode 8, 2004; ROM 0.5-05, 2005). The coefficient of vertical seismicity (CSV) was set as 70 percent of the CSH. Geotechnical Parameters Table 3 shows the mean values of the geotechnical parameters obtained through laboratory and in situ tests on the three rock formations under study. In addition to rock density, the table lists RQD, tensile strength, UCS, and deformability parameters (elastic modulus and Poisson’s ratio).

According to its RQD, the gray dolomite formation (C1 ) is a medium-quality formation, and it corresponds to a hard rock (ISRM, 1981). For this material, cohesion was estimated as being between 200 and 600 kPa, and the angle of friction was estimated between 25° and 35° (González and Ferrer, 2011).

The ocher calcarenite formation (C2 ) is a moderately hard rock (ISRM, 1981). Very scattered RQD values were logged in the drill cores, indicating fair to poor quality. Its cohesion was estimated as being between 50 and 400 kPa, and the angle of friction was estimated between 25° and 35° (González and Ferrer, 2011).

The alternating micritic and brecciated limestone (C3 ) is a good-quality, hard rock (ISRM, 1981). The RMR index was computed for this formation, giving an RMRbasic value of between 58 and 65, which designates these materials as “class III,” medium rock mass quality (Bieniawski, 1981). The RMRcorrected was calculated by factoring the orientation of the slope relative to the main structure of the rock mass, yielding a mean value of around 57. Accordingly, the in situ elastic modulus (Bieniawski, 1978) may be set to 14,000 6

MPa. In addition, the GSI was calculated (Sonmez et al., 2003), giving an average value of 57, and then correlated with the elastic modulus, resulting in a value of 9,700 MPa. Hence, the in situ elastic modulus was estimated at around 12,000 MPa (approximate average value of elastic modulus obtained by correlations with RMR and GSI). Cohesion parameters and the internal angle of friction of this formation were set to 270 kPa and 32°, respectively, based on the RMR ratio (Bieniawski, 1978).

The alluvial materials (Q2 ) have a higher proportion of gravel and pebbles and fewer fines. Sub-rounded gravel and cobbles varying in size between 1 and 15 cm predominate. These clasts are surrounded by a lowplasticity and very dense reddish-brown sandy silt matrix. The bearing capacity varies from low to very low.

Similarly, the anthropogenic fills (R) comprise reddishbrown sandy silts of medium-low plasticity and a moderately firm consistency, with a low bearing capacity.

The values adopted for the different formations studied and used subsequently for the numerical analyses are summarized in Table 4.

FINITE ELEMENT ANALYSIS During the characterization of the geological and geotechnical properties, a karstified area was observed on the left abutment, within the C3 brecciated limestone formation onto which the foundations of the structure were planned to rest. The aspect and extension of this karstification were also observed during excavation (Figure 4). This underlined the need to find a solution, given the serious risk to the stability of the structure.

If karstification cavities or openings appear in foundation areas, the most common treatment is consolidation grouting, which can also improve the watertightness of the foundations, reduce seepage pressures, decrease uplift, and reduce the requirements needed to stabilize the dam (Weaver and Bruce, 2007).

To establish the suitability of using consolidation grouting in the dam, a numerical analysis was developed by using the finite element software Plaxis, version 2016.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Dry Density, (t/m3 ) 2.68 (2.6) 2.58 (2.4) 2.73 (3.7) RQD (%) 56 (11.3) 43 (45.1) 56 (18.2)

Tensile Strength (MPa) 6.46 (27.2) 3.87 (42.8) 6.52 (57.9) Lab. Test 62.97 (38.1) 31.50 (36.4) 42.09 (54.6)

Correlation with Tensile Strength 51.70 (27.2) 50.5 (42.8) 52.17 (57.9)

Compression Test 85,216 (—) 9,482 (39.3) 52,001 (53.2)

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14 27.0 26.0 27.0 21.0 20.0

Unit Weight (kN/m3 ) 3 7 4 — —

Porosity (%) 500.0 100.0 270.0 0.0 —

Effective Cohesion (kPa)

25–35 25–35 32 27 —

Effective Friction Angle (°)

57.3 41.0 47.1 — —

UCS (MPa)

28.7 20.5 23.6 — —

Undrained Shear Resistance (MPa)

12,500 900 12,000 — —

Young’s Modulus (MPa)

Dilatometer Test — — 4,000 (—)

0.19 0.12 0.17 — —

Poisson’s Ratio

RQD* 12,250 (—) 900 (—) 9,340 (—)

Young’s Modulus (MPa) of the Rock Mass

7.4 × 10−6 1.1 × 10−5 3.0 × 10−5 1.0 × 10−2 —

Permeability (m/s)

Poisson’s Ratio 0.19 (15.7) 0.12 (8.6) 0.17 (12.5)

7 Dry Density, (t/m3 ) 2.68 (2.6) 2.58 (2.4) 2.73 (3.7)

RQD (%) 56 (11.3) 43 (45.1) 56 (18.2)

Tensile Strength (MPa) 6.46 (27.2) 3.87 (42.8) 6.52 (57.9)

Lab. Test 62.97 (38.1) 31.50 (36.4) 42.09 (54.6)

Correlation with Tensile Strength 51.70 (27.2) 50.5 (42.8) 52.17 (57.9)

Compression Test 85,216 (—) 9,482 (39.3) 52,001 (53.2)

Gray dolomites (C1 ) Ocher calcarenite (C2 ) Micritic limestones (C3 ) Alluvium (Q2 ) Anthropogenic soil (R)

Formation

27.0 26.0 27.0 21.0 20.0

Unit Weight (kN/m3 )

3 7 4 — —

Porosity (%)

500.0 100.0 270.0 0.0 —

Effective Cohesion (kPa)

25–35 25–35 32 27 —

Effective Friction Angle (°)

57.3 41.0 47.1 — —

UCS (MPa)

28.7 20.5 23.6 — —

Undrained Shear Resistance (MPa)

Table 4. Geotechnical parameters of the Terrateig Dam.

Dilatometer Test — — 4,000 (—)

12,500 900 12,000 — —

0.19 0.12 0.17 — —

Poisson’s Ratio

RQD* 12,250 (—) 900 (—) 9,340 (—)

Young’s Modulus (MPa) of the Rock Mass

Young’s Modulus (MPa)

Ultrasonic Test 37,245 (43.5) 2,521 (33.7) 41,391 (21.6)

Young’s Modulus (MPa) of the Intact Rock

RQD = rock quality designation; UCS = uniaxial compression strength. *According to Bieniawski (1984) and evaluated with the average values resulting from compression and ultrasonic tests.

Formation Gray dolomites (C1 ) Ocher calcarenite (C2 ) Micritic limestones (C3 )

UCS (MPa)

7.4 × 10−6 1.1 × 10−5 3.0 × 10−5 1.0 × 10−2 —

Permeability (m/s)

Poisson’s Ratio 0.19 (15.7) 0.12 (8.6) 0.17 (12.5)

Table 3. Geotechnical parameters obtained from laboratory and in situ tests of the three rock formations under study, where numbers in parentheses are coefficients of variation (%).

Gray dolomites (C1 ) Ocher calcarenite (C2 ) Micritic limestones (C3 ) Alluvium (Q2 ) Anthropogenic soil (R)

Formation

Table 4. Geotechnical parameters of the Terrateig Dam.

Ultrasonic Test 37,245 (43.5) 2,521 (33.7) 41,391 (21.6)

Young’s Modulus (MPa) of the Intact Rock

RQD = rock quality designation; UCS = uniaxial compression strength. *According to Bieniawski (1984) and evaluated with the average values resulting from compression and ultrasonic tests.

Formation Gray dolomites (C1 ) Ocher calcarenite (C2 ) Micritic limestones (C3 )

UCS (MPa)

Table 3. Geotechnical parameters obtained from laboratory and in situ tests of the three rock formations under study, where numbers in parentheses are coefficients of variation (%).

Geological and Geotechnical Dam Study Geological and Geotechnical Dam Study

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

7

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Figure 4. Left abutment, karstification zone in brecciated limestone (C3 ).

Finite Element Modeling of the Dam-Reservoir Interaction A generic cross section of the dam was used to study its foundation. The model dimensions were set as: maximum height = 26.5 m, and length = 400 m, and 15 node triangular elements were employed on the mesh.

The foundation behavior was simulated using the Mohr-Coulomb model, with the elastic part based on Hooke’s law of isotropic elasticity (defined by the elastic modulus and Poisson’s ratio) and the plastic part based on the Mohr-Coulomb failure criterion, which depends on cohesion and the angle of friction, and which was formulated in a non-associated plasticity framework (the plastic potential function also depends on the dilatancy angle). The Mohr-Coulomb model represents the behavior of geotechnical materials in a general way, but it does not include stress dependency, stress-path dependency, strain-dependent stiffness, or anisotropic stiffness. Since the objective of the simulation was a general assessment of the effect of grouting in the dam foundations, the Mohr-Coulomb model was considered to be suitable for the simulation in this case.

Foundation rock mass properties obtained in the previous geotechnical characterization (Table 5) were used in this simulation. The karstified carbonate rocks were simulated as if they were a rock mass with no voids, since after grouting, such cavities are filled with grout to cancel out their effect. For the concrete footings and body of the dam, a linear elastic material was defined.

As seen before in “Seismotectonics” section, the area under study features low seismicity; moreover, the Terrateig Dam is a flood-control structure. Taken together, these two aspects mean that the worst-case scenario would be simultaneous flooding (500 year 8

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

recurrence interval) and an earthquake of maximum severity (5,000 year recurrence interval; see Table 2).

Therefore, there are three possibilities that should be studied: an earthquake; flooding; and a simultaneous earthquake and flood (although this is highly unlikely to occur).

With the aim of observing the effect of the consolidation grouting, two models were considered for the simulation: (1) a reference, or simple model, corresponding to construction of the dam with no grouting of any kind, and the dam being subjected to flooding only (500 year recurrence interval); and (2) a model involving consolidation grouting with the dam being subjected to a simultaneous earthquake and flood (5,000 year and 500 year recurrence intervals, respectively).

The finite element software Plaxis v. 2016 allows different stages of the case under study to be defined, simulating the infrastructure construction process. It is possible, in any stage, to remove ground clusters to reproduce an excavation, add structural elements, or activate loads. Hence, both models of the dam were calculated with the process divided into several stages.

For the simple model, four stages were defined: excavation phase, foundation phase (building of the dam), dry reservoir phase (only deadweight acting), and a 500 year recurrence interval flood phase (deadweight, hydrostatic load, and uplift pressure acting).

For the model including the earthquake and consolidation grouting, the stages included: excavation phase, grouting phase (consolidation grouting was activated in this stage and kept in that state until the end), foundation phase (building of the dam), dry reservoir phase (only deadweight acting), dry reservoir phase with earthquake (deadweight and pseudo-static forces representing the seismic force acting), and a 500 year recurrence interval flood phase with a 5,000-year-recurrence earthquake (deadweight, pseudo-static forces, hydrostatic load, and uplift acting).

Results The results showed that under the impact of a seismic event during flooding, there were no major changes in velocity in the flow network (Figure 5), but adopting the use of grouting materials underneath the foundations significantly reduced the rate of flow in the Terrateig Dam. The worst-case scenario for a recurrence interval of 500 years and maximum reservoir level of 179.17 m.a.s.l. entailed a flow per meter of 2.58 × 10−4 m3 /s/m, with maximums seen under the foundations of the dam.

The models varied little with regard to the total stresses in each phase. The maximums were reached

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Figure 4. Left abutment, karstification zone in brecciated limestone (C3 ).

Finite Element Modeling of the Dam-Reservoir Interaction A generic cross section of the dam was used to study its foundation. The model dimensions were set as: maximum height = 26.5 m, and length = 400 m, and 15 node triangular elements were employed on the mesh.

The foundation behavior was simulated using the Mohr-Coulomb model, with the elastic part based on Hooke’s law of isotropic elasticity (defined by the elastic modulus and Poisson’s ratio) and the plastic part based on the Mohr-Coulomb failure criterion, which depends on cohesion and the angle of friction, and which was formulated in a non-associated plasticity framework (the plastic potential function also depends on the dilatancy angle). The Mohr-Coulomb model represents the behavior of geotechnical materials in a general way, but it does not include stress dependency, stress-path dependency, strain-dependent stiffness, or anisotropic stiffness. Since the objective of the simulation was a general assessment of the effect of grouting in the dam foundations, the Mohr-Coulomb model was considered to be suitable for the simulation in this case.

Foundation rock mass properties obtained in the previous geotechnical characterization (Table 5) were used in this simulation. The karstified carbonate rocks were simulated as if they were a rock mass with no voids, since after grouting, such cavities are filled with grout to cancel out their effect. For the concrete footings and body of the dam, a linear elastic material was defined.

As seen before in “Seismotectonics” section, the area under study features low seismicity; moreover, the Terrateig Dam is a flood-control structure. Taken together, these two aspects mean that the worst-case scenario would be simultaneous flooding (500 year 8

recurrence interval) and an earthquake of maximum severity (5,000 year recurrence interval; see Table 2).

Therefore, there are three possibilities that should be studied: an earthquake; flooding; and a simultaneous earthquake and flood (although this is highly unlikely to occur).

With the aim of observing the effect of the consolidation grouting, two models were considered for the simulation: (1) a reference, or simple model, corresponding to construction of the dam with no grouting of any kind, and the dam being subjected to flooding only (500 year recurrence interval); and (2) a model involving consolidation grouting with the dam being subjected to a simultaneous earthquake and flood (5,000 year and 500 year recurrence intervals, respectively).

The finite element software Plaxis v. 2016 allows different stages of the case under study to be defined, simulating the infrastructure construction process. It is possible, in any stage, to remove ground clusters to reproduce an excavation, add structural elements, or activate loads. Hence, both models of the dam were calculated with the process divided into several stages.

For the simple model, four stages were defined: excavation phase, foundation phase (building of the dam), dry reservoir phase (only deadweight acting), and a 500 year recurrence interval flood phase (deadweight, hydrostatic load, and uplift pressure acting).

For the model including the earthquake and consolidation grouting, the stages included: excavation phase, grouting phase (consolidation grouting was activated in this stage and kept in that state until the end), foundation phase (building of the dam), dry reservoir phase (only deadweight acting), dry reservoir phase with earthquake (deadweight and pseudo-static forces representing the seismic force acting), and a 500 year recurrence interval flood phase with a 5,000-year-recurrence earthquake (deadweight, pseudo-static forces, hydrostatic load, and uplift acting).

Results The results showed that under the impact of a seismic event during flooding, there were no major changes in velocity in the flow network (Figure 5), but adopting the use of grouting materials underneath the foundations significantly reduced the rate of flow in the Terrateig Dam. The worst-case scenario for a recurrence interval of 500 years and maximum reservoir level of 179.17 m.a.s.l. entailed a flow per meter of 2.58 × 10−4 m3 /s/m, with maximums seen under the foundations of the dam.

The models varied little with regard to the total stresses in each phase. The maximums were reached

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Geological and Geotechnical Dam Study

Geological and Geotechnical Dam Study

Figure 5. Comparison of the simple model and the model including earthquake and consolidation grouting. Full reservoir phase. Using Plaxis v. 2016.

Figure 5. Comparison of the simple model and the model including earthquake and consolidation grouting. Full reservoir phase. Using Plaxis v. 2016.

for the dam with the 500 year interval flooding, and a decrease was observed with the addition of consolidation grouting under the foundations.

Finally, vertical and horizontal displacements during flooding were of similar magnitudes and were confined mainly to the upstream face: on the crest in the case of vertical displacement, and at the foot in the horizontal case. Both were within the allowable limits.

for the dam with the 500 year interval flooding, and a decrease was observed with the addition of consolidation grouting under the foundations.

Finally, vertical and horizontal displacements during flooding were of similar magnitudes and were confined mainly to the upstream face: on the crest in the case of vertical displacement, and at the foot in the horizontal case. Both were within the allowable limits.

DAM CONSTRUCTION AND DISCUSSION The C2 formation of ocher calcarenites determined the elevation of the dam foundation, due to the poor quality of that rock mass. This made it necessary to excavate down to the C3 formation along the axis of the dam. However, in the stilling basin zone, the limestone was found directly below the Q2 formation (Figure 6), and it was not necessary to remove C2 . The dam foundation was cleared, cleaned, and washed with pressurized water, before concreting of the blocks started.

Karstic cavities found in the foundation substrate were infilled with concrete.

The creation of a reservoir resulted in high seepage pressures through karstified areas as a consequence of the high hydraulic gradients produced. Those high seepage pressures can enlarge discontinuities and cavities by dissolution, causing an increase in the permeability of the ground and accelerating the process (James, 1992; Romanov et al., 2003; Milanović, 2004; Johnson, 2008; Gutiérrez, 2010; Cooper and Gutiérrez, 2013; and Gutiérrez et al., 2015). In the case of

the Terrateig Dam, a sub-horizontally lying succession of sedimentary rocks is present, and karstified areas appeared along one of the boundaries of the reservoir.

Seepage was reduced and watertightness of the reservoir was assured by installing a grout curtain. The numerical models previously seen in the above section showed that in the worst-case scenario, the flow was significant (around 0.2 L/s/m), even when the grout curtain was installed. Although that scenario has a low probability of occurrence, the flow value obtained gives an idea of the magnitude of the problem. Aside from the reduction in the flow rate, the grout curtain reduces uplift and seepage pressures. The latter lead to a reduction in internal erosion and attenuation of the

Figure 6. Central slope excavation in calcarenites (C2 ).

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

9

DAM CONSTRUCTION AND DISCUSSION The C2 formation of ocher calcarenites determined the elevation of the dam foundation, due to the poor quality of that rock mass. This made it necessary to excavate down to the C3 formation along the axis of the dam. However, in the stilling basin zone, the limestone was found directly below the Q2 formation (Figure 6), and it was not necessary to remove C2 . The dam foundation was cleared, cleaned, and washed with pressurized water, before concreting of the blocks started.

Karstic cavities found in the foundation substrate were infilled with concrete.

The creation of a reservoir resulted in high seepage pressures through karstified areas as a consequence of the high hydraulic gradients produced. Those high seepage pressures can enlarge discontinuities and cavities by dissolution, causing an increase in the permeability of the ground and accelerating the process (James, 1992; Romanov et al., 2003; Milanović, 2004; Johnson, 2008; Gutiérrez, 2010; Cooper and Gutiérrez, 2013; and Gutiérrez et al., 2015). In the case of

the Terrateig Dam, a sub-horizontally lying succession of sedimentary rocks is present, and karstified areas appeared along one of the boundaries of the reservoir.

Seepage was reduced and watertightness of the reservoir was assured by installing a grout curtain. The numerical models previously seen in the above section showed that in the worst-case scenario, the flow was significant (around 0.2 L/s/m), even when the grout curtain was installed. Although that scenario has a low probability of occurrence, the flow value obtained gives an idea of the magnitude of the problem. Aside from the reduction in the flow rate, the grout curtain reduces uplift and seepage pressures. The latter lead to a reduction in internal erosion and attenuation of the

Figure 6. Central slope excavation in calcarenites (C2 ).

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

9

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Figure 7. Geological map of the foundation excavation.

Figure 7. Geological map of the foundation excavation.

enlargement of discontinuities and cavities by dissolution (González and Ferrer, 2011).

If it is assumed, as is done in the numerical model, that the karstified areas may be simulated as a homogeneous material of a given permeability (Table 5), seepage and uplift pressures are proportional to the flow velocity. Thus, since the numerical models show that the installation of a grout curtain reduces flow velocities by around 12 percent, both seepage and uplift pressures are also reduced by the same value. This will alleviate pressures at the dam foundation and reduce internal erosion.

Furthermore, a dam may be affected by absolute or relative strains between adjacent foundation areas.

Strains closer to the surface due to the opening and closing of fissures, or minor shear fracturing in local zones, are irreversible. This typically occurs during construction and filling, and it leads to the most critical situations (Sherard et al., 1974). During the dam body excavation phase, an inactive rotational fault (172/75°) was detected on the left margin of the dam (Figure 7). Due to this failure plane, there was a brecciated (tectonized) zone in the central limestone blocks (Figure 8).

enlargement of discontinuities and cavities by dissolution (González and Ferrer, 2011).

If it is assumed, as is done in the numerical model, that the karstified areas may be simulated as a homogeneous material of a given permeability (Table 5), seepage and uplift pressures are proportional to the flow velocity. Thus, since the numerical models show that the installation of a grout curtain reduces flow velocities by around 12 percent, both seepage and uplift pressures are also reduced by the same value. This will alleviate pressures at the dam foundation and reduce internal erosion.

Figure 8. Central slope excavation, tectonized zone in micritic limestone (C3 ).

10

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Furthermore, a dam may be affected by absolute or relative strains between adjacent foundation areas.

Strains closer to the surface due to the opening and closing of fissures, or minor shear fracturing in local zones, are irreversible. This typically occurs during construction and filling, and it leads to the most critical situations (Sherard et al., 1974). During the dam body excavation phase, an inactive rotational fault (172/75°) was detected on the left margin of the dam (Figure 7). Due to this failure plane, there was a brecciated (tectonized) zone in the central limestone blocks (Figure 8).

Figure 8. Central slope excavation, tectonized zone in micritic limestone (C3 ).

10

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Geological and Geotechnical Dam Study

Geological and Geotechnical Dam Study

Figure 9. Profile of the consolidation grouting.

Figure 9. Profile of the consolidation grouting.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

11

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

11

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Consequently, grouting was employed to reduce the effects of both settlement and seepage, and increase the rigidity of the foundations. This is normally performed using shallow boreholes distributed over the entire foundation area. Consolidation is best performed using the basal concrete lifts as the grout cap. At least 2 m of concrete is recommended, although the thickness of actual concrete will be somewhat less (but always in excess of 1.5 m). The boreholes should be vertical and inclined (normal to the face) to properly seal the longitudinal excavation slopes.

In this project, vertical boreholes were designed using a 3.5 × 4 m pattern for both the foundations of the central blocks and the abutments. Inclined boreholes were designed as a parallel line 2 m from the wall and located every 4 m. Some special vertical boreholes were established according to the 3.5 × 4 m mesh to reinforce those central blocks containing the rotational fault (Figure 9). The boreholes were drilled using rotary-percussion drills, driving the bit from the outside, and in a way that ensured a minimum concrete depth of 2 m. The boreholes were at least 5 m deep, developed with a drilling diameter of 50.8 mm.

The grouting was carried out following the considerations of Kutzner (1996) and Bielza Feliu (1999), who established that grouting pressures should be equal to the live load or the self-weight of geotechnical materials when grouting in a rock mass with a main discontinuity system parallel to the surface (i.e., horizontal).

In this case, grouting pressure is normally increased with the depth. Conversely, when grouting a rock mass with vertical or inclined discontinuity families, grouting pressures should be lower than those pressures that lead to displacement of the rock masses. As a result, the maximum grouting pressure in this case was set as 500 kPa. The cement/water ratio was 1.2.

the abutments. Inclined boreholes were also drilled, arranged on a parallel line 2 m from the footings and spaced every 4 m. Additionally, due to the discovery of a rotational failure in the central blocks, some special vertical boreholes were also drilled in that location (reinforcement grouting). All the boreholes were drilled to ensure a minimum concrete depth of 2 m. The boreholes drilled into the rock mass were at least 5 m deep, had a perforation diameter of 50.8 mm, and had maximum grouting pressure of 500 kPa. The Terrateig Dam is a clear example of the importance of a preliminary geotechnical analysis for establishing the appropriate foundation criteria. This study did not end at the design phase, but monitoring continued during the excavation and concreting of the foundation, to adapt the design solutions to the real needs of the dam. This made it possible to confirm all the planned design elements, and implement new ones, such as the extra grouting in the tectonized areas of the central blocks.

ACKNOWLEDGMENTS The authors of this article would like to thank the Altec-Romymar consortium for providing the initial data, and AYESA S.A. for allowing visits to the work site during dam construction. We also extend our thanks to Ricardo Valiente, MSc., for his contribution to this article. The Portuguese Fundação para a Ciência e a Tecnologia provided funds for the development of the current research of the Geosciences Center. These funds were delivered to the Geosciences Center of the University of Coimbra as a research project (UID/Multi/00073/2013).

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira

Consequently, grouting was employed to reduce the effects of both settlement and seepage, and increase the rigidity of the foundations. This is normally performed using shallow boreholes distributed over the entire foundation area. Consolidation is best performed using the basal concrete lifts as the grout cap. At least 2 m of concrete is recommended, although the thickness of actual concrete will be somewhat less (but always in excess of 1.5 m). The boreholes should be vertical and inclined (normal to the face) to properly seal the longitudinal excavation slopes.

In this project, vertical boreholes were designed using a 3.5 × 4 m pattern for both the foundations of the central blocks and the abutments. Inclined boreholes were designed as a parallel line 2 m from the wall and located every 4 m. Some special vertical boreholes were established according to the 3.5 × 4 m mesh to reinforce those central blocks containing the rotational fault (Figure 9). The boreholes were drilled using rotary-percussion drills, driving the bit from the outside, and in a way that ensured a minimum concrete depth of 2 m. The boreholes were at least 5 m deep, developed with a drilling diameter of 50.8 mm.

The grouting was carried out following the considerations of Kutzner (1996) and Bielza Feliu (1999), who established that grouting pressures should be equal to the live load or the self-weight of geotechnical materials when grouting in a rock mass with a main discontinuity system parallel to the surface (i.e., horizontal).

In this case, grouting pressure is normally increased with the depth. Conversely, when grouting a rock mass with vertical or inclined discontinuity families, grouting pressures should be lower than those pressures that lead to displacement of the rock masses. As a result, the maximum grouting pressure in this case was set as 500 kPa. The cement/water ratio was 1.2.

REFERENCES CONCLUSIONS The Terrateig Dam was built on Cretaceous materials overlain by Quaternary sediments located along the Vernissa riverbed. A complete geological and geotechnical investigation was carried out to characterize the dam foundations.

A karstic zone was detected during the geological investigation. To improve the stability of the dam and consolidate the rock mass, consolidation grouting was conducted. A finite element analysis was run to assess the suitability of grouting. The numerical simulation took into account the simultaneous occurrence of flooding with a 500 year interval recurrence and earthquakes with a 5,000 year interval recurrence.

Grouting was performed through vertical boreholes drilled using a 3.5 × 4 m template mesh on both the foundation of the central blocks of the dam and on 12

Bielza Feliu, A., 1999, Manual de Técnicas de Mejora del Terreno: Entorno Gráfico, Madrid, Spain, 432 p.

Bieniawski, Z. T., 1978, Determining rock mass deformability: Experience from case histories: International Journal Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Vol. 15, No. 5, pp. 237–247.

Bieniawski, Z. T., 1984, Rock Mechanics Design in Mining and Tunnelling: A. A. Balkema, Rotterdam, Netherlands, 280 p.

Bieniawski, Z. T., 1989, Engineering Rock Mass Classifications: John Wiley & Sons, New York, 253 p.

Contreras, J. L. S. and Santamaría, J., 1998, Manual para el Control y Diseño de Voladuras en Obras de Carreteras: Ministerio de Obras Públicas y Transportes, Madrid, 379 p.

Coon, R. F. and Merritt, A. H., 1970, Predicting in situ modulus of deformation using rock quality indexes. In Determination of the In Situ Modulus of Deformation of Rock: American Society for Testing and Materials Publication STP 477, pp. 154–173.

Cooper, A. H. and Gutiérrez, F., 2013, Dealing with gypsum karst problems: Hazards, environmental issues and planning.

In Frumkin, A. (Editors), Treatise on Geomorphology. Karst

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

the abutments. Inclined boreholes were also drilled, arranged on a parallel line 2 m from the footings and spaced every 4 m. Additionally, due to the discovery of a rotational failure in the central blocks, some special vertical boreholes were also drilled in that location (reinforcement grouting). All the boreholes were drilled to ensure a minimum concrete depth of 2 m. The boreholes drilled into the rock mass were at least 5 m deep, had a perforation diameter of 50.8 mm, and had maximum grouting pressure of 500 kPa. The Terrateig Dam is a clear example of the importance of a preliminary geotechnical analysis for establishing the appropriate foundation criteria. This study did not end at the design phase, but monitoring continued during the excavation and concreting of the foundation, to adapt the design solutions to the real needs of the dam. This made it possible to confirm all the planned design elements, and implement new ones, such as the extra grouting in the tectonized areas of the central blocks.

ACKNOWLEDGMENTS The authors of this article would like to thank the Altec-Romymar consortium for providing the initial data, and AYESA S.A. for allowing visits to the work site during dam construction. We also extend our thanks to Ricardo Valiente, MSc., for his contribution to this article. The Portuguese Fundação para a Ciência e a Tecnologia provided funds for the development of the current research of the Geosciences Center. These funds were delivered to the Geosciences Center of the University of Coimbra as a research project (UID/Multi/00073/2013).

REFERENCES

CONCLUSIONS The Terrateig Dam was built on Cretaceous materials overlain by Quaternary sediments located along the Vernissa riverbed. A complete geological and geotechnical investigation was carried out to characterize the dam foundations.

A karstic zone was detected during the geological investigation. To improve the stability of the dam and consolidate the rock mass, consolidation grouting was conducted. A finite element analysis was run to assess the suitability of grouting. The numerical simulation took into account the simultaneous occurrence of flooding with a 500 year interval recurrence and earthquakes with a 5,000 year interval recurrence.

Grouting was performed through vertical boreholes drilled using a 3.5 × 4 m template mesh on both the foundation of the central blocks of the dam and on 12

Bielza Feliu, A., 1999, Manual de Técnicas de Mejora del Terreno: Entorno Gráfico, Madrid, Spain, 432 p.

Bieniawski, Z. T., 1978, Determining rock mass deformability: Experience from case histories: International Journal Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Vol. 15, No. 5, pp. 237–247.

Bieniawski, Z. T., 1984, Rock Mechanics Design in Mining and Tunnelling: A. A. Balkema, Rotterdam, Netherlands, 280 p.

Bieniawski, Z. T., 1989, Engineering Rock Mass Classifications: John Wiley & Sons, New York, 253 p.

Contreras, J. L. S. and Santamaría, J., 1998, Manual para el Control y Diseño de Voladuras en Obras de Carreteras: Ministerio de Obras Públicas y Transportes, Madrid, 379 p.

Coon, R. F. and Merritt, A. H., 1970, Predicting in situ modulus of deformation using rock quality indexes. In Determination of the In Situ Modulus of Deformation of Rock: American Society for Testing and Materials Publication STP 477, pp. 154–173.

Cooper, A. H. and Gutiérrez, F., 2013, Dealing with gypsum karst problems: Hazards, environmental issues and planning.

In Frumkin, A. (Editors), Treatise on Geomorphology. Karst

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Geological and Geotechnical Dam Study Geomorphology, Vol. 6: Elsevier, Amsterdam, Netherlands, pp. 451–462.

Deere, D. U., 1963, Technical description of rock cores for engineering purposes: Felsmechanik und Ingenieurgeologie, Vol. 1, No. 1, pp. 16–22.

Eurocode 8, 2004, EN 1998-5. Design of Structures for Earthquake Resistance—Part 5: Foundations, Retaining Structures and Geotechnical Aspects: Comité Européen de Normalisation (CEN), Brussels, Belgium, 47 p.

Galera, J. M.; Álvarez, M.; and Bieniawski, Z. T., 2005, Evaluation of the deformation modulus of rock masses using RMR: Comparison with dilatometer tests. In Olalla, C.; Perucho, A.; and Romana, M. (Editors), SP5-PRESSIO 2005 International Symposium: American Society for Testing and Materials, Madrid, Spain, pp. 71–77.

Giner, J. J. and Molina, S., 2001, Sismicidad y Riesgo Sísmico en la C.A.V.: Editorial Club Universitario, Alicante, Spain, 49 p.

Giner, J. J.; Molina, S.; and Jáuregui, P. J., 2003, Sismicidad en la Comunidad Valenciana (CV): Física de la Tierra, Vol. 15, pp. 163–187.

González, L. I. and Ferrer, M., 2011, Geological Engineering: CRC Press, London, U.K., 700 p.

Gutiérrez, F., 2010, Hazards associated with karst. In Alcántara, I. and Goudie, A. (Editors), Geomorphological Hazards and Disaster Prevention: Cambridge University Press, Cambridge, U.K., pp. 161–175.

Gutiérrez, F.; Mozafari, M.; Carbonel, D.; Gómez, R.; and Raeisi, E., 2015, Leakage problems in dams built on evaporites. The case of La Loteta Dam (NE Spain), a reservoir in a large karstic depression generated by interstratal salt dissolution: Engineering Geology, Vol. 185, pp. 139–154.

Han, K.; Chen, Y.; Chen, Y.; Gan, F.; Zheng, Z.; and Zhang, W., 2015, Detection method of leakage passages in karst disease reservoirs. A case study of Luotan reservoir in Quanzhou county of Guangxi: Shuili Fadian Xuebao: Journal Hydroelectric Engineering, Vol. 34, No. 11, pp. 116–125.

Hoek, E. and Brown, E. T., 1997, Practical estimates of rock mass strength: International Journal Rock Mechanics and Mining Sciences, Vol .34, No. 8, pp. 1165–1186.

Instituto Geológico y Minero de España (IGME), 1979, Geological Map of Spain (Mapa Geológico de España). Sheet 795: “Jativa”: IGME, Madrid, Spain, scale 1:50,000.

IGME, 1988, Las Aguas Subterráneas en la Comunidad Valenciana Uso, Calidad y Perspectivas de Utilización: IGME, Madrid, Spain, 289 p.

International Society for Rock Mechanics (ISRM), 1981, Description of rocks masses: International Journal Rock Mechanics and Mining Science, No. 18, pp. 85–110.

James, A. N., 1992, Soluble Materials in Civil Engineering: Ellis Horwood Ltd., New York.

Jembere, D. and Yihdego, Y., 2016, Engineering rock mass evaluation for a multi-purpose hydroelectric power plant: Case of Genale Dawa (GD-3), Ethiopia: Journal Geotechnical Geological Engineering, Vol. 34, No. 5, pp. 1593– 1612.

Jiang, Y.; Yang, G. H.; Huang, Z. M.; Qiao, Y. L.; and Zhang, Y. C., 2015, Ground treatment of high-rise buildings in complex karst region. Yantu Lixue: Rock and Soil Mechanics, Vol. 36, pp. 430–438.

Jimenez Salas, J. A. and De Justo Alpañes, J. L., 1975, Geotecnia y Cimientos I. Propiedades de los Suelos y de las Rocas: Editorial Rueda, Madrid, Spain, 466 p.

Johnson, K. S., 2008, Gypsum-karst problems in constructing dams in the USA: Environmental Geology, Vol. 53, pp. 945– 950.

Geological and Geotechnical Dam Study

Kutzner, C., 1996, Grouting of Rock and Soil: A. A. Balkema, Rotterdam, Netherlands, 282 p.

Li, K.; Zhu, C.; Wu, L.; and Huang, L., 2013, Problems caused by the Three Gorges Dam construction in the Yangtze River basin: A review: Environmental Reviews, Vol. 21, No. 3, pp. 127–135.

Mather, P., 2013, Geotechnical aspects of karst within the Swan Coastal Plain, Western Australia: Australian Geomechanics Journal, Vol. 48, No. 2, pp. 49–56.

Matthews, M. C.; Clayton, C. R. I.; and Own, Y., 2000, The use of field geophysical techniques to determine geotechnical stiffness parameters: Proceedings of the Institution of Civil Engineers—Geotechnical Engineering, Vol. 143, No. 1, pp. 31– 42.

Merritt, A. H., 1995, Geotechnical aspects of the design and construction of dams and pressure tunnel in soluble rocks. In Beck, B. F. (Editor), Karst Geohazards: Engineering and Environmental Problems in Karst Terranes: A. A. Balkema, Rotterdam, Netherlands, pp. 3–7.

Milanović, P. T., 2004, Water Resources Engineering in Karst: CRC Press, Boca Raton, FL, 312 p.

Milanović, P. T., 2015, Catalog of engineering works in karst and their effects. In Stevanovic, Z. (Editor), Karst Aquifers— Characterization and Engineering: Springer International Publishing, pp. 361–399.

Miller, R. P., 1965, Engineering Classification and Index Properties for Intact Rock: Unpublished Ph.D. Thesis, University of Illinois, Urbana-Champaign, 300 p.

Mozafari, M. and Raeisi, E., 2015, Understanding karst leakage at the Kowsar Dam, Iran, by hydrogeological analysis: Environmental and Engineering Geoscience, Vol. 21, No. 4, pp. 325– 339.

Mozafari, M. and Raeisi, E., 2016, Salman Farsi Dam reservoir, a successful project on a karstified foundation, SW Iran: Environmental Earth Sciences, Vol. 75, No. 12, Art. 1044, 12 p.

NCSE-02, 2002, Norma de Construcción Sismorresistente: Parte General y Edificación: Ministerio de Fomento, Madrid, Spain, 96 p.

Olalla, C. and Sopeña, L., 1991, Ensayos de Campo: Máster de Ingeniería Geológica, Universitad Complutense de Madrid, Spain, Monografía 5.

Penas, M. J.; Berga, C. L.; and Rodríguez, T. M., 1996, Clasificación de presas en función del riesgo potencial. Criterios básicos y metodología. In SPANCOLD (Editor), V Jornadas Españolas de Presas: Valencia, Spain, 11 p.

ROM 0.5-05, 2005, Recomendaciones Geotécnicas para Obras Marítimas y Portuarias, Capítulo 3: Criterios Geotécnicos: Puertos del Estado, Madrid, Spain, 394 p.

Romanov, D.; Gabrovšek, F.; and Dreybrodt, W., 2003, Dam sites in soluble rocks: A model for increasing leakage by dissolutional widening of fractures beneath a dam: Engineering Geology, Vol. 70, pp. 17–35.

Schaefer, J. A., 2009, Risk evaluation of dams on karst foundations. In Proceedings of the 29th Annual United States Society on Dams Conference: Nashville, TN, pp. 20–24.

Senís, M. V. G., 1990, El karst superficial de la Safor: Cuadernos de Geografía, Vol. 48, pp. 105–126.

Serafim, J. L. and Pereira, J. P., 1983, Considerations of the geomechanics classification of Bieniawski. In Proceedings of the International Symposium on Engineering Geology and Underground Construction: Lisbon, Portugal, Vol. 1, pp. 1133–1142.

Sherard, J. L.; Cluff, L. S.; and Allen, C. R., 1974, Potentially active faults in dam foundations: Geotechnique, Vol. 24, No. 3, pp. 367–428.

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13

Geomorphology, Vol. 6: Elsevier, Amsterdam, Netherlands, pp. 451–462.

Deere, D. U., 1963, Technical description of rock cores for engineering purposes: Felsmechanik und Ingenieurgeologie, Vol. 1, No. 1, pp. 16–22.

Eurocode 8, 2004, EN 1998-5. Design of Structures for Earthquake Resistance—Part 5: Foundations, Retaining Structures and Geotechnical Aspects: Comité Européen de Normalisation (CEN), Brussels, Belgium, 47 p.

Galera, J. M.; Álvarez, M.; and Bieniawski, Z. T., 2005, Evaluation of the deformation modulus of rock masses using RMR: Comparison with dilatometer tests. In Olalla, C.; Perucho, A.; and Romana, M. (Editors), SP5-PRESSIO 2005 International Symposium: American Society for Testing and Materials, Madrid, Spain, pp. 71–77.

Giner, J. J. and Molina, S., 2001, Sismicidad y Riesgo Sísmico en la C.A.V.: Editorial Club Universitario, Alicante, Spain, 49 p.

Giner, J. J.; Molina, S.; and Jáuregui, P. J., 2003, Sismicidad en la Comunidad Valenciana (CV): Física de la Tierra, Vol. 15, pp. 163–187.

González, L. I. and Ferrer, M., 2011, Geological Engineering: CRC Press, London, U.K., 700 p.

Gutiérrez, F., 2010, Hazards associated with karst. In Alcántara, I. and Goudie, A. (Editors), Geomorphological Hazards and Disaster Prevention: Cambridge University Press, Cambridge, U.K., pp. 161–175.

Gutiérrez, F.; Mozafari, M.; Carbonel, D.; Gómez, R.; and Raeisi, E., 2015, Leakage problems in dams built on evaporites. The case of La Loteta Dam (NE Spain), a reservoir in a large karstic depression generated by interstratal salt dissolution: Engineering Geology, Vol. 185, pp. 139–154.

Han, K.; Chen, Y.; Chen, Y.; Gan, F.; Zheng, Z.; and Zhang, W., 2015, Detection method of leakage passages in karst disease reservoirs. A case study of Luotan reservoir in Quanzhou county of Guangxi: Shuili Fadian Xuebao: Journal Hydroelectric Engineering, Vol. 34, No. 11, pp. 116–125.

Hoek, E. and Brown, E. T., 1997, Practical estimates of rock mass strength: International Journal Rock Mechanics and Mining Sciences, Vol .34, No. 8, pp. 1165–1186.

Instituto Geológico y Minero de España (IGME), 1979, Geological Map of Spain (Mapa Geológico de España). Sheet 795: “Jativa”: IGME, Madrid, Spain, scale 1:50,000.

IGME, 1988, Las Aguas Subterráneas en la Comunidad Valenciana Uso, Calidad y Perspectivas de Utilización: IGME, Madrid, Spain, 289 p.

International Society for Rock Mechanics (ISRM), 1981, Description of rocks masses: International Journal Rock Mechanics and Mining Science, No. 18, pp. 85–110.

James, A. N., 1992, Soluble Materials in Civil Engineering: Ellis Horwood Ltd., New York.

Jembere, D. and Yihdego, Y., 2016, Engineering rock mass evaluation for a multi-purpose hydroelectric power plant: Case of Genale Dawa (GD-3), Ethiopia: Journal Geotechnical Geological Engineering, Vol. 34, No. 5, pp. 1593– 1612.

Jiang, Y.; Yang, G. H.; Huang, Z. M.; Qiao, Y. L.; and Zhang, Y. C., 2015, Ground treatment of high-rise buildings in complex karst region. Yantu Lixue: Rock and Soil Mechanics, Vol. 36, pp. 430–438.

Jimenez Salas, J. A. and De Justo Alpañes, J. L., 1975, Geotecnia y Cimientos I. Propiedades de los Suelos y de las Rocas: Editorial Rueda, Madrid, Spain, 466 p.

Johnson, K. S., 2008, Gypsum-karst problems in constructing dams in the USA: Environmental Geology, Vol. 53, pp. 945– 950.

Kutzner, C., 1996, Grouting of Rock and Soil: A. A. Balkema, Rotterdam, Netherlands, 282 p.

Li, K.; Zhu, C.; Wu, L.; and Huang, L., 2013, Problems caused by the Three Gorges Dam construction in the Yangtze River basin: A review: Environmental Reviews, Vol. 21, No. 3, pp. 127–135.

Mather, P., 2013, Geotechnical aspects of karst within the Swan Coastal Plain, Western Australia: Australian Geomechanics Journal, Vol. 48, No. 2, pp. 49–56.

Matthews, M. C.; Clayton, C. R. I.; and Own, Y., 2000, The use of field geophysical techniques to determine geotechnical stiffness parameters: Proceedings of the Institution of Civil Engineers—Geotechnical Engineering, Vol. 143, No. 1, pp. 31– 42.

Merritt, A. H., 1995, Geotechnical aspects of the design and construction of dams and pressure tunnel in soluble rocks. In Beck, B. F. (Editor), Karst Geohazards: Engineering and Environmental Problems in Karst Terranes: A. A. Balkema, Rotterdam, Netherlands, pp. 3–7.

Milanović, P. T., 2004, Water Resources Engineering in Karst: CRC Press, Boca Raton, FL, 312 p.

Milanović, P. T., 2015, Catalog of engineering works in karst and their effects. In Stevanovic, Z. (Editor), Karst Aquifers— Characterization and Engineering: Springer International Publishing, pp. 361–399.

Miller, R. P., 1965, Engineering Classification and Index Properties for Intact Rock: Unpublished Ph.D. Thesis, University of Illinois, Urbana-Champaign, 300 p.

Mozafari, M. and Raeisi, E., 2015, Understanding karst leakage at the Kowsar Dam, Iran, by hydrogeological analysis: Environmental and Engineering Geoscience, Vol. 21, No. 4, pp. 325– 339.

Mozafari, M. and Raeisi, E., 2016, Salman Farsi Dam reservoir, a successful project on a karstified foundation, SW Iran: Environmental Earth Sciences, Vol. 75, No. 12, Art. 1044, 12 p.

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Olalla, C. and Sopeña, L., 1991, Ensayos de Campo: Máster de Ingeniería Geológica, Universitad Complutense de Madrid, Spain, Monografía 5.

Penas, M. J.; Berga, C. L.; and Rodríguez, T. M., 1996, Clasificación de presas en función del riesgo potencial. Criterios básicos y metodología. In SPANCOLD (Editor), V Jornadas Españolas de Presas: Valencia, Spain, 11 p.

ROM 0.5-05, 2005, Recomendaciones Geotécnicas para Obras Marítimas y Portuarias, Capítulo 3: Criterios Geotécnicos: Puertos del Estado, Madrid, Spain, 394 p.

Romanov, D.; Gabrovšek, F.; and Dreybrodt, W., 2003, Dam sites in soluble rocks: A model for increasing leakage by dissolutional widening of fractures beneath a dam: Engineering Geology, Vol. 70, pp. 17–35.

Schaefer, J. A., 2009, Risk evaluation of dams on karst foundations. In Proceedings of the 29th Annual United States Society on Dams Conference: Nashville, TN, pp. 20–24.

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Serafim, J. L. and Pereira, J. P., 1983, Considerations of the geomechanics classification of Bieniawski. In Proceedings of the International Symposium on Engineering Geology and Underground Construction: Lisbon, Portugal, Vol. 1, pp. 1133–1142.

Sherard, J. L.; Cluff, L. S.; and Allen, C. R., 1974, Potentially active faults in dam foundations: Geotechnique, Vol. 24, No. 3, pp. 367–428.

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Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira Sonmez, H.; Gokceoglu, C.; and Ulusay, R., 2003, An application of fuzzy sets to the geological strength index (GSI) system used in rock engineering: Engineering Applications Artificial Intelligence, Vol. 16, No. 3, pp. 251–269.

Sopaci, E. and Akgün, H., 2016, Engineering geological characterization of the Antalya karstic rocks, southern Turkey: Environmental Earth Sciences, Vol. 75, No. 5, pp. 1–20.

Sumi, T., 2008, Designing and operating of flood retention dry dams in Japan and USA. In Proceedings 8th International Conference on Hydro-Science and Engineering ICHE-2008: Nagoya, Japan, 10 p.

Vera, J. A.; Ancochea, E.; Barnolas, A.; Bea, F.; Calvo, J. P.; Civis, J.; de Vicente, G.; Fernández-Gianotti, J.; GarcíaCortés, A.; Pérez-Estaún, A.; Pujalte, V.; Rodríguez-

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Fernández, L. R.; Sopeña, A.; Tejero, A.; and Vera, J. A., 2004, Geología de España: Geological Survey of Spain (SGE)– Instituto Geológico y Minero de España (IGME), Madrid, Spain, 355 p.

Weaver, K. D. and Bruce, D. A., 2007, Dam Foundation Grouting: ASCE Press, Reston, VA, 473 p.

Yihdego, Y., 2016, Evaluation of flow reduction due to hydraulic barrier engineering structure: Case of urban area flood, contamination and pollution risk assessment: Journal Geotechnical Geological Engineering, Vol. 34, No. 5, pp. 1643–1654.

Yihdego, Y., 2017, Hydraulic in situ testing for mining and engineering design: Packer test procedure, preparation, analysis and interpretation. Journal Geotechnical Geological Engineering, Vol. 35, No. 1, pp. 29–44.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Torrijo, Alija, Garzón-Roca, and Quinta-Ferreira Sonmez, H.; Gokceoglu, C.; and Ulusay, R., 2003, An application of fuzzy sets to the geological strength index (GSI) system used in rock engineering: Engineering Applications Artificial Intelligence, Vol. 16, No. 3, pp. 251–269.

Sopaci, E. and Akgün, H., 2016, Engineering geological characterization of the Antalya karstic rocks, southern Turkey: Environmental Earth Sciences, Vol. 75, No. 5, pp. 1–20.

Sumi, T., 2008, Designing and operating of flood retention dry dams in Japan and USA. In Proceedings 8th International Conference on Hydro-Science and Engineering ICHE-2008: Nagoya, Japan, 10 p.

Vera, J. A.; Ancochea, E.; Barnolas, A.; Bea, F.; Calvo, J. P.; Civis, J.; de Vicente, G.; Fernández-Gianotti, J.; GarcíaCortés, A.; Pérez-Estaún, A.; Pujalte, V.; Rodríguez-

14

Fernández, L. R.; Sopeña, A.; Tejero, A.; and Vera, J. A., 2004, Geología de España: Geological Survey of Spain (SGE)– Instituto Geológico y Minero de España (IGME), Madrid, Spain, 355 p.

Weaver, K. D. and Bruce, D. A., 2007, Dam Foundation Grouting: ASCE Press, Reston, VA, 473 p.

Yihdego, Y., 2016, Evaluation of flow reduction due to hydraulic barrier engineering structure: Case of urban area flood, contamination and pollution risk assessment: Journal Geotechnical Geological Engineering, Vol. 34, No. 5, pp. 1643–1654.

Yihdego, Y., 2017, Hydraulic in situ testing for mining and engineering design: Packer test procedure, preparation, analysis and interpretation. Journal Geotechnical Geological Engineering, Vol. 35, No. 1, pp. 29–44.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 1–14

Selection of Suitable Dam Axis Location Considering Permeability and Grout Curtain Optimization

Selection of Suitable Dam Axis Location Considering Permeability and Grout Curtain Optimization

MUSTAFA CAN CANOĞLU*

MUSTAFA CAN CANOĞLU*

Faculty of Engineering and Architecture, Environmental Engineering Department, Sinop University, Osmaniye Village, Nasuhbaşoğlu District, 57000 Sinop, Turkey

Faculty of Engineering and Architecture, Environmental Engineering Department, Sinop University, Osmaniye Village, Nasuhbaşoğlu District, 57000 Sinop, Turkey

Key Terms: Grout Curtain, Dam, Engineering Geology, Active Tectonics, Bedrock Permeability, Site Selection ABSTRACT This study investigated the effects of active tectonism on the construction of hydraulic structures. Apart from the effect of dynamic loads, active tectonism can cause permeability problems. The focus of this study was on overcoming the permeability problems considering the economic yield in terms of grout curtain design and optimum dam axis location. The ground permeability of dam locations is one of the decisive factors affecting the feasibility and economic yield of dam construction.

Techniques (such as grouting) for ensuring ground permeability reduction are generally expensive and timeconsuming; the experience at the first location of the Turgutlu Dam is a case in point. Construction of the first location of Turgutlu Dam was planned on a fault terrace that is part of the North Anatolian Fault Zone, which is the most important active tectonic feature in Turkey. A grout curtain was planned to provide permeability reduction and ground treatment for the terrace material. However, the base elevation of the adjacent valley is deeper, and thus potential leakage to this valley was expected. In spite of its big reservoir area, the Turgutlu Dam Project became infeasible in terms of economic yield due to the ground remediation (construction of grout curtain) costs for this location. To solve this problem, the dam was relocated downstream to avoid the fault terrace, choosing an optimum grout curtain to minimize cost and improve water retention of the reservoir, and increase economic yield of the dam.

INTRODUCTION Dams play an important role contributing to national economies in terms of potable water supply, agricultural irrigation, recreation, and much more. Additionally, the environmental benefits of dams, such as recreation, reliable sources of water for fighting forest *Corresponding author email: mccanoglu@sinop.edu.tr

fires, sustainable energy, and flood protection, should not be overlooked. On the other hand, some dams are problematic in the context of water retention and are not economic due to their unsuitable axis locations.

Permeable foundations can be remediated with the use of cement grouting. A grout curtain has been used at several large dams, such as Atatürk Dam (Turkey), Keban Dam (Turkey), Al Wehdah Dam (Jordan), Douera Dam (Algeria), Bolivar Dam (USA), and Berke Dam (Turkey).

Many researchers have studied dams geotechnically and hydrogeologically from different perspectives, such as earthquake impacts, liquefaction, and landslides (Lombardi, 1985; Nonveiller, 1989; Karagüzel and Kılıç, 2000; Aksoy and Ercanoğlu, 2006, 2007; Ulusay et al., 2007; Gürocak and Alemdağ, 2012; Uromeihy and Farrokhi, 2012; Tunar et al., 2013; Aldemir et al., 2015; Eryılmaz Türkkan and Korkmaz, 2015; Cato and Rogers, 2017; Ekmekci et al., 2017; and Nield, 2017). In particular, dam leakage problems have been studied by Romanov et al. (2003), Türkmen (2003), Ghobadi et al. (2005), Koçbay and Kılıç (2006), Uromeihy and Barzegari (2007), and Canoğlu and Kurtuluş (2017). Kayabaşı et al. (2015) worked on the prediction of Lugeon values, which are the basic in situ test for grouting. Sadeghiyeh et al. (2013) studied the connection between groutability and permeability for Ostur Dam. The study area is situated in the Marmara region, which has a semi-arid, continental climate with hot, dry summers and cold, snowy winters. Turgutlu Dam will supply about 150 ha for first use on agricultural lands and for firefighting and recreation.

Turgutlu Dam is planned to be constructed on the Değirmendere River, located approximately 4 km northeast of the town of Pamukova, in Sakarya Province. Access is provided by an asphalt road throughout the four seasons (Figure 1).

An important factor for selecting a suitable dam location in this region is the existence of geological structures and their seismic impacts due to the North Anatolian Fault Zone (NAFZ). The first location of the Turgutlu Dam was planned on a fault terrace of the North Anatolian Fault (NAF) by structural

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

15

Key Terms: Grout Curtain, Dam, Engineering Geology, Active Tectonics, Bedrock Permeability, Site Selection ABSTRACT This study investigated the effects of active tectonism on the construction of hydraulic structures. Apart from the effect of dynamic loads, active tectonism can cause permeability problems. The focus of this study was on overcoming the permeability problems considering the economic yield in terms of grout curtain design and optimum dam axis location. The ground permeability of dam locations is one of the decisive factors affecting the feasibility and economic yield of dam construction.

Techniques (such as grouting) for ensuring ground permeability reduction are generally expensive and timeconsuming; the experience at the first location of the Turgutlu Dam is a case in point. Construction of the first location of Turgutlu Dam was planned on a fault terrace that is part of the North Anatolian Fault Zone, which is the most important active tectonic feature in Turkey. A grout curtain was planned to provide permeability reduction and ground treatment for the terrace material. However, the base elevation of the adjacent valley is deeper, and thus potential leakage to this valley was expected. In spite of its big reservoir area, the Turgutlu Dam Project became infeasible in terms of economic yield due to the ground remediation (construction of grout curtain) costs for this location. To solve this problem, the dam was relocated downstream to avoid the fault terrace, choosing an optimum grout curtain to minimize cost and improve water retention of the reservoir, and increase economic yield of the dam.

INTRODUCTION Dams play an important role contributing to national economies in terms of potable water supply, agricultural irrigation, recreation, and much more. Additionally, the environmental benefits of dams, such as recreation, reliable sources of water for fighting forest *Corresponding author email: mccanoglu@sinop.edu.tr

fires, sustainable energy, and flood protection, should not be overlooked. On the other hand, some dams are problematic in the context of water retention and are not economic due to their unsuitable axis locations.

Permeable foundations can be remediated with the use of cement grouting. A grout curtain has been used at several large dams, such as Atatürk Dam (Turkey), Keban Dam (Turkey), Al Wehdah Dam (Jordan), Douera Dam (Algeria), Bolivar Dam (USA), and Berke Dam (Turkey).

Many researchers have studied dams geotechnically and hydrogeologically from different perspectives, such as earthquake impacts, liquefaction, and landslides (Lombardi, 1985; Nonveiller, 1989; Karagüzel and Kılıç, 2000; Aksoy and Ercanoğlu, 2006, 2007; Ulusay et al., 2007; Gürocak and Alemdağ, 2012; Uromeihy and Farrokhi, 2012; Tunar et al., 2013; Aldemir et al., 2015; Eryılmaz Türkkan and Korkmaz, 2015; Cato and Rogers, 2017; Ekmekci et al., 2017; and Nield, 2017). In particular, dam leakage problems have been studied by Romanov et al. (2003), Türkmen (2003), Ghobadi et al. (2005), Koçbay and Kılıç (2006), Uromeihy and Barzegari (2007), and Canoğlu and Kurtuluş (2017). Kayabaşı et al. (2015) worked on the prediction of Lugeon values, which are the basic in situ test for grouting. Sadeghiyeh et al. (2013) studied the connection between groutability and permeability for Ostur Dam. The study area is situated in the Marmara region, which has a semi-arid, continental climate with hot, dry summers and cold, snowy winters. Turgutlu Dam will supply about 150 ha for first use on agricultural lands and for firefighting and recreation.

Turgutlu Dam is planned to be constructed on the Değirmendere River, located approximately 4 km northeast of the town of Pamukova, in Sakarya Province. Access is provided by an asphalt road throughout the four seasons (Figure 1).

An important factor for selecting a suitable dam location in this region is the existence of geological structures and their seismic impacts due to the North Anatolian Fault Zone (NAFZ). The first location of the Turgutlu Dam was planned on a fault terrace of the North Anatolian Fault (NAF) by structural

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15

Canoğlu

Canoğlu

Figure 1. Site location map of study area and first axis location planned for Turgutlu Dam (modified from SuYapi, 2013).

Figure 1. Site location map of study area and first axis location planned for Turgutlu Dam (modified from SuYapi, 2013).

engineers looking to achieve economic benefit in terms of water retention in the reservoir area and irrigation of more agricultural lands. However, the terrace material is highly permeable due to its grain size distribution (blocky silty sandy gravel “GW-GP”). In these circumstances, permeability problems and remediation techniques are geotechnically prominent. Remediation techniques, and their cost-benefit for the potential axis, control the feasibility of the structural design.

This study consisted of office pre-studies, field reconnaissance, detailed office work, and a drilling program. Within the scope of the office pre-studies, alternative axis locations and their viabilities were evaluated. The field pre-studies consisted of detailed geological mapping of alternative axis locations and their reservoir areas, as well as evaluating geotechnical risks and permeability problems of axis locations. Within the detailed office work, the suitability of potential dam locations was evaluated in terms of dam body construction costs, approximate grout curtain costs, and the approximate irrigation area. Finally, 16

with the drilling program, geotechnical investigations were performed to determine the feasibility of the dam project in the context of dam foundation permeability.

GEOLOGICAL SETTING OF THE STUDY AREA In the study area and its nearby environs, Precambrian, Paleozoic, Mesozoic, and Cenozoic geological units are observed. The Precambrian Gökgöz Metagranitoids (PGm) underlie the base of the stratigraphic section. The Gökgöz Metagranitoids are covered unconformably by the sedimentary units of the Ordovician Sopalı Formation (Os) and Permian–Triassic İznik Metamorphics (PTim). The sedimentary units of the Cretaceous Abant Formation (KTab) are observed above these units discordantly (Çelik et al., 2009).

Finally, Quaternary-age alluvium and terrace materials unconformably cover all these units. The study area is located in the NAFZ, which includes many

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

engineers looking to achieve economic benefit in terms of water retention in the reservoir area and irrigation of more agricultural lands. However, the terrace material is highly permeable due to its grain size distribution (blocky silty sandy gravel “GW-GP”). In these circumstances, permeability problems and remediation techniques are geotechnically prominent. Remediation techniques, and their cost-benefit for the potential axis, control the feasibility of the structural design.

This study consisted of office pre-studies, field reconnaissance, detailed office work, and a drilling program. Within the scope of the office pre-studies, alternative axis locations and their viabilities were evaluated. The field pre-studies consisted of detailed geological mapping of alternative axis locations and their reservoir areas, as well as evaluating geotechnical risks and permeability problems of axis locations. Within the detailed office work, the suitability of potential dam locations was evaluated in terms of dam body construction costs, approximate grout curtain costs, and the approximate irrigation area. Finally, 16

with the drilling program, geotechnical investigations were performed to determine the feasibility of the dam project in the context of dam foundation permeability.

GEOLOGICAL SETTING OF THE STUDY AREA In the study area and its nearby environs, Precambrian, Paleozoic, Mesozoic, and Cenozoic geological units are observed. The Precambrian Gökgöz Metagranitoids (PGm) underlie the base of the stratigraphic section. The Gökgöz Metagranitoids are covered unconformably by the sedimentary units of the Ordovician Sopalı Formation (Os) and Permian–Triassic İznik Metamorphics (PTim). The sedimentary units of the Cretaceous Abant Formation (KTab) are observed above these units discordantly (Çelik et al., 2009).

Finally, Quaternary-age alluvium and terrace materials unconformably cover all these units. The study area is located in the NAFZ, which includes many

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

Permeability and Grout Curtain Optimization in Dam Axis Location

tectonically active faults that produce many destructive earthquakes (Figure 2).

The irrigation area and the axis location of Turgutlu Dam are located in the NAFZ. The first axis location planned for Turgutlu Dam was located on the secondary arcuate fault of the NAF with uplifted terrace material. The presence of uplifted terrace material shows that this fault is active. Additionally, the NAFZ is the most seismically active fault in Anatolia. A fault terrace, consisting of boulders, gravel, sand, and silt, is present along the left abutment of the reservoir area for the first dam location. This fault terrace has a very permeable prima-facie character (Figure 3a, b, and c).

The lithology of its gravels and blocks is highly variable, and their origin is generally granitic and volcanic (basalt and andesite) rocks and locally limestone. This fault terrace material is sub-angular to sub-rounded, poorly sorted, and well graded, with sizes ranging from fine grains to boulders. The sieve analysis performed on the soil sample obtained from test pits showed that the terrace material contains less than 7% soil passing the 75 μm sieve. The granular nature of the terrace material is a good indicator of permeable ground. The thickness of the fault terrace, observed by the road cut, reaches up to 40 m (Figure 3a).

ENGINEERING GEOLOGY A literature review showed that the primary reason for selecting the first dam location was based on the agricultural economy. Geological mapping, drilling, and in situ testing were performed to evaluate the site suitability. The drilling work consisted of core sampling from boreholes, Lugeon tests, and falling head permeability tests. During this evaluation, a fault fragment of the NAF and its terraced material were observed in the planned dam foundation. The presence of an active fault endangers the dam’s stability under seismic loads for the planned concrete dam. In addition, the fault terrace on the left abutment, exposed over large areas, could have caused potential leakage problems. This situation is seen more clearly on the detailed geologic map of Turgutlu Dam location 1 and its reservoir area (Figure 4). It should also be emphasized that the leakage problems could include potential hazards from internal erosion/piping of terrace material resulting from excessive seepage, which could lead to potential dam failure.

Concrete dam body types should not be considered in this region due to their rigidity under dynamic loads such as earthquakes. Earthfill dams perform better under seismic loading. For this reason, the dam body size is important to consider because of the excavation and transportation costs for construction.

Permeability and Grout Curtain Optimization in Dam Axis Location

Dam location 1 was considered as the best alternative due to its lower construction costs in terms of dam body dimensions. However, due to the highly permeable characteristics of the fault terrace located in the left abutment, the approximate cost of the grout curtain had to be estimated before performing detailed field investigations (drilling operations and in situ geotechnical tests) and Lugeon tests.

Due to the limited budget, a field exploration program for the detailed dimensional analysis of the grout curtain in location 1 was not feasible. The design for the grout curtain was estimated based on the analysis of a geological cross section (Figure 5). Based on the cross-section analysis, the approximate extent and layout of the grout curtain were determined. The boundary between the Precambrian Gökgöz Metagranitoids and Quaternary terrace material (B–D cross-section) was drawn anticipating shallow bedrock depths (Figure 5).

If Turgutlu Dam location 1 had been selected for construction, the approximate amount of grout needed would have been 499 m3 . This is based on the assumption that 50–100 kg of solid material would be injected per 1 m of grout borehole length. It was estimated that 4,325 m of cumulative borehole length would be needed for grouting. If there were no permeable terrace material on the left abutment, the comparable amount of grout would be 213 m3 and only 1,940 m of drilling.

In other words, an extra 2,385 m of drilling depth and 286 m3 of grouting material would be needed for dam location 1 because of the terrace material.

Because of the added cost required to grout the terrace material, other seepage mitigation alternatives were considered. The first alternative considered was a concrete-faced earthfill dam and shotcrete on the left abutment (Figure 5). However, during an earthquake, concrete membranes could be substantially damaged due to their rigid character. Additionally, groundwater flow out of the highly permeable terrace material could cause major landslide events in the reservoir area due to the inhibition of water flux, the shotcrete, and augmentation of the pore-water pressure. For these two reasons, this alternative was discarded.

The second alternative considered to prevent potential leakages through the terrace material was to use geotextiles. This alternative would need elaborate and detailed workmanship and long-term maintenance.

Additionally, it costs much more than a grouting-only option. A cut-off wall was also considered as a costcompetitive alternative to reduce seepage through the fault terrace. However, to construct this cut-off wall for 15 m depth and 500 m length (along section B–D, Figure 5), a huge amount of excavation would be required.

Considering the costs of construction, this alternative was also discarded. Aside from the high construction

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17

tectonically active faults that produce many destructive earthquakes (Figure 2).

The irrigation area and the axis location of Turgutlu Dam are located in the NAFZ. The first axis location planned for Turgutlu Dam was located on the secondary arcuate fault of the NAF with uplifted terrace material. The presence of uplifted terrace material shows that this fault is active. Additionally, the NAFZ is the most seismically active fault in Anatolia. A fault terrace, consisting of boulders, gravel, sand, and silt, is present along the left abutment of the reservoir area for the first dam location. This fault terrace has a very permeable prima-facie character (Figure 3a, b, and c).

The lithology of its gravels and blocks is highly variable, and their origin is generally granitic and volcanic (basalt and andesite) rocks and locally limestone. This fault terrace material is sub-angular to sub-rounded, poorly sorted, and well graded, with sizes ranging from fine grains to boulders. The sieve analysis performed on the soil sample obtained from test pits showed that the terrace material contains less than 7% soil passing the 75 μm sieve. The granular nature of the terrace material is a good indicator of permeable ground. The thickness of the fault terrace, observed by the road cut, reaches up to 40 m (Figure 3a).

ENGINEERING GEOLOGY A literature review showed that the primary reason for selecting the first dam location was based on the agricultural economy. Geological mapping, drilling, and in situ testing were performed to evaluate the site suitability. The drilling work consisted of core sampling from boreholes, Lugeon tests, and falling head permeability tests. During this evaluation, a fault fragment of the NAF and its terraced material were observed in the planned dam foundation. The presence of an active fault endangers the dam’s stability under seismic loads for the planned concrete dam. In addition, the fault terrace on the left abutment, exposed over large areas, could have caused potential leakage problems. This situation is seen more clearly on the detailed geologic map of Turgutlu Dam location 1 and its reservoir area (Figure 4). It should also be emphasized that the leakage problems could include potential hazards from internal erosion/piping of terrace material resulting from excessive seepage, which could lead to potential dam failure.

Concrete dam body types should not be considered in this region due to their rigidity under dynamic loads such as earthquakes. Earthfill dams perform better under seismic loading. For this reason, the dam body size is important to consider because of the excavation and transportation costs for construction.

Dam location 1 was considered as the best alternative due to its lower construction costs in terms of dam body dimensions. However, due to the highly permeable characteristics of the fault terrace located in the left abutment, the approximate cost of the grout curtain had to be estimated before performing detailed field investigations (drilling operations and in situ geotechnical tests) and Lugeon tests.

Due to the limited budget, a field exploration program for the detailed dimensional analysis of the grout curtain in location 1 was not feasible. The design for the grout curtain was estimated based on the analysis of a geological cross section (Figure 5). Based on the cross-section analysis, the approximate extent and layout of the grout curtain were determined. The boundary between the Precambrian Gökgöz Metagranitoids and Quaternary terrace material (B–D cross-section) was drawn anticipating shallow bedrock depths (Figure 5).

If Turgutlu Dam location 1 had been selected for construction, the approximate amount of grout needed would have been 499 m3 . This is based on the assumption that 50–100 kg of solid material would be injected per 1 m of grout borehole length. It was estimated that 4,325 m of cumulative borehole length would be needed for grouting. If there were no permeable terrace material on the left abutment, the comparable amount of grout would be 213 m3 and only 1,940 m of drilling.

In other words, an extra 2,385 m of drilling depth and 286 m3 of grouting material would be needed for dam location 1 because of the terrace material.

Because of the added cost required to grout the terrace material, other seepage mitigation alternatives were considered. The first alternative considered was a concrete-faced earthfill dam and shotcrete on the left abutment (Figure 5). However, during an earthquake, concrete membranes could be substantially damaged due to their rigid character. Additionally, groundwater flow out of the highly permeable terrace material could cause major landslide events in the reservoir area due to the inhibition of water flux, the shotcrete, and augmentation of the pore-water pressure. For these two reasons, this alternative was discarded.

The second alternative considered to prevent potential leakages through the terrace material was to use geotextiles. This alternative would need elaborate and detailed workmanship and long-term maintenance.

Additionally, it costs much more than a grouting-only option. A cut-off wall was also considered as a costcompetitive alternative to reduce seepage through the fault terrace. However, to construct this cut-off wall for 15 m depth and 500 m length (along section B–D, Figure 5), a huge amount of excavation would be required.

Considering the costs of construction, this alternative was also discarded. Aside from the high construction

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Canoğlu

Canoğlu

Figure 2. Geological map of study area showing two potential axis locations of Turgutlu Dam (modified from MTA Genel Mudurlugu, 2002).

Figure 2. Geological map of study area showing two potential axis locations of Turgutlu Dam (modified from MTA Genel Mudurlugu, 2002).

costs, part of the area along section B–C was designated by the Turkish government as a natural protected area, and land modification is forbidden for this kind of land. Considering these circumstances, a new dam axis alternative was required. This new dam axis needed to be as short as possible, relatively impermeable, and have reasonable excavation costs.

costs, part of the area along section B–C was designated by the Turkish government as a natural protected area, and land modification is forbidden for this kind of land. Considering these circumstances, a new dam axis alternative was required. This new dam axis needed to be as short as possible, relatively impermeable, and have reasonable excavation costs.

Figure 3. (A) Left abutment of the Turgutlu Dam location 1. (B) Fault terrace material. (C) Content of terrace material, consisting of boulders, gravel, sand, and silt.

18

Because of the circumstances at the first location, Turgutlu Dam location 2 was identified as a potential dam site location (Figure 4). In order to evaluate dam location 2 in terms of permeability and geotechnical suitability, a geotechnical investigation was performed.

Within the context of the geotechnical investigations, six boreholes and 185 m total depth of drilling were performed along the axis of location 2. Lugeon tests were performed in the boreholes drilled along the dam axis in order to assess the hydraulic conductivity characteristics of the geological units under variable hydrostatic pressure. The hydraulic conductivity of the Quaternary-age alluvium was determined by falling head permeability tests.

The embankment of the Turgutlu Dam at location 2 was planned as a clay-core, homogeneous earthfill dam, considering available construction materials (Figure 4). Parts of the fault terrace materials could be used as filling material. Benefits to this strategy included lower costs for construction materials and increased reservoir area. The maximum height of the dam from the thalweg is 26.7 m, and the height from the foundation is 29.2 m, with a crest length of 214 m.

The minimum water elevation in the reservoir is projected to be 167.15 m, and the maximum water level is projected to be 176.50 m. The inlet elevation of the

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

Figure 3. (A) Left abutment of the Turgutlu Dam location 1. (B) Fault terrace material. (C) Content of terrace material, consisting of boulders, gravel, sand, and silt.

18

Because of the circumstances at the first location, Turgutlu Dam location 2 was identified as a potential dam site location (Figure 4). In order to evaluate dam location 2 in terms of permeability and geotechnical suitability, a geotechnical investigation was performed.

Within the context of the geotechnical investigations, six boreholes and 185 m total depth of drilling were performed along the axis of location 2. Lugeon tests were performed in the boreholes drilled along the dam axis in order to assess the hydraulic conductivity characteristics of the geological units under variable hydrostatic pressure. The hydraulic conductivity of the Quaternary-age alluvium was determined by falling head permeability tests.

The embankment of the Turgutlu Dam at location 2 was planned as a clay-core, homogeneous earthfill dam, considering available construction materials (Figure 4). Parts of the fault terrace materials could be used as filling material. Benefits to this strategy included lower costs for construction materials and increased reservoir area. The maximum height of the dam from the thalweg is 26.7 m, and the height from the foundation is 29.2 m, with a crest length of 214 m.

The minimum water elevation in the reservoir is projected to be 167.15 m, and the maximum water level is projected to be 176.50 m. The inlet elevation of the

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Permeability and Grout Curtain Optimization in Dam Axis Location

Permeability and Grout Curtain Optimization in Dam Axis Location

Figure 4. Geologic map of proposed Turgutlu Dam axes and their reservoir areas.

Figure 4. Geologic map of proposed Turgutlu Dam axes and their reservoir areas.

sluice, which is designed as a concrete jacket penstock pipe type in the right abutment, is 157 m, and the outlet elevation is 154 m. The spillway will be located in the left abutment with a water-stilling basin. A cofferdam, with a height of 10.4 m, is also projected in the upstream reach.

Permeability Characteristics of Dam Location 2 The permeability characteristics of the geological formation at dam location 2 were determined by Lugeon tests. These tests were performed in exploratory boreholes drilled along the dam axis. The boreholes (SK-1, SK-2, SK-3, SK-4, SK-5, and SK-6) are shown in Figure 4. SK-1, SK-2, and SK-5 were drilled in bedrock (Permian-aged Gökgöz Metagranitoid).

Boreholes SK-3, SK-4, and SK-6 were drilled in alluvium to verify the depth of the alluvium and its permeability characteristics, as well as those of the underlying units (Figure 6).

In the core samples obtained from the boreholes drilled for geotechnical investigations, according to the weathering degree of rock masses proposed by ISRM (2007), completely weathered (W4), moderately weathered (W3), slightly weathered (W2), and unweathered (W1) geological units were encountered. The first 8 m in borehole SK-1 and the depths between 3 and 5 m in borehole SK-3 were identified as completely weathered (W4). The first 7 m in borehole SK-2, the depths between 5 and 13 m in borehole SK-3, between 5 and 10 m in borehole SK-4, and the first 9 m in borehole SK-5 were moderately weathered (W3). The depths between 7 and 15 m in borehole SK-1, between 7 and13 m in borehole SK-2, between 13 and 30 m in borehole SK-3, between 9 and 15 m in borehole SK-6, between 10 and 30 m in borehole SK-4, and between 10 and 40 m in borehole SK-5 were slightly weathered (W2). The depths between 15 and 40 m in borehole SK-1 and between 13 and 30 m in borehole SK-2 were unweathered (W1).

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sluice, which is designed as a concrete jacket penstock pipe type in the right abutment, is 157 m, and the outlet elevation is 154 m. The spillway will be located in the left abutment with a water-stilling basin. A cofferdam, with a height of 10.4 m, is also projected in the upstream reach.

Permeability Characteristics of Dam Location 2 The permeability characteristics of the geological formation at dam location 2 were determined by Lugeon tests. These tests were performed in exploratory boreholes drilled along the dam axis. The boreholes (SK-1, SK-2, SK-3, SK-4, SK-5, and SK-6) are shown in Figure 4. SK-1, SK-2, and SK-5 were drilled in bedrock (Permian-aged Gökgöz Metagranitoid).

Boreholes SK-3, SK-4, and SK-6 were drilled in alluvium to verify the depth of the alluvium and its permeability characteristics, as well as those of the underlying units (Figure 6).

In the core samples obtained from the boreholes drilled for geotechnical investigations, according to the weathering degree of rock masses proposed by ISRM (2007), completely weathered (W4), moderately weathered (W3), slightly weathered (W2), and unweathered (W1) geological units were encountered. The first 8 m in borehole SK-1 and the depths between 3 and 5 m in borehole SK-3 were identified as completely weathered (W4). The first 7 m in borehole SK-2, the depths between 5 and 13 m in borehole SK-3, between 5 and 10 m in borehole SK-4, and the first 9 m in borehole SK-5 were moderately weathered (W3). The depths between 7 and 15 m in borehole SK-1, between 7 and13 m in borehole SK-2, between 13 and 30 m in borehole SK-3, between 9 and 15 m in borehole SK-6, between 10 and 30 m in borehole SK-4, and between 10 and 40 m in borehole SK-5 were slightly weathered (W2). The depths between 15 and 40 m in borehole SK-1 and between 13 and 30 m in borehole SK-2 were unweathered (W1).

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Figure 5. Geological cross section showing depth of grout curtain mitigation option through left abutment of Turgutlu Dam location 1.

Figure 5. Geological cross section showing depth of grout curtain mitigation option through left abutment of Turgutlu Dam location 1.

The Lugeon test (known also as the Packer test or water pressure test) is a conventional technique utilized generally for dam projects in order to specify the permeability characteristics of foundation rock under variable hydraulic heads; it was applied to the bore-

holes drilled on Turgutlu Dam location 2. In Turkey, the Lugeon test is generally performed using test interval lengths of 2 m to 5 m. According to Akyüz (2010), for a permeable rock mass, due to its variable physical properties, the test zone can be reduced to 1 m,

The Lugeon test (known also as the Packer test or water pressure test) is a conventional technique utilized generally for dam projects in order to specify the permeability characteristics of foundation rock under variable hydraulic heads; it was applied to the bore-

Figure 6. Engineering geology cross section of dam location 2.

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holes drilled on Turgutlu Dam location 2. In Turkey, the Lugeon test is generally performed using test interval lengths of 2 m to 5 m. According to Akyüz (2010), for a permeable rock mass, due to its variable physical properties, the test zone can be reduced to 1 m,

Figure 6. Engineering geology cross section of dam location 2.

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Permeability and Grout Curtain Optimization in Dam Axis Location Table 1. Permeability classification based on the Lugeon values of rock masses.

Lugeon Values

Permeability Class

<1 1–5 5–25 >25

Impermeable Low permeability Permeable Highly permeable

whereas, in a uniform and impermeable rock mass, the test interval length can be augmented up to 10 m.

One Lugeon signifies the amount of water pumped to a 1 m length of the test zone under 10 atmospheres of hydraulic pressure in 1 minute. This statement is expressed mathematically by Eq. 1.

LU = (Q × 10) / (P × L) ,

(1)

where LU is the Lugeon value (L/min/m), Q is the flow rate or amount of water given to the rock formation per minute (L/min), P is the hydraulic head applied to the test zone (kg/cm2 ), and L is the test length (m).

For the Lugeon test, the pressure applied to the test interval is specified by engineering judgment, depending on the physical properties of the rock, but the general application in Turkey uses test pressures of 2, 4, 6, 8, and 10 kg/cm2 . Each pressure stage is applied to the rock for 10 minutes, and the water leakages are recorded every 5 minutes. Then, 9, 7, 5, 3, and 1 kg/cm2 of test pressure is applied, and water loss is recorded (Canoğlu and Kurtuluş, 2017). The test pressures are adjusted according to depth in order to prevent potential hydraulic fracturing. Test pressures are applied as follows: depths between 0 and 4 m up to 2 kg/cm2 , between 4 and 10 m up to 4 kg/cm2 , between 10 and 20 m up to 6 kg/cm2 , between 20 and 30 m up to 8 kg/cm2 , and between 30 and 40 m up to 10 kg/cm2 . Accordingly, the permeability classification of the rock masses, depending on the Lugeon values, can be interpreted as shown in Table 1.

The permeability profile of dam axis location 2 under variable hydraulic head was determined by the Lugeon tests. The left abutment is represented by boreholes SK-1 and SK-2, the thalweg by boreholes SK-3 and SK-6, and the right abutment by boreholes SK-4 and SK-5 (Figure 7). The Lugeon values listed in Figure 7 are the arithmetic mean of each of the test pressure stages.

Estimation of Water Ingress to the Foundation Excavation The Değirmendere River flows during the rainy season. During the summer and autumn, runoff is not observed, and groundwater flows through the

Permeability and Grout Curtain Optimization in Dam Axis Location

Quaternary-age alluvium. The groundwater depth in the alluvium varies between 0.8 m and 4.0 m, as measured during and after the drilling operation. Falling head permeability tests performed in boreholes SK3 and SK-6 drilled in the alluvium illustrated that the hydraulic conductivity (K) of the alluvium is approximately 10−4 cm/s. After construction has created the foundation excavation, water ingress from the upstream and downstream walls is expected, based on the hydraulic conductivity of the alluvium. The costs of discharging this water ingress is an important cost consideration for construction. For this reason, the flow rate of water ingress into the foundation excavation was estimated using Darcy’s law, with the assumption of alluvium being homogeneous and isotropic. Darcy’s law is expressed as: Q = A × K × i.

(2)

In this formula, Q is the flow rate of the water ingress to the excavation pit, A is the cross-sectional area of the alluvium perpendicular to the water flux, K is the hydraulic conductivity of alluvium, and i is the hydraulic gradient. Calculation of Q was performed based on the following assumptions: (1) The mean alluvium thickness was estimated to be 9 m based on the engineering geology cross section.

(2) The phreatic surface is 4 m, based on measured groundwater levels.

(3) The exposed alluvium width is 50 m, based on the mapped geology.

(4) The excavation depth is 10 m along the dam axis location 2.

(5) The maximum hydraulic head (H) behind the cofferdam is assumed as the free water level, where H = 9 m.

(6) The horizontal distance between the cofferdam and the foundation excavation is 50 m.

(7) Groundwater inflow from the downstream wall is assumed as equal to the water ingress from the upstream excavation surface.

(8) Water ingress from the rock formations is disregarded, because it is assumed to be negligible.

In this case, and So,

iupstream = 9/50 = 018,

(3)

A = 50 m × 10 m = 500 m2 .

(4)

−4

and

Qupstream = 10

× 500 × 0.18 = 9L/s,

Qtotal = 9 × 2 = 18L/s.

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(5)

(6) 21

Table 1. Permeability classification based on the Lugeon values of rock masses.

Lugeon Values

Permeability Class

<1 1–5 5–25 >25

Impermeable Low permeability Permeable Highly permeable

whereas, in a uniform and impermeable rock mass, the test interval length can be augmented up to 10 m.

One Lugeon signifies the amount of water pumped to a 1 m length of the test zone under 10 atmospheres of hydraulic pressure in 1 minute. This statement is expressed mathematically by Eq. 1.

LU = (Q × 10) / (P × L) ,

(1)

where LU is the Lugeon value (L/min/m), Q is the flow rate or amount of water given to the rock formation per minute (L/min), P is the hydraulic head applied to the test zone (kg/cm2 ), and L is the test length (m).

For the Lugeon test, the pressure applied to the test interval is specified by engineering judgment, depending on the physical properties of the rock, but the general application in Turkey uses test pressures of 2, 4, 6, 8, and 10 kg/cm2 . Each pressure stage is applied to the rock for 10 minutes, and the water leakages are recorded every 5 minutes. Then, 9, 7, 5, 3, and 1 kg/cm2 of test pressure is applied, and water loss is recorded (Canoğlu and Kurtuluş, 2017). The test pressures are adjusted according to depth in order to prevent potential hydraulic fracturing. Test pressures are applied as follows: depths between 0 and 4 m up to 2 kg/cm2 , between 4 and 10 m up to 4 kg/cm2 , between 10 and 20 m up to 6 kg/cm2 , between 20 and 30 m up to 8 kg/cm2 , and between 30 and 40 m up to 10 kg/cm2 . Accordingly, the permeability classification of the rock masses, depending on the Lugeon values, can be interpreted as shown in Table 1.

The permeability profile of dam axis location 2 under variable hydraulic head was determined by the Lugeon tests. The left abutment is represented by boreholes SK-1 and SK-2, the thalweg by boreholes SK-3 and SK-6, and the right abutment by boreholes SK-4 and SK-5 (Figure 7). The Lugeon values listed in Figure 7 are the arithmetic mean of each of the test pressure stages.

Estimation of Water Ingress to the Foundation Excavation The Değirmendere River flows during the rainy season. During the summer and autumn, runoff is not observed, and groundwater flows through the

Quaternary-age alluvium. The groundwater depth in the alluvium varies between 0.8 m and 4.0 m, as measured during and after the drilling operation. Falling head permeability tests performed in boreholes SK3 and SK-6 drilled in the alluvium illustrated that the hydraulic conductivity (K) of the alluvium is approximately 10−4 cm/s. After construction has created the foundation excavation, water ingress from the upstream and downstream walls is expected, based on the hydraulic conductivity of the alluvium. The costs of discharging this water ingress is an important cost consideration for construction. For this reason, the flow rate of water ingress into the foundation excavation was estimated using Darcy’s law, with the assumption of alluvium being homogeneous and isotropic. Darcy’s law is expressed as: Q = A × K × i.

(2)

In this formula, Q is the flow rate of the water ingress to the excavation pit, A is the cross-sectional area of the alluvium perpendicular to the water flux, K is the hydraulic conductivity of alluvium, and i is the hydraulic gradient. Calculation of Q was performed based on the following assumptions: (1) The mean alluvium thickness was estimated to be 9 m based on the engineering geology cross section.

(2) The phreatic surface is 4 m, based on measured groundwater levels.

(3) The exposed alluvium width is 50 m, based on the mapped geology.

(4) The excavation depth is 10 m along the dam axis location 2.

(5) The maximum hydraulic head (H) behind the cofferdam is assumed as the free water level, where H = 9 m.

(6) The horizontal distance between the cofferdam and the foundation excavation is 50 m.

(7) Groundwater inflow from the downstream wall is assumed as equal to the water ingress from the upstream excavation surface.

(8) Water ingress from the rock formations is disregarded, because it is assumed to be negligible.

In this case, and So, and

iupstream = 9/50 = 018,

(3)

A = 50 m × 10 m = 500 m2 .

(4)

Qupstream = 10−4 × 500 × 0.18 = 9L/s,

(5)

Qtotal = 9 × 2 = 18L/s.

(6)

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Figure 7. Lugeon profile of dam location 2 for (A) left abutment, (B) thalweg, and (C) right abutment.

Figure 7. Lugeon profile of dam location 2 for (A) left abutment, (B) thalweg, and (C) right abutment.

Water ingress into the foundation excavation with a flow rate of 18 L/s may need to be pumped out using suitable pumping equipment during construction.

OPTIMIZATION OF GROUT CURTAIN DEPTH Many methods have been proposed by many researchers for calculating grout curtain depth (h� ) as a function of the height of dam (h) (Ewert, 2003; Şekercioğlu, 2007; Schleiss and Pougatsch, 2011).

These methods are generally utilized as a final crosscheck, and their results are not strictly reliable without applying engineering judgment. Additionally, all these methods for calculating grout curtain depth generally produce similar results. The formula of Şekercioğlu (2007), shown as Eq. 7 here, which is based on the height of the dam, is well accepted in Turkey. For this reason, Eq. 7 was utilized for this project to determine the grout curtain depth.

(7) h� = 12 h + 15.

Furthermore, the relationship between the groundwater levels of the abutments and the thalweg is also significant for optimizing the grout curtain depth. The groundwater levels (GWL) of each borehole were measured after drilling operations. The measured GWL values of each borehole for the left abutment, thalweg, and right abutment are shown in Table 2.

Based on the measurements shown in Table 2, there is generally a decrease in GWL from the abutments to the thalweg. This indicates that the Değirmendere River is being recharged by groundwater (Figure 8).

22

However, the GWL of borehole SK-4 (right abutment) is deeper than that of boreholes SK-3 and SK-6 (thalweg). This could suggest that the right abutment is more permeable, which is consistent with the Lugeon test results. For this reason, the grout curtain depth in the right abutment was designed to be deeper than the left abutment, taking into consideration the geologic properties of the ground.

As a result of grouting, the expected leakage problems can be reduced or prevented by constructing a grout curtain as presented in Figure 8. For the left abutment, the grout curtain is designed to be 20–25 m below the excavation depth. Approaching the thalweg, the grout curtain depth gradually increases up to 40 m, due to the higher hydraulic head, which favors leakage. The grout curtain depth in the right abutment is planned to be 30–35 m in depth. A single-line grout curtain design was chosen with maximum 3 m grout hole spacing. The length of the grout curtain line is designed at 237 m. The grout holes are designed to be Table 2. Groundwater levels of each borehole.

Borehole Left abutment SK-1 SK-2 Thalweg SK-3 SK-6 Right abutment SK-4 SK-5

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Groundwater Level (m) 6.80 5.90 0.80 3.85 5.35 10.40

Water ingress into the foundation excavation with a flow rate of 18 L/s may need to be pumped out using suitable pumping equipment during construction.

OPTIMIZATION OF GROUT CURTAIN DEPTH Many methods have been proposed by many researchers for calculating grout curtain depth (h� ) as a function of the height of dam (h) (Ewert, 2003; Şekercioğlu, 2007; Schleiss and Pougatsch, 2011).

These methods are generally utilized as a final crosscheck, and their results are not strictly reliable without applying engineering judgment. Additionally, all these methods for calculating grout curtain depth generally produce similar results. The formula of Şekercioğlu (2007), shown as Eq. 7 here, which is based on the height of the dam, is well accepted in Turkey. For this reason, Eq. 7 was utilized for this project to determine the grout curtain depth.

(7) h� = 12 h + 15.

Furthermore, the relationship between the groundwater levels of the abutments and the thalweg is also significant for optimizing the grout curtain depth. The groundwater levels (GWL) of each borehole were measured after drilling operations. The measured GWL values of each borehole for the left abutment, thalweg, and right abutment are shown in Table 2.

Based on the measurements shown in Table 2, there is generally a decrease in GWL from the abutments to the thalweg. This indicates that the Değirmendere River is being recharged by groundwater (Figure 8).

22

However, the GWL of borehole SK-4 (right abutment) is deeper than that of boreholes SK-3 and SK-6 (thalweg). This could suggest that the right abutment is more permeable, which is consistent with the Lugeon test results. For this reason, the grout curtain depth in the right abutment was designed to be deeper than the left abutment, taking into consideration the geologic properties of the ground.

As a result of grouting, the expected leakage problems can be reduced or prevented by constructing a grout curtain as presented in Figure 8. For the left abutment, the grout curtain is designed to be 20–25 m below the excavation depth. Approaching the thalweg, the grout curtain depth gradually increases up to 40 m, due to the higher hydraulic head, which favors leakage. The grout curtain depth in the right abutment is planned to be 30–35 m in depth. A single-line grout curtain design was chosen with maximum 3 m grout hole spacing. The length of the grout curtain line is designed at 237 m. The grout holes are designed to be Table 2. Groundwater levels of each borehole.

Borehole Left abutment SK-1 SK-2 Thalweg SK-3 SK-6 Right abutment SK-4 SK-5

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Groundwater Level (m) 6.80 5.90 0.80 3.85 5.35 10.40

Permeability and Grout Curtain Optimization in Dam Axis Location

Permeability and Grout Curtain Optimization in Dam Axis Location

Figure 8. Permeability cross section of dam location 2 and grout curtain boundaries.

Figure 8. Permeability cross section of dam location 2 and grout curtain boundaries.

vertical with a minimum hole diameter of 76 mm. Stable cement grout was selected as the grout type, and the maximum grouting pressure is specified as 10 kg/cm2 .

RESULTS AND CONCLUSIONS The aim of this study was to design Turgutlu Dam on a suitable dam axis location, considering the amount of water storage and the total irrigation area in terms of economic benefit. For this purpose, dam location 1 was first investigated. However, a fragment of the NAF passes through axis location, with its terraced alluvium. Due to the permeable character of the fault terrace and potential grouting costs, construction of Turgutlu Dam at location 1 would be cost prohibitive.

For this reason, another axis location alternative was investigated, and dam location 2 was selected.

In order to evaluate the feasibility of location 2 in terms of permeability and geotechnical suitability, drilling and in situ testing (Lugeon tests) were performed. The results obtained from the Lugeon tests performed in six boreholes were evaluated in order to design the grout curtain. The left abutment was found to be permeable down to 12 m depth, and below this depth, the abutment is less permeable. The thalweg is generally permeable, but the results from borehole SK6 could be interpreted as low permeability. The right abutment generally has low permeability, except for the 20–25 m level of borehole SK-5 (Figures 7 and

8). It is observed that this level of borehole SK-5 is highly jointed, and the rock core characteristics, which are pertinent to permeability, show anomalies, such as a low rock quality design (RQD) value (about 20%), and low total core recovery (TCR) value (about 50%).

In addition, the 6–10 m level of borehole SK-4 is also highly permeable due to its highly jointed rock core characteristics and degree of weathering.

Furthermore, a connection can be observed between the permeability and the degree of weathering for dam axis location 2 when comparing Figures 6 and 8. The foundation rock unit of dam axis location 2, Gökgöz Metagranitoids, is generally defined as unweathered (W1) and slightly weathered (W2), based on the core samples obtained from the drilling operation. The core samples taken from the near-surface were generally moderately weathered (W3) and totally weathered (W4). Moderately weathered units (W3) tend to be more permeable than unweathered (W1) and slightly weathered (W2) units in terms of water seepage (Figures 6 and 8).

During construction, it is planned to remove 9 m of alluvial thickness at the thalweg, 6 m of weathered unit on the left abutment, and 2.5 m of weathered unit on the right abutment through excavation (Figure 6). Water is expected to seep within the alluvium section at a flow rate of 18 L/s, as estimated from permeability values obtained from falling head permeability tests.

It should be emphasized that the water ingress from

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vertical with a minimum hole diameter of 76 mm. Stable cement grout was selected as the grout type, and the maximum grouting pressure is specified as 10 kg/cm2 .

RESULTS AND CONCLUSIONS The aim of this study was to design Turgutlu Dam on a suitable dam axis location, considering the amount of water storage and the total irrigation area in terms of economic benefit. For this purpose, dam location 1 was first investigated. However, a fragment of the NAF passes through axis location, with its terraced alluvium. Due to the permeable character of the fault terrace and potential grouting costs, construction of Turgutlu Dam at location 1 would be cost prohibitive.

For this reason, another axis location alternative was investigated, and dam location 2 was selected.

In order to evaluate the feasibility of location 2 in terms of permeability and geotechnical suitability, drilling and in situ testing (Lugeon tests) were performed. The results obtained from the Lugeon tests performed in six boreholes were evaluated in order to design the grout curtain. The left abutment was found to be permeable down to 12 m depth, and below this depth, the abutment is less permeable. The thalweg is generally permeable, but the results from borehole SK6 could be interpreted as low permeability. The right abutment generally has low permeability, except for the 20–25 m level of borehole SK-5 (Figures 7 and

8). It is observed that this level of borehole SK-5 is highly jointed, and the rock core characteristics, which are pertinent to permeability, show anomalies, such as a low rock quality design (RQD) value (about 20%), and low total core recovery (TCR) value (about 50%).

In addition, the 6–10 m level of borehole SK-4 is also highly permeable due to its highly jointed rock core characteristics and degree of weathering.

Furthermore, a connection can be observed between the permeability and the degree of weathering for dam axis location 2 when comparing Figures 6 and 8. The foundation rock unit of dam axis location 2, Gökgöz Metagranitoids, is generally defined as unweathered (W1) and slightly weathered (W2), based on the core samples obtained from the drilling operation. The core samples taken from the near-surface were generally moderately weathered (W3) and totally weathered (W4). Moderately weathered units (W3) tend to be more permeable than unweathered (W1) and slightly weathered (W2) units in terms of water seepage (Figures 6 and 8).

During construction, it is planned to remove 9 m of alluvial thickness at the thalweg, 6 m of weathered unit on the left abutment, and 2.5 m of weathered unit on the right abutment through excavation (Figure 6). Water is expected to seep within the alluvium section at a flow rate of 18 L/s, as estimated from permeability values obtained from falling head permeability tests.

It should be emphasized that the water ingress from

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the rock formations was disregarded for the calculation of flow rate. However, bedrock exposures could have potential seepage during excavation from groundwater flow through exposed discontinuities. Although this groundwater inflow is expected to be less than the upstream excavated surface, the hydraulic gradient and overall permeability are lower. This situation should be taken into account during the dewatering operation when construction starts.

Lugeon tests were performed to predict the amount of grout required under variable hydrostatic pressures.

The Lugeon tests indicated that the geological formation under axis location 2 generally has low permeability, except for some permeable zones close to the surface. It is anticipated that groundwater movement from upstream to downstream through these permeable zones will be reduced or prevented by the grout curtain shown in Figure 8. In addition to the grout curtain, due to the higher permeability and lower strength of the bedrock near the top of the rock surface, consolidation grouting will likely be needed to treat open bedrock discontinuities that will potentially be in contact with the dam embankment (Figure 8). Consolidation grouting design was chosen with 7 m depth and 3 m grout hole spacing. The grout holes were designed to be vertical with a minimum hole diameter of 76 mm. Stable cement grout is planned, and the maximum grout pressure is specified as 4 kg/cm2 . Consolidation grouting is generally meant to fill voids, fractured zones, and cracks at and below the surface of the excavated foundation. This foundation treatment is planned to prevent future erosion or piping into the discontinuities and to avoid potential scour of the embankment by groundwater flow in the vicinity of these discontinuities.

ACKNOWLEDGMENTS This work is performed in the context of the “Eskişehir Dams Planning Engineering Services” project of the Turkish Republic Ministry of Forestry and Water Works, General Directorate of State Hydraulic Works, Eskişehir 3 Regional Directorate with contributions from SuYapı Engineering and Consulting Co. The author thanks SuYapi Engineering and Consulting Co. for sharing their information and the State Hydraulic Works, Eskişehir 3 Regional Directorate staff for their exchange of ideas, especially Hayrettin Baysal, Şeref Dağdelen, Feridun İnce, Osman Çakır, and Engin Kaplan.

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Canoğlu, M. C. and Kurtuluş, B., 2017, Permeability of Savcıbey dam (Bilecik) axis location and design of grout curtain: Bulletin Mineral Research Exploration, Vol. 154, pp. 157–168.

Cato, K. D. and Rogers, J. D., 2017, Failure of the Alexander Dam embankment and reconstruction using drainage mitigation on Kauai, 1930–1932: Environmental Engineering Geoscience, Vol. 23, No. 4, pp. 1–21. Çelik, Ö. F.; Gürer, Ö. F.; and Öz, İ., 2009, Geochemical and petrographical properties of granitoidic rocks located between Geyve gorge and Pamukova: Uygulamalı Yerbilimleri, Vol. 1, pp. 61–75 (in Turkish with English abstract).

Ekmekci, M.; Kalaycioglu, N. E.; Acikel, S.; Namkhai, O.; Akman, S. B., 2017, Numerical simulation of uplift pressure and relief drains at a dam reservoir: Environmental Engineering Geoscience, Vol. 23, No. 2, pp. 79–96.

Eryilmaz Türkkan, G. and Korkmaz, S., 2015, Determination of hydraulic conductivity using analytical and numerical methods applied to well and aquifer tests: IMO Teknik Dergi, Vol. 26, pp. 6969–6991 (in Turkish with English abstract).

Ewert, F. K., 2003, Discussion of rock type related criteria for curtain grouting. In The 3rd International Conference on Grouting in Rock and Ground Improvement: American Society of Civil Engineers (ASCE), Special Publication No 120.

Ghobadi, M. H.; Khanlari, G. R.; and Djalali, H., 2005, Seepage problems in the right abutment of the Shahid Abbaspour Dam, southern Iran: Engineering Geology, Vol. 82, pp. 119–126.

Gürocak, Z. and Alemdağ, S., 2012, Assessment of permeability and injection depth at the Atasu dam site (Turkey) based on experimental and numerical analyses: Bulletin Engineering Geology Environment, Vol. 71, pp. 221–229.

ISRM, 2007, Rock Characterization, Testing and Monitoring: International Society of Rock Mechanics Suggested Methods: Pergamon Press, Oxford, U.K., 211 p.

Karagüzel, R. and Kiliç, R., 2000, The effect of the alteration degree of ophiolitic mélange on permeability and grouting: Engineering Geology, Vol. 57, pp. 1–12.

Kayabaşi, A.; Yeşiloğlu-Gültekin, N.; and Gökçeoğlu, C., 2015, Use of non-linear prediction tools to assess rockmass permeability using various discontinuity parameters: Engineering Geology, Vol. 185, pp. 1–9.

Koçbay, A. and Kiliç, R., 2006, Engineering geological assessment of the Obruk dam site (Çorum, Turkey): Engineering Geology, Vol. 87, pp. 141–148.

Lombardi, G., 1985, The role of cohesion in cement grouting of rock. In The 15th ICOLD Congress: Lausanne, Switzerland, ICOLD Paris, pp. 235–261.

Maden Tetkik Arama Genel Mudurlugu, 2002, 1/25000 olcekli Adapazari G24-d3 genel jeoloji haritası;: MTA Jeoloji Etutleri Dairesi, Ankara.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

Canoğlu

the rock formations was disregarded for the calculation of flow rate. However, bedrock exposures could have potential seepage during excavation from groundwater flow through exposed discontinuities. Although this groundwater inflow is expected to be less than the upstream excavated surface, the hydraulic gradient and overall permeability are lower. This situation should be taken into account during the dewatering operation when construction starts.

Lugeon tests were performed to predict the amount of grout required under variable hydrostatic pressures.

The Lugeon tests indicated that the geological formation under axis location 2 generally has low permeability, except for some permeable zones close to the surface. It is anticipated that groundwater movement from upstream to downstream through these permeable zones will be reduced or prevented by the grout curtain shown in Figure 8. In addition to the grout curtain, due to the higher permeability and lower strength of the bedrock near the top of the rock surface, consolidation grouting will likely be needed to treat open bedrock discontinuities that will potentially be in contact with the dam embankment (Figure 8). Consolidation grouting design was chosen with 7 m depth and 3 m grout hole spacing. The grout holes were designed to be vertical with a minimum hole diameter of 76 mm. Stable cement grout is planned, and the maximum grout pressure is specified as 4 kg/cm2 . Consolidation grouting is generally meant to fill voids, fractured zones, and cracks at and below the surface of the excavated foundation. This foundation treatment is planned to prevent future erosion or piping into the discontinuities and to avoid potential scour of the embankment by groundwater flow in the vicinity of these discontinuities.

ACKNOWLEDGMENTS This work is performed in the context of the “Eskişehir Dams Planning Engineering Services” project of the Turkish Republic Ministry of Forestry and Water Works, General Directorate of State Hydraulic Works, Eskişehir 3 Regional Directorate with contributions from SuYapı Engineering and Consulting Co. The author thanks SuYapi Engineering and Consulting Co. for sharing their information and the State Hydraulic Works, Eskişehir 3 Regional Directorate staff for their exchange of ideas, especially Hayrettin Baysal, Şeref Dağdelen, Feridun İnce, Osman Çakır, and Engin Kaplan.

REFERENCES Aksoy, H. and Ercanoğlu, M., 2006, Determination of the rockfall source in an urban settlement area by using a rule-based

24

fuzzy evaluation: Natural Hazards and Earth System Science, Vol. 6, pp. 941–954.

Aksoy, H. and Ercanoğlu, M., 2007, Fuzzified kinematic analysis of discontinuity-controlled rock slope instabilities: Engineering Geology, Vol. 89, pp. 206–219.

Akyüz, S., 2010, Investigation of Permeability Features of Lithologic Units on Kargı Dam Site (Çorum): M.Sc. Thesis, Çukurova University, Adana, Turkey, 134 p. (in Turkish with English abstract).

Aldemir, A.; Yilmaztürk, S. M.; Yücel, A. R.; Binici, B.; Arici, Y.; and Akman, A., 2015, Analysis methods for the investigation of the seismic response of concrete dams: IMO Teknik Dergi, Vol. 26, pp. 6943–6968 (in Turkish with English abstract).

Canoğlu, M. C. and Kurtuluş, B., 2017, Permeability of Savcıbey dam (Bilecik) axis location and design of grout curtain: Bulletin Mineral Research Exploration, Vol. 154, pp. 157–168.

Cato, K. D. and Rogers, J. D., 2017, Failure of the Alexander Dam embankment and reconstruction using drainage mitigation on Kauai, 1930–1932: Environmental Engineering Geoscience, Vol. 23, No. 4, pp. 1–21. Çelik, Ö. F.; Gürer, Ö. F.; and Öz, İ., 2009, Geochemical and petrographical properties of granitoidic rocks located between Geyve gorge and Pamukova: Uygulamalı Yerbilimleri, Vol. 1, pp. 61–75 (in Turkish with English abstract).

Ekmekci, M.; Kalaycioglu, N. E.; Acikel, S.; Namkhai, O.; Akman, S. B., 2017, Numerical simulation of uplift pressure and relief drains at a dam reservoir: Environmental Engineering Geoscience, Vol. 23, No. 2, pp. 79–96.

Eryilmaz Türkkan, G. and Korkmaz, S., 2015, Determination of hydraulic conductivity using analytical and numerical methods applied to well and aquifer tests: IMO Teknik Dergi, Vol. 26, pp. 6969–6991 (in Turkish with English abstract).

Ewert, F. K., 2003, Discussion of rock type related criteria for curtain grouting. In The 3rd International Conference on Grouting in Rock and Ground Improvement: American Society of Civil Engineers (ASCE), Special Publication No 120.

Ghobadi, M. H.; Khanlari, G. R.; and Djalali, H., 2005, Seepage problems in the right abutment of the Shahid Abbaspour Dam, southern Iran: Engineering Geology, Vol. 82, pp. 119–126.

Gürocak, Z. and Alemdağ, S., 2012, Assessment of permeability and injection depth at the Atasu dam site (Turkey) based on experimental and numerical analyses: Bulletin Engineering Geology Environment, Vol. 71, pp. 221–229.

ISRM, 2007, Rock Characterization, Testing and Monitoring: International Society of Rock Mechanics Suggested Methods: Pergamon Press, Oxford, U.K., 211 p.

Karagüzel, R. and Kiliç, R., 2000, The effect of the alteration degree of ophiolitic mélange on permeability and grouting: Engineering Geology, Vol. 57, pp. 1–12.

Kayabaşi, A.; Yeşiloğlu-Gültekin, N.; and Gökçeoğlu, C., 2015, Use of non-linear prediction tools to assess rockmass permeability using various discontinuity parameters: Engineering Geology, Vol. 185, pp. 1–9.

Koçbay, A. and Kiliç, R., 2006, Engineering geological assessment of the Obruk dam site (Çorum, Turkey): Engineering Geology, Vol. 87, pp. 141–148.

Lombardi, G., 1985, The role of cohesion in cement grouting of rock. In The 15th ICOLD Congress: Lausanne, Switzerland, ICOLD Paris, pp. 235–261.

Maden Tetkik Arama Genel Mudurlugu, 2002, 1/25000 olcekli Adapazari G24-d3 genel jeoloji haritası;: MTA Jeoloji Etutleri Dairesi, Ankara.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

Permeability and Grout Curtain Optimization in Dam Axis Location Nield, M. C., 2017, Grout curtain construction at Bolivar Dam, Ohio: Environmental Engineering Geoscience, Vol. 23, No. 4, pp. 1–16.

Nonveiller, E., 1989, Grouting Theory in Practice: Elsevier, Tokyo, Japan, 260 p.

Romanov, D.; Gabrovsek, F.; and Dreybrodt, W., 2003, Dam sites in soluble rocks: A model of increasing leakage by dissolution widening of fractures beneath a dam: Engineering Geology, Vol. 70, pp. 17–35.

Sadeghiyeh, S. M.; Hashemi, M.; and Ajalloeian, R., 2013, Comparison of permeability and groutability of Ostur dam site rock mass for grout curtain design: Rock Mechanics and Rock Engineering, Vol. 46, pp. 341–357.

Schleiss, A. J. and Pougatsch, H., 2011, Les Barrages: Du Projet à la Mise en Service: Presses Polytechniques Universitaires Romandes, Lausanne, Switzerland, 714 p.

Şekercioğlu, E., 2007, Yapıların Projelendirilmesinde Mühendislik Jeolojisi: JMO Yayınları, Ankara, Turkey, 117 p. (in Turkish).

Permeability and Grout Curtain Optimization in Dam Axis Location

SuYapi A.S, 2013, Turgutlu Göleti, Mühendislik Jeolojisi Planlama Raporu: DSI 3, Bölge Müdürlügü, Eskişehir, Turkey, 61 p.

Tunar, N. Ö.; Ulusay, R.; and Işik, N. S., 2013, A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey): Environmental Earth Sciences, Vol. 69, pp. 1871– 1890.

Türkmen, S., 2003, Treatment of the seepage problems at Kalecik dam (Turkey): Engineering Geology, Vol. 68, pp. 159–169.

Ulusay, R.; Tuncay, E.; and Hasançebi, N., 2007, Liquefaction assessments by field-based methodologies for the foundation soils at a dam site in northeast Turkey: Bulletin Engineering Geology Environment, Vol. 66, pp. 361–375.

Uromeihy, A. and Barzegari, G., 2007, Evaluation and treatment of seepage problems at Chapar-Abad dam, Iran: Engineering Geology, Vol. 91, pp. 219–228.

Uromeihy, A. and Farrokhi, R., 2012, Evaluating groutability at the Kemal-Saleh dam based on Lugeon tests: Bulletin Engineering Geology Environment, Vol. 71, pp. 215–219.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

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Nield, M. C., 2017, Grout curtain construction at Bolivar Dam, Ohio: Environmental Engineering Geoscience, Vol. 23, No. 4, pp. 1–16.

Nonveiller, E., 1989, Grouting Theory in Practice: Elsevier, Tokyo, Japan, 260 p.

Romanov, D.; Gabrovsek, F.; and Dreybrodt, W., 2003, Dam sites in soluble rocks: A model of increasing leakage by dissolution widening of fractures beneath a dam: Engineering Geology, Vol. 70, pp. 17–35.

Sadeghiyeh, S. M.; Hashemi, M.; and Ajalloeian, R., 2013, Comparison of permeability and groutability of Ostur dam site rock mass for grout curtain design: Rock Mechanics and Rock Engineering, Vol. 46, pp. 341–357.

Schleiss, A. J. and Pougatsch, H., 2011, Les Barrages: Du Projet à la Mise en Service: Presses Polytechniques Universitaires Romandes, Lausanne, Switzerland, 714 p.

Şekercioğlu, E., 2007, Yapıların Projelendirilmesinde Mühendislik Jeolojisi: JMO Yayınları, Ankara, Turkey, 117 p. (in Turkish).

SuYapi A.S, 2013, Turgutlu Göleti, Mühendislik Jeolojisi Planlama Raporu: DSI 3, Bölge Müdürlügü, Eskişehir, Turkey, 61 p.

Tunar, N. Ö.; Ulusay, R.; and Işik, N. S., 2013, A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey): Environmental Earth Sciences, Vol. 69, pp. 1871– 1890.

Türkmen, S., 2003, Treatment of the seepage problems at Kalecik dam (Turkey): Engineering Geology, Vol. 68, pp. 159–169.

Ulusay, R.; Tuncay, E.; and Hasançebi, N., 2007, Liquefaction assessments by field-based methodologies for the foundation soils at a dam site in northeast Turkey: Bulletin Engineering Geology Environment, Vol. 66, pp. 361–375.

Uromeihy, A. and Barzegari, G., 2007, Evaluation and treatment of seepage problems at Chapar-Abad dam, Iran: Engineering Geology, Vol. 91, pp. 219–228.

Uromeihy, A. and Farrokhi, R., 2012, Evaluating groutability at the Kemal-Saleh dam based on Lugeon tests: Bulletin Engineering Geology Environment, Vol. 71, pp. 215–219.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 15–25

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Engineering Geology, History and Geography of the Pittsburgh, Pennsylvania Area

Engineering Geology, History and Geography of the Pittsburgh, Pennsylvania Area

RICHARD E. GRAY

RICHARD E. GRAY

DiGioia Gray & Associates, 570 Beatty Road, Monroeville, PA 15146

DiGioia Gray & Associates, 570 Beatty Road, Monroeville, PA 15146

BRIAN H. GREENE

BRIAN H. GREENE

Gannett Fleming, Inc., Foster Plaza 8, Suite 400, 730 Holiday Drive, Pittsburgh, PA 15220

Gannett Fleming, Inc., Foster Plaza 8, Suite 400, 730 Holiday Drive, Pittsburgh, PA 15220

RYAN W. FANDRAY*

RYAN W. FANDRAY*

GAI Consultants, Inc., 385 East Waterfront Drive, Homestead, PA 15120

GAI Consultants, Inc., 385 East Waterfront Drive, Homestead, PA 15120

ROBERT J. TURKA

ROBERT J. TURKA

GAI Consultants, Inc., 4200 Triangle Lane, Export, PA 15632

GAI Consultants, Inc., 4200 Triangle Lane, Export, PA 15632

Key Terms: Pittsburgh, Geology, Engineering Geology, Rivers ABSTRACT The City of Pittsburgh, PA is located west of the Appalachian Mountains in the Appalachian Plateaus Province. The relatively flat surface of the plateau is dissected by drainage from the three principal rivers of the region, the Allegheny, Monongahela, and Ohio. The formation of Pittsburghs three rivers and drainages has a long history dating back to before the Pleistocene Epoch, linked closely to the advance and retreat of continental glaciation.

Western Pennsylvania is associated with the westernmost formation of the Appalachian Mountain chain with deformation in the form of a series of nearly flat-lying, gently warped Paleozoic sedimentary rocks. Rocks cropping out in the region range in age from Devonian to Permian. Pennsylvanian strata are dominated by thin cyclic sequences of sandstone, shale, claystone, coal, and limestone. Most of the geologic hazards present in the region include slope instability, expansive shales and slags, mine subsidence, acid mine drainage, pyritic acid rock and flooding. The region also has an abundance of natural resources including coal, natural gas, oil, salt, limestone, sand and gravel and water.

Pittsburgh’s strategic location helped shape westward expansion during the formation of the Nation, largely because of the rivers, which served as an inexpensive, yet efficient means of transportation. Infrastructure was always significant in Pittsburgh. However, the existing ag*Corresponding author email: rfandray@gaiconsultants.com

ing infrastructure are deteriorating. Today, Pittsburgh has transcended the legacy name, “Steel City” and has revitalized itself with nationally-recognized universities and medical centers and a resurgence in natural gas exploration. However, many environmental legacy issues still burden the area.

INTRODUCTION Geographic Setting Although Pittsburgh has a long history as a major industrial center, it occupies a relatively small area, 56 square miles (145 km2 ), and it has a population of approximately 305,000 (U.S. Census Bureau, 2010).

Pittsburgh is located within Allegheny County, which is one of the 67 counties in Pennsylvania. The Greater Pittsburgh region is normally considered to include Allegheny County, the adjacent Armstrong, Beaver, Butler, Fayette, Greene, Washington, and Westmoreland Counties, and a few locations outside of this area that have a direct impact upon the metropolitan area.

These counties comprise 5,921 mi2 (15,334 km2 ) and have a population of more than 2.3 million people (U.S. Census Bureau, 2010).

Pittsburgh is located to the west of the Appalachian Mountains in a moderately dissected portion of the Appalachian Plateau Province (Figure 1). Here, the relatively flat plateau surface is deeply dissected by drainages, which has produced steep-sided valleys having a relief ranging up to 600 ft (182 m). The upland areas generally lie at an elevation greater than 1,200 ft (365 m) above mean sea level and constitute only about 10 to 20 percent of the surface area of the region. Valley slopes account for about 50 to 70 percent of the

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27

Key Terms: Pittsburgh, Geology, Engineering Geology, Rivers ABSTRACT The City of Pittsburgh, PA is located west of the Appalachian Mountains in the Appalachian Plateaus Province. The relatively flat surface of the plateau is dissected by drainage from the three principal rivers of the region, the Allegheny, Monongahela, and Ohio. The formation of Pittsburghs three rivers and drainages has a long history dating back to before the Pleistocene Epoch, linked closely to the advance and retreat of continental glaciation.

Western Pennsylvania is associated with the westernmost formation of the Appalachian Mountain chain with deformation in the form of a series of nearly flat-lying, gently warped Paleozoic sedimentary rocks. Rocks cropping out in the region range in age from Devonian to Permian. Pennsylvanian strata are dominated by thin cyclic sequences of sandstone, shale, claystone, coal, and limestone. Most of the geologic hazards present in the region include slope instability, expansive shales and slags, mine subsidence, acid mine drainage, pyritic acid rock and flooding. The region also has an abundance of natural resources including coal, natural gas, oil, salt, limestone, sand and gravel and water.

Pittsburgh’s strategic location helped shape westward expansion during the formation of the Nation, largely because of the rivers, which served as an inexpensive, yet efficient means of transportation. Infrastructure was always significant in Pittsburgh. However, the existing ag*Corresponding author email: rfandray@gaiconsultants.com

ing infrastructure are deteriorating. Today, Pittsburgh has transcended the legacy name, “Steel City” and has revitalized itself with nationally-recognized universities and medical centers and a resurgence in natural gas exploration. However, many environmental legacy issues still burden the area.

INTRODUCTION Geographic Setting Although Pittsburgh has a long history as a major industrial center, it occupies a relatively small area, 56 square miles (145 km2 ), and it has a population of approximately 305,000 (U.S. Census Bureau, 2010).

Pittsburgh is located within Allegheny County, which is one of the 67 counties in Pennsylvania. The Greater Pittsburgh region is normally considered to include Allegheny County, the adjacent Armstrong, Beaver, Butler, Fayette, Greene, Washington, and Westmoreland Counties, and a few locations outside of this area that have a direct impact upon the metropolitan area.

These counties comprise 5,921 mi2 (15,334 km2 ) and have a population of more than 2.3 million people (U.S. Census Bureau, 2010).

Pittsburgh is located to the west of the Appalachian Mountains in a moderately dissected portion of the Appalachian Plateau Province (Figure 1). Here, the relatively flat plateau surface is deeply dissected by drainages, which has produced steep-sided valleys having a relief ranging up to 600 ft (182 m). The upland areas generally lie at an elevation greater than 1,200 ft (365 m) above mean sea level and constitute only about 10 to 20 percent of the surface area of the region. Valley slopes account for about 50 to 70 percent of the

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Gray, Greene, Fandray, and Turka

Figure 1. Appalachian Plateau, western Pennsylvania (modified from Gray et al., 1979).

area, while the bottomlands constitute 20 percent or less (Gardner, 1980).

Pittsburgh is located at the confluence of the three largest rivers in the region, the Allegheny, Monongahela, and the Ohio (Figure 1). The Allegheny River flows from the north, originating in northern Pennsylvania and southern New York. The Monongahela River flows from the south, originating in eastcentral West Virginia. The Allegheny and Monongahela Rivers meet in Pittsburgh and form the westwardflowing Ohio River. The Ohio River is a major artery of drainage into the interior of the continent, joining the Mississippi River about 930 mi (1,500 km) downstream from Pittsburgh at Cairo, IL (Gardner, 1980).

Climate The Pittsburgh area has four distinct seasons. Fall and spring are generally warm and mild, summers are hot and humid with occasional heat waves, and winters are cold and snowy. Based upon 30 year averages (NOAA, 2014), the mean monthly temperatures are warmest in July (72.6°F; 22.6°C) and coldest in January (28.4°F; −2°C). Pittsburgh averages 9.5 days per year when the temperature reaches 90°F (32.3°C) or higher and 5 days per year when the temperature goes below 0°F (−17.8°C). The highest temperature recorded in Pittsburgh, 103°F (39.4°C), has oc28

Gray, Greene, Fandray, and Turka

curred on three occasions (July 1881, August 1918, and July 1988), whereas the lowest recorded temperature, −22°F (−30°C), occurred once in January 1994.

Average precipitation is 38.2 in. (97 cm) and is relatively evenly distributed through the year, with the driest month (October) averaging 2.29 in. (5.8 cm) of precipitation and the wettest month (June) averaging of 4.3 in. (11 cm) of precipitation. Records indicate that the largest one-day snowfall, 23.6 in. (59.9 cm), fell on March 13, 1993, and that the largest one-day rainfall event, 5.95 in. (15.11 cm), fell on September 17, 2004 (Hurricane Ivan). The second largest rainfall event, 3.6 in. (9.14 cm), fell on September 8, 2004 (Hurricane Frances), only 1 week before the Hurricane Ivan rainfall.

curred on three occasions (July 1881, August 1918, and July 1988), whereas the lowest recorded temperature, −22°F (−30°C), occurred once in January 1994.

Average precipitation is 38.2 in. (97 cm) and is relatively evenly distributed through the year, with the driest month (October) averaging 2.29 in. (5.8 cm) of precipitation and the wettest month (June) averaging of 4.3 in. (11 cm) of precipitation. Records indicate that the largest one-day snowfall, 23.6 in. (59.9 cm), fell on March 13, 1993, and that the largest one-day rainfall event, 5.95 in. (15.11 cm), fell on September 17, 2004 (Hurricane Ivan). The second largest rainfall event, 3.6 in. (9.14 cm), fell on September 8, 2004 (Hurricane Frances), only 1 week before the Hurricane Ivan rainfall.

History and Founding

History and Founding

The first inhabitants of the Pittsburgh region were probably Paleo-Indians, who may have occupied the area about 16,000 years ago, as indicated by archaeological findings at Meadowcroft Rock Shelter located on a small tributary of the Ohio River about 25 mi (40 km) southwest of Pittsburgh. The Paleo-Indians were hunter-gatherers who exploited the abundant animal and plant resources of the region (Gardner, 1980).

The Paleo-Indian culture was followed by the Archaic hunter-gatherer culture, probably between 7,000 and 8,000 years ago, and the Archaic culture was supplanted by the Woodland culture about 3,000 years ago, when agriculture was first introduced in the area.

Two mound-building societies developed along the rivers and streams of this region during the Woodland cultural period. The first were the Adena moundbuilders, who occupied the region from about 3,000 to 2,000 years ago, before they were displaced by the more advanced Hopewell culture, which lasted from about 2,000 years ago to A.D. 500 (Gardner, 1980).

It was the strategic location at the confluence of the rivers that first attracted the attention of European colonists to the “Forks of the Ohio” at what is now Pittsburgh. The conflicts between the British and French in Europe in the early and mid-1700s were transported to North America as both nations struggled for domination of the continent. The French claimed the area west of the Allegheny Mountains as theirs, including the combined Ohio and Allegheny Rivers; the English did not recognize these claims.

A group of English colonials from Virginia formed an organization called the Ohio Land Company, whose members included Governor Dinwiddie of Virginia and Lawrence Washington, George Washington’s older brother. The Ohio Land Company claimed over half a million acres of the area around the Forks of the Ohio for trade and land speculation, land that

The first inhabitants of the Pittsburgh region were probably Paleo-Indians, who may have occupied the area about 16,000 years ago, as indicated by archaeological findings at Meadowcroft Rock Shelter located on a small tributary of the Ohio River about 25 mi (40 km) southwest of Pittsburgh. The Paleo-Indians were hunter-gatherers who exploited the abundant animal and plant resources of the region (Gardner, 1980).

The Paleo-Indian culture was followed by the Archaic hunter-gatherer culture, probably between 7,000 and 8,000 years ago, and the Archaic culture was supplanted by the Woodland culture about 3,000 years ago, when agriculture was first introduced in the area.

Two mound-building societies developed along the rivers and streams of this region during the Woodland cultural period. The first were the Adena moundbuilders, who occupied the region from about 3,000 to 2,000 years ago, before they were displaced by the more advanced Hopewell culture, which lasted from about 2,000 years ago to A.D. 500 (Gardner, 1980).

It was the strategic location at the confluence of the rivers that first attracted the attention of European colonists to the “Forks of the Ohio” at what is now Pittsburgh. The conflicts between the British and French in Europe in the early and mid-1700s were transported to North America as both nations struggled for domination of the continent. The French claimed the area west of the Allegheny Mountains as theirs, including the combined Ohio and Allegheny Rivers; the English did not recognize these claims.

A group of English colonials from Virginia formed an organization called the Ohio Land Company, whose members included Governor Dinwiddie of Virginia and Lawrence Washington, George Washington’s older brother. The Ohio Land Company claimed over half a million acres of the area around the Forks of the Ohio for trade and land speculation, land that

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Figure 1. Appalachian Plateau, western Pennsylvania (modified from Gray et al., 1979).

area, while the bottomlands constitute 20 percent or less (Gardner, 1980).

Pittsburgh is located at the confluence of the three largest rivers in the region, the Allegheny, Monongahela, and the Ohio (Figure 1). The Allegheny River flows from the north, originating in northern Pennsylvania and southern New York. The Monongahela River flows from the south, originating in eastcentral West Virginia. The Allegheny and Monongahela Rivers meet in Pittsburgh and form the westwardflowing Ohio River. The Ohio River is a major artery of drainage into the interior of the continent, joining the Mississippi River about 930 mi (1,500 km) downstream from Pittsburgh at Cairo, IL (Gardner, 1980).

Climate The Pittsburgh area has four distinct seasons. Fall and spring are generally warm and mild, summers are hot and humid with occasional heat waves, and winters are cold and snowy. Based upon 30 year averages (NOAA, 2014), the mean monthly temperatures are warmest in July (72.6°F; 22.6°C) and coldest in January (28.4°F; −2°C). Pittsburgh averages 9.5 days per year when the temperature reaches 90°F (32.3°C) or higher and 5 days per year when the temperature goes below 0°F (−17.8°C). The highest temperature recorded in Pittsburgh, 103°F (39.4°C), has oc28

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Geology of Pittsburgh

the French had previously marked as theirs. Ensuing clashes between the French and English trading in the area prompted Governor Dinwiddie to send a 21-yearold major of the Virginia Militia, George Washington, to deliver a protest to the French (Gardner, 1980).

En route, Major Washington travelled by the Forks and noted:

the French had previously marked as theirs. Ensuing clashes between the French and English trading in the area prompted Governor Dinwiddie to send a 21-yearold major of the Virginia Militia, George Washington, to deliver a protest to the French (Gardner, 1980).

En route, Major Washington travelled by the Forks and noted:

…I spent some time viewing the rivers, and the land in the Fork’ which I think extremely well situated for a fort, as it has absolute command of both rivers …the Land at the point is 20 to 25 feet [6 to 7.5 m] above the common surface of the water; and a considerable bottom of flat, well-timbered land all around it, very convenient for building … (from Washington’s Chronicle, in Lorant, 1975, p. 7)

…I spent some time viewing the rivers, and the land in the Fork’ which I think extremely well situated for a fort, as it has absolute command of both rivers …the Land at the point is 20 to 25 feet [6 to 7.5 m] above the common surface of the water; and a considerable bottom of flat, well-timbered land all around it, very convenient for building … (from Washington’s Chronicle, in Lorant, 1975, p. 7)

The confrontations with the French prompted the Virginians to build a fort at the Forks of the Ohio, as suggested by Washington. Construction of Fort Prince George was initiated in March 1754, and it was the first recorded Euro-American construction on the land that is now Pittsburgh. The unfinished colonial fort was abandoned 1 month later when a superior force of French and Indians threatened attack. The French then erected their own fort, Fort Duquesne, at the Forks of the Ohio. The French controlled the Forks of the Ohio for 4 years, repelling several English attempts to regain control. In November of 1758, the French burned and abandoned Fort Duquesne in the face of imminent attack by British forces headed by General John Forbes and Colonel George Washington. The English erected their own fort on the ruins of Fort Duquesne, and Forbes named it Fort Pitt in honor of the then-current English Prime Minister, William Pitt. Fort Pitt received no attacks from the French, although it was besieged by Indians for 2 months during “Pontiac’s Conspiracy” in 1763. The end of the Indian uprising reduced the need for Fort Pitt, and it was gradually dismantled in the mid-1760s (Gardner, 1980). Figure 2 shows Fort Pitt in 1776. A portion of Fort Pitt has been reconstructed in its original location at what is now Point State Park.

The community that developed around the fort continued to grow as a center of trade for the everincreasing travel from east to west, as Pittsburgh developed as a gateway to the west. Figure 3 shows the locations of Fort Duquesne, Fort Pitt, and Pittsburgh in 1795. When the community was incorporated as a city in 1816, it was the major center for commerce in the west, since most travel from the eastern seaboard to the west went through Pittsburgh. Henry Steele Commager, a noted historian, summarized the situation as follows: …The historical significance of Pittsburgh was determined from the beginning, by geography …The city that

Figure 2. Pittsburgh’s Golden Triangle—1776 (Brookline Connection, 2012).

was to rise at this strategic point on the threshold of the Forks was at once the bridge from the East and the Gateway to the West, the most western of the great cities of the seaboard, the most eastern of the great cities of the valley: it is no accident that it has commanded that position now for a century and a half; its sovereignty unchallenged …

(Lorant, 1975, p. 26)

Pittsburgh’s economy was primarily based on commerce in the late 1700s and early 1800s, thereby living up to its “gateway” status. As Pittsburgh grew, it required an ever-increasing supply of goods, most of which were manufactured in the east. However, transporting large quantities of trade goods and pioneer supplies was incredibly difficult and expensive because the rugged Appalachian Mountain ridges between Pittsburgh and lands to the east were a formidable barrier. For this reason, Pittsburgh was forced to develop its own manufacturing industry, and by 1815, it was producing significant quantities of iron, brass, tin, and glass products. By 1830, the trade-commerce aspect of Pittsburgh’s economy was eclipsed by manufacturing.

Thus, Pittsburgh was founded and began to flourish as a center of commerce and manufacturing because of its geography. However, Pittsburgh was only born of its geography; it owes most of its growth and eventual status as a leading industrial center to its geology (Gardner, 1980). In 1901, U.S. Steel Corporation was formed in Pittsburgh, and by 1911, the city was the nation’s eighth largest city, producing between a third and a half of the nation’s steel.

The most important components affecting the growth of Pittsburgh were the mineral resources of the region, including salt, coal, oil, natural gas, some iron ore, and the availability of attendant requirements such as water, building materials, power, transportation capabilities, and marketability. However, the single most

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29

The confrontations with the French prompted the Virginians to build a fort at the Forks of the Ohio, as suggested by Washington. Construction of Fort Prince George was initiated in March 1754, and it was the first recorded Euro-American construction on the land that is now Pittsburgh. The unfinished colonial fort was abandoned 1 month later when a superior force of French and Indians threatened attack. The French then erected their own fort, Fort Duquesne, at the Forks of the Ohio. The French controlled the Forks of the Ohio for 4 years, repelling several English attempts to regain control. In November of 1758, the French burned and abandoned Fort Duquesne in the face of imminent attack by British forces headed by General John Forbes and Colonel George Washington. The English erected their own fort on the ruins of Fort Duquesne, and Forbes named it Fort Pitt in honor of the then-current English Prime Minister, William Pitt. Fort Pitt received no attacks from the French, although it was besieged by Indians for 2 months during “Pontiac’s Conspiracy” in 1763. The end of the Indian uprising reduced the need for Fort Pitt, and it was gradually dismantled in the mid-1760s (Gardner, 1980). Figure 2 shows Fort Pitt in 1776. A portion of Fort Pitt has been reconstructed in its original location at what is now Point State Park.

The community that developed around the fort continued to grow as a center of trade for the everincreasing travel from east to west, as Pittsburgh developed as a gateway to the west. Figure 3 shows the locations of Fort Duquesne, Fort Pitt, and Pittsburgh in 1795. When the community was incorporated as a city in 1816, it was the major center for commerce in the west, since most travel from the eastern seaboard to the west went through Pittsburgh. Henry Steele Commager, a noted historian, summarized the situation as follows: …The historical significance of Pittsburgh was determined from the beginning, by geography …The city that

Figure 2. Pittsburgh’s Golden Triangle—1776 (Brookline Connection, 2012).

was to rise at this strategic point on the threshold of the Forks was at once the bridge from the East and the Gateway to the West, the most western of the great cities of the seaboard, the most eastern of the great cities of the valley: it is no accident that it has commanded that position now for a century and a half; its sovereignty unchallenged …

(Lorant, 1975, p. 26)

Pittsburgh’s economy was primarily based on commerce in the late 1700s and early 1800s, thereby living up to its “gateway” status. As Pittsburgh grew, it required an ever-increasing supply of goods, most of which were manufactured in the east. However, transporting large quantities of trade goods and pioneer supplies was incredibly difficult and expensive because the rugged Appalachian Mountain ridges between Pittsburgh and lands to the east were a formidable barrier. For this reason, Pittsburgh was forced to develop its own manufacturing industry, and by 1815, it was producing significant quantities of iron, brass, tin, and glass products. By 1830, the trade-commerce aspect of Pittsburgh’s economy was eclipsed by manufacturing.

Thus, Pittsburgh was founded and began to flourish as a center of commerce and manufacturing because of its geography. However, Pittsburgh was only born of its geography; it owes most of its growth and eventual status as a leading industrial center to its geology (Gardner, 1980). In 1901, U.S. Steel Corporation was formed in Pittsburgh, and by 1911, the city was the nation’s eighth largest city, producing between a third and a half of the nation’s steel.

The most important components affecting the growth of Pittsburgh were the mineral resources of the region, including salt, coal, oil, natural gas, some iron ore, and the availability of attendant requirements such as water, building materials, power, transportation capabilities, and marketability. However, the single most

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 3. Map of Pittsburgh in 1795 (Albert, 1896).

Figure 3. Map of Pittsburgh in 1795 (Albert, 1896).

important resource to affect Pittsburgh’s growth and industrial stature was coal (Gardner, 1980).

Coal There are two significant coals that are mined in the Pittsburgh region, the Pittsburgh and Upper Freeport seams. They are two of at least 13 coal seams that have been strip mined and/or deep mined at one place or another in the region.

The Pittsburgh Coal Seam is considered to be one of the richest economic deposits in the world. The U.S. Geological Survey (USGS) estimated that the Pittsburgh Coal alone yielded eight billion tons from the early 1900s to 1965, comprising 35 percent of 30

all bituminous coal in the Appalachian Basin and 21 percent of the cumulative production for the entire United States. The Pittsburgh coal is essentially “worked-out” and no longer deep mined in Pittsburgh (Gardner, 1980), but it is still mined in the southwest corner of the state, where the seam is much deeper.

The Upper Freeport Coal Seam lies about 660 ft (201 m) below the Pittsburgh Coal and has been deep mined in a north-south belt east of the city and just north of the city. However, it is relatively thin and is currently not deep mined under the city.

The first record of coal mining in Pittsburgh was made by Captain Thomas Hutchins in 1759, when he noted a coal mine on the hillside across the

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important resource to affect Pittsburgh’s growth and industrial stature was coal (Gardner, 1980).

Coal There are two significant coals that are mined in the Pittsburgh region, the Pittsburgh and Upper Freeport seams. They are two of at least 13 coal seams that have been strip mined and/or deep mined at one place or another in the region.

The Pittsburgh Coal Seam is considered to be one of the richest economic deposits in the world. The U.S. Geological Survey (USGS) estimated that the Pittsburgh Coal alone yielded eight billion tons from the early 1900s to 1965, comprising 35 percent of 30

all bituminous coal in the Appalachian Basin and 21 percent of the cumulative production for the entire United States. The Pittsburgh coal is essentially “worked-out” and no longer deep mined in Pittsburgh (Gardner, 1980), but it is still mined in the southwest corner of the state, where the seam is much deeper.

The Upper Freeport Coal Seam lies about 660 ft (201 m) below the Pittsburgh Coal and has been deep mined in a north-south belt east of the city and just north of the city. However, it is relatively thin and is currently not deep mined under the city.

The first record of coal mining in Pittsburgh was made by Captain Thomas Hutchins in 1759, when he noted a coal mine on the hillside across the

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Geology of Pittsburgh

Monongahela River from Pittsburgh. The mine was developed in the coal outcrop by the British soldiers on “Coal Hill,” which is now called Mount Washington.

Coal was mined on a small scale until industrialization created a greater fuel demand by the mid-1800s.

The principal user of coal in the Pittsburgh region was the iron and steel industry. The iron industry began almost at the birth of the community. The first iron furnace reported in Pittsburgh was built on Two Mile Run (Shadyside) in 1793, and it closed after only 1 year of operation for lack of iron ore and local timber for fuel. Although Pittsburgh’s first iron furnace was unsuccessful, numerous furnaces operating in outlying areas closer to the local ore deposits did succeed.

Because Pittsburgh was the center of commerce, trade, labor, and marketing, the industry took advantage of these resources, and local iron forging became a lucrative business (Gardner, 1980).

Geology of Pittsburgh

ing rock composed mostly of shale, siltstone, and sandstone. The geologic structure consists of moderateto low-amplitude folds that decrease in frequency and amplitude in a northwestward direction.

The Waynesburg Hills Section is composed of relatively hilly terrain with narrow hilltops and steep-sloped narrow valleys with a modified dendritic drainage pattern. It has moderate relief, with underlying rock types of shale, sandstone, limestone, red shale, and claystone. The geologic structure ranges from low-amplitude folds to horizontal bedding.

A small portion of the northwest section of the Appalachian Plateaus Province, called the Northwestern Glaciated Plateau Section, was glaciated during the Pleistocene Epoch. The closest approach of Wisconsinan ice was about 30 mi (48 km) north of the city.

This was the last ice advance in the area.

Monongahela River from Pittsburgh. The mine was developed in the coal outcrop by the British soldiers on “Coal Hill,” which is now called Mount Washington.

Coal was mined on a small scale until industrialization created a greater fuel demand by the mid-1800s.

The principal user of coal in the Pittsburgh region was the iron and steel industry. The iron industry began almost at the birth of the community. The first iron furnace reported in Pittsburgh was built on Two Mile Run (Shadyside) in 1793, and it closed after only 1 year of operation for lack of iron ore and local timber for fuel. Although Pittsburgh’s first iron furnace was unsuccessful, numerous furnaces operating in outlying areas closer to the local ore deposits did succeed.

Because Pittsburgh was the center of commerce, trade, labor, and marketing, the industry took advantage of these resources, and local iron forging became a lucrative business (Gardner, 1980).

Tectonic Setting REGIONAL GEOLOGY Physiography The physiographic provinces of Pennsylvania are sub-divided into regions that generally have a similar geologic structure, geomorphic history, and climate. Pennsylvania is divided into seven physiographic provinces according to the Pennsylvania Geologic Survey. Additionally, these seven provinces are made up of smaller sections, which themselves have unique characteristics. Figure 4 shows the physiographic provinces in Pennsylvania (Sevon, 2000).

The Pittsburgh region is part of the upland area of the Appalachian Plateau Province. This upland area is a relatively flat surface with deeply dissected drainages that have produced steep-sided valleys with vertical relief on the order of 600 ft (182 km) along the major drainages. The terrain is a dissected mature landscape developed on gently folded to essentially flatlying sedimentary strata. In southwestern Pennsylvania, the structural geologic trends are northeast to southwest. The province is bounded to the southeast by the Ridge and Valley Province and to the northwest by the Central Lowlands Province.

The Appalachian Plateau Province in southwestern Pennsylvania is divided into the Pittsburgh Low Plateau Section, Waynesburg Hills Section, and the Allegheny Mountain Section. The city of Pittsburgh is located in two of the sections, with the Pittsburgh Low Plateau Section to the north and the Waynesburg Hills Section to the south, as shown in Figure 4.

The Pittsburgh Low Plateau Section has a smooth to undulating surface composed of narrow and relatively shallow valleys having a modified dendritic drainage pattern. It has low to moderate relief, with the underly-

Tectonic Setting

The tectonic history of western Pennsylvania is associated with the westernmost formation of the Appalachian Mountain chain. Four different tectonic episodes produced the Appalachian Mountain chain.

A geologic time scale of the major geologic events is shown on Table 1.

The three earliest tectonic events were the Grenville Orogeny, the Taconic Orogeny, and the Acadian Orogeny. These tectonic episodes had some effect on Pittsburgh and the southwestern Pennsylvania area in the way of deeper flexures, compressional stresses, and subsequent minor surface expressions of these deeper mechanisms.

The fourth and final mountain-building event, the Alleghany Orogeny, had the most effect on southwestern Pennsylvania. This event began approximately 300 million years ago during the Pennsylvanian Period and extended into the Permian Period (Hatcher, 2004). It resulted from the collision between the North American and African Plates. Southwestern Pennsylvania received less deformation due to its distance from the collisional area, but stresses imposed by the orogeny resulted in gentle folding of the in-place rocks, creating minor anticlines and synclines triggered by deeper thrust faulting (Schultz et al., 2013).

Southwestern Pennsylvania has experienced multiple cycles of tectonic construction followed by erosion and deposition. Sedimentation in the Northern Appalachians is considered to be complex, with both basin-wide and local factors controlling deposition.

The depositional area of the Appalachian Plateau Province in western Pennsylvania is part of a major structural basin referred to as the Appalachian Coal Basin or Allegheny Synclinorium. The northern portion is often referred to as the Pittsburgh-Huntington

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ing rock composed mostly of shale, siltstone, and sandstone. The geologic structure consists of moderateto low-amplitude folds that decrease in frequency and amplitude in a northwestward direction.

The Waynesburg Hills Section is composed of relatively hilly terrain with narrow hilltops and steep-sloped narrow valleys with a modified dendritic drainage pattern. It has moderate relief, with underlying rock types of shale, sandstone, limestone, red shale, and claystone. The geologic structure ranges from low-amplitude folds to horizontal bedding.

A small portion of the northwest section of the Appalachian Plateaus Province, called the Northwestern Glaciated Plateau Section, was glaciated during the Pleistocene Epoch. The closest approach of Wisconsinan ice was about 30 mi (48 km) north of the city.

This was the last ice advance in the area.

31

REGIONAL GEOLOGY Physiography The physiographic provinces of Pennsylvania are sub-divided into regions that generally have a similar geologic structure, geomorphic history, and climate. Pennsylvania is divided into seven physiographic provinces according to the Pennsylvania Geologic Survey. Additionally, these seven provinces are made up of smaller sections, which themselves have unique characteristics. Figure 4 shows the physiographic provinces in Pennsylvania (Sevon, 2000).

The Pittsburgh region is part of the upland area of the Appalachian Plateau Province. This upland area is a relatively flat surface with deeply dissected drainages that have produced steep-sided valleys with vertical relief on the order of 600 ft (182 km) along the major drainages. The terrain is a dissected mature landscape developed on gently folded to essentially flatlying sedimentary strata. In southwestern Pennsylvania, the structural geologic trends are northeast to southwest. The province is bounded to the southeast by the Ridge and Valley Province and to the northwest by the Central Lowlands Province.

The Appalachian Plateau Province in southwestern Pennsylvania is divided into the Pittsburgh Low Plateau Section, Waynesburg Hills Section, and the Allegheny Mountain Section. The city of Pittsburgh is located in two of the sections, with the Pittsburgh Low Plateau Section to the north and the Waynesburg Hills Section to the south, as shown in Figure 4.

The Pittsburgh Low Plateau Section has a smooth to undulating surface composed of narrow and relatively shallow valleys having a modified dendritic drainage pattern. It has low to moderate relief, with the underly-

The tectonic history of western Pennsylvania is associated with the westernmost formation of the Appalachian Mountain chain. Four different tectonic episodes produced the Appalachian Mountain chain.

A geologic time scale of the major geologic events is shown on Table 1.

The three earliest tectonic events were the Grenville Orogeny, the Taconic Orogeny, and the Acadian Orogeny. These tectonic episodes had some effect on Pittsburgh and the southwestern Pennsylvania area in the way of deeper flexures, compressional stresses, and subsequent minor surface expressions of these deeper mechanisms.

The fourth and final mountain-building event, the Alleghany Orogeny, had the most effect on southwestern Pennsylvania. This event began approximately 300 million years ago during the Pennsylvanian Period and extended into the Permian Period (Hatcher, 2004). It resulted from the collision between the North American and African Plates. Southwestern Pennsylvania received less deformation due to its distance from the collisional area, but stresses imposed by the orogeny resulted in gentle folding of the in-place rocks, creating minor anticlines and synclines triggered by deeper thrust faulting (Schultz et al., 2013).

Southwestern Pennsylvania has experienced multiple cycles of tectonic construction followed by erosion and deposition. Sedimentation in the Northern Appalachians is considered to be complex, with both basin-wide and local factors controlling deposition.

The depositional area of the Appalachian Plateau Province in western Pennsylvania is part of a major structural basin referred to as the Appalachian Coal Basin or Allegheny Synclinorium. The northern portion is often referred to as the Pittsburgh-Huntington

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31

Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 4. Physiographic province map (Sevon, 2000).

Figure 4. Physiographic province map (Sevon, 2000).

Basin or the Dunkard Basin, depending on the location. A highly generalized section through the Allegheny Synclinorium is presented in Figure 5. Updated and more detailed cross sections of the Appalachian Basin are being completed by the USGS to document and improve the understanding of the geologic framework and petroleum systems of the Appalachian Basin. More enhanced cross sections are available, and a recommended publication is by Ryder et al. (2012), titled Geologic Cross Section C-C’ through the Appalachian Basin from Erie County, North-Central Ohio, to the Valley and Ridge Province, Bedford County, South-Central Pennsylvania.

During the Appalachian tectonic events, eroded sediment was transported generally westward from the ancestral Appalachians. Figure 6 illustrates the paleogeography of the basin and source area during the Late Pennsylvanian. An evaluation of sediment deposition into this basin identified multiple sequenced 32

events. This sequencing occurred in conjunction with sea-level changes in southwestern Pennsylvania. See Table 1 for a timescale of the major activities affecting the Pennsylvania region and subsequent rock deposits associated with the activity. A generalized depositional history of the rocks in southwestern Pennsylvania, starting at the base of the stratigraphic column and progressing upward to the surficial rocks of the Pennsylvanian–Permian Periods, is as follows (Slingerland and Beaumont, 1989):

Lower Cambrian (also Catoctin Greenstone) clastic wedge sequence, consisting primarily of sandstones with faulting during late Grenville Orogeny; Cambrian–Ordovician a carbonate sequence composed mostly of limestone and dolostone with some quartzose sandstone;

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Basin or the Dunkard Basin, depending on the location. A highly generalized section through the Allegheny Synclinorium is presented in Figure 5. Updated and more detailed cross sections of the Appalachian Basin are being completed by the USGS to document and improve the understanding of the geologic framework and petroleum systems of the Appalachian Basin. More enhanced cross sections are available, and a recommended publication is by Ryder et al. (2012), titled Geologic Cross Section C-C’ through the Appalachian Basin from Erie County, North-Central Ohio, to the Valley and Ridge Province, Bedford County, South-Central Pennsylvania.

During the Appalachian tectonic events, eroded sediment was transported generally westward from the ancestral Appalachians. Figure 6 illustrates the paleogeography of the basin and source area during the Late Pennsylvanian. An evaluation of sediment deposition into this basin identified multiple sequenced 32

events. This sequencing occurred in conjunction with sea-level changes in southwestern Pennsylvania. See Table 1 for a timescale of the major activities affecting the Pennsylvania region and subsequent rock deposits associated with the activity. A generalized depositional history of the rocks in southwestern Pennsylvania, starting at the base of the stratigraphic column and progressing upward to the surficial rocks of the Pennsylvanian–Permian Periods, is as follows (Slingerland and Beaumont, 1989):

Lower Cambrian (also Catoctin Greenstone) clastic wedge sequence, consisting primarily of sandstones with faulting during late Grenville Orogeny; Cambrian–Ordovician a carbonate sequence composed mostly of limestone and dolostone with some quartzose sandstone;

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Years ago 0 to 1.8 million

Geology of Pittsburgh

Geology of Pittsburgh

Table 1. Geologic timescale of major geologic events in Pennsylvania (Barnes and Sevon, 2002).

Table 1. Geologic timescale of major geologic events in Pennsylvania (Barnes and Sevon, 2002).

Era or Eon Cenozoic Era

1.8 to 66 million 66 to 146 million

Period Quaternary Tertiary

Mesozoic Era

Cretaceous

146 to 200 million

Jurassic

200 to 251 million

Triassic

251 to 299 million

Paleozoic Era

Permian

299 to 359 million

Pennsylvanian and Mississippian (Carboniferous)

359 to 416 million

Devonian

416 to 444 million

Silurian

444 to 488 million

Ordovician

488 to 542 million

Cambrian

542 million to 2.5 billion 2.5 to 4 billion

Proterozoic Eon

4 to 4.5 billion

Pre-Archean Eon

Archean Eon

Activity Affecting Pennsylvania

Main Rock Types or Deposits in Pennsylvania

Dominant Life Forms in Pennsylvania

Years ago

Era or Eon

Glaciation; periglacial erosion and deposition Weathering and erosion; creation of present landscape Erosion and weathering

Sand, silt, clay, gravel Mammals, including humans Sand, silt, gravel Mammals, grasses

0 to 1.8 million

Clay, sand

66 to 146 million

Diabase intrusions; opening of Atlantic Ocean Separation of North America from Africa; sedimentation in rift valley Alleghanian Orogeny: collision of Africa and North America; mountain building, thrust faulting, and folding; much erosion Alluvial deposition; eastward advance of shoreline followed by development of low, flat alluvial plain Acadian Orogeny: collision of Avalonia, Europe, and North America; formation of Catskill Delta Erosion of mountains; deposition of sand and mud Taconic Orogeny: thrusting of volcanic arc; development of Appalachian basin Transgression of the sea; carbonate deposition Accretion of microplates to form Laurentia Bombardment by meteorites and comets; creation of continental crust Formation of Earth and solar system

Diabase

Dinosaurs, mammals, birds Dinosaurs, mammals, birds Dinosaurs, mammals, birds

Sandstone, shale

Insects, amphibians, reptiles

251 to 299 million

Sandstone, siltstone, shale, coal, limestone

Trees, ferns, amphibians, air-breathing molluscs, insects Fish, amphibians, insects, land plants

299 to 359 million

Pennsylvanian and Mississippian (Carboniferous)

359 to 416 million

Devonian

Corals, fish

416 to 444 million

Silurian

Molluscs, bryozoa, graptolites

444 to 488 million

Ordovician

Limestone, dolomite, Trilobites, quartzite brachiopods Schist, slate, marble Blue-green algae, jellyfish, worms None identified Bacteria

488 to 542 million

Cambrian

542 million to 2.5 billion 2.5 to 4 billion

Proterozoic Eon

None identified

4 to 4.5 billion

Pre-Archean Eon

Shale, sandstone, diabase

Conglomerate, sandstone, shale Conglomerate, sandstone, limestone Shale, limestone, dolomite

None identified

Figure 5. Cross section of the geologic structure of the Allegheny Plateau (King, 1977).

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Cenozoic Era

Period

1.8 to 66 million

Quaternary Tertiary

Mesozoic Era

Cretaceous

146 to 200 million

Jurassic

200 to 251 million

Triassic Paleozoic Era

Archean Eon

Permian

Activity Affecting Pennsylvania

Main Rock Types or Deposits in Pennsylvania

Dominant Life Forms in Pennsylvania

Glaciation; periglacial erosion and deposition Weathering and erosion; creation of present landscape Erosion and weathering

Sand, silt, clay, gravel Mammals, including humans Sand, silt, gravel Mammals, grasses

Diabase intrusions; opening of Atlantic Ocean Separation of North America from Africa; sedimentation in rift valley Alleghanian Orogeny: collision of Africa and North America; mountain building, thrust faulting, and folding; much erosion Alluvial deposition; eastward advance of shoreline followed by development of low, flat alluvial plain Acadian Orogeny: collision of Avalonia, Europe, and North America; formation of Catskill Delta Erosion of mountains; deposition of sand and mud Taconic Orogeny: thrusting of volcanic arc; development of Appalachian basin Transgression of the sea; carbonate deposition Accretion of microplates to form Laurentia Bombardment by meteorites and comets; creation of continental crust Formation of Earth and solar system

Diabase

Clay, sand

Shale, sandstone, diabase

Dinosaurs, mammals, birds Dinosaurs, mammals, birds Dinosaurs, mammals, birds

Sandstone, shale

Insects, amphibians, reptiles

Sandstone, siltstone, shale, coal, limestone

Trees, ferns, amphibians, air-breathing molluscs, insects Fish, amphibians, insects, land plants

Conglomerate, sandstone, shale Conglomerate, sandstone, limestone Shale, limestone, dolomite

Corals, fish Molluscs, bryozoa, graptolites

Limestone, dolomite, Trilobites, quartzite brachiopods Schist, slate, marble Blue-green algae, jellyfish, worms None identified Bacteria None identified

None identified

Figure 5. Cross section of the geologic structure of the Allegheny Plateau (King, 1977).

33

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Gray, Greene, Fandray, and Turka

Figure 6. Inferred paleogeography of Pennsylvania during the Late Pennsylvanian when the rocks of Pittsburgh were being deposited (Wagner et al., 1970).

Upper Ordovician clastic sequence of coarse shales,

siltstones, sandstones, and quartz pebble conglomerates associated with the Taconic Orogeny; Silurian thin clastic seams with generally sandy limestones, dolostones, and evaporites.

Silurian–Devonian carbonate sequence of limestone and dolostones; Devonian clastic wedge sequence of mostly gray fluvial and coastal shales, siltstones, and sandstones

Gray, Greene, Fandray, and Turka

with a few mudstones, all associated with the Acadian Orogeny; Mississippian clastic wedge mainly composed of sandstone and shale, with a few conglomerates and limestones and sandy limestone; and Pennsylvanian into the Permian clastic sequence consisting primarily of sandstone, shale, mudstone, and coal from the Alleghany Orogeny with multiple delta complexes in southwestern Pennsylvania.

with a few mudstones, all associated with the Acadian Orogeny; Mississippian clastic wedge mainly composed of sandstone and shale, with a few conglomerates and limestones and sandy limestone; and Pennsylvanian into the Permian clastic sequence consisting primarily of sandstone, shale, mudstone, and coal from the Alleghany Orogeny with multiple delta complexes in southwestern Pennsylvania.

The surficial bedrock of southwestern Pennsylvania shows characteristics associated with deltaic depositional environments with a cyclical nature, indicating a fluctuating sea level resulting from glaciation in the Southern Hemisphere. Figure 7 illustrates a generalized depositional cycle for southwestern Pennsylvania along with the types of depositional environments associated with some of the rock units.

The surficial bedrock of southwestern Pennsylvania shows characteristics associated with deltaic depositional environments with a cyclical nature, indicating a fluctuating sea level resulting from glaciation in the Southern Hemisphere. Figure 7 illustrates a generalized depositional cycle for southwestern Pennsylvania along with the types of depositional environments associated with some of the rock units.

Geologic Setting Rock strata cropping out in the Appalachian Plateau vary in age from Devonian to Permian, as shown on Figure 8. Mississippian- and Devonian-age rocks crop out north of Pittsburgh, as well as on the ridges to the east. Rocks of Pennsylvanian age form the surface strata within the Pittsburgh area. Permianage rock crops out southwest of Pittsburgh.

Figure 6. Inferred paleogeography of Pennsylvania during the Late Pennsylvanian when the rocks of Pittsburgh were being deposited (Wagner et al., 1970).

Upper Ordovician clastic sequence of coarse shales,

siltstones, sandstones, and quartz pebble conglomerates associated with the Taconic Orogeny; Silurian thin clastic seams with generally sandy limestones, dolostones, and evaporites.

Silurian–Devonian carbonate sequence of limestone and dolostones; Devonian clastic wedge sequence of mostly gray fluvial and coastal shales, siltstones, and sandstones

Figure 7. Generalized depositional cycle of southwestern Pennsylvania (Pryor and Sable, 1974).

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Geologic Setting Rock strata cropping out in the Appalachian Plateau vary in age from Devonian to Permian, as shown on Figure 8. Mississippian- and Devonian-age rocks crop out north of Pittsburgh, as well as on the ridges to the east. Rocks of Pennsylvanian age form the surface strata within the Pittsburgh area. Permianage rock crops out southwest of Pittsburgh.

Figure 7. Generalized depositional cycle of southwestern Pennsylvania (Pryor and Sable, 1974).

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 8. Geologic map of Pennsylvania (Pennsylvania Geological Survey, 2007).

Figure 8. Geologic map of Pennsylvania (Pennsylvania Geological Survey, 2007).

The structural trend of the Appalachian Plateau ranges from N30E to N70E (Amdt et al., 1969). The lengths of the anticlines and synclines vary significantly, as shown in Figure 9. The dip associated with these folded structures is generally no more than a few degrees. The most readily identifiable and consistent rock strata are the coal beds and some limestone beds.

Faulting is not common, but some minor localized vertical displacements are present.

Stratigraphy Sedimentary Rocks The surface and near-surface rocks in the greater Pittsburgh area belong to the Permianto Pennsylvanian-age Dunkard Group and the Pennsylvanian-age Monongahela, Conemaugh, and

Allegheny Groups. A generalized stratigraphic column of the Pittsburgh region is presented in Figure 10. A generalized summary of these rock types follows.

Locations of mentioned counties are identified on the Geologic Map of Pennsylvania in Figure 8.

Dunkard Group (Permian and Pennsylvanian)— This group occurs at or near the surface in southern Allegheny County and in central and southern Washington County, which is southwest of the city of Pittsburgh (see Figure 8). The Dunkard unit reaches a maximum thickness of about 1,120 ft (341 m) (Berryhill et al., 1971) in Greene County. It is generally considered non-marine, composed mostly of fine-grained clastics, which frequently are calcareous. However, some findings of linguloid brachiopods in the Washington coal bed in nearby southeastern Ohio and the northern West Virginia panhandle may suggest possible marine brackish conditions extending into the

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The structural trend of the Appalachian Plateau ranges from N30E to N70E (Amdt et al., 1969). The lengths of the anticlines and synclines vary significantly, as shown in Figure 9. The dip associated with these folded structures is generally no more than a few degrees. The most readily identifiable and consistent rock strata are the coal beds and some limestone beds.

Faulting is not common, but some minor localized vertical displacements are present.

Stratigraphy Sedimentary Rocks The surface and near-surface rocks in the greater Pittsburgh area belong to the Permianto Pennsylvanian-age Dunkard Group and the Pennsylvanian-age Monongahela, Conemaugh, and

Allegheny Groups. A generalized stratigraphic column of the Pittsburgh region is presented in Figure 10. A generalized summary of these rock types follows.

Locations of mentioned counties are identified on the Geologic Map of Pennsylvania in Figure 8.

Dunkard Group (Permian and Pennsylvanian)— This group occurs at or near the surface in southern Allegheny County and in central and southern Washington County, which is southwest of the city of Pittsburgh (see Figure 8). The Dunkard unit reaches a maximum thickness of about 1,120 ft (341 m) (Berryhill et al., 1971) in Greene County. It is generally considered non-marine, composed mostly of fine-grained clastics, which frequently are calcareous. However, some findings of linguloid brachiopods in the Washington coal bed in nearby southeastern Ohio and the northern West Virginia panhandle may suggest possible marine brackish conditions extending into the

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 9. Structural folds map of Pennsylvania (Faill, 2011).

Figure 9. Structural folds map of Pennsylvania (Faill, 2011).

Dunkard Group (Cross and Schemel, 1956; Berryhill, 1963). The Dunkard Group consists of the Waynesburg, Washington, and Greene Formations (Berryhill et al., 1971). The lower boundary is defined as the base of the Waynesburg Coal, which is the only coal routinely mined in the Dunkard Group, and the upper boundary is the modern-day erosional surface (Berryhill et al., 1971). The basal Waynesburg Formation consists of shale, sandstone, siltstone, and coal. The overlying Washington Formation outcrops in valley bottoms in the northwest corner of Greene County and consists of limestone, claystone, siltstone, sandstone, carbonaceous shale, and coal. Thick lacustrine limestones are especially prevalent in the Washington Formation. The uppermost Greene Formation, which covers the western half of Greene County and caps the tops of ridges in the eastern part of the county, consists mostly of shale, sandstone, siltstone, and limestone.

Monongahela Group (Pennsylvanian)—The Monongahela Group underlies the Waynesburg Group, extending from the base of the Waynesburg Coal to the base of the Pittsburgh Coal, as shown in Figure 10. The group includes the Uniontown and 36

Pittsburgh Formations. It is a non-marine sedimentary sequence. Coal seams, including the Uniontown, Sewickley, Redstone, and the Pittsburgh Coals, are persistent and are the primary marker beds in the area. This group ranges in thickness between 275 and 290 ft (84 and 88 m) (Berryhill et al., 1971). It consists of cyclic sedimentary sequences formed in a relatively low-energy, marginal upper delta plain having extensive lake and swamp development (Berryhill et al., 1971; Donaldson, 1974). The depositional environments of the coals are identified as tropical swamps in anaerobic conditions.

The Uniontown Formation contains both an upper and lower member separated by the Little Waynesburg Coal. The Upper Member is shale or very thinly bedded sandstone. The Lower Member is mostly sandstone with interbedded coal lenses near its base.

The Pittsburgh Formation contains several coal seams, including the laterally extensive Pittsburgh Coal, which is the basal member of the Pittsburgh Formation. The Pittsburgh Formation is divided into five members: the lower member; Redstone; Fishpot;

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Dunkard Group (Cross and Schemel, 1956; Berryhill, 1963). The Dunkard Group consists of the Waynesburg, Washington, and Greene Formations (Berryhill et al., 1971). The lower boundary is defined as the base of the Waynesburg Coal, which is the only coal routinely mined in the Dunkard Group, and the upper boundary is the modern-day erosional surface (Berryhill et al., 1971). The basal Waynesburg Formation consists of shale, sandstone, siltstone, and coal. The overlying Washington Formation outcrops in valley bottoms in the northwest corner of Greene County and consists of limestone, claystone, siltstone, sandstone, carbonaceous shale, and coal. Thick lacustrine limestones are especially prevalent in the Washington Formation. The uppermost Greene Formation, which covers the western half of Greene County and caps the tops of ridges in the eastern part of the county, consists mostly of shale, sandstone, siltstone, and limestone.

Monongahela Group (Pennsylvanian)—The Monongahela Group underlies the Waynesburg Group, extending from the base of the Waynesburg Coal to the base of the Pittsburgh Coal, as shown in Figure 10. The group includes the Uniontown and 36

Pittsburgh Formations. It is a non-marine sedimentary sequence. Coal seams, including the Uniontown, Sewickley, Redstone, and the Pittsburgh Coals, are persistent and are the primary marker beds in the area. This group ranges in thickness between 275 and 290 ft (84 and 88 m) (Berryhill et al., 1971). It consists of cyclic sedimentary sequences formed in a relatively low-energy, marginal upper delta plain having extensive lake and swamp development (Berryhill et al., 1971; Donaldson, 1974). The depositional environments of the coals are identified as tropical swamps in anaerobic conditions.

The Uniontown Formation contains both an upper and lower member separated by the Little Waynesburg Coal. The Upper Member is shale or very thinly bedded sandstone. The Lower Member is mostly sandstone with interbedded coal lenses near its base.

The Pittsburgh Formation contains several coal seams, including the laterally extensive Pittsburgh Coal, which is the basal member of the Pittsburgh Formation. The Pittsburgh Formation is divided into five members: the lower member; Redstone; Fishpot;

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 10. A generalized stratigraphic column of the Pittsburgh region (Harper, 1990).

Figure 10. A generalized stratigraphic column of the Pittsburgh region (Harper, 1990).

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Gray, Greene, Fandray, and Turka

Sewickley; and the upper member. This formation consists of numerous relatively persistent limestone seams and lesser claystone beds in the upper portion, with the lower portion predominately composed of shale, sandstone, and coal seams.

The lower member includes the approximate 10 ft (3 m) thick and persistent Pittsburgh Coal, overlain by the only coarse clastic rock within the Pittsburgh Formation, the Pittsburgh sandstone. The Pittsburgh sandstone is a persistent fluvial unit that is generally thinly bedded to massive. A major fluvial channel system, flowing north to northwest through what is now Greene and Washington Counties, deposited this unit as an elongate sandstone body up to 80 ft (24 m) thick and several miles wide (Edmunds et al., 1999).

The Redstone member lies stratigraphically above the lower member and is characterized by siltstone and claystone, but it includes a persistent limestone unit. The division between the lower member and the Redstone member is typically marked by the Redstone Coal; however, the coal is laterally discontinuous.

The Fishpot member, the next stratigraphic unit within the Pittsburgh Formation, is the thinnest unit.

The Fishpot member includes mainly siltstone and claystone, along with several thin sandstone bodies.

This formation can be difficult to identify where the Fishpot Coal is absent because it marks the base of the Fishpot.

The Sewickley member represents the thickest limestone sequence, the Benwood Limestone. The Benwood Limestone is a relatively thick interbedded limestone and shale unit that is dolomitic in portions of the region.

The thick upper member of the Pittsburgh Formation contains four limestone units, designated in ascending order as “A,” “B,” “C,” and “D.” These rather persistent limestone seams are interbedded with siltstone and shale seams that are generally in proportion with the thickness of the limestone found above these fine-grained seams. Limestones of the Monongahela Group are freshwater limestones, deposited during highstands in the lakes of alluvial plains.

Conemaugh Group (Pennsylvanian)—The Conemaugh Group underlies the Monongahela Group in southwestern Pennsylvania. It includes the Glenshaw and Casselman Formations and is a clastic sequence dominated by siltstone, claystone, shale, and sandstone. The average thickness of this group is approximately 620 ft (189 m) (Shultz, 1999) in the Pittsburgh area and extends from the base of the Pittsburgh Coal to the top of the Upper Freeport Coal. Bedrock exposure of the Conemaugh Group is limited in southwestern Pennsylvania, with most exposures at and north of Pittsburgh.

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Conemaugh stratigraphy is subdivided into two distinct formations based upon the presence or absence of marine units, with the boundary between them being the top of the persistent Ames Limestone (Flint, 1965). The upper unit, the Casselman Formation, is essentially devoid of marine units, while the lower unit, the Glenshaw Formation, contains widespread marine units (Shultz, 1999). Mineable coals are not common in the Conemaugh Group.

The Casselman Formation extends from the base of the Pittsburgh Coal to the top of the Ames Limestone and consists of a sequence of alternating layers of sandstone, shale, red beds (claystone), non-marine limestone, and thin discontinuous coal seams.

The Birmingham shale is a significant unit within the Casselman Formation. Numerous locations of this strata are exposed around the city. It is generally described as a dark, thinly laminated rock nearly 50 ft (15 m) thick that occurs below the Morgantown sandstone and about 30–60 ft (9–18 m) above the Ames Limestone in Pittsburgh. It consists mainly of finegrained siltstone and shale overbank deposits. Marine fossils have been found in the shale at outcrops along Ohio River Boulevard, which is located just west of Pittsburgh. This transition zone contains marine to brackish fauna and suggests the last marine episode of the Paleozoic in the Pittsburgh area. The brachiopod findings identified in the earlier Dunkard Group suggest the last marine episode may be as late as the Washington Coal seam in areas further west of Pittsburgh.

The Glenshaw Formation extends from the top of the Ames Limestone to the top of the Upper Freeport Coal. The Ames Limestone is a laterally continuous fossiliferous limestone that is generally on the order of 2–4 ft (0.6–1.2 m) thick. It serves as the primary marker bed in the Conemaugh Group and identifies the last certain occurrence of marine conditions in Pittsburgh. The claystones and shales are the weaker units of the formation and are notorious for landslide potential. All of these rock units are commonly interbedded and tend to change lithologically over short lateral distances.

A primary source in the Pittsburgh area for landslides is the Pittsburgh red beds, which is near the top of the Glenshaw Formation. It is a 40–60 ft (12– 18 m) series of mostly reddish, greenish, and grayish claystone and shale, with minor amounts of sandstone and siltstone, that tends to weather deeply on hillsides throughout southwestern Pennsylvania. Claystone is a low-permeability, low-strength rock with weakly connected pore space. Repeated weathering cycles and excessive pore pressure have a tendency to reduce the internal shear strength of this particular rock, leading to failure. In addition, Conemaugh claystones contain

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Gray, Greene, Fandray, and Turka

Sewickley; and the upper member. This formation consists of numerous relatively persistent limestone seams and lesser claystone beds in the upper portion, with the lower portion predominately composed of shale, sandstone, and coal seams.

The lower member includes the approximate 10 ft (3 m) thick and persistent Pittsburgh Coal, overlain by the only coarse clastic rock within the Pittsburgh Formation, the Pittsburgh sandstone. The Pittsburgh sandstone is a persistent fluvial unit that is generally thinly bedded to massive. A major fluvial channel system, flowing north to northwest through what is now Greene and Washington Counties, deposited this unit as an elongate sandstone body up to 80 ft (24 m) thick and several miles wide (Edmunds et al., 1999).

The Redstone member lies stratigraphically above the lower member and is characterized by siltstone and claystone, but it includes a persistent limestone unit. The division between the lower member and the Redstone member is typically marked by the Redstone Coal; however, the coal is laterally discontinuous.

The Fishpot member, the next stratigraphic unit within the Pittsburgh Formation, is the thinnest unit.

The Fishpot member includes mainly siltstone and claystone, along with several thin sandstone bodies.

This formation can be difficult to identify where the Fishpot Coal is absent because it marks the base of the Fishpot.

The Sewickley member represents the thickest limestone sequence, the Benwood Limestone. The Benwood Limestone is a relatively thick interbedded limestone and shale unit that is dolomitic in portions of the region.

The thick upper member of the Pittsburgh Formation contains four limestone units, designated in ascending order as “A,” “B,” “C,” and “D.” These rather persistent limestone seams are interbedded with siltstone and shale seams that are generally in proportion with the thickness of the limestone found above these fine-grained seams. Limestones of the Monongahela Group are freshwater limestones, deposited during highstands in the lakes of alluvial plains.

Conemaugh Group (Pennsylvanian)—The Conemaugh Group underlies the Monongahela Group in southwestern Pennsylvania. It includes the Glenshaw and Casselman Formations and is a clastic sequence dominated by siltstone, claystone, shale, and sandstone. The average thickness of this group is approximately 620 ft (189 m) (Shultz, 1999) in the Pittsburgh area and extends from the base of the Pittsburgh Coal to the top of the Upper Freeport Coal. Bedrock exposure of the Conemaugh Group is limited in southwestern Pennsylvania, with most exposures at and north of Pittsburgh.

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Conemaugh stratigraphy is subdivided into two distinct formations based upon the presence or absence of marine units, with the boundary between them being the top of the persistent Ames Limestone (Flint, 1965). The upper unit, the Casselman Formation, is essentially devoid of marine units, while the lower unit, the Glenshaw Formation, contains widespread marine units (Shultz, 1999). Mineable coals are not common in the Conemaugh Group.

The Casselman Formation extends from the base of the Pittsburgh Coal to the top of the Ames Limestone and consists of a sequence of alternating layers of sandstone, shale, red beds (claystone), non-marine limestone, and thin discontinuous coal seams.

The Birmingham shale is a significant unit within the Casselman Formation. Numerous locations of this strata are exposed around the city. It is generally described as a dark, thinly laminated rock nearly 50 ft (15 m) thick that occurs below the Morgantown sandstone and about 30–60 ft (9–18 m) above the Ames Limestone in Pittsburgh. It consists mainly of finegrained siltstone and shale overbank deposits. Marine fossils have been found in the shale at outcrops along Ohio River Boulevard, which is located just west of Pittsburgh. This transition zone contains marine to brackish fauna and suggests the last marine episode of the Paleozoic in the Pittsburgh area. The brachiopod findings identified in the earlier Dunkard Group suggest the last marine episode may be as late as the Washington Coal seam in areas further west of Pittsburgh.

The Glenshaw Formation extends from the top of the Ames Limestone to the top of the Upper Freeport Coal. The Ames Limestone is a laterally continuous fossiliferous limestone that is generally on the order of 2–4 ft (0.6–1.2 m) thick. It serves as the primary marker bed in the Conemaugh Group and identifies the last certain occurrence of marine conditions in Pittsburgh. The claystones and shales are the weaker units of the formation and are notorious for landslide potential. All of these rock units are commonly interbedded and tend to change lithologically over short lateral distances.

A primary source in the Pittsburgh area for landslides is the Pittsburgh red beds, which is near the top of the Glenshaw Formation. It is a 40–60 ft (12– 18 m) series of mostly reddish, greenish, and grayish claystone and shale, with minor amounts of sandstone and siltstone, that tends to weather deeply on hillsides throughout southwestern Pennsylvania. Claystone is a low-permeability, low-strength rock with weakly connected pore space. Repeated weathering cycles and excessive pore pressure have a tendency to reduce the internal shear strength of this particular rock, leading to failure. In addition, Conemaugh claystones contain

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Geology of Pittsburgh

minerals that tend to expand in the presence of water (Pomeroy, 1982).

These red shales have been interpreted as a paleosol horizon (ancient soil zone) on the Pennsylvanian delta by Donahue and Rollins (1974). They suggested that the red color and the claystone texture are similar to that of a laterite soil weathering profile, with some channel-form structures indicating that these shales may be composed of multiple paleosols. It also has features that may indicate repeated and prolonged subaerial exposure and pedogenesis (Cecil and Dulong, 2004). The pedogenic origin is identified by good exposures of the series displaying evidence of an ancient soil development, with some occasional root casts, slickensides, and calcite-rich nodules.

Allegheny Group (Pennsylvanian)—The Allegheny Group underlies the Conemaugh with a thickness between 270–330 ft (82–100 m) in western Pennsylvania (Edmunds et al, 1999). It begins at the top of the Upper Freeport Coal and extends to the base of the Brookville Coal. This group consists largely of marine units and contains six mineable coals, referred to as the Upper Freeport Coal, Lower Freeport Coal, Upper Kittanning Coal, Middle Kittanning Coal, Lower Kittanning Coal, and the Brookville Coal. These coals crop out north of the Pittsburgh area. Coals and associated strata of the lower Allegheny Group (Brookville through Middle Kittanning Coals) were deposited during a general eastward marine transgression. The setting was a shifting complex of marine to brackish embayments, lower-delta-plain distributaries, and inter-distributary to coastal margin swamps, grading inland to an upper-delta-plain fluvial and interfluvial swamp system (Williams, 1960; Williams and Ferm, 1964; Ferm and Williams, 1965; Ferm and Cavaroc, 1969; and Ferm, 1970, 1974). The upper Allegheny Group (Upper Kittanning through Upper Freeport Coals) was deposited in a relatively high energy, upper-delta-plain fluvial and interfluvial lake and swamp environment during a period of general marine regression (Sholes et al., 1979; Skema et al., 1982).

The Allegheny Group contains a repeating succession of coal, limestone, and clastics, ranging from claystone to coarse sandstone. Most beds exhibit lithologic change both vertically and laterally over short distances, but some coals, and a few marine shales and limestones are continuous over large areas.

Pottsville Group (Pennsylvanian)—The Pennsylvanian-age Pottsville Group is a ridge-forming unit in parts of the Ridge and Valley Province in Pennsylvania and in the Allegheny Mountain section of the Appalachian Plateau Province. The group ranges in thickness from 100 ft (30 m) in western Pennsylvania to 1,600 ft (488 m) in northeastern Pennsylvania

Geology of Pittsburgh

(Edmunds et al., 1999). Because it contains resistant rock units, it tends to form ridges and cap most of the highpoints, including Mount Davis in Somerset County, the highest point in Pennsylvania at 3,213 ft (980 m) in elevation.

The Pottsville Group consists predominately of a well-cemented pebble conglomerate with some sandstones and finer clastics and coal (Edmunds et al., 1999) that range in thickness from about 10 to 70 ft (3 to 21 m). It extends upward from the top of the Mississippian Mauch Chunk Formation to the base of the underclay beneath the Brookville Coal of the Allegheny Group. Abrupt variations in the thickness of the Pottsville Group of up to 100 ft (30 m) have been observed over short distances. The formation has minor marine limestones in northern Pennsylvania. Mining of coal in the Pottsville Group is limited, mainly occurring in the basal part of the formation (McElroy, 2000).

Igneous and Metamorphic Rocks Precambrian basement rock (see Figure 11) underlies all of Pennsylvania, but it is only exposed in the southeastern part of the state. A thick Paleozoic sequence overlies the basement for all of southwestern Pennsylvania. The basement rocks directly under the Pittsburgh region are inferred from limited data found mainly in deep wells located in northwestern Pennsylvania, eastern Ohio, and northwestern West Virginia, as well as from geophysical surveys.

The basement in the Pittsburgh region is at a depth ranging from 14,700 to 16,400 ft (4,480 to 5,000 m), according to the Saylor (1999), and it is believed to have lithologies similar to the Canadian Grenville Belt. The most common lithologies identified are granite, gneiss, biotite granite, and biotite schist (Saylor, 1999), and all of these lithologies have been metamorphosed to the greenschist or amphibole facies (Bass, 1959, 1960; Saylor, 1968).

Some indirect evidence has been found that deformation of the basement exists; however, little physical information is available. Direct investigation and research into the basement are prohibited by depth, and most modern remote-sensing data remain confidential as a result of the increasing gas exploration from the recent Middle Devonian shale gas boom. Other than some glacial erratics derived from Canada, there are no surface metamorphic rocks in western Pennsylvania.

The only known near-surface igneous rock in western Pennsylvania are two separate single-fissure Jurassic kimberlite dikes. The first is the Gates-Adah Dikes, which outcrop near the Monongahela River on the border of Fayette and Greene Counties (south of Pitts-

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minerals that tend to expand in the presence of water (Pomeroy, 1982).

These red shales have been interpreted as a paleosol horizon (ancient soil zone) on the Pennsylvanian delta by Donahue and Rollins (1974). They suggested that the red color and the claystone texture are similar to that of a laterite soil weathering profile, with some channel-form structures indicating that these shales may be composed of multiple paleosols. It also has features that may indicate repeated and prolonged subaerial exposure and pedogenesis (Cecil and Dulong, 2004). The pedogenic origin is identified by good exposures of the series displaying evidence of an ancient soil development, with some occasional root casts, slickensides, and calcite-rich nodules.

Allegheny Group (Pennsylvanian)—The Allegheny Group underlies the Conemaugh with a thickness between 270–330 ft (82–100 m) in western Pennsylvania (Edmunds et al, 1999). It begins at the top of the Upper Freeport Coal and extends to the base of the Brookville Coal. This group consists largely of marine units and contains six mineable coals, referred to as the Upper Freeport Coal, Lower Freeport Coal, Upper Kittanning Coal, Middle Kittanning Coal, Lower Kittanning Coal, and the Brookville Coal. These coals crop out north of the Pittsburgh area. Coals and associated strata of the lower Allegheny Group (Brookville through Middle Kittanning Coals) were deposited during a general eastward marine transgression. The setting was a shifting complex of marine to brackish embayments, lower-delta-plain distributaries, and inter-distributary to coastal margin swamps, grading inland to an upper-delta-plain fluvial and interfluvial swamp system (Williams, 1960; Williams and Ferm, 1964; Ferm and Williams, 1965; Ferm and Cavaroc, 1969; and Ferm, 1970, 1974). The upper Allegheny Group (Upper Kittanning through Upper Freeport Coals) was deposited in a relatively high energy, upper-delta-plain fluvial and interfluvial lake and swamp environment during a period of general marine regression (Sholes et al., 1979; Skema et al., 1982).

The Allegheny Group contains a repeating succession of coal, limestone, and clastics, ranging from claystone to coarse sandstone. Most beds exhibit lithologic change both vertically and laterally over short distances, but some coals, and a few marine shales and limestones are continuous over large areas.

Pottsville Group (Pennsylvanian)—The Pennsylvanian-age Pottsville Group is a ridge-forming unit in parts of the Ridge and Valley Province in Pennsylvania and in the Allegheny Mountain section of the Appalachian Plateau Province. The group ranges in thickness from 100 ft (30 m) in western Pennsylvania to 1,600 ft (488 m) in northeastern Pennsylvania

(Edmunds et al., 1999). Because it contains resistant rock units, it tends to form ridges and cap most of the highpoints, including Mount Davis in Somerset County, the highest point in Pennsylvania at 3,213 ft (980 m) in elevation.

The Pottsville Group consists predominately of a well-cemented pebble conglomerate with some sandstones and finer clastics and coal (Edmunds et al., 1999) that range in thickness from about 10 to 70 ft (3 to 21 m). It extends upward from the top of the Mississippian Mauch Chunk Formation to the base of the underclay beneath the Brookville Coal of the Allegheny Group. Abrupt variations in the thickness of the Pottsville Group of up to 100 ft (30 m) have been observed over short distances. The formation has minor marine limestones in northern Pennsylvania. Mining of coal in the Pottsville Group is limited, mainly occurring in the basal part of the formation (McElroy, 2000).

Igneous and Metamorphic Rocks Precambrian basement rock (see Figure 11) underlies all of Pennsylvania, but it is only exposed in the southeastern part of the state. A thick Paleozoic sequence overlies the basement for all of southwestern Pennsylvania. The basement rocks directly under the Pittsburgh region are inferred from limited data found mainly in deep wells located in northwestern Pennsylvania, eastern Ohio, and northwestern West Virginia, as well as from geophysical surveys.

The basement in the Pittsburgh region is at a depth ranging from 14,700 to 16,400 ft (4,480 to 5,000 m), according to the Saylor (1999), and it is believed to have lithologies similar to the Canadian Grenville Belt. The most common lithologies identified are granite, gneiss, biotite granite, and biotite schist (Saylor, 1999), and all of these lithologies have been metamorphosed to the greenschist or amphibole facies (Bass, 1959, 1960; Saylor, 1968).

Some indirect evidence has been found that deformation of the basement exists; however, little physical information is available. Direct investigation and research into the basement are prohibited by depth, and most modern remote-sensing data remain confidential as a result of the increasing gas exploration from the recent Middle Devonian shale gas boom. Other than some glacial erratics derived from Canada, there are no surface metamorphic rocks in western Pennsylvania.

The only known near-surface igneous rock in western Pennsylvania are two separate single-fissure Jurassic kimberlite dikes. The first is the Gates-Adah Dikes, which outcrop near the Monongahela River on the border of Fayette and Greene Counties (south of Pitts-

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 11. Subsurface rocks below western Pennsylvania (Adapted from Flaherty and Flaherty, 2014; and Wagner et al., 1970).

Figure 11. Subsurface rocks below western Pennsylvania (Adapted from Flaherty and Flaherty, 2014; and Wagner et al., 1970).

burgh), shown on Figure 8. The Gates-Adah kimberlite intruded approximately 170 million years ago (Bikerman et al., 1997), appears to have formed at a relatively shallow depth, and contains mostly pyrope garnets and Alexandrite-effect pyropes.

The other kimberlite intrusion is the DixonvilleTanoma Dike in central Indiana County (northeast of Pittsburgh), as shown on Figure 8. The intrusions 40

are carbonatized hypabyssal kimberlites (Gold et al., 2016). The Dixonville Dike and Tanoma Dike represent the same intrusion, and neither is exposed on the surface; they were initially discovered in the Tanoma Coal Mine while mining the Lower Kittanning Coal.

They extend almost continuously from the Lower Kittanning Coal to the Lower Freeport Coal through a vertical distance of approximately 180 ft (55 m). The

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burgh), shown on Figure 8. The Gates-Adah kimberlite intruded approximately 170 million years ago (Bikerman et al., 1997), appears to have formed at a relatively shallow depth, and contains mostly pyrope garnets and Alexandrite-effect pyropes.

The other kimberlite intrusion is the DixonvilleTanoma Dike in central Indiana County (northeast of Pittsburgh), as shown on Figure 8. The intrusions 40

are carbonatized hypabyssal kimberlites (Gold et al., 2016). The Dixonville Dike and Tanoma Dike represent the same intrusion, and neither is exposed on the surface; they were initially discovered in the Tanoma Coal Mine while mining the Lower Kittanning Coal.

They extend almost continuously from the Lower Kittanning Coal to the Lower Freeport Coal through a vertical distance of approximately 180 ft (55 m). The

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Geology of Pittsburgh

dike is 1–18 in. (2.54–45.72 cm) wide and extends some 7,200 ft (2.19 km) laterally through the mine workings (Gold et al., 2016). The coal mine has closed, and the dike is no longer accessible.

Surficial Geologic and Soil Features Existing and past climatic conditions have resulted in substantial mechanical and chemical weathering, which has produced a residual or colluvial soil mantle over the rocks of the Pittsburgh region. The sedimentary rock strata are normally not exposed, other than in valley walls and excavations into rock. There is considerable evidence that rocks of this region remain highly stressed, and subsequent stress relief due to valley cutting aids in the physical breakup of rock and enhances its susceptibility to chemical weathering (Ferguson, 1967, 1974; Voight, 1974). The most important discontinuities within the surficial rock are joints.

Both tectonic jointing and stress-relief jointing are recognized. Both systematic jointing and non-systematic jointing occur, with the majority of non-systematic joints in the weaker, fine-grained rock.

Joints caused by the local release of residual stress are closely spaced (up to 10 ft [3 m]), whereas joints caused by tectonic stresses exhibit a spacing of many feet (Nickelsen and Hough, 1967). The finer-grained rocks have more closely spaced joints. Nickelsen and Hough (1967) presented details of joint patterns, trends, and spacing in the Appalachian Plateau of Pennsylvania.

Southwestern Pennsylvania is dominated by soil derived from acidic shales and sandstones consisting of clay-sized particles with moderate to substantial amounts of rock fragments. The surficial soils are predominantly silty loams, which are usually well drained.

This region has relatively steep slopes, making erosion a major concern. The available water-holding capacity (i.e., porosity) of many soils in the region is relatively moderate. Residual soils are characteristic of the flat upland surfaces and flat surfaces of larger benches, with colluvial soils forming the slopes. In general, the thickness of residual or colluvial soils in the Pittsburgh region is on the order of 10–30 ft (3–9 m). Alluvial soils fill stream and river valleys and reach thicknesses of up to 100 ft (30 m).

Pleistocene Glaciation The closest extent of continental ice to Pittsburgh was approximately 30–40 mi (48–64 km) northwest.

However, the periglacial activity and sand and gravel outwash are two major results of glaciation that impacted Pittsburgh. Figure 12 shows the limit of glacia-

Geology of Pittsburgh

tion in western Pennsylvania and the present river systems. Extensive periglacial activity south of the glacial limits, consisting of cold wet weather and frequent freeze-thaw cycles, impacted the Pittsburgh area. This severe climate caused extensive mass wasting through rock breakup and downslope movement of broken material. Peltier (1950) and Denny (1956) found fossil periglacial features close to the front of the maximum advance of Wisconsinan glaciations in Pennsylvania, which strongly support influence of Pleistocene periglacial processes on the development of slopes.

Radiocarbon dating of wood from several large colluvial slide masses in western Pennsylvania and West Virginia indicate a Pleistocene age, and thus a periglacial origin, for these deposits (Gray et al., 1979).

Wisconsinan glaciation significantly altered the courses of the Allegheny and Ohio Rivers, and glacial outwash filled the valleys with sand and gravel. Erosion subsequently removed approximately 80 ft (24 m) of the sand and gravel, leaving about 50 ft (15 m) of alluvium, which created a significant aquifer in the river valleys. The alluvium consists of hard, dense sand and gravel, which provide excellent foundation conditions for large buildings and heavy structures along with a high-quality source of durable sand and gravel.

Pittsburgh’s Three Rivers Prior to the Pleistocene glaciation, which began approximately 800,000 to 1,000,000 years ago, the Pittsburgh River was the dominant river in southwestern Pennsylvania (Figure 13). It flowed north to the site of Pittsburgh in a channel approximately coincident with its present channel. From Pittsburgh, it followed the channel of the present Ohio River to Beaver, PA, where it turned north up the present Beaver River Valley and flowed north into the Erigan River or the former “Ancestral Erie Basin,” as shown on Figure 13 (Harper, 1997). The Monongahela River system drained about three fourths of the area in Pennsylvania that is presently drained by the combined Ohio, Monongahela, and Allegheny Rivers and their tributaries (Harper, 2002). The Ohio River was a tributary of the Monongahela. It originated south of Moundsville, WV, and flowed north, joining the Monongahela River just south of New Castle, PA. The Allegheny River was three separate rivers that drained different parts of Pennsylvania (Figure 13).

The “Lower Allegheny” originated in Elk, Forest, and Jefferson Counties, followed the course of the present Clarion River, and then flowed south to join the Monongahela River at what is now Pittsburgh. The “Middle Allegheny” started in Warren County and

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dike is 1–18 in. (2.54–45.72 cm) wide and extends some 7,200 ft (2.19 km) laterally through the mine workings (Gold et al., 2016). The coal mine has closed, and the dike is no longer accessible.

Surficial Geologic and Soil Features Existing and past climatic conditions have resulted in substantial mechanical and chemical weathering, which has produced a residual or colluvial soil mantle over the rocks of the Pittsburgh region. The sedimentary rock strata are normally not exposed, other than in valley walls and excavations into rock. There is considerable evidence that rocks of this region remain highly stressed, and subsequent stress relief due to valley cutting aids in the physical breakup of rock and enhances its susceptibility to chemical weathering (Ferguson, 1967, 1974; Voight, 1974). The most important discontinuities within the surficial rock are joints.

Both tectonic jointing and stress-relief jointing are recognized. Both systematic jointing and non-systematic jointing occur, with the majority of non-systematic joints in the weaker, fine-grained rock.

Joints caused by the local release of residual stress are closely spaced (up to 10 ft [3 m]), whereas joints caused by tectonic stresses exhibit a spacing of many feet (Nickelsen and Hough, 1967). The finer-grained rocks have more closely spaced joints. Nickelsen and Hough (1967) presented details of joint patterns, trends, and spacing in the Appalachian Plateau of Pennsylvania.

Southwestern Pennsylvania is dominated by soil derived from acidic shales and sandstones consisting of clay-sized particles with moderate to substantial amounts of rock fragments. The surficial soils are predominantly silty loams, which are usually well drained.

This region has relatively steep slopes, making erosion a major concern. The available water-holding capacity (i.e., porosity) of many soils in the region is relatively moderate. Residual soils are characteristic of the flat upland surfaces and flat surfaces of larger benches, with colluvial soils forming the slopes. In general, the thickness of residual or colluvial soils in the Pittsburgh region is on the order of 10–30 ft (3–9 m). Alluvial soils fill stream and river valleys and reach thicknesses of up to 100 ft (30 m).

Pleistocene Glaciation The closest extent of continental ice to Pittsburgh was approximately 30–40 mi (48–64 km) northwest.

However, the periglacial activity and sand and gravel outwash are two major results of glaciation that impacted Pittsburgh. Figure 12 shows the limit of glacia-

tion in western Pennsylvania and the present river systems. Extensive periglacial activity south of the glacial limits, consisting of cold wet weather and frequent freeze-thaw cycles, impacted the Pittsburgh area. This severe climate caused extensive mass wasting through rock breakup and downslope movement of broken material. Peltier (1950) and Denny (1956) found fossil periglacial features close to the front of the maximum advance of Wisconsinan glaciations in Pennsylvania, which strongly support influence of Pleistocene periglacial processes on the development of slopes.

Radiocarbon dating of wood from several large colluvial slide masses in western Pennsylvania and West Virginia indicate a Pleistocene age, and thus a periglacial origin, for these deposits (Gray et al., 1979).

Wisconsinan glaciation significantly altered the courses of the Allegheny and Ohio Rivers, and glacial outwash filled the valleys with sand and gravel. Erosion subsequently removed approximately 80 ft (24 m) of the sand and gravel, leaving about 50 ft (15 m) of alluvium, which created a significant aquifer in the river valleys. The alluvium consists of hard, dense sand and gravel, which provide excellent foundation conditions for large buildings and heavy structures along with a high-quality source of durable sand and gravel.

Pittsburgh’s Three Rivers Prior to the Pleistocene glaciation, which began approximately 800,000 to 1,000,000 years ago, the Pittsburgh River was the dominant river in southwestern Pennsylvania (Figure 13). It flowed north to the site of Pittsburgh in a channel approximately coincident with its present channel. From Pittsburgh, it followed the channel of the present Ohio River to Beaver, PA, where it turned north up the present Beaver River Valley and flowed north into the Erigan River or the former “Ancestral Erie Basin,” as shown on Figure 13 (Harper, 1997). The Monongahela River system drained about three fourths of the area in Pennsylvania that is presently drained by the combined Ohio, Monongahela, and Allegheny Rivers and their tributaries (Harper, 2002). The Ohio River was a tributary of the Monongahela. It originated south of Moundsville, WV, and flowed north, joining the Monongahela River just south of New Castle, PA. The Allegheny River was three separate rivers that drained different parts of Pennsylvania (Figure 13).

The “Lower Allegheny” originated in Elk, Forest, and Jefferson Counties, followed the course of the present Clarion River, and then flowed south to join the Monongahela River at what is now Pittsburgh. The “Middle Allegheny” started in Warren County and

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 12. Limit of glaciation in western Pennsylvania and present river systems (Harper, 1997).

Figure 12. Limit of glaciation in western Pennsylvania and present river systems (Harper, 1997).

followed a course through Oil City to Franklin, where it turned northwest along what is now French Creek and flowed across Crawford and Erie Counties into the Erigan River. The “Upper Allegheny” began in northern Pennsylvania and southern New York and flowed from Olean to Dunkirk, NY, into the Erigan River (Harper, 1997).

During the last ice age (Wisconsinan), there were four major advances and retreats of continental ice sheets in North America. At least three of these ice sheets, the pre-Illinoian, Illinoian, and Wisconsinan, extended into western Pennsylvania and disrupted drainage patterns, forming the present drainages (see 42

Figure 12). None of the continental glaciers reached Pittsburgh. The advancing ice sheets blocked the northwest-flowing streams, creating lakes within the existing drainage areas. As the ponded waters rose, they eventually crested and eroded notches in their drainage divides. The escaping waters formed new drainage channels that flowed southwestward, closely paralleling the front of the glaciers. The three Allegheny Rivers coalesced to form one, and the Ohio River became the major drainage system of western Pennsylvania, flowing south and then west along the boundary of the ice to the Mississippi River (Harper, 2002). The Allegheny and Ohio Rivers subsequently

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followed a course through Oil City to Franklin, where it turned northwest along what is now French Creek and flowed across Crawford and Erie Counties into the Erigan River. The “Upper Allegheny” began in northern Pennsylvania and southern New York and flowed from Olean to Dunkirk, NY, into the Erigan River (Harper, 1997).

During the last ice age (Wisconsinan), there were four major advances and retreats of continental ice sheets in North America. At least three of these ice sheets, the pre-Illinoian, Illinoian, and Wisconsinan, extended into western Pennsylvania and disrupted drainage patterns, forming the present drainages (see 42

Figure 12). None of the continental glaciers reached Pittsburgh. The advancing ice sheets blocked the northwest-flowing streams, creating lakes within the existing drainage areas. As the ponded waters rose, they eventually crested and eroded notches in their drainage divides. The escaping waters formed new drainage channels that flowed southwestward, closely paralleling the front of the glaciers. The three Allegheny Rivers coalesced to form one, and the Ohio River became the major drainage system of western Pennsylvania, flowing south and then west along the boundary of the ice to the Mississippi River (Harper, 2002). The Allegheny and Ohio Rivers subsequently

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 13. Western Pennsylvania stream patterns before glaciation (Harper, 1997).

Figure 13. Western Pennsylvania stream patterns before glaciation (Harper, 1997).

served as the major channels for the flow of glacial meltwaters.

The relatively flat hilltops in the Pittsburgh area are 500–600 ft (152–183 m) above river levels. In Tertiary time, downcutting of streams produced a system of broad valleys 350–400 ft (107–122 m) below the hilltops and 200 ft (61 m) above present river levels.

This pre-glacial erosional stage produced valley levels known as the Parker Strath (a Scottish word meaning a wide flat valley) (Heyman, 1970) (Figure 14).

During some pre-Illinoian glaciation, the ancestral Allegheny River was choked with glacial outwash, resulting in the ponding of tributary streams. The allu-

vium of the Monongahela and Youghiogheny River basins is known as the Carmichaels Formation. The Carmichaels Formation is a periglacial alluvial deposit found on multiple terraces generally south and east of Pittsburgh. The deposits typically contain clays, silts, and sands, with some deposit locations containing more cobbles and boulders generally from local sources. Some of the clays are high quality and were once a good source for the early pottery industry in the Pittsburgh area. Figure 14 presents idealized valley cross sections showing erosion levels and valley-fill deposits in Allegheny County. Following the Wisconsinan glaciation, active stream erosion cut down 250

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served as the major channels for the flow of glacial meltwaters.

The relatively flat hilltops in the Pittsburgh area are 500–600 ft (152–183 m) above river levels. In Tertiary time, downcutting of streams produced a system of broad valleys 350–400 ft (107–122 m) below the hilltops and 200 ft (61 m) above present river levels.

This pre-glacial erosional stage produced valley levels known as the Parker Strath (a Scottish word meaning a wide flat valley) (Heyman, 1970) (Figure 14).

During some pre-Illinoian glaciation, the ancestral Allegheny River was choked with glacial outwash, resulting in the ponding of tributary streams. The allu-

vium of the Monongahela and Youghiogheny River basins is known as the Carmichaels Formation. The Carmichaels Formation is a periglacial alluvial deposit found on multiple terraces generally south and east of Pittsburgh. The deposits typically contain clays, silts, and sands, with some deposit locations containing more cobbles and boulders generally from local sources. Some of the clays are high quality and were once a good source for the early pottery industry in the Pittsburgh area. Figure 14 presents idealized valley cross sections showing erosion levels and valley-fill deposits in Allegheny County. Following the Wisconsinan glaciation, active stream erosion cut down 250

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 14. Idealized valley cross section showing erosion levels and the position of valley-fill deposits in Allegheny County (Adamson et al., 1949).

Figure 14. Idealized valley cross section showing erosion levels and the position of valley-fill deposits in Allegheny County (Adamson et al., 1949).

ft (76 m) below the gravel-covered Parker Strath, excavating channels to a depth of 50 ft (15 m) or more below present stream levels (Figure 14). Figure 15 shows the development of the Allegheny and Monongahela River valleys in the last 1 million years.

In cutting new channels, the streams locally took completely new courses, leaving behind great channel loops and meander cut-offs, which cross and re-cross the present valleys high above present stream level. Today, these wide valleys do not contain major streams.

Abandoned channels and terraces occur along all the rivers and larger creeks in the Pittsburgh region that existed during the Pleistocene. Some of these abandoned channels and high-level terraces in the immediate vicinity of Pittsburgh are shown by Figure 16.

One major abandoned channel (1 mi [1.6 km] wide) leaves the Monongahela Valley between Braddock and Swissvale and extends through Swissvale, Wilkinsburg, East Liberty, and the Oakland section of Pittsburgh before rejoining the Monongahela River valley. Today, this abandoned channel is occupied by the Norfolk Southern Railroad main line and the east busway. Excavations anywhere in this valley reveal layers of silt and sand deposited by the “Old Monongahela.” Excavations for the University of Pittsburgh’s Cathedral

ft (76 m) below the gravel-covered Parker Strath, excavating channels to a depth of 50 ft (15 m) or more below present stream levels (Figure 14). Figure 15 shows the development of the Allegheny and Monongahela River valleys in the last 1 million years.

In cutting new channels, the streams locally took completely new courses, leaving behind great channel loops and meander cut-offs, which cross and re-cross the present valleys high above present stream level. Today, these wide valleys do not contain major streams.

Abandoned channels and terraces occur along all the rivers and larger creeks in the Pittsburgh region that existed during the Pleistocene. Some of these abandoned channels and high-level terraces in the immediate vicinity of Pittsburgh are shown by Figure 16.

One major abandoned channel (1 mi [1.6 km] wide) leaves the Monongahela Valley between Braddock and Swissvale and extends through Swissvale, Wilkinsburg, East Liberty, and the Oakland section of Pittsburgh before rejoining the Monongahela River valley. Today, this abandoned channel is occupied by the Norfolk Southern Railroad main line and the east busway. Excavations anywhere in this valley reveal layers of silt and sand deposited by the “Old Monongahela.” Excavations for the University of Pittsburgh’s Cathedral

44

of Learning (skyscraper) in this valley exposed up to 40 ft (12 m) of sand, gravel, and boulders, along with laminated plastic clay (Leighton, 1947).

As noted previously, the alluvium of the Allegheny and Ohio River valleys, in Allegheny County, consists largely of glacial outwash gravel and sand and is the primary source of groundwater in Allegheny County.

Pebbles of crystalline rock transported from as far north as Canada are found included with pebbles of resistant sandstone of local origin and some material from further north in these valley deposits. The finer material is likewise of both remote and local origin.

Most of the commercial gravel deposits in the vicinity of Pittsburgh will pass a 2 in. (5 cm) screen, but boulders are not uncommon. The material is well sorted in some places, but more commonly the grain size varies considerably. Figure 17 presents 12 large bulk grain size distribution curves for the glacial gravels from a deep excavation on the north side of the Ohio River in Pittsburgh. On average, gravel constitutes over 60 percent (by weight) of the glacial outwash.

The average maximum thickness of the valley alluvium is about 60 ft (18 m). Normally, glacial sand and gravel constitute the basal part of the alluvium,

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of Learning (skyscraper) in this valley exposed up to 40 ft (12 m) of sand, gravel, and boulders, along with laminated plastic clay (Leighton, 1947).

As noted previously, the alluvium of the Allegheny and Ohio River valleys, in Allegheny County, consists largely of glacial outwash gravel and sand and is the primary source of groundwater in Allegheny County.

Pebbles of crystalline rock transported from as far north as Canada are found included with pebbles of resistant sandstone of local origin and some material from further north in these valley deposits. The finer material is likewise of both remote and local origin.

Most of the commercial gravel deposits in the vicinity of Pittsburgh will pass a 2 in. (5 cm) screen, but boulders are not uncommon. The material is well sorted in some places, but more commonly the grain size varies considerably. Figure 17 presents 12 large bulk grain size distribution curves for the glacial gravels from a deep excavation on the north side of the Ohio River in Pittsburgh. On average, gravel constitutes over 60 percent (by weight) of the glacial outwash.

The average maximum thickness of the valley alluvium is about 60 ft (18 m). Normally, glacial sand and gravel constitute the basal part of the alluvium,

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 15. Development of Allegheny and Monongahela River valleys in the past 1 million years (Harper, 1997).

Figure 15. Development of Allegheny and Monongahela River valleys in the past 1 million years (Harper, 1997).

which is overlain by recent floodplain deposits ranging in thickness from 0 to 25 ft (0 to 7 m). In parts of the present stream bed, the topmost member of the alluvium is a layer of very fine silt, which to some extent is transitory and is probably scoured during floods and re-deposited as high-water stages decline. Characteristic sections across the Allegheny and Ohio River valleys are shown in Figure 18. Laterally, these alluvial deposits extend the width of the pre-Wisconsinan stream valleys, which are wider than the present streams. Generally, the bedrock floor of the valleys is relatively flat, except in a few areas along the upper Ohio River, where shallow channels were cut into the bedrock floor before the valley aggraded. In Allegheny County, the thickness of water-bearing sand and gravel remains fairly constant across the valleys; however, the sediments thin rapidly near the valley walls (Adamson et al., 1949). Figure 19 shows contours of the rock sur-

face below Pittsburgh’s downtown area, and the approximate eastern limit of water-bearing glacial gravel.

The old valley bedrock floor on the Allegheny River, which declines from an elevation of 682 ft (208 m) above sea level at Tarentum to 661.5 ft (201.6 m) immediately above the junction of the Allegheny and Monongahela Rivers (Pittsburgh’s Point), averages a gradient of 1 ft per mile (30 cm per kilometer). Continuing down the Ohio 13 mi (21 km) from the Point, the ancient valley floor is found at an elevation of 651 ft (198 m), and the average gradient is 0.8 ft per mile (20 cm per kilometer) in this distance. At no place in the Allegheny and Ohio valleys in the county has bedrock been recorded at a depth in excess of 85 ft (25 m) below the average river level.

Within Allegheny County, the maximum thickness of the Monongahela valley alluvium is 65 ft (20 m).

The Monongahela valley floor with a pre-Wisconsinan

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which is overlain by recent floodplain deposits ranging in thickness from 0 to 25 ft (0 to 7 m). In parts of the present stream bed, the topmost member of the alluvium is a layer of very fine silt, which to some extent is transitory and is probably scoured during floods and re-deposited as high-water stages decline. Characteristic sections across the Allegheny and Ohio River valleys are shown in Figure 18. Laterally, these alluvial deposits extend the width of the pre-Wisconsinan stream valleys, which are wider than the present streams. Generally, the bedrock floor of the valleys is relatively flat, except in a few areas along the upper Ohio River, where shallow channels were cut into the bedrock floor before the valley aggraded. In Allegheny County, the thickness of water-bearing sand and gravel remains fairly constant across the valleys; however, the sediments thin rapidly near the valley walls (Adamson et al., 1949). Figure 19 shows contours of the rock sur-

face below Pittsburgh’s downtown area, and the approximate eastern limit of water-bearing glacial gravel.

The old valley bedrock floor on the Allegheny River, which declines from an elevation of 682 ft (208 m) above sea level at Tarentum to 661.5 ft (201.6 m) immediately above the junction of the Allegheny and Monongahela Rivers (Pittsburgh’s Point), averages a gradient of 1 ft per mile (30 cm per kilometer). Continuing down the Ohio 13 mi (21 km) from the Point, the ancient valley floor is found at an elevation of 651 ft (198 m), and the average gradient is 0.8 ft per mile (20 cm per kilometer) in this distance. At no place in the Allegheny and Ohio valleys in the county has bedrock been recorded at a depth in excess of 85 ft (25 m) below the average river level.

Within Allegheny County, the maximum thickness of the Monongahela valley alluvium is 65 ft (20 m).

The Monongahela valley floor with a pre-Wisconsinan

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Gray, Greene, Fandray, and Turka

Figure 16. Abandoned channels and high-level terraces in immediate vicinity of Pittsburgh (Heyman, 1970).

age has a gradient of about 0.8 ft per mile (20 cm per km) from Elizabeth, PA, to the Point, which is a distance of about 23 mi (37 km) (Adamson et al., 1949).

NATURAL RESOURCES Salt, Oil, and Natural Gas Salt was an early high-value mineral and was much sought after on the frontier. It was expensive to haul over the mountains from the east coast, and therefore local sources were sought and established. It was originally obtained by boil-evaporating naturally occurring saline brine discharges in springs in the area. The process was simple; settlers would dig holes, and the holes would fill with brine, which was collected and kettleevaporated to obtain the crystalline salt residue. Later, wells were drilled for salt, which frequently tapped the sandstones in the Pottsville Group, which in turn became known as “salt sands.”

Crude oil was occasionally found in conjunction with the brine in the salt wells and was originally 46

considered a nuisance to be discarded. Samuel Kier (ExplorePAhistory, 2014, Kier Refinery Historical Marker), an American inventor and business man, operated salt wells on his family property located in Tarentum, to the northeast of Pittsburgh. He noticed that the crude oil in the salt wells was similar to what was being prescribed for homeopathic cures for various illnesses and began collecting and bottling the oil and selling it as a “cure-all.” In 1849, he opened a bottling and merchandising house in Pittsburgh, and his “Kiers Rock Oil” was sold throughout the northeastern United States (Figure 20). The oil was sold at the pricey rate of 50 cents (a day’s wages) for a half pint bottle, and the label read “Kiers petroleum or rock oil. Celebrated for its wonderful curative powers. A natural remedy. Procured from a well in Allegheny (County), Pa. Four hundred feet below the earth’s surface.” (Richardson, 1932, p. 55). He also began to experiment with the crude oil as an illuminant and sold the “carbon oil” from a warehouse in Pittsburgh. In order to capitalize on his discovery, he built the first commercial petroleum refinery in Pittsburgh in 1854 to produce illuminating oil from the crude oil he obtained from the family salt wells.

Kier was forced to move his refinery operation out of the city because of local residents’ fear of fire and explosions.

Once it was determined that the “rock oil” had a use, it was collected from the salt wells and from crude oil seeps. In those areas, pits were dug to collect the oil, which was removed and containerized for subsequent sale. Commercial oil production began in Pennsylvania with the drilling of the Drake Well in 1859 (see Figure 21). The well was drilled near Titusville, Venango County, PA, which is located about 100 mi (161 km) north of Pittsburgh, and this was the first internationally economic well drilled intentionally to produce commercially valuable crude oil (Carter and Flaherty, 2011). Oil exploration slowly moved south, and in 1886, the Mount Nebo Field was discovered in nearby Ohio Township, Allegheny County. The slow southward movement of oil recovery activity was due primarily to the increasing depths of the oil-bearing Venango sandstones. The Drake Well was drilled in an area of known oil seeps and had a final depth of about 69 ft (21 m). Oil-bearing Venango sandstones were targeted in that area and were generally deeper, with depths ranging from 300 to 700 ft (91 to 213 m) deep. Similar strata in the Pittsburgh area are at depths between 1,200 and 2,800 ft (366 and 853 m). Such depths required the development of new exploratory and developmental drilling equipment and techniques.

Between 1886 and 1904, almost all of the shallow oil fields in Allegheny County had been found and exploited, and the local oil industry started to decline.

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Gray, Greene, Fandray, and Turka

Figure 16. Abandoned channels and high-level terraces in immediate vicinity of Pittsburgh (Heyman, 1970).

age has a gradient of about 0.8 ft per mile (20 cm per km) from Elizabeth, PA, to the Point, which is a distance of about 23 mi (37 km) (Adamson et al., 1949).

NATURAL RESOURCES Salt, Oil, and Natural Gas Salt was an early high-value mineral and was much sought after on the frontier. It was expensive to haul over the mountains from the east coast, and therefore local sources were sought and established. It was originally obtained by boil-evaporating naturally occurring saline brine discharges in springs in the area. The process was simple; settlers would dig holes, and the holes would fill with brine, which was collected and kettleevaporated to obtain the crystalline salt residue. Later, wells were drilled for salt, which frequently tapped the sandstones in the Pottsville Group, which in turn became known as “salt sands.”

Crude oil was occasionally found in conjunction with the brine in the salt wells and was originally 46

considered a nuisance to be discarded. Samuel Kier (ExplorePAhistory, 2014, Kier Refinery Historical Marker), an American inventor and business man, operated salt wells on his family property located in Tarentum, to the northeast of Pittsburgh. He noticed that the crude oil in the salt wells was similar to what was being prescribed for homeopathic cures for various illnesses and began collecting and bottling the oil and selling it as a “cure-all.” In 1849, he opened a bottling and merchandising house in Pittsburgh, and his “Kiers Rock Oil” was sold throughout the northeastern United States (Figure 20). The oil was sold at the pricey rate of 50 cents (a day’s wages) for a half pint bottle, and the label read “Kiers petroleum or rock oil. Celebrated for its wonderful curative powers. A natural remedy. Procured from a well in Allegheny (County), Pa. Four hundred feet below the earth’s surface.” (Richardson, 1932, p. 55). He also began to experiment with the crude oil as an illuminant and sold the “carbon oil” from a warehouse in Pittsburgh. In order to capitalize on his discovery, he built the first commercial petroleum refinery in Pittsburgh in 1854 to produce illuminating oil from the crude oil he obtained from the family salt wells.

Kier was forced to move his refinery operation out of the city because of local residents’ fear of fire and explosions.

Once it was determined that the “rock oil” had a use, it was collected from the salt wells and from crude oil seeps. In those areas, pits were dug to collect the oil, which was removed and containerized for subsequent sale. Commercial oil production began in Pennsylvania with the drilling of the Drake Well in 1859 (see Figure 21). The well was drilled near Titusville, Venango County, PA, which is located about 100 mi (161 km) north of Pittsburgh, and this was the first internationally economic well drilled intentionally to produce commercially valuable crude oil (Carter and Flaherty, 2011). Oil exploration slowly moved south, and in 1886, the Mount Nebo Field was discovered in nearby Ohio Township, Allegheny County. The slow southward movement of oil recovery activity was due primarily to the increasing depths of the oil-bearing Venango sandstones. The Drake Well was drilled in an area of known oil seeps and had a final depth of about 69 ft (21 m). Oil-bearing Venango sandstones were targeted in that area and were generally deeper, with depths ranging from 300 to 700 ft (91 to 213 m) deep. Similar strata in the Pittsburgh area are at depths between 1,200 and 2,800 ft (366 and 853 m). Such depths required the development of new exploratory and developmental drilling equipment and techniques.

Between 1886 and 1904, almost all of the shallow oil fields in Allegheny County had been found and exploited, and the local oil industry started to decline.

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 17. Twelve large bulk grain-size distributions for glacial gravels (DiGioia, Gray & Associates, 2007).

Figure 17. Twelve large bulk grain-size distributions for glacial gravels (DiGioia, Gray & Associates, 2007).

Pittsburgh profited by more than just the oil from the wells, because it was the largest industrialized city near the new oil fields. By the 1870s, there were more than 50 oil refineries operating in the area, with a total production of more than 35,000 barrels of oil per day (Gardner, 1980).

The nation’s first commercial gas well, the Haymaker well in Murrysville, PA, about 20 mi (32 km) east of Pittsburgh, was drilled in 1878. Gas from that well was piped into Pittsburgh in 1883, which

was at the technical limit of such pipelines for that time.

Figure 22 is a map showing the oil and gas fields of Pennsylvania (McCoy and Schmitt, 2007). Limited amounts of gas and oil from “shallow” Mississippian and Devonian sandstones are still produced in the area from some of the early wells. Several of the depleted gas and oil fields in the area are now utilized as gas storage fields by some of the regional gas companies.

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Pittsburgh profited by more than just the oil from the wells, because it was the largest industrialized city near the new oil fields. By the 1870s, there were more than 50 oil refineries operating in the area, with a total production of more than 35,000 barrels of oil per day (Gardner, 1980).

The nation’s first commercial gas well, the Haymaker well in Murrysville, PA, about 20 mi (32 km) east of Pittsburgh, was drilled in 1878. Gas from that well was piped into Pittsburgh in 1883, which

was at the technical limit of such pipelines for that time.

Figure 22 is a map showing the oil and gas fields of Pennsylvania (McCoy and Schmitt, 2007). Limited amounts of gas and oil from “shallow” Mississippian and Devonian sandstones are still produced in the area from some of the early wells. Several of the depleted gas and oil fields in the area are now utilized as gas storage fields by some of the regional gas companies.

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 18. Sections across Allegheny and Ohio River valleys (Adamson et al., 1949).

Figure 18. Sections across Allegheny and Ohio River valleys (Adamson et al., 1949).

In recent years, the industry has seen a rebirth with the development of natural gas with the Middle Devonian Marcellus Shale, which is at a depth of around 6,000 ft (1.8 km) in the Pittsburgh area. Much news attention is given to the Marcellus Shale, because it is thought to contain about 50 trillion cubic feet (1.4 trillion cubic meters) of natural gas and is recovered using fracking techniques, which are being widely debated in regard to possible environmental impacts associated with development. Another identified natural gas source in the area is the Upper Ordovician Utica Shale, which underlies the Marcellus Shale and has a correspondingly larger lateral extent. The Utica Shale in the Pittsburgh area lies at a depth of about 10,000– 12,000 ft (3–3.6 km). It is estimated to contain about 38 trillion cubic feet (1.07 trillion cubic meters) of yetundiscovered, technically recoverable natural gas (at the mean estimate), according to the first assessment of this continuous (unconventional) natural gas accumulation by the U.S. Geological Survey (Schenk et al., 2012). The Utica Shale has a corresponding mean es48

timate of 940 million barrels of unconventional oil resources and a mean estimate of 208 million barrels of unconventional natural gas liquids. The Marcellus and Utica Shales are the current big plays in western Pennsylvania, but other shale formations are also being developed. Some of these other Upper Devonian formations include the Burket-Geneseo, Middlesex, Pipe Creek, and Rhinestreet Shales. This group of Upper Devonian shales could have substantial potential for western Pennsylvania.

Coal Pennsylvania is located at the northern end of the Appalachian Coal Basin. Coal beds underlie about 15,000 mi2 (38,850 km2 ) of the state (see Figure 23).

All significant coal beds in Pennsylvania are Pennsylvanian or Permian in age. Prior to any mining, Pennsylvania contained over 75 billion tons of bituminous coal and almost 23 billion tons of anthracite and semianthracite coal (Edmunds, 2002).

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In recent years, the industry has seen a rebirth with the development of natural gas with the Middle Devonian Marcellus Shale, which is at a depth of around 6,000 ft (1.8 km) in the Pittsburgh area. Much news attention is given to the Marcellus Shale, because it is thought to contain about 50 trillion cubic feet (1.4 trillion cubic meters) of natural gas and is recovered using fracking techniques, which are being widely debated in regard to possible environmental impacts associated with development. Another identified natural gas source in the area is the Upper Ordovician Utica Shale, which underlies the Marcellus Shale and has a correspondingly larger lateral extent. The Utica Shale in the Pittsburgh area lies at a depth of about 10,000– 12,000 ft (3–3.6 km). It is estimated to contain about 38 trillion cubic feet (1.07 trillion cubic meters) of yetundiscovered, technically recoverable natural gas (at the mean estimate), according to the first assessment of this continuous (unconventional) natural gas accumulation by the U.S. Geological Survey (Schenk et al., 2012). The Utica Shale has a corresponding mean es48

timate of 940 million barrels of unconventional oil resources and a mean estimate of 208 million barrels of unconventional natural gas liquids. The Marcellus and Utica Shales are the current big plays in western Pennsylvania, but other shale formations are also being developed. Some of these other Upper Devonian formations include the Burket-Geneseo, Middlesex, Pipe Creek, and Rhinestreet Shales. This group of Upper Devonian shales could have substantial potential for western Pennsylvania.

Coal Pennsylvania is located at the northern end of the Appalachian Coal Basin. Coal beds underlie about 15,000 mi2 (38,850 km2 ) of the state (see Figure 23).

All significant coal beds in Pennsylvania are Pennsylvanian or Permian in age. Prior to any mining, Pennsylvania contained over 75 billion tons of bituminous coal and almost 23 billion tons of anthracite and semianthracite coal (Edmunds, 2002).

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 19. Contours of the rock surface below downtown Pittsburgh and the eastern limit of water-bearing glacial gravel (Van Tuyl, 1951).

Figure 19. Contours of the rock surface below downtown Pittsburgh and the eastern limit of water-bearing glacial gravel (Van Tuyl, 1951).

Early Coal Mining Coal was first mined commercially in the United States in 1745 near Richmond, VA. In 1760, British soldiers started mining the Pittsburgh Coal seam on Coal Hill (now Mount Washington) across the Monongahela River from Fort Pitt (Figure 3). By 1800, only Pittsburgh and Richmond, VA, were using coal to any extent for domestic purposes. In early 1807, a Mr. Cuming, traveling from Philadelphia to Pittsburgh, upon reaching Greensburg, PA, wrote:

Early Coal Mining

“On entering Habach’s tavern, I was no little surprised to see a fine coal fire, and I was informed that coal is the principal fuel of the country, fifty or sixty miles ‘round Pittsburgh’. It is laid down at the doors here for six cents a bushel.” (Eavenson, 1939, p. 39)

In Pittsburgh, 10 collieries (e.g., a coal mine with connected coal-processing structures) were working in Coal Hill in 1837 (Eavenson, 1939). By 1865, coke produced from coal was increasingly important in iron processing (Gregory, 1980). There are few reports on

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49

Coal was first mined commercially in the United States in 1745 near Richmond, VA. In 1760, British soldiers started mining the Pittsburgh Coal seam on Coal Hill (now Mount Washington) across the Monongahela River from Fort Pitt (Figure 3). By 1800, only Pittsburgh and Richmond, VA, were using coal to any extent for domestic purposes. In early 1807, a Mr. Cuming, traveling from Philadelphia to Pittsburgh, upon reaching Greensburg, PA, wrote:

“On entering Habach’s tavern, I was no little surprised to see a fine coal fire, and I was informed that coal is the principal fuel of the country, fifty or sixty miles ‘round Pittsburgh’. It is laid down at the doors here for six cents a bushel.” (Eavenson, 1939, p. 39)

In Pittsburgh, 10 collieries (e.g., a coal mine with connected coal-processing structures) were working in Coal Hill in 1837 (Eavenson, 1939). By 1865, coke produced from coal was increasingly important in iron processing (Gregory, 1980). There are few reports on

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Gray, Greene, Fandray, and Turka

Figure 20. Kier’s rock oil advertising poster (Flaherty and Flaherty, 2014).

coal and coke production before 1870 and no accurate records until 1885 (Eavenson, 1942).

Mining Methods Room-and-pillar mining originated as a method of extracting as much coal as possible while still providing roof control by means of coal pillars. During the 18th

Figure 21. Replica of Drake Well, Titusville, PA (Flaherty and Flaherty, 2014).

50

and 19th centuries, mines were small, hand-excavated operations under shallow cover using hillside adits to enter the coal seam. Coal was cheap, and the spacing, size, and regularity of pillars were somewhat arbitrary (Figure 24). Coal pillars were left in place as a matter of convenience and safety to the miners. Increased production by the mid- to late 19th century brought mechanization and ventilation requirements to mines that necessitated a systematic arrangement of pillars, but it still resulted in considerable coal being left underground. Mining often extended to where the overburden was only 25 ft (7.6 m) thick. Early extraction ratios, i.e., the proportion of coal removed, averaged 30 to 40 percent. Since coal deposits were widespread and accessible, little effort was made to improve extraction ratios.

In the latter part of the 19th century, totalextraction mining was initiated to achieve greater production of the coal, which was becoming increasingly valued for its coking properties by the steel industry and as the preferred feedstock for manufactured gas plants. Total-extraction mining was first implemented in existing partial-extraction mines of the day.

The distinction from partial-extraction mines was that the long, narrow pillars left between rooms during the initial mining were now being extracted in a second stage of mining. Subsidence of the ground surface in a properly executed operation took place contemporaneously with pillar extraction (Gray and Bruhn, 1984).

Wide rooms and narrow pillars (10–15 ft [3–4.5 m] wide) continued in total-extraction mines because it was believed that more lump coal could be produced by room mining than by extracting the pillars left between rooms. However, by the 1920s, block systems of mining came into favor (see Figure 25), wherein square or rectangular pillars 50–100 ft (15–30 m) on a side were separated by narrow rooms and entries, reducing roof deterioration, roof falls, and support problems during pillar extraction (Paul and Plein, 1935).

From 1948 to 1952, most remaining mines of the old pattern were converted to the block system as continuous mining machines were introduced on a large scale.

Subsequently, as break lines controlling failure of the mine roof parallel to the pillar faces replaced angled break lines, the transition to the relatively efficient pillar extraction methods of today was essentially complete (Gray and Bruhn, 1984).

Longwall mining is another total-extraction technique. Entries for access and ventilation are very similar to those for room-and-pillar mining. The extraction face of a mine panel is equipped with a row of hydraulic roof supports, a coal conveyor, and a machine to break the coal from the panel face. The system (see Figure 26) is designed to support only the area at the

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Gray, Greene, Fandray, and Turka

Figure 20. Kier’s rock oil advertising poster (Flaherty and Flaherty, 2014).

coal and coke production before 1870 and no accurate records until 1885 (Eavenson, 1942).

Mining Methods Room-and-pillar mining originated as a method of extracting as much coal as possible while still providing roof control by means of coal pillars. During the 18th

Figure 21. Replica of Drake Well, Titusville, PA (Flaherty and Flaherty, 2014).

50

and 19th centuries, mines were small, hand-excavated operations under shallow cover using hillside adits to enter the coal seam. Coal was cheap, and the spacing, size, and regularity of pillars were somewhat arbitrary (Figure 24). Coal pillars were left in place as a matter of convenience and safety to the miners. Increased production by the mid- to late 19th century brought mechanization and ventilation requirements to mines that necessitated a systematic arrangement of pillars, but it still resulted in considerable coal being left underground. Mining often extended to where the overburden was only 25 ft (7.6 m) thick. Early extraction ratios, i.e., the proportion of coal removed, averaged 30 to 40 percent. Since coal deposits were widespread and accessible, little effort was made to improve extraction ratios.

In the latter part of the 19th century, totalextraction mining was initiated to achieve greater production of the coal, which was becoming increasingly valued for its coking properties by the steel industry and as the preferred feedstock for manufactured gas plants. Total-extraction mining was first implemented in existing partial-extraction mines of the day.

The distinction from partial-extraction mines was that the long, narrow pillars left between rooms during the initial mining were now being extracted in a second stage of mining. Subsidence of the ground surface in a properly executed operation took place contemporaneously with pillar extraction (Gray and Bruhn, 1984).

Wide rooms and narrow pillars (10–15 ft [3–4.5 m] wide) continued in total-extraction mines because it was believed that more lump coal could be produced by room mining than by extracting the pillars left between rooms. However, by the 1920s, block systems of mining came into favor (see Figure 25), wherein square or rectangular pillars 50–100 ft (15–30 m) on a side were separated by narrow rooms and entries, reducing roof deterioration, roof falls, and support problems during pillar extraction (Paul and Plein, 1935).

From 1948 to 1952, most remaining mines of the old pattern were converted to the block system as continuous mining machines were introduced on a large scale.

Subsequently, as break lines controlling failure of the mine roof parallel to the pillar faces replaced angled break lines, the transition to the relatively efficient pillar extraction methods of today was essentially complete (Gray and Bruhn, 1984).

Longwall mining is another total-extraction technique. Entries for access and ventilation are very similar to those for room-and-pillar mining. The extraction face of a mine panel is equipped with a row of hydraulic roof supports, a coal conveyor, and a machine to break the coal from the panel face. The system (see Figure 26) is designed to support only the area at the

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 22. Oil and gas fields near Pittsburgh (Flaherty and Flaherty, 2014).

Figure 22. Oil and gas fields near Pittsburgh (Flaherty and Flaherty, 2014).

coal panel face and allow caving of the mine roof behind the support system, with the roof support system and conveyor automatically advanced as mining proceeds. Coal pillars supporting the entries are generally not recoverable (Gray and Bruhn, 1984). In longwall mining, the width of mined panels can exceed 1,200 ft (366 m), and the length of the panels can be 1 mi (1.6 km) or more. The advantage is that it is a one-stage operation. It was tried in the United States prior to 1900, but it was not found to be economical here until 1960, after development of self-advancing roof supports (Poad, 1977).

Virtually all of the economically minable bituminous coal resources of Pennsylvania are confined to 10 important coal beds in the Allegheny, Monongahela, and Dunkard Groups.

The Pittsburgh Coal is the most important seam in Pennsylvania. In 2010, 16 longwalls (41 percent of

the U.S. total) under operation in the Pittsburgh Coal, including seven in Pennsylvania and 12 in West Virginia (Fiscor, 2011). In spite of extensive mining, it still represents one third of the recoverable reserves over 36 in. (1 m) thick and almost all of the reserves over 60 in. (1.5 m) thick. Most of the remaining Pittsburgh Coal is in Washington and Greene Counties south of Pittsburgh. It is a single, very persistent bed, generally between 4 and 10 ft (1.2 and 3 m) thick, and it is absent only in relatively limited areas (McCulloch et al., 1975; Socolow et al., 1980). The Pittsburgh Coal is of excellent quality overall and has been widely used for metallurgical-grade coke. Except in northwestern Washington County and eastern Greene County, its sulfur content is less than 2 percent (Socolow et al., 1980). Almost all production of the Pittsburgh Coal, past and present, is from underground mines.

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coal panel face and allow caving of the mine roof behind the support system, with the roof support system and conveyor automatically advanced as mining proceeds. Coal pillars supporting the entries are generally not recoverable (Gray and Bruhn, 1984). In longwall mining, the width of mined panels can exceed 1,200 ft (366 m), and the length of the panels can be 1 mi (1.6 km) or more. The advantage is that it is a one-stage operation. It was tried in the United States prior to 1900, but it was not found to be economical here until 1960, after development of self-advancing roof supports (Poad, 1977).

Virtually all of the economically minable bituminous coal resources of Pennsylvania are confined to 10 important coal beds in the Allegheny, Monongahela, and Dunkard Groups.

The Pittsburgh Coal is the most important seam in Pennsylvania. In 2010, 16 longwalls (41 percent of

the U.S. total) under operation in the Pittsburgh Coal, including seven in Pennsylvania and 12 in West Virginia (Fiscor, 2011). In spite of extensive mining, it still represents one third of the recoverable reserves over 36 in. (1 m) thick and almost all of the reserves over 60 in. (1.5 m) thick. Most of the remaining Pittsburgh Coal is in Washington and Greene Counties south of Pittsburgh. It is a single, very persistent bed, generally between 4 and 10 ft (1.2 and 3 m) thick, and it is absent only in relatively limited areas (McCulloch et al., 1975; Socolow et al., 1980). The Pittsburgh Coal is of excellent quality overall and has been widely used for metallurgical-grade coke. Except in northwestern Washington County and eastern Greene County, its sulfur content is less than 2 percent (Socolow et al., 1980). Almost all production of the Pittsburgh Coal, past and present, is from underground mines.

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 23. Distribution of Pennsylvania coals (Pennsylvania Department of Conservation and Natural Resources, 2000).

Figure 23. Distribution of Pennsylvania coals (Pennsylvania Department of Conservation and Natural Resources, 2000).

In the Pittsburgh area, the Upper Freeport Coal is the second most important bed in terms of mining and reserves (see Figure 10).

Pennsylvania bituminous coal (41,303 short tons in 20015) is mined for three markets: electric power generation, industrial use, and foreign export. The domestic distribution varies, but in 2015, electric utilities consumed 93 percent, and industrial use, including coke, consumed 6 percent. Foreign exports were approximately 7,298 short tons (U.S. Energy Information Administration, 2015).

Aggregates Major sources of construction aggregates in the Pittsburgh area are sand and gravel, crushed stone, and repurposed steel mill slag (O’Neil, 1974). Sand and gravel are primarily glacially derived material, while 52

the crushed stone is manufactured from local limestones and sandstones, and slag is a man-made byproduct resulting from iron and steel production.

As noted earlier, multiple periods of continental glaciation occurred to the north of Pennsylvania and into northwestern Pennsylvania. Much of the material deposited by the glaciers is located in the northern portion of the state, along the borders of the ice advance or behind them as surficial features (moraines, eskers, kames, etc.). However, with the melting of the glaciers, larger amounts of sand and gravel were transported to the south by the meltwater and were deposited in the valleys of the Allegheny, Ohio, and Beaver Rivers and their tributaries. The repetitive advance and retreat of the ice sheets resulted in multiple periods of sand and gravel deposition in the river valleys. During periods of significant deposition, the river valleys would fill with outwash deposits and aggrade. During the periods

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In the Pittsburgh area, the Upper Freeport Coal is the second most important bed in terms of mining and reserves (see Figure 10).

Pennsylvania bituminous coal (41,303 short tons in 20015) is mined for three markets: electric power generation, industrial use, and foreign export. The domestic distribution varies, but in 2015, electric utilities consumed 93 percent, and industrial use, including coke, consumed 6 percent. Foreign exports were approximately 7,298 short tons (U.S. Energy Information Administration, 2015).

Aggregates Major sources of construction aggregates in the Pittsburgh area are sand and gravel, crushed stone, and repurposed steel mill slag (O’Neil, 1974). Sand and gravel are primarily glacially derived material, while 52

the crushed stone is manufactured from local limestones and sandstones, and slag is a man-made byproduct resulting from iron and steel production.

As noted earlier, multiple periods of continental glaciation occurred to the north of Pennsylvania and into northwestern Pennsylvania. Much of the material deposited by the glaciers is located in the northern portion of the state, along the borders of the ice advance or behind them as surficial features (moraines, eskers, kames, etc.). However, with the melting of the glaciers, larger amounts of sand and gravel were transported to the south by the meltwater and were deposited in the valleys of the Allegheny, Ohio, and Beaver Rivers and their tributaries. The repetitive advance and retreat of the ice sheets resulted in multiple periods of sand and gravel deposition in the river valleys. During periods of significant deposition, the river valleys would fill with outwash deposits and aggrade. During the periods

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Geology of Pittsburgh

Figure 24. Old room-and-pillar mine (Gray and Meyers, 1970).

between the deposition events, the rivers would down cut, leaving behind outwash terraces along the banks of the rivers and in the surrounding upland areas. By the end of continental glaciation, the outwash deposits had been reworked numerous times by the glacial meltwaters, which had cleaned and sorted the sands and gravels and also tended to break down the softer materials, leaving hard, sound fragments. The end result is that significant deposits of sand and gravel can be found within the riverbeds, their floodplains, and the higher river terraces.

Original bodies of pre-Illinoian-age glacial outwash sand and gravel deposits were estimated to have exceeded 120 ft (37 m) in places and were generally found to be 90 ft (27 m) thick or less. Many of the gravels derived from less resistant rocks tend to be weathered, owing to the older age of the deposits, but the sand generally remains hard, being derived primarily from quartz-rich crystalline source rocks. The younger Wisconsinan-age sands and gravels were estimated to have been at least 150 ft (45 m) thick in places, but they are generally found to be somewhat thinner, with measured sections generally about 70–80 ft (21–24 m) thick or less. The gravel in these deposits is relatively unweathered, so the deposits tend to be excellent sources of high-quality sand and gravel.

Geology of Pittsburgh

Limestone is the primary source for crushed stone aggregate in the Pittsburgh region, followed by sandstone, which in the 1970s accounted for less than 10 percent of the overall crushed stone market (O’Neil, 1974). The most important sources of limestone in the area are the Loyalhanna and Vanport Limestones. The Loyalhanna Limestone is Mississippian in age and is a massive fine-grained siliceous carbonate composed of quartz grains in a limestone matrix. The bed varies from 40 to 70 ft (12 to 21 m) thick and is considered a good-quality coarse aggregate. Nearby occurrences are in the ridges to the east of Pittsburgh; however, the currently operating quarries are 50 mi (80 km) or more from Pittsburgh (Barnes, 2011), somewhat limiting the marketability of the stone because of the associated transportation costs. Uses today include coarse aggregate for concrete, base and sub-base roadway material, roadway surface treatment, riprap, and railroad ballast. An important past use of the Loyalhanna Limestone was in the old Belgium block streetpaving industry. These blocks were used in the 1800s and early 1900s on many inclined streets of Pittsburgh and surrounding areas, in higher-volume traffic areas, and in the more wealthy areas as an upgrade to wood and cobblestone. Few of these surface roads remain, but some persist as sub-base to today’s asphalt road surfaces.

The Vanport Limestone, which is located in the Pennsylvanian-age Allegheny Group, is generally a massive, dense, fossiliferous, marine limestone. The thickness of the Vanport unit is quite variable. It is generally on the order of 15–20 ft (4.5–6 m) thick, but it has been found to be absent in some areas. The greatest measured bed thickness ranges from 40 to 45 ft (12 to 14 m). It is not an exceptionally high-grade stone. It is used as flux for iron and steel production, for cement and agricultural limestone, and for flue-gas scrubbing lime, as well as for coarse aggregate. The Vanport Limestone is not used for highway surface treatment because it polishes with traffic wear and develops a high skid characteristic (i.e., it becomes slick).

Although there are significant reserves in the counties to the north of Pittsburgh, the operating quarries are 35 mi (56 km) or more (Barnes, 2011) from the city, resulting in transportation costs that limit its marketability.

Slag piles are concentrated in Pittsburgh and surrounding areas generally close to the historic and existing iron and steel mill facilities. In the region, there are two types of slag: (1) slag from open hearth, basic oxygen, and electric furnaces used in steel production, and (2) blast furnace slag from the production of iron. The steel-making operations produce one basic type of slag, but the blast furnace slag can be any of three different, but basically chemically

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53

Figure 24. Old room-and-pillar mine (Gray and Meyers, 1970).

between the deposition events, the rivers would down cut, leaving behind outwash terraces along the banks of the rivers and in the surrounding upland areas. By the end of continental glaciation, the outwash deposits had been reworked numerous times by the glacial meltwaters, which had cleaned and sorted the sands and gravels and also tended to break down the softer materials, leaving hard, sound fragments. The end result is that significant deposits of sand and gravel can be found within the riverbeds, their floodplains, and the higher river terraces.

Original bodies of pre-Illinoian-age glacial outwash sand and gravel deposits were estimated to have exceeded 120 ft (37 m) in places and were generally found to be 90 ft (27 m) thick or less. Many of the gravels derived from less resistant rocks tend to be weathered, owing to the older age of the deposits, but the sand generally remains hard, being derived primarily from quartz-rich crystalline source rocks. The younger Wisconsinan-age sands and gravels were estimated to have been at least 150 ft (45 m) thick in places, but they are generally found to be somewhat thinner, with measured sections generally about 70–80 ft (21–24 m) thick or less. The gravel in these deposits is relatively unweathered, so the deposits tend to be excellent sources of high-quality sand and gravel.

Limestone is the primary source for crushed stone aggregate in the Pittsburgh region, followed by sandstone, which in the 1970s accounted for less than 10 percent of the overall crushed stone market (O’Neil, 1974). The most important sources of limestone in the area are the Loyalhanna and Vanport Limestones. The Loyalhanna Limestone is Mississippian in age and is a massive fine-grained siliceous carbonate composed of quartz grains in a limestone matrix. The bed varies from 40 to 70 ft (12 to 21 m) thick and is considered a good-quality coarse aggregate. Nearby occurrences are in the ridges to the east of Pittsburgh; however, the currently operating quarries are 50 mi (80 km) or more from Pittsburgh (Barnes, 2011), somewhat limiting the marketability of the stone because of the associated transportation costs. Uses today include coarse aggregate for concrete, base and sub-base roadway material, roadway surface treatment, riprap, and railroad ballast. An important past use of the Loyalhanna Limestone was in the old Belgium block streetpaving industry. These blocks were used in the 1800s and early 1900s on many inclined streets of Pittsburgh and surrounding areas, in higher-volume traffic areas, and in the more wealthy areas as an upgrade to wood and cobblestone. Few of these surface roads remain, but some persist as sub-base to today’s asphalt road surfaces.

The Vanport Limestone, which is located in the Pennsylvanian-age Allegheny Group, is generally a massive, dense, fossiliferous, marine limestone. The thickness of the Vanport unit is quite variable. It is generally on the order of 15–20 ft (4.5–6 m) thick, but it has been found to be absent in some areas. The greatest measured bed thickness ranges from 40 to 45 ft (12 to 14 m). It is not an exceptionally high-grade stone. It is used as flux for iron and steel production, for cement and agricultural limestone, and for flue-gas scrubbing lime, as well as for coarse aggregate. The Vanport Limestone is not used for highway surface treatment because it polishes with traffic wear and develops a high skid characteristic (i.e., it becomes slick).

Although there are significant reserves in the counties to the north of Pittsburgh, the operating quarries are 35 mi (56 km) or more (Barnes, 2011) from the city, resulting in transportation costs that limit its marketability.

Slag piles are concentrated in Pittsburgh and surrounding areas generally close to the historic and existing iron and steel mill facilities. In the region, there are two types of slag: (1) slag from open hearth, basic oxygen, and electric furnaces used in steel production, and (2) blast furnace slag from the production of iron. The steel-making operations produce one basic type of slag, but the blast furnace slag can be any of three different, but basically chemically

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 25. Example of room-and-pillar mining (Gray et al., 1974).

Figure 25. Example of room-and-pillar mining (Gray et al., 1974).

identical materials, depending on how the hot slag was when tipped and cooled: (1) air-cooled slag, which is cooled naturally and is crushed and screened to produce a coarse aggregate that is used in concrete and road base; (2) granulated slag, which is formed when slag is quickly quenched in water, creating a glassy, sand-sized granular product that is used in many applications for which sand is used, and for agricultural liming; and (3) lightweight or expanded slag, which is created by the controlled processing of molten slag with water, forming a lightweight material with a bulk relative density of about 70 percent that of aircooled slag (FHA, 2012). Open hearth slag is used primarily as railroad ballast and has been used in the past as a base or sub-base material in highway construction. Open hearth slag and other slag from steelmaking furnaces can be expansive when exposed to 54

water and should not be used in confined areas without laboratory confirmation testing. More detailed information is provided in the section on expansive slags.

There are other potential but minor aggregate sources in the area, including other limestones, a number of sandstone units, sintered fly ash, and expanded clays and shales.

Glass Pittsburgh was once recognized as the center of glassmaking. The first two glass factories west of the Appalachian Mountains were opened in 1797 in the Pittsburgh area (Fleming, 1922). Both made window glass and bottles. The success of these glassmaking facilities encouraged development of additional

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identical materials, depending on how the hot slag was when tipped and cooled: (1) air-cooled slag, which is cooled naturally and is crushed and screened to produce a coarse aggregate that is used in concrete and road base; (2) granulated slag, which is formed when slag is quickly quenched in water, creating a glassy, sand-sized granular product that is used in many applications for which sand is used, and for agricultural liming; and (3) lightweight or expanded slag, which is created by the controlled processing of molten slag with water, forming a lightweight material with a bulk relative density of about 70 percent that of aircooled slag (FHA, 2012). Open hearth slag is used primarily as railroad ballast and has been used in the past as a base or sub-base material in highway construction. Open hearth slag and other slag from steelmaking furnaces can be expansive when exposed to 54

water and should not be used in confined areas without laboratory confirmation testing. More detailed information is provided in the section on expansive slags.

There are other potential but minor aggregate sources in the area, including other limestones, a number of sandstone units, sintered fly ash, and expanded clays and shales.

Glass Pittsburgh was once recognized as the center of glassmaking. The first two glass factories west of the Appalachian Mountains were opened in 1797 in the Pittsburgh area (Fleming, 1922). Both made window glass and bottles. The success of these glassmaking facilities encouraged development of additional

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 26. Longwall mine (Turka and Gray, 2005).

Figure 26. Longwall mine (Turka and Gray, 2005).

glassmaking facilities in and around Pittsburgh. Some specialized in particular glassmaking areas, while others continued with more residential commodities. An embargo in the early 1800s and the War of 1812 prevented foreign glass from entering the United States, thus catapulting domestic glass manufacturing to fill the demand (Flannery, 2009). By the Civil War, the Pittsburgh region reigned as the center of the nation’s glass industry.

The reason for the regions’ glassmaking success was the abundance of coal for the furnaces, facility space, nearby raw materials, available crafters of the products, and the ability to transport the materials along the rivers (Fleming, 1922). The main raw materials

used to make glass are quartz sand or silica, potash (or soda) as a flux, and lime as a stabilizer (Fleming, 1922).

The sand initially came from sand bars and longitudinal bars from the nearby major rivers and later from the larger tributaries of the region. Potash was generally obtained from the ashes left after wood burning or other plant material, which was an abundant waste product in the Pittsburgh area at that time. Soda was crushed carbonate material from nearby rock formations in the Pittsburgh area, as well as the lime from nearby limestone quarries.

The successful run of glassmaking in Pittsburgh ended by the 1920s, when most of the glass factories had moved from the region due to high taxation,

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glassmaking facilities in and around Pittsburgh. Some specialized in particular glassmaking areas, while others continued with more residential commodities. An embargo in the early 1800s and the War of 1812 prevented foreign glass from entering the United States, thus catapulting domestic glass manufacturing to fill the demand (Flannery, 2009). By the Civil War, the Pittsburgh region reigned as the center of the nation’s glass industry.

The reason for the regions’ glassmaking success was the abundance of coal for the furnaces, facility space, nearby raw materials, available crafters of the products, and the ability to transport the materials along the rivers (Fleming, 1922). The main raw materials

used to make glass are quartz sand or silica, potash (or soda) as a flux, and lime as a stabilizer (Fleming, 1922).

The sand initially came from sand bars and longitudinal bars from the nearby major rivers and later from the larger tributaries of the region. Potash was generally obtained from the ashes left after wood burning or other plant material, which was an abundant waste product in the Pittsburgh area at that time. Soda was crushed carbonate material from nearby rock formations in the Pittsburgh area, as well as the lime from nearby limestone quarries.

The successful run of glassmaking in Pittsburgh ended by the 1920s, when most of the glass factories had moved from the region due to high taxation,

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decline of natural resources, and lack of available real estate for expansion (Hawkins, 2009). Very few remnants of these facilities remain today.

Iron Ore Although Allegheny County, which eventually became the steel capital of the world, does not contain significant iron ore, siderite ores are present in Pennsylvanian-age rocks in adjacent counties.

Most of the siderite ores are nodular or concretionary. Enriched, secondary limonite deposits commonly developed from weathering of the carbonate nodules. Siderite ores generally ranged from 30 to 40 percent iron, whereas the enriched limonitic derivatives averaged about 50 percent. In the early charcoaliron furnaces, the lower-grade unaltered siderite ores were mixed with limonitic ores from the same mine.

The last extensive mining of carbonate ore took place in Fayette and Westmoreland Counties prior to 1900 (Inners, 1999). The great era of carbonate-charcoal iron production in western Pennsylvania lasted from the late 1700s to 1855. As the original hardwood forests were cleared, fuel for the iron furnaces switched in the 1850s to coal. About 1875, coal was replaced by coke (White, 1979) from local coal. Limestone flux was added to the furnaces to bond with molten ironore impurities, creating a glassy slag.

The early Pittsburgh region furnaces produced cast iron, which has a high carbon content (3–4.5 percent), making it brittle after casting. This cast iron was either cast directly into goods or into ingots for transport to iron foundries, where the ingots were converted into a more workable form, wrought iron (Hannibal et al., 2011).

Pennsylvania’s first iron furnace began production in 1692 (Hannibal et al., 2011). By the time of the American Revolution, there were nearly 60 iron furnaces in Pennsylvania, and by 1841, there were well over 200 (Moldenke, 1920). Pittsburgh’s first iron furnace was erected in 1792, but it eventually failed due to the absence of local resources. In the first half of the 19th century, Pittsburgh was not known for its cast iron production, but for the foundries that converted the cast iron into wrought iron (Moldenke, 1920).

Development of the Superior ore province in the Great Lakes region eventually put the iron mining industry of western Pennsylvania out of business. However, the iron and steel industry in Pittsburgh continued to grow because bituminous coal (and its coke) became an important ingredient in the process by the mid-1800s, and Pittsburgh was the hub of coal production. The large, high-quality iron ore deposits of Minnesota were mined and carried on the Great Lakes by freighters, which transferred the ore to trains and then 56

Gray, Greene, Fandray, and Turka

transported the ore to Pittsburgh. These trains also transported coal north from the Pittsburgh area. The Great Lakes freighters then distributed the coal to the states adjoining the Great Lakes. Over time, loading and unloading facilities for the freighters and the trains significantly grew in size and efficiency. The freighters also increased dramatically in size, the largest being 1,013.5 ft (308.91 m) in length with a capacity near 70,000 gross tons (Bawal, 2011). Eventually, Pittsburgh became the largest iron- and steel-producing center in the world (Gardner, 1980).

Water Supply Water has always been readily available to Pittsburgh and the surrounding communities from the abundance of surface water in the Allegheny, Monongahela, and Ohio Rivers. Annual mean discharge data, based on nearby long-term USGS stream gauging stations, show the Allegheny River (USGS, 2015a, Allegheny River) at 19,750 cubic feet per second (cfs) (559 cubic meters per second [cms]) and the Monongahela River (USGS, 2015b, Monongahela River) at 12,650 cfs (358 cms), resulting in flow at the head of the Ohio River (at Pittsburgh; USGS, 2011) of about 32,400 cfs (917 cms).

The most plentiful groundwater source is from the glacial outwash alluvium that overlies the bedrock of the major stream valleys of the Allegheny, Ohio, and Beaver Rivers (Gallaher, 1973). This alluvial aquifer generally consists of an older, basal portion that overlies bedrock and an upper portion that was recently deposited. Groundwater is derived primarily from the basal portion of the alluvium, and the relative groundwater yield from it depends upon the river system in which it is located. The Allegheny River valley generally has the coarsest basal alluvium, composed primarily of sand and gravel derived from melting glaciers to the north, while the Monongahela River valley contains finer-grained silts, sands, and clays derived from erosion of the local argillaceous rock lying east and south of Pittsburgh. Alluvium in the Ohio River is a mixture of alluvium from the two rivers. The permeability can change significantly over short distances within the alluvium, but for comparative purposes, well yields in the Ohio and Allegheny valleys average about 350 gallons per minute (gpm) (1,325 liters per minute [lpm]), while yields from the Monongahela valley wells average about 125 gpm (473 lpm).

Groundwater is available from the Pennsylvanianage rocks nearly everywhere in the Pittsburgh area, but the yields from wells tend to be significantly lower than from the alluvial deposits. The well yields from rock wells tend to be highly variable, with many of the yields being less than 5 gpm (19 lpm), but some wells

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decline of natural resources, and lack of available real estate for expansion (Hawkins, 2009). Very few remnants of these facilities remain today.

Iron Ore Although Allegheny County, which eventually became the steel capital of the world, does not contain significant iron ore, siderite ores are present in Pennsylvanian-age rocks in adjacent counties.

Most of the siderite ores are nodular or concretionary. Enriched, secondary limonite deposits commonly developed from weathering of the carbonate nodules. Siderite ores generally ranged from 30 to 40 percent iron, whereas the enriched limonitic derivatives averaged about 50 percent. In the early charcoaliron furnaces, the lower-grade unaltered siderite ores were mixed with limonitic ores from the same mine.

The last extensive mining of carbonate ore took place in Fayette and Westmoreland Counties prior to 1900 (Inners, 1999). The great era of carbonate-charcoal iron production in western Pennsylvania lasted from the late 1700s to 1855. As the original hardwood forests were cleared, fuel for the iron furnaces switched in the 1850s to coal. About 1875, coal was replaced by coke (White, 1979) from local coal. Limestone flux was added to the furnaces to bond with molten ironore impurities, creating a glassy slag.

The early Pittsburgh region furnaces produced cast iron, which has a high carbon content (3–4.5 percent), making it brittle after casting. This cast iron was either cast directly into goods or into ingots for transport to iron foundries, where the ingots were converted into a more workable form, wrought iron (Hannibal et al., 2011).

Pennsylvania’s first iron furnace began production in 1692 (Hannibal et al., 2011). By the time of the American Revolution, there were nearly 60 iron furnaces in Pennsylvania, and by 1841, there were well over 200 (Moldenke, 1920). Pittsburgh’s first iron furnace was erected in 1792, but it eventually failed due to the absence of local resources. In the first half of the 19th century, Pittsburgh was not known for its cast iron production, but for the foundries that converted the cast iron into wrought iron (Moldenke, 1920).

Development of the Superior ore province in the Great Lakes region eventually put the iron mining industry of western Pennsylvania out of business. However, the iron and steel industry in Pittsburgh continued to grow because bituminous coal (and its coke) became an important ingredient in the process by the mid-1800s, and Pittsburgh was the hub of coal production. The large, high-quality iron ore deposits of Minnesota were mined and carried on the Great Lakes by freighters, which transferred the ore to trains and then 56

transported the ore to Pittsburgh. These trains also transported coal north from the Pittsburgh area. The Great Lakes freighters then distributed the coal to the states adjoining the Great Lakes. Over time, loading and unloading facilities for the freighters and the trains significantly grew in size and efficiency. The freighters also increased dramatically in size, the largest being 1,013.5 ft (308.91 m) in length with a capacity near 70,000 gross tons (Bawal, 2011). Eventually, Pittsburgh became the largest iron- and steel-producing center in the world (Gardner, 1980).

Water Supply Water has always been readily available to Pittsburgh and the surrounding communities from the abundance of surface water in the Allegheny, Monongahela, and Ohio Rivers. Annual mean discharge data, based on nearby long-term USGS stream gauging stations, show the Allegheny River (USGS, 2015a, Allegheny River) at 19,750 cubic feet per second (cfs) (559 cubic meters per second [cms]) and the Monongahela River (USGS, 2015b, Monongahela River) at 12,650 cfs (358 cms), resulting in flow at the head of the Ohio River (at Pittsburgh; USGS, 2011) of about 32,400 cfs (917 cms).

The most plentiful groundwater source is from the glacial outwash alluvium that overlies the bedrock of the major stream valleys of the Allegheny, Ohio, and Beaver Rivers (Gallaher, 1973). This alluvial aquifer generally consists of an older, basal portion that overlies bedrock and an upper portion that was recently deposited. Groundwater is derived primarily from the basal portion of the alluvium, and the relative groundwater yield from it depends upon the river system in which it is located. The Allegheny River valley generally has the coarsest basal alluvium, composed primarily of sand and gravel derived from melting glaciers to the north, while the Monongahela River valley contains finer-grained silts, sands, and clays derived from erosion of the local argillaceous rock lying east and south of Pittsburgh. Alluvium in the Ohio River is a mixture of alluvium from the two rivers. The permeability can change significantly over short distances within the alluvium, but for comparative purposes, well yields in the Ohio and Allegheny valleys average about 350 gallons per minute (gpm) (1,325 liters per minute [lpm]), while yields from the Monongahela valley wells average about 125 gpm (473 lpm).

Groundwater is available from the Pennsylvanianage rocks nearly everywhere in the Pittsburgh area, but the yields from wells tend to be significantly lower than from the alluvial deposits. The well yields from rock wells tend to be highly variable, with many of the yields being less than 5 gpm (19 lpm), but some wells

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 27. Stress-relief fractures (Wyrick and Borchers, 1981).

Figure 27. Stress-relief fractures (Wyrick and Borchers, 1981).

reach yields of 75 to 100 gpm (284–379 lpm) (Gallaher, 1973).

The primary aquifers are the harder rocks (sandstones, limestones), which have minimal primary permeability, but which tend to be highly fractured, resulting in significant, natural secondary permeability. Much of the secondary permeability in the sandstones and limestones is created by stress-relief fracturing (Ferguson, 1967) caused by erosion and unloading of the rock units along stream valleys, along with tensional and compressional fracturing along the axes of the structural folds in the area. Valley stress relief, discovered and described by Ferguson (1967) and further described by Ferguson and Hamel (1981), involves physical stress release changes to the physical integrity of the flat-lying sedimentary rock layers as a valley is cut through the layers by erosion. As overburden is removed, stresses contained within the rocks are released. This generally manifests itself as open, tension-related near-vertical features in valley walls and compression features taking the form of lowangle thrust faults in the valley floors. Harry Ferguson and his U.S. Army Corps of Engineers colleagues observed this phenomenon in numerous excavations into Pittsburgh area river bottoms during construction of the series of Ohio River navigation locks and dams.

Figure 27 illustrates the process of valley stress relief.

There are 78 public water supply systems in Allegheny County that service 99 percent of the almost 1,225,000 county residents. The systems, including the

system for the City of Pittsburgh, are overseen by the Allegheny County Health Department. Pittsburgh neighborhoods north of the Monongahela River are serviced by the Pittsburgh Water and Sewer Authority (PWSA, 2014), which serves 196,000 water and sewer customers within the city.

The first documented public water supply system in Pittsburgh was constructed in 1802 and consisted of four wells serving a population of about 1,600 residents. By 1828, the rapid growth of the city resulted in water shortages that eventually required construction of a river pumping station along the Allegheny River.

The station supplied 40,000 gallons (151,416 liters) of water per day. The systems were expanded and updated as the population grew and the city expanded, reaching 9 million gallons per day (mgd) (34 million liters per day [lpd]) by 1884 and 15 mgd (57 lpd) by 1878, to service a population of 106,000 people. Water treatment was initiated in 1902 using primarily filtration. The first complete chemical treatment system of the water was installed in the 1960s, followed by replacement of slow sand filters with a dual-media, rapid sand filter system in 1969 (PWSA, 2014).

Groundwater wells continued to be used in the city but were not the primary source of drinking water.

In 1927, beginning with a well for the Stanley Theater, several of the water wells in the city were drilled strictly for air-conditioning purposes (Van Tuyl, 1951).

By 1950, the volume of groundwater utilized for air conditioning had increased to about 500 million gal-

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57

reach yields of 75 to 100 gpm (284–379 lpm) (Gallaher, 1973).

The primary aquifers are the harder rocks (sandstones, limestones), which have minimal primary permeability, but which tend to be highly fractured, resulting in significant, natural secondary permeability. Much of the secondary permeability in the sandstones and limestones is created by stress-relief fracturing (Ferguson, 1967) caused by erosion and unloading of the rock units along stream valleys, along with tensional and compressional fracturing along the axes of the structural folds in the area. Valley stress relief, discovered and described by Ferguson (1967) and further described by Ferguson and Hamel (1981), involves physical stress release changes to the physical integrity of the flat-lying sedimentary rock layers as a valley is cut through the layers by erosion. As overburden is removed, stresses contained within the rocks are released. This generally manifests itself as open, tension-related near-vertical features in valley walls and compression features taking the form of lowangle thrust faults in the valley floors. Harry Ferguson and his U.S. Army Corps of Engineers colleagues observed this phenomenon in numerous excavations into Pittsburgh area river bottoms during construction of the series of Ohio River navigation locks and dams.

Figure 27 illustrates the process of valley stress relief.

There are 78 public water supply systems in Allegheny County that service 99 percent of the almost 1,225,000 county residents. The systems, including the

system for the City of Pittsburgh, are overseen by the Allegheny County Health Department. Pittsburgh neighborhoods north of the Monongahela River are serviced by the Pittsburgh Water and Sewer Authority (PWSA, 2014), which serves 196,000 water and sewer customers within the city.

The first documented public water supply system in Pittsburgh was constructed in 1802 and consisted of four wells serving a population of about 1,600 residents. By 1828, the rapid growth of the city resulted in water shortages that eventually required construction of a river pumping station along the Allegheny River.

The station supplied 40,000 gallons (151,416 liters) of water per day. The systems were expanded and updated as the population grew and the city expanded, reaching 9 million gallons per day (mgd) (34 million liters per day [lpd]) by 1884 and 15 mgd (57 lpd) by 1878, to service a population of 106,000 people. Water treatment was initiated in 1902 using primarily filtration. The first complete chemical treatment system of the water was installed in the 1960s, followed by replacement of slow sand filters with a dual-media, rapid sand filter system in 1969 (PWSA, 2014).

Groundwater wells continued to be used in the city but were not the primary source of drinking water.

In 1927, beginning with a well for the Stanley Theater, several of the water wells in the city were drilled strictly for air-conditioning purposes (Van Tuyl, 1951).

By 1950, the volume of groundwater utilized for air conditioning had increased to about 500 million gal-

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Gray, Greene, Fandray, and Turka

Figure 28. Aerial view of Allegheny Dam 5 and hydropower plant.

lons (1.8 billion liters) per year, or about 25 percent of the total groundwater usage per year. On a daily rate basis, during the average air-conditioning season (100–120 days), the air-conditioning use in 1950 was about 50 percent of the total groundwater use per day.

Utilizing the alluvial aquifer under the city for airconditioning purposes has continued into the 21st century, as evidenced by the 2007 installation of a subsurface geothermal heat pump system into the alluvium underlying Point State Park (at the confluence of the three rivers) to heat, as well as cool, the blockhouse museum of Fort Pitt.

Hydropower Hydropower has been a part of the Pittsburgh region for many years. Four of the U.S. Army Corps of Engineers Pittsburgh District reservoirs currently generate hydropower: Kinzua Dam and Reservoir, Youghiogheny Dam and Reservoir, and Conemaugh Dam and Reservoir, and a fourth, Mahoning Dam, recently started generating hydropower (Kurka et al., 2014). Kinzua Dam and Reservoir is located on the Allegheny River near Warren, PA. At this location, the electric utility First Energy (contemporary survivor of Associated Gas & Electric Co. [AGECO], 1906–1946) draws water both from the U.S. Corps of Engineers’ Allegheny Reservoir and also from a pumped storage reservoir located high above the left abutment of the dam. The project is a peaking plant, which means that it pumps water up to the storage reservoir at night when electric rates are low, and then it sends the water down an inclined power tunnel to the power plant during the day when power demand is high. As mentioned, two other U.S. Corps of Engineers’ reservoirs also have hydropower generation: Youghiogheny Dam 58

located south of Pittsburgh, and Conemaugh Dam located northeast of Pittsburgh. Mahoning Dam is a concrete gravity structure, also located northeast of Pittsburgh, that was built originally with a penstock, allowing the project to be fitted for future power generation. The penstock has been retrofitted with a turbine and downstream power plant to generate hydropower.

Construction of the power plant at Mahoning Dam has been completed.

There are five low-head hydroelectric plants currently in place at existing locks and dams (L/D) near Pittsburgh. Four are located on the Allegheny River above Pittsburgh at L/D 5 (at Freeport, PA); L/D 6 (at Clinton, PA); L/D 8 (at Templeton, PA); and L/D 9 (at Rimer, PA). The fifth is at Hannibal Locks and Dam, located on the Ohio River close to Wheeling, WV. The four low-head hydroelectric plants located on the Allegheny River were built in the late 1980s.

Figure 28 provides an aerial view of the plant at Allegheny Dam 5 (Freeport, PA). At each of these five sites, the generating plant is located on the side of the river opposite the navigation lock. Federal tax credits have stimulated private electric power developers to file power-generation permits for many of the remaining navigation structures and flood-control reservoirs.

The Federal Energy Regulatory Commission licensing process, however, is rigorous and lengthy, and, therefore, at this time, further hydropower development in the region will occur only gradually, consistent with the response of the government.

Gray, Greene, Fandray, and Turka

Figure 28. Aerial view of Allegheny Dam 5 and hydropower plant.

lons (1.8 billion liters) per year, or about 25 percent of the total groundwater usage per year. On a daily rate basis, during the average air-conditioning season (100–120 days), the air-conditioning use in 1950 was about 50 percent of the total groundwater use per day.

Utilizing the alluvial aquifer under the city for airconditioning purposes has continued into the 21st century, as evidenced by the 2007 installation of a subsurface geothermal heat pump system into the alluvium underlying Point State Park (at the confluence of the three rivers) to heat, as well as cool, the blockhouse museum of Fort Pitt.

GEOLOGIC CONSTRAINTS Seismicity and Earthquake Hazard Southwestern Pennsylvania, including Pittsburgh, is a relatively inactive seismic area. Earthquake activity in surrounding areas is somewhat more intense. These areas include the Piedmont Province in eastern Pennsylvania, northwestern Ohio, and New York State immediately east of Buffalo at Attica, NY, and in the St. Lawrence River Valley.

Pennsylvania earthquakes are generally small. The largest earthquake-of-record in Pennsylvania, a magnitude 5.2 (mbLg), occurred on September 25, 1998, in northwestern Pennsylvania near the Ohio border (Fleeger et al., 1999). Only twice per decade, on average, is an earthquake epicentered within Pennsylvania that is large enough (Richter magnitude 3 or greater) to be felt in an area of several hundred square kilometers (Gordon and Dewey, 1999). The Pennsylvania Geologic Survey’s Map 69, Earthquake Catalog and Epicenter Map of Pennsylvania (Faill, 2004), is the basic reference document showing the locations of, and listing, all recorded seismic events since 1724 in

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Hydropower Hydropower has been a part of the Pittsburgh region for many years. Four of the U.S. Army Corps of Engineers Pittsburgh District reservoirs currently generate hydropower: Kinzua Dam and Reservoir, Youghiogheny Dam and Reservoir, and Conemaugh Dam and Reservoir, and a fourth, Mahoning Dam, recently started generating hydropower (Kurka et al., 2014). Kinzua Dam and Reservoir is located on the Allegheny River near Warren, PA. At this location, the electric utility First Energy (contemporary survivor of Associated Gas & Electric Co. [AGECO], 1906–1946) draws water both from the U.S. Corps of Engineers’ Allegheny Reservoir and also from a pumped storage reservoir located high above the left abutment of the dam. The project is a peaking plant, which means that it pumps water up to the storage reservoir at night when electric rates are low, and then it sends the water down an inclined power tunnel to the power plant during the day when power demand is high. As mentioned, two other U.S. Corps of Engineers’ reservoirs also have hydropower generation: Youghiogheny Dam 58

located south of Pittsburgh, and Conemaugh Dam located northeast of Pittsburgh. Mahoning Dam is a concrete gravity structure, also located northeast of Pittsburgh, that was built originally with a penstock, allowing the project to be fitted for future power generation. The penstock has been retrofitted with a turbine and downstream power plant to generate hydropower.

Construction of the power plant at Mahoning Dam has been completed.

There are five low-head hydroelectric plants currently in place at existing locks and dams (L/D) near Pittsburgh. Four are located on the Allegheny River above Pittsburgh at L/D 5 (at Freeport, PA); L/D 6 (at Clinton, PA); L/D 8 (at Templeton, PA); and L/D 9 (at Rimer, PA). The fifth is at Hannibal Locks and Dam, located on the Ohio River close to Wheeling, WV. The four low-head hydroelectric plants located on the Allegheny River were built in the late 1980s.

Figure 28 provides an aerial view of the plant at Allegheny Dam 5 (Freeport, PA). At each of these five sites, the generating plant is located on the side of the river opposite the navigation lock. Federal tax credits have stimulated private electric power developers to file power-generation permits for many of the remaining navigation structures and flood-control reservoirs.

The Federal Energy Regulatory Commission licensing process, however, is rigorous and lengthy, and, therefore, at this time, further hydropower development in the region will occur only gradually, consistent with the response of the government.

GEOLOGIC CONSTRAINTS Seismicity and Earthquake Hazard Southwestern Pennsylvania, including Pittsburgh, is a relatively inactive seismic area. Earthquake activity in surrounding areas is somewhat more intense. These areas include the Piedmont Province in eastern Pennsylvania, northwestern Ohio, and New York State immediately east of Buffalo at Attica, NY, and in the St. Lawrence River Valley.

Pennsylvania earthquakes are generally small. The largest earthquake-of-record in Pennsylvania, a magnitude 5.2 (mbLg), occurred on September 25, 1998, in northwestern Pennsylvania near the Ohio border (Fleeger et al., 1999). Only twice per decade, on average, is an earthquake epicentered within Pennsylvania that is large enough (Richter magnitude 3 or greater) to be felt in an area of several hundred square kilometers (Gordon and Dewey, 1999). The Pennsylvania Geologic Survey’s Map 69, Earthquake Catalog and Epicenter Map of Pennsylvania (Faill, 2004), is the basic reference document showing the locations of, and listing, all recorded seismic events since 1724 in

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 29. Small-offset normal fault near Pittsburgh (photo courtesy John Harper, Pennsylvania Geological Survey).

Figure 30. Typical low-angle thrust fault near Pittsburgh (photo courtesy John Harper, Pennsylvania Geological Survey).

Figure 29. Small-offset normal fault near Pittsburgh (photo courtesy John Harper, Pennsylvania Geological Survey).

Figure 30. Typical low-angle thrust fault near Pittsburgh (photo courtesy John Harper, Pennsylvania Geological Survey).

Pennsylvania and surrounding areas. Some of the events that have been cataloged as “earthquakes” in the greater Ridge and Valley or Appalachian Plateau Provinces were not tectonic earthquakes but mine explosions or related to mine subsidence (Gordon and Dewey, 1999).

About 35 earthquakes have caused slight damage in Pennsylvania since the beginning of the American Colonial period. Occasional broken windows, cracked plaster, and glassware toppled from shelves are characteristic of this type of damage. Nearly one half of these damaging events had out-of-state epicenters.

Foremost among this class of distant earthquakes that were felt strongly in Pennsylvania were a trio of major earthquakes near New Madrid, MO, in 1811–1812, and the Charleston, SC, earthquake in 1886. Most earthquakes with epicenters inside the state have been located in southeastern Pennsylvania (Gordon and Dewey, 1999). Scharnberger (2003) provided general information on the nature, occurrence, history, and earthquake hazards in Pennsylvania.

One of the most structurally complex areas, typical of the relative importance of faults to the design and construction of engineered works, is located about 16 mi (26 km) north of the city, and it is a faultedrock zone observable along the CSX Railroad tracks at the Bakerstown Station rock cut. Figure 31 is a representation of the west wall of the cut, depicting highangle faulting within the Casselman Formation shales and claystones. Faulting is present within these finegrained rocks of lower mass shear strength, but it does not penetrate the overlying Morgantown sandstone.

This has been interpreted to indicate that the faulting ceased before deposition of the overlying stratum, the Morgantown sandstone (Wagner et al., 1970).

Several normal faults cut the Ames Limestone near Creighton, PA, located about 15 mi (24 km) northeast of the city, creating a block of rock that has dropped down between the faults, forming a classic graben structure. Reverse faults are far less common in Allegheny County than are normal faults (J. A. Harper, personal communication, 2012). One of the better examples can be seen in a road cut along PA Route 28 at Tarentum, PA. At this location, a portion of the lighter-colored Mahoning sandstone can be seen thrust upwards over and into darker-colored shales.

A suspected strike-slip fault, representing the least common of fault orientations around Pittsburgh, is inferred from displacement of the crystalline basement rocks at some 16,000 ft (4.9 km) beneath Pittsburgh detected by magnetic geophysical surveys (Harper, 2012).

In 2010, construction at a sewage treatment plant in Sewickley Township, 18 mi (29 km) southeast of downtown Pittsburgh, revealed an ancient, but locally significant fault. At this location, the Pennsylvanian-

Pennsylvania and surrounding areas. Some of the events that have been cataloged as “earthquakes” in the greater Ridge and Valley or Appalachian Plateau Provinces were not tectonic earthquakes but mine explosions or related to mine subsidence (Gordon and Dewey, 1999).

About 35 earthquakes have caused slight damage in Pennsylvania since the beginning of the American Colonial period. Occasional broken windows, cracked plaster, and glassware toppled from shelves are characteristic of this type of damage. Nearly one half of these damaging events had out-of-state epicenters.

Foremost among this class of distant earthquakes that were felt strongly in Pennsylvania were a trio of major earthquakes near New Madrid, MO, in 1811–1812, and the Charleston, SC, earthquake in 1886. Most earthquakes with epicenters inside the state have been located in southeastern Pennsylvania (Gordon and Dewey, 1999). Scharnberger (2003) provided general information on the nature, occurrence, history, and earthquake hazards in Pennsylvania.

One of the most structurally complex areas, typical of the relative importance of faults to the design and construction of engineered works, is located about 16 mi (26 km) north of the city, and it is a faultedrock zone observable along the CSX Railroad tracks at the Bakerstown Station rock cut. Figure 31 is a representation of the west wall of the cut, depicting highangle faulting within the Casselman Formation shales and claystones. Faulting is present within these finegrained rocks of lower mass shear strength, but it does not penetrate the overlying Morgantown sandstone.

This has been interpreted to indicate that the faulting ceased before deposition of the overlying stratum, the Morgantown sandstone (Wagner et al., 1970).

Several normal faults cut the Ames Limestone near Creighton, PA, located about 15 mi (24 km) northeast of the city, creating a block of rock that has dropped down between the faults, forming a classic graben structure. Reverse faults are far less common in Allegheny County than are normal faults (J. A. Harper, personal communication, 2012). One of the better examples can be seen in a road cut along PA Route 28 at Tarentum, PA. At this location, a portion of the lighter-colored Mahoning sandstone can be seen thrust upwards over and into darker-colored shales.

A suspected strike-slip fault, representing the least common of fault orientations around Pittsburgh, is inferred from displacement of the crystalline basement rocks at some 16,000 ft (4.9 km) beneath Pittsburgh detected by magnetic geophysical surveys (Harper, 2012).

In 2010, construction at a sewage treatment plant in Sewickley Township, 18 mi (29 km) southeast of downtown Pittsburgh, revealed an ancient, but locally significant fault. At this location, the Pennsylvanian-

Faults Bedrock faults in the Pittsburgh region exhibit relatively small displacements. These include normal faults and thrust faults. The faults that have been identified to date are not capable of generating significant earthquakes. An example of a small listric normal fault resulting from rotational slump near Pittsburgh is depicted in Figure 29, and a typical low-angle thrust fault is shown in Figure 30. A key process in the development of small faults of importance to the region is valley stress relief, as previously described in the section on water supply.

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Faults Bedrock faults in the Pittsburgh region exhibit relatively small displacements. These include normal faults and thrust faults. The faults that have been identified to date are not capable of generating significant earthquakes. An example of a small listric normal fault resulting from rotational slump near Pittsburgh is depicted in Figure 29, and a typical low-angle thrust fault is shown in Figure 30. A key process in the development of small faults of importance to the region is valley stress relief, as previously described in the section on water supply.

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Gray, Greene, Fandray, and Turka

Figure 31. High-angle faulting within the Casselman Formation shales and claystones north of Pittsburgh (Shultz and Harper, 1996).

Figure 31. High-angle faulting within the Casselman Formation shales and claystones north of Pittsburgh (Shultz and Harper, 1996).

aged sedimentary strata exhibit gentle northeastsouthwest–trending folds, the dip of the beds is very slight (1–2 degrees), and tectonic faults are rare (Hamel, 2011). Available mine maps for the area indicate the plant is underlain by abandoned room-andpillar workings within the Pittsburgh Coal. The floor of the mined seam is at a depth of approximately 90 ft (27 m). Excavation for a raw sewage pump station exposed a major tectonic fault zone at least 500 ft (152 m) wide and 20 ft (6 m) thick with a brecciated zone containing sandstone blocks up to 15 ft (4.6 m) in diameter in a matrix of finer breccia and fault gouge (Hamel, 2011). The fault was mapped as having both thrust and transverse components and appears to have been related to the brittle response of the gentle folding of interbedded stronger and weaker sedimentary rocks during the Alleghanian Orogeny.

Hamel (2011) indicated that faulting of this type should be routinely expected and considered for site investigations related to foundation and other loadsensitive future engineering projects in the Pittsburgh region.

60

Landslides The Allegheny Plateau has long been recognized as an area of major landslide severity, with its steep hillsides, thick soil cover, and precipitation of 35–45 in.

(89–114 cm) per year (Figure 32). It is a naturally dissected upland surface developed on gently folded but essentially flat-lying sedimentary rocks.

Slope Formation Current slope development in the unglaciated portion of the Appalachian Plateau is consistent with flatlying sedimentary rocks in a temperate, humid climate. The occurrence of alternating weak and resistant rock strata is reflected topographically by breaks in slope and somewhat subdued to well-developed erosional benches (Gray and Gardner, 1977; Gray et al., 1979).

Existing and past climatic conditions, including periglacial effects, have resulted in substantial mechanical and chemical weathering, which produced a

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aged sedimentary strata exhibit gentle northeastsouthwest–trending folds, the dip of the beds is very slight (1–2 degrees), and tectonic faults are rare (Hamel, 2011). Available mine maps for the area indicate the plant is underlain by abandoned room-andpillar workings within the Pittsburgh Coal. The floor of the mined seam is at a depth of approximately 90 ft (27 m). Excavation for a raw sewage pump station exposed a major tectonic fault zone at least 500 ft (152 m) wide and 20 ft (6 m) thick with a brecciated zone containing sandstone blocks up to 15 ft (4.6 m) in diameter in a matrix of finer breccia and fault gouge (Hamel, 2011). The fault was mapped as having both thrust and transverse components and appears to have been related to the brittle response of the gentle folding of interbedded stronger and weaker sedimentary rocks during the Alleghanian Orogeny.

Hamel (2011) indicated that faulting of this type should be routinely expected and considered for site investigations related to foundation and other loadsensitive future engineering projects in the Pittsburgh region.

60

Landslides The Allegheny Plateau has long been recognized as an area of major landslide severity, with its steep hillsides, thick soil cover, and precipitation of 35–45 in.

(89–114 cm) per year (Figure 32). It is a naturally dissected upland surface developed on gently folded but essentially flat-lying sedimentary rocks.

Slope Formation Current slope development in the unglaciated portion of the Appalachian Plateau is consistent with flatlying sedimentary rocks in a temperate, humid climate. The occurrence of alternating weak and resistant rock strata is reflected topographically by breaks in slope and somewhat subdued to well-developed erosional benches (Gray and Gardner, 1977; Gray et al., 1979).

Existing and past climatic conditions, including periglacial effects, have resulted in substantial mechanical and chemical weathering, which produced a

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Geology of Pittsburgh

Figure 32. Landslide incidence map of the United States (Radbruch-Hall et al., 1978).

Figure 32. Landslide incidence map of the United States (Radbruch-Hall et al., 1978).

residual or colluvial soil mantle over almost the entire rock surface. The most significant periglacial effects were the greater rates of weathering, increased soil formation, and subsequent mass wasting (Denny, 1956; Philbrick, 1961; and Rapp, 1967).

Downslope movement of the soil results in its accumulation at the toes of slopes in colluvial masses.

These colluvial soils tend to be 5–30 ft (1.5–9 m) thick on slopes and generally increase in thickness (to a maximum of about 100 ft [30 m]) near the toes of slopes, unless there is active stream erosion (see Figure 33). Colluvial soils are generally stiff to hard, and individual samples have relatively high shear strengths.

However, creep or sliding processes (or both) during slope development generally reduce the shear strength along movement surfaces to residual or near-residual levels (Gray et al., 1979). These low-shear-strength surfaces can occur at several levels within the colluvial mass, but there is always a low-shear-strength surface at the soil-rock interface (Deere and Patton, 1971). As the slope materials seek equilibrium between stress and strength, the soil mantle moves downslope, and the mean slope angle decreases until a state of marginal equilibrium is achieved. This natural slope-

flattening process accounts for the relatively thick soil cover on mature colluvial slopes, particularly at the base of slopes. Deere and Patton (1971) suggested that there are no stable natural slopes in the Appalachian Plateau, where the slope inclination exceeds 12–14 degrees. Terzaghi and Peck (1948) reported movements on slopes as flat as 10 degrees, whereas Gray and Donovan (1971) demonstrated that several mature colluvial slopes, with evidence of pre-existing failure surfaces, had slope angles ranging from 7 to 10 degrees.

Gray and Gardner (1977) presented observations on the development of colluvial slopes.

Numerous field observations suggest that colluvial slopes, which may creep at rates of a few centimeters per year, visually appear stable unless disturbed by cutting, filling, drainage changes, or extreme precipitation events (Gray et al., 2011).

Landsliding As stated above, the Allegheny Plateau is recognized as having some of the most severe landsliding in the United States (Ladd, 1927–1928; Sharpe and

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61

residual or colluvial soil mantle over almost the entire rock surface. The most significant periglacial effects were the greater rates of weathering, increased soil formation, and subsequent mass wasting (Denny, 1956; Philbrick, 1961; and Rapp, 1967).

Downslope movement of the soil results in its accumulation at the toes of slopes in colluvial masses.

These colluvial soils tend to be 5–30 ft (1.5–9 m) thick on slopes and generally increase in thickness (to a maximum of about 100 ft [30 m]) near the toes of slopes, unless there is active stream erosion (see Figure 33). Colluvial soils are generally stiff to hard, and individual samples have relatively high shear strengths.

However, creep or sliding processes (or both) during slope development generally reduce the shear strength along movement surfaces to residual or near-residual levels (Gray et al., 1979). These low-shear-strength surfaces can occur at several levels within the colluvial mass, but there is always a low-shear-strength surface at the soil-rock interface (Deere and Patton, 1971). As the slope materials seek equilibrium between stress and strength, the soil mantle moves downslope, and the mean slope angle decreases until a state of marginal equilibrium is achieved. This natural slope-

flattening process accounts for the relatively thick soil cover on mature colluvial slopes, particularly at the base of slopes. Deere and Patton (1971) suggested that there are no stable natural slopes in the Appalachian Plateau, where the slope inclination exceeds 12–14 degrees. Terzaghi and Peck (1948) reported movements on slopes as flat as 10 degrees, whereas Gray and Donovan (1971) demonstrated that several mature colluvial slopes, with evidence of pre-existing failure surfaces, had slope angles ranging from 7 to 10 degrees.

Gray and Gardner (1977) presented observations on the development of colluvial slopes.

Numerous field observations suggest that colluvial slopes, which may creep at rates of a few centimeters per year, visually appear stable unless disturbed by cutting, filling, drainage changes, or extreme precipitation events (Gray et al., 2011).

Landsliding As stated above, the Allegheny Plateau is recognized as having some of the most severe landsliding in the United States (Ladd, 1927–1928; Sharpe and

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61

Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 33. Thick colluvial soil cover.

Figure 33. Thick colluvial soil cover.

Dosch, 1942; Ackenheil, 1954; Eckel, 1958; and Baker and Chieruzzi, 1959). Most landslides in the Allegheny Plateau occur in hillside soil masses, with the most common being slump-type slides or slow earth flows, which range in size up to several million cubic yards.

Rockfalls, the next most common type of slide in the area, are typically much smaller, with maximum volumes on the order of a few hundred cubic yards. The best-documented rockslide occurred at the Brilliant Cut in Pittsburgh in 1941 (Hamel, 1972) (see landslide case histories in the following section). At present, deep-seated rockslides are uncommon in the area.

However, during the Pleistocene Epoch, when climate was more severe and rivers were rapidly downcutting their valleys, this type of slide is believed to have been common. Other types of slide movements are relatively rare. Injuries and fatalities due to landslides are rare and result mainly from rockfalls on highway slopes and soil failure in construction trench excavations.

Residual strength values play an important role in the evaluation of landslides and the design of remedial measures in the area. The colluvium generally exhibits strain-softening behavior (Skempton, 1964), and its residual (large-displacement) shear strength is 62

generally less than half its peak (small-displacement) strength at a given effective normal stress. For effective normal stresses of less than about 50 psi (345 kPa), the peak strength of claystone colluvium is commonly characterized by cohesion intercepts of 1 to 5 psi (7 to 34 kPa) and friction angles of 20 to 25 degrees, while the residual strength is usually characterized by negligible cohesion intercepts and friction angles of 8 to 20 degrees. Measured residual friction angles for most claystone-derived colluvium are on the order of 11 to 16 degrees (Gray et al., 1979). Experience in calculation of strength data from colluvial slide masses (Hamel, 1969, 1980, 2004; Hamel and Flint, 1969, 1972; and Gray and Donovan, 1971) indicates that in-place shear strengths are characterized by residual friction angles of 13 to 16 degrees, with a zero cohesion intercept.

The largest slides usually result from disturbance of ancient landslide masses in soils and/or rock. These ancient landslides appear to have occurred mainly in moister periglacial conditions (Gray et al., 1979; Hamel, 1998). Limited radiocarbon dating of wood in the colluvium (Philbrick, 1961; D’Appolonia et al., 1967) suggested a Pleistocene age for some of these

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Dosch, 1942; Ackenheil, 1954; Eckel, 1958; and Baker and Chieruzzi, 1959). Most landslides in the Allegheny Plateau occur in hillside soil masses, with the most common being slump-type slides or slow earth flows, which range in size up to several million cubic yards.

Rockfalls, the next most common type of slide in the area, are typically much smaller, with maximum volumes on the order of a few hundred cubic yards. The best-documented rockslide occurred at the Brilliant Cut in Pittsburgh in 1941 (Hamel, 1972) (see landslide case histories in the following section). At present, deep-seated rockslides are uncommon in the area.

However, during the Pleistocene Epoch, when climate was more severe and rivers were rapidly downcutting their valleys, this type of slide is believed to have been common. Other types of slide movements are relatively rare. Injuries and fatalities due to landslides are rare and result mainly from rockfalls on highway slopes and soil failure in construction trench excavations.

Residual strength values play an important role in the evaluation of landslides and the design of remedial measures in the area. The colluvium generally exhibits strain-softening behavior (Skempton, 1964), and its residual (large-displacement) shear strength is 62

generally less than half its peak (small-displacement) strength at a given effective normal stress. For effective normal stresses of less than about 50 psi (345 kPa), the peak strength of claystone colluvium is commonly characterized by cohesion intercepts of 1 to 5 psi (7 to 34 kPa) and friction angles of 20 to 25 degrees, while the residual strength is usually characterized by negligible cohesion intercepts and friction angles of 8 to 20 degrees. Measured residual friction angles for most claystone-derived colluvium are on the order of 11 to 16 degrees (Gray et al., 1979). Experience in calculation of strength data from colluvial slide masses (Hamel, 1969, 1980, 2004; Hamel and Flint, 1969, 1972; and Gray and Donovan, 1971) indicates that in-place shear strengths are characterized by residual friction angles of 13 to 16 degrees, with a zero cohesion intercept.

The largest slides usually result from disturbance of ancient landslide masses in soils and/or rock. These ancient landslides appear to have occurred mainly in moister periglacial conditions (Gray et al., 1979; Hamel, 1998). Limited radiocarbon dating of wood in the colluvium (Philbrick, 1961; D’Appolonia et al., 1967) suggested a Pleistocene age for some of these

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

deposits. Peltier (1950) and Denny (1956) found fossil periglacial features close to the front of the maximum advance of the Wisconsin glaciation in Pennsylvania that strongly supported the influence of Pleistocene periglacial processes on slopes.

Rockfalls result from differential weathering that creates unsupported, resistant rock overhangs. Rates of undercutting have been observed that vary from 1 to 7 in. (2.5 to 17.8 cm) per year, based on measurements conducted over a period of several years (Philbrick, 1959; Bonk, 1964).

Fleming and Taylor (1980) published landslide damage estimates for Allegheny County (Pittsburgh and suburbs) from 1970 to 1976. Annual costs ranged from $1.2 to $4.0 million over this 7 year period and averaged $2.2 million per year. The maximum annual cost of $4 million was for 1972, the year of Tropical Storm Agnes.

Landslide Case Histories Brilliant Cut Rockslide—Several rockfalls and landslides in the Pittsburgh, PA, area, have been costly in terms of lives and money. An historic case involved the failure of 110,000 cubic yards (84,101 m3 ) of rock that broke away from a large railroad cut in Pittsburgh on March 20, 1941 (Hamel, 1972). The area of the catastrophic rockslide is known as the Brilliant Cut. The rock cut was located on the nose of a hill at the junction of an abandoned tributary valley and the Allegheny River valley. The hill consists of nearly horizontal beds of sandstone, shale, siltstone, claystone, limestone, and coal. The cut was originally excavated in the early 1900s, and it experienced its first rockslide in 1904. In 1930, the railroad tracks were relocated farther into the rock slope, triggering two additional slope failures (Xanthakos et al., 1994). In addition, in the 1930s, a 1 ft (0.3 m) wide joint opened in the rock mass that extended to the crest of the hill. The joint was persistent, extending through the rock layers, and it has been interpreted to be a valley stress relief joint (Hamel, 1972).

The March 1941 rockslide displaced multiple sets of railroad tracks and derailed an operating train. The remedial rock excavation cost was about $100,000. Analyses conducted subsequent to the slope failure indicated that the rockslide was triggered by cleft water pressure that had built up within the master rock joint, primarily because natural drainage from within the slope had been blocked by large buildups of ice.

Aliquippa Rockslide—On December 22, 1942, about 150 cubic yards (115 m3 ) of rock plunged off a highway cut on the west bank of the Ohio River about 16 mi (26 km) downstream of Pittsburgh, killing many factory workers riding in a bus (Gray et al., 1979). On

Geology of Pittsburgh

that day, at 5:03 p.m., an Ohio Valley Motor Coach bus left from Aliquippa (the site of an operating steel plant) for Pittsburgh. The bus was filled with wartime steel workers on their way home following completion of a work shift. At 5:12 p.m., the time that victim’s watches stopped, the bus was demolished by an avalanche of rock, which had been loosened by freezing and thawing, falling 75 ft (23 m) down the hillside and crushing the bus. Two of the largest blocks were estimated to be in the range of 100 tons each. The accident killed 22 passengers and injured three.

The valley wall at the location of the rockslide was approximately 360 ft (110 m) high with a mean inclination of 30 to 35 degrees (Gray et al., 1979). Adjustments to the slope were made in 1922 with the excavation of a 45 ft (14 m) sidehill cut. At the road level, an ∼15 ft (4.5 m) section of erodible clay shale was exposed and overlain by 6 ft (1.8 m) of soft claystone. These weak rock layers were overlain by about 18 ft (5.4 m) of hard sandy shale with numerous joints oriented parallel to the valley wall. The clayshale and claystone units rapidly weathered, undercutting the hard sandy shale above. Records supplied by Ackenheil (1954) indicate that at least nine major rockfalls occurred on this section of road between 1932 and 1954. This event remains the worst rockslide to occur in the Pittsburgh region. This slope was later redesigned to minimize rockfalls, and reconstruction of the slope was completed in 1956.

Route 51 Rockfall of 1983—On February 16, 1983, two persons were killed as an estimated 400 tons of rock had fallen to the road surface below in an area locally known as Saw Mill Run Boulevard. The rockslide occurred several minutes after explosives had been used to free unstable, overhanging rock on part of the cliff face located above Route 51 during a construction project that was under way. A contractor at the site was working to stabilize a rock overhang, and they had released stopped traffic, which they had been holding back during periods of blasting. Within several minutes after traffic was permitted to flow after the last blasting operation, the rockfall occurred without warning.

Expansive Shales and Slags Expansive Shales Structural damage due to heaving caused by expansive sulfide minerals in shales was first recorded in western Pennsylvania in 1950 (Dougherty and Barsotti, 1972). Heaving of the ground results from oxidation of sulfide minerals such as pyrite and marcasite. Finely divided, black, amorphous sulfide minerals are very susceptible to oxidation due to their relatively

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63

deposits. Peltier (1950) and Denny (1956) found fossil periglacial features close to the front of the maximum advance of the Wisconsin glaciation in Pennsylvania that strongly supported the influence of Pleistocene periglacial processes on slopes.

Rockfalls result from differential weathering that creates unsupported, resistant rock overhangs. Rates of undercutting have been observed that vary from 1 to 7 in. (2.5 to 17.8 cm) per year, based on measurements conducted over a period of several years (Philbrick, 1959; Bonk, 1964).

Fleming and Taylor (1980) published landslide damage estimates for Allegheny County (Pittsburgh and suburbs) from 1970 to 1976. Annual costs ranged from $1.2 to $4.0 million over this 7 year period and averaged $2.2 million per year. The maximum annual cost of $4 million was for 1972, the year of Tropical Storm Agnes.

Landslide Case Histories Brilliant Cut Rockslide—Several rockfalls and landslides in the Pittsburgh, PA, area, have been costly in terms of lives and money. An historic case involved the failure of 110,000 cubic yards (84,101 m3 ) of rock that broke away from a large railroad cut in Pittsburgh on March 20, 1941 (Hamel, 1972). The area of the catastrophic rockslide is known as the Brilliant Cut. The rock cut was located on the nose of a hill at the junction of an abandoned tributary valley and the Allegheny River valley. The hill consists of nearly horizontal beds of sandstone, shale, siltstone, claystone, limestone, and coal. The cut was originally excavated in the early 1900s, and it experienced its first rockslide in 1904. In 1930, the railroad tracks were relocated farther into the rock slope, triggering two additional slope failures (Xanthakos et al., 1994). In addition, in the 1930s, a 1 ft (0.3 m) wide joint opened in the rock mass that extended to the crest of the hill. The joint was persistent, extending through the rock layers, and it has been interpreted to be a valley stress relief joint (Hamel, 1972).

The March 1941 rockslide displaced multiple sets of railroad tracks and derailed an operating train. The remedial rock excavation cost was about $100,000. Analyses conducted subsequent to the slope failure indicated that the rockslide was triggered by cleft water pressure that had built up within the master rock joint, primarily because natural drainage from within the slope had been blocked by large buildups of ice.

Aliquippa Rockslide—On December 22, 1942, about 150 cubic yards (115 m3 ) of rock plunged off a highway cut on the west bank of the Ohio River about 16 mi (26 km) downstream of Pittsburgh, killing many factory workers riding in a bus (Gray et al., 1979). On

that day, at 5:03 p.m., an Ohio Valley Motor Coach bus left from Aliquippa (the site of an operating steel plant) for Pittsburgh. The bus was filled with wartime steel workers on their way home following completion of a work shift. At 5:12 p.m., the time that victim’s watches stopped, the bus was demolished by an avalanche of rock, which had been loosened by freezing and thawing, falling 75 ft (23 m) down the hillside and crushing the bus. Two of the largest blocks were estimated to be in the range of 100 tons each. The accident killed 22 passengers and injured three.

The valley wall at the location of the rockslide was approximately 360 ft (110 m) high with a mean inclination of 30 to 35 degrees (Gray et al., 1979). Adjustments to the slope were made in 1922 with the excavation of a 45 ft (14 m) sidehill cut. At the road level, an ∼15 ft (4.5 m) section of erodible clay shale was exposed and overlain by 6 ft (1.8 m) of soft claystone. These weak rock layers were overlain by about 18 ft (5.4 m) of hard sandy shale with numerous joints oriented parallel to the valley wall. The clayshale and claystone units rapidly weathered, undercutting the hard sandy shale above. Records supplied by Ackenheil (1954) indicate that at least nine major rockfalls occurred on this section of road between 1932 and 1954. This event remains the worst rockslide to occur in the Pittsburgh region. This slope was later redesigned to minimize rockfalls, and reconstruction of the slope was completed in 1956.

Route 51 Rockfall of 1983—On February 16, 1983, two persons were killed as an estimated 400 tons of rock had fallen to the road surface below in an area locally known as Saw Mill Run Boulevard. The rockslide occurred several minutes after explosives had been used to free unstable, overhanging rock on part of the cliff face located above Route 51 during a construction project that was under way. A contractor at the site was working to stabilize a rock overhang, and they had released stopped traffic, which they had been holding back during periods of blasting. Within several minutes after traffic was permitted to flow after the last blasting operation, the rockfall occurred without warning.

Expansive Shales and Slags Expansive Shales Structural damage due to heaving caused by expansive sulfide minerals in shales was first recorded in western Pennsylvania in 1950 (Dougherty and Barsotti, 1972). Heaving of the ground results from oxidation of sulfide minerals such as pyrite and marcasite. Finely divided, black, amorphous sulfide minerals are very susceptible to oxidation due to their relatively

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63

Gray, Greene, Fandray, and Turka

large surface area. These expansive rocks are created in depositional environments where large volumes of decomposing organic material are exposed to low-oxygen and low-energy conditions, such as in swamps or lagoons. When freshly exposed by excavation, such as in a rock cut or a foundation excavation, they rapidly oxidize, and the sulfide minerals change into new minerals with greater volume, creating rock expansion that damages overlying or adjacent structures.

These expansive shale (and coal) seams are found throughout the stratigraphy in the Pittsburgh area, so avoidance can be difficult. Also, Pittsburgh’s topography of steep hills and narrow valleys can typically require rock cuts and excavation to prepare sites for construction, so building in freshly exposed rock in building sites is very common.

The iron sulfide content of the expansive shales usually exceeds 1 percent by weight. However, damaging heave is reported for sulfide contents as low as 0.1 percent. Many of the expansive shales, although not all, are dark in color. These dark shales are often called carbonaceous shale, which implies the shale’s dark color is due to high carbon content. Often, the dark color is due to black amorphous sulfide minerals rather than carbon.

Researchers report that weathering of the shale is partly biochemical and caused by autotrophic bacteria belonging to the Thiobacillus-Ferrobacillus group.

The preferred environment for this expansion process seems to be warm and relatively dry, with a plentiful supply of air (Penner et al., 1973). No clear relationship has been identified between the amount of heaving and iron sulfide content or thickness of the shale (Dougherty and Barsotti, 1972). When identified in the planning stage of a project, the common avoidance methods in the Pittsburgh area include: (1) overexcavation of the shale by some interval (dependent on specific location and building loads) and backfill with inert, non-expansive fill such as slag or gravel; (2) installation of deep foundations (drilled piers, drilled-in piles) to extend below the expansive shale and properly base the structure on load-bearing beams above the shale, avoiding contact; (3) grading of the site to remove the potentially expansive shale; or (4) construction of the building grade so that inert fill is placed over the top of the shale without exposing the shale, with the fill being of sufficient thickness to attenuate heave and minimize any heave that may occur. If none of these alternatives can be done, the expansive shales are sealed with concrete or bitumastic materials in an attempt to prevent oxidation. However, there remains some risk of heave, because sealing is not a long-term solution since most seals eventually leak.

Although no correlations have been identified that relate maximum heave to thickness of the expansive 64

shale or percent of sulfide content (Dougherty and Barsotti, 1972), heave is a process that can continue for many years. Heave can be substantial because the oxidized iron sulfides occupy ten times more space than un-oxidized material, and the splitting of the shale causes it to occupy a greater volume (ENR, 1960). The ENR article indicates structures continued to heave 25 to 40 years after their construction. In one case, a lightly loaded column was raised 4 in. (10 cm) by the heave of the expansive shale (ENR, 1960). Spanovich and Fewell (1969) reported their observations verifying heave pressures exceeding 6,000 pounds per square foot (psf) (29,295 kg/m2 ).

A prime example of expansive shale in the Pittsburgh area is the Queen of Angels (originally named St. Agnes) School in North Huntingdon, PA (15 mi [24 km] east of Pittsburgh). It was built in 1961 as a one-story, slab-on-grade building with the walls supported on grade beams that spanned between spread footing foundations. The walls and floors began to crack shortly after the school opened. The building continued to heave, and engineering studies in 1989, 1992, 1994, and 1997 found the damage was becoming progressively worse. In 1999, it was concluded the school’s main structural support system had failed and that repairs estimated at more than $2.5 million were required. The 39 year old building was closed, and it was demolished in 2000 (Reeger, 2012).

Expansive Slags Again, because of Pittsburgh’s steep hills and narrow valleys and the minimal flat-land available, large development areas throughout the region were dependent upon fill. A by-product of all the once-numerous large steel making facilities in Pittsburgh was slag.

Much of the slag was used in continued development of the steel-making facilities along waterways, and much was discarded. However, because of its abundance and low cost, it was made commercially available. The problem with using some forms of the material was the tendency for it to expand when it was used beneath foundations, structures, and roadways, which caused excessive heaving and buckling damage.

The slag would continue to expand until all of the reactive calcium oxide was hydrated, which could take several months or years. The number of damage cases due to expansive slags is relatively few because producers of potentially expansive slag learned not to use it in their own plants and generally placed such slag in waste dumps, and also because the material is no longer readily available as the steel industry is essentially depleted. Most of the damage in the Pittsburgh area occurred in the 1960s and 1970s, when steel pro-

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Gray, Greene, Fandray, and Turka

large surface area. These expansive rocks are created in depositional environments where large volumes of decomposing organic material are exposed to low-oxygen and low-energy conditions, such as in swamps or lagoons. When freshly exposed by excavation, such as in a rock cut or a foundation excavation, they rapidly oxidize, and the sulfide minerals change into new minerals with greater volume, creating rock expansion that damages overlying or adjacent structures.

These expansive shale (and coal) seams are found throughout the stratigraphy in the Pittsburgh area, so avoidance can be difficult. Also, Pittsburgh’s topography of steep hills and narrow valleys can typically require rock cuts and excavation to prepare sites for construction, so building in freshly exposed rock in building sites is very common.

The iron sulfide content of the expansive shales usually exceeds 1 percent by weight. However, damaging heave is reported for sulfide contents as low as 0.1 percent. Many of the expansive shales, although not all, are dark in color. These dark shales are often called carbonaceous shale, which implies the shale’s dark color is due to high carbon content. Often, the dark color is due to black amorphous sulfide minerals rather than carbon.

Researchers report that weathering of the shale is partly biochemical and caused by autotrophic bacteria belonging to the Thiobacillus-Ferrobacillus group.

The preferred environment for this expansion process seems to be warm and relatively dry, with a plentiful supply of air (Penner et al., 1973). No clear relationship has been identified between the amount of heaving and iron sulfide content or thickness of the shale (Dougherty and Barsotti, 1972). When identified in the planning stage of a project, the common avoidance methods in the Pittsburgh area include: (1) overexcavation of the shale by some interval (dependent on specific location and building loads) and backfill with inert, non-expansive fill such as slag or gravel; (2) installation of deep foundations (drilled piers, drilled-in piles) to extend below the expansive shale and properly base the structure on load-bearing beams above the shale, avoiding contact; (3) grading of the site to remove the potentially expansive shale; or (4) construction of the building grade so that inert fill is placed over the top of the shale without exposing the shale, with the fill being of sufficient thickness to attenuate heave and minimize any heave that may occur. If none of these alternatives can be done, the expansive shales are sealed with concrete or bitumastic materials in an attempt to prevent oxidation. However, there remains some risk of heave, because sealing is not a long-term solution since most seals eventually leak.

Although no correlations have been identified that relate maximum heave to thickness of the expansive 64

shale or percent of sulfide content (Dougherty and Barsotti, 1972), heave is a process that can continue for many years. Heave can be substantial because the oxidized iron sulfides occupy ten times more space than un-oxidized material, and the splitting of the shale causes it to occupy a greater volume (ENR, 1960). The ENR article indicates structures continued to heave 25 to 40 years after their construction. In one case, a lightly loaded column was raised 4 in. (10 cm) by the heave of the expansive shale (ENR, 1960). Spanovich and Fewell (1969) reported their observations verifying heave pressures exceeding 6,000 pounds per square foot (psf) (29,295 kg/m2 ).

A prime example of expansive shale in the Pittsburgh area is the Queen of Angels (originally named St. Agnes) School in North Huntingdon, PA (15 mi [24 km] east of Pittsburgh). It was built in 1961 as a one-story, slab-on-grade building with the walls supported on grade beams that spanned between spread footing foundations. The walls and floors began to crack shortly after the school opened. The building continued to heave, and engineering studies in 1989, 1992, 1994, and 1997 found the damage was becoming progressively worse. In 1999, it was concluded the school’s main structural support system had failed and that repairs estimated at more than $2.5 million were required. The 39 year old building was closed, and it was demolished in 2000 (Reeger, 2012).

Expansive Slags Again, because of Pittsburgh’s steep hills and narrow valleys and the minimal flat-land available, large development areas throughout the region were dependent upon fill. A by-product of all the once-numerous large steel making facilities in Pittsburgh was slag.

Much of the slag was used in continued development of the steel-making facilities along waterways, and much was discarded. However, because of its abundance and low cost, it was made commercially available. The problem with using some forms of the material was the tendency for it to expand when it was used beneath foundations, structures, and roadways, which caused excessive heaving and buckling damage.

The slag would continue to expand until all of the reactive calcium oxide was hydrated, which could take several months or years. The number of damage cases due to expansive slags is relatively few because producers of potentially expansive slag learned not to use it in their own plants and generally placed such slag in waste dumps, and also because the material is no longer readily available as the steel industry is essentially depleted. Most of the damage in the Pittsburgh area occurred in the 1960s and 1970s, when steel pro-

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Geology of Pittsburgh

duction was at its highest and the effects were less known.

The iron and steel industry produces a variety of slags as by-products of its operations. Iron blast furnace slag, both air cooled and granulated, has a long history of use. However, steel slags from open hearth, basic oxygen, and electric furnaces have exhibited these expansive properties (Crawford and Burn, 1969).

Expansion of slags occurs when free calcium and magnesium oxides (CaO and MgO) take on water. Particle size is an important factor controlling the rate of expansion, since the smaller the size, the greater is the surface area and the greater is the exposure to moisture.

duction was at its highest and the effects were less known.

The iron and steel industry produces a variety of slags as by-products of its operations. Iron blast furnace slag, both air cooled and granulated, has a long history of use. However, steel slags from open hearth, basic oxygen, and electric furnaces have exhibited these expansive properties (Crawford and Burn, 1969).

Expansion of slags occurs when free calcium and magnesium oxides (CaO and MgO) take on water. Particle size is an important factor controlling the rate of expansion, since the smaller the size, the greater is the surface area and the greater is the exposure to moisture.

Flooding Pittsburgh has experienced a wide range of flood hazards, including hurricane-related rainfall events, spring snowmelt, and releases related to ice-jam flooding. Due to its location at the headwaters of the Ohio River, the region is historically susceptible to flooding. In the headwaters region of the Ohio Basin, slopes are often steep, and runoff into tributaries and rivers occurs rapidly. As in other intensely urbanized areas with moderately high precipitation and ground that prevents potential infiltration, the transfer from rainfall to flood management is nearly instantaneous, and stream surges can mount significantly within 24 hours.

The headwaters region of the Ohio River receives one of the highest annual rainfall amounts in the country and also has one of the lowest evaporation rates (W. C. Loehlein, personal communication, 2010). The region also has one of the highest reliabilities of receiving its annual rainfall in the world. Unlike most regions, the area surrounding Pittsburgh has historically had flooding from every direction, for example, from storms that cross over the Great Lakes to the northwest, from thunderstorm activity originating in the Gulf of Mexico, and from hurricanes that form in the Atlantic Ocean. The distinctive four seasons that are present in the region include average winter snow accumulations of 40–60 in. (101–152 cm) per year that contribute to the area’s flood-prone nature. Because of the area’s significant relief, flooding of Pittsburgh can occur within 24 hours after the initiation of a storm event.

Flooding in Pittsburgh has occurred historically dating back to the early settlement of the region (see Figure 34). One of the earliest recorded floods was at Fort Pitt in January 1762. Many homes were filled with water, and the village surrounding the fort was covered in mud. No one, however, drowned by what was then reported as “ye Deluge or Inundation” (Johnson, 1978, p. 8).

Flooding Figure 34. Historical flood levels at the Point (photo courtesy of the U.S. Army Corps of Engineers).

Many devastating floods have impacted Pittsburgh.

On April 6 and April 19, 1852, floodwaters reached 28 ft (8.5 m) and 34.9 ft (10.6 m), respectively, on the Pittsburgh river gauge. Normal river stage at Pittsburgh is ∼16 ft (4.9 m), and flood stage at the Point has been established as being any level above 24 ft (7.3 m). On the Allegheny River just above Pittsburgh, many residents were routinely prepared to take to standby rafts for protection from the rising waters. The “St. Valentine’s Day Flood” of 1884 peaked in the city at a stage of 36.3 ft (11 m), leaving at least 10,000 Pittsburghers homeless and some 15,000 out of work (Johnson, 1978). Farther down the Ohio River, conditions were even more serious where private and municipal levees were overtopped.

Devastating flooding again plagued Pittsburgh in 1907, leading to the formation of a Pittsburgh Flood Commission to evaluate flooding in the city. It was the first of its kind. The voluminous commission report, which was released in 1912, predicted that Pittsburgh would someday experience a 40 ft (12 m) flood stage and recommended construction of a system of reservoirs and levees to protect the city (Johnson, 1978).

Several surveys were undertaken to determine the optimal sites for dams that would impound reservoirs and act to attenuate flooding downstream. Some of the major river systems evaluated for such projects were the Allegheny, Mahoning, and Shenango Rivers. Following a flood in 1913, the U.S. Army Corps of Engineers took a more aggressive approach to flooding problems.

This was likely a direct reaction to the strong opinions of President Theodore Roosevelt. Roosevelt declared that it was imperative for the federal government to build multipurpose dams and reservoirs to conserve flood waters for later use in irrigation, hy-

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Pittsburgh has experienced a wide range of flood hazards, including hurricane-related rainfall events, spring snowmelt, and releases related to ice-jam flooding. Due to its location at the headwaters of the Ohio River, the region is historically susceptible to flooding. In the headwaters region of the Ohio Basin, slopes are often steep, and runoff into tributaries and rivers occurs rapidly. As in other intensely urbanized areas with moderately high precipitation and ground that prevents potential infiltration, the transfer from rainfall to flood management is nearly instantaneous, and stream surges can mount significantly within 24 hours.

The headwaters region of the Ohio River receives one of the highest annual rainfall amounts in the country and also has one of the lowest evaporation rates (W. C. Loehlein, personal communication, 2010). The region also has one of the highest reliabilities of receiving its annual rainfall in the world. Unlike most regions, the area surrounding Pittsburgh has historically had flooding from every direction, for example, from storms that cross over the Great Lakes to the northwest, from thunderstorm activity originating in the Gulf of Mexico, and from hurricanes that form in the Atlantic Ocean. The distinctive four seasons that are present in the region include average winter snow accumulations of 40–60 in. (101–152 cm) per year that contribute to the area’s flood-prone nature. Because of the area’s significant relief, flooding of Pittsburgh can occur within 24 hours after the initiation of a storm event.

Flooding in Pittsburgh has occurred historically dating back to the early settlement of the region (see Figure 34). One of the earliest recorded floods was at Fort Pitt in January 1762. Many homes were filled with water, and the village surrounding the fort was covered in mud. No one, however, drowned by what was then reported as “ye Deluge or Inundation” (Johnson, 1978, p. 8).

Figure 34. Historical flood levels at the Point (photo courtesy of the U.S. Army Corps of Engineers).

Many devastating floods have impacted Pittsburgh.

On April 6 and April 19, 1852, floodwaters reached 28 ft (8.5 m) and 34.9 ft (10.6 m), respectively, on the Pittsburgh river gauge. Normal river stage at Pittsburgh is ∼16 ft (4.9 m), and flood stage at the Point has been established as being any level above 24 ft (7.3 m). On the Allegheny River just above Pittsburgh, many residents were routinely prepared to take to standby rafts for protection from the rising waters. The “St. Valentine’s Day Flood” of 1884 peaked in the city at a stage of 36.3 ft (11 m), leaving at least 10,000 Pittsburghers homeless and some 15,000 out of work (Johnson, 1978). Farther down the Ohio River, conditions were even more serious where private and municipal levees were overtopped.

Devastating flooding again plagued Pittsburgh in 1907, leading to the formation of a Pittsburgh Flood Commission to evaluate flooding in the city. It was the first of its kind. The voluminous commission report, which was released in 1912, predicted that Pittsburgh would someday experience a 40 ft (12 m) flood stage and recommended construction of a system of reservoirs and levees to protect the city (Johnson, 1978).

Several surveys were undertaken to determine the optimal sites for dams that would impound reservoirs and act to attenuate flooding downstream. Some of the major river systems evaluated for such projects were the Allegheny, Mahoning, and Shenango Rivers. Following a flood in 1913, the U.S. Army Corps of Engineers took a more aggressive approach to flooding problems.

This was likely a direct reaction to the strong opinions of President Theodore Roosevelt. Roosevelt declared that it was imperative for the federal government to build multipurpose dams and reservoirs to conserve flood waters for later use in irrigation, hy-

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droelectric power generation, and improving dry season flows (Johnson, 1978). In direct response to this national attention, the Ohio River Flood Board was formed to initiate America’s first regional flood mitigation planning. Additional floods impacted Pittsburgh, with the most significant one occurring in March 1936.

That flood peaked at over 30 ft (9.1 m) above normal river level (46.4 ft [14.1 m] actual water depth). This event was then calculated to represent a record-setting 500 year flood, and it is considered as the worst flood to impact the Pittsburgh region and the city to date.

Subsequent engineered flood control was constructed by the U.S. Corps of Engineers in 1938. The severity of the flooding in Pittsburgh was demonstrated to be greatly reduced during the more recent floods that occurred in 1972, associated with Hurricane Agnes, and in 1996, by the system of upstream flood-control reservoirs.

The Great Flood of 1889 On May 31, 1889, approximately 60 mi (97 km) east of Pittsburgh, a man-made disaster of unrivaled proportions took place in the city of Johnstown, PA. It was the Johnstown Flood (or the “Great Flood of 1889” as it became known locally). Although not directly associated with the Pittsburgh region, the flows from the watershed in Johnstown end up in the Allegheny River and ultimately pass the Point at Pittsburgh. Heavy rains poured down over this direct upper sub-basin of the Ohio River for several days (Law, 1997). The area surrounding Johnstown remains naturally prone to flooding due to its position at the confluence of the Little Conemaugh River and Stony Creek, which combine to form the Conemaugh River. The area above Johnstown consists of a 657 mi2 (1,701 km2 ) watershed within the Allegheny Plateau. Adding to these factors, artificial narrowing of the riverbed because of early industrial development made the city even more flood-prone. The Conemaugh River immediately downstream of Johnstown is hemmed in by steep mountain slopes.

Upstream of Johnstown, near the small town of South Fork, the South Fork Dam was built between 1838 and 1853 by the Commonwealth of Pennsylvania as part of a canal water delivery system to be used as a source of water for a canal basin in Johnstown (McCullough, 1968). With railroads superseding canal barge transport, the obsolete South Fork Lake was sold to the Pennsylvania Railroad, and later sold again to private interests. A group of notable Pittsburgh businessmen, including coal and coke magnate Henry Clay Frick and steel magnate Andrew Carnegie, led the group to purchase the reservoir, modify it, and convert it into a private resort lake for wealthy industrial66

Figure 35. Artist’s depiction of South Fork Dam prior to its 1889 failure (National Park Service, 2008).

ists of Pittsburgh. They built cottages and a clubhouse to create the South Fork Fishing and Hunting Club, an exclusive mountain retreat. Membership grew to include over 50 wealthy Pittsburgh steel, coal, and railroad industrialists. Changes to the lake, which was renamed Lake Conemaugh, included lowering the dam that impounded the lake to make its top wide enough to hold a road, and putting a fish screen in the spillway, which unfortunately could also trap debris. These alterations increased the vulnerability of the dam to overtopping.

Lake Conemaugh sat at 450 ft (137 m) in elevation above Johnstown. The lake was about 2 mi (3.2 km) long, approximately 1 mi (1.6 km) wide, and 60 ft (18 m) deep near the dam. The lake had a perimeter of 7 mi (11.2 km) and held 20 million tons of water. When the water was at its highest point in the spring, the lake covered over 400 acres (1.6 km2 ). The dam was 72 ft (22 m) high and 931 ft (284 m) long. Between 1881, when the club was opened, and 1889, the dam frequently leaked and was patched, mostly with mud and straw. Additionally, a previous owner removed and sold for scrap the three cast iron discharge pipes that had allowed a controlled release of water, as a form of safety-related control of the impounded water level. There had been some speculation as to the dam’s integrity, raised by the head of the Cambria Iron Works, which was located directly downstream in Johnstown. Cambria Iron Works, which was Carnegie Steel’s chief competitor, at that time boasted the world’s largest annual steel production.

Despite these concerns, no major corrective action was taken, and the flawed dam continued to impound Lake Conemaugh (McCullough, 1968) as depicted on Figure 35.

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droelectric power generation, and improving dry season flows (Johnson, 1978). In direct response to this national attention, the Ohio River Flood Board was formed to initiate America’s first regional flood mitigation planning. Additional floods impacted Pittsburgh, with the most significant one occurring in March 1936.

That flood peaked at over 30 ft (9.1 m) above normal river level (46.4 ft [14.1 m] actual water depth). This event was then calculated to represent a record-setting 500 year flood, and it is considered as the worst flood to impact the Pittsburgh region and the city to date.

Subsequent engineered flood control was constructed by the U.S. Corps of Engineers in 1938. The severity of the flooding in Pittsburgh was demonstrated to be greatly reduced during the more recent floods that occurred in 1972, associated with Hurricane Agnes, and in 1996, by the system of upstream flood-control reservoirs.

The Great Flood of 1889 On May 31, 1889, approximately 60 mi (97 km) east of Pittsburgh, a man-made disaster of unrivaled proportions took place in the city of Johnstown, PA. It was the Johnstown Flood (or the “Great Flood of 1889” as it became known locally). Although not directly associated with the Pittsburgh region, the flows from the watershed in Johnstown end up in the Allegheny River and ultimately pass the Point at Pittsburgh. Heavy rains poured down over this direct upper sub-basin of the Ohio River for several days (Law, 1997). The area surrounding Johnstown remains naturally prone to flooding due to its position at the confluence of the Little Conemaugh River and Stony Creek, which combine to form the Conemaugh River. The area above Johnstown consists of a 657 mi2 (1,701 km2 ) watershed within the Allegheny Plateau. Adding to these factors, artificial narrowing of the riverbed because of early industrial development made the city even more flood-prone. The Conemaugh River immediately downstream of Johnstown is hemmed in by steep mountain slopes.

Upstream of Johnstown, near the small town of South Fork, the South Fork Dam was built between 1838 and 1853 by the Commonwealth of Pennsylvania as part of a canal water delivery system to be used as a source of water for a canal basin in Johnstown (McCullough, 1968). With railroads superseding canal barge transport, the obsolete South Fork Lake was sold to the Pennsylvania Railroad, and later sold again to private interests. A group of notable Pittsburgh businessmen, including coal and coke magnate Henry Clay Frick and steel magnate Andrew Carnegie, led the group to purchase the reservoir, modify it, and convert it into a private resort lake for wealthy industrial66

Figure 35. Artist’s depiction of South Fork Dam prior to its 1889 failure (National Park Service, 2008).

ists of Pittsburgh. They built cottages and a clubhouse to create the South Fork Fishing and Hunting Club, an exclusive mountain retreat. Membership grew to include over 50 wealthy Pittsburgh steel, coal, and railroad industrialists. Changes to the lake, which was renamed Lake Conemaugh, included lowering the dam that impounded the lake to make its top wide enough to hold a road, and putting a fish screen in the spillway, which unfortunately could also trap debris. These alterations increased the vulnerability of the dam to overtopping.

Lake Conemaugh sat at 450 ft (137 m) in elevation above Johnstown. The lake was about 2 mi (3.2 km) long, approximately 1 mi (1.6 km) wide, and 60 ft (18 m) deep near the dam. The lake had a perimeter of 7 mi (11.2 km) and held 20 million tons of water. When the water was at its highest point in the spring, the lake covered over 400 acres (1.6 km2 ). The dam was 72 ft (22 m) high and 931 ft (284 m) long. Between 1881, when the club was opened, and 1889, the dam frequently leaked and was patched, mostly with mud and straw. Additionally, a previous owner removed and sold for scrap the three cast iron discharge pipes that had allowed a controlled release of water, as a form of safety-related control of the impounded water level. There had been some speculation as to the dam’s integrity, raised by the head of the Cambria Iron Works, which was located directly downstream in Johnstown. Cambria Iron Works, which was Carnegie Steel’s chief competitor, at that time boasted the world’s largest annual steel production.

Despite these concerns, no major corrective action was taken, and the flawed dam continued to impound Lake Conemaugh (McCullough, 1968) as depicted on Figure 35.

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Geology of Pittsburgh

Figure 36. Flood aftermath in Johnstown (National Park Service, 2008).

In late May 1889, a major storm formed over the Midwest, moving east. When the storm struck the Johnstown–South Fork area 2 days later, it was the largest recorded rain event in that part of the country (Law, 1997). The U.S. Army Signal Corps estimated that 6–10 in. (15–25 cm) of rain fell within 24 hours over the entire region of west-central Pennsylvania. During the night, small creeks became roaring torrents, ripping out trees and carrying significant amounts of debris. Most telegraph lines were struck down, and rail lines were washed away. Before long, the Conemaugh River overflowed its banks. At around 3:10 p.m. on May 31, 1889, the South Fork Dam failed, allowing the 20 million tons of Lake Conemaugh to cascade down the narrowly channeled Little Conemaugh River. It took about 40 minutes for the entire lake to drain. As the flood wave made its way to Johnstown, it picked up and carried an immense amount of debris, and there was total devastation in the city (see Figure 36). In some areas of the Little Conemaugh River, the narrowly constrained river transferred the flood at high velocity, and its own valley bottom was eroded down to bedrock. The death and destruction in Johnstown were nothing less than a total catastrophe.

The total death toll was 2,209, making the disaster the largest loss of civilian life in the United States at the time, and South Fork the worst dam failure in United States history when measured in terms of loss of life.

The remnants of the failed dam can be seen in place today as depicted on Figure 37. Following the tragic failure of the South Fork Dam in 1889 and the subsequent failure of Austin Dam in north-central Pennsylvania in 1911 (Greene and Christ, 1998), Pennsylvania instituted one of the first state dam safety commissions in the nation in 1913.

Figure 36. Flood aftermath in Johnstown (National Park Service, 2008).

Figure 37. Current photograph of South Fork Dam depicting abutment remnants (National Park Service, 2008).

The Pittsburgh Flood of 1936 The March 1936 St. Patrick’s Day Flood was the largest flood of record in the Upper Ohio River valley. This flood prompted the passage of the Flood Control Act of 1936 by Congress. Following record floods along the middle Ohio River in January 1937 and the lower Ohio River in March 1937, the 1936 act was amended with more projects and funded in 1938 for the construction of most of the flood protection projects east of the Mississippi River.

The result in the Upper Ohio River Basin was a system that currently consists of 16 federally built floodcontrol and multiple-purpose dams. This reservoir system has proven to have substantially reduced flood damages in Pittsburgh and communities downstream of the city. For example, these projects combined to reduce the 1972 Hurricane Agnes flood by an estimated 12 ft (3.6 m) at Pittsburgh. Without the upstream reservoirs, this flood would have been 2 ft (0.6 m) higher than the record flood level recorded in March 1936.

The January 1996 flood was reduced by 10 ft (3 m) at Pittsburgh; otherwise, it would have equaled the flood elevations recorded during the March 1936 flood.

Coal Mine Subsidence Historical Background Mining in western Pennsylvania was concentrated in the Pittsburgh Coal seam, which was accessed by

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In late May 1889, a major storm formed over the Midwest, moving east. When the storm struck the Johnstown–South Fork area 2 days later, it was the largest recorded rain event in that part of the country (Law, 1997). The U.S. Army Signal Corps estimated that 6–10 in. (15–25 cm) of rain fell within 24 hours over the entire region of west-central Pennsylvania. During the night, small creeks became roaring torrents, ripping out trees and carrying significant amounts of debris. Most telegraph lines were struck down, and rail lines were washed away. Before long, the Conemaugh River overflowed its banks. At around 3:10 p.m. on May 31, 1889, the South Fork Dam failed, allowing the 20 million tons of Lake Conemaugh to cascade down the narrowly channeled Little Conemaugh River. It took about 40 minutes for the entire lake to drain. As the flood wave made its way to Johnstown, it picked up and carried an immense amount of debris, and there was total devastation in the city (see Figure 36). In some areas of the Little Conemaugh River, the narrowly constrained river transferred the flood at high velocity, and its own valley bottom was eroded down to bedrock. The death and destruction in Johnstown were nothing less than a total catastrophe.

The total death toll was 2,209, making the disaster the largest loss of civilian life in the United States at the time, and South Fork the worst dam failure in United States history when measured in terms of loss of life.

The remnants of the failed dam can be seen in place today as depicted on Figure 37. Following the tragic failure of the South Fork Dam in 1889 and the subsequent failure of Austin Dam in north-central Pennsylvania in 1911 (Greene and Christ, 1998), Pennsylvania instituted one of the first state dam safety commissions in the nation in 1913.

Figure 37. Current photograph of South Fork Dam depicting abutment remnants (National Park Service, 2008).

The Pittsburgh Flood of 1936 The March 1936 St. Patrick’s Day Flood was the largest flood of record in the Upper Ohio River valley. This flood prompted the passage of the Flood Control Act of 1936 by Congress. Following record floods along the middle Ohio River in January 1937 and the lower Ohio River in March 1937, the 1936 act was amended with more projects and funded in 1938 for the construction of most of the flood protection projects east of the Mississippi River.

The result in the Upper Ohio River Basin was a system that currently consists of 16 federally built floodcontrol and multiple-purpose dams. This reservoir system has proven to have substantially reduced flood damages in Pittsburgh and communities downstream of the city. For example, these projects combined to reduce the 1972 Hurricane Agnes flood by an estimated 12 ft (3.6 m) at Pittsburgh. Without the upstream reservoirs, this flood would have been 2 ft (0.6 m) higher than the record flood level recorded in March 1936.

The January 1996 flood was reduced by 10 ft (3 m) at Pittsburgh; otherwise, it would have equaled the flood elevations recorded during the March 1936 flood.

Coal Mine Subsidence Historical Background Mining in western Pennsylvania was concentrated in the Pittsburgh Coal seam, which was accessed by

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adits driven into hillsides. From Coal Hill, mining progressed up the Monongahela River valley and over time moved inland away from the river, which was still extensively used for transportation of coal to markets. The land surface above the mines was largely used for pasture or agriculture. In the late 1940s and the 1950s, rapidly expanding suburbs were constructed over both abandoned and active mines. Over the abandoned mines, most problems were related to sinkhole formation in areas of shallow mining.

In abandoned mine areas, concerns for subsidence damage due to pillar failure were mainly limited to schools and large commercial developments. Most active mines, by this time, were using full-extraction room-and-pillar mining. The mining companies had purchased the coal many years before, generally with a waiver of surface damage or the right to legally subside the land surface. However, many coal-mining companies, recognizing social problems, offered protection to surface landowners, and starting in 1957, one company even guaranteed safety from subsidence if approximately 50 percent of the coal was purchased by homeowners and left in place by the mining company. The extent of support for a home was usually determined by providing a zone 15 ft (4.5 m) in width around the periphery of the home. This area was then projected downward and outward at an angle of 15 degrees from the vertical to the level of the mine and referred to by the industry as the angle of draw. This projected area became the recommended area of support defined as the limits of subsidence over a particular mined-out area. Unmined pillars of coal equivalent in area to 50 percent of the support area were left in place to prevent subsidence, as indicated in Figure 38. For an average coal-seam thickness of 6 ft (1.8 m), which is typical of the Pittsburgh Coal, approximately 10,000 tons of coal per acre are present. The cost to purchase support for a single dwelling located a significant distance above a mine was often prohibitive to homeowners. For groups of homes where the support areas overlapped, the shared cost was greatly reduced.

In 10 years, one company that guaranteed surface protection provided support for 635 homes and had to make repairs on approximately 2 percent of the homes (Gray and Meyers, 1970).

The Bituminous Mine Subsidence and Land Conservation Act of 1966 was enacted by the Commonwealth of Pennsylvania to prevent undermining that would damage any public buildings or any noncommercial structures customarily used by the public, such as churches, schools, hospitals, and municipal utilities or municipal public services operations, homes, and cemeteries. This law covered only structures existing at the time of enactment. For new structures, the mining law required subsequent property68

ownership deeds to indicate the existence or lack of existence of subsurface support. Prior to mining, the coal company was required to contact property owners and assign a price for leaving coal pillar support as previously described. If the price was not agreeable to the property owner, then the Secretary of the State Department of Mines and Mineral Industries (now the Pennsylvania Department of Environmental Protection [PADEP], 2014) assigned a mediator to determine just compensation for the coal to be left in place for surface support (Gray and Meyers, 1970). The Surface Mining Control and Reclamation Act of 1977 imposed land-use controls on active mines. This law requires an evaluation of whether subsidence can occur and cause material damage or diminution of use of structures or renewable resource lands. If a potential for damage is present, a plan to prevent or mitigate the damage is required.

Coal Extraction and Subsidence Subsidence does not occur until mining removes a significant amount of coal. Significant factors are related to the geometry of the mine, its depth, and the physical characteristics of the coal and overlying rock strata. In many ways, all interests are met if complete extraction occurs in a large part of the mine that results in subsidence of the ground surface concurrent with mining. Many mines in operation today utilize longwall mining, which removes all coal from large areas, or total-extraction room-and-pillar mining, which systematically removes the coal pillars from one end of a large panel to the other. Total extraction in room-andpillar mines has been practiced in the Pittsburgh region since the latter part of the 19th century.

Subsidence contemporaneous with longwall or total-extraction room-and-pillar mining is similar and ceases in a few months to a few years after mining.

However, other mines only remove a portion of the coal, leaving pillars of coal in place. Uniformly spaced pillars, if of sufficient size relative to the strength of the mine roof, floor, and coal itself, can support the overlying rock strata without subsidence. If the coal pillars are too weak, subsidence will eventually occur. This is the case with many old mines. Subsidence over abandoned mines may continue for many years and is often sporadic.

The availability and quality of mine maps varies throughout the United States. In the Pittsburgh region, mine maps are usually available for all but the earliest or very small mines. Large mining companies became common after the Civil War, resulting in excellent maps. Turka et al. (1996) discussed mine map accuracy.

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adits driven into hillsides. From Coal Hill, mining progressed up the Monongahela River valley and over time moved inland away from the river, which was still extensively used for transportation of coal to markets. The land surface above the mines was largely used for pasture or agriculture. In the late 1940s and the 1950s, rapidly expanding suburbs were constructed over both abandoned and active mines. Over the abandoned mines, most problems were related to sinkhole formation in areas of shallow mining.

In abandoned mine areas, concerns for subsidence damage due to pillar failure were mainly limited to schools and large commercial developments. Most active mines, by this time, were using full-extraction room-and-pillar mining. The mining companies had purchased the coal many years before, generally with a waiver of surface damage or the right to legally subside the land surface. However, many coal-mining companies, recognizing social problems, offered protection to surface landowners, and starting in 1957, one company even guaranteed safety from subsidence if approximately 50 percent of the coal was purchased by homeowners and left in place by the mining company. The extent of support for a home was usually determined by providing a zone 15 ft (4.5 m) in width around the periphery of the home. This area was then projected downward and outward at an angle of 15 degrees from the vertical to the level of the mine and referred to by the industry as the angle of draw. This projected area became the recommended area of support defined as the limits of subsidence over a particular mined-out area. Unmined pillars of coal equivalent in area to 50 percent of the support area were left in place to prevent subsidence, as indicated in Figure 38. For an average coal-seam thickness of 6 ft (1.8 m), which is typical of the Pittsburgh Coal, approximately 10,000 tons of coal per acre are present. The cost to purchase support for a single dwelling located a significant distance above a mine was often prohibitive to homeowners. For groups of homes where the support areas overlapped, the shared cost was greatly reduced.

In 10 years, one company that guaranteed surface protection provided support for 635 homes and had to make repairs on approximately 2 percent of the homes (Gray and Meyers, 1970).

The Bituminous Mine Subsidence and Land Conservation Act of 1966 was enacted by the Commonwealth of Pennsylvania to prevent undermining that would damage any public buildings or any noncommercial structures customarily used by the public, such as churches, schools, hospitals, and municipal utilities or municipal public services operations, homes, and cemeteries. This law covered only structures existing at the time of enactment. For new structures, the mining law required subsequent property68

ownership deeds to indicate the existence or lack of existence of subsurface support. Prior to mining, the coal company was required to contact property owners and assign a price for leaving coal pillar support as previously described. If the price was not agreeable to the property owner, then the Secretary of the State Department of Mines and Mineral Industries (now the Pennsylvania Department of Environmental Protection [PADEP], 2014) assigned a mediator to determine just compensation for the coal to be left in place for surface support (Gray and Meyers, 1970). The Surface Mining Control and Reclamation Act of 1977 imposed land-use controls on active mines. This law requires an evaluation of whether subsidence can occur and cause material damage or diminution of use of structures or renewable resource lands. If a potential for damage is present, a plan to prevent or mitigate the damage is required.

Coal Extraction and Subsidence Subsidence does not occur until mining removes a significant amount of coal. Significant factors are related to the geometry of the mine, its depth, and the physical characteristics of the coal and overlying rock strata. In many ways, all interests are met if complete extraction occurs in a large part of the mine that results in subsidence of the ground surface concurrent with mining. Many mines in operation today utilize longwall mining, which removes all coal from large areas, or total-extraction room-and-pillar mining, which systematically removes the coal pillars from one end of a large panel to the other. Total extraction in room-andpillar mines has been practiced in the Pittsburgh region since the latter part of the 19th century.

Subsidence contemporaneous with longwall or total-extraction room-and-pillar mining is similar and ceases in a few months to a few years after mining.

However, other mines only remove a portion of the coal, leaving pillars of coal in place. Uniformly spaced pillars, if of sufficient size relative to the strength of the mine roof, floor, and coal itself, can support the overlying rock strata without subsidence. If the coal pillars are too weak, subsidence will eventually occur. This is the case with many old mines. Subsidence over abandoned mines may continue for many years and is often sporadic.

The availability and quality of mine maps varies throughout the United States. In the Pittsburgh region, mine maps are usually available for all but the earliest or very small mines. Large mining companies became common after the Civil War, resulting in excellent maps. Turka et al. (1996) discussed mine map accuracy.

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Geology of Pittsburgh

Figure 38. Coal pillar support (Gray and Meyers, 1970).

Figure 38. Coal pillar support (Gray and Meyers, 1970).

Ground Movements over Longwall Mines The angle-of-draw previously defined the limits of subsidence over a particular mined-out area. However, small movements outside the angle of draw associated with longwall mining were recognized about 20 years ago in Australia (Hebblewhite, 2001). Although the mechanism of these movements remains uncertain, possible explanations include one, or a combination of factors such as post-mining stress relaxation, valley bulging, regional joint patterns, shearing of valley walls, and bedding-plane shear failure (Hebblewhite, 2001). These movements, sometimes described as far-field movements, may occur over a mile from the longwall panel and, thus, well outside the angle of draw (Hebblewhite, 2001; Waddington and Associates, 2002).

Similar movements have been recently recognized in southwestern Pennsylvania in studies of longwall mining under Interstate 70 in Washington County, PA, near the split between Interstate 70 and 79 (GeoTDR, Inc., 2001) and in the remedial investigation of leakage from Ryerson Station State Park Dam, located in northwestern Greene County, in 2005 (Hebblewhite

and Gray, 2014). In monitoring the mining under Interstate 70, time domain reflectometry (TDR) cables, installed in deep boreholes, recorded deformation over 1,000 ft (305 m) in front of the advancing mine panel, well beyond the limits of theoretically anticipated movement around the active mine panel (GeoTDR, Inc., 2001). Mining of a longwall panel 2,500 ft (762 m) south of Ryerson Station State Park Dam is the only apparent concurrent cause of beddingplane slip in rock beneath the dam that was recorded by slope inclinometers (Hebblewhite and Gray, 2014).

Subsidence Modes Topographic ground surface subsidence features over mines are classified as sinkholes or troughs (Figure 39). A sinkhole is a depression in the ground surface that occurs from collapse of the overburden into a mine opening (a room or an entry). A trough is a shallow, commonly broad, dish-shaped depression that develops when the overburden sags downward into a mine opening in response to coal extraction, crushing of mine pillars, or punching of pillars into the mine floor. Troughs develop over both active and

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Ground Movements over Longwall Mines The angle-of-draw previously defined the limits of subsidence over a particular mined-out area. However, small movements outside the angle of draw associated with longwall mining were recognized about 20 years ago in Australia (Hebblewhite, 2001). Although the mechanism of these movements remains uncertain, possible explanations include one, or a combination of factors such as post-mining stress relaxation, valley bulging, regional joint patterns, shearing of valley walls, and bedding-plane shear failure (Hebblewhite, 2001). These movements, sometimes described as far-field movements, may occur over a mile from the longwall panel and, thus, well outside the angle of draw (Hebblewhite, 2001; Waddington and Associates, 2002).

Similar movements have been recently recognized in southwestern Pennsylvania in studies of longwall mining under Interstate 70 in Washington County, PA, near the split between Interstate 70 and 79 (GeoTDR, Inc., 2001) and in the remedial investigation of leakage from Ryerson Station State Park Dam, located in northwestern Greene County, in 2005 (Hebblewhite

and Gray, 2014). In monitoring the mining under Interstate 70, time domain reflectometry (TDR) cables, installed in deep boreholes, recorded deformation over 1,000 ft (305 m) in front of the advancing mine panel, well beyond the limits of theoretically anticipated movement around the active mine panel (GeoTDR, Inc., 2001). Mining of a longwall panel 2,500 ft (762 m) south of Ryerson Station State Park Dam is the only apparent concurrent cause of beddingplane slip in rock beneath the dam that was recorded by slope inclinometers (Hebblewhite and Gray, 2014).

Subsidence Modes Topographic ground surface subsidence features over mines are classified as sinkholes or troughs (Figure 39). A sinkhole is a depression in the ground surface that occurs from collapse of the overburden into a mine opening (a room or an entry). A trough is a shallow, commonly broad, dish-shaped depression that develops when the overburden sags downward into a mine opening in response to coal extraction, crushing of mine pillars, or punching of pillars into the mine floor. Troughs develop over both active and

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Gray, Greene, Fandray, and Turka

Figure 39. Modes of mine subsidence (Gray, 1999).

Figure 39. Modes of mine subsidence (Gray, 1999).

abandoned mines. There appears to be no safe depth of mining that prevents trough development.

Sinkholes generally develop where the cover above a mine is relatively thin (Figure 40). Competent strata above the coal limit sinkhole development (Figure 39).

Piggott and Eynon (1978) indicated that sinkhole development normally occurs where the interval to the ground surface is less than three to five times the thickness of the extracted seam and that the maximum overburden interval is up to 10 times the thickness of the extracted seam. In western Pennsylvania, most sinkholes develop where the soil and rock above a mine are less than 50 ft (15 m) thick (Bruhn et al., 1978). A study of subsidence in the Pittsburgh area revealed that

Figure 40. Coal mine sinkhole (photo by S. English, 1969).

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the majority of sinkholes, which constituted about 95 percent of all reported subsidence incidents, occurred on sites located less than 60 ft (18 m) above mine level (Bruhn et al., 1981).

Abandoned Mines Figures 41 and 42 show subsidence damage over abandoned mines. It appears that:

abandoned mines. There appears to be no safe depth of mining that prevents trough development.

Sinkholes generally develop where the cover above a mine is relatively thin (Figure 40). Competent strata above the coal limit sinkhole development (Figure 39).

Piggott and Eynon (1978) indicated that sinkhole development normally occurs where the interval to the ground surface is less than three to five times the thickness of the extracted seam and that the maximum overburden interval is up to 10 times the thickness of the extracted seam. In western Pennsylvania, most sinkholes develop where the soil and rock above a mine are less than 50 ft (15 m) thick (Bruhn et al., 1978). A study of subsidence in the Pittsburgh area revealed that

Figure 41. Building damage caused by subsidence, with coal at 175 ft (53 m) depth (Gray, 1999).

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Figure 40. Coal mine sinkhole (photo by S. English, 1969).

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the majority of sinkholes, which constituted about 95 percent of all reported subsidence incidents, occurred on sites located less than 60 ft (18 m) above mine level (Bruhn et al., 1981).

Abandoned Mines Figures 41 and 42 show subsidence damage over abandoned mines. It appears that:

Figure 41. Building damage caused by subsidence, with coal at 175 ft (53 m) depth (Gray, 1999).

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Geology of Pittsburgh

Figure 42. House damaged by sinkhole subsidence, Connellsville, PA (photo by R. Turka, 1979).

(1) unless total extraction has occurred, there is no overburden interval above an abandoned mine that is safe from subsidence, nor is there necessarily a reduction in severity of damage with an increased overburden interval; (2) subsidence occurs at reduced frequency with increasing overburden thickness; and (3) unless total extraction has been achieved, subsidence may occur long after mining and may not be limited to a single episode (Gray, 1988).

Item (3) implies that the possibility of future subsidence at a site cannot be ruled out merely because subsidence has not occurred in the first 50 to 100 years after mining. If abandoned mine openings beneath a site have not been designed for long-term stability, the potential for subsidence remains until the openings collapse, or until they are stabilized by backfilling, grout columns, or some other means of engineered remedial ground support (Gray et al., 1974). Precisely when collapse might take place in the absence of stabilization is not predictable. Even after subsidence has taken place at a particular site, the possibility of future additional subsidence may remain. Multiple episodes of subsidence have been documented at many sites in the Pittsburgh region (Gray et al., 1977). Pillar failure can fall into three general categories: delayed, progressive, or sporadic (Abel and Lee, 1980). Site surveillance programs of a few months’ duration or, in fact, indefinite duration cannot provide definitive evidence that a site overlying a mine with open voids will not experience future subsidence (Bruhn et al., 1981).

Insurance programs to provide assistance if and when subsidence occurs appear to be desirable (DuMontelle et al., 1981). Pennsylvania and other states have mine-subsidence insurance programs. Such

Geology of Pittsburgh

an approach appears to be more desirable than largescale urban stabilization programs for residential areas (Gray, 1983).

an approach appears to be more desirable than largescale urban stabilization programs for residential areas (Gray, 1983).

Volcanism

Volcanism

The Pittsburgh region contains no volcanoes or volcanic deposits. The closest volcano to Pittsburgh, Mount Tremblant, is almost 500 mi (800 km) north in Quebec Province, Canada. However, in 1766, Reverend Charles Beatty, a well-educated English Presbyterian minister, visited Pittsburgh and climbed Coal Hill where British Soldiers were mining the Pittsburgh Coal. Reverend Beatty wrote in his journal:

The Pittsburgh region contains no volcanoes or volcanic deposits. The closest volcano to Pittsburgh, Mount Tremblant, is almost 500 mi (800 km) north in Quebec Province, Canada. However, in 1766, Reverend Charles Beatty, a well-educated English Presbyterian minister, visited Pittsburgh and climbed Coal Hill where British Soldiers were mining the Pittsburgh Coal. Reverend Beatty wrote in his journal:

“In the afternoon we cross the Mocconghehela River accompanied by two gentlemen, and went up the hill opposite the fort, but a very difficult ascent, in order to take a view of that part of it more particularly from which the garrison is supplied with coals, which is not far from the top. A fire being made by the workmen not far from the place where they dug the coal, and left burning when they went away, by the small dust communicated itself to the body of the coals and set it on fire, and has now been burning almost a twelve month entirely underground, for the space of twenty yards or more along the face of the hill or rock, the way the vein of coal extends, the smoke ascending up through the chinks of the rocks. The earth in some places is so warm that we could hardly bear to stand upon it: at one place where the smoke came up we opened a hole in the earth till it was so hot as to burn paper thrown into it; the steam that came out was so strong of sulphur that we could scare bear it. We found pieces of matter there, some of which appeared to be sulphur, other nitre, and some a mixture of both. If these strata be large in this mountain it may become a volcano. The smoke arising out of this mountain appears to be much greater in rainy weather than at other times. The fire has already undermined some part of the mountain so that great fragments of it, and trees with their roots are fallen down its face. On the top of the Mountain is a very rich soil covered with fine verdure, and has a very easy slope on the other side, so that it may be easily cultivated.” (Eavenson, 1942, p. 25)

Figure 42. House damaged by sinkhole subsidence, Connellsville, PA (photo by R. Turka, 1979).

(1) unless total extraction has occurred, there is no overburden interval above an abandoned mine that is safe from subsidence, nor is there necessarily a reduction in severity of damage with an increased overburden interval; (2) subsidence occurs at reduced frequency with increasing overburden thickness; and (3) unless total extraction has been achieved, subsidence may occur long after mining and may not be limited to a single episode (Gray, 1988).

Although, today such a ridiculous idea is amusing, at that time it was the accepted wisdom in Europe.

Abraham Werner, the most renowned geologist in Europe, believed coal was the fuel of volcanoes into the 1800s (Adams, 1938).

Acid Rock Acid rock drainage is the water-quality hazard resulting from the oxidation of iron sulfide minerals (Nordstrom and Alpers, 1999). In the Pittsburgh area and elsewhere in the coal-bearing Pennsylvanian-age rocks, it is common to encounter acid mine drainage generated by coal and pyritic shale.

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Item (3) implies that the possibility of future subsidence at a site cannot be ruled out merely because subsidence has not occurred in the first 50 to 100 years after mining. If abandoned mine openings beneath a site have not been designed for long-term stability, the potential for subsidence remains until the openings collapse, or until they are stabilized by backfilling, grout columns, or some other means of engineered remedial ground support (Gray et al., 1974). Precisely when collapse might take place in the absence of stabilization is not predictable. Even after subsidence has taken place at a particular site, the possibility of future additional subsidence may remain. Multiple episodes of subsidence have been documented at many sites in the Pittsburgh region (Gray et al., 1977). Pillar failure can fall into three general categories: delayed, progressive, or sporadic (Abel and Lee, 1980). Site surveillance programs of a few months’ duration or, in fact, indefinite duration cannot provide definitive evidence that a site overlying a mine with open voids will not experience future subsidence (Bruhn et al., 1981).

Insurance programs to provide assistance if and when subsidence occurs appear to be desirable (DuMontelle et al., 1981). Pennsylvania and other states have mine-subsidence insurance programs. Such

“In the afternoon we cross the Mocconghehela River accompanied by two gentlemen, and went up the hill opposite the fort, but a very difficult ascent, in order to take a view of that part of it more particularly from which the garrison is supplied with coals, which is not far from the top. A fire being made by the workmen not far from the place where they dug the coal, and left burning when they went away, by the small dust communicated itself to the body of the coals and set it on fire, and has now been burning almost a twelve month entirely underground, for the space of twenty yards or more along the face of the hill or rock, the way the vein of coal extends, the smoke ascending up through the chinks of the rocks. The earth in some places is so warm that we could hardly bear to stand upon it: at one place where the smoke came up we opened a hole in the earth till it was so hot as to burn paper thrown into it; the steam that came out was so strong of sulphur that we could scare bear it. We found pieces of matter there, some of which appeared to be sulphur, other nitre, and some a mixture of both. If these strata be large in this mountain it may become a volcano. The smoke arising out of this mountain appears to be much greater in rainy weather than at other times. The fire has already undermined some part of the mountain so that great fragments of it, and trees with their roots are fallen down its face. On the top of the Mountain is a very rich soil covered with fine verdure, and has a very easy slope on the other side, so that it may be easily cultivated.” (Eavenson, 1942, p. 25)

Although, today such a ridiculous idea is amusing, at that time it was the accepted wisdom in Europe.

Abraham Werner, the most renowned geologist in Europe, believed coal was the fuel of volcanoes into the 1800s (Adams, 1938).

Acid Rock Acid rock drainage is the water-quality hazard resulting from the oxidation of iron sulfide minerals (Nordstrom and Alpers, 1999). In the Pittsburgh area and elsewhere in the coal-bearing Pennsylvanian-age rocks, it is common to encounter acid mine drainage generated by coal and pyritic shale.

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However, acid rock drainage resulting from other sources was virtually unknown in the area until 2003.

At that time, an excavation for Interstate 99 (I-99) at the Skytop site on Bald Eagle Mountain, located to the west of State College in Centre County, PA, exposed pyrite-rich rocks associated with a zinc-lead deposit within a sandstone ridge. As part of the I-99 work, this sandstone was excavated, crushed, and used locally as road base and fill. Within months, acidic (pH <3), metal-laden seeps and surface runoff were generated from the crushed rock fill and the exposed pyritic deposits in the road cut. This raised concerns about surface water and groundwater contamination and prompted a halt in road construction and the beginning of a costly program of environmental remediation. The Skytop site posed a reclamation challenge because the road base and fills were deposited over a large area, there was a lack of neutralizing minerals in the host rock, and the acidic drainage exhibited low pH and a complex chemistry. The situation at Skytop was more extreme than situations involving acid mine drainage from coal mines and is comparable to environmental problems that develop at abandoned metal mines (Hammarstrom et al., 2005). Pennsylvania had developed special handling techniques for coal surface mines spoil and for acid-producing materials in highway construction prior to the Skytop incident. However, pyrite-rich sandstones such as those encountered at Skytop had not been identified prior to the highway excavation, and, therefore, no plans were prepared for handling the acid rock. The potential for situations similar to what had happened at Skytop, where unexpected acid rock might be encountered, prompted the Pennsylvania Geological Survey to prepare a publication on acid rock in the commonwealth.

The resultant open-file publication (Pennsylvania Geological Survey, 2005) includes a map showing the formations that may contain acid-forming minerals (primarily pyrite). The publication also includes text describing each of the formations. In the Pittsburgh area, the identified areas correspond with the coalbearing formations.

TRANSPORTATION The regional topography, consisting of major rivers, steep hillsides, and flat hilltops, resulting from the underlying geology required a unique transportation infrastructure in Pittsburgh that included roads, tunnels, bridges, railroads, inclines, bike paths, and stairways.

Most of the transportation methods were used to move resources to local and distant markets. Pittsburgh’s strategic location as a “gateway to the West” resulted in use of the river valleys as the primary transportation corridors, as they still are today.

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Canals Philadelphia had been the leading seaport on the Atlantic Coast in the 1700s, but in the early 1800s, completion of the Erie Canal to the north, connecting New York City to the Great Lakes via the Hudson and Mohawk Rivers, and Maryland’s National Road to the south, connecting Baltimore to the Ohio River at Wheeling, WV (Shank, 1981), resulted in the growth of those two seaports as the emergent gateways to the great American West. People and goods transported through Pennsylvania from the east coast to Pittsburgh were moved primarily by coaches and wagons via a system of locally owned and constructed turnpikes.

Movement of people and freight by this pioneer system was slow and of limited capacity, resulting in high transportation costs. Conestoga wagons were used to carry freight over the roads and took about 23 days to go from Philadelphia to Pittsburgh.

Pennsylvania constructed a system of canals in order to improve the transportation from Philadelphia and the east coast to Pittsburgh and to compete with New York City and Baltimore. The trunk section of the Pennsylvania Canal system, referred to as the Main Line of Public Works, ran from Philadelphia to Pittsburgh and covered a distance of 395 mi (636 km). Construction began in 1826, and the final link, the Allegheny Portage Railroad, was completed in 1834.

The canal boats moved at an average of about 4 mi per hour (mph) (6.4 kilometers per hour). The canals were generally 40 ft (12 m) wide and 4 ft (1.2 m) deep with locks to change elevation. There were towpaths on either side of the canals for the animals pulling the canal boats. The canal boats could carry the same loads as the Conestoga wagons and shortened the trip from Philadelphia to Pittsburgh to about 4.5 days and later to 3.5 days when steam locomotives replaced animals on the canal towpaths. The boats varied in size, with the largest being 79 ft (23 m) long and capable of carrying 25 passengers and 30 tons (27 metric tons) of freight (Shank, 1981).

The canal approached Pittsburgh along the north side of the Allegheny River and then split; one branch extended to the north shore of the Allegheny River for access to the Ohio River, and the other branch passed over the Allegheny River and into Pittsburgh via an aqueduct that was 1,100 ft (335 m) long (Figure 43).

From the aqueduct, the canal passed to the main terminal and turning basin. The canal continued to the south through a tunnel completed in 1828 and ended on the south side of the city at a lock structure providing access to the Monongahela River. Originally, the plan had been to extend the Chesapeake and Ohio (C&O) Canal to Pittsburgh and connect the two canal systems at the lock structure, but the C&O canal was

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However, acid rock drainage resulting from other sources was virtually unknown in the area until 2003.

At that time, an excavation for Interstate 99 (I-99) at the Skytop site on Bald Eagle Mountain, located to the west of State College in Centre County, PA, exposed pyrite-rich rocks associated with a zinc-lead deposit within a sandstone ridge. As part of the I-99 work, this sandstone was excavated, crushed, and used locally as road base and fill. Within months, acidic (pH <3), metal-laden seeps and surface runoff were generated from the crushed rock fill and the exposed pyritic deposits in the road cut. This raised concerns about surface water and groundwater contamination and prompted a halt in road construction and the beginning of a costly program of environmental remediation. The Skytop site posed a reclamation challenge because the road base and fills were deposited over a large area, there was a lack of neutralizing minerals in the host rock, and the acidic drainage exhibited low pH and a complex chemistry. The situation at Skytop was more extreme than situations involving acid mine drainage from coal mines and is comparable to environmental problems that develop at abandoned metal mines (Hammarstrom et al., 2005). Pennsylvania had developed special handling techniques for coal surface mines spoil and for acid-producing materials in highway construction prior to the Skytop incident. However, pyrite-rich sandstones such as those encountered at Skytop had not been identified prior to the highway excavation, and, therefore, no plans were prepared for handling the acid rock. The potential for situations similar to what had happened at Skytop, where unexpected acid rock might be encountered, prompted the Pennsylvania Geological Survey to prepare a publication on acid rock in the commonwealth.

The resultant open-file publication (Pennsylvania Geological Survey, 2005) includes a map showing the formations that may contain acid-forming minerals (primarily pyrite). The publication also includes text describing each of the formations. In the Pittsburgh area, the identified areas correspond with the coalbearing formations.

TRANSPORTATION The regional topography, consisting of major rivers, steep hillsides, and flat hilltops, resulting from the underlying geology required a unique transportation infrastructure in Pittsburgh that included roads, tunnels, bridges, railroads, inclines, bike paths, and stairways.

Most of the transportation methods were used to move resources to local and distant markets. Pittsburgh’s strategic location as a “gateway to the West” resulted in use of the river valleys as the primary transportation corridors, as they still are today.

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Canals Philadelphia had been the leading seaport on the Atlantic Coast in the 1700s, but in the early 1800s, completion of the Erie Canal to the north, connecting New York City to the Great Lakes via the Hudson and Mohawk Rivers, and Maryland’s National Road to the south, connecting Baltimore to the Ohio River at Wheeling, WV (Shank, 1981), resulted in the growth of those two seaports as the emergent gateways to the great American West. People and goods transported through Pennsylvania from the east coast to Pittsburgh were moved primarily by coaches and wagons via a system of locally owned and constructed turnpikes.

Movement of people and freight by this pioneer system was slow and of limited capacity, resulting in high transportation costs. Conestoga wagons were used to carry freight over the roads and took about 23 days to go from Philadelphia to Pittsburgh.

Pennsylvania constructed a system of canals in order to improve the transportation from Philadelphia and the east coast to Pittsburgh and to compete with New York City and Baltimore. The trunk section of the Pennsylvania Canal system, referred to as the Main Line of Public Works, ran from Philadelphia to Pittsburgh and covered a distance of 395 mi (636 km). Construction began in 1826, and the final link, the Allegheny Portage Railroad, was completed in 1834.

The canal boats moved at an average of about 4 mi per hour (mph) (6.4 kilometers per hour). The canals were generally 40 ft (12 m) wide and 4 ft (1.2 m) deep with locks to change elevation. There were towpaths on either side of the canals for the animals pulling the canal boats. The canal boats could carry the same loads as the Conestoga wagons and shortened the trip from Philadelphia to Pittsburgh to about 4.5 days and later to 3.5 days when steam locomotives replaced animals on the canal towpaths. The boats varied in size, with the largest being 79 ft (23 m) long and capable of carrying 25 passengers and 30 tons (27 metric tons) of freight (Shank, 1981).

The canal approached Pittsburgh along the north side of the Allegheny River and then split; one branch extended to the north shore of the Allegheny River for access to the Ohio River, and the other branch passed over the Allegheny River and into Pittsburgh via an aqueduct that was 1,100 ft (335 m) long (Figure 43).

From the aqueduct, the canal passed to the main terminal and turning basin. The canal continued to the south through a tunnel completed in 1828 and ended on the south side of the city at a lock structure providing access to the Monongahela River. Originally, the plan had been to extend the Chesapeake and Ohio (C&O) Canal to Pittsburgh and connect the two canal systems at the lock structure, but the C&O canal was

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 43. Pittsburgh map showing canal (Darby, 1828).

Figure 43. Pittsburgh map showing canal (Darby, 1828).

never extended that far. The original aqueduct over the Allegheny River was replaced in 1844 by John A. Roebling’s first wire cable suspension bridge, the Allegheny Aqueduct (ExplorePAHistory, 2014, Roeblings). Mr. Roebling lived at that time in Saxonburg, PA, about an hour north of Pittsburgh, where he was attempting to establish a settlement of German immigrants. In 1841, he also obtained a contract to replace the hemp ropes used to pull the boats on the Portage Railroad with wire rope, and he built a factory at Saxonburg to make the needed cable. Aside from the Allegheny Aqueduct, he also designed two other suspension bridges in the city, the Smithfield Street Bridge over the Monongahela River in 1846, which was replaced in 1883, and the Sixth Street Bridge over the Allegheny River in 1859, which was also replaced multiple times and now has a different name.

In 1854, the Pennsylvania Railroad initiated rail service between Philadelphia and Pittsburgh, reducing the travel time to only 13 hours. The railroads quickly made the canals obsolete, and the canal system was eventually sold at a loss to the Pennsylvania Railroad in 1857. They briefly ran the system and then shut it down, using some sections for rail lines and continuing to operate other sections. The last canal section near Harrisburg was shut down in 1901.

The canal tunnel that carried the canal from the Allegheny to the Monongahela River was uncovered during the foundation excavation for the USX Tower (built as the headquarters office of U.S. Steel) in 1967 (now UPMC Building). Figure 44 shows the tunnel

Figure 44. Tunnels exposed during USX Tower construction (Rathke, 1968).

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never extended that far. The original aqueduct over the Allegheny River was replaced in 1844 by John A. Roebling’s first wire cable suspension bridge, the Allegheny Aqueduct (ExplorePAHistory, 2014, Roeblings). Mr. Roebling lived at that time in Saxonburg, PA, about an hour north of Pittsburgh, where he was attempting to establish a settlement of German immigrants. In 1841, he also obtained a contract to replace the hemp ropes used to pull the boats on the Portage Railroad with wire rope, and he built a factory at Saxonburg to make the needed cable. Aside from the Allegheny Aqueduct, he also designed two other suspension bridges in the city, the Smithfield Street Bridge over the Monongahela River in 1846, which was replaced in 1883, and the Sixth Street Bridge over the Allegheny River in 1859, which was also replaced multiple times and now has a different name.

In 1854, the Pennsylvania Railroad initiated rail service between Philadelphia and Pittsburgh, reducing the travel time to only 13 hours. The railroads quickly made the canals obsolete, and the canal system was eventually sold at a loss to the Pennsylvania Railroad in 1857. They briefly ran the system and then shut it down, using some sections for rail lines and continuing to operate other sections. The last canal section near Harrisburg was shut down in 1901.

The canal tunnel that carried the canal from the Allegheny to the Monongahela River was uncovered during the foundation excavation for the USX Tower (built as the headquarters office of U.S. Steel) in 1967 (now UPMC Building). Figure 44 shows the tunnel

Figure 44. Tunnels exposed during USX Tower construction (Rathke, 1968).

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as it was exposed during construction, along with a nearby rail tunnel.

River Navigation Structures Since early settlement of western Pennsylvania, the three rivers have served the region for basic transportation and shipment of goods and cargo by barges. As pushed by towboats, this transport mode continues, commonly referred to as “tows.” The amount of coal transported down river from Pittsburgh jumped greatly following the Civil War (Johnson, 1978). The size of the tows also grew with the amount of coal hauled for its increasing down-river demand.

Due to the escalating coal trade, the U.S. Army Corps of Engineers began studying methods to produce a reliable navigation depth on the Ohio River.

The U.S. Army Corps of Engineers launched an international study to analyze other navigation projects worldwide. The study led to the determination that construction of an integrated system of locks and dams, each forming a downstream pool (defined as a reach of artificially deepened river) was the best solution to meet the demands of growing navigation industry. The increased storage capacity of each “pool” increased the amount of river water that could be managed by sequential release from each pool proceeding down river.

Opening of the first lock and dam on the Ohio at Davis Island in 1885, located downstream of Pittsburgh, proved to be a significant technologic advance for the civil engineering profession at large. At Davis Island Lock and Dam, the wooden timber wicket dam was almost 1,900 ft (579 m) long, and the dimensionstone masonry lock, at 600 ft (183 m) long and 110 ft (36 m) wide, was the world’s largest river navigation structure at that time. Even then, the stone-masonry lock at Davis Island was wider than the reinforced concrete locks built in 1914 at the Panama Canal (Johnson, 1978).

In 1910, the Rivers and Harbors Act was authorized

by Congress, providing for the systematic construction of a system of locks and dams along the Ohio River, and this project was completed in 1929. The project produced 51 wooden wicket dams and typical lock chambers 600 ft (183 m) long by 110 ft (36 m) wide lock chambers along the length of the river starting at Pittsburgh. Wicket dams were composed of moveable slab sections that were hinged at the bottom and held upright by adjustable props. Wicket dams in the Pittsburgh region were the earliest to be replaced by mass concrete dams.

Taken together, the systems of locks and dams on the three rivers of the Pittsburgh region have been 74

described as “rivers that are highways.” Even today, they are the most efficient means by which to move bulk commodities such as coal and construction aggregates and, as such, are more cost effective than rail or truck transport. Throughout the late 19th and early 20th centuries, the Monongahela River has carried a greater tonnage than any other inland river in America (Johnson, 1978). In comparison with the mighty Ohio and Mississippi Rivers, the Monongahela River was called the “Little Giant” because of the tonnage it transported annually. Moving coal to steel mills in the western Pennsylvania towns upstream and downstream of Pittsburgh was of great importance, especially to the war effort in the late 1930s and early 1940s.

During the 1940s, a shift from steam-propelled to diesel-powered towboats allowed for larger tows on the river. However, this meant that tows had to be disassembled, in order to lock all the barges through in multiple lockages, and then reassembled before continuing. This functional inconvenience backed up river traffic and increased expenses for the river towboat industry. Even as modernization of locks in the lower Ohio River was initiated in the 1950s to handle the larger tows, the locks in the Pittsburgh region remained unchanged. In the upper Ohio River, nearest Pittsburgh, each river navigation dam was a gated type or a simple concrete weir, which had two parallel, adjoining locks: one 600 ft (183 m) by 110 ft (36 m) main chamber and a 360 ft (110 m) long by 56 ft (17 m) wide auxiliary chamber.

The Pittsburgh District of the U.S. Corps of Engineers currently operates and maintains 23 locks and dams on the three rivers (see Figure 45). This represents the largest number of navigation projects in any district of the corps, and it systematically provides a 9 ft (2.6 m) minimum navigation “pool” depth.

In the 1990s, a new lock and dam project was built on the Monongahela River south of Pittsburgh. The project was Grays Landing Locks and Dam, and it involved traditional cofferdam construction. Steel sheet piles were used to form a series of interconnecting coffer cells. Once completed, the inner cofferdam area was pumped dry. Excavation of alluvial sediments was carried down to “top of bedrock.” At these variable depths, additional rock removal was continued in order to establish a foundation within competent bedrock. Once the final excavation was performed, concrete was placed on the prepared rock foundation.

Recent construction involved the 2004 completion of a new gated dam on the Monongahela River, known as Braddock Locks and Dam, located 11 mi (18 km) upstream of Pittsburgh. This project employed innovative float-in construction techniques,

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as it was exposed during construction, along with a nearby rail tunnel.

River Navigation Structures Since early settlement of western Pennsylvania, the three rivers have served the region for basic transportation and shipment of goods and cargo by barges. As pushed by towboats, this transport mode continues, commonly referred to as “tows.” The amount of coal transported down river from Pittsburgh jumped greatly following the Civil War (Johnson, 1978). The size of the tows also grew with the amount of coal hauled for its increasing down-river demand.

Due to the escalating coal trade, the U.S. Army Corps of Engineers began studying methods to produce a reliable navigation depth on the Ohio River.

The U.S. Army Corps of Engineers launched an international study to analyze other navigation projects worldwide. The study led to the determination that construction of an integrated system of locks and dams, each forming a downstream pool (defined as a reach of artificially deepened river) was the best solution to meet the demands of growing navigation industry. The increased storage capacity of each “pool” increased the amount of river water that could be managed by sequential release from each pool proceeding down river.

Opening of the first lock and dam on the Ohio at Davis Island in 1885, located downstream of Pittsburgh, proved to be a significant technologic advance for the civil engineering profession at large. At Davis Island Lock and Dam, the wooden timber wicket dam was almost 1,900 ft (579 m) long, and the dimensionstone masonry lock, at 600 ft (183 m) long and 110 ft (36 m) wide, was the world’s largest river navigation structure at that time. Even then, the stone-masonry lock at Davis Island was wider than the reinforced concrete locks built in 1914 at the Panama Canal (Johnson, 1978).

In 1910, the Rivers and Harbors Act was authorized

by Congress, providing for the systematic construction of a system of locks and dams along the Ohio River, and this project was completed in 1929. The project produced 51 wooden wicket dams and typical lock chambers 600 ft (183 m) long by 110 ft (36 m) wide lock chambers along the length of the river starting at Pittsburgh. Wicket dams were composed of moveable slab sections that were hinged at the bottom and held upright by adjustable props. Wicket dams in the Pittsburgh region were the earliest to be replaced by mass concrete dams.

Taken together, the systems of locks and dams on the three rivers of the Pittsburgh region have been 74

described as “rivers that are highways.” Even today, they are the most efficient means by which to move bulk commodities such as coal and construction aggregates and, as such, are more cost effective than rail or truck transport. Throughout the late 19th and early 20th centuries, the Monongahela River has carried a greater tonnage than any other inland river in America (Johnson, 1978). In comparison with the mighty Ohio and Mississippi Rivers, the Monongahela River was called the “Little Giant” because of the tonnage it transported annually. Moving coal to steel mills in the western Pennsylvania towns upstream and downstream of Pittsburgh was of great importance, especially to the war effort in the late 1930s and early 1940s.

During the 1940s, a shift from steam-propelled to diesel-powered towboats allowed for larger tows on the river. However, this meant that tows had to be disassembled, in order to lock all the barges through in multiple lockages, and then reassembled before continuing. This functional inconvenience backed up river traffic and increased expenses for the river towboat industry. Even as modernization of locks in the lower Ohio River was initiated in the 1950s to handle the larger tows, the locks in the Pittsburgh region remained unchanged. In the upper Ohio River, nearest Pittsburgh, each river navigation dam was a gated type or a simple concrete weir, which had two parallel, adjoining locks: one 600 ft (183 m) by 110 ft (36 m) main chamber and a 360 ft (110 m) long by 56 ft (17 m) wide auxiliary chamber.

The Pittsburgh District of the U.S. Corps of Engineers currently operates and maintains 23 locks and dams on the three rivers (see Figure 45). This represents the largest number of navigation projects in any district of the corps, and it systematically provides a 9 ft (2.6 m) minimum navigation “pool” depth.

In the 1990s, a new lock and dam project was built on the Monongahela River south of Pittsburgh. The project was Grays Landing Locks and Dam, and it involved traditional cofferdam construction. Steel sheet piles were used to form a series of interconnecting coffer cells. Once completed, the inner cofferdam area was pumped dry. Excavation of alluvial sediments was carried down to “top of bedrock.” At these variable depths, additional rock removal was continued in order to establish a foundation within competent bedrock. Once the final excavation was performed, concrete was placed on the prepared rock foundation.

Recent construction involved the 2004 completion of a new gated dam on the Monongahela River, known as Braddock Locks and Dam, located 11 mi (18 km) upstream of Pittsburgh. This project employed innovative float-in construction techniques,

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 45. Location of locks and dams on Pittsburgh’s three rivers (photo courtesy of the Port of Pittsburgh Commission).

Figure 45. Location of locks and dams on Pittsburgh’s three rivers (photo courtesy of the Port of Pittsburgh Commission).

which involved two large precast segments set down on nearly 90 reinforced concrete drilled shafts embedded 16 ft (4.9 m) into bedrock (Edwardo et al., 2002). In addition, construction is currently under way at Charleroi Locks and Dam, located 40 mi (64 km) upstream of Pittsburgh, which will provide two new lock chambers 720 ft (220 m) long by 84 ft (26 m) wide.

Rail Systems When Pittsburgh was incorporated as a city in 1816, it was the major center for commerce in the west, and most travel from the east coast went through it.

Around 1830, the commerce aspect of Pittsburgh’s economy was surpassed by its manufacturing base. To transport bulk goods, including coal, an economical

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which involved two large precast segments set down on nearly 90 reinforced concrete drilled shafts embedded 16 ft (4.9 m) into bedrock (Edwardo et al., 2002). In addition, construction is currently under way at Charleroi Locks and Dam, located 40 mi (64 km) upstream of Pittsburgh, which will provide two new lock chambers 720 ft (220 m) long by 84 ft (26 m) wide.

Rail Systems When Pittsburgh was incorporated as a city in 1816, it was the major center for commerce in the west, and most travel from the east coast went through it.

Around 1830, the commerce aspect of Pittsburgh’s economy was surpassed by its manufacturing base. To transport bulk goods, including coal, an economical

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Gray, Greene, Fandray, and Turka

and reliable mode of transportation was needed. The first rationally designed transportation network was the local railroad. This system was intended to transfer coal and goods to the industries within and surrounding Pittsburgh. Topography initially restricted population growth to the city and railroad corridor expansion to the river valleys. However, with the development of the abundant Pittsburgh Coal seam, which resulted in newly established farm roads and communities in these mining areas, the railroad lines began following the contours of the nearly flat-lying Pittsburgh Coal seam. Bridge structures developed as the railroads required “jumping” from one hillside to another to be in close contact with the mining areas. Like all other railroads of that time, they relied on horses or mules for power. Not much faster than wagons or canal boats, their main advantage was smooth-running rails.

The transition to the widespread interstate railroad system was a long battle. Pennsylvania had no urgent reason to invest in railroad technology until 1825, when the Erie Canal linked New York City’s ports to Midwest markets (Finch, 1988). Once the Erie Canal opened, shipping costs from New York to the Midwest dropped significantly, and the time it took to ship the goods was cut significantly. This greatly increased trade for New York City businesses while bypassing Pittsburgh and Philadelphia.

Shipping by water was still cheaper than by rail, but the railroads did have the advantage of traveling where rivers didn’t flow. A result was the combined use of trains and rivers together (Fleming, 1916).

Started in 1834, the state-owned Main Line of Public Works used canal boats where possible on relatively level ground and a combination of gravity and stationary steam engines where necessary in the mountains (Baer, 1996). This patchwork of canals, railroads, and inclined planes offered a 3 to 4 day journey from Philadelphia to Pittsburgh. However, it was soon ended by the cheaper, all-purpose, all-weather railroads. The interstate railroads entered the area in the 1850s. In 1852, the Ohio and Pennsylvania Railroad began service between Cleveland and Allegheny City (present-day North Side), and in 1854, the Pennsylvania Railroad began service between Pittsburgh and Philadelphia. An historical map of the Pittsburgh railroads is shown on Figure 46. A journey between Philadelphia and Pittsburgh now took only 13 hours.

The Pennsylvania Railroad was the largest railroad in the world for much of its 121 year life span, absorbing many other railroads as it grew. It hauled more freight and passengers than any other railroad in the world during that time (Baer, 1996).

The railroad system in Pittsburgh flourished for many years. From the beginning of the industrial era through its collapse in the 1980s, Pittsburgh was al76

Gray, Greene, Fandray, and Turka

ways a key market for the nation’s largest and most important railroads. At one time, up to 22 railroads, including main lines and branches, entered Pittsburgh (Fleming, 1916). They comprised the lines of the Pennsylvania System, the New York Central Lines, the Baltimore and Ohio, the Buffalo, Rochester and Pittsburgh, the Pittsburgh, Bessemer and Lake Erie (the Carnegie Road), and the Wabash. However, with the coming of publicly funded highways and the availability of automobiles after World War II, railroads began a long downward slide. Despite the near collapse of heavy industry in the northeast, Pittsburgh still remains an important link in the nation’s rail network. Current railroads in Pittsburgh include: Norfolk Southern, CSX, Amtrak, Wheeling & Lake Erie, and the Allegheny Valley Railroad.

Another rail system that once existed in Pittsburgh was the inter-city trolley car. It started in the late 1800s and early 1900s and followed the farm roads lying at the ridge tops, the alignments of the railroad network, and many abandoned railroad corridors. They became most popular in the 1940s and 1950s as an economical mass-transit solution for the expanding city of Pittsburgh (see Figure 47). A fleet of more than 600 trolleys was in use in 1948 (Bennear, 1995). The demise of the trolley was due to the speed and flexibility of gasolinepowered buses. By the early 1970s, the fleet had dwindled to 95 cars and 4 lines. By 1985, almost all trolley rails were overlain by asphalt, with few cars and lines existing. Today, a light rail system in Pittsburgh known as the “T” has replaced remnants of the trolley lines.

These lines run between downtown Pittsburgh and the South Hills suburbs. In town, these lines become Pittsburgh’s subway. The most recent addition included a tunnel under the Allegheny River to the north side of Pittsburgh, as described in the section of this paper on tunnels.

Inclines In the mid- to late 1800s, the land on the floodplains within and surrounding Pittsburgh had become crowded by industrial and commercial development. Land for residential housing was available on the tops of the surrounding bluffs, such as on Mount Washington (Coal Hill), but traversing the 300–400 ft (91–122 m) of elevation change was arduous. The answer to this situation was inclined railways or funiculars, which are referred to as inclines in the Pittsburgh area. The inclines are composed of two parallel sets of railway tracks with a car on each track. The cars are connected by a single cable that passes through a pulley at the top of the incline. The cars counterbalance one another so that the engine that moves the

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

and reliable mode of transportation was needed. The first rationally designed transportation network was the local railroad. This system was intended to transfer coal and goods to the industries within and surrounding Pittsburgh. Topography initially restricted population growth to the city and railroad corridor expansion to the river valleys. However, with the development of the abundant Pittsburgh Coal seam, which resulted in newly established farm roads and communities in these mining areas, the railroad lines began following the contours of the nearly flat-lying Pittsburgh Coal seam. Bridge structures developed as the railroads required “jumping” from one hillside to another to be in close contact with the mining areas. Like all other railroads of that time, they relied on horses or mules for power. Not much faster than wagons or canal boats, their main advantage was smooth-running rails.

The transition to the widespread interstate railroad system was a long battle. Pennsylvania had no urgent reason to invest in railroad technology until 1825, when the Erie Canal linked New York City’s ports to Midwest markets (Finch, 1988). Once the Erie Canal opened, shipping costs from New York to the Midwest dropped significantly, and the time it took to ship the goods was cut significantly. This greatly increased trade for New York City businesses while bypassing Pittsburgh and Philadelphia.

Shipping by water was still cheaper than by rail, but the railroads did have the advantage of traveling where rivers didn’t flow. A result was the combined use of trains and rivers together (Fleming, 1916).

Started in 1834, the state-owned Main Line of Public Works used canal boats where possible on relatively level ground and a combination of gravity and stationary steam engines where necessary in the mountains (Baer, 1996). This patchwork of canals, railroads, and inclined planes offered a 3 to 4 day journey from Philadelphia to Pittsburgh. However, it was soon ended by the cheaper, all-purpose, all-weather railroads. The interstate railroads entered the area in the 1850s. In 1852, the Ohio and Pennsylvania Railroad began service between Cleveland and Allegheny City (present-day North Side), and in 1854, the Pennsylvania Railroad began service between Pittsburgh and Philadelphia. An historical map of the Pittsburgh railroads is shown on Figure 46. A journey between Philadelphia and Pittsburgh now took only 13 hours.

The Pennsylvania Railroad was the largest railroad in the world for much of its 121 year life span, absorbing many other railroads as it grew. It hauled more freight and passengers than any other railroad in the world during that time (Baer, 1996).

The railroad system in Pittsburgh flourished for many years. From the beginning of the industrial era through its collapse in the 1980s, Pittsburgh was al76

ways a key market for the nation’s largest and most important railroads. At one time, up to 22 railroads, including main lines and branches, entered Pittsburgh (Fleming, 1916). They comprised the lines of the Pennsylvania System, the New York Central Lines, the Baltimore and Ohio, the Buffalo, Rochester and Pittsburgh, the Pittsburgh, Bessemer and Lake Erie (the Carnegie Road), and the Wabash. However, with the coming of publicly funded highways and the availability of automobiles after World War II, railroads began a long downward slide. Despite the near collapse of heavy industry in the northeast, Pittsburgh still remains an important link in the nation’s rail network. Current railroads in Pittsburgh include: Norfolk Southern, CSX, Amtrak, Wheeling & Lake Erie, and the Allegheny Valley Railroad.

Another rail system that once existed in Pittsburgh was the inter-city trolley car. It started in the late 1800s and early 1900s and followed the farm roads lying at the ridge tops, the alignments of the railroad network, and many abandoned railroad corridors. They became most popular in the 1940s and 1950s as an economical mass-transit solution for the expanding city of Pittsburgh (see Figure 47). A fleet of more than 600 trolleys was in use in 1948 (Bennear, 1995). The demise of the trolley was due to the speed and flexibility of gasolinepowered buses. By the early 1970s, the fleet had dwindled to 95 cars and 4 lines. By 1985, almost all trolley rails were overlain by asphalt, with few cars and lines existing. Today, a light rail system in Pittsburgh known as the “T” has replaced remnants of the trolley lines.

These lines run between downtown Pittsburgh and the South Hills suburbs. In town, these lines become Pittsburgh’s subway. The most recent addition included a tunnel under the Allegheny River to the north side of Pittsburgh, as described in the section of this paper on tunnels.

Inclines In the mid- to late 1800s, the land on the floodplains within and surrounding Pittsburgh had become crowded by industrial and commercial development. Land for residential housing was available on the tops of the surrounding bluffs, such as on Mount Washington (Coal Hill), but traversing the 300–400 ft (91–122 m) of elevation change was arduous. The answer to this situation was inclined railways or funiculars, which are referred to as inclines in the Pittsburgh area. The inclines are composed of two parallel sets of railway tracks with a car on each track. The cars are connected by a single cable that passes through a pulley at the top of the incline. The cars counterbalance one another so that the engine that moves the

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Geology of Pittsburgh

Figure 46. Map of Pittsburgh railroads in 1855 (Pennsylvania Railroad, 1948).

Figure 46. Map of Pittsburgh railroads in 1855 (Pennsylvania Railroad, 1948).

cars only needs to overcome the weight difference in the cars plus any frictional forces.

The first incline built in Pittsburgh, the Monongahela Incline, opened on May 28, 1870. From that time until the opening of the last incline in 1901, between 15 and 20 inclines were built in Pittsburgh (Old Pitts-

Figure 47. August 1964 photo taken along the P&WVRR tracks looking down at a Pittsburgh Railways inbound Shannon trolley.

burgh Maps, 2012). Most of the inclines were built to negotiate the steep bluffs on the south side of the Monongahela River, but a few were built on the north side of the city to the north of the Allegheny River.

Most of the inclines were built solely for passengers, but some were built for freight. The Monongahela passenger incline had a companion freight incline that was built and remained in service until 1935.

The inclines fell out of use as personal vehicles became common, and most of them were closed during the first half of the twentieth century. Only two, the Monongahela and the Duquesne Inclines, remain in operation. Both are located on the south side of the city.

The Monongahela Incline, shown in Figure 48, is 635 ft (194 m) long with a grade of 78 percent (38 degrees) and an elevation change of just over 367 ft (112 km). It is owned and operated by the Port Authority of Allegheny County and has been in constant operation since it was constructed. It has undergone major renovations and upgrades.

The Duquesne Incline is located opposite the Point.

It is 793 ft (242 m) long with a grade of 58 percent (30 degrees) and an elevation change of 400 ft (122 m). The Society for the Preservation of the Duquesne Heights Incline raised money in 1963 to save the incline. It still

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77

cars only needs to overcome the weight difference in the cars plus any frictional forces.

The first incline built in Pittsburgh, the Monongahela Incline, opened on May 28, 1870. From that time until the opening of the last incline in 1901, between 15 and 20 inclines were built in Pittsburgh (Old Pitts-

Figure 47. August 1964 photo taken along the P&WVRR tracks looking down at a Pittsburgh Railways inbound Shannon trolley.

burgh Maps, 2012). Most of the inclines were built to negotiate the steep bluffs on the south side of the Monongahela River, but a few were built on the north side of the city to the north of the Allegheny River.

Most of the inclines were built solely for passengers, but some were built for freight. The Monongahela passenger incline had a companion freight incline that was built and remained in service until 1935.

The inclines fell out of use as personal vehicles became common, and most of them were closed during the first half of the twentieth century. Only two, the Monongahela and the Duquesne Inclines, remain in operation. Both are located on the south side of the city.

The Monongahela Incline, shown in Figure 48, is 635 ft (194 m) long with a grade of 78 percent (38 degrees) and an elevation change of just over 367 ft (112 km). It is owned and operated by the Port Authority of Allegheny County and has been in constant operation since it was constructed. It has undergone major renovations and upgrades.

The Duquesne Incline is located opposite the Point.

It is 793 ft (242 m) long with a grade of 58 percent (30 degrees) and an elevation change of 400 ft (122 m). The Society for the Preservation of the Duquesne Heights Incline raised money in 1963 to save the incline. It still

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Gray, Greene, Fandray, and Turka

Gray, Greene, Fandray, and Turka

Figure 48. Monongahela Incline.

has the same Victorian cars with the original woodwork. The engines have been converted from steam to electric power.

Bridges (by Thomas Leech, professional engineer [P.E.], Gannett Fleming, Inc.) “There is something intensely dramatic and fanciful in the appeal of the bridge to all classes of people, under all conditions of nature. All traffic converges and concentrates on the bridges. They become a daily necessity and a familiar benefactor, giving convenient passage over some natural obstruction.” (Kidney, 1999, p. 29)

In Pittsburgh, bridges are all around us. They cross mighty rivers, small streams, and deep chasms. Allegheny County, including the city of Pittsburgh, includes over 2,000 bridges of varying types, materials, and sizes. Some bridges are quite new; others are quite old. Some are distinct and magnificent; others are quite ordinary. Many bridges have seen a service life well over 100 years. Many replace one or even two earlier bridges at the same site. Each bridge records in its composition, in essence, a genetic code of its era of construction. This genetic code records both an engineering and architectural imprint of the age in which it was built. All of these bridges have been distinctly shaped by both the geography and geology of the area.

River Crossings The Monongahela River (i.e., river with sliding banks, Delaware Native American) and the Allegheny River (i.e., river of the Alligewi, Delaware Native American) form the Ohio River (i.e., the good river, Seneca Native American) at the “Point” in Pittsburgh (Bright, 2004). At present, there are 30 river crossings 78

Figure 48. Monongahela Incline.

Figure 49. Smithfield Street Bridge in downtown Pittsburgh: Historic American Engineering Record collection (Cridlebaugh, 1999).

in the city of Pittsburgh and another 29 river crossings in other communities within Allegheny County.

Pittsburgh rivals other “bridge” cities of the world, including Paris with its 38 river crossings within the city proper, and Venice with its 409 bridges spanning 150 canals, but with only four bridges that cross the Grand Canal (Cridlebaugh, 2009).

As Pittsburgh emerged as a city in the early 1800s, the rivers were a formidable barrier to transportation.

The first river crossings relied on geographic features, such as fords in the rivers by way of sand bar islands.

These crossings were later replaced with ferry service near the fords. The locations of fords and subsequent ferries later became sites of the first river bridges constructed in Pittsburgh. The first established river crossing within Pittsburgh was the site of the present Smithfield Street Bridge over the Monongahela River, initially a river ford, which later was replaced with the nearby Jones Ferry (Cridlebaugh, 2009). The ferry service was subsequently replaced by a wooden covered bridge in 1818, which later was destroyed by the great fire of 1845 (Lorant, 1975). The present Smithfield Street Bridge, a third-generation replacement bridge, is an elegant lenticular steel truss and an American Society of Civil Engineers (ASCE) Civil Engineering Landmark. The present bridge was constructed in 1881 and is recognized as the oldest standing bridge in the city (Figure 49). The second established ferry, Robinson’s Ferry, connected the North Side (previously Allegheny City) with downtown Pittsburgh in close proximity to the present Sixth Street Bridge. In 1819, the first span across the Allegheny River was a wooden covered bridge constructed at this site. It was ultimately replaced by the present third-generation Sixth

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

has the same Victorian cars with the original woodwork. The engines have been converted from steam to electric power.

Bridges (by Thomas Leech, professional engineer [P.E.], Gannett Fleming, Inc.) “There is something intensely dramatic and fanciful in the appeal of the bridge to all classes of people, under all conditions of nature. All traffic converges and concentrates on the bridges. They become a daily necessity and a familiar benefactor, giving convenient passage over some natural obstruction.” (Kidney, 1999, p. 29)

In Pittsburgh, bridges are all around us. They cross mighty rivers, small streams, and deep chasms. Allegheny County, including the city of Pittsburgh, includes over 2,000 bridges of varying types, materials, and sizes. Some bridges are quite new; others are quite old. Some are distinct and magnificent; others are quite ordinary. Many bridges have seen a service life well over 100 years. Many replace one or even two earlier bridges at the same site. Each bridge records in its composition, in essence, a genetic code of its era of construction. This genetic code records both an engineering and architectural imprint of the age in which it was built. All of these bridges have been distinctly shaped by both the geography and geology of the area.

River Crossings The Monongahela River (i.e., river with sliding banks, Delaware Native American) and the Allegheny River (i.e., river of the Alligewi, Delaware Native American) form the Ohio River (i.e., the good river, Seneca Native American) at the “Point” in Pittsburgh (Bright, 2004). At present, there are 30 river crossings 78

Figure 49. Smithfield Street Bridge in downtown Pittsburgh: Historic American Engineering Record collection (Cridlebaugh, 1999).

in the city of Pittsburgh and another 29 river crossings in other communities within Allegheny County.

Pittsburgh rivals other “bridge” cities of the world, including Paris with its 38 river crossings within the city proper, and Venice with its 409 bridges spanning 150 canals, but with only four bridges that cross the Grand Canal (Cridlebaugh, 2009).

As Pittsburgh emerged as a city in the early 1800s, the rivers were a formidable barrier to transportation.

The first river crossings relied on geographic features, such as fords in the rivers by way of sand bar islands.

These crossings were later replaced with ferry service near the fords. The locations of fords and subsequent ferries later became sites of the first river bridges constructed in Pittsburgh. The first established river crossing within Pittsburgh was the site of the present Smithfield Street Bridge over the Monongahela River, initially a river ford, which later was replaced with the nearby Jones Ferry (Cridlebaugh, 2009). The ferry service was subsequently replaced by a wooden covered bridge in 1818, which later was destroyed by the great fire of 1845 (Lorant, 1975). The present Smithfield Street Bridge, a third-generation replacement bridge, is an elegant lenticular steel truss and an American Society of Civil Engineers (ASCE) Civil Engineering Landmark. The present bridge was constructed in 1881 and is recognized as the oldest standing bridge in the city (Figure 49). The second established ferry, Robinson’s Ferry, connected the North Side (previously Allegheny City) with downtown Pittsburgh in close proximity to the present Sixth Street Bridge. In 1819, the first span across the Allegheny River was a wooden covered bridge constructed at this site. It was ultimately replaced by the present third-generation Sixth

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Figure 50. Sixth Street Bridge in downtown Pittsburgh: Historic American Engineering Record collection (Cridlebaugh, 1999).

Street Bridge, a self-anchored suspension span, one of the 1928 Three Sisters Bridges, which is recognized as the only surviving eyebar chain suspension bridge in America (Figure 50). Quickly, transportation routes developed around these ferry crossings, and the rivers of Pittsburgh now contain a myriad of bridges with unique structural form and complexity, all of which is a testament to Pittsburgh’s prominence as an historic center of civil engineering practice. The main spans of the river crossings range from 400 ft (120 m) to 800 ft (240 m), consistent with navigation requirements, and the present 59 river crossings typically comprise various steel superstructures, egalitarian trusses, and plate girder bridges and visually appealing tied arch and suspension bridges.

As Pittsburgh grew to become an industrial power, the surface transportation routes shifted from town centric to bypass or through routes as the transportation routes ultimately shifted to interstate corridors, presently converging at the “Point” in Pittsburgh. Three generations of bridges have spanned the Monongahela River at the “Point,” including the 1875 Point suspension bridge, the 1927 steel cantilever truss, and the current 1959 Fort Pitt (I-279/I-376) steel double-deck tied arch. Three generations of bridges also have spanned the Allegheny River at the “Point,” including the 1874 Union, wooden covered bridge, the 1915 two-span steel trussed Manchester Bridge, and the current 1969 Fort Duquesne (I-279) steel doubledeck tied arch.

The transportation networks within Pittsburgh and the surrounding communities in Allegheny County required an array of valley crossings that are supported by nearly 2,000 bridge structures. Many of the valleys

Geology of Pittsburgh

Figure 51. George Westinghouse Bridge: Historic American Engineering Record collection (Cridlebaugh, 1999).

are quite steep sided, and many interesting structures were designed with heights as much as 200 ft (60 m) above the valley floors and spans reaching 300 ft (90 m) and more. Structural forms include routine steel and concrete girders, steel box girders, steel trusses, steel viaducts, and high-level steel plate girders. Additionally, with competent bedrock so close to ground surface, even in the steepest of valley settings, there is ample opportunity to build structures that rely on lateral thrust principles. A wide variety of steel rigid frame, steel high-level arch, and concrete high-level arch bridges can be found in the Pittsburgh region.

An example of a concrete high-level arch is the George Westinghouse Bridge, which is shown on Figure 51.

Tunnels Western Pennsylvania has a place in tunnel history.

The first railroad tunnel in the United States was the Staple Bend Tunnel, which is located about 60 mi (97 km) east of Pittsburgh along the Conemaugh River near Johnstown, PA (National Park Service, 2013).

It was excavated between 1831 and 1833 as part of the Allegheny Portage Railroad, which was part of the Pennsylvania Canal that connected Philadelphia to Pittsburgh. The same Pennsylvania Canal also had a tunnel under downtown Pittsburgh. It is located under Grant’s Hill, which is now Grant Street in the downtown area. The tunnel still exists, but it is sealed (see Figure 45). The Pennsylvania Canal Tunnel, which was constructed between 1827 and 1830, is considered to be Pittsburgh’s oldest transportation tunnel.

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Figure 50. Sixth Street Bridge in downtown Pittsburgh: Historic American Engineering Record collection (Cridlebaugh, 1999).

Street Bridge, a self-anchored suspension span, one of the 1928 Three Sisters Bridges, which is recognized as the only surviving eyebar chain suspension bridge in America (Figure 50). Quickly, transportation routes developed around these ferry crossings, and the rivers of Pittsburgh now contain a myriad of bridges with unique structural form and complexity, all of which is a testament to Pittsburgh’s prominence as an historic center of civil engineering practice. The main spans of the river crossings range from 400 ft (120 m) to 800 ft (240 m), consistent with navigation requirements, and the present 59 river crossings typically comprise various steel superstructures, egalitarian trusses, and plate girder bridges and visually appealing tied arch and suspension bridges.

As Pittsburgh grew to become an industrial power, the surface transportation routes shifted from town centric to bypass or through routes as the transportation routes ultimately shifted to interstate corridors, presently converging at the “Point” in Pittsburgh. Three generations of bridges have spanned the Monongahela River at the “Point,” including the 1875 Point suspension bridge, the 1927 steel cantilever truss, and the current 1959 Fort Pitt (I-279/I-376) steel double-deck tied arch. Three generations of bridges also have spanned the Allegheny River at the “Point,” including the 1874 Union, wooden covered bridge, the 1915 two-span steel trussed Manchester Bridge, and the current 1969 Fort Duquesne (I-279) steel doubledeck tied arch.

The transportation networks within Pittsburgh and the surrounding communities in Allegheny County required an array of valley crossings that are supported by nearly 2,000 bridge structures. Many of the valleys

Figure 51. George Westinghouse Bridge: Historic American Engineering Record collection (Cridlebaugh, 1999).

are quite steep sided, and many interesting structures were designed with heights as much as 200 ft (60 m) above the valley floors and spans reaching 300 ft (90 m) and more. Structural forms include routine steel and concrete girders, steel box girders, steel trusses, steel viaducts, and high-level steel plate girders. Additionally, with competent bedrock so close to ground surface, even in the steepest of valley settings, there is ample opportunity to build structures that rely on lateral thrust principles. A wide variety of steel rigid frame, steel high-level arch, and concrete high-level arch bridges can be found in the Pittsburgh region.

An example of a concrete high-level arch is the George Westinghouse Bridge, which is shown on Figure 51.

Tunnels Western Pennsylvania has a place in tunnel history.

The first railroad tunnel in the United States was the Staple Bend Tunnel, which is located about 60 mi (97 km) east of Pittsburgh along the Conemaugh River near Johnstown, PA (National Park Service, 2013).

It was excavated between 1831 and 1833 as part of the Allegheny Portage Railroad, which was part of the Pennsylvania Canal that connected Philadelphia to Pittsburgh. The same Pennsylvania Canal also had a tunnel under downtown Pittsburgh. It is located under Grant’s Hill, which is now Grant Street in the downtown area. The tunnel still exists, but it is sealed (see Figure 45). The Pennsylvania Canal Tunnel, which was constructed between 1827 and 1830, is considered to be Pittsburgh’s oldest transportation tunnel.

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Today, Pittsburgh has 11 tunnels, according to the Pittsburgh Bridges and Tunnels website (Cridlebaugh, 1999). See Figure 52 for the tunnel locations.

From Pittsburgh to the east, the tunnels include:

(1) Panhandle Railroad Tunnel runs under Grant’s Hill in downtown Pittsburgh in rock belonging to the Glenshaw Formation of the Conemaugh Group, and it is now sealed.

(2) Armstrong Tunnel is an automobile tunnel under Duquesne University on the bluff just east of downtown Pittsburgh in rock of the Casselman Formation of the Conemaugh Group.

It is a prominent tunnel in Pittsburgh known mostly for an approximate 45 degree bend. It was built in 1926–1927 with a length about 1,320 ft (402 m). The bend was created to avoid possible mines, some property rights (including Duquesne University), and to connect alignments with existing or proposed roads.

(3) LTV South Side Works Railroad Tunnel is owned by CSX and is a cut/cover tunnel with cut-stone side walls and a steel beam ceiling located under the South Side neighborhood of Pittsburgh.

(4) Neville Street Tunnel (or Schenley Railroad Tunnel) is used by CSX. It is located in the Oakland neighborhood of Pittsburgh and is a cut/cover tunnel about 70 ft (21 m) below the grade of Neville Street.

(5) Squirrel Hill Tunnel is an automobile tunnel under the Squirrel Hill neighborhood of Pittsburgh through rock of the Casselman Formation of the Conemaugh Group.

From Pittsburgh to the west, the tunnels include:

(6) Corliss Street Tunnel is an automobile tunnel through the Norfolk Southern Railroad embankment, West End section of Pittsburgh.

(7) Fort Pitt Tunnel is an automobile tunnel through Mount Washington through rock of the Casselman Formation of the Conemaugh Group.

(8) Wabash Tunnel was built in 1902–1904 for the Wabash-Pittsburg Terminal Railroad through Mount Washington, now retrofitted for automobile traffic. It has a vertical-wall horseshoe profile and concrete lining, and it is 3,342 ft (1,019 m) long through rock of the Casselman Formation of the Conemaugh Group.

(9) Mount Washington Transit Tunnel hosts the Port Authority “T” and South Busway through Mount Washington, and it was built in 1904 with a concrete-lined vertical-wall horseshoe profile. It was excavated through rock of

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the Casselman Formation of the Conemaugh Group with an approximate length of 3,500 ft (1,067 m).

(10) The Port Authority North Shore Connector runs under the Allegheny River between downtown Pittsburgh and Pittsburgh’s North Shore.

It is the latest tunnel constructed in Pittsburgh as part of the “T” and subway system. Additional information is provided in the “Major Engineering Structures” section.

(11) Liberty Tunnel is an automobile tunnel through Mount Washington through rock of the Casselman Formation of the Conemaugh Group.

Much of the heaviest automobile traffic is associated with the tunnels, because motorists tend to slow down approaching and traveling through them, which is ironic because these structures were supposed to reduce driving time. Notable tunnels of the area include the Liberty Tunnel, which connects the south suburbs to the city, and the two interstate I-376 highway tunnels (Squirrel Hill and Fort Pitt), which connect the east and west suburbs to the city.

Mount Washington is nearly 400 ft (122 m) high along the length of Pittsburgh’s downtown area, and it posed a barrier to the development of the South Hills.

In order to provide access, the Liberty Tunnel, which is considered to be the first modern automobile tunnel in the United States, was excavated through Mount Washington. It consists of twin concrete-lined tunnels in a vertical-wall horseshoe profile. The county began construction of the tunnel in the winter of 1919, and the excavation was completed in July 1922. The rock excavated was mostly “green” and “red” claystone and soft laminated sandstone of the Casselman Formation of the Conemaugh Group, with a minor amount of more competent “blue” sandstone (Public Works, 1921). Most of the excavation was considered treacherous due to the poor condition of the soft rock. The tunnels are 5,889 ft (1,795 m) long and 28.6 ft (8.7 m) wide, with 20.75 ft (6.3 m) clearance in the arch portion of the tunnels and a 14.5 ft (4.4 m) vertical entrance clearance. It opened in 1924 with restricted use until the ventilation system was completed in 1925. The tunnel was owned by Allegheny County until it was transferred to the Pennsylvania Department of Transportation (PennDOT).

Construction of the Squirrel Hill Tunnel started prior to World War II, was delayed until after the war, and was completed in 1953. Figure 53 shows the tunnel excavation. It is the principal highway route from the eastern suburbs of Pittsburgh into the city.

The cost to construct the tunnel was $18 million and was the most costly project by the State Highways Department at that time. The tunnel consists of twin

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Today, Pittsburgh has 11 tunnels, according to the Pittsburgh Bridges and Tunnels website (Cridlebaugh, 1999). See Figure 52 for the tunnel locations.

From Pittsburgh to the east, the tunnels include:

(1) Panhandle Railroad Tunnel runs under Grant’s Hill in downtown Pittsburgh in rock belonging to the Glenshaw Formation of the Conemaugh Group, and it is now sealed.

(2) Armstrong Tunnel is an automobile tunnel under Duquesne University on the bluff just east of downtown Pittsburgh in rock of the Casselman Formation of the Conemaugh Group.

It is a prominent tunnel in Pittsburgh known mostly for an approximate 45 degree bend. It was built in 1926–1927 with a length about 1,320 ft (402 m). The bend was created to avoid possible mines, some property rights (including Duquesne University), and to connect alignments with existing or proposed roads.

(3) LTV South Side Works Railroad Tunnel is owned by CSX and is a cut/cover tunnel with cut-stone side walls and a steel beam ceiling located under the South Side neighborhood of Pittsburgh.

(4) Neville Street Tunnel (or Schenley Railroad Tunnel) is used by CSX. It is located in the Oakland neighborhood of Pittsburgh and is a cut/cover tunnel about 70 ft (21 m) below the grade of Neville Street.

(5) Squirrel Hill Tunnel is an automobile tunnel under the Squirrel Hill neighborhood of Pittsburgh through rock of the Casselman Formation of the Conemaugh Group.

From Pittsburgh to the west, the tunnels include:

(6) Corliss Street Tunnel is an automobile tunnel through the Norfolk Southern Railroad embankment, West End section of Pittsburgh.

(7) Fort Pitt Tunnel is an automobile tunnel through Mount Washington through rock of the Casselman Formation of the Conemaugh Group.

(8) Wabash Tunnel was built in 1902–1904 for the Wabash-Pittsburg Terminal Railroad through Mount Washington, now retrofitted for automobile traffic. It has a vertical-wall horseshoe profile and concrete lining, and it is 3,342 ft (1,019 m) long through rock of the Casselman Formation of the Conemaugh Group.

(9) Mount Washington Transit Tunnel hosts the Port Authority “T” and South Busway through Mount Washington, and it was built in 1904 with a concrete-lined vertical-wall horseshoe profile. It was excavated through rock of

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the Casselman Formation of the Conemaugh Group with an approximate length of 3,500 ft (1,067 m).

(10) The Port Authority North Shore Connector runs under the Allegheny River between downtown Pittsburgh and Pittsburgh’s North Shore.

It is the latest tunnel constructed in Pittsburgh as part of the “T” and subway system. Additional information is provided in the “Major Engineering Structures” section.

(11) Liberty Tunnel is an automobile tunnel through Mount Washington through rock of the Casselman Formation of the Conemaugh Group.

Much of the heaviest automobile traffic is associated with the tunnels, because motorists tend to slow down approaching and traveling through them, which is ironic because these structures were supposed to reduce driving time. Notable tunnels of the area include the Liberty Tunnel, which connects the south suburbs to the city, and the two interstate I-376 highway tunnels (Squirrel Hill and Fort Pitt), which connect the east and west suburbs to the city.

Mount Washington is nearly 400 ft (122 m) high along the length of Pittsburgh’s downtown area, and it posed a barrier to the development of the South Hills.

In order to provide access, the Liberty Tunnel, which is considered to be the first modern automobile tunnel in the United States, was excavated through Mount Washington. It consists of twin concrete-lined tunnels in a vertical-wall horseshoe profile. The county began construction of the tunnel in the winter of 1919, and the excavation was completed in July 1922. The rock excavated was mostly “green” and “red” claystone and soft laminated sandstone of the Casselman Formation of the Conemaugh Group, with a minor amount of more competent “blue” sandstone (Public Works, 1921). Most of the excavation was considered treacherous due to the poor condition of the soft rock. The tunnels are 5,889 ft (1,795 m) long and 28.6 ft (8.7 m) wide, with 20.75 ft (6.3 m) clearance in the arch portion of the tunnels and a 14.5 ft (4.4 m) vertical entrance clearance. It opened in 1924 with restricted use until the ventilation system was completed in 1925. The tunnel was owned by Allegheny County until it was transferred to the Pennsylvania Department of Transportation (PennDOT).

Construction of the Squirrel Hill Tunnel started prior to World War II, was delayed until after the war, and was completed in 1953. Figure 53 shows the tunnel excavation. It is the principal highway route from the eastern suburbs of Pittsburgh into the city.

The cost to construct the tunnel was $18 million and was the most costly project by the State Highways Department at that time. The tunnel consists of twin

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Geology of Pittsburgh

Figure 52. Tunnel locations in Pittsburgh (main map courtesy of John Harper, Pennsylvania Geological Survey).

Figure 52. Tunnel locations in Pittsburgh (main map courtesy of John Harper, Pennsylvania Geological Survey).

Figure 53. Squirrel Hill Tunnel construction, 1953 (Collier, 2014; taken from Historical Society of Western Pennsylvania).

arch-shaped reinforced concrete bores that are 4,225 ft (1,288 m) long and approximately 29 ft (8.8 m) wide with a ceiling height of 13.5 ft (4.1 m). Vertical clearances are changing with the current rehabilitation project. The tunnel design was based on subsurface evaluations made from conventional borings, which revealed rather poor-quality rock would be encountered in excavating the tunnels. To adequately support the conditions, permanent steel supports were installed as the tunnel lining, and grout was placed outside of that lining. The grout was used to impregnate, strengthen, and seal the weak and shattered rock adjacent to the tunnel (Pennsylvania Department of Transportation, 2014, District 11 website, 2014 summary update).

The Fort Pitt Tunnel goes through Mount Washington, formerly Coal Hill. It is unique in that the outbound portal is lower than the inbound portal on the downtown side of the tunnel. The downtown por-

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Figure 53. Squirrel Hill Tunnel construction, 1953 (Collier, 2014; taken from Historical Society of Western Pennsylvania).

arch-shaped reinforced concrete bores that are 4,225 ft (1,288 m) long and approximately 29 ft (8.8 m) wide with a ceiling height of 13.5 ft (4.1 m). Vertical clearances are changing with the current rehabilitation project. The tunnel design was based on subsurface evaluations made from conventional borings, which revealed rather poor-quality rock would be encountered in excavating the tunnels. To adequately support the conditions, permanent steel supports were installed as the tunnel lining, and grout was placed outside of that lining. The grout was used to impregnate, strengthen, and seal the weak and shattered rock adjacent to the tunnel (Pennsylvania Department of Transportation, 2014, District 11 website, 2014 summary update).

The Fort Pitt Tunnel goes through Mount Washington, formerly Coal Hill. It is unique in that the outbound portal is lower than the inbound portal on the downtown side of the tunnel. The downtown por-

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tals are vertically offset to accommodate traffic of the stacked deck from the Fort Pitt Bridge, while the westbound portals are at the same elevation. The Fort Pitt Tunnel is similar in design to the Squirrel Hill Tunnel.

Construction of the Fort Pitt Tunnel started in 1957 and was completed in 1960 by the Pennsylvania Department of Highways at a cost of $17 million. The total length of the tunnels is 3,614 ft (1,101 m), with an estimated opening of each portal at 28 ft (8.5 m) wide and a ceiling height of 13.5 ft (4.1 m). The Fort Pitt Tunnel is regarded as the “best way to enter an American city,” because motorists emerging from the tunnel are suddenly presented with a dramatic view of Pittsburgh (Lorant, 1964, p. 395).

MAJOR ENGINEERING STRUCTURES Foundations The topography and geology of Pittsburgh result in many foundation types being used to support structures. The type and size of structure, site-specific conditions, local practice, and the designer’s preference may influence the type of foundation selected as much as geology. There are areas where special foundation problems such as soft soils, subsidence due to mining, expansive shale, and landslides exist. In general, residual soils throughout Pittsburgh are adequate to support the foundations of homes and light-commercial buildings. For heavy foundation loads, rock normally provides adequate support, except where deeply weathered. Some local claystones and shales slake or dry out when exposed to the atmosphere and require immediate covering to avoid further deterioration and additional excavation. Pile driving can shatter these shales and claystones, and piles may have to be re-driven several times before deeper competent rock is encountered. A foundation designer must consider both surface and underground mining as potential sites for differential settlement, subsidence, slope instability, mine and refuse fires, and acidic soil, rock, and water. Shales should be considered a foundation problem until their potential for heaving is determined.

The alluvial soils in the Monongahela River drainage are generally soft, and large structures normally require foundations extending to or into rock to avoid excessive settlements. The glacial gravels in the Allegheny and Ohio River Valleys are generally dense and can carry significant foundation loads with only minor settlement. These dense glacial sand and gravel deposits occur in downtown Pittsburgh. In the area between the rivers, the contours of the top of rock rise away from the rivers, and the sand and gravel deposit ends around Smithfield Street between Fourth 82

and Sixth Avenues, as shown on Figure 20 (Van Tuyl, 1951).

Various foundation types have been used to support buildings on the dense glacial gravel in downtown Pittsburgh. They include spread footings, a mat foundation, and friction piles. However, the three Gateway office buildings adjacent to Point State Park are an anomaly in that they are supported on H-piles driven through the glacial gravels to rock. Where the dense glacial gravel is not present, east of Smithfield Street, buildings are generally supported by spread footings or drilled piers bearing on rock.

In recent years, larger-scale projects, including the Braddock Dam, the PPG Paints Hockey Arena, the University of Pittsburgh Medical Center (UPMC) East Hospital, and the Pennsylvania Turnpike Bridge crossing the Allegheny River at Harmarville, 14 mi (22.5 km) north of downtown Pittsburgh, have been constructed. The size of the projects justified the use of Osterberg load cell tests to determine the bearing and side shear properties for optimizing the design of drilled piers in rock.

Some site and projects of interest are described as follows: Point State Park Point State Park comprises 36 acres (14.6 ha) at the confluence of the Allegheny and Monongahela Rivers.

The park recognizes Pittsburgh’s past and present, including the strategic importance and historic role that Pittsburgh’s Point had in the development of the United States. The Ohio River afforded great influence over more than 200,000 mi2 (517,998 km2 ) of undeveloped territory downstream of the Point. In the early 1800s, swarms of settlers moved through Pittsburgh on their way west. Traffic down the Ohio reached a volume of more than 1,000 boats per year leaving Pittsburgh, with 20,000 people and more than 12,000 head of livestock, wagons, provisions, and household goods.

Following capture of the French Fort Duquesne in 1758, the English proceeded to construct the most impressive fort on the American Frontier, Fort Pitt.

Point State Park includes parts of the Fort Pitt Bastions, and the original Fort Pitt Block House built in 1764. The Fort Pitt Blockhouse is the oldest architectural landmark in Pittsburgh and is the nation’s only authenticated pre–Revolutionary War structure west of the Appalachian Mountains (Pennsylvania Department of Conservation and Natural Resources, 2015).

Much of the structure is intact, including the stone foundation, brick, and timber elements that are largely original to its 1764 construction. The wall footing was uncovered in the early 1940s and found to be made of almost entirely of relatively small, light greenish-gray

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Gray, Greene, Fandray, and Turka

tals are vertically offset to accommodate traffic of the stacked deck from the Fort Pitt Bridge, while the westbound portals are at the same elevation. The Fort Pitt Tunnel is similar in design to the Squirrel Hill Tunnel.

Construction of the Fort Pitt Tunnel started in 1957 and was completed in 1960 by the Pennsylvania Department of Highways at a cost of $17 million. The total length of the tunnels is 3,614 ft (1,101 m), with an estimated opening of each portal at 28 ft (8.5 m) wide and a ceiling height of 13.5 ft (4.1 m). The Fort Pitt Tunnel is regarded as the “best way to enter an American city,” because motorists emerging from the tunnel are suddenly presented with a dramatic view of Pittsburgh (Lorant, 1964, p. 395).

MAJOR ENGINEERING STRUCTURES Foundations The topography and geology of Pittsburgh result in many foundation types being used to support structures. The type and size of structure, site-specific conditions, local practice, and the designer’s preference may influence the type of foundation selected as much as geology. There are areas where special foundation problems such as soft soils, subsidence due to mining, expansive shale, and landslides exist. In general, residual soils throughout Pittsburgh are adequate to support the foundations of homes and light-commercial buildings. For heavy foundation loads, rock normally provides adequate support, except where deeply weathered. Some local claystones and shales slake or dry out when exposed to the atmosphere and require immediate covering to avoid further deterioration and additional excavation. Pile driving can shatter these shales and claystones, and piles may have to be re-driven several times before deeper competent rock is encountered. A foundation designer must consider both surface and underground mining as potential sites for differential settlement, subsidence, slope instability, mine and refuse fires, and acidic soil, rock, and water. Shales should be considered a foundation problem until their potential for heaving is determined.

The alluvial soils in the Monongahela River drainage are generally soft, and large structures normally require foundations extending to or into rock to avoid excessive settlements. The glacial gravels in the Allegheny and Ohio River Valleys are generally dense and can carry significant foundation loads with only minor settlement. These dense glacial sand and gravel deposits occur in downtown Pittsburgh. In the area between the rivers, the contours of the top of rock rise away from the rivers, and the sand and gravel deposit ends around Smithfield Street between Fourth 82

and Sixth Avenues, as shown on Figure 20 (Van Tuyl, 1951).

Various foundation types have been used to support buildings on the dense glacial gravel in downtown Pittsburgh. They include spread footings, a mat foundation, and friction piles. However, the three Gateway office buildings adjacent to Point State Park are an anomaly in that they are supported on H-piles driven through the glacial gravels to rock. Where the dense glacial gravel is not present, east of Smithfield Street, buildings are generally supported by spread footings or drilled piers bearing on rock.

In recent years, larger-scale projects, including the Braddock Dam, the PPG Paints Hockey Arena, the University of Pittsburgh Medical Center (UPMC) East Hospital, and the Pennsylvania Turnpike Bridge crossing the Allegheny River at Harmarville, 14 mi (22.5 km) north of downtown Pittsburgh, have been constructed. The size of the projects justified the use of Osterberg load cell tests to determine the bearing and side shear properties for optimizing the design of drilled piers in rock.

Some site and projects of interest are described as follows: Point State Park Point State Park comprises 36 acres (14.6 ha) at the confluence of the Allegheny and Monongahela Rivers.

The park recognizes Pittsburgh’s past and present, including the strategic importance and historic role that Pittsburgh’s Point had in the development of the United States. The Ohio River afforded great influence over more than 200,000 mi2 (517,998 km2 ) of undeveloped territory downstream of the Point. In the early 1800s, swarms of settlers moved through Pittsburgh on their way west. Traffic down the Ohio reached a volume of more than 1,000 boats per year leaving Pittsburgh, with 20,000 people and more than 12,000 head of livestock, wagons, provisions, and household goods.

Following capture of the French Fort Duquesne in 1758, the English proceeded to construct the most impressive fort on the American Frontier, Fort Pitt.

Point State Park includes parts of the Fort Pitt Bastions, and the original Fort Pitt Block House built in 1764. The Fort Pitt Blockhouse is the oldest architectural landmark in Pittsburgh and is the nation’s only authenticated pre–Revolutionary War structure west of the Appalachian Mountains (Pennsylvania Department of Conservation and Natural Resources, 2015).

Much of the structure is intact, including the stone foundation, brick, and timber elements that are largely original to its 1764 construction. The wall footing was uncovered in the early 1940s and found to be made of almost entirely of relatively small, light greenish-gray

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

Figure 54. Fountain at Point State Park (photo courtesy of Linda Kaplan, Gannett Fleming, Inc.).

sandstone (possibly Connellsville Sandstone) blocks, with some locations consisting of glacially imported granitic blocks placed directly on glacial outwash material (Bliss, 1943). In addition, the park contains a fountain, dedicated in 1974, said to be the largest in the United States, which propels water upwards approximately 200 ft (61 m) (Figure 54). The 73,000 gallons of water in the closed-loop system are drawn from glacial gravels 50 ft (15 m) beneath the Point (Compressed Air Magazine, 1974).

U.S. Steel Tower (Formerly Known as USX Tower or U.S. Steel Building) The U.S. Steel Tower, first known as the U.S. Steel Building and then the USX Tower, is a 64 story (841.0 ft or 256 m high) skyscraper located on Grant Street in downtown Pittsburgh. Construction started in March 1967 and was completed September 30, 1971. At 841 ft (256 m) above street level, the U.S. Steel Building was the tallest building between New York and Chicago until 1987. The building site occupies a portion of Grant’s Hill, a prominent feature in the early history of Pittsburgh. In September 1758, Major James Grant

Geology of Pittsburgh

led an advance column of 800 men of British General John Forbes’ army against Fort Duquesne. The British force was repelled on a hill east of the Point, with 342 men killed, wounded, or captured. Major Grant was captured, but paroled soon after. When General Forbes occupied the abandoned Fort Duquesne on November 25, 1758, the nearby site of the battle was named Grant’s Hill (Pittsburgh Post-Gazette, 2008).

Grant’s Hill was leveled on several occasions, by a total of approximately 20 ft (6 m). Excavation for the U.S. Steel Building foundation extended up to 90 ft (27 m) below grade, bypassing previous fill material and poor rock conditions. A continuous concrete mat foundation with a thickness of up to 12 ft (3.7 m) was used for the structure and was placed on a competent shaly sandstone to reduce settlement issues (U.S. Steel Tower, 2015).

The excavation uncovered two tunnels that had been constructed through Grant’s Hill (Figure 44). One was an 810 ft (247 m) Pennsylvania Canal tunnel constructed in 1834. The second was the Pittsburgh and Steubenville Extension Railroad tunnel. This railroad was a link between the Pennsylvania Railroad’s western terminus and the eastern terminus of the Steubenville Railroad Company. When this rail link opened in 1865, it extended the Pennsylvania Railroad’s trade and transportation network into Ohio, as far as Columbus. This tunnel was built using cut-andcover techniques. A trench, approximately 35 ft (10.7 m) wide, was excavated from the ground surface to elevation 780 ft (238 m), and the tunnel was constructed within the trench, and then the excavation was backfilled. The average height of the tunnel side walls was 18 ft (5.5 m). A five-course brick arch was supported on the walls. The railroad tunnel was rehabilitated to serve as an underground right-of-way and station area (Midtown Station) for the Light Rail Transit Subway (HAER, 1985).

During the 1965–1967 construction of the U.S. Steel Building, a new single-track tunnel, measuring 409 ft (125 m) long and 17.4 ft (5.3 m) wide, was built within the subterranean levels of the building as part of Pittsburgh’s Light Rail Subway. The support systems for the tunnel and the building were designed to be independent of each other, so that train vibrations would not disturb the building’s structural integrity, and the weight of the building would not bear on the tunnel.

The U.S. Steel Building tunnel begins 1,029.6 ft (314 m) from the south portal, is rectilinear in design, and has two safety bays measuring 1 ft (0.3 m) deep and approximately 5 ft (1.5 m) wide.

The U.S. Steel Building made history by being the first to use liquid-filled fireproofed columns. U.S. Steel deliberately placed the massive steel columns on the exterior of the building to showcase a new product

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Figure 54. Fountain at Point State Park (photo courtesy of Linda Kaplan, Gannett Fleming, Inc.).

sandstone (possibly Connellsville Sandstone) blocks, with some locations consisting of glacially imported granitic blocks placed directly on glacial outwash material (Bliss, 1943). In addition, the park contains a fountain, dedicated in 1974, said to be the largest in the United States, which propels water upwards approximately 200 ft (61 m) (Figure 54). The 73,000 gallons of water in the closed-loop system are drawn from glacial gravels 50 ft (15 m) beneath the Point (Compressed Air Magazine, 1974).

U.S. Steel Tower (Formerly Known as USX Tower or U.S. Steel Building) The U.S. Steel Tower, first known as the U.S. Steel Building and then the USX Tower, is a 64 story (841.0 ft or 256 m high) skyscraper located on Grant Street in downtown Pittsburgh. Construction started in March 1967 and was completed September 30, 1971. At 841 ft (256 m) above street level, the U.S. Steel Building was the tallest building between New York and Chicago until 1987. The building site occupies a portion of Grant’s Hill, a prominent feature in the early history of Pittsburgh. In September 1758, Major James Grant

led an advance column of 800 men of British General John Forbes’ army against Fort Duquesne. The British force was repelled on a hill east of the Point, with 342 men killed, wounded, or captured. Major Grant was captured, but paroled soon after. When General Forbes occupied the abandoned Fort Duquesne on November 25, 1758, the nearby site of the battle was named Grant’s Hill (Pittsburgh Post-Gazette, 2008).

Grant’s Hill was leveled on several occasions, by a total of approximately 20 ft (6 m). Excavation for the U.S. Steel Building foundation extended up to 90 ft (27 m) below grade, bypassing previous fill material and poor rock conditions. A continuous concrete mat foundation with a thickness of up to 12 ft (3.7 m) was used for the structure and was placed on a competent shaly sandstone to reduce settlement issues (U.S. Steel Tower, 2015).

The excavation uncovered two tunnels that had been constructed through Grant’s Hill (Figure 44). One was an 810 ft (247 m) Pennsylvania Canal tunnel constructed in 1834. The second was the Pittsburgh and Steubenville Extension Railroad tunnel. This railroad was a link between the Pennsylvania Railroad’s western terminus and the eastern terminus of the Steubenville Railroad Company. When this rail link opened in 1865, it extended the Pennsylvania Railroad’s trade and transportation network into Ohio, as far as Columbus. This tunnel was built using cut-andcover techniques. A trench, approximately 35 ft (10.7 m) wide, was excavated from the ground surface to elevation 780 ft (238 m), and the tunnel was constructed within the trench, and then the excavation was backfilled. The average height of the tunnel side walls was 18 ft (5.5 m). A five-course brick arch was supported on the walls. The railroad tunnel was rehabilitated to serve as an underground right-of-way and station area (Midtown Station) for the Light Rail Transit Subway (HAER, 1985).

During the 1965–1967 construction of the U.S. Steel Building, a new single-track tunnel, measuring 409 ft (125 m) long and 17.4 ft (5.3 m) wide, was built within the subterranean levels of the building as part of Pittsburgh’s Light Rail Subway. The support systems for the tunnel and the building were designed to be independent of each other, so that train vibrations would not disturb the building’s structural integrity, and the weight of the building would not bear on the tunnel.

The U.S. Steel Building tunnel begins 1,029.6 ft (314 m) from the south portal, is rectilinear in design, and has two safety bays measuring 1 ft (0.3 m) deep and approximately 5 ft (1.5 m) wide.

The U.S. Steel Building made history by being the first to use liquid-filled fireproofed columns. U.S. Steel deliberately placed the massive steel columns on the exterior of the building to showcase a new product

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called Cor-ten steel. Cor-ten resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and doesn’t need painting and costly rust-prevention maintenance over the years. The initial weathering of the material resulted in a discoloration of the surrounding city sidewalks, as well as other nearby buildings. A cleanup effort was conducted by the corporation once weathering was complete to undo this damage, but the sidewalks still have a decidedly rusty tinge.

The Cor-Ten steel for the building was made at the former U.S. Steel Homestead Works and contains over 44,000 tons (39,916 metric tons) of structural steel (U.S. Steel Tower, 2015).

Subway Pittsburgh’s subway system was constructed in the early 1980s. The project’s goal was to upgrade the city’s streetcar lines into a modern 10.5 mi (17 km) long light rail transit (LRT) system with two connecting exclusive bus roadways. Most of the rail system is in the suburbs south of the Monongahela River and is almost entirely on non-exclusive right of way at grade. After crossing the river into downtown Pittsburgh, the transit line dives into a 1.1 mi (1.8 km) long Y-shaped subway layout consisting of new and renovated two-track tunnels. This portion of the project accounted for only about one seventh of the project’s $480 million cost.

The Port Authority of Allegheny County held the cost down by purchasing an old railroad bridge across the river along with a tunnel that ran north across the city. New subway work, all cut-and-cover, included building the large Midtown Station at the intersection of the subway Y and a line running east through Wood Street Station and terminating at Gateway Center.

One of the most challenging sections was the Wood Street Station, extending out below storage vaults under the sidewalks to adjacent building lines. Alluvial sand and gravel up to 40 ft (12 m) thick is found at this location, so some form of shoring of the excavation and nearby structures was necessary. Hayward Baker Co. conducted the work, and it represented the largest chemical grouting job ever performed in the United States to that date (Karol, 2003). This $2.5 million job was a showcase for non-destructive testing. Work was monitored by the cross-hole seismic method. Hayward Baker injected a 13,000 ft2 (1,208 m2 ) area beneath Sixth Avenue with 1 million gallons of chemical grout, turning the sand and gravel into a solid matrix that was excavated without danger while shoring up six adjacent buildings. The grout consisted of a proprietary formulation of sodium silicate and a number of reactants. The subway was completed in late 1984.

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The North Shore Connector is a light rail extension that opened in 2012. The connector extends the Pittsburgh LRT system from its previous terminus at Gateway Center Station in the Central Business District to the new North Side Station and Allegheny Station on the North Shore by way of a tunnel under the Allegheny River.

The North Shore neighborhood of Pittsburgh evolved from a “sea of asphalt” in the 1990s to a bustling extension of the Central Business District, reflecting approximately $1 billion dollars of investment and construction in the first decade of the 2000s (O’Neill, 2008; Schmitz, 2010). The North Shore Connector links Pittsburgh’s previously existing light rail network to the new businesses and attractions of the North Shore, serving commuters, visitors, and sports event attendees alike (Fontaine, 2012).

The North Side Station serves PNC Park (1.75 million annual baseball fans) and the Community College of Allegheny County (7,200 students). The Allegheny Station serves residents in Allegheny West and Manchester, as well as visitors to Heinz Field (500,000 annual Steeler fans, excluding concerts), the Carnegie Science Center (700,000 annual visitors), Children’s Museum of Pittsburgh (250,000 annual visitors), and the Rivers Casino (Port Authority of Allegheny County, 2015, North Shore Connector). During weekdays, downtown-destined vehicle commuters utilize the connector by parking in one of the many North Shore parking facilities and completing their commute on the connector (Shumway, 2012). The North Shore lacks the parking capacity to serve additional sports fans, so the North Shore connector helps to alleviate the congestion by making it easier for fans to park downtown and travel to the North Shore stadiums (Lord, 2010).

The new subway section was constructed by cutand-cover techniques from the Gateway Center 400 ft (122 m) to the Stanwix Street receiving pit. The subway construction consisted of twin bored tunnels, 22 ft (6.7 m) in diameter, from the Stanwix Street receiving pit to the West General Robinson launch pit, a length of 2,240 ft (683 m), including 875 ft (67 m) beneath the Allegheny River. From the General Robinson Street launch pit, the subway was constructed by cut-andcover techniques for a distance of 1,200 ft (366 m).

From this north portal, the line is elevated for 2,000 ft (610 m) to Allegheny Station. Figure 55 shows a map of the tunnel alignment and Pittsburgh’s subway stations.

The top of the twin tunnels lies 20–25 ft (6–7.6 m) below the riverbed. The German tunnel-boring machine (TBM) assembly began in November 2007. The TBM, measuring 200 ft (61 m) long and weighing 500 tons (453 metric tons), was lowered into a 55 ft

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called Cor-ten steel. Cor-ten resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and doesn’t need painting and costly rust-prevention maintenance over the years. The initial weathering of the material resulted in a discoloration of the surrounding city sidewalks, as well as other nearby buildings. A cleanup effort was conducted by the corporation once weathering was complete to undo this damage, but the sidewalks still have a decidedly rusty tinge.

The Cor-Ten steel for the building was made at the former U.S. Steel Homestead Works and contains over 44,000 tons (39,916 metric tons) of structural steel (U.S. Steel Tower, 2015).

Subway Pittsburgh’s subway system was constructed in the early 1980s. The project’s goal was to upgrade the city’s streetcar lines into a modern 10.5 mi (17 km) long light rail transit (LRT) system with two connecting exclusive bus roadways. Most of the rail system is in the suburbs south of the Monongahela River and is almost entirely on non-exclusive right of way at grade. After crossing the river into downtown Pittsburgh, the transit line dives into a 1.1 mi (1.8 km) long Y-shaped subway layout consisting of new and renovated two-track tunnels. This portion of the project accounted for only about one seventh of the project’s $480 million cost.

The Port Authority of Allegheny County held the cost down by purchasing an old railroad bridge across the river along with a tunnel that ran north across the city. New subway work, all cut-and-cover, included building the large Midtown Station at the intersection of the subway Y and a line running east through Wood Street Station and terminating at Gateway Center.

One of the most challenging sections was the Wood Street Station, extending out below storage vaults under the sidewalks to adjacent building lines. Alluvial sand and gravel up to 40 ft (12 m) thick is found at this location, so some form of shoring of the excavation and nearby structures was necessary. Hayward Baker Co. conducted the work, and it represented the largest chemical grouting job ever performed in the United States to that date (Karol, 2003). This $2.5 million job was a showcase for non-destructive testing. Work was monitored by the cross-hole seismic method. Hayward Baker injected a 13,000 ft2 (1,208 m2 ) area beneath Sixth Avenue with 1 million gallons of chemical grout, turning the sand and gravel into a solid matrix that was excavated without danger while shoring up six adjacent buildings. The grout consisted of a proprietary formulation of sodium silicate and a number of reactants. The subway was completed in late 1984.

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The North Shore Connector is a light rail extension that opened in 2012. The connector extends the Pittsburgh LRT system from its previous terminus at Gateway Center Station in the Central Business District to the new North Side Station and Allegheny Station on the North Shore by way of a tunnel under the Allegheny River.

The North Shore neighborhood of Pittsburgh evolved from a “sea of asphalt” in the 1990s to a bustling extension of the Central Business District, reflecting approximately $1 billion dollars of investment and construction in the first decade of the 2000s (O’Neill, 2008; Schmitz, 2010). The North Shore Connector links Pittsburgh’s previously existing light rail network to the new businesses and attractions of the North Shore, serving commuters, visitors, and sports event attendees alike (Fontaine, 2012).

The North Side Station serves PNC Park (1.75 million annual baseball fans) and the Community College of Allegheny County (7,200 students). The Allegheny Station serves residents in Allegheny West and Manchester, as well as visitors to Heinz Field (500,000 annual Steeler fans, excluding concerts), the Carnegie Science Center (700,000 annual visitors), Children’s Museum of Pittsburgh (250,000 annual visitors), and the Rivers Casino (Port Authority of Allegheny County, 2015, North Shore Connector). During weekdays, downtown-destined vehicle commuters utilize the connector by parking in one of the many North Shore parking facilities and completing their commute on the connector (Shumway, 2012). The North Shore lacks the parking capacity to serve additional sports fans, so the North Shore connector helps to alleviate the congestion by making it easier for fans to park downtown and travel to the North Shore stadiums (Lord, 2010).

The new subway section was constructed by cutand-cover techniques from the Gateway Center 400 ft (122 m) to the Stanwix Street receiving pit. The subway construction consisted of twin bored tunnels, 22 ft (6.7 m) in diameter, from the Stanwix Street receiving pit to the West General Robinson launch pit, a length of 2,240 ft (683 m), including 875 ft (67 m) beneath the Allegheny River. From the General Robinson Street launch pit, the subway was constructed by cut-andcover techniques for a distance of 1,200 ft (366 m).

From this north portal, the line is elevated for 2,000 ft (610 m) to Allegheny Station. Figure 55 shows a map of the tunnel alignment and Pittsburgh’s subway stations.

The top of the twin tunnels lies 20–25 ft (6–7.6 m) below the riverbed. The German tunnel-boring machine (TBM) assembly began in November 2007. The TBM, measuring 200 ft (61 m) long and weighing 500 tons (453 metric tons), was lowered into a 55 ft

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Geology of Pittsburgh

Figure 55. Map of the North Shore Connector Tunnel and subway stations (Port Authority of Allegheny County, 2012).

Figure 55. Map of the North Shore Connector Tunnel and subway stations (Port Authority of Allegheny County, 2012).

(16.8 m) deep launch pit excavated near the intersection of West General Robinson Street and Mazeroski Way near PNC Park. The TBM began work in January 2008 and completed the twin bores in January 2009 (Wargo et al., 2009).

In July 10, 2008, the TBM penetrated through into the receiving pit at Stanwix Street near Penn Avenue downtown. The machine was hoisted by crane, turned around and began digging the second parallel tunnel September 3, arriving back at the North Side launch pit January 15, 2009. Completing the second tunnel in 4.5 months showed the benefit from experiences gained; the second tunnel was a full month faster than the first.

The laser-guided, slurry-pressure-balanced, mixedshield TBM had a 22 ft (6.7 m) diameter rotating head (typically 1 RPM), featuring 17 in. (43 cm) cutters, driven by electric motors. Digging through

glacial/fluvial gravel and rock, the working face was stabilized with a pressurized bentonite-water slurry; the excavated material was transported by the clay slurry through pipes back to a separation plant aboveground. Excavated sand and gravel were separated from the slurry, allowing the slurry to be reused and the other materials to be reserved for future use elsewhere. The TBM’s cutting face had a diameter that was 1 in. (2.5 cm) larger than the rest of the machine. This small annulus reduced side friction of the TBM shield, enabling it to move more easily, assisting in steering the machine, and thus controlling alignment (Wargo et al., 2009). The TBM was generally operated in two 12 hour shifts, five days a week, averaging 34 ft (10 m) per day. As the front of the TBM cut, a steel shield in the trailing section held the cavity open, and 4 ft (1.2 m) wide, pre-cast concrete segments were bolted together to form the tunnel liner (seven modules com-

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(16.8 m) deep launch pit excavated near the intersection of West General Robinson Street and Mazeroski Way near PNC Park. The TBM began work in January 2008 and completed the twin bores in January 2009 (Wargo et al., 2009).

In July 10, 2008, the TBM penetrated through into the receiving pit at Stanwix Street near Penn Avenue downtown. The machine was hoisted by crane, turned around and began digging the second parallel tunnel September 3, arriving back at the North Side launch pit January 15, 2009. Completing the second tunnel in 4.5 months showed the benefit from experiences gained; the second tunnel was a full month faster than the first.

The laser-guided, slurry-pressure-balanced, mixedshield TBM had a 22 ft (6.7 m) diameter rotating head (typically 1 RPM), featuring 17 in. (43 cm) cutters, driven by electric motors. Digging through

glacial/fluvial gravel and rock, the working face was stabilized with a pressurized bentonite-water slurry; the excavated material was transported by the clay slurry through pipes back to a separation plant aboveground. Excavated sand and gravel were separated from the slurry, allowing the slurry to be reused and the other materials to be reserved for future use elsewhere. The TBM’s cutting face had a diameter that was 1 in. (2.5 cm) larger than the rest of the machine. This small annulus reduced side friction of the TBM shield, enabling it to move more easily, assisting in steering the machine, and thus controlling alignment (Wargo et al., 2009). The TBM was generally operated in two 12 hour shifts, five days a week, averaging 34 ft (10 m) per day. As the front of the TBM cut, a steel shield in the trailing section held the cavity open, and 4 ft (1.2 m) wide, pre-cast concrete segments were bolted together to form the tunnel liner (seven modules com-

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Gray, Greene, Fandray, and Turka

Figure 56. Interior of the completed North Shore Connector Tunnel (photo courtesy of Port Authority of Allegheny County, 2012).

Figure 57. 1936 flooding in downtown Pittsburgh (courtesy of Reddit, 2015).

Figure 56. Interior of the completed North Shore Connector Tunnel (photo courtesy of Port Authority of Allegheny County, 2012).

Figure 57. 1936 flooding in downtown Pittsburgh (courtesy of Reddit, 2015).

pleted the circumference of a given ring). The TBM then used hydraulic legs to push off the placed concrete rings as it moved forward. The complete mining assembly measured approximately 150 ft (46 m) from the cutter head to the end of the trailing gantry system.

Paralleling the western side of Mazeroski Way, the 2,240 ft (683 m) TBM section of the tunnel passes below the Equitable Resources building. The tunnel descends on a 6.6 percent grade from the North Shore to a depth of 69 ft (21 m) (25 ft [7.6 m] river depth, 22 ft [6.7 m] further to top of 22 ft [6.7 m] diameter tunnel bore). Below the Allegheny River, the path turns left then right, about 45 degrees each time, to align with Stanwix Street. The tunnel ascends a 7.6 percent grade to arrive at the Gateway Station. Figure 56 shows a photograph of the completed North Shore Connector tunnel.

The key challenges of the North Shore Connector projects included the following: threading the tunnels through the pile-supported foundation of a downtown Pittsburgh landmark building; passing under the 25 ft (7.6 m) deep Allegheny River; and tunneling beneath a busy downtown street adjacent to Penn Avenue Place, and an historically important building founded on spread footings. In addition, controlling ground movement to mitigate the potential for damage to buildings was of paramount importance (Wargo et al., 2009).

The North Shore Connectors original budget was estimated at $350 million. The final cost was $523.4 million (Schmitz, 2010).

managing stream flow within the Ohio River Basin in terms of flood control, navigation, power, irrigation, and other possible uses. As a result of intense lobbying by the Ohio River Flood Board and with financial cooperation from the Commonwealth of Pennsylvania, the Pittsburgh District of the U.S. Army Corps of Engineers (Pittsburgh District) completed its first comprehensive River Basin Report in 1935. The report proposed a series of dams that would create reservoirs in the headwaters of the Ohio River Basin. This report represented the complete commitment by the Pittsburgh District to the concept of dams utilized for multipurpose water resource development in addition to flood control (Johnson, 1978). Multipurpose projects can include a combination of flood control, water flow for reliable navigation, water quality, recreation, and hydropower generation.

Historic flooding has been common in the Pittsburgh region. Towards noon on St. Patrick’s Day in 1936, waters began to fill the valleys in Johnstown, PA. Much like the devastating flood of 1889, the narrow, natural, topographic channels of Stoney Creek and the Little Conemaugh River were incapable of passing much of the rising volume of flood waters through the City of Johnstown, resulting in major flooding. “A scene of inconceivable desolation, following devastation by a flood that rivaled the deluge caused by the historic dam break in 1889” was cited by a reporter from the Engineering News-Record in his description of Johnstown after the flood (Johnson, 1978, p. 24). The floodwater surges moved downstream to Pittsburgh, where water filled the downtown, and many residents took to boats to navigate the city streets (see Figure 57). The rivers crested at 46 ft (14 m), which is 30 ft (9 m) above normal river stage in Pittsburgh, on March

pleted the circumference of a given ring). The TBM then used hydraulic legs to push off the placed concrete rings as it moved forward. The complete mining assembly measured approximately 150 ft (46 m) from the cutter head to the end of the trailing gantry system.

Paralleling the western side of Mazeroski Way, the 2,240 ft (683 m) TBM section of the tunnel passes below the Equitable Resources building. The tunnel descends on a 6.6 percent grade from the North Shore to a depth of 69 ft (21 m) (25 ft [7.6 m] river depth, 22 ft [6.7 m] further to top of 22 ft [6.7 m] diameter tunnel bore). Below the Allegheny River, the path turns left then right, about 45 degrees each time, to align with Stanwix Street. The tunnel ascends a 7.6 percent grade to arrive at the Gateway Station. Figure 56 shows a photograph of the completed North Shore Connector tunnel.

The key challenges of the North Shore Connector projects included the following: threading the tunnels through the pile-supported foundation of a downtown Pittsburgh landmark building; passing under the 25 ft (7.6 m) deep Allegheny River; and tunneling beneath a busy downtown street adjacent to Penn Avenue Place, and an historically important building founded on spread footings. In addition, controlling ground movement to mitigate the potential for damage to buildings was of paramount importance (Wargo et al., 2009).

The North Shore Connectors original budget was estimated at $350 million. The final cost was $523.4 million (Schmitz, 2010).

managing stream flow within the Ohio River Basin in terms of flood control, navigation, power, irrigation, and other possible uses. As a result of intense lobbying by the Ohio River Flood Board and with financial cooperation from the Commonwealth of Pennsylvania, the Pittsburgh District of the U.S. Army Corps of Engineers (Pittsburgh District) completed its first comprehensive River Basin Report in 1935. The report proposed a series of dams that would create reservoirs in the headwaters of the Ohio River Basin. This report represented the complete commitment by the Pittsburgh District to the concept of dams utilized for multipurpose water resource development in addition to flood control (Johnson, 1978). Multipurpose projects can include a combination of flood control, water flow for reliable navigation, water quality, recreation, and hydropower generation.

Historic flooding has been common in the Pittsburgh region. Towards noon on St. Patrick’s Day in 1936, waters began to fill the valleys in Johnstown, PA. Much like the devastating flood of 1889, the narrow, natural, topographic channels of Stoney Creek and the Little Conemaugh River were incapable of passing much of the rising volume of flood waters through the City of Johnstown, resulting in major flooding. “A scene of inconceivable desolation, following devastation by a flood that rivaled the deluge caused by the historic dam break in 1889” was cited by a reporter from the Engineering News-Record in his description of Johnstown after the flood (Johnson, 1978, p. 24). The floodwater surges moved downstream to Pittsburgh, where water filled the downtown, and many residents took to boats to navigate the city streets (see Figure 57). The rivers crested at 46 ft (14 m), which is 30 ft (9 m) above normal river stage in Pittsburgh, on March

Dams The Ohio River Flood Board, established by the federal government in 1912, examined many strategies for 86

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Dams The Ohio River Flood Board, established by the federal government in 1912, examined many strategies for 86

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

Geology of Pittsburgh

18, 1936. This flooding surpassed prior record stages by more than 5 ft (1.5 m) and resulted in flooding of 62 percent of the downtown “Golden Triangle” area of the city.

It became clear following the March 1936 flood that series of dams and reservoirs were was needed to protect the city from a real and recurring topographically driven flood threat. Congress passed the federal Flood Water Control Act of 1936, authorizing and funding these secondary flood-control structures, including dams and levees, mostly located on tributaries to the three major rivers. Several of the dams built in the Upper Ohio River Basin that protect Pittsburgh today were authorized by this act. One of the most significant retention structures is Kinzua Dam, located on the Allegheny River near Warren, PA. Other flood-control structures authorized by this federal act include Tionesta Dam, Crooked Creek Dam, Conemaugh Dam, and Loyalhanna Dam, all located in the Allegheny River basin above Pittsburgh. In addition, Youghiogheny Dam, located on a tributary to the Monongahela River, was also authorized.

Tygart Dam, which also protects Pittsburgh, was under construction by the Pittsburgh District prior to the Flood Control Act of 1936. It is located on the Tygart River, a tributary to the Monongahela River, at Grafton, WV, and was completed in 1938 at cost of $18.5 million dollars. At the time it was built, Tygart Dam was the highest concrete gravity dam east of the Mississippi. Tygart Dam is a multipurpose project that provides significant flood and flow control to areas downstream, including Morgantown, WV, and ultimately Pittsburgh. Tygart Dam, in addition to the five dams built in response to the act, formed the mainstay of comprehensive surface-water management by the Pittsburgh District in the Upper Ohio River Basin.

Eventually, the total number of dam projects constructed and operated by the Pittsburgh District reached the current level of 16. The project that forms the largest single reservoir in the basin, at a length of over 26 mi. (42 km), is Kinzua Dam, located on the Allegheny River near the Pennsylvania–New York border. Kinzua Dam is the only dam on the mainstem Allegheny River that flows south to the city of Pittsburgh. It is a combination concrete gravity and earth-rock fill dam and is what many believe to be one of Dr. Shailer Philbrick’s finest foundation designs. Dr. Philbrick was the Pittsburgh District geologist for the foundation of the dam. The original siting of the dam axis was more than 1 mi (1.6 km) upstream from its present-day location. On account of considerable depth to sound bedrock (silt-shale), the original design called for a rather deep excavation with cofferdam construction and construction of a concrete gravity dam. Dr. Philbrick conducted a detailed field

Geology of Pittsburgh

investigation, which included studying the glacial history of the valley and then planning and conducting an extensive program of core borings and geophysical surveys in reaches downstream of the originally selected site. With these data in hand, he proposed an alternate location for the construction of the dam axis, so the dam was fit to the site geologic conditions and the cost estimate was reduced. The design modification was accomplished by constructing a concrete gravity dam section where bedrock was shallow on the left side of the valley and an earth-rock fill embankment on the right side of the valley where bedrock was much deeper. The concrete gravity dam was cast in progressive monolithic sections, so as to permit river flow to continue throughout construction. The embankment was constructed on alluvial soils with an upstream clay-soil blanket. The clay blanket was subsequently tied into a concrete cut-off wall taken to significant depths within the river valley alluvium. This was the first slurry cut-off wall constructed for a dam in the United States (Legget and Karrow, 1983). The earth-rock embankment has a wrap-around section that ties it into the concrete gravity section of the dam.

Construction of the dam was completed in 1965. The project has a pumped storage hydropower unit that is operated by a private utility in cooperation with the Pittsburgh District.

The primary purpose of the project is flood mitigation, but the other uses, including water supply, recreation, and hydropower, are carefully balanced to optimize the use of the available water. The ASCE Pittsburgh Section bestowed its Outstanding Civil Engineering Award on the project, recognizing its innovation. The optimized foundation design saved several million dollars. Dr. Philbrick received the Association of Environmental & Engineering Geologists (AEG) Claire P. Holdredge Award in 1977 for his seminal paper “Kinzua Dam and the Glacial Foreland” (Philbrick, 1976). Two honorary members of AEG, Dr. Shailer Philbrick and Harry Ferguson, a coworker and successor as district geologist, were instrumental in developing efficient foundation designs for most of the flood-control dams located within the Pittsburgh District.

History of Cofferdam Construction Cofferdams have a long history of use in the Pittsburgh region, in particular for concrete gravity dams and for the construction of navigation locks and dams founded on bedrock. The earliest local cofferdams date back to 1878, with federal government construction of the Davis Island Lock and Dam, the first navigation project to be constructed on the Ohio River. Davis Island is located downstream of Pittsburgh. Between

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18, 1936. This flooding surpassed prior record stages by more than 5 ft (1.5 m) and resulted in flooding of 62 percent of the downtown “Golden Triangle” area of the city.

It became clear following the March 1936 flood that series of dams and reservoirs were was needed to protect the city from a real and recurring topographically driven flood threat. Congress passed the federal Flood Water Control Act of 1936, authorizing and funding these secondary flood-control structures, including dams and levees, mostly located on tributaries to the three major rivers. Several of the dams built in the Upper Ohio River Basin that protect Pittsburgh today were authorized by this act. One of the most significant retention structures is Kinzua Dam, located on the Allegheny River near Warren, PA. Other flood-control structures authorized by this federal act include Tionesta Dam, Crooked Creek Dam, Conemaugh Dam, and Loyalhanna Dam, all located in the Allegheny River basin above Pittsburgh. In addition, Youghiogheny Dam, located on a tributary to the Monongahela River, was also authorized.

Tygart Dam, which also protects Pittsburgh, was under construction by the Pittsburgh District prior to the Flood Control Act of 1936. It is located on the Tygart River, a tributary to the Monongahela River, at Grafton, WV, and was completed in 1938 at cost of $18.5 million dollars. At the time it was built, Tygart Dam was the highest concrete gravity dam east of the Mississippi. Tygart Dam is a multipurpose project that provides significant flood and flow control to areas downstream, including Morgantown, WV, and ultimately Pittsburgh. Tygart Dam, in addition to the five dams built in response to the act, formed the mainstay of comprehensive surface-water management by the Pittsburgh District in the Upper Ohio River Basin.

Eventually, the total number of dam projects constructed and operated by the Pittsburgh District reached the current level of 16. The project that forms the largest single reservoir in the basin, at a length of over 26 mi. (42 km), is Kinzua Dam, located on the Allegheny River near the Pennsylvania–New York border. Kinzua Dam is the only dam on the mainstem Allegheny River that flows south to the city of Pittsburgh. It is a combination concrete gravity and earth-rock fill dam and is what many believe to be one of Dr. Shailer Philbrick’s finest foundation designs. Dr. Philbrick was the Pittsburgh District geologist for the foundation of the dam. The original siting of the dam axis was more than 1 mi (1.6 km) upstream from its present-day location. On account of considerable depth to sound bedrock (silt-shale), the original design called for a rather deep excavation with cofferdam construction and construction of a concrete gravity dam. Dr. Philbrick conducted a detailed field

investigation, which included studying the glacial history of the valley and then planning and conducting an extensive program of core borings and geophysical surveys in reaches downstream of the originally selected site. With these data in hand, he proposed an alternate location for the construction of the dam axis, so the dam was fit to the site geologic conditions and the cost estimate was reduced. The design modification was accomplished by constructing a concrete gravity dam section where bedrock was shallow on the left side of the valley and an earth-rock fill embankment on the right side of the valley where bedrock was much deeper. The concrete gravity dam was cast in progressive monolithic sections, so as to permit river flow to continue throughout construction. The embankment was constructed on alluvial soils with an upstream clay-soil blanket. The clay blanket was subsequently tied into a concrete cut-off wall taken to significant depths within the river valley alluvium. This was the first slurry cut-off wall constructed for a dam in the United States (Legget and Karrow, 1983). The earth-rock embankment has a wrap-around section that ties it into the concrete gravity section of the dam.

Construction of the dam was completed in 1965. The project has a pumped storage hydropower unit that is operated by a private utility in cooperation with the Pittsburgh District.

The primary purpose of the project is flood mitigation, but the other uses, including water supply, recreation, and hydropower, are carefully balanced to optimize the use of the available water. The ASCE Pittsburgh Section bestowed its Outstanding Civil Engineering Award on the project, recognizing its innovation. The optimized foundation design saved several million dollars. Dr. Philbrick received the Association of Environmental & Engineering Geologists (AEG) Claire P. Holdredge Award in 1977 for his seminal paper “Kinzua Dam and the Glacial Foreland” (Philbrick, 1976). Two honorary members of AEG, Dr. Shailer Philbrick and Harry Ferguson, a coworker and successor as district geologist, were instrumental in developing efficient foundation designs for most of the flood-control dams located within the Pittsburgh District.

History of Cofferdam Construction Cofferdams have a long history of use in the Pittsburgh region, in particular for concrete gravity dams and for the construction of navigation locks and dams founded on bedrock. The earliest local cofferdams date back to 1878, with federal government construction of the Davis Island Lock and Dam, the first navigation project to be constructed on the Ohio River. Davis Island is located downstream of Pittsburgh. Between

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1878, when construction began, and 1885, when completed, the Davis Island Lock and Dam project incorporated seven very rudimentary wooden but successful cofferdams. O’Bannon (2009) suggested that the cofferdams were designed and constructed in conformance with principles outlined in: An Elementary Course of Civil Engineering, for Use of the Cadets of the United States Military Academy (Mahan, 1837).

Cofferdam construction continued on the three rivers from the late 1800s to late 1900s and eventually transitioned from wood to steel sheet pile. From a geological standpoint, cofferdams permitted complete dewatering and then open excavation of river alluvial sediments to reach bedrock and into the rock until a suitable foundation level was encountered. Once uncovered, standard practice was to clean the exposed rock with brushes and high-pressure water jets, clean and treat rock defects with dental concrete, and then cast dam-base concrete on the prepared surface as soon as practical, as a means to avoid any deterioration by air or water slaking (in the case of fine-grained argillaceous bedrock).

In the later 1990s, a highly unique cofferdam was built on the Monongahela River near the Pennsylvania–West Virginia border. The old existing navigation lock at Point Marion, PA, built in 1926, had exceeded its design life. A new, larger lock was needed to improve both structure reliability and to ensure continuous river passage. The challenge for the U.S. Army Corps of Engineers was to build a larger lock chamber (84 ft [26 m] by 720 ft [219 m]) on the landward side of the existing lock chamber (56 ft [17 m] by 360 ft [110 m]). Construction of a lock landward of an existing lock had only been attempted once before in the United States, in 1961, at the General Joe Wheeler Lock and Dam on the Tennessee River in northern Alabama. Construction at the General Joe Wheeler Lock and Dam met with disaster when, during excavation for the new lock, the land wall of the existing lock slid into the excavation. This resulted in loss of life and closure of the river to navigation for several years. The sliding failure was determined to be related to weak clay shale seams in the underlying limestone, a condition that had not been identified during the site investigation (Terzaghi, 1962).

The Pittsburgh District undertook similar construction at Point Marion Lock and Dam with the experience of Wheeler Lock well in mind. This facility is located on the Monongahela River on the Pennsylvania– West Virginia border, about 70 mi. (113 km) upstream from Pittsburgh. Construction of the new lock chamber had to be accomplished while keeping the existing lock chamber in service to accommodate on-going river navigation (Greene et al., 1993). Three rows of high-capacity rock anchors (nearly 500 total) were 88

Figure 58. Rock anchor configuration for Point Marion Lock cofferdam (Greene et al., 1993).

installed through the landward wall of the existing lock and anchored into the underlying claystones, siltstones, and sandstones, so that the wall could be incorporated as a portion of the cofferdam for the new lock.

One row of vertical anchors was installed prior to excavation, and two rows of inclined anchors were placed as the excavation was carried two lifts deeper (see Figure 58). A large portion of the land-wall foundation of the existing lock was on claystone, and therefore it was of the utmost importance that the sliding and overturning stability of the wall be improved (Greene et al., 1993). An extensive instrumentation program was installed to monitor movements and water levels; this program included shear strips, inclinometers, piezometers, and load cells placed on selected inclined rock anchors. The new lock was completed in the early 1990s, and in 1994, the ASCE Pittsburgh Section awarded Point Marion Lock and Dam the Outstanding Civil Engineering Achievement Award. This distinction was primarily due to the unique cofferdam design and construction.

Post Cofferdam In-the-Wet Construction In the late 1990s, replacement of the 100 year old Braddock Dam became necessary. Braddock Dam was part of the Braddock Locks and Dam navigation project, located only 12 mi. (19 km) upstream from Pittsburgh, and it was the first lock and dam on the Monongahela River. Braddock Dam introduced a new type of in-river construction that did not employ the use of cofferdams. This project represented innovation and was a major departure from the proven methods that had been used for several decades. The Braddock Dam employed “float-in” or “in-the-wet construction.” The project began in 1999 and was completed in 2004. It represented the first time in the his-

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Gray, Greene, Fandray, and Turka

1878, when construction began, and 1885, when completed, the Davis Island Lock and Dam project incorporated seven very rudimentary wooden but successful cofferdams. O’Bannon (2009) suggested that the cofferdams were designed and constructed in conformance with principles outlined in: An Elementary Course of Civil Engineering, for Use of the Cadets of the United States Military Academy (Mahan, 1837).

Cofferdam construction continued on the three rivers from the late 1800s to late 1900s and eventually transitioned from wood to steel sheet pile. From a geological standpoint, cofferdams permitted complete dewatering and then open excavation of river alluvial sediments to reach bedrock and into the rock until a suitable foundation level was encountered. Once uncovered, standard practice was to clean the exposed rock with brushes and high-pressure water jets, clean and treat rock defects with dental concrete, and then cast dam-base concrete on the prepared surface as soon as practical, as a means to avoid any deterioration by air or water slaking (in the case of fine-grained argillaceous bedrock).

In the later 1990s, a highly unique cofferdam was built on the Monongahela River near the Pennsylvania–West Virginia border. The old existing navigation lock at Point Marion, PA, built in 1926, had exceeded its design life. A new, larger lock was needed to improve both structure reliability and to ensure continuous river passage. The challenge for the U.S. Army Corps of Engineers was to build a larger lock chamber (84 ft [26 m] by 720 ft [219 m]) on the landward side of the existing lock chamber (56 ft [17 m] by 360 ft [110 m]). Construction of a lock landward of an existing lock had only been attempted once before in the United States, in 1961, at the General Joe Wheeler Lock and Dam on the Tennessee River in northern Alabama. Construction at the General Joe Wheeler Lock and Dam met with disaster when, during excavation for the new lock, the land wall of the existing lock slid into the excavation. This resulted in loss of life and closure of the river to navigation for several years. The sliding failure was determined to be related to weak clay shale seams in the underlying limestone, a condition that had not been identified during the site investigation (Terzaghi, 1962).

The Pittsburgh District undertook similar construction at Point Marion Lock and Dam with the experience of Wheeler Lock well in mind. This facility is located on the Monongahela River on the Pennsylvania– West Virginia border, about 70 mi. (113 km) upstream from Pittsburgh. Construction of the new lock chamber had to be accomplished while keeping the existing lock chamber in service to accommodate on-going river navigation (Greene et al., 1993). Three rows of high-capacity rock anchors (nearly 500 total) were 88

Figure 58. Rock anchor configuration for Point Marion Lock cofferdam (Greene et al., 1993).

installed through the landward wall of the existing lock and anchored into the underlying claystones, siltstones, and sandstones, so that the wall could be incorporated as a portion of the cofferdam for the new lock.

One row of vertical anchors was installed prior to excavation, and two rows of inclined anchors were placed as the excavation was carried two lifts deeper (see Figure 58). A large portion of the land-wall foundation of the existing lock was on claystone, and therefore it was of the utmost importance that the sliding and overturning stability of the wall be improved (Greene et al., 1993). An extensive instrumentation program was installed to monitor movements and water levels; this program included shear strips, inclinometers, piezometers, and load cells placed on selected inclined rock anchors. The new lock was completed in the early 1990s, and in 1994, the ASCE Pittsburgh Section awarded Point Marion Lock and Dam the Outstanding Civil Engineering Achievement Award. This distinction was primarily due to the unique cofferdam design and construction.

Post Cofferdam In-the-Wet Construction In the late 1990s, replacement of the 100 year old Braddock Dam became necessary. Braddock Dam was part of the Braddock Locks and Dam navigation project, located only 12 mi. (19 km) upstream from Pittsburgh, and it was the first lock and dam on the Monongahela River. Braddock Dam introduced a new type of in-river construction that did not employ the use of cofferdams. This project represented innovation and was a major departure from the proven methods that had been used for several decades. The Braddock Dam employed “float-in” or “in-the-wet construction.” The project began in 1999 and was completed in 2004. It represented the first time in the his-

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Figure 59. Braddock Dam segment–foundation interface (courtesy of the U.S. Army Corps of Engineers, Pittsburgh District).

tory of an inland navigation system that a concrete dam had been floated into place (Edwardo et al., 2002).

As opposed to traditional “in-the-dry” methods of cofferdam construction, the “in-the-wet” method permitted drilled shaft foundations to be built at the site while the two dam segments, which were composed of a combination of pre-cast concrete panels and conventional concrete, were fabricated at an off-site casting basin located downstream of Pittsburgh. Eighty-nine reinforced concrete drilled shafts were installed within the footprint of the dam. Each shaft was 78 in. (2 m) in diameter and 40 ft (12 m) long, which included a 15–20 ft (4.5–6 m) long drilled rock socket. Approximately 20 percent of the drilled shafts were affixed with circular-form, hydraulic flat jacks, which were subsequently used to level the segments of the dam. Once the drilled shafts were completed, the concrete segments were floated upriver, passing through three locks, to the location of the new dam site (Edwardo et al., 2002).

Segment 1 was a 330 ft (100 m) long by 104 ft (32 m) wide concrete section of the dam, and it weighed nearly 11,600 tons (10,000 metric tons), (see Figure 59). The segment was lowered onto the drilled shaft foundations by filling the structure with water and sinking it. The segment-shaft connections were grouted under water, and the interior of the segment was filled with tremie concrete, thus displacing the water. A neat cement grout was used to fill the 1 ft (0.3 m) void that existed between the base of the dam and a pre-placed graded gravel base under the footprint of the dam.

Steel sheet piles (Z-type) driven to rock at both the upstream and downstream limits of the dam served as an additional barrier to prevent seepage under the dam.

Geology of Pittsburgh

Figure 60. Completed Braddock Dam in 2004 (courtesy of the U.S. Army Corps of Engineers, Pittsburgh District).

Segment 2, which measured 265 ft (81 m) by 104 ft (32 m) and weighed 9,000 tons (8,164 metric tons), was installed in the same manner as segment 1.

To complete the Braddock Dam project, the existing 100 year old fixed-crest dam, located approximately 600 ft (182 m) downstream, was completely removed to the riverbed, and the demolished concrete was used for creation of underwater simulated reefs to promote fish habitat. Another environmental aspect of the project was that the dredged material from the footprint of the new dam was tested and found to be suitable for riverside disposal. Some 400,000 yards (305,821 m3 ) of dredged material provided cover for the restoration of a nearby brownfield site (an abandoned steel mill property). A photograph of the completed Braddock Dam is shown in Figure 60.

UNDERGROUND STORAGE For over a century, there has been underground dimension-stone mining of the Vanport Limestone, near Pittsburgh. Several of these abandoned roomand-pillar limestone quarry mines are now used for office space, records storage, vehicle and recreational vehicle (RV) storage, growing mushrooms, manufacture of precision telescope lenses, and even the filming of movies (Kochanov and Bragonier, 2005).

The second largest employer in Butler County is the Boyers underground mine-storage facility, which is located approximately 40 mi. (64 km) north of Pittsburgh. This facility contains offices for six different agencies, including the Office of Personnel Management, Social Security Administration, and The Smithsonian Institution, with a combined on-state

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Figure 59. Braddock Dam segment–foundation interface (courtesy of the U.S. Army Corps of Engineers, Pittsburgh District).

tory of an inland navigation system that a concrete dam had been floated into place (Edwardo et al., 2002).

As opposed to traditional “in-the-dry” methods of cofferdam construction, the “in-the-wet” method permitted drilled shaft foundations to be built at the site while the two dam segments, which were composed of a combination of pre-cast concrete panels and conventional concrete, were fabricated at an off-site casting basin located downstream of Pittsburgh. Eighty-nine reinforced concrete drilled shafts were installed within the footprint of the dam. Each shaft was 78 in. (2 m) in diameter and 40 ft (12 m) long, which included a 15–20 ft (4.5–6 m) long drilled rock socket. Approximately 20 percent of the drilled shafts were affixed with circular-form, hydraulic flat jacks, which were subsequently used to level the segments of the dam. Once the drilled shafts were completed, the concrete segments were floated upriver, passing through three locks, to the location of the new dam site (Edwardo et al., 2002).

Segment 1 was a 330 ft (100 m) long by 104 ft (32 m) wide concrete section of the dam, and it weighed nearly 11,600 tons (10,000 metric tons), (see Figure 59). The segment was lowered onto the drilled shaft foundations by filling the structure with water and sinking it. The segment-shaft connections were grouted under water, and the interior of the segment was filled with tremie concrete, thus displacing the water. A neat cement grout was used to fill the 1 ft (0.3 m) void that existed between the base of the dam and a pre-placed graded gravel base under the footprint of the dam.

Steel sheet piles (Z-type) driven to rock at both the upstream and downstream limits of the dam served as an additional barrier to prevent seepage under the dam.

Figure 60. Completed Braddock Dam in 2004 (courtesy of the U.S. Army Corps of Engineers, Pittsburgh District).

Segment 2, which measured 265 ft (81 m) by 104 ft (32 m) and weighed 9,000 tons (8,164 metric tons), was installed in the same manner as segment 1.

To complete the Braddock Dam project, the existing 100 year old fixed-crest dam, located approximately 600 ft (182 m) downstream, was completely removed to the riverbed, and the demolished concrete was used for creation of underwater simulated reefs to promote fish habitat. Another environmental aspect of the project was that the dredged material from the footprint of the new dam was tested and found to be suitable for riverside disposal. Some 400,000 yards (305,821 m3 ) of dredged material provided cover for the restoration of a nearby brownfield site (an abandoned steel mill property). A photograph of the completed Braddock Dam is shown in Figure 60.

UNDERGROUND STORAGE For over a century, there has been underground dimension-stone mining of the Vanport Limestone, near Pittsburgh. Several of these abandoned roomand-pillar limestone quarry mines are now used for office space, records storage, vehicle and recreational vehicle (RV) storage, growing mushrooms, manufacture of precision telescope lenses, and even the filming of movies (Kochanov and Bragonier, 2005).

The second largest employer in Butler County is the Boyers underground mine-storage facility, which is located approximately 40 mi. (64 km) north of Pittsburgh. This facility contains offices for six different agencies, including the Office of Personnel Management, Social Security Administration, and The Smithsonian Institution, with a combined on-state

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payroll of some 3,000 federal employees, and a private sector record storage firm as well.

The world’s largest mushroom growing facility is in Worthington, which is located about 35 mi. (56 km) northeast of Pittsburgh. This re-purposed former limestone quarry mine features a controlled entry and egress at more than 300 ft (91 m) below the ground surface, and it has been stabilized and improved for production for as far as 0.75 mi (1.2 km) in from the entry portal. The entire original mined area consists of about 150 mi. (241 km) of through-pillar pair passageways that were created by the termination of the rock-production life, now more than 75 years ago. The mine environment, with its constant cool temperature (62°F) and high humidity, is ideal for growing mushrooms.

The Wampum Mine facility, which is also located north of Pittsburgh, is currently used for records storage and was the site for filming portions of the movie “The Zombies” (Kochanov and Bragonier, 2005). The mine had been used during the early years of the Atomic Age to store nuclear materials. The most unique use of the mine occurred in the late 1990s, when a telescope mirror, which at that time was the world’s largest single-piece optical element, was manufactured within the Wampum Mine. The mirror blank, initially fabricated by Corning, Inc., measured over 27 ft (8 m) in diameter and was about 9 in. (23 cm) thick.

A Pittsburgh firm, Contraves, converted a portion of the Wampum Mine into an optical fabrication facility where the mirror was ground, polished, and tested.

The mirror was finished in 1997 and was installed in a telescope at the Mauna Kea Observatory in Hawaii.

In addition to converted mined areas, depleted gas and oil fields have been converted for current natural gas storage. One of more noted gas storage fields in the area is under the Oakford Natural Gas Storage facility about 25 mi. (40 km) east of Pittsburgh. It is one of the largest underground storage facilities in Pennsylvania, and it provides temporary storage for natural gas originating from the South and Midwest for markets in the Northeast and the Mid-Atlantic region.

There are two separate storage zones. One is in the Lower Mississippian Murrysville Sand, and the other is in an Upper Devonian sandstone called the “Fifth Sand” (Enbridge, 2017). These storage fields are both geologically contained by stratigraphic and structural characteristics particular to this area.

ENVIRONMENTAL CONCERNS Abandoned Mine Lands One unintended and poorly considered legacy of the mining of the abundant coal resources in the Pitts90

burgh region is the mining-related problems that remain, problems that are generally referred to as abandoned mine lands or AML. AML problems include mine subsidence; unfilled or improperly filled shafts, slopes, and drifts; mine and spoil pile (culm bank) fires; unstable slopes; gas problems stemming from methane, carbon monoxide, carbon dioxide, or hydrogen sulfide; and acid mine drainage.

Coals was mined nearly everywhere in the Pittsburgh region, and now the AML problems are found nearly everywhere as well. The shallow depth to the Pittsburgh Coal, its significant thickness, and the early mining methods and laws, such as 50 percent mining for surface support, came together to create an almost ideal environment for mine subsidence. Much of the area to the east and south of the city is underlain by shallow, abandoned room-and-pillar mining where the overburden thickness is less than 100 ft (30 m), and often less than 50 ft (15 m). An engineering-based study of subsidence over the Pittsburgh Coal (Gray et al., 1977) that was completed in 1976 determined that 251 of the 352 documented incidents of subsidence (about 71 percent) occurred in Allegheny County. This was attributed in part to the area being one of the earliest mined and also to being one of the most densely populated sectors of the region.

There are over 34,000 documented AML features in the state and 296 documented AML sites in Allegheny County alone. Figure 61 shows the current number of AML sites by county in Pennsylvania. As can be seen from Figure 61, the problem is extensive, and the number of AML sites for all of the surrounding mined counties is similar. Figure 62 shows the distribution of individual AML sites in Allegheny County. The Federal Office of Surface Mining had defined three priority levels for pre-law AML sites under the Surface Mining Control and Reclamation Act of 1977 (SMCRA). They initiated an inventory of priority 1 (P1) and priority 2 (P2) AML sites, which are the sites that are counted and are shown on Figure 62, and now the state maintains the inventory (PADEP, 2014). Those sites are generally defined as requiring reclamation to protect the public health and safety from extreme danger of adverse effects (P1) or just from the adverse effects (P2) of coal-mining practices.

Priority 3, the sites requiring restoration of land and water resources because of environmental degradation previously caused by the adverse effects of coal mining, are generally not included in the AML inventory list. These sites, which include mine water discharges, abandoned surface mines, and abandoned mine spoil dumps that are not included within P1 and P2 sites, are considered to have a very low priority for reclamation, even though they are as ubiquitous as the P1 and P2 sites.

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payroll of some 3,000 federal employees, and a private sector record storage firm as well.

The world’s largest mushroom growing facility is in Worthington, which is located about 35 mi. (56 km) northeast of Pittsburgh. This re-purposed former limestone quarry mine features a controlled entry and egress at more than 300 ft (91 m) below the ground surface, and it has been stabilized and improved for production for as far as 0.75 mi (1.2 km) in from the entry portal. The entire original mined area consists of about 150 mi. (241 km) of through-pillar pair passageways that were created by the termination of the rock-production life, now more than 75 years ago. The mine environment, with its constant cool temperature (62°F) and high humidity, is ideal for growing mushrooms.

The Wampum Mine facility, which is also located north of Pittsburgh, is currently used for records storage and was the site for filming portions of the movie “The Zombies” (Kochanov and Bragonier, 2005). The mine had been used during the early years of the Atomic Age to store nuclear materials. The most unique use of the mine occurred in the late 1990s, when a telescope mirror, which at that time was the world’s largest single-piece optical element, was manufactured within the Wampum Mine. The mirror blank, initially fabricated by Corning, Inc., measured over 27 ft (8 m) in diameter and was about 9 in. (23 cm) thick.

A Pittsburgh firm, Contraves, converted a portion of the Wampum Mine into an optical fabrication facility where the mirror was ground, polished, and tested.

The mirror was finished in 1997 and was installed in a telescope at the Mauna Kea Observatory in Hawaii.

In addition to converted mined areas, depleted gas and oil fields have been converted for current natural gas storage. One of more noted gas storage fields in the area is under the Oakford Natural Gas Storage facility about 25 mi. (40 km) east of Pittsburgh. It is one of the largest underground storage facilities in Pennsylvania, and it provides temporary storage for natural gas originating from the South and Midwest for markets in the Northeast and the Mid-Atlantic region.

There are two separate storage zones. One is in the Lower Mississippian Murrysville Sand, and the other is in an Upper Devonian sandstone called the “Fifth Sand” (Enbridge, 2017). These storage fields are both geologically contained by stratigraphic and structural characteristics particular to this area.

ENVIRONMENTAL CONCERNS Abandoned Mine Lands One unintended and poorly considered legacy of the mining of the abundant coal resources in the Pitts90

burgh region is the mining-related problems that remain, problems that are generally referred to as abandoned mine lands or AML. AML problems include mine subsidence; unfilled or improperly filled shafts, slopes, and drifts; mine and spoil pile (culm bank) fires; unstable slopes; gas problems stemming from methane, carbon monoxide, carbon dioxide, or hydrogen sulfide; and acid mine drainage.

Coals was mined nearly everywhere in the Pittsburgh region, and now the AML problems are found nearly everywhere as well. The shallow depth to the Pittsburgh Coal, its significant thickness, and the early mining methods and laws, such as 50 percent mining for surface support, came together to create an almost ideal environment for mine subsidence. Much of the area to the east and south of the city is underlain by shallow, abandoned room-and-pillar mining where the overburden thickness is less than 100 ft (30 m), and often less than 50 ft (15 m). An engineering-based study of subsidence over the Pittsburgh Coal (Gray et al., 1977) that was completed in 1976 determined that 251 of the 352 documented incidents of subsidence (about 71 percent) occurred in Allegheny County. This was attributed in part to the area being one of the earliest mined and also to being one of the most densely populated sectors of the region.

There are over 34,000 documented AML features in the state and 296 documented AML sites in Allegheny County alone. Figure 61 shows the current number of AML sites by county in Pennsylvania. As can be seen from Figure 61, the problem is extensive, and the number of AML sites for all of the surrounding mined counties is similar. Figure 62 shows the distribution of individual AML sites in Allegheny County. The Federal Office of Surface Mining had defined three priority levels for pre-law AML sites under the Surface Mining Control and Reclamation Act of 1977 (SMCRA). They initiated an inventory of priority 1 (P1) and priority 2 (P2) AML sites, which are the sites that are counted and are shown on Figure 62, and now the state maintains the inventory (PADEP, 2014). Those sites are generally defined as requiring reclamation to protect the public health and safety from extreme danger of adverse effects (P1) or just from the adverse effects (P2) of coal-mining practices.

Priority 3, the sites requiring restoration of land and water resources because of environmental degradation previously caused by the adverse effects of coal mining, are generally not included in the AML inventory list. These sites, which include mine water discharges, abandoned surface mines, and abandoned mine spoil dumps that are not included within P1 and P2 sites, are considered to have a very low priority for reclamation, even though they are as ubiquitous as the P1 and P2 sites.

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 61. Abandoned mine lands (AML) sites in Pennsylvania by county (PADEP, 2014).

Figure 61. Abandoned mine lands (AML) sites in Pennsylvania by county (PADEP, 2014).

Hydraulic Fracturing Fluids Associated with Natural Gas In recent years, there has been a boom in the exploration and production of natural gas and natural gas liquids associated with the Marcellus Shale Formation (Pennsylvania Department of Conservation and Natural Resources, 2014). Significant secondary natural gas recovery has resulted from physically improving the permeability of the host rock shale through the process of hydraulic fracturing (fracking) in conjunction with lateral drilling (Figure 63). However, there is controversy concerning the volume, chemical additives, and ultimate fate of fluids used in the hydraulic fracking process. Some 6 to 10 million gallons of freshwater combined with surfactants, chemical additives, and propping sand are used to frack a single well, and to keep the induced fractures open to radially

inward flow of formation gas. The actual volume of water, sand, and chemicals used is largely dependent on the length of the lateral leg of the borehole. Fluids used in the hydrofracturing process return to the surface as flowback and produced water and must be recovered with the enhanced flow of natural gas and then treated appropriately and disposed in a regulatory/permitted manner. Major flowback constituents of regulatory concern are released chlorides and total dissolved solids, both which have been used to fingerprint the fluids, if and when they may be detected in surface water. Some of the drillers have elected to dispose of the recovered fluids in Class 2 deep injection wells in neighboring Ohio, and some operators are recycling their produced fluids for re-use in other fracking operations. Flowback is first treated in public and industrial wastewater treatment facilities. Prior studies by the U.S. Army Corps of Engineers (USACE,

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Hydraulic Fracturing Fluids Associated with Natural Gas In recent years, there has been a boom in the exploration and production of natural gas and natural gas liquids associated with the Marcellus Shale Formation (Pennsylvania Department of Conservation and Natural Resources, 2014). Significant secondary natural gas recovery has resulted from physically improving the permeability of the host rock shale through the process of hydraulic fracturing (fracking) in conjunction with lateral drilling (Figure 63). However, there is controversy concerning the volume, chemical additives, and ultimate fate of fluids used in the hydraulic fracking process. Some 6 to 10 million gallons of freshwater combined with surfactants, chemical additives, and propping sand are used to frack a single well, and to keep the induced fractures open to radially

inward flow of formation gas. The actual volume of water, sand, and chemicals used is largely dependent on the length of the lateral leg of the borehole. Fluids used in the hydrofracturing process return to the surface as flowback and produced water and must be recovered with the enhanced flow of natural gas and then treated appropriately and disposed in a regulatory/permitted manner. Major flowback constituents of regulatory concern are released chlorides and total dissolved solids, both which have been used to fingerprint the fluids, if and when they may be detected in surface water. Some of the drillers have elected to dispose of the recovered fluids in Class 2 deep injection wells in neighboring Ohio, and some operators are recycling their produced fluids for re-use in other fracking operations. Flowback is first treated in public and industrial wastewater treatment facilities. Prior studies by the U.S. Army Corps of Engineers (USACE,

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Figure 62. Abandoned mine lands (AML) inventory in Allegheny County (PADEP, 2014).

Figure 62. Abandoned mine lands (AML) inventory in Allegheny County (PADEP, 2014).

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Geology of Pittsburgh

Geology of Pittsburgh

Figure 63. Schematic diagram of shale gas well hydrofracturing (US EPA, 2016).

Figure 63. Schematic diagram of shale gas well hydrofracturing (US EPA, 2016).

2012) have shown that the quality of the Monongahela River water has been a concern in the sense of the Federal Clean Water Act (as amended). The U.S. Army Corps of Engineers has confirmed that the primary water-quality problems within the Monongahela River watershed are related to acid mine drainage, traditional gas drilling, industrial/municipal pollution, and in some cases Marcellus Shale gas production.

State and federal environmental agencies are working with the gas drilling firms to ensure that fair but important environmental limits are placed on the disposal of gas-filled recovery fluids.

Low-Level Nuclear Waste—Shallow Land Disposal Area The Parks Township Shallow Land Disposal Area (SLDA) site, located approximately 23 mi. (37 km) east-northeast of Pittsburgh, encompasses 44 acres (17.8 hectares) of private land presently owned by BWX Technologies. Land use within the vicinity of the SLDA site is mixed, consisting of small residential communities, individual rural residences, small farms

with croplands and pastures, idle farmland, forested areas, and light industrial properties (USACE, 2002).

The Nuclear Materials and Equipment Corporation (NUMEC), which was a predecessor of BWX Technologies, disposed of low-level radioactive waste (LLW) materials, generated from national defense programs, on-site between 1961 and 1970 in accordance with Atomic Energy Commission regulations (predecessor to the present Nuclear Regulatory Commission). BWX Technologies presently is licensed by the Nuclear Regulatory Commission to properly maintain the site to ensure the protection of caretaker staff and of the general surrounding public. The SLDA site consists of 10 trenches containing contaminated soil and other waste materials. The estimated quantity of contaminated waste material from the trenches is approximately 24,300 yd3 (688 m3 ). This equates to the area of a football field 12 ft (3.6 m) deep. The contaminated waste included uranium, thorium, americium, and plutonium.

In the early 1900s, the Upper Freeport Coal was deep-mined at a depth of 60–100 ft (18–30 m) beneath the uphill portion of the site and surface mined later

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2012) have shown that the quality of the Monongahela River water has been a concern in the sense of the Federal Clean Water Act (as amended). The U.S. Army Corps of Engineers has confirmed that the primary water-quality problems within the Monongahela River watershed are related to acid mine drainage, traditional gas drilling, industrial/municipal pollution, and in some cases Marcellus Shale gas production.

State and federal environmental agencies are working with the gas drilling firms to ensure that fair but important environmental limits are placed on the disposal of gas-filled recovery fluids.

Low-Level Nuclear Waste—Shallow Land Disposal Area The Parks Township Shallow Land Disposal Area (SLDA) site, located approximately 23 mi. (37 km) east-northeast of Pittsburgh, encompasses 44 acres (17.8 hectares) of private land presently owned by BWX Technologies. Land use within the vicinity of the SLDA site is mixed, consisting of small residential communities, individual rural residences, small farms

with croplands and pastures, idle farmland, forested areas, and light industrial properties (USACE, 2002).

The Nuclear Materials and Equipment Corporation (NUMEC), which was a predecessor of BWX Technologies, disposed of low-level radioactive waste (LLW) materials, generated from national defense programs, on-site between 1961 and 1970 in accordance with Atomic Energy Commission regulations (predecessor to the present Nuclear Regulatory Commission). BWX Technologies presently is licensed by the Nuclear Regulatory Commission to properly maintain the site to ensure the protection of caretaker staff and of the general surrounding public. The SLDA site consists of 10 trenches containing contaminated soil and other waste materials. The estimated quantity of contaminated waste material from the trenches is approximately 24,300 yd3 (688 m3 ). This equates to the area of a football field 12 ft (3.6 m) deep. The contaminated waste included uranium, thorium, americium, and plutonium.

In the early 1900s, the Upper Freeport Coal was deep-mined at a depth of 60–100 ft (18–30 m) beneath the uphill portion of the site and surface mined later

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on the downhill portion (USACE, 2002). Nine of the trenches are on the uphill portion of the site in 11–16 ft (3.3–4.8 m) of Pleistocene terrace deposits that overlie 54–80 ft (16–24 m) of shale and sandstone, above the mined Upper Freeport Coal. The tenth trench, in the strip mine downhill of the other trenches, is located within the strip mine spoil, and it rests on a clay and shale layer below the Upper Freeport Coal.

In January 2002, Congress directed the U.S. Army Corps of Engineers to clean up radioactive waste at the SLDA site. At the time of this writing, all of the excavated contaminated material has been packaged and transported from the project site to a secure landfill meeting containment requirements of the federal Resource Conservation and Recovery Act of 1976 (as amended). The remedial action wastewater treatment plant (WWTP) has been disassembled and removed from the project site. The purpose of the WWTP was to capture, filter, and contain suspended waste particulates from remedial action wastewater used during remediation activities (USACE, 2007). A late 2014 contract was planned for construction of a new long-term wastewater treatment plant at the site.

CONCLUSION Pittsburgh has a rich history, and its Three Rivers have always played a major role in the city’s growth and development. No longer known as just “The Steel City,” Pittsburgh is a major metropolitan area rich with mineral resources and abundant surface and groundwater supplies. The city is now vibrant, with a bright future, with new construction, and with a greatly improved natural environment. Air quality has improved, as has the quality of the region’s three rivers, the Allegheny, Monongahela, and the Ohio.

Western Pennsylvania enjoys abundant natural resources. Coal and natural gas produced from shale formations are the significant energy resources of the area. Acid mine drainage remains a legacy environmental impact from past coal mining.

Geohazards are present in the Pittsburgh region, including slope instability, mine subsidence, expansive shales and slags, and pyritic acid rock. The local infrastructure is aging, and there is a need to repair major highways, including the Pennsylvania Turnpike, the oldest interstate in the nation. Pittsburgh is a city of bridges, and many are in need of repair or replacement.

The river navigation system of locks and dams is aging, and one major replacement project is under way on the Monongahela River, with others being planned for the Ohio River.

Pittsburgh is a city with a bright future as its industrial base changes and the region’s abundant natural 94

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resources are utilized. Water is plentiful and is used in many ways to benefit the citizens of the region.

ACKNOWLEDGMENTS The authors would like to gratefully acknowledge the support of Joseph Krupansky, AEG Geology of the Cities of the World series editor, during key phases of the preparation of this paper. His constant encouragement and advice, especially during the peer review process and leading to publication of the paper, were invaluable. Thanks are due to George Gardner, because much of the text of the Introduction herein was abstracted from his excellent discussion in the 1980 Guidebook of the 45th Annual Field Conference of Pennsylvania Geologists. Mr. Thomas Leech, P.E. of Gannett Fleming, Inc., generously contributed the section of the paper on Pittsburgh’s prominent bridges. The authors also wish to acknowledge the assistance of Jessica Krupansky, who graciously volunteered to improve a number of the graphics and figures contained within the paper. Her skills in electronic graphics significantly contributed to the improvement of many of the figures, which resulted in an overall improvement to the final manuscript. For the 5 years that the manuscript was in preparation, Wendy Kowalski, of DiGioia Gray & Associates, provided immeasurable support in managing the numerous drafts and facilitating frequent communications among the four coauthors. Finally, the authors wish to acknowledge the comments and suggestions for editorial improvements made by the peer reviewers during the editorial review process. These comments and suggestions greatly improved the draft version of the final manuscript.

REFERENCES Abel, J. F., Jr., and Lee, R. T., 1980, Lithologic Controls on Subsidence: Preprint No. 80–314, Society of Mining Engineers of American Institute of Mining, Metallurgical and Petroleum Engineers, Englewood, CO, 16 p.

Ackenheil, A. C., 1954, A Soil Mechanics and Engineering Geology Analysis of Landslides in the Area of Pittsburgh, Pennsylvania: Ph.D. Dissertation, University of Pittsburgh, Pittsburgh, PA, 121 p. (University Microfilms, Ann Arbor, MI, Publication 9957, 1962.)

Adams, F. D., 1938, The Birth and Development of the Geological Sciences: Dover Publications, New York. 506 p.

Adamson, J. H., Jr.; Graham, J. B.; and Klein, N. H., 1949, Groundwater Resources of the Valley-Filled Deposits of Allegheny County, Pennsylvania: Bulletin W8, Pennsylvania Geologic Survey, Harrisburg, PA. 181 p.

Albert, G. D., 1896, Map of Pittsburgh in 1795, The Frontier Forts of Western Pennsylvania: Report of the Commission to Locate the Site of the Frontier Forts of Pennsylvania, Volume Two, Clarence M. Busch, State Printer of Pennsylvania, Harrisburg, PA. 310 p.

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on the downhill portion (USACE, 2002). Nine of the trenches are on the uphill portion of the site in 11–16 ft (3.3–4.8 m) of Pleistocene terrace deposits that overlie 54–80 ft (16–24 m) of shale and sandstone, above the mined Upper Freeport Coal. The tenth trench, in the strip mine downhill of the other trenches, is located within the strip mine spoil, and it rests on a clay and shale layer below the Upper Freeport Coal.

In January 2002, Congress directed the U.S. Army Corps of Engineers to clean up radioactive waste at the SLDA site. At the time of this writing, all of the excavated contaminated material has been packaged and transported from the project site to a secure landfill meeting containment requirements of the federal Resource Conservation and Recovery Act of 1976 (as amended). The remedial action wastewater treatment plant (WWTP) has been disassembled and removed from the project site. The purpose of the WWTP was to capture, filter, and contain suspended waste particulates from remedial action wastewater used during remediation activities (USACE, 2007). A late 2014 contract was planned for construction of a new long-term wastewater treatment plant at the site.

CONCLUSION Pittsburgh has a rich history, and its Three Rivers have always played a major role in the city’s growth and development. No longer known as just “The Steel City,” Pittsburgh is a major metropolitan area rich with mineral resources and abundant surface and groundwater supplies. The city is now vibrant, with a bright future, with new construction, and with a greatly improved natural environment. Air quality has improved, as has the quality of the region’s three rivers, the Allegheny, Monongahela, and the Ohio.

Western Pennsylvania enjoys abundant natural resources. Coal and natural gas produced from shale formations are the significant energy resources of the area. Acid mine drainage remains a legacy environmental impact from past coal mining.

Geohazards are present in the Pittsburgh region, including slope instability, mine subsidence, expansive shales and slags, and pyritic acid rock. The local infrastructure is aging, and there is a need to repair major highways, including the Pennsylvania Turnpike, the oldest interstate in the nation. Pittsburgh is a city of bridges, and many are in need of repair or replacement.

The river navigation system of locks and dams is aging, and one major replacement project is under way on the Monongahela River, with others being planned for the Ohio River.

Pittsburgh is a city with a bright future as its industrial base changes and the region’s abundant natural 94

resources are utilized. Water is plentiful and is used in many ways to benefit the citizens of the region.

ACKNOWLEDGMENTS The authors would like to gratefully acknowledge the support of Joseph Krupansky, AEG Geology of the Cities of the World series editor, during key phases of the preparation of this paper. His constant encouragement and advice, especially during the peer review process and leading to publication of the paper, were invaluable. Thanks are due to George Gardner, because much of the text of the Introduction herein was abstracted from his excellent discussion in the 1980 Guidebook of the 45th Annual Field Conference of Pennsylvania Geologists. Mr. Thomas Leech, P.E. of Gannett Fleming, Inc., generously contributed the section of the paper on Pittsburgh’s prominent bridges. The authors also wish to acknowledge the assistance of Jessica Krupansky, who graciously volunteered to improve a number of the graphics and figures contained within the paper. Her skills in electronic graphics significantly contributed to the improvement of many of the figures, which resulted in an overall improvement to the final manuscript. For the 5 years that the manuscript was in preparation, Wendy Kowalski, of DiGioia Gray & Associates, provided immeasurable support in managing the numerous drafts and facilitating frequent communications among the four coauthors. Finally, the authors wish to acknowledge the comments and suggestions for editorial improvements made by the peer reviewers during the editorial review process. These comments and suggestions greatly improved the draft version of the final manuscript.

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Ackenheil, A. C., 1954, A Soil Mechanics and Engineering Geology Analysis of Landslides in the Area of Pittsburgh, Pennsylvania: Ph.D. Dissertation, University of Pittsburgh, Pittsburgh, PA, 121 p. (University Microfilms, Ann Arbor, MI, Publication 9957, 1962.)

Adams, F. D., 1938, The Birth and Development of the Geological Sciences: Dover Publications, New York. 506 p.

Adamson, J. H., Jr.; Graham, J. B.; and Klein, N. H., 1949, Groundwater Resources of the Valley-Filled Deposits of Allegheny County, Pennsylvania: Bulletin W8, Pennsylvania Geologic Survey, Harrisburg, PA. 181 p.

Albert, G. D., 1896, Map of Pittsburgh in 1795, The Frontier Forts of Western Pennsylvania: Report of the Commission to Locate the Site of the Frontier Forts of Pennsylvania, Volume Two, Clarence M. Busch, State Printer of Pennsylvania, Harrisburg, PA. 310 p.

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Baker, F. F. and Chieruzzi, R., 1959, Regional concept of landslide occurrence: Highway Research Board Bulletin 216, pp.

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Bass, M. N., 1959, Basement rocks from the Sandhill well, Wood County, West Virginia. In Woodward, H. P. (Chairman), A Symposium on the Sandhill Deep Well, Wood County, West Virginia: West Virginia Geological Survey Report of Investigations 18, pp. 145–168.

Bass, M. N., 1960, Grenville boundary in Ohio: Journal of Geology, Vol. 68, pp. 673–677.

Bawal, R. A., 2011, Superships of the Great Lakes: Thousand-Foot Ships on the Great Lakes, 1st ed.: Inland Expressions, Clinton Township, MI, 94 p.

Bennear, S., 1995, Pittsburgh Railways, PCC Era/Early PAT; A Brief History: Electronic document, available at http://www.pittsburghtransit.info/index.html Berryhill, H. L., 1963, Geology and Coal Resources of Belmont County, Ohio: U.S. Geological Survey Professional Paper 380, 113 p.

Berryhill, H. L., Jr.; Schweinfurth, S. P.; and Kent, B. H., 1971, Coal-Bearing Upper Pennsylvanian and Lower Permian Rocks, Washington Area, Pennsylvania: U.S. Geological Survey Professional Paper 621, 47 p.

Bikerman, M.; Prellwitz, H. S.; Dembosky, J.; Simonetti, A.; and Bell, K., 1997, New phlogopite K-Ar dates and the age of southwestern Pennsylvania kimberlite dikes: Northeastern Geology and Environmental Sciences, Vol. 19, pp. 302–308.

Bliss, W., 1943, Part One of the Report of the Point Park Commission, Pittsburgh, Pennsylvania: Point Park Commission, Unpublished report on file in the Division of Archaeology at The State Museum of Pennsylvania, Harrisburg, PA. 225 p.

Bonk, J. G., 1964, The Weathering of Pittsburgh Redbeds: M.S. Thesis, University of Pittsburgh, Pittsburgh, PA, 39 p.

Bright, W., 2004, Native American Placenames of the United States: University of Oklahoma Press, Norman, OK. 600 p.

Brookline Connection, 2012, Pittsburgh’s Golden Triangle—1776: Electronic document, available at www .brooklineconnection.com/history/Facts/Point1776.html Bruhn, R. W.; Magnuson, M. O.; and Gray, R. E., 1978, Subsidence over the mined-out Pittsburgh Coal. In Coal Mine Subsidence Session, American Society of Civil Engineers Spring Convention: ASCE Preprint 3293, American Society of Civil Engineers, Pittsburgh, PA. Bruhn, R. W.; Magnuson, M. O.; and Gray, R. E., 1981, Subsidence over abandoned mines in the Pittsburgh Coalbed. In Geddes, J. (Editor), Proceedings of the 2nd International Con-

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ference, Ground Movements and Structures; Cardiff, Wales, 1980: Pentech Press, London, U.K., pp. 142–156.

Carter, K. M. and Flaherty, K. J., 2011, The old, the crude, and the muddy—Oil history in western Pennsylvania. In Ruffolo, R. M. and Ciampaglio, C. N. (Editors), From the Shield to the Sea—Geological Field Trips from the 2011 Joint Meeting of the GSA Northeastern and North-Central Sections: Field Guide 20, Geological Society of America, Boulder, CO, pp. 169–185.

Cecil, C. B. and Dulong, F. T., 2004, The Paleozoic record of changes in global climate and sea level; central Appalachian basin. In Southworth, S. and Burton, W. (Editors), Geology of the National Capital Region: Field Trip Guidebook: U.S. Geological Survey Circular 1264, pp. 77–135.

Collier, S., 2014, The Way We Were—150 Years of Pittsburgh History, Squirrel Hill Tunnel Construction, 1953: Pittsburgh Magazine, taken from Historical Society of Western Pennsylvania, Electronic document, available at http://www.pittsburghmagazine.com/Pittsburgh-Magazine/ December - 2013 / The - Way - We - Were /, date accessed 10/06/2014.

Compressed Air Magazine, 1974, Fountain Focal Point: A Watery Tribute Rises to Pittsburgh’s Rich Historic Past and Post-War Civic Renaissance: Compressed Air: A Review of the Capabilities and Economies of Air and Gases, November 1974, pp.

8–11.

Crawford, C. B. and Burn, K. N., 1969, Building damage from expansive steel slag backfill: Proceedings of the American Society of Civil Engineers, Vol. 96, No. SM4, pp. 1325–1334, with discussion in four subsequent issues.

Cridlebaugh, B. S., 1999, Bridges and Tunnels of Allegheny County and Pittsburgh, Pennsylvania (10/03/2009): Electronic document, available at http://pghbridges.com Cridlebaugh, B. S., 2009, Field notes: How many bridges in Pittsburgh? In Bridges and Tunnels of Allegheny County and Pittsburgh, Pennsylvania (Page created: August 11, 2004): Electronic document, available at http://pghbridges.com Cross, A. T. and Schemel, M. P., 1956, Geology of the Ohio River valley in West Virginia. In Geology and Economic Resources of the Ohio River Valley in West Virginia: West Virginia Geological and Economic Survey XXII, pp. 1–149.

D’Appolonia, E.; Alperstein, R.; and D’Appolonia, D. J., 1967, Behavior of a colluvial slope: Proceedings of the American Society of Civil Engineers, Journal of Soil Mechanics & Foundations Division, Vol. 93, No. SM4, pp. 447–473.

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Denny, C. S., 1956, Surficial Geology and Geomorphology of Potter County, Pennsylvania: U.S. Geological Survey Professional Paper 288, 72 p.

DiGioia, Gray & Associates, 2007, Twelve Large Bulk GrainSize Distributions for Glacial Gravels, North Shore Connector Project: Launch Pit Excavation Grouting Report: DiGioia, Gray & Associates, Monroeville, PA. Donahue, J. and Rollins, H. B., 1974, Paleoecological anatomy of a Conemaugh (Pennsylvanian) marine event. In Briggs, G. (Editor), Carboniferous of the Southeastern United States: Spe-

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Bass, M. N., 1960, Grenville boundary in Ohio: Journal of Geology, Vol. 68, pp. 673–677.

Bawal, R. A., 2011, Superships of the Great Lakes: Thousand-Foot Ships on the Great Lakes, 1st ed.: Inland Expressions, Clinton Township, MI, 94 p.

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Bikerman, M.; Prellwitz, H. S.; Dembosky, J.; Simonetti, A.; and Bell, K., 1997, New phlogopite K-Ar dates and the age of southwestern Pennsylvania kimberlite dikes: Northeastern Geology and Environmental Sciences, Vol. 19, pp. 302–308.

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ference, Ground Movements and Structures; Cardiff, Wales, 1980: Pentech Press, London, U.K., pp. 142–156.

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Cecil, C. B. and Dulong, F. T., 2004, The Paleozoic record of changes in global climate and sea level; central Appalachian basin. In Southworth, S. and Burton, W. (Editors), Geology of the National Capital Region: Field Trip Guidebook: U.S. Geological Survey Circular 1264, pp. 77–135.

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8–11.

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D’Appolonia, E.; Alperstein, R.; and D’Appolonia, D. J., 1967, Behavior of a colluvial slope: Proceedings of the American Society of Civil Engineers, Journal of Soil Mechanics & Foundations Division, Vol. 93, No. SM4, pp. 447–473.

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Fleming, R. W. and Taylor, F. A., 1980, Estimating the Costs of Landslide Damage in the United States: U.S. Geological Survey Circular 832, 21 p.

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Fontaine, T., 2012, Connector boosts Port Authority ridership: Pittsburgh Tribune-Review, May 16, 2012: Electronic document, available at http://triblive.com Gallaher, J. T., 1973, Summary Ground-water Resources of Allegheny County, Pennsylvania: Pennsylvania Geological Survey, 4th Series, Water Resource Report 35.

Gardner, G. D., 1980, An introduction to the geology of Pittsburgh and its impact on the activities of man. In Adams, W. R.; Briggs, R. P.; Ferguson, H. F.; Flint, N. K.; and Skinner, W. S. (Editors), Land Use and Abuse: The Allegheny County

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Geology of Pittsburgh Problem: 1980 Guidebook 45th Annual Field Conference of Pennsylvania Geologists, Pittsburgh, PA, 1980, p. 1–18.

GeoTDR, Inc., 2001, Effects of Undermining Interstate Route 70, South Strabane Township, Washington County, Pennsylvania, November 1999 to October 2000: Prepared for Pennsylvania Department of Environmental Protection, Bureau of Mining and Reclamation, Harrisburg, PA. Gold, D.; Doden, A. G.; Mbalu-Keswa, C.; Tedeski, J. R.; and Mathur, R., 2016, The rogue kimberlite dikes in Indiana County, Pennsylvania: Part 1. Unusual intrusive habit of kimberlite dikes in coal seams. In Anthony, R. (Editor), Guidebook 81st Annual Field Conference of Pennsylvania Geologists, October 6–8, 2016: Pennsylvania Geological Survey, Pittsburgh, PA, pp. 121–160.

Gordon, D. W. and Dewey, J. W., 1999, Earthquakes. In Shultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, 4th Series, Special Publication 1, pp. 762–769.

Gray, R. E., 1983, Alternative measures in undermined areas. In Proceedings of the 1983 GSA Northeastern Section Meeting: Northeastern Environmental Science, Vol. 2, No. 2, pp. 21–26.

Gray, R. E., 1988, Coal mine subsidence and structures. In Siriwardane, H. (Editor), Proceedings on Mine-Induced Subsidence: Effects on Engineered Structures, May 1988: GT Special Publication 19, ASCE Geotechnical Division, Nashville, TN. Gray, R. E., 1999, Land Subsidence - Mines. In Schultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, 4th Series, Special Publication 1, pp. 724–729.

Gray, R. E. and Bruhn, R. W., 1984, Coal mine subsidence— eastern United States. In Holzer, T. (Editor), Man-Induced Land Subsidence: Reviews in Engineering Geology VI, Geological Society of America, Boulder, CO. Gray, R. E.; Bruhn, R. W.; and Turka, R. J., 1977, Study and Analysis of Surface Subsidence Over the Mined Pittsburgh Coalbed: U.S. Bureau of Mines, July 1977, Monroeville, PA,415 p.

Gray, R. E. and Donovan, T. D., 1971, Discussion of slope stability in residual soils. In Proceedings of the Fourth Panamerican Conference on Soil Mechanics and Foundation Engineering, Vol. 3: ASCE, New York, pp. 127–130.

Gray, R. E.; Ferguson, H. F.; and Hamel, J. V., 1979, Slope stability in the Appalachian Plateau of Pennsylvania and West Virginia. In Voight, B. (Editor), Rockslides and Avalanches: Developments in Geotechnical Engineering 14B, Elsevier, New York, pp. 447–471.

Gray, R. E.; Gamble, J. C.; McLaren, R. J.; and Rogers, D. J., 1974, State-of-the-Art of Subsidence Control: Report ARC 7311-2550, prepared for the Appalachian Regional Commission and Pennsylvania Department of Environmental Resources

by General Analytics, Inc. (predecessor of company to GAI Consultants, Inc.), Monroeville, PA (available from NTIS, PB242465).

Gray, R. E. and Gardner, G. D., 1977, Processes of colluvial slope development, McMechen, WV. In Proceedings of the Symposium of the International Association of Engineering Geology: Landslides and Other Mass Movements, Prague, Czechoslovakia: International Association for Engineering Geology and the Environment Bulletin 16, pp. 29–32.

Gray, R. E.; Hamel, J. V.; and Adams, W. R., Jr., 2011, Landslides in the vicinity of Pittsburgh, Pennsylvania. In Ruffolo, R. M. and Ciampaglio, C. N. (Editors), From the Shield to the Sea: Geological Field Trips from the 2011 Joint Meeting of the GSA Northeastern and North-Central Sections: Field Guide 20, Geological Society of America, Boulder, CO, pp. 61–85.

Geology of Pittsburgh

Gray, R. E. and Meyers, J. F., 1970, Mine subsidence and support methods in the Pittsburgh area: ASCE Journal of the Soil Mechanics and Foundations Division, Vol. 96, No. SM4, pp. 1267– 1287.

Greene, B. H. and Christ, C. A., 1998, Mistakes of man: The Austin dam disaster of 1911: Pennsylvania Geology, Vol. 29, No. 2, pp. 7–14.

Greene, B. H.; Gerlach, J. A.; and Schaffer, A., 1993, Geotechnical design and instrumentation of an anchored cofferdam: Bulletin Association of Engineering Geologists, Vol. XXX, No. 3, pp. 265–279.

Gregory, C. E., 1980, A Concise History of Mining: Pergamon Press, New York, 259 p.

HAER, 1985, No. PA – 70 (Historic American Engineering Record) Mid-Atlantic Region National Park Service, Department of the Interior, Philadelphia, Pennsylvania.

Hamel, J. V., 1969, Stability of Slopes in Soft, Altered Rocks: Ph.D. Thesis, University of Pittsburgh, Pittsburgh, PA (University Microfilms, Ann Arbor, MI, 70-23, 232).

Hamel, J. V., 1972, The slide at Brilliant Cut. In Cording, E. J. (Editor), Stability of Rock Slopes, Proceedings 13th Symposium on Rock Mechanics, University of Illinois, Urbana, IL: American Society of Civil Engineers, New York, pp. 487– 510.

Hamel, J. V., 1980, Geology and slope stability in western Pennsylvania: Bulletin Association of Engineering Geologists, Vol. 17, pp. 1–26.

Hamel, J. V., 1998, Mechanism of Pleistocene rock slides near Pittsburgh, Pennsylvania: International Journal of Rock Mechanics and Mining Science, Vol. 35, No. 4–5, Paper No. 32.

Hamel, J. V., 2004, Discussion of residual shear strength mobilized in first-time slope failures: ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, pp. 544–546.

Hamel, J. V., 2011, Sewage treatment plant on a major fault zone, Sewickley Township, Pennsylvania: Geological Society of America Abstracts with Programs, Vol. 43, No. 1, pp. 95.

Hamel, J. V. and Flint, N. K., 1969, A Slope Stability Study on Interstate Routes 279 and 79 near Pittsburgh, Pennsylvania: Report by Departments of Civil Engineering and Earth and Planetary Sciences, University of Pittsburgh to Pennsylvania Department of Highways and U.S. Department of Transportation, Bureau of Public Roads, Pittsburgh, PA. Hamel, J. V. and Flint, N. K., 1972, Failure of colluvial slope: ASCE Soil Mechanics and Foundations Division Journal, Vol. 98, No. SM2, pp. 167–180.

Hammarstrom, J. M.; Brady, K.; and Cravotta, C. A., III, 2005, Acid-Rock Drainage at Skytop, Centre County, Pennsylvania, 2004: U.S. Geological Survey Open-File Report 2005-1148.

Hannibal, J. T.; Gerke, T. L.; McGuire, M. K.; Edenborn, H. M.; Holstein, A. L.; and Parker, D., 2011, Early industrial geology of western Pennsylvania and eastern Ohio: Early gristmills and iron furnaces west of the Alleghenies and their geologic contexts. In Ruffolo, R. M. and Ciampaglio, C. N. (Editors), From the Shield to the Sea: Geological Field Trips from the 2011 Joint Meeting of the GSA Northeastern and NorthCentral Sections: Field Guide 20, Geological Society of America, Boulder, CO, pp. 143–167.

Harper, J. S., 1990, Fossil Collecting in the Pittsburgh Area: Field Trip Guidebook, Pittsburgh Geological Society, Pittsburgh, PA, 50 p.

Harper, J. A., 1997, Of ice and waters flowing: The formation of Pittsburgh’s three rivers: Pennsylvania Geology, Vol. 28, No. 3, pp. 2–8.

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Problem: 1980 Guidebook 45th Annual Field Conference of Pennsylvania Geologists, Pittsburgh, PA, 1980, p. 1–18.

GeoTDR, Inc., 2001, Effects of Undermining Interstate Route 70, South Strabane Township, Washington County, Pennsylvania, November 1999 to October 2000: Prepared for Pennsylvania Department of Environmental Protection, Bureau of Mining and Reclamation, Harrisburg, PA. Gold, D.; Doden, A. G.; Mbalu-Keswa, C.; Tedeski, J. R.; and Mathur, R., 2016, The rogue kimberlite dikes in Indiana County, Pennsylvania: Part 1. Unusual intrusive habit of kimberlite dikes in coal seams. In Anthony, R. (Editor), Guidebook 81st Annual Field Conference of Pennsylvania Geologists, October 6–8, 2016: Pennsylvania Geological Survey, Pittsburgh, PA, pp. 121–160.

Gordon, D. W. and Dewey, J. W., 1999, Earthquakes. In Shultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, 4th Series, Special Publication 1, pp. 762–769.

Gray, R. E., 1983, Alternative measures in undermined areas. In Proceedings of the 1983 GSA Northeastern Section Meeting: Northeastern Environmental Science, Vol. 2, No. 2, pp. 21–26.

Gray, R. E., 1988, Coal mine subsidence and structures. In Siriwardane, H. (Editor), Proceedings on Mine-Induced Subsidence: Effects on Engineered Structures, May 1988: GT Special Publication 19, ASCE Geotechnical Division, Nashville, TN. Gray, R. E., 1999, Land Subsidence - Mines. In Schultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, 4th Series, Special Publication 1, pp. 724–729.

Gray, R. E. and Bruhn, R. W., 1984, Coal mine subsidence— eastern United States. In Holzer, T. (Editor), Man-Induced Land Subsidence: Reviews in Engineering Geology VI, Geological Society of America, Boulder, CO. Gray, R. E.; Bruhn, R. W.; and Turka, R. J., 1977, Study and Analysis of Surface Subsidence Over the Mined Pittsburgh Coalbed: U.S. Bureau of Mines, July 1977, Monroeville, PA,415 p.

Gray, R. E. and Donovan, T. D., 1971, Discussion of slope stability in residual soils. In Proceedings of the Fourth Panamerican Conference on Soil Mechanics and Foundation Engineering, Vol. 3: ASCE, New York, pp. 127–130.

Gray, R. E.; Ferguson, H. F.; and Hamel, J. V., 1979, Slope stability in the Appalachian Plateau of Pennsylvania and West Virginia. In Voight, B. (Editor), Rockslides and Avalanches: Developments in Geotechnical Engineering 14B, Elsevier, New York, pp. 447–471.

Gray, R. E.; Gamble, J. C.; McLaren, R. J.; and Rogers, D. J., 1974, State-of-the-Art of Subsidence Control: Report ARC 7311-2550, prepared for the Appalachian Regional Commission and Pennsylvania Department of Environmental Resources

by General Analytics, Inc. (predecessor of company to GAI Consultants, Inc.), Monroeville, PA (available from NTIS, PB242465).

Gray, R. E. and Gardner, G. D., 1977, Processes of colluvial slope development, McMechen, WV. In Proceedings of the Symposium of the International Association of Engineering Geology: Landslides and Other Mass Movements, Prague, Czechoslovakia: International Association for Engineering Geology and the Environment Bulletin 16, pp. 29–32.

Gray, R. E.; Hamel, J. V.; and Adams, W. R., Jr., 2011, Landslides in the vicinity of Pittsburgh, Pennsylvania. In Ruffolo, R. M. and Ciampaglio, C. N. (Editors), From the Shield to the Sea: Geological Field Trips from the 2011 Joint Meeting of the GSA Northeastern and North-Central Sections: Field Guide 20, Geological Society of America, Boulder, CO, pp. 61–85.

Gray, R. E. and Meyers, J. F., 1970, Mine subsidence and support methods in the Pittsburgh area: ASCE Journal of the Soil Mechanics and Foundations Division, Vol. 96, No. SM4, pp. 1267– 1287.

Greene, B. H. and Christ, C. A., 1998, Mistakes of man: The Austin dam disaster of 1911: Pennsylvania Geology, Vol. 29, No. 2, pp. 7–14.

Greene, B. H.; Gerlach, J. A.; and Schaffer, A., 1993, Geotechnical design and instrumentation of an anchored cofferdam: Bulletin Association of Engineering Geologists, Vol. XXX, No. 3, pp. 265–279.

Gregory, C. E., 1980, A Concise History of Mining: Pergamon Press, New York, 259 p.

HAER, 1985, No. PA – 70 (Historic American Engineering Record) Mid-Atlantic Region National Park Service, Department of the Interior, Philadelphia, Pennsylvania.

Hamel, J. V., 1969, Stability of Slopes in Soft, Altered Rocks: Ph.D. Thesis, University of Pittsburgh, Pittsburgh, PA (University Microfilms, Ann Arbor, MI, 70-23, 232).

Hamel, J. V., 1972, The slide at Brilliant Cut. In Cording, E. J. (Editor), Stability of Rock Slopes, Proceedings 13th Symposium on Rock Mechanics, University of Illinois, Urbana, IL: American Society of Civil Engineers, New York, pp. 487– 510.

Hamel, J. V., 1980, Geology and slope stability in western Pennsylvania: Bulletin Association of Engineering Geologists, Vol. 17, pp. 1–26.

Hamel, J. V., 1998, Mechanism of Pleistocene rock slides near Pittsburgh, Pennsylvania: International Journal of Rock Mechanics and Mining Science, Vol. 35, No. 4–5, Paper No. 32.

Hamel, J. V., 2004, Discussion of residual shear strength mobilized in first-time slope failures: ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, pp. 544–546.

Hamel, J. V., 2011, Sewage treatment plant on a major fault zone, Sewickley Township, Pennsylvania: Geological Society of America Abstracts with Programs, Vol. 43, No. 1, pp. 95.

Hamel, J. V. and Flint, N. K., 1969, A Slope Stability Study on Interstate Routes 279 and 79 near Pittsburgh, Pennsylvania: Report by Departments of Civil Engineering and Earth and Planetary Sciences, University of Pittsburgh to Pennsylvania Department of Highways and U.S. Department of Transportation, Bureau of Public Roads, Pittsburgh, PA. Hamel, J. V. and Flint, N. K., 1972, Failure of colluvial slope: ASCE Soil Mechanics and Foundations Division Journal, Vol. 98, No. SM2, pp. 167–180.

Hammarstrom, J. M.; Brady, K.; and Cravotta, C. A., III, 2005, Acid-Rock Drainage at Skytop, Centre County, Pennsylvania, 2004: U.S. Geological Survey Open-File Report 2005-1148.

Hannibal, J. T.; Gerke, T. L.; McGuire, M. K.; Edenborn, H. M.; Holstein, A. L.; and Parker, D., 2011, Early industrial geology of western Pennsylvania and eastern Ohio: Early gristmills and iron furnaces west of the Alleghenies and their geologic contexts. In Ruffolo, R. M. and Ciampaglio, C. N. (Editors), From the Shield to the Sea: Geological Field Trips from the 2011 Joint Meeting of the GSA Northeastern and NorthCentral Sections: Field Guide 20, Geological Society of America, Boulder, CO, pp. 143–167.

Harper, J. S., 1990, Fossil Collecting in the Pittsburgh Area: Field Trip Guidebook, Pittsburgh Geological Society, Pittsburgh, PA, 50 p.

Harper, J. A., 1997, Of ice and waters flowing: The formation of Pittsburgh’s three rivers: Pennsylvania Geology, Vol. 28, No. 3, pp. 2–8.

Environmental & Engineering Geoscience, Vol. XXV, No. 1, February 2019, pp. 27–101

97

Gray, Greene, Fandray, and Turka Harper, J. A., 2002, Lake Monongahela: Anatomy of an immense ice age pond: Pennsylvania Geology, Vol. 32, No. 1, pp. 2–12.

Harper, J. A., 2012, (personal communication) Pennyslvania Geological Survey, 400 Waterfront Drive, Pittsburgh, PA, 15222.

Hatcher, R. D., Jr., 2004, Regional geology of North America, southern and central Appalachians. In Selley, R. C., Encyclopedia of Geology: Elsevier Publishers, London, U.K., pp. 72– 81.

Hawkins, J. W., 2009, Glasshouses and Glass Manufacturers of the Pittsburgh Region: 1795–1910: iUniverse, Inc., New York, 584 p.

Hebblewhite, B., 2001, Regional horizontal movements associated with longwall mining. In Holt, G, et al. (Editors), Coal Mine Subsidence - Current Practice and Issues, Coal Mine Subsidence – Current Practice and Issues, presented at Coal Mine Subsidence - Current Practice and Issues, Maitland, NSW, 01 August 2001, pp. 113–122.

Hebblewhite, B. K. and Gray, R. E., 2014, Non-conventional subsidence behavior and impacts: Ryerson State Park Dam, Pennsylvania USA, case study. In Kay, D. and Li, G. (Editors), Proceedings of the 9th Triennial Conference on Mine Subsidence: Mine Subsidence Technological Society, Pokolbin, NSW, Australia.

Heyman, L., 1970, History of Pittsburgh’s rivers. In Wagner, W. R., et al. (Editors), Geology of the Pittsburgh Area: General Geology Report G59, 4th Series, Pennsylvania Geological Survey, Harrisburg, PA. Inners, J. D., 1999, Metallic mineral deposits—Sedimentary and meta sedimentary iron deposits. In Shultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, Harrisburg, PA. Johnson, L. R., 1978, The Headwaters District, A History of the Pittsburgh District: U.S. Army Corps of Engineers, prepared for the U.S. Army Corps of Engineers, Pittsburgh, PA, 380 p.

Karol, R. H., 2003, Chemical Grouting and Soil Stabilization, 3rd ed.: Marcel Dekker Inc., New York, pp. 9–22.

Kidney, W. C., 1999, Pittsburgh’s Bridges, Architecture and Engineering: Pittsburgh History and Landmarks Foundation, Pittsburgh, PA, 234 p.

King, P. B., 1977, The Evolution of North America: Princeton University Press, Princeton, NJ, 197 p.

Kochanov, W. and Bragonier, W. A., 2005, Some findings relevant to the regional distribution of the Vanport Limestone.

In, Fleeger, G. M. and J. A. Harper, (Editors), Type sections and stereotype sections: glacial and bedrock geology in Beaver, Lawrence, Mercer, and Crawford Counties, Guidebook, 70th Annual Field Conference of Pennsylvania Geologists, Sharon, PA, pp. 35–43.

Kurka, M.; Gamer, M.; and Retzlaff, S., 2014, Energizing investments in hydropower: The Military Engineer, Vol. 106, No. 690, pp. 59–60.

Ladd, G. E., 1927–1928, Landslides and their relation to highways: A report of observations made in West Virginia and Ohio to determine the cause of slides and devise means of control: Public Roads, Part 1, Vol. 8, No. 2, pp. 21–35; Part 2, Vol. 9, No. 8, pp. 153–163.

Law, A. S., 1997, The Great Flood, Johnstown Pennsylvania, 1889: Johnstown Area Heritage Association, Johnstown, PA, 106 p.

Legget, R. F. and Karrow, P. F., 1983, Handbook of Geology in Civil Engineering: McGraw-Hill Book Company, New York, 1,340 p.

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Gray, Greene, Fandray, and Turka Harper, J. A., 2002, Lake Monongahela: Anatomy of an immense ice age pond: Pennsylvania Geology, Vol. 32, No. 1, pp. 2–12.

Harper, J. A., 2012, (personal communication) Pennyslvania Geological Survey, 400 Waterfront Drive, Pittsburgh, PA, 15222.

Hatcher, R. D., Jr., 2004, Regional geology of North America, southern and central Appalachians. In Selley, R. C., Encyclopedia of Geology: Elsevier Publishers, London, U.K., pp. 72– 81.

Hawkins, J. W., 2009, Glasshouses and Glass Manufacturers of the Pittsburgh Region: 1795–1910: iUniverse, Inc., New York, 584 p.

Hebblewhite, B., 2001, Regional horizontal movements associated with longwall mining. In Holt, G, et al. (Editors), Coal Mine Subsidence - Current Practice and Issues, Coal Mine Subsidence – Current Practice and Issues, presented at Coal Mine Subsidence - Current Practice and Issues, Maitland, NSW, 01 August 2001, pp. 113–122.

Hebblewhite, B. K. and Gray, R. E., 2014, Non-conventional subsidence behavior and impacts: Ryerson State Park Dam, Pennsylvania USA, case study. In Kay, D. and Li, G. (Editors), Proceedings of the 9th Triennial Conference on Mine Subsidence: Mine Subsidence Technological Society, Pokolbin, NSW, Australia.

Heyman, L., 1970, History of Pittsburgh’s rivers. In Wagner, W. R., et al. (Editors), Geology of the Pittsburgh Area: General Geology Report G59, 4th Series, Pennsylvania Geological Survey, Harrisburg, PA. Inners, J. D., 1999, Metallic mineral deposits—Sedimentary and meta sedimentary iron deposits. In Shultz, C. H. (Editor), The Geology of Pennsylvania: Pennsylvania Geological Survey, Harrisburg, PA. Johnson, L. R., 1978, The Headwaters District, A History of the Pittsburgh District: U.S. Army Corps of Engineers, prepared for the U.S. Army Corps of Engineers, Pittsburgh, PA, 380 p.

Karol, R. H., 2003, Chemical Grouting and Soil Stabilization, 3rd ed.: Marcel Dekker Inc., New York, pp. 9–22.

Kidney, W. C., 1999, Pittsburgh’s Bridges, Architecture and Engineering: Pittsburgh History and Landmarks Foundation, Pittsburgh, PA, 234 p.

King, P. B., 1977, The Evolution of North America: Princeton University Press, Princeton, NJ, 197 p.

Kochanov, W. and Bragonier, W. A., 2005, Some findings relevant to the regional distribution of the Vanport Limestone.

In, Fleeger, G. M. and J. A. Harper, (Editors), Type sections and stereotype sections: glacial and bedrock geology in Beaver, Lawrence, Mercer, and Crawford Counties, Guidebook, 70th Annual Field Conference of Pennsylvania Geologists, Sharon, PA, pp. 35–43.

Kurka, M.; Gamer, M.; and Retzlaff, S., 2014, Energizing investments in hydropower: The Military Engineer, Vol. 106, No. 690, pp. 59–60.

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U.S. Steel Tower, 2015, U.S. Steel Tower: Electronic document, available at https://skyscraperpage.com/cities/ ?buildingID=207 Van Tuyl, D. W., 1951, Ground Water for Air Conditioning at Pittsburgh, Pennsylvania: Bulletin W 10, U.S. Geological Survey and Pennsylvania Geological Survey, Fourth Series, Harrisburg, PA, 34 p.

Voight, B., 1974, A mechanism for “locking-in” orogenic stress: American Journal of Science, Vol. 274, pp. 662–665.

Waddington & Associates Pty Limited, 2002, ACARP Research Project No. C9067, Research into the Impacts of Mine Subsidence on the Strata and Hydrology of River Valleys and Development of Management Guidelines for Undermining Cliffs, Gorges and River Systems: Australian Coal Association Research Program, Brisbane, Queensland, Australia.

Wagner, W. R.; Heyman, L.; Gray, R. E.; Belz, D. J.; Lund, R.; Cate, A. S.; and Edgerton, C. D., 1970, Geology of the Pittsburgh Area: General Geology Report G 59, Pennsylvania Geological Survey, 4th Series, Harrisburg, PA, 145 p.

Wargo, K. A.; Roy, P. A.; Boscardin, M. D.; Miller, A. J.; and DiRocco, K., 2009, Tight fit tunneling: Civil Engineering, Vol. 79, No. 3, pp. 58–65.

White, J. R., 1979, Nineteenth century blast furnaces of Mercer County: A postscript: Mercer County History, Vol. 9, pp. 3– 20.

Williams, E. H., 1960, Marine and fresh water fossiliferous beds in the Pottsville and Allegheny Groups of western Pennsylvania: Journal of Paleontology, Vol. 34, No. 5, pp. 908–922.

Williams, E. H. and Ferm, J. C., 1964, Sedimentary facies in the Lower Allegheny rocks of western Pennsylvania: Journal of Sedimentary Petrology, Vol. 35, No. 2, pp. 319–330.

Wyrick, G. G. and Borchers, J. W., 1981, Hydrologic Effects of Stress-Relief Fracturing in an Appalachian Valley: U.S. Geological Survey Water-Supply Paper 2177, 51 p.

Xanthakos, P. P.; Abramson, L.; and Bruce, D. A., 1994, Ground Control and Improvement: John Wiley & Sons, Inc., 913 p.

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