Global journal 41

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014

ISSN:- 2349–283X

LIQUEFACTION HAZARD ASSESSMENT OF RAMGARH TAL PARIYOJNA 1Abhishek

Kumar Tiwari Department of Civil Engineering, Madan Mohan Malviya University of Technology, Gorakhpur, India Email: abhicivilengg07@gmail.com

2Dr.S.M

Ali Jawaid Department of Civil Engineering, Madan Mohan Malviya University of Technology, Gorakhpur, India Email: smaj@rediffmail.com

ABSTRACT: Determination of liquefaction potential due to earthquake is complex geotechnical problem.

Many factors including soil parameters and seismic characteristics influence this phenomenon. The devastating damage of liquefaction induced ground failures in the Alaska 1964 and Niigata 1964 earthquakes serve as a clear reminder of such events. Liquefaction is one of the ground failures in potential earth science hazard. Since Gorakhpur falls in the area with high seismic probability, there is need for the assessment of liquefaction potential, so the study area is “Ramgarh Tal Pariyojna” to recognize the conditions that exist in a soil deposit before an earthquake in order to identify liquefaction.

Results of an extensive analysis for determination of liquefaction hazard analysis of “Ramgarh Tal Pariyojna of Gorakhpur city at different locations is addressed here. The simplified procedure suggested by seed & Idriss (1971) on the basis of field performance data is used for determination of liquefaction potential and also to present a liquefaction hazard map using SPT data collected from the various sites at different locations of “Ramgarh Tal Pariyojna”. From the analysis it is observed that the areas with river channel deposit are the most hazardous area for liquefaction. From the study it is also concluded that if acceleration level is increased then more area will be affected due to liquefaction. In this study we concluded that if earthquake more than or equal to 6.5 ritcher scale occurs in Gorakhpur region, it will be extensively damaged due to liquefaction. The percentage of silt and poorly graded sand is high in the area under “Ramgarh Tal Pariyojna” indicating that there is a great chance of soil liquefaction. Here liquefaction potential analysis is done to determine the factor of safety at different depth. The structure constructed should be liquefaction resistant i.e., designing the foundation elements to resist the effects of liquefaction if at all it is necessary to construct the structure on liquefiable soil because of favourable location, space restriction and other reasons.

Keywords: Liquefaction, microzonation, standard penetration test, Seismic Hazard 1. INTRODUCTION Gorakhpur lies between Latitude 26˚ 13´ N and 27˚29´N and long.83˚05´E and 83˚56´E.the district occupies the north-eastern corner of the state along with the state of Deoria, & comprises a large stretch of country lying to the north of river Ghaghra, the deep stream of which forms its boundary with district Azamgarh. In the earthquake zonal map of India the district lies in zone IV liable to moderate damage by earthquakes. Although no major earthquake occurred close to it, the tract being not far from the Great Himalayan Boundary fault, experiences the effects of moderate to great earthquake occurring there. The seismic intensity may not exceed VIII on the Modified Mercalli 1931. As India experiencing lots of seismic threats and Liquefaction is one of the major types for ground failure. Liquefaction is a soil behaviour phenomenon in which a saturated soil losses a substantial amount of

strength due to high excess pore-water pressure generated by and accumulated during strong earthquake ground shaking. Large numbers of liquefaction studies were conducted in all the earthquake prone areas of the world. After the 2001 Bhuj earthquake, attracted the great attention of liquefaction studies.

Soil liquefaction has been a major cause of damage to soil structure, lifelines and building foundation. Zoning for liquefaction, therefore, has been an important goal for seismic hazard mitigation.

Gorakhpur region is potentially prone to damaging earthquakes, as it is located in an active seismic zone IV. Because of the haphazard urbanization and increasing population in the Gorakhpur region now, it has become very essential to carry out studies on different aspects of the earthquake hazard leading to long term earthquake vulnerability reduction

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 program. This situation has created the necessity for carrying out a detailed seismic hazard assessment of the city and an awareness building measures to the people of Gorakhpur regarding the earthquake safety.

So seeing the fact the study area is “RAMGARH TAL PARIYOJNA”, Gorakhpur, Ramgarh Tal, and a natural lake, which is situated to the southeast of Gorakhpur in Uttar Pradesh and covers an area of about 723 hectare. The catchment area around the lake is approximately 1632 acres, out of which, 1235 acres land is under Gorakhpur Development authority (GDA).

Liquefaction is one of the main effects of an earthquake that is responsible to structural failure and damage to roads, pipelines and infrastructures. In Gorakhpur region in spite of weak subsurface condition, many tall buildings have been built and the number is constantly rising. Most of these buildings (Except commercial, governmental and organizational buildings) have been constructed without adequate research on the subsurface sediment conditions and hence may run a high risk that they are not properly designed to withstand the particular accelerations at the site. Looking at this situation, the study on subsurface geology is very important, as it helps for the study of seismic hazard and hence for the earthquake vulnerability reduction program. For the study of subsurface geology, the generation of a geological database is important which can be done by the collection of borehole data. One other potential source of useful information for subsurface information, geophysical measurements, are completely lacking for Gorakhpur region. The work is done to analyse the liquefaction potential of “Ramgarh Tal Pariyojna” in Gorakhpur city using SPT data collected from the various sites of Pariyojna by simplified procedure of Seed & Idriss (1982).

The geological, geotechnical, and seismological details of an area have to be studied which forms important parameters and information to analyse Liquefaction potential of this region.

The main objectives of this work is to1. Estimate the liquefaction resistance of soils using SPT data.

2. Estimate the maximum or equivalent cyclic shear stress likely to be induced in a soil deposit during an earthquake;

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3. Estimate the liquefaction potential.

4. Prepare liquefaction hazard zonation map.

LIQUEFACTION AND ITS MECHANISM Soil liquefaction has been a major cause of damage to soil structure, lifelines and building foundation. Zoning for liquefaction, therefore, has been an important goal for seismic hazard mitigation. Soil liquefaction occurs in loose, saturated cohesionless soil units (sands and silts) and sensitive clays when a sudden loss of strength and loss of stiffness is experienced, sometimes resulting in large, permanent displacements of the ground. Even thin lenses of loose saturated silts and sands may cause an overlying sloping soil mass to slide laterally along the liquefied layer during earthquakes.

Liquefaction beneath and in the vicinity of a waste containment unit can result in localized bearing capacity failures, lateral spreading, and excessive settlement that can have severe consequences upon the integrity of waste containment systems. Liquefaction-associated lateral spreading and flow failures can also affect the global stability of a waste containment facility.

There is need to understand the mechanism of soil liquefaction, where it occurs and why it occurs so often during earthquake. Liquefaction of soil is a process by which sediments below the water table lose their shear strength and behave more as viscous liquid than as a solid.

The water in the soil voids exerts pressure upon the soil particles. If the pressure is low enough, the soil stays stable. However, once the water pressure exceeds a certain level, it forces the soil particles to move relative to each other, thus causing the strength of the soil to decrease and failure of the soil. So when the earthquake occurs the shear waves passes through saturated soil layers and causes the granular soil structure to deform and weak part of soil begins to collapse.

Then collapse soil starts filling the lower layer and forces the pore water pressure in this to increase layer. If increased water pressure cannot be released, it will continue to build up and after a certain limit effective stress of the soil becomes zero .If situation aroused then the soil layer losses its shear strength and it cannot certain the total weight of the soil layer above,

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thus the upper layer soils are ready to move down and behaves as a viscous liquid, if then it is said to be soil liquefaction occurred.

produces unacceptably large permanent deformation during earthquake shaking, which is also known as lateral spreading. It can occur on very gently sloping ground or on virtually flat ground adjacent to bodies of water.

Flow liquefaction occurs much less frequently than cyclic mobility but its effects are usually far more severe. Besides these two types, Ground oscillation, loss of bearing strength and sand boils are common phenomena of Liquefaction.

Fig-1. Mechanism of Liquefaction (courtesy: http://www.cee.ehime-u.ac.jp)

Geology of Gorakhpur The district of Gorakhpur lies between Lat. 26°13′N and 27°29′N and Long. 83°05′E and 83°56′E. The district occupies the north-eastern corner of the state along with the district of Deoria, and comprises a large stretch of country lying to the north of the river Rapti, the deep stream of which forms its southern boundary with the Azamgarh district. On the west, the boundary marches along Basti and on the east adjoins Deoria and the Chhoti Gandak Nadi and further south the Jharna Nala forms the dividing line. To the north lies Nepal. Gorakhpur has also a lake Ramgarh Tal Lake, which is 18 km bigger.

It is bigger than Dal Lake of Kashmir which is of 15.5 km Ramgarh Tal. It's vast and provides home to various types of fishes. Geography it is located on the bank of river Rapti and Rohani, a Ganges tributary originating in Nepal that sometimes causes severe floods. The Rapti is interconnected through many other small rivers following meandering courses across the Gangetic Plain.

The district presents characteristics distinct from natural features of the western districts of Uttar Pradesh. This difference is due primarily to the relative proximity of the Himalayas, the outermost foothills of which are only a few kilometres from the northern borders. The peak of Dhaulagiri, some 8,230 meters above sea-level, is visible under favourable climatic conditions as far south as Gorakhpur itself. The district geology is primarily river born alluvium. Few mineral products are mined in Gorakhpur, with the most common being a nodular limestone conglomerate known as kankar, brick, and saltpetre. The last occurs principally in the south and south-east and is manufactured in a crude state in considerable quantities most of it being exported to markets of Bihar. In the Bans gaon

Liquefaction occurs in saturated soils, in which the space between individual particles is completely filled with water. Its effects are most commonly observed in low-lying areas near bodies of water such as rivers, lakes, bays, and oceans (ABAG's Report, "Real dirt on Liquefaction”, 2001).

Liquefaction occurs in Cohesionless sand deposited in alluvial environment. Areas of high liquefaction potentials are alluvial floodplains, deltaic deposits, estuaries deposit, colluvial and aeolian deposit, artificial fill etc. Areas of medium liquefaction potentials are alluvial fans, channel deposits, and beaches. Areas of coarse deposits and rock debris do not undergo liquefaction. The susceptibility to liquefaction depends on the density of the sand and intensity of ground motion (amplitude and duration).

According to Kramer (1996), two types of liquefaction exist.

Flow Liquefaction: It occurs when the shear stress required for static equilibrium of a soil mass (The static shear stress) is greater than the shear strength of the soil in its liquefied state. When liquefaction occurs in such case the strength of the soil decreases and the ability of soil deposit to support for the structure is reduced.

Flow liquefaction failures are characterized by the sudden nature of their origin, the speed with which they develop and the large distance cover over which the liquefied materials often move.

Cyclic mobility: It occurs when the static shear stress is less than the shear strength of the liquefied soil. It

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 tehsil kankar is most abundant and quarries are seen at many places. It is also extracted from some places in Mahrajganj tehsil. Lime is obtained by burning kankar. Brick clay is abundant everywhere and bricks are made all over the district. The soil in the district is light sandy or dense clay of yellowish brown colour.

The sand found in the rivers is medium to coarse grained, greyish white to brownish in colour and is suitable for construction. The high seismic activity occurred in Nepal, the Gorakhpur lies in the border of Nepal. This impasses a very high risk of an earthquake disaster in Gorakhpur resulting into great damage. To determine the potential hazard due to an earthquake

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appropriate site characterization and determination of the soil properties are essential in order to suitably design a structure.

Ramgarh Tal, a natural lake, is situated to the southeast of Gorakhpur in Uttar Pradesh and covers an area of about 723 ha. The catchment area around the lake is approximately 1632 acres, out of which, 1235 acres land is under Gorakhpur Development authority (GDA).As we know that Gorakhpur is under seismic zone the need of liquefaction analysis requires the characterization of soil profile. So my work is to analyse the liquefaction potential of an area and the liquefaction potential map.

Fig-2. Map of “Ramgarh Tal Pariyojna” GENERATION OF SUBSURFACE DATA AND DATA ACQUISITION Collection and organisation of the data The effective management of borehole data is crucial for many applications in the geosciences; among which is earthquake microzonation (Houlding, 1994). Collection and organization of data-extensive borehole data is collected from various locations of Ramgarh Tal pariyojna and seventeen borehole data were collected at different sites shown in fig 3.1 for liquefaction zonation. The collected geotechnical data is in different formats depending upon the source of organization and the particular project. Data is then synthesized and was brought to common platform needed for the geotechnical characterization and liquefaction study. The data is given in appendix.

Data acquisition Data acquisition is one of the most difficult parts of a research work. It is time consuming and more personal relations are required, in order to contact people in institutions that might have relevant data.

Data management All the data managed in a same platform so as to easily accessible. Data used to analyse liquefaction potential of a soil, Microsoft Excel 2000 and Microsoft Access were used to store the borehole data. Initially the data were entered in the Excel sheets. After the data acquisition was completed, all the boreholes were grouped according to their types and source as shown in the tables given in appendix.

The deep bore holes are used to study the geological evaluation of the site. Three tables are

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 generated - One containing attributes such as: Borehole_id, location, depth range, geological information, Soil type, thickness of the layers, SPT ‘N’, corrected N-value and SPT curve. The second and third type of tables includes the geotechnical information with the following attributes: Borehole-id, Location, Depth range, particle size distribution, consistency limit, soil classification, Moisture content, Bulk Density, Unit weight, and, shear characteristics.

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Table: 02. SUMMARY OF MECHANICAL GRADING AND CONSISTANCY LIMIT Site: Proposed GDA Staff Quarter Building, Siddhartha Enclave, Gorakhpur Bore Hole No-01

APPENDIX-1 Table: 01.BORELOG CHART AND SPT CURVE Site: Proposed GDA Staff Quarter Building, Siddhartha Enclave, Gorakhpur Bore Hole No-01 Table: 03. SUMMARY OF LABORATORY RESULTS Site: Proposed GDA Staff Quarter Building, Siddhartha Enclave, Gorakhpur Bore Hole No-01

Fig-3. Map of Ramgarh Tal pariyojna representing Location of Bore Holes

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 LITREATURE REVIEW A liquefaction analysis should, at a minimum, address the following:  Developing a detailed understanding of site conditions, the soil stratigraphy, material properties and their variability, and the areal extent of potential critical layers.

Developing simplified cross-sections amenable to analysis. SPT procedures are widely used in practice to characterize the soil (field data are easier to obtain on loose cohesion less soils than trying to obtain and test undisturbed samples). The data needs to be corrected as necessary, for example, using the normalized SPT blow count [(N1)60] or the normalized CPT. The total vertical stress (σvo) and effective vertical stress (σvo') in each stratum also need to be evaluated. This should take into account the changes in overburden stress across the lateral extent of each critical layer, and the temporal high phreatic and piezometric surfaces,  Calculation of the force required to liquefy the critical zones, based on the characteristics of the critical zone(s) (e.g., fines content, normalized standardized blow count, overburden stresses, level of saturation),  Calculation of the design earthquake’s effect on each potentially liquefiable layer should be performed using the site-specific in situ soil data and an understanding of the earthquake magnitude potential for the facility, and  Computing the factor of safety against liquefaction for each liquefaction susceptible critical Field Methods The use of insitu testing is the dominant approach in common engineering practice for quantitative assessment of liquefaction potential. Calculation of two variables is required for evaluation of liquefaction resistance of soils (Seed et al, 2001; Youd et al, 2001).They is as follows 1. The seismic demand on a soil layer expressed in terms of CSR and 2. The capacity of the soil to resist liquefaction expressed in terms of CRR.

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The models proposed by Seed & Idriss methods are extensively used for predicting liquefaction potential using field data.

Seed & Idriss method After the disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors Seed and Idriss (1971), developed and published a methodology termed the ‘‘simplified procedure’’ for evaluating liquefaction resistance of soils.

Seed and Idriss (1971) developed and published the basic ‘‘simplified procedure.’’ That procedure has been modified and improved periodically since that time, primarily through landmark papers by Seed (1979), Seed and Idriss (1982), and Seed et al. (1985). In 1985, Whitman (1985) convened a workshop on behalf of the National Research Council (NRC), USA in which 36 experts and observers thoroughly reviewed the state-of-knowledge and the state-of-the-art for assessing liquefaction hazard. That workshop produced a report (NRC 1985) that has become a widely used standard and reference for liquefaction hazard assessment. Liquefaction is defined as the transformation of a granular material from a solid to a liquefied state as a consequence of increased pore-water pressure and reduced effective stress (Marcuson 1978). Increased pore-water pressure is induced by the tendency of granular materials to compact when subjected to cyclic shear deformations. The change of state occurs most readily in loose to moderately dense granular soils with poor drainage, such as silty sands or sands and gravels capped by or containing seams of impermeable sediment. As liquefaction occurs, the soil stratum softens, allowing large cyclic deformations to occur. In loose materials, the softening is also accompanied by a loss of shear strength that may lead to large shear deformations or even flow failure under moderate to high shear stresses, such as beneath a foundation or sloping ground. In moderately dense to dense materials, liquefaction leads to transient softening and increased cyclic shear strains, but a tendency to dilate during shear inhibits major strength loss and large ground deformations. A condition of cyclic mobility or cyclic liquefaction may develop following liquefaction of moderately dense granular

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 materials. Beneath gently sloping to flat ground, liquefaction may lead to ground oscillation or lateral spread as a consequence of either flow deformation or cyclic mobility. Loose soils also compact during liquefaction and reconsolidation, leading to ground settlement.

Sand boils may also erupt as excess pore water pressures dissipate.

CYCLIC STRESS RATIO (CSR) AND CYCLICRESISTANCE RATIO (CRR) Calculation, or estimation, of two variables is required for evaluation of liquefaction resistance of soils: (1) the seismic demand on a soil layer, expressed in terms of CSR; and (2) the capacity of the soil to resist liquefaction, expressed in terms of CRR. EVALUATION OF CSR Seed and Idriss (1971) formulated the following equation for calculation of the cyclic stress ratio:

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Blake (1996) approximated the mean curve plotted in Fig. 2.6 by the following equation:

(3) Where z= depth beneath ground surface in meters. Eq. (3) yields essentially the same values for rd as (2), but is easier to program and may be used in routine engineering practice.

CSR = (τav /σvo) = 0.65(amax /g) (σvo /σ'vo)rd (1) Where amax = peak horizontal acceleration at the ground surface generated by the earthquake; g = acceleration of gravity; σvo and σ'vo are total and effective vertical overburden stresses, respectively; and rd= stress reduction coefficient. For routine practice and noncritical projects, the following equations may be used to estimate average values of rd (Liao and Whitman 1986b): rd= 1.0 -0.00765z for z ≤ 9.15 m (2a) rd= 1.174 -0.0267z for 9.15 m <z ≤23 m (2b) Where z= depth below ground surface in meters.

Some investigators have suggested additional equations for estimating rd at greater depths (Robertson and Wride 1998), but evaluation of liquefaction at these greater depths is beyond the depths where the simplified procedure is verified and where routine applications should be applied. Mean values of rd calculated from (2) are plotted in Fig. 4, along with the mean and range of values proposed by Seed and Idriss (1971). With past practice, rd values determined from (2) are suitable for use in routine engineering practice. Factor rd calculated from (2) are the mean of a wide range of possible rd, and that the range of rd increases with depth (Golesorkhi 1989).For ease of computation,

FIG-4. rd versus Depth Curves Developed by Seed and Idriss(1971) with Added MeanValue Lines Plotted from Eq. (2) EVALUATION OF LIQUEFACTION RESISTANCE (CRR) A plausible method for evaluating CRR is to retrieve and test undisturbed soil specimens in the laboratory. Unfortunately, in situ stress states generally cannot be reestablished in the laboratory, and specimens of granular soils retrieved with typical drilling and sampling techniques are too disturbed to yield meaningful results. Only through specialized sampling techniques, such as ground freezing, can sufficiently undisturbed specimens be obtained.

Criteria for evaluation of liquefaction resistance based on the SPT Criteria for evaluation of liquefaction resistance based on the SPT have been rather robust over the years. Those criteria are largely embodied in the CSR versus (N1)60 plots reproduced in Fig. 5, (N1)60 is the SPT blow count normalized to an overburden pressure of approximately 100 kPa (1 ton/sqft) and a hammer energy ratio or hammer efficiency of 60%. Fig. 2.7 is a graph of

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 calculated CSR and corresponding (N1)60 data from sites where liquefaction effects were or were not observed following past earthquakes with magnitudes of approximately 7.5. CRR curves on this graph were conservatively positioned to separate regions with data indicative of liquefaction from regions with data indicative of nonliquefaction. Curves were developed for granular soils with the fines contents of 5% or less, 15%, and 35% as shown on the plot. The CRR curve for fines contents<5% is the basic penetration criterion for the simplified procedure and is referred to hereafter as the ‘‘SPT clean sand base curve.’’

The CRR curves in Fig. 2 are valid only for magnitude 7.5 earthquakes. Scaling factors to adjust CRR curves to other magnitudes are addressed in a later section of this report.

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Rauch (1998), approximated the clean-sand base curve plotted in Fig.5, by the following equation:

(4) This equation is valid for (N1)60< 30. For (N1)60≥30, clean granular soils are too dense to liquefy and are classed as nonliquefiable. This equation may be used in spreadsheets and other analytical techniques to approximate the cleansand base curve for routine engineering calculations.

FIG-5. SPT Clean-Sand Base Curve for Magnitude 7.5 Earthquakes with Data from Liquefaction Case Histories (Modified from Seed et al. 1985) Influence of Fines Content In the original development, Seed et al. (1985) noted an apparent increase of CRR with increased fines content. Whether this increase is caused by an increase of liquefaction resistance or a decrease of penetration resistance is not clear.

Based on the empirical data available, Seed et al. developed CRR curves for various fines contents reproduced in Fig. 5.

The following equations were developed by Seed and Idriss (1971) with the assistance of R. B. Seed for correction of (N1)60 to an equivalent clean sand value, (N1)60cs:

(N1)60cs= α+β (N1)60

(5)

α= 0 for FC ≤5%

(6a)

α= exp [1.76 2 (190/FC)] for 5% < FC < 35% (6b) α= 5.0 for FC ≥35% (6c) β= 1.0 for FC ≤5% (7a) 1.5 β= [0.99 1 (FC /1,000)] for 5% < FC < 35% (7b) β= 1.2 for FC ≥35% (7c)

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Where α and β= coefficients determined from the following relationships: These equations may be used for routine liquefaction resistance calculations. A backcalculated curve for a fines content of 35% is essentially congruent with the 35% curve plotted in Fig. 5. The back-calculated curve for fines contents of 15%plots to the right of the original 15% curve.

Other Corrections Several factors in addition to fines content and grain characteristics influence SPT results, as noted in. Eq. (8) incorporates these corrections (N1)60 = Nm CN CE CB CR CS (8) Where:Nm= measured standard penetration resistance; CN=factor to normalize Nm to a common reference effective overburden stress; CE= correction for hammer energy ratio (ER); CB= correction factor for borehole diameter; CR= correction factor for rod length; and CS= correction for samplers with or without liners.

Because SPT N-values increase with increasing effective overburden stress, an overburden stress correction factor is applied (Seed and Idriss 1982). This factor is commonly calculated from the following equation (Liao and Whitman 1986a): CN= (P /σ'VO) (9) Where:CN normalizes Nm to an effective overburden pressure of σ'vo approximately 100 kPa (1 atm) Pa. CN should not exceed a value of 1.7 The effective overburden pressure σ'vo applied in equation (8) should be the overburden pressure at the time of drilling and testing. Although a higher ground-water level might be used for conservatism in the liquefaction resistance calculations, the CN factor must be based on the stresses present at the time of the testing.

FIG-6. CN Curves for Various Sands Based on Field and Laboratory Test Data along with Suggested CN Curve Determined from Eqs. (9) and (10) (Modified from Castro 1995) Skempton (1986) suggested and Robertson and Wride (1998) updated correction factors for rod lengths <10 m, borehole diameters outside the recommended interval (65–125mm), and sampling tubes without liners. Range for these correction factors is listed in Table 2.3 For liquefaction resistance calculations and rod lengths <3 m, a CR of 0.75 should be applied as was done by Seed et al. (1985) in formulating the simplified procedure.

STANDARD PENETRATION TEST (SPT) The standard penetration test (SPT) is an empirical dynamic penetration test developed in USA in the 1920’s and was usually carried out in 50 to 100 mm diameter wash borings. The test is most commonly used in situ test especially for cohesionless soils, which cannot be easily sampled. The test is extremely used for determining the relative density, bearing capacity and the angle of shearing resistance of the cohesionless soil. The test is performed using a split barrel sample tube of 50 mm external diameter, 35 mm internal diameter and about 65 mm in length as specified in BS 1377.

In this process, a hammer of 63.5 kg weight with a free fall height of 750 mm is used to drive the sampler. Initially the sampler is driven 150 mm into the sand to seat the sampler and by-pass any disturbed sand at the bottom of the borehole. The number of blows required to drive the sampler a further 300 mm is then recorded. This number is

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 called the Standard penetration resistance (N) value. If 50 blows are reached before a penetration of 30 cm no further blows should be recorded. If the test is to be carried out in gravelly soils, the driving shoe is replaced by the 600 cone.

SPT test is very specific tool for the liquefaction hazard analysis. It also has the unique feature of supplying samples for soil classification purpose.

Usually SPT is conducted at every 1 m depth or at the change of stratum.

The N-values are extensively used in determining the bearing capacity and predicting the settlement of cohesionless soil and are described by a number of authors (Meyerhof, 1956; Terzaghi and Peck, 1967). It has wide application in determining the liquefaction susceptibility of a place.

There are a number of factors involved in the SPT, which can affect the blow count, mainly related to poor testing practice. The standard penetration number is corrected for dilatancy effect and overburden effect (Craig, 1986) (i) Dilatancy correction Silty fine sands and fine sands below the water table develop pore pressure, which is not easily dissipated. The pore pressure affects the resistance of the soil and hence the penetration number (N). Terzaghi and peck (1967) recommend the following correction in the case of silty fine sands when the observed value of N exceeds 15.

1

N'= 15 + (N -15) 2

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hammer being referred to as the rod energy ratio, which varies between 45% and 78% for the operating procedures used in several countries. It has been recommended that a standard rod energy ratio of 60% should be adopted and that all measured N values should be normalized by simple proportion of energy ratios, to this standard: the normalized values are denoted (N1)60.

Standard penetration resistance depends not only on relative density but also on the effective stresses at the depth of measurements. Effective stresses can be represented to a first approximation by effective overburden pressure.

This dependence was first demonstrated in the laboratory by Gibbs and Holtz and was later confirmed in the field. Sand at the same relative density would thus give different value of standard penetration resistance at different depths. Several proposals have been made for the correction of measured N values. The corrected value (N1) is related to the measured value (N) by the factor CN, where N1 = CN N (11) CN = Correction factor and can be obtained from the graph prepared by Liao and Whitman, (1986).

Also CN=â&#x2C6;&#x161;

1 đ?&#x153;&#x17D;

(12)

´

SPT correction factor, CN

(10) (Craig, 1988)

Where:Nâ&#x20AC;&#x2122; â&#x20AC;&#x201C; Corrected SPT value N â&#x20AC;&#x201C; Observed SPT value.

If NR â&#x2030;¤ 15, Nc =NR (ii)Overburden Pressure Skempton summarized the evidence regarding the influence of test procedure on the value of standard penetration resistance (Craig, 1986).

Measured N value should be corrected to allow for the different methods of releasing the hammer, the type of anvil and the total length of boring rods. Only the energy delivered to the sampler is applied in penetrating the sand, the ratio of the delivered energy to the free fall energy of the

Fig -7: SPT overburden correction factor after Liao and Whiteman (1986)

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(N1)60 is the standard penetration resistance normalized to a rod energy ratio of 60% and an effective overburden pressure of 100 kN/m2.

MAGNITUDE SCALING FACTORS (MSFs) The clean-sand base or CRR curves in Fig. 5, only to magnitude 7.5 earthquakes. To adjust the clean-sand curves to magnitudes smaller or larger than 7.5, Seed and Idriss (1982) introduced correction factors termed ‘‘magnitude scaling factors (MSFs)’’. These factors are used to scale the CRR base curves upward or downward on CRR versus (N1)60, qc1N, or Vs1 plots.

Conversely, magnitude weighting factors, which are the inverse of magnitude scaling factors, may be applied to correct CSR for magnitude. Either correcting CRR via magnitude scaling factors, or correcting CSR via magnitude weighting factors, leads to the same final result.

To illustrate the influence of magnitude scaling factors on calculated hazard, the equation for factor of safety (FS) against liquefaction is written in terms of CRR, CSR, and MSF as follows: FS = (CRR7.5/CSR) MSF

(13)

Where CSR = calculated cyclic stress ratio generated by the earthquake shaking; and CRR7.5 = cyclic resistance ratio for magnitude 7.5 earthquakes. CRR7.5 is determined from Fig. 2 7 for SPT data, MSF= Magnitude Scaling Factor.

In 2001 Youd and Idriss recommend the following equation for obtaining MSF MSF=102.24/Mw2.56, Where, Mw= Magnitude of earthquake When the design ground motion is conservative, earthquake-related permanent ground deformation is generally small if FS ≥ 1.

Liquefaction Hazard Assessment /Liquefaction potential Analysis If potential exists for liquefaction at a facility, additional subsurface investigation may be necessary. Once all testing is complete, a factor of safety against liquefaction is then calculated for each critical layer that may liquefy.

Fig-8, Flow chart for Liquefaction Hazard Assessment As mentioned that our first aim is to analyse liquefaction potential of soil and to prepare liquefaction susceptibility map of “Ramgarh Tal pariyojna” using borehole data. Liquefaction phenomena have been recorded in many parts of the world, where ground shaking is frequent and soils consist of loose fine sand where the water table is shallow. Liquefaction of saturated loose sands and silty sands induce flow slides, differential settlement, and subsidence, leading damage to buildings and infrastructure and eventually to loss of life.

Determination of liquefaction potential due to earthquake is complex geotechnical problem.

Many factors including soil parameters and seismic characteristics influence this phenomenon To assess the liquefaction hazard in an area, it is important to examine the geotechnical characteristics like grain size distribution, percentage of silt, water table ,water table depth,D50 value and SPT ‘N’ value. The percentage of silt and poorly graded sand is high in the area under “Ramgarh Tal Pariyojna” indicating that there is a great chance of soil liquefaction. Here liquefaction potential analysis is done to determine the factor of safety at different depth. The liquefaction potential of “Ramgarh Tal Pariyojna” in Gorakhpur city using SPT data collected from the various sites of pariyojna is estimated by simplified procedure of Seed & Idriss (1982).

The methodology used to estimate the liquefaction potential is given as example for one borehole Excel spread sheet used to calculate the

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GJESR RESEARCH PAPER VOL. 1 [ISSUE 10] NOVEMBER, 2014 Factor of Safety with depth and enclosed in tables

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shown below.

Table: 04. LIQUIFACTION ASSESSMENT OF PROPOSED GDA STAFF QUARTER BUILDING, SIDDHARTHA ENCLAVE, GORAKHPUR (BORE HOLE-1)

RESULTS AND ITS DISCUSSIONS Result of liquefaction is shown with depth for of each site of bore holes and graph shows factor of safety vs. depth.

Factor of Safety (FS) 0

0

0 .2

0 .4

0 .6

0 .8

1

1 .2

1 .4

1 .6

2

4

8

Depth (m)

Bore hole Number 1 (BH1) The analysis of SPT results at Bore hole number 1(BH1) shows that the strata between depths 13.65-15.05 m are Non-Liquefiable, and the strata between 1.65-12.5 m are liable to liquefy under earthquake shaking corresponding to peak horizontal ground acceleration of 0.33g.

8

10

12

14

16

Depth vs Factor of Safety

Fig-9. Depth vs. Factor of Safety (Bore Hole-1)

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Factor of Safety 0

0

0.5

1

1.5

2

2.5

depthbh1 vs. FS bh1 2

depthbh2 vs. FS bh2 depthbh3 vs. FS bh3 depthbh4 vs. FS bh4

4

depthbh5 vs. FS bh5 depthbh6 vs. FS bh6

Depth (m)

6

depthbh7 vs. FS bh7 depthbh8 vs. FS bh8 depthbh9 vs. FS bh9

8

depthbh10 vs. FS bh10 depthbh10 vs. FS bh11 depthbh12 vs. FS bh12

10

depthbh13 vs. FS bh13 depthbh14 vs. FS bh14 depthbh15 vs. FS bh15

12

depthbh17 vs. FS bh17 14

16

Depth vs Factor of Safety

Fig-10. Depth vs Factor of safety of all borehole

Fig-11- Depth wise liquefaction of each bore hole

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Fig-12. - Liquefaction Hazard map of Ramgarh Tal Pariyojna CONCLUSION Based on the study for assessment of liquefaction potential for “Ramgarh Tal Pariyojna”, it is concluded that soil of study area is susceptible to liquefaction extra care should be taken against liquefaction during construction upon this type of soil. The Study area being a reclaimed area has a top layer of loose fine sand followed by soft to medium or loose sandy silt or clayey silt is also susceptible to liquefaction.

In this study we concluded that if earthquake more than or equal to 6.5 ritcher scale occurs in Gorakhpur region, it will be extensively damaged due to liquefaction. 

In the fig 19, we have bore hole position wise combined data of all the studied boreholes and depth wise zone of liquefaction, and zone of no liquefaction.

Observation of combined graph shows liquefaction potential for each borehole and depth upto which soil may liquefy during an earthquake, for the design of any structure in the considered area, if liquefaction is to be considered then an average depth of 6m can be taken for the analysis purposes.

An average

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liquefaction is observed upto the depth 6m. 

In fig 18. combined graph is drawn between factor of safety and depth of borehole in which all soils below factor of safety -1 is susceptible to liquefaction and should be considered for mitigation before building a structure on it.



The percentage of silt and poorly graded sand is high in the area under “Ramgarh Tal Pariyojna” indicating that there is a great chance of soil liquefaction. Here liquefaction potential analysis is done to determine the factor of safety at different depth.

Construction on liquefaction susceptible soils is to be avoided. It is required to characterize the soil at a particular building site according to the various criteria’s available to determine the liquefaction potential of the soil in a site.

The structure constructed should be liquefaction resistant i.e., designing the foundation elements to resist the effects of liquefaction if at all it is necessary to construct the structure on liquefiable soil



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

because of favourable location, space restriction and other reasons.

This involves mitigation of the liquefaction hazards by improving the strength, density and drainage characteristics of the soil. This can be done using variety of soil improvement techniques.

REFERENCES

1.

ABAG (2001). “Bay area Liquefaction Hazard” The REAL Dirt on Liquefaction. (http://www.abag.ca.gov/bayarea/eqmaps/li quefac/liquefac.html,) 2. ABAG (2001). “Collection and analysis of Liquefaction data from the Northridge and Loma Prieta Earthquakes” Appendix C 3. Andrus, R. D. and Stokoe, K. H.( 1997) “Liquefaction Resistance of Roils from Shear Wave Velocity. In Proceedings of NCEER Workshop on Evaluation of Liquefaction Resistance of Soils, , pp. 89–128..

4. Craig, R.F. (1986). “Soil Mechanics” (4th edition). Van Nostrand Reinhold co.ltd. (UK).

5. IS: 1893-2002, “Criteria for Earthquake Resistant Design of Structures”.

6. Iwasaki, T., Tokida, K., Tatsuoka, F., Watanabe, S.,Yasuda, and Sato, H. (1982), Microzonation for soil Liquefaction Potential Using Simplified Methods”. In Proceedings of Third International Conference on Microzonation, Seattle, , vol. 3,pp. 1310–1330.

7. Youd T. L and I. M. Idriss, Editors, (1997).

National Centre for Earthquake Engineering Research (NCEER), Proceedings of the NCEER Workshop on Evaluation of Liquefaction Resistance of Soils,., Technical Report NCEER97-022 8. Rao, K. S. (2003), Seismic Microzonation of Delhi region. In Proceedings of 12th Asian Regional Conference, Singapore, , vol. 1, pp.

327–330.

9. Rao, K. S. (2001) and Mohanty, W. K., “Microzonation of Delhi region: An approach”.

J. Indian Build. Congr., 8, 102–114.

10. Rao, K. S. (2001), Liquefaction Studies for seismic Microzonation of Delhi region. In Indian Geotechnical Conference, vol. 2, pp.

44–51.

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11. Rao, K. S., Stability and rehabilitation aspects of earth dams damaged during the Bhuj earthquake, India. Proc. Forensic Geotech.

Engg., 2003, 1, 151–158.

12. Seed, H. B. and Idriss, I. M., (1971) Simplified Procedure for Evaluating Soil Liquefaction Potential. J. Soil Mech. Found. Div., , 97, 1249– 1273.

13. Seed, H. B., (1979) “Soil Liquefaction and Cyclic Mobility Evaluation for Level Ground During Earthquakes”. J. Geotech. Eng. Div., , 105, 210–255.

14. Seed, H.B., and Idriss, I.M., and Arango, I. (1983). Evaluation of liquefaction potential Using Field Performance data. ASCE Journal of Geotechnical Engineering, 109(3), 458482.

15. Seed, H.B. (1997),”Soil Liquefaction and Cyclic Mobility Evaluation Level Ground During Earthquake”, J. of Geotech Engrg Div, ASCE, 22(3), pp. 298-307.

16. Seed H.B., Tokimatsu, K., L.F. and Chung, R.M. (1985). “The Influence of SPT Procedures in soil Liquefaction Resistance Evaluations”, J. of Geotech Engrg Div, ASCE, 111(20), pp.

1425-1445.

17. Whitman, R.V., 1971. Resistance of Soil to Liquefaction and Settlement. Soils Found 11 (4), 59–68.

18. Youd, T. L. and Perkins, D. M, (2004) Mapping Liquefaction Induced Ground Failure Potential. J. Geotech. Eng. Div. ASCE, 1978, 104, 433–446. DST Report, Geo-Scientific Studies in and around Delhi, , p. 74.

19. Youd, T.L. and Idriss, (2001).Liquefaction Resistance of Soils: Summary Report from 1996 NCEER and 1998 NCEER/NSF Workshop on Evaluation of Liquefaction Resistance of Soils”, J. of Geotech& Geo- env., ASCE 127(4) pp.297 20. Youd, T. L., 1991. Mapping of Earthquake Induced Liquefaction for Seismic Zonation.

Proc. Fourth Int. Int. Conf. Seismic Zonation 1, pp. 111-147 21. Youd, T.L.,(1984a).Recurrence of Liquefaction at the same site, Proceedings, 8th World Conference on Earthquake Engineering, Vol. 3, pp. 2313-238.

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Proc. ASCE Civil Eng., v.104, n0. GT4, p. 433-446.

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