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Issue 2 • 2019
Load testing for the Réseau électrique Métropolitain project Pilingin Industry Canada Montreal
PIC Pile Testing: defining anomalies, flaws and defects
When deep foundation magazine work goes electric
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In this issue
Published by DEL Communications Inc. Suite 300, 6 Roslyn Road Winnipeg, Manitoba Canada R3L 0G5 President & CEO: David Langstaff Managing Editor: Lyndon McLean lyndon@delcommunications.com
PILING INDUSTRY NEWS
Visions of the Emirates: Liebherr at work in the Palm Islands 4 Piling Industry Canada Pile Dynamics, Inc. Introduces the Shaft Area Profile Evaluator (SHAPE) 6
PIC
Pile Testing - Anomalies, Flaws and Defects 8
magazine
Equipment Profile
When deep foundation work goes electric 12
O-Cell Load testing of large-diameter single-drilled shaft foundations for the REM project in Montreal 16 Report on infrastructure calls for greater and urgent investment in core works 24
Equipment Profile
Pile Master Air Hammers Hit the Pile Driving Market 25
Advertising Account Executives: Jennifer Hebert, Michelle Raike Production services provided by: S.G. Bennett Marketing Services www.sgbennett.com Art Director: Kathy Cable Layout: Dana Jensen Advertising Art: Dave Bamburak © Copyright 2019. DEL Communications Inc. All rights reserved.The contents of this publication may not be reproduced by any means, in whole or in part, without prior written consent of the publisher. While every effort has been made to ensure the accuracy of the information contained herein and the reliability of the source, the publisherin no way guarantees nor warrants the information and is not responsible for errors, omissions or statements made by advertisers. Opinions and recommendations made by contributors or advertisers are not necessarily those of the publisher, its directors, officers or employees.
Index to advertisers Arntzen Corporation................................................................26 Canadian Piledriving Equipment Inc...............................2 Czm Foundation Drilling......................................................25 Equipment Corporation of America.................14 & 15 Fraser River Pile & Dredge (GP) Inc................................24 Hercules Machinery Corporation....................................17
Sales Manager: Dayna Oulion dayna@delcommunications.com
Interpipe Inc..................................................................................23 Keller Foundations, Llc............................................................5 Liebherr Werk Nenzing Gmbh...............OFC, 3 & OBC Loadtest............................................................................................13 Nucor Skyline...................................................................................7 Samuel Roll Form Group.......................................................11
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When deep foundation work goes electric: First application of global innovation It is a unique construction site: the use of machines with an electric drive means deep foundation work can for the first time be executed emission-free. With the LB 16 unplugged the first battery-powered drilling rig is used on one of the largest roadwork sites in western Austria. The absence of a combustion engine has two particular advantages: the LB 16 unplugged produces no local exhaust emissions and also generates considerably less noise. “You don’t have to shout all the time. You can talk normally and your colleague hears, even when standing further away. Otherwise, when the engines are running at full power they are very loud and you always have to raise your voice, which is a burden in itself. You also don’t hear little things in the surrounding area, which you do now during ongoing site work,” explains foreman Sebastian Timpe.
Piling Industry Canada • December 2019 3
Piling Industry News
Visions of the Emirates: when the superlative becomes reality Burj Khalifa, the tallest building in the world, dominates the town at a height of 828 metres and is a symbol of the building boom in the Emirates. To the west of Palm Jumeirah, the artificial island in the shape of a palm tree, the new port with a size of almost 2 million square metres is emerging as a further prestige project of Dubai. It includes 1,110 berths for 1,400 yachts, a terminal for cruise ships, luxury hotels, shopping centres, residential buildings and a 135-metre-high lighthouse. What is so special about it? The harbour is a cornerstone for a vision of the Emirates.
Ground Improvement For the project to be a success, the building ground must be improved along the 2,675-metre long coast. For this purpose, Keller is compacting more than 7 million cubic metres of sand in an area of 380,000 square metres. Through deep compaction,
the load-bearing capacity of the ground to support construction loads is enhanced and the settlement of the ground is reduced. Keller is a pioneer for soil compaction and has been involved in several large construction sites in the United Arab Emirates, including “Palm Islands”. For the current harbour project, the company is using a duty cycle crawler crane from the Liebherr HS series. The HS 8130 is equipped with a vibroflot for deep compaction.
Efficient Realisation The long boom of the HS 8130 provides Keller with a large working radius. Without having to change the position of the duty cycle crawler crane, a wide radius of building ground can be compacted. The radius is a particular advantage for the steep drop into the sea. Work of this kind is usually carried out from a barge. Or land is temporar-
ily reclaimed for the task and subsequently restored to the sea. Both these methods are considerably more time-consuming and cost intensive. Thanks to the deep compaction using the HS 8130, Keller improves the building ground down to a depth of 19 metres. The aim is to withstand a construction load of 200 kPa. In order to verify the geotechnical requirements of the ground, approximately 600 compaction points are being tested using SPT (Standard Penetration Test). In addition to the large radius of the HS 8130, the complete HS series has proven itself through its all-rounder qualities. The new harbour in the Persian Gulf is the cornerstone for the Emirates’ vision of attracting 20 million tourists per year from 2020. For the harbour project in Dubai, Keller also has two drilling rigs and two crawler cranes from Liebherr in operation. l
Keller is using a HS 8130 with vibro-flot for the soil compaction work.
Keller is a pioneer for soil compaction and has been involved in several large construction sites in the United Arab Emirates, including “Palm Islands”.
4 PIC Magazine • December 2019
Piling Industry News
Pile Dynamics, Inc. Introduces the Shaft Area Profile Evaluator (SHAPE) Drilled shafts are rarely ideal cylinders, and irregularities in the shaft construction can affect shaft performance. PDI’s Shaft Area Profile Evaluator (SHAPE) offers quality control of shaft radius, volume, and verticality. SHAPE is a cost-effective quality assurance testing device used for deep foundations such as drilled shafts, bored piles, slurry walls, barrettes, and more to better characterize the three-dimensional profile of these and other excavated deep-foundation elements. It provides a fast, economical representation of the foundation excavation and verticality prior to placing concrete in wet conditions. “We felt the market needed a modern and rugged device where we eliminate common points of failure such as electronic cables running from the surface to the device to provide increased accuracy and performance,” says George Piscsalko, President of PDI.
6 PIC Magazine • December 2019
SHAPE’s drilling stem advancement rate is approximately one foot per second, offering simplicity in analysis with a clean signal and 3D profile views. It is a completely wireless device, requiring no electronic cabling from the surface to the device during operation. This increases overall system reliability. SHAPE automatically corrects for changes in wave speed with depth by measuring the wave speed at each measurement location along the length of the excavation and adjusting the radius calculation based on the measured wave speed at any depth location. SHAPE samples all eight sensors simultaneously at a high rate of speed, allowing the SHAPE to be quickly deployed and construction to continue promptly. The SHAPE can be operated on site or remotely with PDI’s SiteLink® technology. SHAPE is the latest addition to Pile Dynamics extensive line of quality-assurance and quality-control systems for the deep foundations industry. For more information visit www.pile.com/shape or contact info@pile.com today. l
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Pile Testing: Anomalies, Flaws and Defects By Joram M. Amir, Ph.D., C.E., D.GE, Piletest.com Ltd.
Pile integrity means strict adherence to the relevant drawings and specifications. This includes the pile geometry (e.g., length, diameter or width, and verticality) as well as continuity and material properties. Since the construction process of piles is practically blind, practitioners realized early on that pile integrity should not be taken for granted. Starting in the early 1960s, the discipline of pile integrity testing has made giant steps in both testing methods and their implementation worldwide. Presently, the prevalent methods are the low-strain impact method (ASTM D5882, Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations) and the crosshole ultrasonic method (ASTM D6760, Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing). In comparison with the widespread advancements in instrumentation, the piling industry has not yet reached a consensus regarding the interpretation of the test results and acceptance criteria. Often, this creates unnecessary friction and even litigation between the parties involved. To avoid these consequences, the parties must first agree
8 PIC Magazine • December 2019
about the facts by adopting established definitions to the following three terms that today are often confused: anomaly, flaw, and defect. The following sections suggest such definitions, which are supported by commonly occurring examples.
Definitions Based on the technical paper by Amir, “Single-Tube Ultrasonic Testing of Pile Integrity,� which was published in the proceedings of the ASCE 2002 Deep Foundation Congress, the following definitions are intended to make a clear distinction between the results of the integrity tests, the physical condition of the pile and the necessary action, if any. The terms were incorporated in ASTM D6760 and can also be visualized using a Venn diagram in which they can be depicted and distinguished. Anomaly: Any irregular feature in the results from the nondestructive testing (NDT). An anomaly may be due to the testing instrument (e.g., noise), the means used (e.g., access tube debonding), the surrounding soil (e.g., abrupt changes of soil friction) or the pile itself.
It is the responsibility of the personnel and/or agency performing the testing to gather and analyze all relevant data and to try to resolve every anomaly. Flaw: Any deviation from the planned shape or composition of the pile, which does not necessarily detract from the performance of the pile. Defect: A flaw that, because of either size or location, may detract from the resistance, durability and/or performance of the pile. The geotechnical engineer and the structural engineer are jointly responsible for deciding whether a specific flaw constitutes a defect.
constant values of FAT and RE. However, below this depth and down to about 29.3 metres (96 feet), the FAT gradually decreases from 330 μsec to 100 μsec, doubtlessly an anomaly. A quick questioning onsite revealed the reason; the foundation element was reinforced only in the upper 21 metres (69 feet). Nevertheless, the engineer required that the access tubes be extended all the way to the bottom of the barrette. With no rebar cage to keep them aligned, the access tubes dangled freely and likely moved toward each other. This result had certainly nothing to do with the barrette itself and, accordingly, was not declared a flaw. The following reflectogram was generated from low-strain impact testing of a driven pile that was 27 metres (88.6 feet) long. From a review of the output (Fig 3), a major anomaly appears at a depth of about 12.5 metres (41 feet). However, after questioning the client about the pile, it was discovered that this pile consisted of two interlocked sections. What appeared as a discontinuity in the reflectogram was actually just the joint between the two sections and was therefore not declared a flaw.
Fig1 - Venn diagram of the five typical zones
EXAMPLES In the Venn diagram (Fig 1) we can distinguish between five zones related to results of pile integrity tests. The following examples illuminate each of these zones with actual case histories taken from the authors' archives:
I - Anomaly That Is Not a Flaw An anomaly that is not a flaw, also known as a false positive, will be illustrated using two cases: one from crosshole ultrasonic testing of a barrette and one from low-strain impact testing on a pile. As shown on the graphic “Ultrasonic test results on a barrette,” (Fig 2) the first arrival time (FAT) is shown in red and the relative energy (RE) in shown in blue. Down to a depth of about 22 metres (72 feet), both curves appear rather regular (i.e., relatively straight lines) with nearly
Fig2 - Ultrasonic test results on a barrette
Fig3 - Results of low-strain impact testing on a driven pile
II - Anomaly That Is a Flaw An anomaly that is a flaw includes “soft bottom” conditions, which occur when the bottom of a drilled shaft constructed using a drilling support fluid (i.e., slurry) is not cleaned properly. The only existing method in which the soft bottom condition is detected and appears as an anomaly is the crosshole ultrasonic logging (CSL) method. With the CSL method, a soft bottom condition manifests as a large increase in the FAT with a corresponding decrease of the RE (Fig 4). Understandably, a soft bottom condition anomaly should be reported as a flaw.
Fig4 - A soft bottom anomaly Piling Industry Canada • December 2019 9
III - Flaw That Is Not an Anomaly and Not a Defect A flaw that is not an anomaly and not a defect includes a minor soil pocket in the pile which is, by definition, a flaw (Fig 5). However, due to its small size, the flaw may be undetectable even by today's most sensitive instruments and, therefore, cannot produce an anomaly. Fortunately, such a small flaw affects neither the capacity nor the durability of the foundation element; thus, the flaw is not a defect.
Fig7 - A defect in a drilled shaft
V-Defect That Is Not an Anomaly
Fig5 - A small flaw
IV - Anomaly That Is a Defect An example of when an anomaly is actually a defect (i.e., true positive) is discussed hereafter. From the results of CSL testing performed on a drilled shaft, a major anomaly was discovered at a depths between 1.8 and three metres (six and 10 feet), where the FAT increased from 190 μsec to a maximum of about 330 μsec, an increase of about 74 per cent. The attenuation increased by 16 dB, which was an 84 per cent decrease in the energy (Fig 6). Since this feature was quite shallow and the groundwater level much deeper than the location of the anomaly, it was decided to excavate around the pile to expose the anomaly. Upon excavating around the pile, visual observations confirmed the test results and suspicions that this anomaly was indeed a flaw. Due to its size and location, the flaw was justly classified as a defect (Fig 7).
A defect that is not an anomaly (i.e., a false negative) represents all the true defects that go undetected, such as: • Soft bottom conditions that were undetected by either the low strain impact method or thermal imaging. • Deviation from the vertical, which is not detected unless tested using a dedicated system. • Large bulges, which are undetectable by CSL testing. However, defects such as the ones listed above could have been detected by selecting a proper test method.
DFI White Paper A team of experts was formed from the DFI Testing and Evaluation Committee and was chaired by Anna Sellountou, Ph.D., P.E., of Pile Dynamics, Inc. (PDI), to develop guidance on evaluating and interpreting the results of CSL testing. Recently, the team completed the white paper titled “Terminology and Evaluation Criteria of Crosshole Sonic Logging (CSL) as applied to Deep Foundations”. Based on an extensive literature survey and on the experience of the team members, the document essentially adopts the definitions presented above, defines three levels of anomalies and recommends the actions to be takes in each case in an attempt to resolve the anomaly. The white paper is currently under review and should be available through DFI later this year. l Author info: Joram M. Amir, Ph.D., C.E., D.GE., is a Licensed Engineer No. 147 (Geotechnics and Structures) in Israel. With close to 60 years of experience as a geotechnical consultant, he also serves as the chairman of Piletest.com Ltd., developing innovative systems for pile integrity testing.
Fig6 – Ultrasonic test results on a drilled shaft 10 PIC Magazine • December 2019
This article was originally published in DFI’s bi-monthly magazine, Deep Foundations, May/June 2019 issue. DFI is an international technical association of firms and individuals involved in the deep foundations and related industry. Deep Foundations is a member publication. To join DFI and receive the magazine, go to www.dfi.org for further information.
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When deep foundation work goes electric:
First application of global innovation It is a unique construction site: the use of machines with an electric drive means deep foundation work can for the first time be executed almost emission-free. It is a trouble spot in the western Austrian road network: the Bludenz-Bürs junction of the A14 motorway. There are frequent traffic jams and hold-ups due to congestion. In order to avoid dangerous tailbacks on the motorway, by the end of 2021 ASFINAG is to build a large roundabout with two bridges over the A14, as well as two new connections to regional roads, also with a roundabout and water protection facility. The local company i+R is carrying out the deep foundation work on the west side. For this purpose, i+R is using the world’s first drilling rig on the market with “Lo-
cal Zero Emission”. The LB 16 unplugged, which was recently launched by Liebherr, has an electro-hydraulic drive concept and can also be used cable-free thanks to the battery, i.e. unplugged.
The challenge Certainly aware of the responsibility for the environment and society, the alternative drive concept is well received by the customer. “Sustainability in the construction industry is not a foreign concept, but common practice for ASFINAG. Innovative developments like the world’s first drilling rig with zero emissions show that also on ASFINAG construction sites there is enough room for environmentally friendly construction practices,” says Andreas
Impressive: The first battery-powered drilling rig in the world at work in Bürs.
12 PIC Magazine • December 2019
Fromm, Managing Director of ASFINAG Bau Management GmbH. The challenges for i+R are the narrow construction site itself and the restricted working height. The pile foundations must be placed directly under a power line. Therefore, the drilling rig is designed as a low head (i.e. with a shorter leader). During the project, i+R is installing 148 piles and drilling 1,742 metres into the ground. Approximately 1,200 cubic metres of concrete are being poured, and the piles vary between 10 and 14 metres in depth and have a diameter of 900 millimetres. Due to the restricted working height, casing pipes with a shorter length (two metres) have to be used and the reinforcement cages have to be inserted in sections. The machine achieves approximately two piles per day.
Electrifying: The LB 16 unplugged with electrohydraulic drive can also be used without cables.
The benefits The absence of a combustion engine has two particular advantages: the LB 16 unplugged produces no local exhaust emissions and also generates considerably less noise. “You don’t have to shout all the time. You can talk normally and your colleague hears, even when standing further away. Otherwise, when the engines are running at full power, they are very loud and you always have to raise your voice, which is a burden in itself. You also don’t hear little things in the surrounding area, which you do now during ongoing site work,” explains foreman Sebastian Timpe. The quieter environment is therefore also a safety-relevant aspect in regular construction site operation. The machine has no restrictions in terms of performance and application compared with the conventional version. The battery is designed to last one working day (10 hours). It can be easily charged overnight using a standard construction site electric supply (32 A, 63 A).
Shorter: Due to the power line, the drilling rig is designed as a low head.
Local Zero Emission Sometimes the concrete is delivered by a Liebherr concrete mixer ETM 905 with electric drum drive. In normal operation, the battery capacity is sufficient for the entire working day. As a plug-in hybrid the battery can be charged during the journey or externally via a plug (e.g. at a concrete mixing plant). i+R also uses an electric compact excavator. Thus, deep foundation work on a construction site is carried out for the first time using almost exclusively electrically driven machines. Therefore, the best possible combination of customer benefit, environmental compatibility, and efficiency is achieved. Estimated over one year, approximately 35,000 litres of diesel can be saved and more than 92 tonnes of CO2 emissions can be avoided. “The construction site at Bludenz-Bürs is a win-win situation for everyone: enhanced safety and fewer traffic jams for the local Vorarlberg people, and environmentally friendly use of construction machines on the currently largest ASFINAG construction site in Vorarlberg,” says Andreas Fromm. l
INSPECT WITH Real-Time Excavation Inspection Remove the uncertainty in drilled shaft excavation conditions with SONICaliper inspection. Using sonar technology, it provides a full 360-degree, threedimensional measurement of shaft excavations for a profile of shape, volume, alignment and verticality. With detailed results — designers, contractors and owners know that shafts have been constructed according to specification and meet quality standards. FUGRO LOADTEST 800 368 1138 info@loadtest.com www.loadtest.com Piling Industry Canada • December 2019 13
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O-Cell Load testing of large-diameter single-drilled shaft foundations for the REM project in Montreal By Riad Diab, Louis D’Amours, and Malek Bouteldja, SNC-Lavalin, Montreal, Quebec, Canada Edited by William F. “Bubba” Knight, Fugro Loadtest, Gainesville, FL. Introduction The Réseau Électrique Métropolitain (REM), a $6.5 billion designbuild project, is being constructed by a Joint Venture comprised of SNC Lavalin, Dragados Canada, Group Aecon Quebec, Pomerleau, and EBC, partnering with Aecom and SNC Lavalin as the lead design firms. The project, referred to as REM, is a fully automated light rail transit (LRT) proposed by the Caisse de dépôt et placement du Québec (CDPQ) Infra, to serve the major metropolitan areas in Montreal, Canada. The 67 kilometres (km) REM will be one of the world’s largest automated transportation systems in the world. As Figure 1 shows, the REM will link downtown Montreal, South Shore, West Island (Sainte-Anne-De-Bellevue), North Shore (DeuxMontagnes), and the Montreal-Pierre Elliott Trudeau International Airport. The project comprises four segments: South Shore (SS) will cross the St. Lawrence River on the new Champlain Bridge; the Deux Montagnes (DM) segment, which is basically a conversion of the existing Deux-Montagnes line; the Sainte-Anne-De-Bellevue (SADB) segment; and the airport segment. Over 25 km will be constructed on an elevated structure founded on over 650 single-drilled shafts socketed into rock.
One advantage of using a single shaft is the ease of construction, especially close to existing structures. However, the major disadvantage is the lack of redundancy. This highlights the importance of design calibration. Depending on the structural loads and site conditions, the drilled shafts will range from two to 3.2 metres (m) in diameter with embedment of up to nine metres within the sound rock calibrated with full scale Osterberg Cells Load tests.
Site Geologic Conditions The general geology of the layout consists of a till deposit overlying the bedrock at varying depths (two to 17 m). The surface of the bedrock is altered and fractured for depths varying from one to three. Three rock types are encountered along the REM alignment. Limestone and dolomite are the main rock formations along DM and SADB. Shale is the only rock type along the SS segment.
Testing objectives To optimize drilled shaft design using higher resistance values, fullscale Osterberg Cell bidirectional static load test were performed in each of the encountered rock formations; limestone, dolomite and shale. As O-cell tests were performed for, the new Champlain Bridge project in the shale permission was obtained to use those results. Accordingly, one each O-Cell test was performed in the dolomite and limestone. The tests established the drilled shaft side and base resistance ultimate limit state design values for the construction means and methods planned for production foundations. The test also allowed calibrated development of an equivalent top load-settlement curve for production piles for use in for serviceability limit state settlement estimates.
Subsurface Investigation
Figure 1. REM project alignment 16 PIC Magazine • December 2019
Load test location soil and rock investigations included SPT borings, pressuremeter, dilatometer and vane shear tests in cohesive soil. The laboratory program consisted of soils sieve and hydrometer analysis and rock unconfined compressive tests and elastic modulus. At the SADB load test location, the overburden soil consisted of an upper 4.4 m clayey silt deposit which the field vane indicated a 57 kPa undrained shear strength, underlain by a layer of glacial till consisting mainly of very dense silty sand and gravel.
The bedrock surface was a poor quality, weathered metamorphosed conglomerate located at depths of 11.4 to 12.1 m with an RQD of 25 per cent. Below was a dolomite in poor to good quality with a 69 per cent RQD. At the DM load test location, the upper 3 m of overburden is a silt and sandy silt fill material with an average SPT ‘N’ values of 4 blows/0.3 m, underlain by a four-metre glacial till layer of silty sand, average SPT ‘N’ value 14 blows/0.3 m. The limestone surface encountered at a seven metre depth was of bad quality for 0.75 m, RQD of 22, with quality increasing from good to excellent as exhibited by RQD averaging 83. Table 1 defines more specific rock parameters for the test sites:
Construction procedure A hydraulic rig inserted a 1,300 mm diameter permanent steel casing through the overburden and the fractured rock to refusal. After casing seating and cleaning of overburden, an auger and bucket alternated to drill a 1,180 mm shaft socket with a minimum of 300 mm of recess. A cleaning bucket then obtained a relatively flat shaft base. Verticality checks were accomplished by measuring drilling rig alignment with a 1.2 meters long spirit level targeting verticality of zero to two per cent. Figure 2 shows the placement of the casing and the soil excavation. After base cleaning, the O-cell assembly placement into the excavation and temporarily supported from the outer steel casing. Crosshole Sonic Logging (CSL) tubes attached to the reinforcement cage interior and the five-inch OD tremie pipe pre-inserted through the loading plates to facilitate placement. Figure 3 shows images of the reinforcement cage, instrumentation and O-cell assembly. Figure 3a depicts images of the cage placement and top of the O-cell test shaft. Concrete placement initiated through the tremie at the shaft base. Continuous monitoring of the volume of concrete in the shaft (top of concrete elevation) to the volume delivered from the trucks occurred at all times. Tremie pipe embedment into the concrete stayed greater than 3M at all times. Confirmation of concrete construction quality control occurred through Ultrasonic Crosshole Testing (CSL) and pile integrity testing.
Figure 2. Casing placement and soil excavation
Load Test Results Fugro Loadtest performed the O-Cell bi-directional static load tests, on full-scale non-production test shafts, July 9, 2018 in the doTable 1. Rock Parameters
Parameters Rock type Average RQD along the shaft Average joint modification factor, α Average intact rock modulus, Ei Average dilatometer modulus, Ed1 Poisson ratio, μ Average rock unconfined compressive strength, qu Coefficient of discontinuity spacing, Ksp Geologic Strength Index, GSI 1
As obtained from dilatometer tests
18 PIC Magazine • December 2019
SADB DM Dolomite Limestone 67 per cent 83 per cent 0.72 0.82 75.6 GPa 56.7 GPa 12.2 GPa 12.7 GPa 0.33 0.29 145 MPa 68 MPa 0.20 0.20 59 61
Figure 3. Instrumentation & reinforcement cage O-Cell assembly Figure 3a. Reinforcement cage O-Cell assembly placement & top of O-cell test shaft
lomite and July 12, 2018 for the limestone. Performed in accordance with ASTM D1143 Loading Procedure, A – Quick Test, each test used one (1) 13.8 MN bidirectional embedded jack (O-cell) to load the shaft socket base against the socket side resistance. The concept known as the “Chicago Method”, which consists of utilizing a smaller base area to maximize the unit base pressure, was used. Therefore, the reactions from a 720-millimetre-diameter base area acted against the side shear from a 1,180-millimetre-diameter socket. Table 2 below shows the drilled shaft properties. The detailed load-displacement curves for the dolomite and limestone test shafts are in Figures 4a and 4b, respectively. Table 2 details the bottom O-cell plate suspended slightly above the shaft base prior to concreting. The measured unit base resistance for Table 2. Drilled Shaft Properties
Characteristics Nominal pile diameter in soil and fractured rock Nominal pile diameter in sound rock Length of pile below the base of O-cell: O-cell top plate diameter O-cell bottom plate diameter Assumed concrete unit weight Concrete compressive strength on the day of the test Assumed concrete elastic modulus Pile tip elevation Bottom of permanent casing elevation Maximum bi-directional load applied to the pile
SADB 1,300 mm 1,180 mm 100 mm 880 mm 720 mm 2,322 kg/m3 47.4 MPa 33,104 MPa 11.65 m 14.75 m 20.53 MN
the test shafts were modified using a 2(vert):1(horiz) projected area for the concrete-filled clearances below the base plate, dolomite - 100 mm; limestone - 130mm. Each test shaft had four levels of sister bar vibrating wire strain gages attached diametrically opposite on the reinforcing cage. For the socket below the casing, Zone 1 is between the O-cell and Level 1 strain gages and Zone 2 is between the Level 1 and 2 strain gages. Figures 5a and 5b show the calculated unit skin friction versus pile vertical displacement in these zones. The results indicate that the shaft load response in the cased zone above the socket was negligible. Accordingly, production pile design neglected load capacity in the cased zone for analysis and recommendations. DM 1,300 mm 1,180 mm 130 mm 880 mm 720 mm 2,322 kg/m3 41.4 MPa 30,936 MPa 19.49 m 22.59 m 20.56 MN Piling Industry Canada • December 2019 19
Figure 4a. O-cell Load-Displacement Curves in Dolomite
Figure 4b. O-cell Load-Displacement Curves in Limestone
Figure 5a. Mobilized unit skin friction vs displacement in dolomite
Figure 5b. Mobilized unit skin friction vs displacement in limestone
Figure 6a. Skin Friction and End Bearing from O-cell Test for dolomite
Figure 6b. Skin Friction and End Bearing from O-cell Test for limestone
For the Chicago Method: a scaling effect for developing the displacement versus unit end bearing curves using the theory of elasticity to estimate the displacement of the entire pile base area (1.09 m2) associated with the pressure from the bottom O-cell plate (0.41 m2) applied. In other words, the pile tip displacement is modeled with the bottom plate stresses applied over the entire base area. 20 PIC Magazine • December 2019
Figures 6a and 6b present the pile tip displacement versus the measured unit end bearing, the above-discussed corrected end bearing for the full base in the dolomite and limestone, with the mobilized skin friction curves also plotted.
Design Implications
3. Tip Resistance Contribution
Major factors affecting foundation designs included wind, collision and seismic lateral and overturning forces. Accordingly, all shafts were designed for a minimum socket of one diameter into sound rock for lateral stability. Lateral testing was also performed and will be discussed in part two to be published in the following PIC edition. Shaft axial design optimization includes both the toe and side resistance for socket capacity.
As documented in the literature and confirmed by the load test, the end bearing resistance mobilizes at larger displacements (three to five per cent of the diameter) than the displacement (10 mm) required to mobilize skin friction. Therefore, the total ultimate axial resistance of a drilled shaft socketed into rock corresponds to mobilization of the full available side resistance plus a fraction of the available base resistance. At the maximum skin friction vertical displacement, the O-cell test mobilized 8.8 MN for dolomite and 4.9 MN for limestone, reference Figure 6. Therefore, the dolomite had 30 per cent of the total resistance (29.3 MN) and the limestone had 19 per cent of the total resistance (25.1 MN) for end bearing at the maximum mobilized skin friction displacements.
1. Skin Friction A typical design approach for side resistance is presented in equation (1):
4. Load-Displacement Curve Where: Pa is the atmospheric pressure C is an empirical constant qu is the lesser of unconfined compressive of rock strength or the compressive concrete strength Canadian Foundation Engineering Manual (CFEM) 2006 recommends a C between 0.63 and 1.41 whereas AAHTO 2017 recommends a C of 1. To calibrate the parameter C against the results of the O-cell test for the dolomite and limestone the maximum unit skin friction mobilized were 1.80 MPa and 1.87 MPa respectively. A back calculation for these values reveal values of C as 0.82 and 0.92. Noting a rock strength of qu, 145 MPa and 68 MPa and the concrete strength of 47.4 and 41.4 MPa, the concrete compressive strength controlled the design. As the maximum measured side resistance was less than the nominal (ultimate) strength value, likely, from the concrete compressive strength at testing being higher than the anticipated design concrete strength of 35 MPa. Back-correlations represent lower bounds, as geotechnical failure was not achieved. Thus considering maximum measured values as the ultimate unit skin friction is conservative. Realizing the ultimate resistance was not attained the value of C for both tests likely approaches the AASHTO unity.
2. Base Resistance The test shafts measured base resistance occurred at relative displacements of just over 1% of the shaft diameter, which did not mobilize the rock formation geotechnical bearing capacity limit. CFEM (2006) gives ultimate end bearing as:
Where: Ksp is the coefficient of discontinuity spacing d is a depth factor = 1+0.4 (L/D) ≤ 3 Considering the test shafts rock qu of 145 MPa for dolomite and 48.5 MPa for limestone, the calculated unit base resistance (qt) values are about 175 and 60 MPa respectively. With the maximum measured unit base resistance of about 19 MPa in both cases, the mobilized end bearing was well below the nominal unit base resistance.
The equivalent top-loaded load-displacement curve was constructed by summing the loads recorded in side and in end resistance corresponding to the same upward and downward movement, respectively. This procedure was followed point by point up to the maximum-recorded side shear load. Since the end bearing movement was much larger than the skin friction movement, the side shear curve was extrapolated using a hyperbolic curve fitting technique. Figure 8 shows the constructed load- settlement for the load test in limestone (DM). A similar load-displacement (not included) was constructed for dolomite.
Calibration of axial resistance for other locations 1. Skin friction To optimize ultimate unit skin friction design at other alignment locations where the rock is of different (lower or higher) quality needed addressing. To accomplish this a joint modification factor, α, which is a function of RQD and joint type (i.e., open vs. closed) is introduced as shown in Equation (5). Values of α (Table 3) were selected using the guidelines presented in AASHTO (2017) Table 10.8.3.5.4b-1.
Where C1 represents the ratio of C, 0.82 for dolomite and 0.92 for limestone, to the value of α at the load test locations, 0.72 for dolomite and 0.82 for limestone. Therefore, the following values of C1 are being used in the analysis: C1 = 1.14 for dolomite (SADB) C1 = 1.12 for limestone (DM) This adjusts skin friction up or down proportionally to the ratio of α of the rock at the specific location to the value of α of the rock at the appropriate load test location
2. Tip Resistance Contribution To establish the tip contribution to the total ultimate axial capacity, the displacement incompatibility of skin friction and end bearing required considering. The CFEM (2006) recommends the use of the Pells and Turner (1979) approach to estimate the tip contribution. As expected, the longer the embedment depth into sound rock (rock socket), the smaller the load reaching the socket base. Also, the smaller the ratio of conPiling Industry Canada • December 2019 21
crete modulus to rock mass modulus Ec/Er, the smaller the tip resistance contribution. At the test locations where the ratio of L/r was 5.2 and Ec/Er was 2.7 in dolomite and 2.4 in limestone this approach predicts 8 per cent of the total resistance as end bearing for both limestone and dolomite. As previously noted, the O-Cell tests showed that, the dolomite had 30 per cent of the total resistance (29.3 MN) and the limestone had 19 per cent of the total resistance (25.1 MN) for end bearing at the maximum mobilized skin friction displacements. To optimize and calibrate the tip resistance contribution for different L/r ratios and different rock qualities, the load test results were used to plot the best estimate curve for Ec/Er = 2.7 (dolomite) and 2.4
(limestone) as shown on Figures 7a and 7b below (red curves). To introduce a margin of safety the curves were adjusted by a factor of 0.7. Continuing design optimization for estimating production shafts tip resistance contribution, the tip resistance obtained from the curves could be multiplied by an adjustment factor equal to: Table 2. Drilled Shaft Properties
L/r ratio Limestone 2 1.2 4 1.4 6 1.6
Dolomite 1.75 2.60 4.00
Linear interpolation could be used for different L/r ratio.
Figure 7a. Design Load Distribution in a Rock Socket for dolomite
Figure 7b. Design Load Distribution in a Rock Socket for limestone
Figure 8. Skin Friction and End Bearing from O-cell Test at SADB
Figure 9. Normalized load-displacement relationship for limestone (DM)
22 PIC Magazine • December 2019
and base resistance that exceeded the loadsolution quantified the design parameters ing system capacity, thus not mobilizing in the full slip zone for use on production In order to calibrate the load-settlement nominal strength values. Back analysis of the foundations. curve for other locations where the rock measured side resistance for the empirical The load test results on this project proconditions and shaft diameters are different, parameter C suggested a range between 0.82 vided verification of the design producing the closed-form solutions proposed by Kuland 0.92. As the ultimate resistance was not significant saving of the total socket length. hawy and Carter (1992) was used. Accordachieved, estimating drilled shaft side resising to the solution, the skin friction in rock For a more detailed discussion of the ensocket develops through shearing of bond tance for hard rock by the current AASHTO gineering judgement implemented with the between the concrete and the rock (bond), appear reasonable. The load tests showed the referenced code methods and subsequent sliding friction between concrete shaft and load transferred to the tip was larger than references, kindly refer to “Load Testing of rock (friction), and dilation of an unboundthat predicted by the CFEM approach. Large Diameter Single Drilled Shaft Foundaed rock-concrete interface (dilation). Calibration of the load test equivalent top tions for the REM Project in Montreal” Riad Trial and error analysis of the full slip beload-settlement curve to the closed form Diab, et. al, Geo St Johns 2019. l havior adjusting the rock-concrete cohesion, c, rock-concrete friction angle, φ, and the angle of dilation ψ, for load settlement curve matching (Figure 8), arrived at values of c = ONTARIO 1.4 MPa, φ = 26 degrees, and ψInterpipe =1.2 degrees. Inc. is a steel pipe distributor of new 3320 Miles Road, RR#3 Figure 9 details analysis adjusted rock structural steel pipe. We have two andforused Mount Hope, Ontario quality and shaft size variations alongstocking the large locations of Seamless, ERW, L0R 1WO alignment developed for a service limit state and DSAW pipe. Spiralweld settlement check. Local: (905) 679-6999 ONTARIO Interpipe Inc. is a steel pipe distributor of new ONTARIO 3320 Road, RR#3468-7473 TollMiles Free: (877) 3320 RR#3 and used structural steel pipe. We have two Conclusions andin used structural of steel pipe.thicknesses We have 3” OD – 48” OD a variety wall MountMiles Hope,Road, Ontario Mount Hope, Ontario Fax: large stocking locations of of Seamless, ERW, several stocking locations Seamless, L0R 1WO(905) 679-6544 The drilled shaft load tests are in limestone L0R 1WO stocked in Spiralweld both locations. and DSAW pipe. ERW, Spiralweld and DSAW pipe. and in dolomite proved high values of side Local: (905) 679-6999
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Report on infrastructure calls for greater and urgent investment in core works, says CCA Canada’s public infrastructure requires urgent attention in the coming decades in order to reverse the current state of disrepair, according to the 2019 edition of the Canadian Infrastructure Report Card (CIRC). “Data from the report revealed that Canada’s public infrastructure is at serious risk,” said Mary Van Buren, CCA president. “It will require rehabilitation and replacement in the next few decades to ensure services provided continue to meet the needs of communities.” The report, released by founding CIRC partners (CCA, Canadian Public Works Association, Canadian Society for Civil Engineering and the Federation for Canadian Municipalities), provides a timely update on the state of Canada’s public infrastructure across
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