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By Sina Z. Yekta, Zhangwei Ning, Pierre Frappin

This paper describes a DC (direct current) electrical resistivity method, which uses the contrasts in resistivity measurements to estimate the diameter of jet grouted columns as soon as they have been completed, with varying depth and water table, and without excavation. The measurement procedure is illustrated by several examples of application sites, including the Grand Paris tunneling works during the last 3 years where the method was systematically recommended in quality control for jet grouting works.

Sep 8, 2021

By Kim Chan, Bryn Thomas, Ben Dening

"Increased rail capacity is required into Kooragang Coal Terminal near Newcastle, NSW, Australia to relieve rail traffic congestion and improve management of train arrivals. An additional arrivals track is proposed on new embankment within a heavily constrained site located between existing railway tracks, a high pressure gas pipeline located 7m beyond the toe of the embankment and an environmentally sensitive wetland area. Ground conditions at the site consist of deep soft estuarine clays, a soil profile which is consistently encountered throughout this part of the east coast of Australia. Upon determining that a ground improvement solution was required to ensure global embankment stability, various solutions were considered including a piled viaduct, retaining walls, dry deep soil mix (DSM) columns and concrete injected columns (CICs). DSM columns were adopted as the design solution, a decision which was driven by the presence of sensitive infrastructure and a confined site. DSM offered further advantages including reduced impacts on temporary working platform design, where the use of a thinner platform could be justified owing to the lower track loads of a DSM rig relative to other ground improvement techniques.INTRODUCTIONThis paper presents a case study of the design of DSM ground improvement works to provide support for and enable safe construction of a new railway embankment over deep soft soils with a number of nearby infrastructure and other constraints. The project site is approximately 1km long and is constrained by existing railway tracks, a high pressure gas pipeline and a wetland area of ecological significance. Due to the site constraints and ground conditions, a number of ground improvement techniques were considered during the design process, with DSM columns eventually adopted. This paper discusses the design development and the particular suitability of the technique for use in this application.SITE DESCRIPTIONLandformThe site is located along the northern boundary of the Kooragang Coal Terminal (KCT) at Kooragang Island (KI), a collection of former islands located near the mouth of the Hunter River, north of Newcastle, NSW. The topography of the original area was generally flat with mudflats, swamps and mangroves existing along tidal water courses. Subsequent dredged fill reclamation and development has amalgamated the previous islands into the current KI. The site area extends over numerous channel infills including the buried former course of the Moschetto Channel (paleochannel).Figure 1 shows the proposed 1km long new rail corridor construction area in relation to the various natural and man-made site constraints including existing tracks, the high pressure gas pipeline, the wetland area and the existing reclaimed area."

Jan 1, 2015

By Nino Catalano, Meeok Kim, Gordon Chen

"The design of the below grade structure of Brigham Building for the Future (BBF) included three different areas to provide power generation and medical facilities as well as a parking garage. The three areas are divided and bounded by 3 foot thick slurry walls. Because each area has different depths and functions, the excavation and construction of the below grade structure presented considerable design challenges. The intricate sequence of excavation and construction between the areas was numerically simulated using a finite element analysis to assess the behavior of the slurry wall and the retained soil. The slurry wall and the related bracing system were modeled as a linear elastic beam and truss element respectively while the soil behavior was simulated using a hardening soil model. The interaction between slurry wall and soil was facilitated by the implementation of an interface element in the numerical model. The design of bracing system to adequately support the slurry walls during the excavation was done based on the envelope of the numerical responses in stage analysis. Predicted lateral displacements of slurry walls were later compared with the field measuring data. The comparison indicated a close agreement.INTRODUCTIONBrigham Building for the Future (BBF) is located in the Brigham and Women’s Longwood medical campus of Boston. The building will serve, once completed, as a biomedical research center and clinical facility to carry out a commitment by Brigham and Women’s Hospital to be the most technologically advanced facility in the country.The 11 story building will also feature a roof garden. The below grade portion of the building has a footprint of 265 feet wide and 210 feet long and is divided into three areas, a 6 stories garage, a cogeneration plant, and an imaging center. BBF was designed and constructed to achieve LEED Gold certification and will have high efficiency and improved sustainability as a medical facility. Ground breaking was in May, 2013. Below grade construction was completed in April, 2014 and the entire building will be finished in late 2016.As shown in Figure 1, the garage area has the largest foot print, 265 feet wide and 125 feet long. The lowest floor of the garage is located about 70 feet below grade. The co-generation plant is about 190 feet wide and 85 long and 50 feet deep. The imagining center is the smallest among three areas. It is 75 feet wide and 85 feet long and 22 feet deep. The areas are separated and bounded by 3 feet thick slurry walls.The perimeter and inner slurry walls were designed to support column loads from the above grade structures, lateral soil pressures and earthquake loads as per the building’s permanent condition and requirement. However the contractor was required to design the temporary bracing and the reinforcement for the slurry walls to resist construction stage loadings."

Jan 1, 2017

By Jason Buenker, Molly Winston

Torque-installed piles are gaining popularity in Southern California as the go-to deep foundation element for small- to medium-capacity loads in urban environments. The torque-installed pile is a displacement- based screwed pipe pile with a closed-end conical tip welded to the bottom of the pipe. Torque-installed piles are most efficient in loose to medium dense soils with high liquefaction potential. Where used properly, torque-installed piles can be installed faster, require less clean-up, and create less onsite vibration/disturbance than other pile alternatives. However, torque-installed piles are not applicable in all soil conditions and care must be used to apply the pile effectively in the correct subsurface environment. This paper will review current Southern California state-of-the-practice for torque-installed pile design and construction, potential roadblocks to successful installation, and available capacities from load tests. INTRODUCTION Torque-installed piles are a type of full-displacement screwed pipe pile originally developed in Southern California circa 2001 by Substructure Support, Inc. The pile is unique for its proprietary closed-end conical tip shown in Fig. 1. The tip has a welded steel-helix plate and cutter teeth that allow the pile to be advanced efficiently under applied torque and down pressure (crowd). Since original development of the pile, several contractors or manufacturers have proposed similar proprietary screw-type piles with comparable conical tips. Pile installation is relatively quiet, vibration-free, does not generate spoils, and faster than comparable pile types. The pile was originally developed as an alternative to driven pile foundations and remains a critical substitute to driven foundations in urban environments. Torque-installed piles are conventionally specified as 12 ¾-inch outside diameter (OD) steel pipes with a ⅜-inch-thick wall, although larger sizes with alternative dimensions have been used outside Southern California. Pile installation lengths generally range from 30 to 50 feet but may reach 80 feet or greater where soil conditions permit. The pile is generally backfilled with concrete following installation to increase lateral pile stiffness and may incorporate rebar cages or other reinforcing steel to facilitate connections to structural elements. The pile is frequently specified using performance-based specifications that encourage contractor innovation and use of proprietary installation means and methods.

Jan 1, 2019

By Drew M. Kurtz, Jeff L. Rai, Sara F. Frailey, Mohammad Ayub Iqbal

"This paper presents the foundation changes made for a five-span bridge over the Lehigh River constructed as a design-build project. During excavation within the cofferdam at Pier 2 for the construction of a spread footing to bear on rock, it proved extremely difficult to control the water entering the excavation as the sheet pile tips were variable due to the bedrock pinnacles and a weathered rock zone above the top of rock allowing water to pass below the sheeting. Water also entered from the bottom of the excavation, possibly due to the presence of solution openings within the dolomite bedrock. After repeated failures to achieve subgrade elevation and maintain a dry excavation, a design change to drilled shafts was made. Additional borings were performed for each of the shaft locations to explore the area underlain by karstic dolomite rock. A seal consisting of tremie concrete with adequate weight was placed to counter the differential head of water and the three drilled shafts (with minimum 25 feet [7.62 meter] rock sockets) were installed. A detailed construction sequence was followed and advanced quality control testing was performed. The construction of Pier 2 was completed successfully.1. INTRODUCTIONThis paper presents the description of the design change made from spread footing to drilled shafts as a result of site conditions encountered during the excavation for the spread footing for a bridge pier in the Lehigh River in Allentown, Pennsylvania. The bridge is located in an area underlain with dolomite rock, presenting karstic conditions including irregular top of rock and solution openings that provided high hydraulic conductivity below the top of rock. Also, the presence of a zone of weathered rock and pinnacle rock prevented the advancement of sheet piles when constructing the cofferdam. Thus, the difficulties of advancing the excavation to the desired spread footing level resulted in the design change to drilled shafts during construction. Since the project was Design-Build, the design could be changed by a collaborative process through the efforts of the Contractor, its geotechnical and structural engineers, and the State's (owner's) geotechnical and structural engineers and construction management staff."

Jan 1, 2016

By Lassaad Hazzar

The ultimate lateral resistance of piles in cohesive soil is studied using the well-known finite difference code, FLAC2D. The Modified Cam Clay (MCC) constitutive relation is adopted in the analyses to model the cohesive soil behavior, whereas the structural pile model with three degree of freedoms, available in FLAC2D library, is adopted to model the piles. The reliability of Broms's method, still used in the current design practice of piles under lateral loads, is verified. Comparisons between the ultimate lateral resistances of piles and those deduced from the graphs proposed by Broms (1964) are presented in graphs. Different factors thought to affect the lateral resistance of piles in cohesive soil, not adequately considered in Broms's method, such as clay stiffness, pile length, pile diameter and axial load are parametrically studied. A special concern is devoted to elucidate the effects of over-consolidation ratio (OCR) on the ultimate lateral resistance of piles in cohesive soil.

Aug 1, 2013

By John P. Turner, Steven S. Dapp, Dan A. Brown

"The Goethals Bridge Replacement (GBR) spanning the Arthur Kill Waterway between Elizabeth, NJ and Staten Island, NY is supported on over 200 drilled shaft foundations ranging in diameter from 4.5 ft to 10 ft and socketed into Passaic Formation siltstone. Four drilled shafts, two on each side of the bridge (NJ and NY), were load tested using the bi-directional axial load method. Axial test results demonstrate that RQD, taken by itself, is not necessarily a reliable indicator of side or base resistance. High recovery with low RQD can be a function of horizontally bedded siltstone and shale where the individual pieces of core do not exceed four inches, but may still provide very high side and base resistance. Axial testing was followed by a lateral rapid-load test (Statnamic) on each of the same four shafts. In addition, one of the shafts was subjected to a static lateral load test to validate the rapid-load method as being representative of static loading conditions. Results of the axial load tests provide the basis of unit side and unit base resistances used in the LRFD design of the rock sockets for axial loading, while results of the static and Statnamic lateral load tests were used to calibrate p-y curve parameters used for design under lateral and moment loading. This paper describes implementation of the load testing program and its role in the design process.INTRODUCTIONDesign of drilled shaft foundations for the Goethals Bridge Replacement (GBR) required load testing in order to validate the parameters used for calculating geotechnical axial and lateral resistances. The bridge, including foundations, was designed in accordance with the AASHTO LRFD design specifications, 6th Edition (2012). The bridge owner is the Port Authority of New York and New Jersey (PANYNJ). One of the PANYNJ project requirements was stated as follows:“Perform a minimum of two (2) separate axial compression load tests (one [1] in New York and one [1] in New Jersey) for each demonstration shaft of different size and construction methodology to verify the design assumptions and construction procedures. At a minimum, one (1) demonstration shaft is required to be representative of production shafts with a diameter within one (1) foot above or below the demonstration shaft diameter.Conduct a minimum of two (2) lateral load tests (one [1] in New York and one [1] in New Jersey) for each demonstration shaft of different size and construction methodology. At a minimum, one (1) demonstration shaft is required to be representative of production shafts with a diameter within one (1) foot above or below the demonstration shaft diameter.”"

Jan 1, 2016

By Zachary Q. Maassen

Upon approval from the Las Vegas Convention and Visitors Authority (LVCVA), Turner/Martin Harris, A Joint Venture began construction on the estimated $860 million expansion for the Las Vegas Convention Center District Plan. Totaling around 600 shafts (60 feet depth and 3-foot diameter), the foundation installation completed via uncased drilled shaft operation, spanned from October to December of 2018. During this installation, flowback water from the water table was encountered that contained various solids ranging from cobbles to clays to silts, as well as trace amounts of contaminants of concern (COCs) left behind as a result of previous business that used to occupy the same real estate as the current expansion; more specifically, Perchloroethylene (PCE), an organic chemical widely used as a solvent and degreaser. With over 2.5 million gallons of waste slurry to be treated, technologies were deployed to reclassify the waste from liquid to solid waste as well as recover and treat the water for reuse in land spraying applications. Utilizing these technologies, it is estimated that 1.2 million gallons of water was able to be reclaimed along with over 6,400 tons of solids; resulting in hundreds of thousands of dollars in cost and environmental savings. PROJECT OVERVIEW Amidst its famous attractions from gambling to world class entertainment, Las Vegas has long been highlighted as the “No. 1 trade show destination in North America for 24 consecutive years” (LVCVA, 2018). Each year, Las Vegas hosts approximately 22,000 meetings, conventions and trade shows, which support an estimated 65,000 jobs paying $2.7 billion in wages and salaries. In 2017, the Las Vegas Convention Center hosted 21 percent of convention attendees traveling to southern Nevada, which supported approximately 13,800 jobs, paying more than $576 million in wages and salaries. Including indirect and induced impacts, the Las Vegas Convention Center’s attendees generated $2.1 billion in economic impact for the local economy (LVCVA, 2018) . This substantial economic impact of course due in part to the attractions Las Vegas offers to its trade show attendees, along with Las Vegas’ easy accessibility to major metropolises along the West Coast and reasonable travel prices offered if coming in from the East, allows for a very attractive venue. And while being a famous destination is great for business, the city wants to further distinguish itself by offering the best venue as well. For this reason, the Las Vegas Convention and Visitors Authority (LVCVA) approved a three-phase expansion plan for the Las Vegas Convention Center District totaling well over a billion dollars, slated for completion by 2023.

Jan 1, 2019

By Ed Kase

Cross-hole sonic logging (CSL) has become the universal standard, nondestructive testing (NDT) method used in evaluating the integrity of foundation structures to maintain quality assurance and quality control (QA/QC) of transportation facilities and infrastructures. Tomography, based on three-dimensional cross-hole sonic logging data processing technology, offers an improvement over the techniques currently used to characterize the interior structure of drilled shafts. The underlying concept for seismic tomography is based on the principle that acoustic waves propagate at different velocities through different types of material or the same material with different physical properties. Three-dimensional velocity tomographic images provide greater detail of the interior structure, making defects easier to classify with respect to size and location within the foundation structure. By accurately classifying these defects, an engineer has the information necessary to accurately assess whether these structures meet the applicable design requirements, allowing them to repair or replace inadequate foundation structures. The end result is that the foundation structures will meet the safety and service life requirements for their project. This paper will present applications of seismic tomography, illustrating how seismic imaging can provide accurate information regarding the integrity of foundation structures.

Jan 1, 2003

By Jack Hayes

The design and construction of deep foundations involve many uncertainties. For the designer there are uncertainties regarding soil and ground water variability, regarding sampling and lab testing, regarding analytical techniques and regarding construction technique. The latter being the uncertainty over which the engineer has least control and which may have the greatest impact on capacity. Foundations with a high design factor of uncertainty can be very costly. Foundations designed with a high factor of uncertainty may have a low factor of safety, which can be even more costly.

Jan 1, 2000

By Challa Venkata Rami Reddy, Anindya Roy, G. R. Konni

This paper presents the results of pile lateral capacities obtained from both conventional design and fullscale pile lateral load tests. Conventional design using P-Y curve analysis is very commonly being used by designers; designers use well accepted software programs like Lpile and Allpile for analysis. However, these programs do not cover the soil models to simulate engineering behavior of marine carbonate sands; which generally have different engineering behavior than silica/quarts sands. In this study, the existing soil models for common sands have been used to assess pile lateral capacities and these results are compared with the results from full-scale instrumented pile lateral load tests performed in compacted marine carbonate sand fills of artificial island constructed for oil and gas facilities in Abu Dhabi. The objective of this study was to verify the applicability of the existing sand soil models for carbonate sands and also to verify the associated conservatism in the pile lateral capacities. This study shows that the actual pile lateral response is much stiffer than what was anticipated through the LPile analysis. Therefore, further research focus may be required to capture the engineering behavior of the marine carbonate sands to develop specific P-Y curves.

Sep 8, 2021

By Garland Likins

High strain PDA testing has become common for verification of capacity of both driven and bored piles. It is equally applicable to Augered-Cast-in-Place (ACIP) Piles. It also evaluates other aspects of the installation such as integrity. The benefit of high strain dynamic test results for the relatively low cost of the tests compared to conventional static testing has resulted in widespread use. The method is described and specific procedures for testing ACIP piles are outlined. Example results demonstrate the application.

Jan 1, 2000

By Bradley J. Fleming

Although soil improvement and its application to deep foundations is gaining popularity in the engineering community, this technique is not widely used in high seismic regions due to lack of fundamental understanding of both the behavior of improved soils under high-strain cyclic loading and the interactions between the pile, improved soil, and unimproved soil. This paper describes part of an ongoing Network for Earthquake Engineering Simulation (NEES) project, where two identical full-scale steel pipe piles were driven at a soft clay site in Oklahoma. The soil surrounding one of these piles was improved using the cement deep soil mixing technique in order to enhance its lateral load behavior. Both piles were tested for seismic resistance using dynamic and quasi-static loading. The pile in unimproved soil provided larger displacements with limited lateral force resistance. This pile was subjected to lateral displacements of up to 400 mm, but experienced minimum inelastic actions. On the other hand, the pile in improved soil reached its lateral capacity at a displacement of 100 mm, at which point the critical region at the base of the pile just above the improved ground experienced buckling and fractured due to low cycle fatigue. Compared to the pile in unimproved soil, the improved ground increased the system strength by 42%. Although the soil was improved over 2900 mm, the effective improvement depth was approximately 1300 mm below the ground surface. In this paper, it is demonstrated that the effects of block type soil improvement of limited horizontal and vertical dimensions can be described using a simplified theoretical approach involving a modification to the well-known p-y representation of soil response. An example using this method is presented and shown to give adequate support to a standard 12-inch diameter steel pipe pile embedded in soft soil.

By Michael W. Oakland

Weidlinger Associates was retained to evaluate the foundations supporting ten oil storage tanks at a tank farm on the east coast. The tanks were constructed over the site of a landfill which was underlain by deep organic deposits. The tanks were typically 48 ft. in height and ranged in diameter from 60 to 150 ft. The tanks were supported on both wood and steel pipe piles. After more than 35 years of service, an inspection found that up to 25 percent of the piles had separated from the mat foundation. The operations at the facility were temporarily stopped pending further investigation. Weidlinger developed comprehensive finite element models of the foundations for each tank and used random generators to conduct Monte Carlo simulations the range of scenarios of detached support conditions since it was not possible to survey all the piles below the tanks. To confirm the modeled performance and verify stability, each tank was also load tested using water with electronic instrumentation installed by Geo-Instruments. The instrumentation provided real time, web based monitoring during testing in areas which would otherwise be inaccessible during loading. Through inspection, complex modeling and sophisticated load testing, Weidlinger and Geo-Instruments were able to show that all but one of the tanks could safely be put back into service. This paper details the analysis, Monte Carlo simulations and instrumentation and load testing performed for this unique project.

Jan 1, 2009

By Jin-Wei Huang, Bradley J. Fleming, Sri Sritharan

"Although soil improvement and its application to deep foundations is gaining popularity in the engineering community, this technique is not widely used in high seismic regions due to lack of fundamental understanding of both the behavior of improved soils under high-strain cyclic loading and the interactions between the pile, improved soil, and unimproved soil. This paper describes part of an ongoing Network for Earthquake Engineering Simulation (NEES) project, where two identical full-scale steel pipe piles were driven at a soft clay site in Oklahoma. The soil surrounding one of these piles was improved using the cement deep soil mixing technique in order to enhance its lateral load behavior. Both piles were tested for seismic resistance using dynamic and quasi-static loading.The pile in unimproved soil provided larger displacements with limited lateral force resistance. This pile was subjected to lateral displacements of up to 400 mm, but experienced minimum inelastic actions. On the other hand, the pile in improved soil reached its lateral capacity at a displacement of 100 mm, at which point the critical region at the base of the pile just above the improved ground experienced buckling and fractured due to low cycle fatigue. Compared to the pile in unimproved soil, the improved ground increased the system strength by 42%. Although the soil was improved over 2900 mm, the effective improvement depth was approximately 1300 mm below the ground surface.In this paper, it is demonstrated that the effects of block type soil improvement of limited horizontal and vertical dimensions can be described using a simplified theoretical approach involving a modification to the well-known p-y representation of soil response. An example using this method is presented and shown to give adequate support to a standard 12-inch diameter steel pipe pile embedded in soft soil,IntroductionPilings are the preferred foundation support for many civil engineering structures including highway bridges, railroad bridges, and port wharves. These structures and their foundations are subjected to forces created by earthquakes, wind, waves, water current, vessel impact, ice, and gravity. All loads applied to the superstructure must be transmitted to the foundation where they are resisted by the surrounding soil. With significant lateral loads, use of pile foundations may be the only solution to transmit large structural loads to competent soils. Piles supported by competent soils are relatively easy to design and costs are often attainable. However, thick layers of weak soils such as soft clays are widespread in high seismic areas (e.g., San Francisco, southern Nevada, Washington, Eastern Missouri, and Arkansas), exacerbating design challenges. Soft clays reduce the lateral resistance of the pile-soil system, making the pile foundation less cost effective. In this case, the current design practice is to use an increased number of larger diameter piles, which is a costly alternative (see SDC, Caltrans 2010). An innovative and more cost-efficient solution to this problem is to improve the soil within a short depth surrounding the foundation, thereby increasing its lateral stiffness. Some well-known methods for improving soil include deep soil mixing, stone columns, and simple soft soil replacement with select granular material."

Jan 1, 2017

By Hamed Layssi, Farid Moradi, Thomas Tingson

This paper describes the feasibility and pilot study of of using existing non-destructive testing solutions for evaluating structural integrity and mechanical performance of mass concrete foundations. This paper includes two pilot studies using well-known NDT methods (i.e., Crosshole Sonic Logging and seismic tomography) for new applications (i.e., NDT inspection of mass concrete foundations). In the first case, we will examine an existing mass concrete foundation block with internal cracking, which has negatively impacted the strength and stiffness of the foundation block. A combination of pulse velocity and 2D tomography was used to evaluate the structural integrity in the foundation block. In the second case, the quality and integrity of newly built mass foundations were evaluated using Crosshole Sonic Logging (CSL). The methods are combined to locate potential sub-surface defects such as large voids and discontinuities. This paper aims to study the effectiveness of the NDT methods of Deep Foundations to assess the quality and structural integrity of new and existing mass foundations and explore the opportunity to extend the capabilities of these tests beyond their conventional use.

Sep 8, 2021

By Anahita Modiriasari, Benjamin S. Rivers

Measurement while drilling (MWD) is a subsurface exploration technique associated with real-time and continuous monitoring and recording of drilling data during the drilling process. This technique can be used for underground investigations to differentiate ground strata, detect the presence of fractures and voids, and evaluate geological features and mechanical properties of geomaterial. When MWD is used for geotechnical investigations, it can improve site characterization, identify variable conditions, improve design and construction, lead to shorter project delivery times, reduce the cost and risks associated with limited subsurface data and geotechnical uncertainties, and maximum return-on-investment. Given these benefits, MWD is gaining attention among transportation agencies and the geotechnical industry. Federal Highway Administration’s (FHWA’s) innovation deployment program “Every Day Counts (EDC-5)” includes the implementation of Advanced Geotechnical Methods in Exploration (A-GaME), which aims to implement effective, underutilized subsurface exploration methods, including MWD, in U.S. practice. This paper provides an overview of the MWD technology for geotechnical site investigations and presents a case history where MWD was employed to design deep foundation for the construction of a building in Massachusetts. The advantages of this technology for risk reduction and project cost and time saving are also discussed.

Oct 1, 2022

By Lucian Bogdan

On many occasions during construction and service life of the structure, it is crucial to know the load in post tensioning tendons and anchors. Although there are many methods to measure the tendon force, most of them are cumbersome, expensive and the accuracy differs depending on the method used Dyna Force sensor uses the Elasto-magnetic technology (EM) and non destructive testing (NDT) to direct measure stress level in prestressed strands or bars installed on ground anchors or post tensioning tendons. Dyna Force sensor can be used to rapidly read the change in load during proof and performance tests and compare with the pressure gauge and during the life on the anchor to monitor existing lock-off load. It can be used also to determine the load along the bonded length of the anchor allowing the contractor to increase or decrease this length. The paper presents Dyna Force operating principle and some applications. In conclusion, the Elasto magnetic technology applied through Dyna Force is a new and easy to use approach to monitor anchor load during proof test and service life of the structure.

Jan 1, 2009

By Chris Leach, Lucie Spencer

This case study describes the geotechnical aspects of the basement construction for a multi-storey, residential and hotel complex located in the newly developed Elizabeth Quay precinct in Perth, Western Australia. The development included a three-level basement for car parking covering the full site area which was constructed using the top-down construction sequence. Soil conditions generally comprised 2m of fill overlying medium to dense clayey sands that in turn were generally overlying a very stiff clay stratum at approximately 13m depth. Bedrock level was generally encountered at approximately 22m to 35m below ground level. The ground water table was at a depth of approximately 1m below the existing ground surface level. A site boundary basement wall was constructed using a diaphragm wall retention system. The majority of the vertical loads from the building were transferred to the Kings Park Formation (KPF) bedrock through the use of foundation piles constructed by the CFA method. The CFA piles were installed from existing ground level, resulting in approximately 9m sacrificial concrete length from pile platform level to basement 3 (B3) level. The permanent column loads are such that a single CFA pile was not structurally adequate. To allow a full CFA foundation system to be adopted, an innovative design and construction approach was developed for these heavily loaded columns. This paper discusses the site technical details and the design and construction aspects required to meet the challenges offered by this project.

Nov 1, 2022

By M. Hesham El Naggar, Mehdi Heidari

"Equivalent fixed-base cantilever model is a common approach for performance base seismic design of bridge structures supported by extended pile-shaft. In this method, global displacement ductility factor is related to local curvature ductility demand by assuming a concentrated plastic hinge at location of maximum bending moment. Equivalent plastic hinge length is one of the key parameters that should be assumed accurately in kinematic expression of the cantilever model. Although, some expressions have proposed to estimate the length of the in-ground plastic hinge; however, these relations yield differing results. In this paper, a general expression is derived based on the concept of distributed plasticity to predict the plastic region of yielded piles in clay and sand. A length modification factor is defined to relate the equivalent length of plastic hinge to the real plastic zone. Then, results from nonlinear pushover analyses are used to propose an equation for the modification factor as a function of displacement ductility factor.IntroductionDuring severe earthquake events, development of the plastic hinge in pile foundation below ground level is inevitable for bridge structures supported on extended pile-shafts. A common approach for seismic design of the yielding pile-shafts is to replace the pile-soil system by an equivalent fixed-base cantilever assuming the equivalent system has the same global response as that of the pile-shaft (Budek et al. 2000; Chai 2002). In this method, plastic curvature is concentrated at the center of the equivalent plastic hinge below ground surface. Prior knowledge of plastic-hinge length is essential for proper assessment of assess plastic displacement at the top of the pile-shaft. Unfortunately, existing recommendations for estimating plastichinge length are largely incomplete and/or inadequate.During the last two decades, several relationships have proposed for evaluating the equivalent plastic hinge length, Lp, based on experimental and numerical studies. Budek et al. (2000) conducted numerical modeling to calculate the plastic-hinge length of piles embedded in cohesionless soil. They found that the plastichinge length varies linearly with both soil stiffness and aboveground height, e. Chai and Hutchinson (2002) conducted full-scale experimental tests on reinforced concrete piles in sand. They reported that Lp depends primarily on the aboveground height of the pile, neither sensitive to the soil stiffness nor to the value of displacement ductility factor. They stated that the equivalent plastic hinge length is relatively independent of the displacement ductility factor and is not very sensitive to the change in soil density. On the contrary, Goel (2014) and Liu et al. (2016) conducted nonlinear numerical analyses which revealed that Lp changes with the displacement ductility factor and even suggested that using different values of Lp for different seismic design levels is essential for a reliable estimation of the ductility capacity."

Jan 1, 2017