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By Howard A. Perko, Margaret Dring, Gerald Verbeek, Scott Slaughter

Helical piles have become a widely used deep foundation system in recent years due to their many inherent advantages. The cone penetration test (CPT) is commonly used in geotechnical practice to evaluate subsurface conditions for deep foundation design as the method provides a continuous soil profile in a short amount of time, measures in-situ soil strength, and in many ways behaves similar to a “mini pile” during penetration. In the CPT test, an instrumented cone is hydraulically advanced into the soil at a constant rate. As the cone is advanced, strain gauges embedded in the cone body continuously measure the tip resistance and side friction. In addition, a piezometer element is commonly used to measure the (dynamic) pore water pressure in the soil as the cone is advanced. A study was conducted comparing the CPT tip resistance to helical pile installation torque and capacity. In this paper, the outcome of this study was compared with historical data of helical pile installation torque records, static analysis predictions using commonly used techniques, and pile load test results over a wide range of soil conditions. A literature review was also conducted where a comparison was made for CPT tip resistance and helical pile installation torque data with previously published correlations.

Sep 8, 2021

By Kalyani Devabhaktuni, Mike Minton, Mark T. Howe, Yan Zhang

During the procurement phase of a Design-Build (DB) project, design-build contractors must often commit to a fixed price based on limited or incomplete geotechnical information. This lack of information can result in an inaccurate assessment and allocation of project risk to either the contracting authority or the DB contractor. This paper presents a case study of an elevated water tank supported by mixed ground improvement techniques, including Vibro-Compaction (VC), Aggregate Piers (AP) and Compaction Grouting (CG) in East St. Louis, Illinois. An adaptive design and contracting approach provided the best value solution for a complicated set of geotechnical problems, including static bearing capacity and settlement concerns as well as liquefaction induced settlement. Close cooperation between the owner, the tank contractor, the geotechnical engineer and the ground improvement contractor was essential to produce an effective solution. Ground Improvement techniques resolved the geotechnical challenges at the site through adaptive design methods, utilizing progressive rounds of verification and real time data acquisition to achieve performance objectives. This paper details the evaluation of geotechnical criteria, the selection of ground improvement techniques, the adaptive design and implementation of ground improvements, as well as contracting methodologies used to ensure that the best value was provided. PROJECT INFORMATION In November, 2016, CB&I Storage Tank Solutions (McDermott) submitted a design/build proposal for an elevated water tank for Illinois American Water Company (IAW) in East St. Louis, Illinois. The purpose of this tank was to have backup water capacity for power generation. In the RFP, IAW requested two alternate styles of tank: Option 1, a 1250 Million Gallon (MG) Composite Elevated Tank or Option 2, a 1250 MG Waterspheroid tank. Option 1 consisted of a steel tank supported on a concrete tower. Option 2 consisted of a steel tank supported on a steel shaft. The height (determined by IAW) was 140 feet to the top capacity line measured from top of floor slab.

Jan 1, 2019

By J. Hamada, K. Yamashita, Y. Shigeno, T. Tanikawa

"This paper offers a case history of piled raft foundation in soft ground supporting a twelve-story building in Tokyo. To increase bearing capacity of the soft soil as well as a countermeasure of liquefaction, grid-form deep cement mixing walls (DMWs) were employed with the piled raft. Based on the long-term monitoring results, the ratio of the load carried by the DMWs to the effective structure load after the construction of the raft was estimated to be 0.3 while that carried by the piles was 0.7. In order to clarify the contribution of the DMWs to bearing the structure load, numerical simulation of the settlement and the load sharing among the piles, the DMWs and the unstabilized soil was performed using a three-dimensional finite element model. The results of the numerical simulation agreed well with the measured values, when the Young’s modulus of the DMWs obtained from the unconfined compressive tests was adopted and the shear modulus of the soft soil was reduced to 50% of that at small strains.INTRODUCTIONIn recent years, piled raft foundations have been used in many countries as building foundations. The effectiveness of piled rafts in reducing average and differential settlements has been confirmed not only on favorable ground conditions as shown by Katzenbach et al. (2000), Poulos (2001) and Mandolini et al. (2005), but also on unfavorable ground conditions such as soft clay and/or liquefiable sand using ground improvement technique (Yamashita et al., 2011a; Yamashita et al., 2011b; Yamashita et al. 2013). Grid type ground improvement using the Deep Mixing Method has been applied to sandy ground as a countermeasure of liquefaction to increase liquefaction resistance of unstabilized soil left in the grid walls where its shear deformation during seismic motion is reduced by the confinement effect of the grid walls (Kitazume, 2013). The high applicability of the method was demonstrated in the 1995 Hyogoken-Nambu earthquake and the 2011 off the Pacific coast of Tohoku Earthquake (Tokimatsu et al., 1996; Uchida et al., 2012a; Uchida et al., 2012b).This paper offers a case history of piled raft foundation in soft ground supporting a twelve-story building in Tokyo. To increase bearing capacity of the soft soil as well as a countermeasure of liquefaction, grid-form deep cement mixing walls (DMWs) were employed with the piled raft. First, the results of long-term field monitoring on the settlement and the load sharing among the piles, the DMWs and the unstabilized soil are briefly described. Next, to clarify the contribution of the DMWs to bearing the structure load, the foundation behavior is simulated using a three-dimensional finite element model, and then the results of the numerical simulation are discussed."

Jan 1, 2015

By David M. Rempe

The purpose of this standard is to provide a method for testing of cushion materials that leads to uniform results when employed by various organizations and laboratories. The load-deflection characteristics measured using this method are intended to provide input data for analysis of pile driving, as in wave equation analysis of pile driving. It should be recognized, however, that there are several factors which may cause a difference in performance between the test samples under laboratory conditions and actual cushion materials under pile driving conditions. These factors include variations in material properties from sample to sample, compaction and/or deterioration of the materials with use, eccentric loading due to misalignment, confinement effects or the cushion container or inter layered materials, head buildup, rate of loading, etc. In order to obtain representative load-deflection characteristics, therefore, testing of cushion specimens which have been subjected to actual pile driving conditions is encouraged 1 such specimen should be tested at various stages of the useful life of the cushion. The users of the data are cautioned to determine if the particular wave equation program they are using requires either the secant or tangent definition of the stiffness and modulus of elasticity.

Dec 1, 1984

By Martin Mcdermott, Kevin Tehansky, Robert Ross, Jeffrey Goodwin

A foundation value engineering redesign is a collaboration between the project owner, original design team, general contractor, foundation contractor and redesign team. Without the acceptance and collaborative effort of all the stakeholders, the redesign process is doomed to failure. For the addition at the Hackensack (New Jersey) University Medical Center (HUMC) we had just such a collaborative effort for the drilled shaft redesign. For a successful redesign effort, the collaboration between the foundation contractor and their redesign team needs to fully exploit the contractor’s specific equipment and experience and convey how to apply this to the project as a whole to ensure everyone is confident that the project design goals are being met. For the HUMC project, applied load testing of the drilled shafts (bi-directional and lateral) were used to provide ultimate geotechnical design values for the redesign effort. By utilizing the contractor’s preferred equipment and the redesign team’s testing and application expertise, the redesign collaboration was able to enhance a good design and make it into a great project.

By Clinton O. Rex, Adam S. Hurley, W. Morgan NeSmith

"Hartsfield-Jackson Atlanta International Airport underwent a $1.2 billion dollar expansion project centered on the construction of the new Maynard H. Jackson International Terminal. Passenger access between the new International Terminal and the domestic airport facilities is primarily via underground Automated People Mover (APM) trains. Prior to this expansion, the APM tunnel terminated beneath Concourse E, which previously served all international flights. The new International Terminal is located approximately ½-mile from the previous terminus of the APM tunnel.A paper describing the general approach to excavation support for construction of the entire APM tunnel extension from under Concourse E to the new International Terminal was published by two of the authors (Hurley and NeSmith, 2014). One of the features of note of the approach involved the intersection of the proposed new alignment of the APM tunnel extension under Concourse E with the old terminus. Specifically, the new tunnel extension conflicted with the location of the existing Auger Pressure Grouted (APG) piles supporting four columns in Concourse E. This paper presents design and installation details of the micropile underpinning approach used to support the existing columns to allow for the proposed excavation including the cutting and removal of the existing APG piles, while allowing Concourse E to remain in service during construction.PROJECT DETAILSGeneralThe construction of the APM extension required an excavation support system for a 450-ft long, 55-ft deep excavation across Taxiway Dixie and a 900-ft long, 30-ft deep excavation beneath the basement of existing Concourse E. The excavation under Concourse E required both excavation support and support of the existing columns over the proposed excavation zone. A general overview of the work area is shown on Figure 1."

Jan 1, 2017

Abouleid,A.F.327 Ajdic, I.451 Albert, L.F. 221,307 Alem, A. 525 Asama, T. 431 Avgherinos, P. J. 373 Baker Jr, C.N. 331 Balossi Restelli, A. 171 Beckwith,G.H.33 Bellini, A. 469 Bermingham, P. 481 Bertero,M. 171,535 Beyer, M. 503 Bottiau, M.41 Botto, G. 205 Bruskeland, O. 337 Budhu, M. 349 Bullivant, R.A. 181 Bustamante, M.G. 185, 475, 535

Jan 1, 1994

By Kevin R. Johnson, Matt Caskey, Bryan Plaskett

Working in urban environments presents unique logistical challenges beyond those typically associated with traditional geotechnical design and construction. These challenges can include constrained sites with limited access and laydown area, vibration concerns for adjacent structures, and the need to complete work within limited schedules. When challenging geotechnical conditions like variable bedrock elevations are present, the need to balance performance requirements with logistical constraints become the driving factor when selecting deep foundation systems. This paper focuses on the deep foundations used for a new elevated pedestrian bridge at a major health care facility in Tampa, Florida. In addition to the technical design requirements, the owner required a deep foundation system that could offer low vibrations, rapid production, and clean installation to limit impacts on their properties and the public roadway that separated them. The paper describes the project specific geotechnical and design conditions, describes Ductile Iron Pile design, and focuses on how installation of the system addressed the unique logistical challenges. In addition, the implementation of a full-scale load testing program to assess compression, uplift, and lateral design capacities is presented. This paper represents one of the few published references for Ductile Iron Piles on projects in the United States.

Oct 1, 2022

By Jeffrey C. Schuh, Logan Bloemer, Daniel P. Dietzler

Over the past 30 years, the authors have encountered numerous projects where recognizing the geology, soil properties and groundwater conditions, and considering alternative construction techniques have promoted efficient and cost-saving construction. The construction documents for these projects, produced by various engineering firms, provided basic information on geotechnical conditions. The authors became involved in each project either because there was a problem during design or construction or, as a contractor, won the project because they saw a value engineering opportunity to take advantage of the geologic setting of the project to design and build alternatives to what the designer depicted. Understanding the geologic setting is critical before planning and designing begins. Being able to work with the geology and the materials on site is preferred before specifying more costly and complex solutions, which often require the importing of materials and adherence to unnecessary and/or inappropriate specifications. Failing to understand the geology or not knowing all the techniques available for construction can lead designers to develop solutions that could be inappropriate. This paper presents several examples of value engineering and project performance enhancements developed through knowledge of basic soil mechanics and implementing innovative solutions. History and Background Most people attend DFI meetings, present their experiences, listen to others, and read articles and papers with the hope they can learn from others. Geotechnical engineers and contractors often interface with others in the execution of projects who have, at best, a rudimentary knowledge of geology and soil mechanics. Of course, there is a need for architects, bankers, and regulators, etc., but they typically do not have much interest in the nuances of geotechnical engineering, which relies on both art and science. Thus, significant time is spent educating counterparts in the need for comprehensive subsurface investigation programs and the intricacies of construction in the “dirt,” as they typically refer to soil and rock.

Jan 1, 2019

By T Vijayakumar, Vipul Dobhada, Rajesh Patel, Swarnadip Dey, Naveen Babu D

The most challenging scope of any bridge project in marine or inter tidal zone is to construct sub structure like well Foundation, group pile, pile cap etc. Similarly, it also affects the marine environment/ecology to a great extent. Understanding the level of difficulties and aiding to provide an environment friendly solution, various options are analysed to overcome these and found mono pile to be the best alternative in this context. Generally, the foundation type of any bridge constructed in river, marine or intertidal zone in India is preferred for group piles. For the first time, monopile is being accepted as the foundation of bridge in India at Mumbai Coastal Road Project. The diameters of the monopiles used in this project are 2.5 m and 3.2 m. Hence, the challenges involved in monopile construction and experiences to overcome it are worth to share. Here, a brief discussion on environmental, geological issues and the needs of monopile as the foundation of bridge has been discussed. Furthermore, the monopile construction stages and confirmation of monopile capacity through different load tests have been elaborated.

Sep 1, 2022

By Martin B. Hudson, Kenneth S. Hudson, Gwendolyn Arreguin

A twin high-rise project site in Century City posed several foundation engineering challenges for the design team. One portion of the twin high-rise project site was required to utilize top-down construction in order to allow a driveway to remain open during construction of the project’s 40-foot deep excavation. The challenge was compounded by the need to utilize a mat foundation to support the high-rise construction and yet have temporary drilled shafts through the mat foundation area that would not create excessive differential settlement. This was accomplished by constructing a deck supported by eight drilled end- bearing drilled shafts with Osterberg load cells and five 7-foot-diameter end-bearing drilled shafts. The Osterberg load cells served to verify the capacity of each of the drilled shafts and preload the soils at the drilled shaft tips. The 7-foot-diameter shafts were constructed with bond breakers to prevent skin friction but instead mobilize end bearing (for settlement compatibility with the surrounding mat foundation). After the drilled shafts were placed, then top-down construction began beneath the driveway, leaving the driveway supported on the drilled shafts. Construction challenges included drilling of the shafts through previously abandoned tieback anchors from an adjacent parking structure basement, as well as cemented layers within the rock materials. The paper describes the use of the various analytical methods used to calculate capacities and check settlement compatibility, the construction and testing methods utilized, and the construction challenges encountered. INTRODUCTION Wood Environment and Infrastructure Solutions, Inc. (hereafter referred to as Wood) performed a geotechnical investigation for the New Century Plaza currently being constructed in the Century City District of Los Angeles, California. The New Century Plaza project consists of the construction of two new towers (designated as North and South Buildings) and the rehabilitation of the existing Hyatt Regency Century Plaza Hotel. The existing hotel tower is 15 stories in height above the existing grade and is underlain by four subterranean basement parking levels. The new North and South Buildings will stand approximately 46 stories in height above the existing grade to accommodate residential use. The new towers are planned west of the existing hotel. The site was previously occupied by the existing hotel subterranean parking structure and overlying podium structure, and a loading dock in the southwest portion of the site. The former western portion of the podium and subterranean parking structure west of the existing hotel building western edge were demolished to allow for new subterranean levels, a new podium structure, and the new towers. The lowest floor of the proposed subterranean level required excavation on the order of 35 to 80 feet.

Jan 1, 2019

By Brenton Cook, Daniel Mageau, Larry Applegate, Aaron McCain

"Ground freezing was successfully used to create an impermeable barrier wall along 3,000 feet of the downtown Seattle waterfront as part of the Seattle Seawall Replacement Project. This $360 million re-development involved removing the original 1930-era seawall and replacing it with a new, seismically resistant concrete wall supported on fill soil improved by jet-grout. The replacement wall was one of the largest construction projects in the state of Washington at the time. Ground freezing is typically used as both a structural shoring wall and groundwater cutoff. However, at this project it was used primarily as a cutoff wall to stop groundwater seepage into the 16-foot deep excavation from the landside areas.The project was divided into ten boxes (sections), each typically 200 to 600 feet in length. Only a few boxes were under construction at one time to reduce the impact on tourist-dependent local businesses. Soil conditions in the freeze zone consisted of sand, gravel and silt fill with abundant wood and debris. Tidally influenced groundwater, much of it contaminated, was difficult and expensive to control using wells during initial stages of construction. For all subsequent stages, a frozen soil wall extending to about 35 feet in depth was used to stop groundwater seepage into the excavation. An additional benefit of ground freezing included elimination of potential settlement beneath nearby buildings, utilities, and the Alaskan Way Viaduct that would likely have occurred with the use of conventional dewatering wells. The frozen soil wall crossed more than 130 buried utility locations (including water, sewer, storm, electrical, fiber optic, phone, gas, steam) with no damage. The frozen soil wall was very successful and limited groundwater influx from the landside to the seawall excavation to a negligible amount so that pumping, storage and treatment of contaminated groundwater was essentially eliminated."

Jan 1, 2016

By Akshay Sakhuja, M. S. Karthika, R. Vignesh

"The bridge across River Mandovi in Goa is a cable stay bridge structure proposed parallel, along existing bridges for regulation and reduction of vehicular traffic; the entire bridge structure is supported on pile foundation socketed in rock. This paper describes drilling related issue encountered during execution of pile where bed rock varies considerably from factual geotechnical investigation, which in turn affected the productivity of bored piles socketed in rock then chiseling is advocated for rock socketing with limited number of blows based on penetration resistance of rock encountered or equivalent energy principle to increase the productivity and also to avoid excess chiseling which otherwise would have fractured the rock mass below and around the pile tip resulting in increased settlement of pile subjected to design load. Contractor decision on socket length have been taken without compromising either quality or productivity; the paper presents various procedures and the equipment involved for installation of pile in rock along with the conclusion related to termination of pile in rock and also the lessons learned in process.INTRODUCTIONPile foundations are generally used to transfer heavy loads in deeper bearing stratum if the soil immediately beneath the base of the foundation does not have sufficient capacity. The bridge across River Mandovi, Goa is in its construction phase as a part of the development plan of Goa State Infrastructure Development Corporation Ltd (GSIDC). The project was awarded to M/s. L&T Construction, Heavy Civil Infrastructure; subsequently the geotechnical investigation was awarded to M/s L&T Geostructures.The client has specified the foundation of the bridge as rock-socketed. Rock socketing is generally done to achieve higher bearing pressure through concrete-rock shear interface which many building codes permit. The design and construction of rock socketed pile foundation entails a detailed analysis and judgement on the superstructure loads, predominant geological conditions as well as ground water levels. The termination of pile is normally based on thumb rule of half to three times the pile diameter into the rock. Quite often the criteria is based on chisel penetration rate (Gandhi,1990) In fact, this is the key factor to consider appropriate and economical depth of embedment of pile into rock stratum which necessitates enormous understanding on the type and quality of rock strata encountered which may significantly influence the selection of suitable rotary rig for pile installation. Such criteria are site specific and also applicable for the set of equipment used for the particular project."

Jan 1, 2015

By Maurizio Siepi, Bruno Vingiani, Claudio Asioli

"The article describes an emergency rehabilitation intervention executed at Buyo Dam, in Ivory Coast, to intercept a significant water seepage occurring through the foundation of this zoned earthfill retaining structure constructed in the late Seventies. To solve the problem, a 800 mm thick, 400 m long impervious cut-off wall (COW) was constructed on the right side of the embankment, operating from the dam crest and with the reservoir almost at its maximum level. The use of an innovative pre-mixed self-hardening grout, with a target hydraulic conductivity coefficient (k) lower than 10-9 m/s, was considered the only way to match the tight working schedule and the strict requirements for the filling material of the COW.Presentation of the Hydroelectric Scheme of BuyoThe hydroelectric scheme of Buyo, located at 6°14’28” N 7°20’45 W on the Sassandra River, in Ivory Coast (Figure 1), was built in the late Seventies for agriculture and power generation. With a reservoir of 8.3 billion m3 and an installed power capacity of 165 MW, enough to supply electricity to 111,000 homes, it represents an installation of great significance for this West African country."

Jan 1, 2016

By V K. Panwar, Sampat Raj

At a Fertilizer plant located in the southern part of India, 74 numbers of pump foundations have shown non-uniform settlements causing the tilting of pump foundations under self-weight primarily due to the presence of varying thickness of the heterogeneous subsoil beneath the pump foundations and soil erosion because of water seepage through deeper excavations in the close vicinity. Various corrective measures have been explored and taking due cognizance of the prevailing subsoil conditions, site constraints, and constructability aspects, micropiling has been adopted. This paper presents the site problem and details of remedial measures adopted for rehabilitation of the distressed pump foundations. The main objective of this paper is to provide guidelines for designer during design and detail engineering stage to avoid similar nature of problems and also to provide a solution concept to tackle similar nature of problem(s) if encountered at site.

Nov 1, 2022

By Gust Van Lysebetten, Monika de Vos

The objectives of monitoring geotechnical structures can be very diverse, including optimisation of the design, quality control, long term performance assessment, and approval of innovative execution techniques. In this context, new measurement techniques, based on optical fibres, offer the possibility of accurate strain and temperature monitoring with very small sensors and limited numbers of cables. This paper briefly presents optical fibre sensing techniques and illustrates their application to geotechnical structures by means of some projects, carried out by the Belgian Building Research Institute (BBRI).

May 1, 2022

By Patrick Granitzki, Alicia Plinio, Janitha Batagoda, Peter Howell

The City of Newark is making a comeback with new mixed-use multi-storied Residential Development projects. The majority of developers tend to use driven H-pile deep foundation systems to support their super-structures. A different approach was recommended for one particular new development near the Passaic River. The surficial geology included glacial deposits consisting of loose to dense sand overlaying relatively soft silt and clay and a lower stratum of medium-dense sand. During a preliminary site investigation for the project, bedrock was encountered at depths ranging between approximately 168 feet to 182 feet below the ground surface. Design capacity required a single pile of 200 tons. Two different pile foundation systems were evaluated in conjunction to the typical driven H-pile system in order to review potential costs and construction schedule impacts. The two alternative pile systems evaluated were tapered tube piles and drilled displacement piles. Theoretical calculations were followed by in-situ load testing. The field testing results indicated the use of drilled displacement piles as the best option for a portion of the proposed building. This paper discusses the different piles systems considered, installation and using drilled displacement piles to minimize cost and optimize construction.

Sep 8, 2021

By Paul C. Schmall, Kevin Clarke, Paul J. Lewis, John M. Stanbury

"The $200M rehabilitation of the more than 100-year-old Gowanus Flushing Tunnel and pumping station located on the Gowanus Canal in Brooklyn, NY required deep excavations in an extremely congested urban environment. The environment posed significant challenges, including: support of excavation for protection of existing structures, excavation through man-made fill while eliminating groundwater inflow due to potentially contaminated groundwater chemistry; discharge and disposal impacts; and potential settlement of surrounding structures. This paper will present the design and construction challenges associated with the construction of a new combined sewer overflow (CSO) chamberwhich included a jet grout bottom seal, to mitigate groundwater inflow during excavation. The foundation for the finished structure also included a unique system incorporating the jet grout bottom seal elements with deep jet grout columns (piles) acting as the foundation system for the final structure. Design and construction challenges included highly variable soil conditions such as man-made fill, obstructions from previous construction, presence of an organic stratum, and conflicts with existing timber foundation piles. The jet grout bottom seal was constructed in loose sands with the deeper jet grout foundation elements extending to bear on a dense sand stratum. Challenges associated with the bottom seal included grid spacing and construction sequencing. Wet in wet sequencing was used to mitigate potential windows in the bottom seal further complicated by shadowing from existing timber foundation piles.Introduction And BackgroundModernization of the Gowanus Tunnel Pumping System required deep excavations in the extremely congested urban environment of Brooklyn, NY. The project location is shown on Fig. 1 and 2. The focus of this paper is to present the design and construction challenges associated with the support of excavation, control of groundwater, and ultimate foundation support for the combined sewer overflow (CSO) bypass chamber extension. The project site was tightly constrained by adjacent, active roadways and underground utilities, as well as residential and industrial structures. Therefore, excavation support was required to limit ground movement and maintain the integrity of the surrounding facilities. Excavation depths to as much as 16 ft below ground level, 8 ft below groundwater, required that seepage and groundwater be controlled so as to minimize pumping and disposal of groundwater and maintain the surrounding groundwater levels to avoid potential settlement of adjacent roadways, utilities, and structures. In addition, the subsurface conditions required that the proposed CSO bypass chamber extension be supported on a deep foundation to avoid differential and total settlements that may be detrimental to the existing and expanded structure. A plan view of the existing CSO bypass chamber and the proposed extension is shown on Fig. 3."

Jan 1, 2016

By Burt G. Look, David W. Lacey

"Certification of foundation capacity during the construction phase is often assessed by strength or weathering state descriptors based on visual observations. This case study used the Point Load Index (PLI) test as a quantitative tool in the construction certification of a pile’s design capacity. Construction phase tests were completed on irregular sized rock samples whilst comparable design phase testing was completed on intact rock core samples. Statistical comparisons were made to assess the repeatability between the PLI tests, with best-fit Probability Distribution Functions (PDFs) determined for both datasets. Pronounced differences were observed based on the PDF adopted to characterize the PLI dataset, the consequence of which would be a significant change to the pile’s design capacity. The adoption of the lower quartile value is shown to satisfy both design conservatism and construction simplicity requirements. The commonly held belief that rock samples produced during socket excavation may be biased towards the higher strength portion of the rock mass, is shown to be invalid for this site. As the central bridge piers were certified using Plate Load Tests (PLTs), the resultant load-settlement relationships were compared with the PLI strength assessments made for similar materials recovered from the adjacent abutment piles.INTRODUCTIONThe upgrade of the Foxwell Road Overpass across the Pacific Motorway in South East Queensland required the duplication of an existing four span bridge structure. The foundations of the new bridge included the installation of 1.2m diameter cast in place (bored) piles at the bridge abutments and 900mm diameter cast in place (bored) piles below a retaining wall to be constructed adjacent to the existing abutment.The site geology was dominated by the Palaeozoic Neranleigh–Fernvale Beds, predominantly comprised of argillite, sandstone and greywacke. Limited soil materials existed at the site, with Extremely Weathered (EW) rock typically encountered within metres of the existing ground surface. The exception to the existence of shallow rock were locations where existing filling of the site had occurred – i.e. approach embankments to existing bridge structure.Capacity of pile sockets is typically assessed onsite by descriptive rock strength or weathering assessment. Such descriptors encompass a wide range of values and lack precision. Due to the subjectivity of such assessment techniques – a factor of 3 is often observed in terms of strength assessment based on one’s interpretation of rock strength descriptors alone – uncertainty on site often occurs regardless of whether a lower bound, average or other characteristic design parameter applies."

Jan 1, 1900

By Dan A. Brown

The foundations at the Huey P. Long Bridge in New Orleans presented special challenges for construction due to the requirements for very deep drilled shafts in the Mississippi River beneath the existing bridge structure. Drilled shafts were constructed to depths of approximately 200ft in alluvial soils using a rotator system with full-length segmental casing, and base grouted to improve axial resistance. This paper describes the design and construction of the work platform to provide access to the restricted-access site beneath the existing bridge, the approach used to construct the drilled shafts, and the results of a load test program to verify the axial resistance.

Jan 1, 2010