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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 Nadir Ansari, Brian W. Wilson, Marina S. W. Li

"A hybrid Deep Mixing (DM) shoring system was recently constructed for a high-rise development in downtown Vancouver, British Columbia, Canada for the temporary support of a five-level basement excavation. The site is bounded by an existing bridge off-ramp structure along its longest side and by city streets on the other two sides, which formed a truncated triangle in plan. A conventional secant pile wall was installed along the longest side, about 380 ft (116 m) in length, of the site. Hybrid shoring walls (HSW) 1 and 2 were installed along two shorter sides with each being 235 to 246 ft (72 to 75 m) long. HSW 3 completed the excavation support system along the shortest side with a length of about 55 ft (17 m). Cutter soil mixing (CSM) was proposed by the excavation and shoring design-build team in lieu of conventional secant piling. CSM was the preferred method to construct the infill panels between soldier piles because of the speed at which the shoring system could be constructed in the variable fill, peat, wood waste and overburden. Design ConsiderationsTo minimize the impact on buried utilities along the outside perimeter of the excavation, the temporary shoring was designed to limit the lateral displacements to less than 0.8 in (20 mm). Factors taken into consideration for shoring design included the lateral earth pressures from the fill and native soils, groundwater pressures, temporary construction loads (e.g., crane or heavy plant/equipment), and permanent structural requirements. The subsurface conditions at this site typically consisted of fill (cohesive and granular), overlying peat and/or wood waste, overlying clayey silt to sandy silt, overlying weathered to dense to very dense clayey silt till to sandy silt till with silt layers. Localized, perched groundwater was observed within the fill, peat, wood waste and sandy silt layers above the dense till."

Jan 1, 2017

By Phil Wilkinson, Sam Whitaker

"The installation of large (XL) diameter monopiles offshore typically requires expensive and specialist plant, equipment and vessels. Due to the increasing size (weight, diameter and length) of the foundations, in order to mitigate installation risk, the use of large diameter drills is becoming an increasing requirement.Project developers often try to avoid drilling operations due to the time associated with the drilling process. This restricts projects in terms of location and it also overlooks the additional engineering benefits drilling can bring to monopile foundation design e.g. reduced foundation material and better fatigue design life.By comparing the lessons learned of three milestone overwater drilling projects; methods of maximising drill speed and decreasing drilling process time is established. Particular emphasis is put on pile internal relief drilling in a process known as Drive-Drill-Drive (DDD).The milestone overwater drilling projects are North Hoyle Offshore Wind Farm (OWF) (2003); Flamanville EPR cooling water outlet shaft (2008); and Gwynt-y-Mor OWF (2014).By evaluating the effect of foundation pile diameter on drilling process times, example foundation installation costs are derived and used to show that incorporating drilling as part of a process may not be cost prohibitive to projectsContinued advances in drill technology, and drilling rates of penetration, combined with an integrated approach to foundation design, challenge whether hammering only is always the optimal solution for XL monopile installation."

Jan 1, 2017

By Renato P. Cunha

The paper explores a parametric analysis of a four-pile group in contact (hence piled raft) and without contact (hence standard pile group) with the superficial soil layer, under a combined set of loadings (moment M, vertical V and horizontal H forces). The major design parameters of interest, as total and differential settlements, and raft bending moments and shear stresses are assessed under aforementioned distinct conditions. The slenderness ratio of the piles is also varied along the analyses, allowing the establishment of its influence on the derived parameters.

Jan 1, 2006

By Lois G. Schwarz

I did a project (Sungai Piah) as a consultant to your firm in Malaysia, where we were faced with a similar situation as sketched out in your question. The following is what we did for the grouting of the primary holes, which were both located upstream of the plug as well as downstream: We used a hydrophobic MDI based semi-rigid polyurethane prepolymer in the first phase of the grouting operation when grouting under water flow conditions. Then in the second phase and also for the contact grouting we used a two component water compatible polyurethane elastomer. And then for deeper formation grouting, when all the water flow had been stemmed in the vicinity of the plug, we used a regular (balanced stable) cement based grout. So it may not exactly answer your question, but we first used hydrophobic grout because it is very efficient to grout a formation through which water flows. We didn't stop all the leaks day-lighting downstream of the plug or all water running through the formation near the plug, but the flow of water through the rock formation adjacent to the plug was reduced by 99.9%, after completing the urethane grouting. This facilitated the placement of cement based suspension grouts without wash-out.

Feb 10, 2003

By Chaz Weaver, James Sheahan, Michael Mo

"The Virginia Department of Transportation (VDOT) undertook a program to replace four bridges along approximately 4 mi (6.4 km) of US 340 in Northwest Virginia. Two of these bridges, which span Compton Creek and the Norfolk Southern Railroad respectively, are the subject of this article. HDR provided roadway and structural design as well as geotechnical engineering services for the Norfolk Southern Railroad Bridge while their subconsultant, Saeed Associates, provided structural engineering services in support of the HDR roadway and geotechnical team for the Compton Creek Bridge.The project is located in the Valley and Ridge Geologic Province of Virginia, on an alignment that is adjacent to the Shenandoah River. The project lies within the Beekmantown Group consisting of limestone and dolostone that are prevalent and prone to karstic activity in a band that passes through the project area and north into Central and Eastern Pennsylvania. This area has been impacted by karst limestone conditions where caves and sinkhole activity is common. Caves at Luray and Front Royal, located to the south and north of the project, respectively, are popular public attractions.Since the potential for variability of subsurface conditions can be, and often is, greater in karst terrain, the need to develop a design that provides as much flexibility as possible during construction, and then to be prepared to efficiently review and respond to construction questions is heightened. Coordination and communication among the design staff, VDOT’s design and construction staff, and the contractor was a key factor in completion of this project.Compton Creek BridgeThe alignment for the new Compton Creek Bridge is located about 125 ft (38 m) west of the existing bridge, placing it between that bridge and the existing Norfolk Southern Railroad Bridge. No information about the foundations was available for the existing bridges. Borings in the Compton Creek valley encountered extensive voids (some clay filled and some open) with numerous boulders, rock ledges and pinnacles, particularly on the north side of the creek. Geophysical and geotechnical investigations indicated that below a poor and variable upper zone of rock was a layer of more competent and consistent limestone, which appeared to contain little or no voids."

Jan 1, 2017

By Steffen Schweizer, Tadeusz Brzozowski, Alfred Koller, Michał Topolnicki, Jürgen Wäger, Grzegorz Sołtys

A full scale test has been conducted to determine ground bearing pressure under rig tracks. The track loads were recorded in real time using Liebherr's Ground Pressure Visualisation system, and the vertical stress induced in the ground was measured with pressure cells embedded in the ground. It has been found that the recommendation of EN 16228 regarding determination of the track length is oversimplified. The contact length should dependent on the susceptibility of the working platform. It has been also demonstrated that the corrected pressure distributions under the tracks influence the dimensioning of the working platforms. As a result, the designed working platform may actually be less secure than is shown by conventional calculations.

May 1, 2022

By Camilo A. Alvarez, Stephen K. Harris, Brian R. Zuckerman, Philip J. Meymand, Danielle M. Steinmetz

"The sleek new air traffic control tower at the San Francisco International Airport stands at 221 feet tall and is set to replace the existing air traffic control tower by 2016. This aluminum-clad, torch-like structure and three-story Integrated Facilities Building at the base are situated between Terminal 1 and Terminal 2 adjacent to the tarmac. Berkel & Company Contractors, Inc. and Simpson Gumpertz & Heger Inc. worked in conjunction with structural engineers from Walter P. Moore Engineers and Consultants, geotechnical engineers from URS Corporation, architects from Fentress Architects, and general contractors from Hensel Phelps Construction Company on the performance-based design of a foundation to support this critical facility, which is located in a high seismic zone and situated on the very soft soil of the San Francisco Bay margin. With the loading demands and performance criteria established and Young Bay Mud thicknesses ranging from 44 to 47 feet thick across the site, the design team employed a total of 214 24-inch diameter Auger Pressure Grouted piles, which were drilled into the underlying Franciscan Formation as deep as 148 feet below existing grade. Pile reinforcement included full-length confined cages.The piles were designed to resist Maximum Considered Earthquake axial demands as high as 1,400 kips in compression and 700 kips in tension. The performance-based pile design included verification of shear capacity under double-plastic-hinge flexural mechanisms, verification of pile ductility via non-linear moment-curvature analyses, and consideration of curvatures due to kinematic as well as inertial loading.The team implemented an extensive pile load test program including a full-scale static compressive load test on a sacrificial test pile and five non-destructive high-strain dynamic load tests, four of which were performed on indicator piles that were later used as part of the foundation system. These piles were monitored with extensive embedded instrumentation throughout their length, including strain gauges and accelerometers."

Jan 1, 2017

By Leo Panian

Over the last decade, drilled and post-grouted micropile foundations have come to be increasingly relied upon for resisting seismic loads in building foundations on the West Coast. Micropiles have been successfully deployed in a range of soil conditions, in vertical as well as battered configurations, to support a variety of structural systems difficult soils. Their high load capacity in tension as well as in compression, their ability to be installed in confined spaces with minimal overhead clearance, and their ability to be directly tested in an installation have made them indispensable for seismic strengthening of existing structures. More recently, growing industry experience along with improvements in design guidelines have led to wider acceptance of micropiles among engineers and building officials. The increasing availability of the specialized materials, coupled with growing familiarity with drilling technologies among design-build contractors has made micropiles more cost-effective and competitive. For the first time, micropiles are finding applications in the construction of new buildings, where they are combined with shallow footings in hybrid foundations to efficiently resist seismic loads. These new applications rely on more intensive engineering analyses to evaluate the performance of micropile foundation systems and develop detailed requirements for design and construction. This paper describes the design approaches and the analytical methods for the seismic design of hybrid micropile foundations, and provides examples of recent construction projects that demonstrate the application.

Jan 1, 2010

By Henry Zhang

This paper presents two case studies of large diameter driven tubular steel piles for the ongoing Woolgoolga to Ballina Pacific Highway upgrade (W2B). This project forms part of Australia’s largest regional infrastructure project and will upgrade about 155 kilometers of highway to four-lane, divided road. There are more than 170 bridges on W2B, and driven tubular steel piles are adopted on 43 bridges between Glenugie and Ballina. Driven piles terminating in soil or basalt is a big challenge faced by both designers and piling contractors due to 1) the uncertainty of expected pile unit shaft and base resistance in different soils; 2) whether plugging is formed; and 3) highly variable basalt strength and thickness near top of the rock. If these risks are not adequately managed during design or construction stages, it could lead to unexpected project delay, extra time and cost or pile toe damage in basalt. This paper describes two case studies, one for piles designed to terminate in soils and the other for piles designed to terminate in basalt. How these risks were assessed and managed during detailed design, procurement, hammer selection, pile installation and verification will be discussed in details with lessons learnt summerised in the conclusion.

Nov 1, 2022

By Diego Bellato

Production data recorded by special foundation rigs during construction activities at the site are commonly used for quality assurance / quality control procedures and, in particular, to prove that the installed foundation elements comply with the geometrical and quality requirements defined in the design specifications. Parameters such as crowd force, penetration/withdrawal rate, rotational speed etc. are usually presented in reports in the form of depth and/or time profiles. This type of protocols are already standard QA/QC solutions for ground improvement methods like deep soil mixing or jet-grouting, but they are quite rarely applied in combination with other techniques like diaphragm walls or Kelly drilling. In the latter cases, one of the main reasons behind this lack of site documentation is related to the difficulty in interpreting huge amount of data collected during the creation of single elements, which, in some cases, can last several days (not always in a row). In addition, the building sequence is often characterized by many alternated operations involving different movements of the rig and the use of different tools. In this context, the identification of specific construction activities based only on the mere exam of the time profiles of the recorded production parameters is extremely difficult. In this paper, the time profiles of production parameters obtained from a fully-cased Kelly drilling rig employed on a site in Karlsruhe (Germany) have been investigated and compared with a detailed series of activities deduced from a video filmed during installation. Typical time profile patterns associated to specific procedures have been identified by combining the different information available. The outcome of this study helped project engineers to automatize the recognition of activities directly from production data and led to an overall understanding and optimization of the construction process. INTRODUCTION The special foundation industry is characterized by the use of highly sophisticated machinery for the realization of geotechnical systems such as piled rafts, retaining walls and slabs for excavation pits, cut-off walls for levees and embankments or ground improvement solutions. Rigs can vary in size, weight, and power and can be provided with several drilling tools to cope with the different soil conditions (e.g. clay, sand, rock) and the different geometries of the elements to be built at the site (e.g. micro-piles, large- diameter bored piles, diaphragm walls, anchors). Due to the challenging construction procedures, various types of sensors have started to be mounted on the equipment in the last decades to monitor the behavior of some important machine parameters and to inform rig operators about the on-going process and the status of their devices.

Jan 1, 2019

By J. E. De Waele, J. J. Lee, M. J. Mulheron, Luke R. Deamer

There is increasing demand for geotechnical contractors to commit to carbon reduction, net zero or science based targets. A lot of focus has therefore been placed on using low carbon materials and low emission rigs. However, whilst these are ways to help reduce carbon, there is a need to look beyond just substituting materials and fuels to meet net zero. Using the IEMA carbon hierarchy, there is a need to first look at eliminating and reducing emissions, before considering substitute materials. For example, in geotechnical designs, this may mean considering using ground improvement or reducing the number of piles, before considering using low carbon cements. Equally, for remaining emissions, this hierarchy means considering carbon negative products to offset emissions, such as ground source heat pumps. This hierarchy can also be applied throughout geotechnical contractor organisations. For example, considering video conferencing for meetings, before considering public transport or using an electric vehicle. This article explores the carbon hierarchy and how it can be applied to all areas of a geotechnical contractor’s business. Only through embedding this hierarchy across the business can geotechnical contractors achieve the step change required to meet net zero.

May 1, 2022

By Satyajit Vaidya, Rudolph Frizzi, Sandy Larimer

"This paper presents a case history in design and construction of a deep foundation system that included high-capacity open-ended driven piles constructed to support a high-rise building in Manhattan, New York. The project site is bordered by existing buildings, active streets, and critical public transportation infrastructure, which were considered in the new building’s deep foundation and seismic design. This paper focuses on driven pile foundation design and installation through relatively loose soil deposits. Unique design aspects included seismic design considerations, and pile splice design for open-ended steel pipe piles subject to significant uplift and lateral loading. Unique construction aspects included quality assurance of open-ended steel pipe pile splices, and uplift and lateral load testing of driven piles installed in close proximity to other foundation elements installed for the project.SITE CONDITIONS AND SUBSURFACE CONDITIONSThe project site is located in Manhattan, New York, and is bordered by existing buildings, active streets, and critical public transportation infrastructure that is located about 60 feet from the site. The existing sidewalk grades around the site are between about el 4 and about el 13; elevations are referenced to the North American Vertical Datum 1988 (NAVD88).Subsurface conditions at the site generally consist of successive strata of historic fill, former river bottom deposits consisting of compressible clayey soils, and medium dense to dense sand, overlying mica schist bedrock. A generalized subsurface profile is shown in Fig. 1. The historic fill stratum is about 10 to 45 feet thick, and generally consists of loose to medium dense sandy soils with varying proportions of silt, gravel, and miscellaneous debris such as brick, concrete, and glass fragments. The underlying former river bottom deposit stratum is up to about 15 to 20 feet thick, and generally consists of very soft to very stiff clay and lenses of very loose to loose sand. Medium dense to dense sand was generally observed below the historic fill and former river bottom deposit strata and overlying bedrock. Top of bedrock was generally observed at about 80 to 105 feet (i.e. at about el -75 to el -100), except in the southeastern portion of the site where the top of rock was observed as deep as about 140 feet (i.e., at about el -135). Groundwater levels typically ranged between about el 1.5 and el -0.5."

Jan 1, 2016

By Esam Abraham

A 13.6 mile portion of the 500 kV Tehachapi Renewable Transmission Project crosses the mountains of the Angeles National Forest. Access and environmental constraints precluded road development for most transmission tower foundations, tower erection and conductor stringing operations. Because of the access constraints, helicopter-supported micropile foundation construction was used for this steep and environmentally sensitive portion of the project. The general methodologies incorporated on the project represent innovative implementations of micropile design criteria, preconstruction micropile installation and verification testing, on-site geotechnical characterization, micropile and pile cap installation, and proof load testing. Challenges in constructing the 224 foundations for 56 transmission towers provide lessons learned related to transmission lattice steel tower specific design constraints, construction challenges (environmental and geotechnical), and construction schedule.

Jan 1, 2010

By David Peterson, Terry Tucker, Rafael Serrano

"The Alameda Corridor-East (ACE) Construction Authority awarded a $172.6 million contract to Walsh Construction Company (Walsh) for the construction of a 2.2 mi (3.5 km) long grade separation including a 1.4 mi (2.3 km) long trench that will allow Union Pacific Railroad (UPRR) and Amtrak passenger trains to operate below ground through the city of San Gabriel, Calif. The project is necessary as the ACE trade corridor accommodates approximately 60% of the shipping containers that move from San Pedro Bay, the busiest port facility in the western hemisphere, to the rest of the country via an extensive rail network. Rail traffic is expected to increase by as much as 160% by 2020, and the resultant delays to vehicular traffic is projected to increase by an estimated 300%. The San Gabriel Trench Project is designed to mitigate the effects of this increased train and vehicle traffic throughout the San Gabriel Valley. Malcolm Drilling Company (Malcolm) was selected by Walsh to perform the specialty foundation and ground improvement work for the San Gabriel Trench.This project is part of ACE’s program to create 22 grade separations and safety improvements at 39 grade crossings throughout the San Gabriel Valley. In addition to safety improvements that will eliminate crossing collisions and delays to emergency responders, the project will reduce vehicle congestion and emissions from passenger cars and trucks having to wait for passing trains, and the project will also reduce locomotive horn and crossing bell noise to local residents.Construction of this portion of the project began in late 2012, and it is scheduled to be completed by the end of 2017, having created approximately 9,000 jobs during this period. The project is being funded from Proposition 1B transportation bonds approved by California in 2006, the Metropolitan Transportation Authority (MTA) Measure “R,” and other local and federal funds. The overall project cost is estimated to be $313 million."

Jan 1, 2017

By Dempsey S. Thieman

Innovative marine bulkhead design and construction techniques were used in the fast-track design and construction of a high-capacity, deep-water dock in the highly seismic region of Alaska?s Aleutian Islands. The geotechnical investigation and design through construction phases were completed in just eight months. The adaptable OPEN CELL® design, readily available standard flat sheet pile and an experienced contractor were integral to the successful completion of the project. The cost of the structure was determined to be approximately 50 percent of a comparable pile-supported platform dock structure, allowed higher load capacity, rapid construction, less maintenance, and provided substantially more uplands. This paper details the design and construction of this unique and challenging project. The OPEN CELL structure is a vertical flexible membrane system that offers significant advantages over other structure types: ? Its flexible membrane structure is not dependent on toe embedment for stability. ? Poor soil conditions, shallow bedrock, high seismic loads, deep water, scour, etc., can be accommodated due to its adaptable design. ? It has a very high load capacity?capable of several thousand pounds per square foot. ? Allows buried utilities which results in lower cost and reduces freezing conditions ? The sheet pile tail walls can be extended to provide increased global stability if needed. ? Standard sheet pile and connectors with traditional installation techniques allow accelerated construction schedules.

Jan 1, 2008

By Nagarajan. D, Raja Rajan. K, Vijayakumar. T

Major bridges crossing mighty rivers must be constructed in flowing water. Constructing the sub-structure in water has been a challenging job for contractor. Special construction techniques with marine fleets to be adopted for waterfront construction. Enabling works like temporary piling platform and cofferdam used for pile and pile cap construction. Apart from this, enabling works like load out jetty to transport the materials from land to water; temporary walkway for access of workman to work location; temporary access bridge for construction vehicles movement; temporary liners for tower crane foundation; Concrete block to act as dead man anchor for barge movements were all required by the contractor for smooth functioning of site as per construction schedule. Investment in enabling works by contractor plays a significant role on profit margin of the project and of course with utmost safety. Design of enabling works for waterfront structures involves hydrological data like afflux, bathymetry survey, current force, scour depth and wave force to be taken cautiously for safe and economic design. Type of foundation and pile/well cap top level corresponding to water levels shall influence the construction scheme. Usage of geotechnical software like Wallap and Plaxis required for enabling work design to enhance the safety of the structure. Bathymetry and soil condition play a critical role in design and construction of enabling works. Water Discharge quantity in river along with water levels like low water level, high flood level, seasonal fluctuation of water levels has a great impact on design of enabling works. Establishing enabling works for waterfront construction near to an existing bridge is an additional challenge for the contractor. Along with design, constructing the enabling works in water requires special construction methodology and sequence of work. This paper shall provide insights on overview of design and construction of enabling works for waterfront construction.

Nov 1, 2022

By Andrew McNamara, Stuart Norman, Matthew Dearing, Michael Pelken, Asha Panchal

The deep foundations industry has largely remained unchanged since in the advent of CFA piling in the 1960s. Piles have consequently been designed and constructed following the traditional codes and standards without much regard for optimising in-life efficiency or end-of-life reuse. After existing developments have been demolished there is little motivation to reuse existing piled foundations as their load bearing capacity and structural integrity cannot be verified. Therefore piling contractors are increasingly spending more resources on coring through existing piles, only to be replaced with larger diameter or deeper piles. The hollow element of the HIPER® Pile provides access to the entire length of the pile to permit inspections and a shaft in which the pile can be extended if needed. This paper presents and compares the embodied carbon savings, both during construction and through foundation reuse, from a HIPER® Pile scheme compared with the traditional solid pile scheme. A discussion on the benefits of this technology and its implications on warranties and approvals is also presented to motivate the foundations industry to embrace whole lifecycle assessments and support the journey to net-zero carbon.

May 1, 2022

By Ke Yang, Robert Liang

"Drilled shaft foundations are widely used for many types of structures, especially for highway bridges, high rise buildings, and costal structures. The lateral design considerations are crucial for those structures that are subjected to lateral thrust forces, winds, waves, and earthquakes. The p-y analysis is the most widely used method for the analysis and design of drilled shafts for lateral load applications in soils. However, existing p-y criteria were developed based on the lateral load tests on small diameter drilled shafts in soils. Although, a lot of lateral load tests have been conducted, there are a limited number of lateral load tests on large diameter drilled shafts embedded in clay. In this paper, a lateral load test on 2.44 m diameter fully instrumented drilled shafts in clay is presented. The site specific p-y curves are derived based on strain gage readings. The existing p-y curves are found to be much softer than the site specific p-y curves. Correspondingly, the deflection at the top of the test shaft under the maximum applied load is predicted to be eight times larger than the measured value using existing p-y criteria. A new p-y criterion is proposed in this paper. The proposed p-y criterion is proven to be able to capture the site specific p-y curves of the load test and to predict closely the deflections at the top of the test shaft. INTRODUCTIONDrilled shaft foundations are widely used for many types of structures, especially for highway bridges and costal structures. The lateral design considerations are crucial for those structures that are subjected to lateral thrust forces, winds, waves, and earthquakes. Although efforts have been made on studying lateral response of drilled shafts; nevertheless, only limited studies have been published on the behavior of large diameter drilled shafts under lateral loads and the corresponding design methods."

Jan 1, 2005

By Paul Doherty

It is known that the axial capacity of a displacement piles installed in clay varies with time. Consolidation theory suggests that dissipation of porewater pressure set-up during pile installation would lead to increased effective stress and hence higher pile resistance. In recent years a number of case histories have reported time dependent capacity increases for piles installed in sand. Although there is some debate regarding the physical mechanisms controlling this phenomenon, known as ageing, it is unrelated to pore pressure dissipation as piles in sand are installed in primarily drained conditions. A series of field tests designed to investigate ageing effects in soft clay are presented in this paper. Full-scale load tests on 6m long 250 mm square concrete piles, which were driven into soft clay are described. The piles were first tested approximately 100 days after installation, at which stage full equalization of the excess pore pressures had occurred. Static load tests were then performed up to 10 years after pile installation. The piles exhibited significant ageing, with their shaft resistance increasing by up to 66% over a 10 year period. Possible mechanisms for such aging characteristics are explored.

Jan 1, 2011