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By D. Kolymbas

A simple formula is introduced which allows the evaluation of dynamic pile tests. The following case is considered: The pile top is dynamically loaded by an impact. The velocity v of the pile top is recorded over the time. Let v1 and v2 be the first and the second maximum of this curve. Then, the pile bearing capacity (resulting from ideally plastic resistance at the pile wall and at the tip) can be set approximately equal to Z(v1- ½ v2), where Z is the impedance of the pile cross section. Due to the assumption of ideal plastic resistances, radiation damping needs not be taken into account. Material damping may be important in rate sensitive soils (such as clay, even if it is highly overconsolidated). A simple correction procedure for material damping is proposed.

Jan 1, 1989

By Yahia M. Al-Smadi

Effect of lateral loading against existing sheet pile wall and distribution of gravity loading due to various number of construction loading scenarios were studied. The objective of this effort was to determine the loading case that permits the contractor to utilize a 400 ton crane at the specified location with the existing limitation imposed on site. Staged analysis was determined as the methodology that will more accurately predict the exiting and additional stress due to the impose crane loading. A reliable and robust analysis (ANSYS) software was used to complete both 2D and 3D finite element model and analysis. Analysis model parameters such as material properties, non-linear behavior of the soil, and meshing are presented and discussed. At the conclusion specific range of crane operation and pick weights operating on existing concrete mat supported on top of an existing tunnel was reviewed and deemed acceptable.

Jan 1, 2010

By Paul Summers, Kevin Richardson, Willem (Billy) Villet, Paul J. Sabatini, Edward C. Clukey

"Between 2008 and 2009, more than 6,000, 23-m long deep mixing method (DMM) elements were constructed to support 124 concrete mats comprising the foundations for the process trains for an LNG facility. The Owner requested first-of-its-kind analyses and assessments to confirm the quality and reliability of the DMM foundation. This paper provides information on these assessments and the procedures used to ultimately conclude that a fit-for-purpose foundation system was constructed.During early phases of construction, several DMM test cores revealed nodules of unmixed clay in upper core samples. A comprehensive review of available DMM core information was undertaken. It was concluded that the amount of coring being conducted as part of the contractor’s QA/QC program should be increased to achieve a foundation system with the required level of reliability.Three-dimensional finite element analyses were completed considering various distributions of defects in the DMM elements and the effects of potential downdrag on DMM elements. Calculated mat settlements and mat stresses were compared to cases without defects in the DMM elements. Various distributions of loaded and unloaded mat areas and number and position (both in the subsurface and laterally) of defects were considered. Four (of the 124) mats were identified as potentially “at-risk”. The settlement performance of these mats is currently being monitored and, to date, performance has been acceptable.IntroductionThe foundation support system for the process train at a major LNG facility comprises more than 6,000, 23-m long DMM elements. The general subsurface stratigraphy at the project site comprises (from the ground surface): (i) up to 8 m of fill sand initially placed underwater building to a stable construction platform; (ii) up to 12 m of soft organic clay (Unit II clay); and (iii) clayey sand and sand layers becoming progressively denser with depth (Unit III sands). Each DMM element comprised two secant 1.5-m diameter DMM columns. DMM elements were typically arranged as cells enclosing one, two, or three DMM elements."

Jan 1, 2017

By Amy B. Cerato

The application of this study is to use helical anchors as a foundation system for small wind tower (1 ? 10 kW) guyed cables. Helical anchors are currently used to anchor guyed cables of telecommunication and electric towers. However, the increased dynamic vibrations a wind turbine adds to the tower and foundation system under working loads, as well as extreme environmental conditions (e.g., straight line winds, ice load or sudden furling shocks), require additional knowledge about the behavior of helical anchors. These field conditions were simulated in this study by instrumenting a working tower with load cells and 3-axis accelerometers to gather data on wind speed and tower response. These tower responses were then transmitted to the helical anchors through an extensive, large-scale testing program that included monitoring the performance of the helical anchor foundation under dynamic loads, subject to natural variations in both wind regimes, precipitation (water level) and variations in helical anchor geometry. This paper specifically discusses the effects of helical anchor geometry on helical anchor performance under long-term dynamic loads.

Jan 1, 2008

By Joel L. Volterra

Since 1910, Mueser Rutledge Consulting Engineers (MRCE) has regularly provided professional engineering services including inspection of pile load tests. Historically, such services included on-site inspection of the driving of test piles and subsequent static load tests by qualified Geotechnical Engineers. Load testing procedures are specified by local or State Building Codes, locally the 1968 Building Code of the City of New York (1968 BCCNY). Between 1968 and 2008, the 1968 BCCNY required a minimum 48-hour hold period for standard loads per pile type, an extended 96-hour hold period for higher capacity piles, and a settlement criterion that the pile maintain a test load equal to two times the design load with less than 0.012 inches of settlement over the last 48 hours of the hold period. Effective July 2008, the new 2008 BCCNY shortened the hold period and relaxed the settlement criteria to that which is more similar to other governing codes and standards such as the International Building Code (IBC 2006) and the American Society for Testing and Materials (ASTM). MRCE implemented an automated load test monitoring system to reduce costs and to alleviate or minimize overnight and off-hour staffing for load test readings. Initially, a series of linear variable differential transformers (LVDTs) and data loggers were included in the Contractor?s load test setup to electronically record pile head settlement and where applicable, settlement of telltales installed to varying depths in the pile. A pressure gage was subsequently added in the hydraulic line, then a load cell, strain gages, and remote access using modems. The ease of the setup and modular adaptive nature of this system have proven it to be a useful tool and improved our ability to better serve our clients and manage our pile load testing services.

Jan 1, 2008

By Peter Yen

This session consists of five papers. Three involved research on the properties of grout materials, specifically ultrafine cements and polyurethane grouts. Two papers present the development of soil grouting technology and monitoring methods. Of great interest are the papers on ultrafine grout penetrability testing focusing on the pressure filtration effects encountered in permeation grouting applications (Ericksson, Stille and Mittag, Savidis). The comparison testing of hydrophilic and hydrophobic polyurethane grouts submitted by Vrignaud, Ballivy, Perret and Fernagu assessed the long-term performance of these materials for repairing saturated cracks in concrete, subject to thermal expansion and contraction. Two very practical papers present the development of soil grouting, where permeation, fracture, replacement, jetting and other grouting techniques are utilized. The papers by Lees with Chuaqui and Warner present experience with ultrafine and other commonly used grout materials. Methods to measure and monitor the injection process and verify production progress are discussed.

Feb 10, 2003

By K. K. S. Ho

In Hong Kong the design of excavated piles in weathered granite has conventionally been based on a rule-of-thumb which relates the allowable base bearing capacity to the SPT N value, with no allowance for skin friction. This rule-of-thumb has been shown to generally lead to conservative designs. To improve the overall understanding of load-transfer mechanism of excavated piles in weathered granite, instrumented pile load tests have been conducted. This paper summarises a selection of instrumented pile load test data in Hong Kong and the observations made of the results, which indicate that there was considerable scatter in the back-calculated skin friction values. However, the mobilized skin friction was shown to be significant which can lead to substantial savings in design.

Jan 1, 1996

By Yogesh Prashar

Three conventional uplift tests and 12 Rapid Pile Load Tests (RLT) were performed on total of fifteen 16-inch square pre-cast concrete driven piles at a test site in Emeryville California in December of 2000. The uplift tests were performed in accordance with ASTM standards, and the RLTs were performed using a FUNDEX RLT. The RLT is carried out by dropping a mass of 25-tons on top of the pile, thereby inducing a force that is measured by a load cell. An optical lens records the vertical deflection of LED's that are mounted on the pile. Ultimate uplift and compression capacities of each of the fifteen piles were determined using the Davisson method. Soil parameters were calibrated by back-calculation (cohesion and internal angle of friction) using both the results of conventional uplift load versus deflection curve, as well as the results of the triaxial compression tests. A two-dimensional finite difference model including soil elements, and structural elements representing the test pile was setup using the computer program Fast Lagrangian Analysis of Continua (FLAC). FLAC was used to simulate both the uplift as well as the RLT. Strength increase of cohesive material was also accounted for in the analysis. Numerically simulated and theoretically computed pile capacity curves and axial deformation variation with applied load curves are in close agreement to the observed curve during the field test. Conclusions are made from this test site regarding the factors influencing results of RLT.

Jan 1, 2002

By Harry Schnabel, Mitchell L. Fong, Douglas R. Jenevein, Thomas S. Lee

"The Warm Springs Extension (WSX) is one of a series of projects that will eventually extend the Bay Area Rapid Transit System (BART) from Fremont to San Jose, California. A cut and cover tunnel was used for a portion of the extension that runs through Fremont Central Park to minimize the impacts that an at-grade railway would have on the Park. A cement deep soil mix (CDSM) wall was selected by the engineer as the preferred method of providing structural support and groundwater cut-off for a portion of the tunnel where it passes through an important aquifer and near Lake Elizabeth. In addition to the CDSM wall, a jet grout plug was constructed at the base of the tunnel to provide a complete groundwater cut-off.This paper will discuss the unique quality assurance and quality control measures taken for the soil mix wall and jet grout plug as well as the methods used to repair leaks and mitigate water seepage through the exposed wall and grout plug.PROJECT DESCRIPTIONThe Bay Area Rapid Transit (BART) Warm Springs Extension (WSX) project is located south of the existing Fremont BART station extending 8.9-km (5.4 miles) to Warm Springs District in Fremont, California. The WSX project has been divided into two contracts with different delivery methods. In order to minimize impacts to Fremont Central Park, a subway was selected at this portion of the alignment under a conventional design/bid/build contract.The Fremont Central Park Subway (FCPS) which begins on the south side of Walnut Ave and ends just north of Paseo Padre Parkway and is about 2.3-km (1.4 miles) long. Fig. 1 shows the entire WSX and the FCPS project. The FCPS contract consists of a cut-and-cover subway box, subway transition structures, ventilation structures and a section of which transverses Lake Elizabeth (a man-made lake). The geologic conditions consist of fill (sand, silt, clay and construction debris), Young Alluvium (clay and silt), Basin Deposits (clay, silt, and sand), and Older Alluvium (sand and gravel) as shown in Fig. 2.HYDROGEOLOGY OF THE PROJECT SITEThe FCPS is dominated by two geologic features - the Hayward Fault and the Above Hayward Fault (AHF) aquifer. The AHF aquifer provides a significant source and storage of water for the local water district. The underground subway will penetrate this aquifer and is up to 11m (36 ft) below the groundwater table. No groundwater was allowed to be pumped during construction of the subway box by Alameda County Water District (ACWD). To facilitate excavation for the subway box, temporary cut-off walls and a grout plug were designed to retain and resist high differential hydraulic pressure. The following section describes the selection of a deep soil mixing method for water cutoff. Design of the grout plug has been described in Lee, et al., 2011 and Fong and Lee, 2009, and is not the focus of this paper."

Jan 1, 2015

By B. M. Das

Laboratory model test results for the ultimate uplift capacity of rough rigid single and group piles embedded in sand have been presented. Model tests on single piles were conducted in loose, medium, and dense sand. The uplift tests on group piles were conducted in medium sand only. Based on the present model test results, tentative relationships for the estimation of the ultimate uplift capacity of single pile have been presented. The efficiency of group piles is a function of the length-to-diameter ratio, center-to-center spacing to diameter ratio, number of piles in a group, and the degree of compaction of sand.

Jan 1, 1989

By Shawna Munn, Jakub Hudler

This paper outlines the use of tunneling headwall softeyes for transit construction projects in the Greater Toronto Area (GTA) over the past decade. Due to spatial constraints, tunnel boring machines were used to construct the underground tunnels requiring the design of launch and exit shafts with headwall softeyes to facilitate tunneling operations. Variable ground conditions and shaft geometries lead to the development of innovative headwall and tunnel softeye design applications using fiber reinforced polymer (FRP) elements (beams, reinforcing bars, and tiebacks). This paper outlines the challenges and benefits associated with designing and constructing shafts using various systems. Lessons learned throughout design and construction of more than 20 structures over the past 10 years are outlined. The constructability challenges with using FRP and design performance are also discussed. For over a decade, the City of Toronto has been expanding its metropolitan transit network with a variety of new transit construction projects. Two recent projects in the Greater Toronto Area (GTA) for underground infrastructure include the Toronto York Spadina Subway Extension and the Eglinton Crosstown Light Rail Transit project. These add a total of 31 new stations and 18.6 km (11.5 miles) of underground transit (TTC 2017) (EllisDon 2016). Due to ground conditions and spatial constraints of existing surface infrastructure, these projects utilized tunnel boring machines (TBMs) to construct the underground tunnels requiring the design of various types of shafts and headwalls to facilitate underground tunneling operations. To allow for tunneling through the headwalls, these shafts were designed with “softeyes” - a section of the wall without metal reinforcement that allows the TBMs to tunnel through.

Jan 1, 2018

By Jom Gentry

Acrylamide chemical grout (C3H2NO) has been successfully used for over 50 years to control groundwater and stop infiltration. This paper will address three unique projects involving the control of groundwater with each study providing special circumstances and geological conditions: encapsulation of radioactive hazardous waste in the United States, a tailings dam for a large copper/gold mine in Argentina and 27 miles of leaking subway in Canada. The primary reasons for selecting acrylamide grout were based on the following characteristics: thinnest chemical grout on the market, a true solution grout which contains no suspended solids in the blended product, flexible gel set times, and a 362 year half-life in soil as determined by the U.S. Department of Energy.

By Michael Lane

With the success of their existing casino operation on the Ohio River in Lawrenceburg, Indiana, the Indiana Gaming Co., LP planned a major expansion of the current facilities. This expansion includes a second 1400+/- car parking garage, a new surface parking lot, elevated walkways, and a new floating casino that will double their present square footage and consolidate all of the gaming activity to one floor. In March of 2006 Richard Goettle, Inc. was awarded the general contract to construct a 260? x 520? boat slip for the new Argosy VII floating casino. An Open Cell® bulkhead system was specified as the means for constructing the new slip. Our contract included the purchase and installation of 300,000 square feet of PS27.5 sheet pile, excavation of 230,000 cubic yards of soil, and a 3300 square foot Mechanically Stabilized Earth wall.

Jan 1, 2008

By William Van Impe

A most renewing and promissing soil displacement screw pile is called the O-pile. The O-screw pile is a soil displacement auger pile based on a screwing in - screwing out procedure. The displacement auger head consists of a discontinuously diameter - increasing steel tip, on top of which the continuous screw flange with variable pitch is mounted. The soil displacement is kinematically ensured by downwardly oriented slots mounted on the auger head at different well chosen locations on the flanges. This leads to a very efficient lower energy screwing-in sequence of the pile and consequently to a high penetration rate. A test loading program of instrumented O-piles has been carried out in order to evaluate the load settlement behaviour, the shaft and tip capacity of the O-pile, including its specific installation parameters.

Jan 1, 1996

By Ronald D. Boyer

"Early in the design stage of Meadowlands Xanadu, the client’s project director informed me that “after construction, nobody is going to come to Xanadu to see the foundations.” My response was, “Well, that’s good, because the only reason someone would come to see the foundations is if there is a problem with them.” The client’s real message was clear: the money for the project would be better spent on architectural design components and interior finishes that would attract high-end tenants and entertainment seekers. The foundations, however, were challenging. The sheer size of the Xanadu development, the varying depths to rock, the loading conditions associated with the different structures, and the construction sequencing required the use of multiple deep foundation types and specialty foundation contractors. Xanadu, when completed, will consist of over 2.5 million sq ft of entertainment venues, restaurants and retail stores; America’s first i n d o o r s n o w dome; North America’s tallest (287 ft high) Ferris wheel; and four parking decks. Finished grades for Xanadu were essentially within about 1 to 2 ft of existing grades at the site, except for a 5 acre wetlands area, which received about 8 ft of new fill. Before the current construction, the approximate 75-acre Xanadu site was occupied by the Continental Airlines (now Izod) Arena, on-grade parking lots and the wetlands area. The Arena property is part of the New Jersey Sports and Exposition Authority (NJSEA) Meadowlands Sports Complex, which also includes Giants Stadium and the Racetrack, and is located in East Rutherford, N. J. Subsurface ConditionsThe site subsurface conditions include fill materials underlain by organic silt and peat (former marsh deposits or “meadowmat”), varved clay, glacial till and shale bedrock. The Xanadu site had been a marsh until the Sports Complex was created by filling in the early 1970s. The fill consists of dredged materials from Lower New York Harbor imported by hydraulic pipeline from the Hudson River. The fill also includes “historic fill,” defined as nonindigenous material deposited to raise the topographic elevation of a site, such as construction debris and other nonhazardous solid waste, and was generally encountered in thicknesses ranging from 8 ft to 18 ft. Within the previously developed portion of the site, a layer of marsh deposits consisting of peat and organic silt was encountered beneath the fill in thicknesses ranging from two ft to seven ft. Within the existing wetlands area, the marsh deposits were up to 10 ft below existing grade. The varved clay stratum was six ft to 36 ft thick. The depth to shale rock increases from approximately 15 ft near the west side of the site to approximately 80 ft near the south side. Groundwater was tidally influenced and varied from about 6 to 12 feet below both existing and proposed grade."

Jan 1, 2009

By Zhou Haizuo, Diao Yu, Zheng Gang

"The conventional design method for the embankment supported by DM columns usually assumes the simultaneous failure of all the columns. However, the progressive failure may occur in practice, especially considering that many researches have justified the critical load of DM columns is bending moment. In this study, a finite difference method was adopted to simulate the embankment on soft clay improved by DM columns. An increasing surcharge was applied on the embankment surface to investigate the mechanism of the progressive failure of columns beneath embankment. To capture the brittle bending failure of the DM columns, the model employed a cut-off method, in which the column was separated on failed section as long as the ultimate bending failure was reached. Furthermore, high-strength DM columns were used to enhance the global stability of embankment in this study. The numerical results showed that the ultimate bending failure was first reached at the column beneath embankment toe, and then a continuous collapse extended to the column beneath the embankment shoulder. It is found that the reinforcement could be obviously effective when the reinforced area of high-strength DM columns was extended to a certain area.INTRODUCTIONDeep mixed (DM) columns have been commonly used as a soil-improvement technique to increase stability and to reduce settlement of embankment. Research on failure modes of DM columns owing to embankment fill and surcharge has been the subject of interest for a number of investigators (Miyake 1991; Kitazume 2000; Han 2005; 2006).The potential failure modes of DM column include bending, inclination, shearing, rotating, soil flowing and a combination of these modes (Kitazume and Terashi 1991; Broms 1999). Many researchers have found that bending failure of DM columns was more critical than the shear failure. A centrifuge test was performed by Kitazume (2000) and the results showed that the columns failed in bending before shear failure. In addition, several numerical computations illustrated that design method using the shear strength overestimated the stability of embankment over DM columns (Han and Huang 2005; 2006; Navin 2006; Liu 2007; Wang 1996). In practice, an equivalent shear strength method based on bending failure could better reflect the stability of embankment (Zheng 2010; China Code JGJ79-2011)."

Jan 1, 2015

By Jon H. Gould

This paper describes the following at the new Advanced Solid Rocket Motor (ASRM) nozzle manufacturing facility, which is being constructed inside an existing manufacturing facility: 1) generalized subsurface conditions, 2) pile load test program and evaluation, 3) pile selection, 4) problems associated with pile driving operations, and 5) production pile installation. The poor subsurface conditions, known and unknown underground obstructions, and work environment inside the existing building, used to manufacture the Space Shuttle external fuel tanks, required special pile installation equipment, procedures, and work schedules to install the economical pile foundation system ahead of schedule and without a lost time accident. GEOTECHNICAL STUDIES In April and May 1990, 16 soil test borings were drilled inside the existing building with a truck-mounted drill rig. The borings extended to depths ranging from 60 to 65 ft (18.3 to 19.8 m) below the floor slab. Typically, the silty and clayey soils were sampled by pushing "undisturbed" Shelby tubes, and the more sandy soils were sampled by driving a Standard Penetration Test (SPT) split-spoon sampler. The unconfined compressive strength, water content, and unit weight of the Shelby tube samples were measured in the laboratory. A geotechnical report was issued in May 1990 presenting the results of the field and laboratory testing and foundation recommendations (Gilbert, 1990).

Jan 1, 1992

By Muhannad T. Suleiman

Temperatures below freezing significantly enhance the soil shear strength and stiffness and to a lesser extent increase the compressive strength of concrete as well as the yield and ultimate strength of reinforcing steel. Consequently, the lateral load resistance of bridge columns supported by drilled shafts becomes dependent on seasonal weather conditions. To investigate the effects of seasonal freezing on the behavior of bridge columns supported by drilled shafts, large-scale field lateral load tests were conducted at 23°C (73.4°F) and -10°C (14°F) on two identical units at an field test site, which consisted of glacial till soil classified as low plastic clay. The bridge column-drilled shaft systems were subjected to cyclic lateral load with the maximum lateral column top displacements reaching approximately ±30 cm (±11.8 in.). The soil at the test site was characterized at different temperatures using unconfined compression tests in the laboratory as well as in-situ Cone Penetration and Pressuremeter Tests. Using these test results, the lateral load behavior of the column-drilled shaft systems were analyzed utilizing numerical models that consisted of beam elements representing the concrete column and the shaft and lateral springs representing nonlinear p-y response of soil. This paper focuses on comparing the calculated responses of test units with different p-y curves that were developed for the soil near the ground surface using the laboratory and in-situ tests. From the experimental study, the response of the unit tested at -10°C (14°F) was found to show 44% increase in lateral force resistance and 0.84 m (2.76 ft) upward shift of the maximum moment location compared to the response of the identical unit tested at 23°C (73.4°F). Theoretical behavior that included the temperature effects on soil, concrete and steel properties provided good correlation with the measured responses when the soil near the ground surface was modeled using the unconfined compression test or the Cone Penetration Test data, but not the Pressuremeter test data.

Jan 1, 2006

By Mary Ellen Bruce Large, Antonio Marinucci, Silas C. Nichols

Tip post-grouting of bored pile (drilled shaft) foundations refers to a method where cementitious grout is injected beneath the tip of a shaft to improve the overall performance of the constructed foundation. This technique, when performed satisfactorily and in the appropriate ground conditions, enhances axial load-displacement performance by improving the mobilization of pile’s resistance. Potential benefits associated with tip post-grouting include reduced settlement under loading, better alignment of load transfer curves, and improved ground beneath the base of the bored pile. However, to be able to realize the benefits attributed to this method, the design, construction, of both the bored pile and the post-grouting system must meet a minimum level for quality assurance. The various factors affecting the successful installation and performance of a bored pile (e.g., workmanship, base cleanliness, borehole integrity, and concrete placement) have been discussed by numerous practitioners and researchers in the available technical literature. For a conventional (i.e., ungrouted) bored pile, acceptance is based on a combination of visual inspection, material testing, and the results of integrity and/or performance testing of the constructed pile. A properly executed tip post-grouting program can be a relatively comprehensive and complex process, which is typically evaluated throughout the construction process based on the results of prior projects and/or on test pile(s) at the particular site. For tip post- grouting programs, verification procedures and acceptance criteria should be established during and incorporated into the design process to ensure design intent and objectives are achieved. Project specifications should be produced to ensure performance requirements are achieved. This paper will present and discuss factors affecting the successful execution of tip post-grouting, including grouting criteria, instrumentation, reliability and uncertainty with the method and outcome, and verification and acceptance. INTRODUCTION Constructing bored piles (drilled shafts) is increasingly more challenging given the lack of ideal site locations, tight project site confines, difficult or restricted access, greater demands on drilling equipment, and close proximity to adjacent structures. To evaluate the feasibility of bored piles as an appropriate foundation system, a myriad of factors is evaluated during design, including site conditions and constraints, budgeting and scheduling, reliability and risk exposure, presence of and depth to adequate load bearing soils/rock, and the magnitude of the imposed loading. Moreover, updated design codes increased load demand per element, and improved material strengths have led to more complex foundation designs, larger foundation elements, and significant increases in load magnitude. Monopile (monoshaft) foundations have been utilized where one large bored pile is used in lieu of a group of piles connected via a pile cap. In addition, to accommodate the design criteria, site conditions, and imposed loading, the geometry of the bored piles being designed and installed have been as large as 13 feet (4 m) or greater in diameter and to depths in excess of 260 feet (80 m).

Jan 1, 2018

By Adnan A. Malik, Tadashi Maejima, Jiro Kuwano

"Previous studies revealed that the helix deflection reduced the end bearing capacity of screw pile in dense ground even if the installation process is completed with minimal soil disturbance. The ultimate end bearing capacity in dense ground is difficult to achieve during the full-scale pile load test due to the limitation of the loading system. Therefore, in the present study, model scale of testing is selected to investigate the effect of helix deflection on load settlement behavior of single helix screw pile under increasing stress level. It is observed from the test results that the applied surcharge pressure, which is used to simulate the effect of stress level, is decreased with increase in model ground thickness. This decrease in the stress level is due to the frictional resistance between the container wall and sand. It is also observed that the end bearing capacity of screw pile increases with the increase in stress level but at gradually decreasing rate. The test results indicated that the helix deflection during the pile load test should not be more than critical deflection (0.72 mm average) of the helix to avoid any reduction in the end bearing capacity of screw pile. The helix deflection, which is measured after the pile load tests are also compared with the equations of flat circular plate having uniformly distributed load over the plate with simply supported and fixed inner edges.INTRODUCTIONThe screw pile consists of a central steel shaft with one or more helices attached at different location on the central shaft. The installation mechanism of screw pile consists of torque and pushing force. The screw pile installation mechanism can affect the unit weight of the ground during its installation. This effect is small in cohesive soils but it is quite noticeable in loose to medium dense sands (Adams 2011; Santos et al. 2013). The pushing force should be controlled in such a manner that pile penetration should be at least 80% of the pitch of the helix, during each revolution (Perko, 2009)."

Jan 1, 2017