Search Documents

By Maurice Bottiau

It is a quite challenging objective to aim at covering in one paper the most recent evolution in piling and deep foundations technologies. This report has to be understood within the limits of the session 2b. It will therefore concentrate on the technological evolution of deep foundation techniques, addressing design issues only when directly related to execution aspects. For the same reason, it will not address the related codes, as a separate session of this conference is specifically dedicated to this topic. Monitoring and deep excavations being covered in other sessions, they will only be addressed when clearly relevant. We will try to show, from a practical viewpoint what are the main changes and the most exciting or critical issues over the last years, as they appear from the topics addressed in the literature or in the papers published in this session of the conference. As the paper mostly intends to explain trends and critical topics, it cannot be exhaustive, neither can it give the full description of the case studies. The author invites the reader to read the full papers, for a more complete description. We have divided our report in three main topics: Piling, soil improvement and treatment and retaining walls. Anchors and tie-backs will not be treated, neither tunneling.

Jan 1, 2006

By T. G. Davies

The paper presents design equations for singly laterally loaded piles embedded in sand. These equations were obtained from a comprehensive nonlinear analysis of free and fixed head piles subjected to horizontal loads. The sand is modelled as an elastic-perfectly plastic material whose strength and stiffness are proportional to depth below ground level. The soil's response is described by means of a boundary element representation of the continuum while the pile itself is created as an elastic beam. Equations for the latter are derived directly from the Bernoulli-Euler theory and are coupled with those describing the non-linear soil response. The effects of bearing failure along the front, face of the pile, shear failure along its sides and tension failure at the back face are accounted for in the analysis. Simple equations are presented to describe both the elastic and inelastic responses. The only sol parameters required to use these equations are the angle of internal friction of the sand and a parameter characterizing the rate of increase of the sand's modulus with depth. The latter can be taken as equivalent to the modulus of subgrade reaction. The results of this analysis show that soil yielding is very significant at working load levels, resulting in substantial increase in bending moments and lateral deflection.

Jan 1, 2010

By Abhijit R. Sheth, Craig M. Benedict, John Brun, Ara G. Mouradian

"Amtrak recently replaced the 1907-era bascule two-track bridge over the Niantic River between East Lyme and Waterford, Connecticut. The project included new approach embankments, with approximately 2,500 lineal feet of retaining wall along the west approach and 780 lineal feet of retaining wall along the east approach. The paper focuses on the design and construction of the east approach retaining wall, whose alignment is directly adjacent to an existing wetland area which required protection. An anchored prestressed concrete sheet pile retaining wall was selected for the east approach. A combination of concrete anchor piles and ground anchors were used to support the wall. The design of the wall took into account two simultaneous train live loads, support of electric traction catenary structure foundations, and construction live load, while at the same time preventing permanent impacts to the adjacent wetlands. The design considered challenging subsurface conditions, shallow groundwater, the close proximity of the existing operating tracks, construction staging, and storm surge events in Long Island Sound.INTRODUCTION AND PROJECT HISTORYThe National Railroad Passenger Corporation (Amtrak) recently replaced the 1907-era bascule two-track bridge (No. 116.74) over the Niantic River, between East Lyme and Waterford, Connecticut, along the heavily-traveled Northeast Corridor (NEC). The two NEC tracks, which carry over 50 trains per day, run east-west over a narrow spit of land known as “The Bar”, which separates the Niantic River’s marine estuary to the north from the Niantic Bay to the south, before crossing the river. The bay is an arm of Long Island Sound and is occasionally subject to storm surge from hurricanes.The 1907 bridge was built as a replacement for the previous 1891-era swing-span bridge, and was constructed parallel to, and 49 feet north of, the swing-span structure. The two-track 1907 bridge consisted of a single-leaf bascule span and four approach spans supported on stone masonry piers and abutments. The new bridge increases horizontal navigational clearance for marine traffic in the river from 45 feet to 100 feet, and vertical clearance from 11.5 feet to 16 feet above mean high water with the bridge in closed position. The new bridge, constructed 58 feet south of the 1907 structure, features a single-leaf bascule span of 141.5 feet, with an approach span on either side."

Jan 1, 2017

By Ruth McKeown, Gilson de F. N. Gitirana, Murray Fredlund, HaiHua Lu

The current design standards for the use of anchors in slopes is based on two-dimensional (2D) limit equilibrium analyses. Anchors are considered as discrete loads and the 2D anchor, factored based on the spacing distance, corresponds to extending anchors indefinitely in the third dimension. A three-dimensional (3D) analysis offers a more realistic representation of the problem, including the true discrete nature of the anchor point loads. This paper explores the typical differences between analyzing anchors in 2D and 3D, using four typical conceptual models. Slopes with constant cross sections were shown to be adequately represented by the traditional 2D approach. The maximum difference between 2D and 3D models was 21% and becomes negligible for lower anchor spacing values, as expected. A slope with an external load was analyzed to evaluate critical slip surfaces with lower aspect ratios. Slip surfaces with lower aspect ratios presented higher edge effects that contributed to the stability of the slope. The results indicate that optimum design requires the 3D evaluation of field conditions inducing low aspect ratios, such as concave and convex surfaces, weak layers, and external loads. INTRODUCTION Slopes may be stabilized using a variety of solutions, including anchors. When performing an analysis, geotechnical engineers often follow the traditional two-dimensional (2D), Limit Equilibrium Method (LEM). It is important to understand the consequences and limitations of the assumptions on which the 2D LEM is based. There are numerous studies on anchors that show the importance of considering the actual three-dimensional field conditions. Desai et al. (1986) proposed a three-dimensional procedure based on the Finite Element Method and considering elastoplastic behavior and interface elements, to account for stress and displacement distributions, the relative motion between the anchors and the soil mass, and nonlinear soil behavior. Several important stabilization mechanisms were explained. The role of grout injection was evaluated in terms of the produced normal stresses along the anchor-soil bounding surface. The approach was shown to reproduce adequately experimental tests on a sand, proving realistic stress distributions around the anchor. Nonlinear soil behavior influenced to a large extend relative interface motions. Michalowski (1989) applied an upper-bound limit analysis in 3D to slope stability analyses. Anchors were not specifically considered in this study, but the consideration of locally loaded conditions shed light on important modeling aspects. The manner how the slide mechanism becomes three- dimensional as the slope is locally loaded was demonstrated. This emphasizes the fact that anchors should produce field conditions that require 3D analysis approaches.

Jan 1, 2019

By Walter G. Brusey

This paper describes a comprehensive pile test program conducted at John F. Kennedy International Airport (JFKIA) to evaluate pile types and design capacities ranging from 890 to 4450 KN (100 to 500 tons). Driven cased piles and drilled shafts, both standard construction and post-grouted after installation, were tested with platform loads extending to 8900 KN (1,000 tons). Alternate load test procedures were developed, extensive structural integrity testing and dynamic load tests were performed on selected shafts. A brief update is provided covering the application of results of the test program to pile selection for support of major structures incorporated in the on going redevelopment of JFKIA.

Jan 1, 2000

By Walter E. Vanderpool

Three drilled foundations for an elevated water-tank were instrumented, tested and monitored during construction and the first two years in service. One shaft was load tested by the Osterberg method. A void was detected in one shaft by cross-hole sonic logging, pulse-echo logging and concrete coring. The void was instrumented, hydrostatically tested and pressure grouted. The shaft was ?abandoned? and replaced by two smaller shafts with a straddle beam cap. One of the replacement shafts and the cap were instrumented. The strain that appeared in the abandoned shaft, the replacement shaft and the cap were monitored during the remainder of the construction, through the commissioning test and the first two years of service. The results demonstrate the precision and sensitivity of the vibrating wire strain gage.

Jan 1, 2004

By Richard T. Stain

"In 2001, a pile trial site was established at Limelette in Belgium consisting of 25 displacement screw piles and 5 driven pre-cast piles. Interested parties were invited to participate in a pile prediction event, whereby they would submit predicted static load test behaviour in the form of load settlement plots. These predictions could be based on soil investigation results supplied by the organizers, or dynamic load test measurements.Following the submission deadline, the organisers released the results of static load tests for comparison.Of all the six participants, including Statnamic, the SIMBAT method was independently accredited with achieving the best predictions.This paper examines at the differences between SIMBAT and other systems, and presents the correlations from the Limelette trial.INTRODUCTIONThe Belgian Building Research Institute (BBRI) initiated an ambitious research programme involving the construction and testing of some 60 trial piles spread between two sites, a clay site at Sint Kateline Waver and a sandy site at the BBRI headquarters at Limelette. The project was financed largely by the Belgian Ministry of Economic affairs. (ref 1.) This paper refers only to the second site.At Limelette, six different types of displacement pile were installed: one driven pre-cast and five cast in place screw piles - Atlas, DeWaal, Fundex, Olivier and Omega. A detailed site investigation was carried out including in-situ and laboratory tests.An international pile capacity prediction event was publicised, participants being invited to predict static pile behaviour. Predictions could be based on:"

Jan 1, 2005

By Anil Bhandari

Using subsurface data collected at each drilled shaft location is an ideal approach for conducting drilled shaft design. However, conducting subsurface tests at each drilled shaft location and subsequently performing the drilled shaft design can be a daunting task for a noise barrier wall that is divided into six (6) sections and stretches for approximately four (4) miles. In addition, having individual drilled shaft designs complicates the construction process. Grouping the subsurface conditions into broad categories and performing the design for each of those categories is an attractive alternative to the design per boring approach. Currently there are no existing guidelines to aid a designer on grouping the subsurface conditions for the drilled shaft design for the noise barrier walls. Therefore, a method was developed based on the Standard Penetration Test (SPT) N values of the near surface soils to categorize the soil profiles into distinct categories. Since the soil engineering properties of the near surface soils are known to be critical for drilled shaft lateral capacity, these soils were emphasized in the methodology. This method was successfully implemented for the design of drilled shafts supporting the noise barrier walls along the I-20 in Columbia, SC. For this project, two distinct soil profiles, labeled as ?strong? and ?weak?, were used. An overview of the soil profile grouping methodology is presented as well as the vertical and lateral drilled shaft capacity analyses for this project for the two general soil profiles. The analyses indicated that the axial capacity governed the design in the ?weak? soil profile and the lateral capacity controlled the design in the ?strong? soil profile. However, this is not a generalization and whether the axial or the lateral capacity governs the design of drilled shaft depends on the soil profile and design loads. Nonetheless, our findings emphasize that both lateral and axial capacity should be checked for drilled shaft design even when the vertical load are minor.

Jan 1, 2011

By Nino Catalano, Meeok Kim, Gordon Chen

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

Jan 1, 2017

By Armin W. Stuedlein, Steven R. Saye

The differences between calculated axial pile capacity and the capacity realized during and following installation has long presented a significant concern for foundation engineers and contractors. Such differences have increased in prevalence with the increased use of larger diameter steel pipe piles and the significant increase in design-build contracting. The writers present concepts to close the gap between calculated axial pile capacity and the capacity realized during and following installation of driven pile foundations, including: (1) pile set-up in plastic soils, (2) limitation of re-driving of piles after setup which serves to reduce pile capacity, (3) the use of a vibratory hammer to install piles in cohesive soils disturbs the supporting soils and reduces the pile side resistance capacity significantly, and (4) long pile installation times for open-ended piles can damage the pile side resistance. Examples are presented from practice to illustrate these concepts and to guide pile installation planning to recognize the installation impacts and either consider alternate installation approaches or to properly consider the installation impacts during design.

By Mario Aiezza

This paper outlines the results of a relationship developed during the design and construction of the foundations for the Gallery Towers project in Melbourne. Both the builder and the piling contractor were determined to arrive at a satisfactory foundation solution to the problems encountered at the site. The scope of piling work was to provide load-bearing piles under the building columns, some of which were located within a retention system that also required a piling solution. Geological conditions were variable and challenging. The site area was small and located adjacent to the National Arts Centre in the developed Southbank area, a high density office area. This presented logistical problems in limiting construction traffic on site and also demanding minimal noise and vibration emanating from piling activities. The piling contractor, Vibro-Pile, and the builder, Walter Construction Group, faced the challenges presented with a refreshing cooperative attitude that was beneficial to both companies. Commercial issues rising from design and construction problems were first put apart in order to allow the respective technical department of each company to work with minimum constraints to achieve the most cost effective solution. In the process usual adversarial attitudes resulting in loss of time and money was avoided. A number of issues were addressed successfully at minimum cost and time during this contract. Despite the difficulties encountered, the job was completed on time and with negligible claims for extras, resulting in the development of a strong mutual respect between both companies.

Jan 1, 2002

By Martin B. Hudson, Andrew K. Cho, Rolff B. Knobel, Les R. Chernauskas, Jonathan L. Ernst

ABSTRACT The Bruce Museum, located in Greenwich, Connecticut, is home to an extensive display of art and natural history exhibitions. A large addition was designed to be constructed adjacent to the museum requiring new spread footings to be installed up to 16.5 feet below the existing foundations. The soil conditions at the site consist of highly variable sand and gravel overlying weathered rock and sound bedrock. The Contract Documents called for traditional foundation underpinning. Traditional underpinning techniques, however, presented two major challenges on this Project; (1) deep underpinning pits would be required involving multiple levels and staging with tieback support and (2) the highly variable soil and bedrock composition and elevations presented uncertainty in the design and construction of the pits. In lieu of traditional underpinning, Geosciences Testing and Research, Inc. (GTR) proposed an “active” soil nail underpinning system. A major reason that the soil nail underpinning option was feasible, related to the fact that the soil nails and facing could be installed slightly in front of the existing footings rather than directly underneath the existing footings. The soil nail wall design involved one to four rows of soil nails with nail positions and wall depth able to be adjusted “on the fly” as excavation progressed depending on the field conditions encountered. To create the “active system,” the soil nails were pre-loaded to mitigate wall deformations that would be associated with a standard passive soil nail wall design. To evaluate the performance of the active soil nail wall and confirm design assumptions, an extensive automated monitoring, on-site testing and inspection program was proposed and executed by GTR to monitor deformations of the wall and the museum in real-time, evaluate and confirm bedrock and soil bond stresses and ensure that each soil nail was pre-loaded and locked off. Careful analysis, planning, and use of the observational method illustrates the importance of collaboration between design and construction personnel and applying engineering judgement throughout construction. The use of the observational method includes the potential for modifying design based on conditions observed. This paper presents a unique case study of the “active” soil nail underpinning system to support and protect sensitive structures, close collaboration between design and construction facilitated by real-time deformation monitoring, and its successful application as a safe and cost-effective alternative to traditional underpinning.

Oct 1, 2022

By Dean E. Matthews

The concept of a pile for construction is credited to a Neolithic tribe called the "Swiss Lake Dwellers" who lived in what is now Switzerland about 6,000 years ago. They used piling, not for supporting heavy loads as we do today, but for elevation to protect themselves from wildlife. The Romans often used piles, and built many structures, including buildings, homes, bridges, roads and viaducts on piling. The Romans built the first bridge across the Tiber River in Rome on timber piles in B.C. 1620. Homes in the cities of Venice and Ravenna were built on piles from B.C. 100 to A.D. 400. The Romans also built the first bridge across the Thames River in London in A.D. 60 on timber piling.

Jan 1, 2003

By Jorj O. Osterberg

The Osterberg (O-Cell) Method makes it possible to separate the side shear resistance (skin friction) from end bearing. The O-Cell is placed on or near the bottom of a drilled shaft and after the concrete is poured and cured, an equal upward and downward pressure is applied. From the test, the load-upward deflection curve in side shear and the load-downward deflection curve in end bearing are drawn. Typical curves are shown where the ultimate load in side-shear is reached and where the ultimate load in end bearing is reached. Several examples of tests in which the test load reached ultimate loads far in excess of what was expected are shown. The side shear in rock sockets is shown to be much larger than generally estimated. Examples are given of where side shear is smaller than expected and the reasons discussed. Disturbance of the sides of drilled holes due to poor construction techniques and ways to avoid these conditions are considered. Examples of bottom hole disturbance are given and ways to prevent the disturbance are discussed. A graph showing the actual measured capacity of drilled shafts compared to the estimated capacity as a function of the hardness and strength of the soil or rock is presented.

Jan 1, 1999

By Antonio A. Cristóvão, Alexandre Pinto

"Abstract Deep foundations of buildings using driven ductile iron micropiles TRIM solutions, leads to recognized advantages, from technical, schedule and economic points of view. High production rates together with the possibility of using conventional equipment, duly adapted, confer this solution a high versatility.The aim of this paper is to describe the main design criteria adopted for the foundations of the Church ""Nossa Senhora dos Navegantes"" building in Lisbon - Portugal. In addition, results of a full scale load test carried out at site are presented, confirming the adequacy of the solution to the geological and geotechnical scenario, which is characterized by the proximity of the Tagus River Basin as well as the presence of heterogeneous landfill material and alluvial layers of soft clay (muds).1. INTRODUCTION Located on the right bank of the Tagus River, in Lisbon, the new Church building of ""Nossa Senhora dos Navegantes"", patroness of fisherman and navigators, with three or four upper floors, is surrounded by a school and by new residential buildings.The Tagus River basin is known by its alluvial soft soils, achieving, in certain areas, more than 50m meters depth, challenging the construction of new facilities due to the significant unfavorable geotechnical conditions.With a modern an unusual architecture, allusive to the ships used by the Portuguese navigators, the building has a reinforced concrete structure, with one basement and three upper floors. A bell tower with about 40m high, emerging from the structure, marks the landscape with the presence of this religious building (figure 2).For all the reasons previously described, geotechnical engineers play a crucial role on the design of valid foundation solutions, from both technical and economic point of view. Ideally, the solutions adopted should be supported by full scale load tests, performed at site, so that design assumptions could be verified and adjusted on time."

Jan 1, 2014

By W. Lum

In the U.S., flexible metal pipe culverts are designed by ring compression theory because the pipes are capable of deflecting and deriving side support from surrounding ground. For economy, tunnel liners are often designed as flexible structures that depend on the lateral pressure of the surrounding ground to maintain stability. In this paper, simple formulas are presented to determine the maximum deflection a concrete tunnel liner may assume and the ring compressive strength of the deflected liner. A tunnel can then be constructed to work within these limits. Similar techniques may be used to design concrete pipes.

Jan 1, 2010

By Anne Lemnitzer

Full-Scale cyclic field testing was performed on a 3x3 pile group consisting of nine cast-in-drilled-hole (CIDH) reinforced concrete shafts and a comparable single-shaft in order to investigate group interaction effects. Both specimens were constructed with pile diameters of d = 0.61m (2 ft), fixed head boundary conditions, and placed in stiff clayey soil at a test site near the LAX Airport in Southern California. Internal instrumentation was installed in the single pile as well as in three piles within the pile group to obtain pile curvatures. External instrumentation controlled the lateral displacement of the specimens. A combination of experimentally and analytically obtained p-y curves for the single pile was used to simulate results for piles located in the group when field data were not available. All test specimens were tested to structural failure and excavated after test completion to investigate pile damage and plastic hinge formations. Calculated group interaction factors ranged between 1.0 at very small displacement levels of <2.5 mm (0.1 in), 0.8 at the initiation of the pile-soil-pile interaction, i.e. between 4 mm - 15 mm (0.16-0.6 in), and increased towards 0.9 near structural failure (displacement >25 mm or 1 in). A literature set of p-multipliers was found to reproduce an accurate fit to the available load displacement test data from the group.

Jan 1, 2010

By Randy R. Huberty

Although originally designed with deep foundations consisting of all driven steel H piles and drilled caissons, a unique application of Augered Cast-in-Place (ACIP) piles as an alternate design resulted in a significant cost savings for the Midfield Terminal Project at the Pittsburgh International Airport. The project was enormous in scope covering an area two miles long by one mile wide, with changes in elevation of over 200 ft. The varying geology combined with the large amounts of fill required resulted in a complex set of geotechnical design parameters that had to be evaluated through both load testing and analyses. A total of almost 400,000 lineal feet of ACIP piles were installed for this project.

Jan 1, 2001

By A. Bozorgzadeh, B. M. Jensen, B. N. Koelling, B. R. Murtaugh

"The Service Base mooring system originally consisted of two general types of structures, 19 timber piles cabled together and steel three-legged pipe piles. The St. Louis District fleet moored to the fleet barges which were tied off to shore-side concrete deadman and supported on the landward side by the timber and steel piles. The purpose of this project was to replace the existing floating wharf mooring system at the St. Louis Service Base. The Marine Design Center of the U.S. Corps of Engineers developed a three pile cluster system concept. The clusters consisted of one vertical pile and two batter piles. Piles in rock sockets were selected to resist the uplift loads due to high wind loads on the tall, spare lock gates stored at the floating wharf. This paper focuses on the design of the rock sockets for steel pipe piles with large uplift loads and the lessons learned during the design and construction of this system.INTRODUCTIONBackgroundThe U.S. Army Corps of Engineers’ St. Louis District is located at the critical transition point on the Mississippi River where it is a “locking river” north of St. Louis and an “open river” to the south. The St. Louis District is responsible for maintaining navigation channels on the Mississippi River, the Illinois River and the Kaskaskia River. It is also responsible for the operation and maintenance of five locks and dams within its geographic boundaries.The St. Louis District utilizes a fleet of vessels (dredges, crane barges, motor vessels, and barges) to support the navigation mission identified above. The St. Louis District Service Base, located in St. Louis, Missouri, serves as the base of operations for the district fleet. This riverfront facility originally consisted of a floating wharf, a railroad trestle, and a walkway down the river bank to the floating wharf. Historically, there have been two fleeting areas at the Service Base. The main fleeting area was approximately 965 feet long and consisted of six fleet barges (Figure 1). This area supported the Dredge Potter and its attendant fleet. The upper fleeting area was approximately 1,050 feet long and consisted of various stop log, crane and work barges, dredge pipe pontoons and work flats."

Jan 1, 2017

By Hubert Law, Dan A. Brown, Kyle M. Rollins

"Soil mixing and jet grouting provide a means to significantly increase the lateral resistance of pile group foundations with relatively little investment of time, effort, and expense compared to the cost for additional piles necessary to produce the same increased resistance. Comparative field testing conducted on full-scale pile groups before and after treatment of small soil volumes showed significant improvement in lateral resistance. The lateral resistance of the pile group increased by 60% due to soil mixing and by 180% due to jet grouting. To provide additional understanding regarding the influence of the soil mix strength, depth of improvement and width of improvement, a series of parametric studies were performed using a 3D finite element model. This set of “virtual load tests” was then combined with the results from the actual field tests to help develop a simplified model to account for observed behavior. In general, the testing and analysis indicate the pile group and the surrounding improved soil block generally act as an equivalent “super pile”. The passive force, side shear and base shear on the improved soil surrounding the pile group itself increased lateral resistance. This increase in resistance from the soil block can be added to the lateral resistance of the pile group.INTRODUCTIONThe lateral resistance of pile groups is often critical to the design of bridges and high-rise structures subject to seismic, wind, wave and landslide forces. Typically, when analyses indicate that the lateral resistance of a foundation is inadequate, additional piles, drilled shafts or micro-piles are added to increase the lateral resistance. Furthermore, an expanded pile cap or connecting beam is often required to structurally connect the new piles to the existing pile group. While this approach provides the required lateral resistance, it may also be relatively expensive and time consuming. An alternative approach is to use soil improvement techniques to increase the strength and stiffness of the surrounding soil and thereby increase the lateral resistance of the pile group. The improved zone could potentially be relatively shallow because the lateral resistance of piles is typically transferred within 5 to 10 pile diameters. For example, the soil around the periphery of the foundation could be relatively easily improved for an existing foundation as illustrated in Fig. 1(a) using a variety of soil improvement techniques. Alternatively, the soil under the foundation could be improved for a new foundation or even for an existing foundation with a technique such as jet grouting (see Fig. 1(b)). Improving the soil under the foundation would have the potential for producing greater increases in lateral resistance because the improvement would reach interior piles. In addition, the process of creating a cemented “soilcrete” zone around pile foundations could potentially produce a zone which would behave like a reinforced “superpile” with increased structural stiffness."

Jan 1, 2015