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

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

By Ali Ebrahimi, Meena L. Viswanath, John F. Beech, Mustafa B. Erten, Ming Zhu

"Excessive deformation of a cantilever sheetpile wall can occur due to dredging, excavation, backfilling, or long-term creep behavior of soil. A buttressing berm constructed in front of the wall can be considered as a mitigation technique to prevent or decrease the deformation by increasing the passive earth pressure and thus improving the wall stability. The effect of the buttressing berm on the stability and deformation of a sheetpile depends on the berm geometry (i.e., the thickness/depth and the width) as well as the properties of the sheetpile and the adjacent soils. A parametric study was conducted using a conventional limit equilibrium method. Design charts were prepared to evaluate the effect of a buttressing berm and the soil friction angle on the wall stability and deformation. These charts can be used as a tool by geotechnical engineers to make a quick estimate of the required size of a buttressing berm in case of calculated or unexpected excessive deformation of a sheetpile. An analysis of the effect of a buttressing berm on the stresses and deformation of a sheetpile was also compared with the results from finite element analysis. The results of this comparison are discussed.INTRODUCTIONCantilever sheetpile walls are commonly used to support excavations. Sheetpiles are hot rolled or cold formed sections of steel made to interlock with adjacent sections to form a continuous structure providing lateral support. Sheetpile walls can be cantilever walls or anchored with tiebacks. To construct a cantilever sheetpile wall, sheetpiles are driven by pile drivers or vibrated in to a design depth sufficiently below the depth of excavation. Excavation can then proceed in front of the sheetpile wall, which resists the earth pressure loading from behind the wall. The design depth and geometry of the sheetpile wall depend on the soil conditions, the depth of excavation, and the tolerable deformation. In certain cases, when a small buttress of soil can be left immediately adjacent to the sheetpile wall, the required depth or geometry of the sheetpile wall can be reduced or adjusted, which can significantly decrease the cost of procuring and installing the wall. Such a buttress can also serve as a short-term or long-term remedy in case of observed excessive deformation in a constructed wall. Traditional methods of analyzing the stability of a sheetpile wall do not account for the passive pressure effects of this small buttress. In this paper, a parametric study was performed for a variety of soil types and wall and buttress geometries by implementing traditional limit equilibrium methods in commercial software and design charts were created illustrating the effect of a buttressing berm on sheetpile deflection. Selected cases were then modeled in a finite element software to compare the results with the traditional limit equilibrium method. The resulting design charts can be used as a tool by geotechnical engineers looking to reduce the design geometry of a sheetpile wall or address observed excessive deformation in a constructed sheetpile wall."

Jan 1, 2016

By Larry Rayburn

Design of cost effective engineered solutions to complex problems requires the team efforts of the owner, the designer and the specialty construction contractor. The basic ingredients of success required to remain competitive and still produce a quality product are creative design based on experience and sound engineering principles, plus practical aspects of constructibility. The three case histories describe creative design/construct approaches that benefited all parties. 1. Introduction The increasing demand placed on specialty contractors to provide cost effective buildable solutions to complex construction problems compels us in the industry to be highly innovative. The practice of geotechnical engineering is considered more of an "art" than perhaps the other disciplines within civil engineering largely because of the basic nature and variability of soil and rock. The geotechnical design engineer must have the knowledge of the components of his design and know the limitations of his equipment and labor force. Thus, for the design/build specialty contractor the potential for creation of unusual solutions to difficult problems is quite high.

Jan 1, 1991

By Venkata Krishnaiah Yeddala, Sai Vivek Adari, Suresh Kumar Velugu

Assam cancer care foundation (ACCF) proposed the construction of hospitals and related facilities across 18 locations in the state of Assam-India. Tezpur is one among the 18 locations of Assam with high seismic risk. The strata at the site are comprised of mostly fine silty sands of lower SPT- N values. The water table is also encountered and ranging from 1 m to 2 m below EGL. Since the site lies in seismic zone V as per IS 1893, detailed liquefaction analysis is carried out for all five boreholes and indicates that soil is liquefiable and ground improvement is inevitable up to a depth of 15 m below existing ground level. To mitigate the liquefaction potential and enhance the seismic performance of the soil, ground improvement using stone columns by Wet top feed Vibro-replacement method is proposed. Also, the differential settlements can be avoided effectively under the raft foundation with Vibro Stone Columns. In this paper, field test validation results such as Pre and post-SPTs and ECPTs to access the extent of ground improvement, along with other information adopted in this project presented.

Nov 1, 2022

By Alan J. Lutenegger

Some years ago, a method was developed to incorporate a grout column around square-shaft helical screw-piles and anchors to increase shaft buckling resistance under compression loading. An additional benefit of this grouted shaft is to increase the load capacity in both compression and tension, depending on the geometry of the lead helical section and the soil conditions. Because of the unique construction procedure, the contribution of the shaft to the total capacity has largely been unknown. The behavior of grouted shaft helical anchors in clay was investigated by performing full-scale axial uplift (tension) load tests on a series of anchors installed at the University of Massachusetts Geotechnical Test Site. In order to isolate the contribution of the grouted shaft to the total load capacity, anchors were installed with a wooden dowel connection between the lead helical section and extension sections on three of the four anchors so that only the shaft resistance would be measured during the load tests. The grouted shafts ranged in length from 10 to 30 ft (3 to 9 m). Initial tests were performed approximately 5½ months after installation. Nearly four years after the initial tests were performed, the tests were repeated to evaluate any significant change in capacity with time and/or repeat testing (preshearing). The soil conditions at the site are presented along with the load-displacement curves for both the initial and repeat teats and a discussion of the analysis of the results. Repeat load tests showed an increase in capacity from the initial testing, however the percent increase was not the same for all depths. The results demonstrate that considerable shaft resistance can be developed in clays from the grouted shafts as might be expected. Depending on the L/D ratio of the shaft and the contribution of the lead helical section, at working loads the shaft capacity can dominate the behavior.

Jan 1, 2011

By Vijaya Bhushan Rao, Jason Redgers

The typical Vibrocompaction projects undertaken in the UAE are on reclaimed Sands. These Sands which are predominantly the crushable, calcareous, carbonate sands found locally as opposed to the more common quartz or silica sands that are featured in most design literature. The famous reclamations such as the iconic Palm Jumeirah in Dubai, often have specification for mitigation of liquefaction induced settlements, bearing capacity increases and total and differential settlement requirements. Often these performance targets are achieved by the means of achieving a particular relative density that are generally measured by a defined Cone Penetration Test, CPT targeting values of cone resistance (Qc), MPa at respective depth zones. In this paper some case studies are presented, where soil suitability for deep compaction by vibratory methods was firstly assessed for suitability using the Massarsch, 1991 compactability chart prior to the application of vibrocompaction and its subsequent evaluation. One such project named the Island Development required 17 to 23m depth of penetration only to treat the lower 5 to 6m of sand above rockhead as eventually the top 15m of sand will be further excavated to allow for the construction of basement. The paper will present pre and post CPT results, the results of initial site calibration trials and evaluation of the completed works.

Oct 1, 2022

By David A. Hart, Barry P. Osborn, Richard J. Totty, Ana T. Carvalho, Max B. Elliott

This paper addresses the experience designing and installing bored piles for the King’s Cross area. This includes continuous flight auger and rotary bored piles, with a range of diameters between 600 mm and 1200 mm, reaching a maximum depth of 56 m below ground level. Existing Network Rail Thameslink twin bored running tunnels are located directly beneath the subject plots. These tunnels have an external diameter of 6.6 m and the crowns of the tunnels are very shallow, in some cases just 10 m below the existing ground level. Some plots needed piles to be installed in close proximity to the tunnels, which required additional control measures and contingency plans. Pile verticality was monitored as the tip of each pile advanced and in-tunnel monitoring readings were verified and are presented. Lessons learned from designing, installing and testing the piles and monitoring the tunnels are addressed in this paper.

May 1, 2022

By Rouzbeh Vakili, Adel M. Hanna

"The application of piled raft foundations has significantly increased during the last few years. In this system, the raft and the pile group collectively transfer the applied building load to the underlying soil layers. Determination of load sharing between the raft and the piles derives the complexity of piled raft designs due to its multi-parameter nature. These parameters are but not limited to: soil density, pile length, pile spacing, raft geometry, and piles installation technique. This study is to examine experimentally the effect of sand density and pile installation techniques on the load sharing mechanism. Experimentally, tests were conducted on a square rigid raft with a single pile in sand under three different soil densities; 30%, 45%, and 60%. The experimental results are used to determine the pile and the raft shares in non-displacement and displacement piled raft systems. The results of this study reveal that soil density changes the load sharing of displacement piled raft; the pile share increases in higher soil density. However, this is not the case in non-displacement piled raft and load sharing is independent of soil density in working loads.IntroductionThe piled raft foundation is a combination of shallow and deep foundation which transfers the superstructure load to the soil by a complex soilstructure interaction. The interacting mechanism among foundation elements and their surrounding soil is illustrated schematically in Figure 1 and could be classified into two categories: (1) pile-soil-pile and (2) pile-soil-raft. The pile-soil-pile interaction is the same as the free standing pile group and is a function of pile spacing and pile installation method. Pile-soil-raft interaction, which only involves in piled raft foundation design, could be affected by: the length, spacing, and roughness of the pile, the rigidity and dimension of the cap, soil condition, and the pile installation method. Pile-soil-raft interaction could have favourable and unfavourable effects on bearing capacity and settlement, respectively. The pressure between the cap and the soil favourably increases the horizontal stress on the pile shaft and consequently increase the shaft resistance. Whereas, this pressure induces negative skin friction on the piles which increases the settlement. The pile-soil-raft interaction mainly controls the load sharing mechanism of piled raft foundation when pile spacing (S) is more than 3.5dp."

Jan 1, 2017

By Paul J. Axtell

This case history describes the foundation design and construction for the New Mississippi River Bridge, presently under construction in St. Louis, Missouri. The 1,500 ft (457.2 m) main span of the cable-stayed bridge is supported by two delta tower pylons in the river, with anchor piers on each bank. The final foundation design was completed as a part of an Alternate Technical Concept (ATC) proposal by the winning construction team, and utilized drilled shafts up to 11.5-ft (3.5-m) diameter that were socketed into very hard limestone. As part of the ATC foundation design, a full-scale, bi-directional static load test was performed to verify the design and allow use of higher resistance values. This paper presents the results of the site exploration, construction of the load test shaft, details of the load testing, and a comparison of the test results with various design parameters.

Jan 1, 2011

By Bernardo J. Jiménez Vega, Edy L. T. Montalvan PhD

The experience gained during more than 900 Crosshole Sonic Logging (CSL) tests on drilled shafts shows the importance of establishing proper project acceptance and repair protocols. Drilled shaft evaluation is a multidisciplinary task that should not be left solely to the outcome of the CSL test. This test allows to characterize and delimit areas of different qualities of concrete, and it is important that all the interested parties understand the difference between flaws and defects. The information presented here is intended to give a guideline to contractors, inspectors, engineers, owners and clients on how to deal with acceptance and remediation of defective drilled shafts, detected using CSL tests. A database of flaws is presented depending on their location, intensity and remediation method. Procedures that allow the flaws to be analyzed are presented in order to dismiss or classify them as defects. In many cases, the CSL test may indicate an anomaly, but by coring the concrete and analyzing the structural demands and conditions, the flaw can be classified as non-severe. When flaws are classified as defects, their repair will depend on the area where they are located in the drilled shaft pile. In this document two procedures are described for repairing defects depending on their location. For defects in the drilled shaft head area, the procedure takes into account the interaction between the new and old concrete. For repairing the middle zone of the drilled shaft by grouting, the major concerns are the difficulty of accessing through the drilled shaft at deep depths and the communication between boreholes. For defects at the drilled shaft tip, two proposed remediation methods are presented. Finally, tomography tests are presented to compare the effectiveness of remediation by grouting.

Oct 1, 2022

By Piotr Kozlowski, Stanley L. Worst, Matthew J. Niermann

The Waterman Hospital in Tavares, Florida was undergoing an expansion and required a below-grade excavation immediately adjacent to the Emergency Department. This wing of the hospital was under high traffic and required uninterrupted access for ambulances as well as helicopter landings. The below-grade expansion was also next to a part of the hospital which did not have a basement. Tiedback soldier beams and wood lagging were used as the earth retention system where the shoring line was not immediately adjacent to the existing structure. Structural jet grout underpinning was used to support the existing building and to serve as the earth retention system in the more sensitive area. Jet grout underpinning was chosen to minimize movements, loss of ground and settlement of the structure which was bearing on clean sand deposits. This paper will discuss the design, quality control and construction of jet grouting and its application to this project. INTRODUCTION Project Background The expansion of the Waterman Hospital included an addition to the Emergency Department. This addition was located adjacent to the existing hospital building in a congested area with limited access. The north side of the addition was bordered by the ambulance drop-off area. The south side of the addition was bordered by the helipad landing area. Both areas had to remain open and fully accessible 24 hours a day, 7 days a week.

Jan 1, 2019

By Douglas G. Baker, Jason K. Braund-Read, Megan R. Sheffer

"Mica Dam, owned by British Columbia Hydro, is an 820 ft high earthfill embankment dam that was completed in 1973. The dam consists of a thin central impervious till core supported by upstream and downstream compacted sand, gravel and cobble shell zones, founded on bedrock and valley bottom alluvium deposits. In 2012, a project was started to install new piezometric instrumentation within the dam’s foundation and downstream shell zone.Deep drilling in large embankment dams is very difficult and requires careful planning to select a methodology capable of reaching the target locations, while ensuring that no damage is done to the surrounding dam fill zones. At Mica Dam, the drilling could only be carried out from the Dam Crest and drillholes had to be carefully oriented to avoid intersecting any existing dam instrumentation. The drilling work therefore required angled drillholes, at depths of up to 855 ft, through heavily compacted sands, gravels and cobbles, and to significant depths below the standing water table.During the planning stages for the Project, in early 2013, the preferred drilling method was selected and a drilling contractor was engaged for the drilling work. Critical dam safety concerns were identified and addressed during the design stage of the Project with the drilling contractor, so that risk mitigation measures and response plans could be effectively developed.This paper explains how background information and prior drilling experience influenced the final design and implementation of the drilling techniques used in 2013 to successfully drill the deep holes and carry out the piezometer installations in Mica Dam. Drilling procedures, instrumentation design and installation methods, as well as risk mitigation measures, are discussed."

Jan 1, 2017

By Wesley Schmutzler

The Deep Mixing Method (DMM) was employed to raise and support the LPV (Lake Pontchartrain and Vicinity) -111 Levee in New Orleans. Even using innovative technologies, the tight schedule to achieve the 100 year elevation by June 1, 2011 was a daunting endeavor. The size and scope of DMM proposed for LPV-111 was on a scale never attempted outside of Japan. Over 1.65 million cubic yards of DMM was installed. LPV-111 is adjacent to the Bayou Sauvage Wildlife Refuge, which is the largest urban National Wildlife refuge in the United States. By utilizing DMM to control settlement and improve stability of the taller levee, side slopes were steepened from the conventional 1V:4H to 1V:2.85H, thus avoiding encroachment into the Bayou Sauvage and reducing the amount of clay needed for the completed levee. The COE utilized Early Contractor Involvement (ECI) for this contract. The ECI process allowed for input from the DMM contractor, TREVIICOS South, in order to optimize equipment resources and material requirements. This paper gives an overview of the extensive DMM requirements for LPV-111 and explains the benefits of the ECI process.

By Ramanathan C, Prasad P. V. S. R

The most critical challenge for any large size storage structures to be constructed on soft compressible soils is bearing capacity and consolidation settlements. Consolidation is the time dependent phenomena, as expulsion of water from soil voids on application of external load will take longer period. It is mainly influenced by soil consistency, permeability, thickness of compressible stratum and presence of free draining layers. This study deals with the foundation solution of a large size Mounded Storage Vessel (MSV) to be constructed on thick compressible stratum whose loading intensity is around 155 kPa and the estimated settlements are greater than 400 mm. Hence, the foundation solution using vibro stone columns is adopted as an effective technique to address the challenges of excess settlements and inadequate bearing capacity. Further to keep settlements within the permissible limit of 50 mm, preloading technique with 60% of actual loading intensity will be utilized. The consolidation analysis of stone column reinforced foundations is carried based on the method given by Han and Ye (2001). The quality of the stone columns is ensured by real time quality control measures and the performance of the stone columns shall be ensured by vertical load tests. Ground settlements was closely monitored with proper instrumentations and the actual degree of consolidation has been verified by Asaoka’s (1978) method.

Sep 1, 2022

By A. Flora, E. Bilotta, F. Foria, V. Nappa

"All the typical applications of deep mixing rely on the good mechanical properties of the improved columns to strengthen or stiffen the ground for a number of geotechnical applications.This paper focuses on a completely different kind of deep mixing, carried out in order to obtain columns much softer than the surrounding soil. This kind of deep mixing, named Soft Deep Mixing (SDM), is introduced as an original means to tackle seismic risk, and can be convenient when the existing structure to be protected has a historic relevance that cannot be altered with structural modifications. The idea is that properly assembled layers made of partially overlapped SDM columns, with dynamic impedance much smaller than that of the surrounding soil, will filter and reflect most of the seismic energy.The paper presents the results of some 2D parametric numerical analyses aimed to investigate the seismic performance of this innovative approach. Simplified dynamic inputs (Ricker wavelets, having only one largely predominant frequency) were adopted to better understand the effect of signal frequency. The analyses show that the effectiveness of the soft grouted isolating barrier depends on soil and SDM geometrical, physical and mechanical properties, as well as on the frequency content of the seismic input.INTRODUCTIONPassive structural systems installed at the foundation level of existing buildings are a common solution to protect them against earthquakes. However, installation procedures are expensive and not always feasible, as for instance in the case of valuable buildings. As an alternative, ground improvement techniques can be used to modify ground properties, in order to mitigate the intensity of shaking at ground level. The propagation of shear waves in the ground can be modified by introducing a layer of artificially modified material, having a dynamic impedance (defined as n =p VS, where p is the material density and VS the velocity of shear waves) very different from that of the natural soil. Both very high or very low values of the dynamic impedance of the grouted soil (nt) can be effective in reducing the overall transmitted energy, with the difference that – for a given reduction of the transmitted energy - stiff grouted layers tend to filter the low frequency components of the amplitude spectrum without modifying in a significant way the high frequency components, while soft grouted layers have the opposite effect. Then, ideally the choice of the best grouting technique should be made considering the effects of the different frequency components on the building to be protected. These effects are detrimental for the structure when they are close to its natural frequency: high frequency components result into large structural loads on massive squat structures (high natural frequency), and low frequency components may be critical for tall and flexible structures (low natural frequency). Therefore, the typical procedure of stiffening the uppermost soil layers regardless of the kind of building to be protected is not necessarily beneficial, and for the case of squat structures soft grouting should be preferred. However, this procedure has not been taken into account yet in the engineering practice, and may pose static problems at ground level (i.e. excessive static settlements)."

Jan 1, 2015

By Dr Karsten Galipp, Kai-Julian I. Hendler, Prof. Manuel G. Pinheiro, Dr Peter J. Bourne-Webb

With a share of approximately 11% of global greenhouse gas emissions, the construction industry contributes significantly towards climate change. This is why construction projects should not only be assessed on costs and technical solutions, but also on their carbon emissions. Life Cycle Assessment (LCA) is a tool which can quantify the environmental impacts of a construction project over its entire lifetime. The objective of this study was to determine the carbon footprint of three types of quay wall structures, namely sheet pile combi-walls, open piled decks and caissons using an LCA approach. Each of these quay walls were studied under the same boundary conditions, such as design life, ground conditions, dimensions, location and so on. The analysis showed that the sheet pile wall has the lowest carbon footprint whereas the open piled structure has the highest. Furthermore, it could be shown that the largest share of greenhouse gases (approximately 80%) is emitted during the production of construction materials. The transportation of materials and construction activities each contributed under 12% to total emissions. The sensitivity analysis showed that with innovative approaches, such as adapting the concrete mix design, the carbon footprint could be reduced by 26% to 40%.

May 1, 2022

By Tony Brunger, Abid O. Adekunte, George Munteanu, David Greentree

A number of novel solutions have been proposed in recent years as alternatives to props and tie-backs in deep excavation support e.g. Adekunte (2008), Deschamps et. al. (2008), Adekunte et al. (2010) and Adekunte (2014). A number of these non-standard restraining solutions involve the construction of permanent or temporary vertical or raking buttress piles that are rigidly connected to the excavation support wall at regular intervals along the wall run. This paper chiefly focuses on the design and construction of twin-vertical buttress piles as restraining systems behind or in front of embedded retaining walls. The system essentially relies on the push-pull mechanism that develops between the twin piles, to maintain the overall stability of the excavation support. The paper’s main areas of concentration include; finite element modelling, geostructural design, construction procedure, instrumentation and monitoring that are associated with the application of twin- buttress pile systems. These are supported with project details of three recently completed high-end luxurious residential developments in Greater London, England, on which the twin-buttress pile system was used to restrain the excavation support walls for the basements on the sites. The mode of application of the system varies across the three sites. While the system was adopted as a long term solution behind the retaining wall on one of the sites, it was designed and constructed for temporary use in front of the retaining walls on the other two sites. Instrumentation and monitoring results from all the sites show the non-traditional system to be safe and effective, whilst having significant beneficial effects on construction programme, sequence of works and project cost.

Jan 1, 2018

"What can we do in ground engineering to reduce damage to the environment, to repair historic pollution, to reduce our demand on basic resources and to reduce the carbon footprint of our industry? Some developments in geotechnical engineering are already heading in the right direction. These include reductions of ground pollution from grouting, improved dewatering procedures and advances in mix-in-place processes, ground improvement and jet grouting.There is increased interest in certain promising technologies (for example, drilled partial or full displacement piles), but this approach remains for the moment somewhat avant-garde. These piles require substantially greater power to install, and the overall sustainability balance for general application has yet to be shown to be in their favour. They are particularly suited to polluted sites where the problem of dealing with spoil would be costly and where, in the past, driven cast in-situ piles would have been employed. Drilled displacement piles offer some environmental benefit over driven piles in that they cause far less drawdown of potentially contaminated near-surface ground into sensitive, underlying aquifers.There is also great interest in various means of increasing the frictional capacity of bored piles, both conventional auger and continuous flight auger (CFA) piles, by threading or ribbing the soil/pile interface. The increase in adhesion capacity allows reduction in the pile dimensions necessary for a specific load. This obviously leads to less construction waste, but also to less permanent material consumption in the piles and also in the pile caps.The role of ground improvement remains significant for brown land sites and lower capacity foundations. Information technology (IT) has improved the quality assurance of stone column construction, for example. From the sustainability point of view, this is a good news method; here is no cement, no pollution and little obstruction to future redevelopment. We now need to introduce recycled crushed materials instead of natural aggregate as general practice and the technique’s green credentials will be really compelling."

Jan 1, 2009

By Christopher Sammon, Nicholas Turus

"The demand for underground parking in South Florida has increased as a result of changes to the local building code, coupled with developers’ desire to improve building aesthetics and provide much needed walk in retail space for high-end structures. Historically, underground construction was uncommon in South Florida due to the high groundwater level and porous soil/rock. Conventional dewatering methods become ineffective only a short depth below the ground surface and deeper excavations have required a tremie seal solution consisting of wet excavation and the pouring a temporary unreinforced slab under a water head. However, as excavation area and depth increase, the cost and schedule of the tremie seal method become problematic. For these reasons developers and construction teams alike have looked to contractors in South Florida for alternative means of construction.This paper details the construction of two sites in South Florida where Deep Soil Mixing (DSM) technology offered an efficient alternative to tremie seal construction. The Brickell City Centre required excavation of 8 acres to depths of 30 feet, and augercast piles up to 36” diameter and 110 feet in depth. The second site, Jade Signature, required an excavation of up to 41 feet directly adjacent to the Atlantic beachfront. Due to the concerns over differential settlement, the project featured a soil mixed gravity wall that was designed and installed to allow for completion of the tower prior to excavating the adjacent garage.Both projects involved improving every square inch of ground beneath the planned project excavation. The developed DSM seal slab solution creates a nearly impervious excavation at excavation invert with the strength to resist hydrostatic uplift forces. Low permeability site perimeter walls are constructed to complete the sealed excavation and reinforced with either beams or sheet piles for structural support. Augercast piles required for the permanent hydrostatic concrete slab supplement the uplift capacity of the DSM. After DSM and augercast piles are installed from grade, the site is excavated in dry conditions."

Jan 1, 2017

By Leonardo Massone

The p-y method is one of the most popular methods in pile design and has been calibrated for various boundary conditions using numerical and experimental studies during recent years. Most studies on reinforced concrete (RC) piles have included the impact of flexural nonlinearity, (e.g. nonlinear moment?curvature relations) but not considered associated pile shear deformations when deriving p-y curves from field data. Common p-y curves may be better applicable for piles with flexure dominated failures (e.g. piles with free- head boundary conditions). For piles with fixed head boundaries (i.e. rotation restrained piles) shear deformations could be of significant influence. To study this problem, a coupled shear flexure interaction model for axial-bending-shear behavior coded in OpenSees was applied to a 0.61 m (2 ft) diameter flagpole and a 0.61m (2 ft) diameter fixed head pile specimen to investigate the possible influence of shear deformations to the overall pile responses. The surrounding soil was represented by p-y curves derived from prior large scale testing on piles with similar boundary conditions. Analysis results show that for flagpole piles, shear forces and shear deformations were insignificant. Considerable contributions of pile shear displacements and forces were observed for the fixed head pile, with shear displacements contributing up to 40% of the total pile displacement. Results suggest that nonlinear shear deformations for reinforced concrete piles should be considered for fixed-head or similar conditions, and that currently used p-y curves may underestimate the actual lateral pile displacement and possibly lead to unsafe design for the particular boundary condition.

Jan 1, 2012