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By Masaki Kitazume, Yoshiaki Kikuchi

"Abstract Pile foundation is one of fundamental techniques to improve the bearing capacity and settlement characteristics of superstructures. Wide varieties of piles having various shape, size and material were developed and have been applied to a lot of construction projects throughout the world. The deep mixing method, an in-situ admixture stabilization method, was developed in 1970s in Japan and the European countries, and has been frequently applied to many construction projects for various improvement purposes such as increasing bearing capacity and horizontal resistance, reducing ground settlement, preventing liquefaction and so on. The design methods, execution procedure and quality control and assurance (QC/QA) of the method are standardized or specified in many countries. These standards, specification and/or technical manual have been a remarkable contribution to spread the techniques throughout the world. The QC/QA is one of the major concerns for clients and engineers who have poor or no experience of the technologies. In order to assure the high quality of deep mixing work in the global market, it is necessary to establish the concept of QC/QA and correlate the output of different procedures. Upon the request by the organizing committee of the DFI-EFFC International Conference on Piling & Deep Foundations, the authors conducted survey of the specifications and standards on the piling and deep mixing technologies in Asian countries. In this manuscript, the results of survey are briefly introduced by comparing these specifications and standards.IntroductionThe pile foundation is one of fundamental techniques to improve the bearing capacity and settlement characteristics of superstructures. Wide varieties of piles having various shape, size and material were developed and have been applied to a lot of construction projects throughout the world. The design method, execution procedure and quality control and assurance of pile foundations are standardized in many countries based on the accumulate research results, laboratory and field experiences. In Japan, steel pipe piles are mainly constructed by hammer driven in port construction. On the other hand, precast pre-stressed concrete piles or cast-in-place piles are mainly used in on land construction. When precast pre-stressed concrete piles are constructed, piles are usually set by inner excavation method because of preventing noise and vibration problems. More than 50 years ago, noise and vibration problems had not been serious problem in Japan, but around 50 years ago, they became serious and now less noise and vibration construction methods are used for pile construction on land in Japan. In Asian countries, though piles used for construction have a lot of variety, precast pre-stressed piles are commonly used. In this report, execution controls of construction methods of steel pipe piles and precast concrete piles are mainly considered."

Jan 1, 2014

By V. M. Troughton

Large diameter bored piles with grouted bases have been adopted for the foundations of the majority of the buildings at Canary Wharf in London's Docklands, including a deep basement car park. The piles are founded in the Thanet Sand which forms part of London's aquifer where water levels are reported to be slowly rising. A special pile test has been carried out to determine the effects of both the basement excavation and a possible long term rise in the groundwater level on the performance of base grouted piles. These effects were simulated by injecting water around the pile toe and thus reducing the vertical effective stress. In this paper the test layout and procedures are described and the results are presented. The test results showed that the reduction in pile base resistance under increased water pressures was less than predicted by conventional design methods based on vertical effective stress. The end bearing resistance was found to be proportional to the mean effective stress.

Jan 1, 1989

By Carl D. Ealy

Work is being done to web enable the FHWA Deep foundation Load Test Database. Originally designed to function in the client server environment via modem, access to the database both for data maintenance and user queries has been upgraded to take advantage of the Internet and current and future information technology innovations. The DFLTD will be part of an Automated Geotechnical Information and Design Aid System, the object of which is to assist those involved with managing and maintaining our nation's highway infrastructure. The system will also meet the needs of university and other research institutions for a statistically meaningful source of high quality data for the development and verification of improved analysis methods, in-situ testing methods, etc.

Jan 1, 2002

By Anuj K. Singh, Shuvranshu Rout, Manos De

"Foundation for tracks of coke transfer car and dust extraction pipe was designed as series of isolated foundations spaced at 11.0m along length of coke oven battery resting on soil at depth of 2.5m. In one region the foundations are close to adjacent 12m deep underground junction house. Five foundations in this zone were constructed on backfilled soil without proper compaction instead of engineering soil fill or concrete fill. The foundations settled under loads and the supported frame structure tilted after equipment erection and during trials endangering the safety of the structure and equipment operation. The distorted structure had to be rectified in-situ by arresting settlement. In order to stabilize the foundation and supported structure the supporting soil had to be strengthened in situ without any dismantling, reconstruction and adverse effect to equipment operation. This paper presents the case study on the evaluation of defects for the foundation failure and analysis of the problem, proposed rectification of the situation by appropriate soil stabilization scheme, monitoring of the stabilization operations and verification of effectiveness of the rectification work by measurement of settlements. The implemented solution has ensured safety of the structure and equipment without any adverse impact on normal operation.INTRODUCTION AND BACKGROUNDNew Coke Oven Battery was being installed for an integrated Steel Plant. The hot coke from oven is pushed out after completion of coking process through a coke transfer car onto a hot coke receiving car. The coke transfer car runs on rail track parallel to the line of ovens forming the coke oven battery. One rail is supported on the structure of the operating platform of the battery and the second rail rests on independent structure of track beams. A large diameter pipe for extraction of the dust emitted during coke pushing operation is also supported on the same structure that supports the track beams. The entire structure rests on columns spaced at approximately 11.0m along the length of the battery. The columns transfer load to ground through individual foundations resting on competent subsoil strata.Two sets of foundations for the rail track beam support and dust extraction pipe support are adjacent to deep underground junction house of coke carrying conveyor. The depth of the pit for the junction house is 12m. The layout and arrangement of the foundations in this region around the junction house (JH-1) is shown in the “Figs. 1a, 1b”."

Jan 1, 2017

By Bengt H. Fellenius

"ABSTRACTAn example from a guidelines document for the Eurocode is discussed that addresses design for geotechnical strength of piled foundations in settling soil, generating drag force and downdrag. A modified example of geotechnical response is then analyzed in a failure mode, Ultimate Limit States (ULS), and stationary long-term state, Serviceable Limit States (SLS). It is shown that the Eurocode principles, when applied to correctly determined forces, results in an irrational and costly design. The results of the analysis of the modified example are applied to eight different codes pertaining to piled foundations from USA, Canada, Europe, and other countries. Several of the codes require that the drag force be included as a load in a ULS design, which an absurd and costly requirement, in some codes, in one case made even worse by combining drag force with live load. A major weakness of almost all codes is their minimal treatment and sometimes total absence of aspects of settlement of piled foundation. In contrast, my main argument is that design for capacity, whether in working stress approach, or by LFRD or ULS approaches, is not always safe unless a thorough settlement analysis shows that the design also meets the requirements of the SLS.1. INTRODUCTIONFirst, there were analysis, design, and construction establishing a State-of-Practice, SOP. Then, came codes and specifications summarizing the SOP, as interpreted by a committee. When the state-of-art, SOA, was not understood by that SOP-interpreting committee, the codes and specifications are uneconomical and, sometimes, also unsafe.The paper first presents an example quoted from two commentaries on the Eurocode 7 on design for geotechnical strength by the Eurocode (1997). The example is then modified to a more realistic case and analyzed in failure mode (ultimate limit states, ULS) and in the context of settlement (serviceability limit states, SLS). The analysis results are then applied to eight codes addressing piled foundation design and changes necessary for the referenced codes and specifications to be closer to the SOA are identified."

Jan 1, 2014

By Michel Bustamante

The occasional substandard performances of continuous flight auger in particular soil conditions have prompted the drilling rig manufacturer to improve the standard CFA in order to reduce its negative effects. A real improvement of interest was the launching of the double rotary CFA system. The promising features of the latter have incited the authors to implement an extensive experimental research on pile constructed using this type of technique but in the specific context of cohesive soils. Short-term static load tests were carried out on a total of 9 test piles of various installation techniques in order to compare the respective performances. The promising features of the double rotary CFA have incited the LCPC & Durmeyer Company to implement an extensive experimental research on this type of pile technique but in the specific context of cohesive soils and more particularly in clayey marls. After load tests completion the research has been completed by an excavation of the double rotary CFA piles. All the collected data concerning the implemented program are reported.

Jan 1, 2002

By A. Holeyman

The displacement compaction piles described in the paper are installed using a heavy casing or tube and an internal drop hammer. The casing which initially is closed at the bottom by a sand plug displaces the surrounding soil during the driving. Additional sand is rammed down through the casing during the extraction of the casing. The applications and limitations of the method are reviewed in the paper. The importance of checking the sand compaction piles during and after the installation is stressed. Indications of the compaction of the surrounding soil during the driving can be obtained by comparing the initial and the redriving logs of the casing as well as from the volume of sand added. A method to estimate the increase of the mean cone resistance as measured by CPT tests in sandy and silty soils is presented. The governing parameters are the volume of the added sand, the granulometric index and the initial cone resistance.

Jan 1, 2010

By Balu E. George, Subhadeep Banerjee, Shailesh R. Gandhi

"A three-dimensional analysis of laterally loaded helical piles installed in cohesionless soil is presented. Finite Element Analysis was conducted using commercially available Plaxis 3D AE version, assuming Mohr-Coulomb failure for soil. Pile is modelled as plate elements with a single helical blade attached to a hollow shaft. The ultimate load for various configurations is examined considering deformation criteria. The Bending Moment distribution and maximum lateral deflection are also discussed. It was observed that the ultimate lateral load carrying capacity increased by presence of helical blade and the maximum deflection also got reduced. The diameter of the helical blade was found to have significant effect on the lateral deflection, maximum bending moment and the ultimate load. However, the observations from the study suggest that the presence of helical blade seizes to produce considerable effect after a certain depth. Difference in failure pattern with regard to the distribution of soil resistance observed for different geometries considered for numerical analysis are also touched upon.INTRODUCTIONHelical piles or screw anchor piles have gained popularity due to fast installation, instant use, and other advantages over the traditional piles. They are usually used to support structures like solar panels, light houses, and other light structures which are subjected to uplift loads. However, such structures are often subjected to significant lateral loads as well. Under lateral loads, the response of helical piles can be different from that of a conventional pile due to the presence of the bearing provided by the helical blade. However, the proper design remains a concern due to lack of work carried out on the lateral capacity of helical piles.The lateral performance of helical piles is significant because they can act as efficient alternative to conventional piling systems in many applications.The lateral load capacity of screw anchor piles with different number of helices were examined by Mittal et al. (2010) by experiments in sand. They found that the lateral load capacity of piles increases with addition of helical blades. Prasad and Rao (1996) examined the lateral capacity of helical piles in clay by experiments on model piles and found that the lateral capacity of helical piles were more than that of the straight shaft piles. It was observed that the lateral capacity increase with embedment depth and shear strength of soil. Sakr (2009) studied lateral performance of two section helical piles in soft soil. The investigation by Prasad and Chari (1999) reported that the pressure distribution across the diameter is not uniform for circular piles, but it is maximum at the centre and almost zero at the two edges.Puri et al. (1984) after conducting model tests on single-helix, two-helix, and three-helix anchors installed in sand, proposed a mathematical model that was fashioned after Matlock and Reese’s elastic theory model. Elkasabgy and Naggar (2015) investigated he lateral performance of full scale large capacity helical piles in structured cohesive soils and reported the modulus of sub-grade reaction to be non linear."

Jan 1, 2017

By Austin Metz, Kevin Stanton, Ramin Motamed

"A recent study calibrated Load and Resistance Factor Design (LRFD) resistance factors for local soil conditions in the Las Vegas Valley. As a part of this calibration, an extensive database of drilled shaft load tests and associated subsurface soil information were collected and compiled. This database, deemed the Nevada Department of Transportation Deep Foundation Load Test Database or NDFLTD, was designed with the presentation of load test data, the subsurface soil conditions, and the spatial distribution of the data in mind. In addition, the NDFLTD was developed in a way that allows additional data to be added as it becomes available. As such, the rules of database normalization were followed to allow for additional and different types of data to be added to the database and reports. Microsoft Access was chosen to present the data because it is easily accessible to anyone with Microsoft office software, it has a quick learning curve, and it has the ability to present a relational database. The largest obstacle faced when creating the NDFLTD was normalizing the data used in the LRFD calibration, with the goal of reaching the 5th normal form.INTRODUCTIONLRFD is based on statistical performance of engineering components, as opposed to the more traditional Allowable Strength Design (ASD), which divides the strength of a component by a safety factor. Calibration of resistance factors for LRFD requires a robust statistical analysis of past performance. For drilled shafts this requires a database of full scale load tests (Abu-Hejleh et al. 2014). The FHWA developed the largest US based deep foundation load test database, deemed the DFLTD, collecting data from 1985 to 2003 when funds ran out (Abu-Hejleh et al. 2014). Recently, the DFLTD has been updated to modern standards (Petek et al. 2016). In October of 2007, the FHWA mandated state department of transportations (DOTs) to follow AAHSTO LRFD guidelines for their highway foundation designs (Abu-Hejleh et al. 2014). Since then multiple state DOTs have developed their own, region specific deep foundation load test databases. Florida has a long history of developing databases for deep foundation LRFD resistance factor calibration, with the two main databases being the FL database, and The Deep Foundations Database (Abu-Hejleh et al. 2014). Iowa developed a Microsoft Access based database in 2014 (Garder et al. 2014). Oregon developed a database compiling pertinent data from the DFLTD, Florida DOT’s Deep Foundation Database, as well as from other databases (Smith et al. 2011). Illinois developed the “International Database” for static and dynamic reliability based calibration (Long et al. 2009). Louisiana developed a database for LRFD Calibration of driven piles in 2009 (Abu-Farsakh et al. 2009). The California Department of Transportation has its own internal foundation database, which is housed within the Foundation Testing Branch archive (Smith et al. 2011). In 2016, the Nevada Department of Transportation (NDOT) presented its own LRFD calibration for the Las Vegas Valley (Stanton et al. 2017), and the NDFLTD was developed as a part of that project (Motamed et al. 2016)."

Jan 1, 2017

By K. Rainer Massarsch, Bengt H. Fellenius

"Abstract Vibrations generated during the driving of piles or sheet piles can affect buildings or installations in the ground. However, observed building damage is not always caused directly by dynamic effects, but can also be related to foundation conditions. The importance of geotechnical conditions is usually not taken into consideration in most vibration standards. This paper describes how building foundations, and in particular mixed foundation types, are especially sensitive to ground vibrations. A method is presented for assessing the risk of settlement due to vibrations in granular soils. Also, a simple concept is proposed for estimating settlements in the vicinity of driven piles.1. INTRODUCTIONUnder unfavorable conditions, the installation of piles or sheet piles can cause damage to buildings or other structures on the ground. Frequently, such damage is attributed to vibrations of the building itself. In many countries, national or international standards are used to assess the risk of vibration damage to buildings. As such standards are often prepared by engineers with little or no geotechnical knowledge, the effects of ground conditions on vibration propagation and damage to building foundations are generally not recognized, and damage criteria based solely on the dynamic response of buildings neglect the importance of damage mechanisms governed by geotechnical conditions. One potentially important damage mechanism is differential settlement below buildings, especially when these are founded on loose granular soils. When seeking guidance in the literature, little or no information can be found regarding methods to assess permissible levels of ground vibrations with respect to risk for settlement.This paper focuses on building damage that can be attributed to foundation conditions. In the case of ground vibrations due to pile and sheet pile driving, differential settlements are of particular importance as the ground vibrations attenuate relatively rapidly from the source. Consequently, settlement below part of the building, which is located close to the vibration source, can be significantly larger than at a distance further away.Piles are often a cost-effective foundation solution for buildings on loose and compressible soil, frequently located in urbanized areas. Sheet piles are commonly used as support for deep excavations. While impact driving is most commonly used to install piles, vibrators are frequently used for driving (and extraction) of sheet piles. It is important to recognize the fundamental differences between impact and vibratory driving. During impact driving, the pile is subjected to stress waves of short duration. The driving process creates vibrations, which radiate from the shaft and/or the toe of the pile into the soil. The larger the intensity of the stress wave, the larger the dynamic force and the intensity of ground vibrations. In addition to the vibration intensity, which often is expressed in terms of particle velocity, also the vibration frequency is important. When the dominant frequencies of the generated vibrations harmonize with the resonance frequency of buildings or building elements, the risk of building damage increases."

Jan 1, 2014

By Damian R. Siebert

Risk-reduction measures implemented during the design and construction of a 21-story pile-supported building adjacent to a below-grade 100-year-old sewer structure were keys to a successful foundation system. Avoiding damage to the existing sewer structure during construction activities and the future ability to access the structure post-construction were the main concerns for the utility owner. Clear communication and a deliberate design process between all parties ? utility owner, building owner, structural engineer, geotechnical engineer, architect, and contractor ? were integral to the project?s success. This collaborative process helped all parties to understand the risks, both real and perceived, and to develop mitigation measures to reduce the risks. Bringing together all parties to engage in dialogue and encouraging open communication throughout the project were paramount to its success. By implementing the joint design plan, using mutually-acceptable construction techniques, and careful monitoring, the building foundation was successfully installed and all parties? risks were averted.

Jan 1, 2011

By Brian H. Greene

The U.S. Army Corps of Engineers, Pittsburgh District, is in the final phases of modernizing the locks and dams on the Monongahela River. One facet of this modernization is to replace the existing Locks 4 located on the Monongahela River approximately 40 river miles upstream from Pittsburgh, Pennsylvania. The existing locks consist of a 56-foot x 720-foot main chamber and a riverside 56-foot x 360-foot auxiliary chamber built in the 1930s. Two new lock chambers, each 84-foot wide by 720-foot long, will be constructed at the location of existing Locks 4 and will be named Charleroi Locks. The purpose of the new project is to facilitate navigation on the lower Monongahela River. Pittsburgh is currently the second largest inland waterway port in the nation, and the new locks will be an important component of the navigational infrastructure. The existing lock walls are of mass concrete construction and are founded on wooden timber piles driven to rock through alluvial sands and gravels. The new lock walls were designed to be supported by approximately 300 reinforced concrete drilled shafts, varying in diameter from 4 to 6 feet. To handle axial loads, the drilled shafts were designed for end bearing, with some skin friction. The tips of the shafts will be founded within competent rock. Since the walls will undergo lateral loads, the drilled shaft design also had to consider this loading condition. Some of the drilled shafts will be installed within coffer boxes, which will incorporate a tremie concrete seal down to top of rock. Complicating the design even further was the fact that some portions of the new walls will be supported by shafts that extend some 9 feet above top of rock through alluvial soils, producing a cantilever effect. The first phase of the new lock construction was initiated in the summer of 2005 with a contract awarded to replace the river wall. This required shutting down the existing riverside lock chamber and diverting all river traffic to the longer existing land chamber. The foundation of the new river wall will use 144 drilled shafts. To optimize the design embedment of drilled shafts in rock for the river wall, an exploratory drilling program was conducted by the contractor in July and August, 2005. Based on the quality of the sedimentary bedrock, the shafts will be embedded in rock from 31 to 38 feet. To achieve adequate end bearing resistance, the tips of each shaft will extend through predominantly claystones into a more competent siltstone unit for a minimum embedment of one foot. The contractor also performed an exploratory pile driving program to aid in the construction of the drilled shaft casing and the cut off walls that will encapsulate the river wall. Two demonstration drilled shafts located outside the footprint of the new river wall, will be constructed prior to the drilling of any production shafts. The demonstration drilled shafts will verify that the contractor is able to meet the design criteria and quality requirements of the contract. The river wall contract is currently underway and is scheduled to be completed in 2010.

Jan 1, 2006

By Richard J. Finno

This paper presents an overview of methods that can be used to predict damage to buildings as a result of excavation-induced ground movements and describes an adaptive management approach for predicting, monitoring, and controlling excavation-induced ground movements. Successful updating of performance predictions depends equally on reasonable numerical simulations of performance, the type of monitoring data used as observations, and the optimization techniques used to minimize the difference between predictions and observed performance. This paper summarizes each of these factors and emphasizes their inter-dependence. Case studies are presented to illustrate the capabilities of this approach. Examples are given to show how optimized parameters based upon data obtained at early stages of excavation can be used to predict performance at latter stages, and how they can be applied to other excavations in similar geologic conditions.

Jan 1, 2010

By D. A. Bruce

The use of small diameter cast-in-place bored piles is becoming increasingly popular in the United States. Such inserts are used as conventional load bearing piles, and are generally referred to as pin piles. The other major application is for the in situ reinforcement of soil slopes or excavations. The paper reviews the applications, construction, design and performance of inserts of each type.

Jan 1, 1989

By Walter I. Paniagua

A housing complex of 76 buildings is being constructed in the city of Morelia, in western central Mexico; the buildings are 5 levels high, with a shallow concrete slab foundation. Soil conditions include a soft clay stratum, with up to 8 m depth, in a highly seismic area. Pile foundations and micro-piles were considered, but discarded due to economic factors. The alternative of soil improvement with rigid inclusions was used. An FEM (Finite Element Method) analysis was conducted to determine the diameter, spacing, length and arrangement of the inclusions. Construction was implemented with traditional methods: soil boring, and mortar tremied with pipe and the aid of a sock to contain the material (no steel reinforcement was used). So far, 46 buildings have been built, and level measurements for 18 buildings have been recorded since 2006, with resulting good behavior in both total and differential settlements.

Jan 1, 2008

By Jon Sinnreich

Ensuring the accuracy of collected data during deep foundation static load tests is of paramount importance. Typically, pile head displacements are measured relative to a purpose-built reference system, which is assumed to be fixed. This study presents a simplified error analysis of this assumption, illustrates the potential magnitude of these errors, and proposes an improved method of pile head displacement monitoring.

Jan 1, 2009

By Alexander B. Reeb, Richard J. Varuso, George M. Filz, Jehu B. Johnson

"T-walls, which are concrete floodwalls in an inverted “T” shape, are an integral component of the Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS). In order to resist large lateral flood loads, T-walls are typically supported on long batter piles that extend through the weak and compressible clays and peats commonly encountered in southern Louisiana. Since the piles are battered, settlement of the compressible foundation soils can result in loads acting normal to the piles and induce pile bending moments. Therefore, the design of pile-supported T-walls is a complex soil-structure interaction problem that requires detailed and careful numerical analysis to accurately estimate the stresses and bending moments in the piles. For this paper, numerical analyses were performed for three cross sections that each included a two-pile T wall system that was installed within a 15-ft tall new levee embankment. The cross sections were identical except that the elevation of the T-wall base was varied. This paper discusses the analyses, and it compares the influence of settlements and flood loading on the pile stresses and bending moments. In addition, this paper includes general recommendations for the analysis and design of pile-supported T-walls in practice.INTRODUCTION AND BACKGROUNDThe recently completed Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS) includes 350 miles of levees and floodwalls and is designed to defend against a 100-year storm surge event. The floodwalls predominantly consist of I-walls and T-walls. I-walls are comprised of a sheet pile wall curtain capped with a monolithic concrete wall above grade. T-walls are similar to I-walls, but they include a wide concrete base at grade, which forms an inverted “T” shape, and they are generally supported by long batter piles that provide additional lateral and rotational stability for resisting flood loads.During Hurricane Katrina, several I-walls failed, resulting in large breaches and devastating flooding (Duncan et al. 2008, IPET 2009). T-walls on the other hand performed quite well, including T-walls that were overtopped and eroded on the protected side, yet still did not collapse. As part of the HSDRSS, more conservative designs and height restrictions were required for I-walls (USACE 2011), and a number of I-wall sections were replaced with T-walls. However, the design of pile-supported T-walls is complex and requires careful consideration of both flood loading and settlements."

Jan 1, 2017

By J. A. Yeats

This paper describes the loading to 25MN of a 1.2m diameter bored cast-in-situ test pile founded in the Thanet Sand which was base grouted. The pile was sleeved over the major portion of its length to test primarily the base response of the pile. The results are presented and compared with similar pile load tests in Thanet Sand.

Jan 1, 1989

By Frederick C. Rhyner

Drilled shafts have become an economical foundation choice for bridges in the northeast United States, especially when they can be constructed over water without the use of cofferdams. For the Boscawen-Canterbury Bridge over the Merrimack River in New Hampshire, an unusual design was used to avoid the use of cofferdams and avoid the need for pier caps at the waterline. This design used a pair of integral drilled shaft ? columns to form a bent type of substructure for support. Drilled shafts were 8-foot diameter, about 90 feet deep, with 16-foot long rock sockets. These are integrally constructed with 6-foot diameter reinforced concrete columns extending 37 feet from the waterline to the superstructure. Design load cases focused on lateral loads from ice flows, stream flows, wind and seismic events. Alternative analyses using different methods were made to check the design results. This paper discusses the subsurface conditions, design of the drilled shafts and columns, rebar and joint detailing issues, and construction of the drilled shafts.

Jan 1, 2004

By Mostafa Mossaad, Ali Helwa, Manal Salem

Support of excavation (SOE) design practice tends to model SOE elements using two-dimensional (2D) analyses to avoid the complexity associated with three-dimensional (3D) analyses. Such practice overlooks soil arching in the horizontal plane and prevents designers from accounting for elements such as capping beams as part of the statical system. This study simulates square excavations supported by cantilever slurry walls in dry cohesionless soil using 2D and 3D finite element (FE) models. First, side support wall behavior is compared from 2D and 3D FE models for variable excavation length to depth (L/H) ratios. Second, the effect of slurry wall lateral bending stiffness on wall behavior is studied by modeling the wall using plate element with isotropic and anisotropic wall stiffness. Finally, the sensitivity of cantilever wall behavior to the presence of capping beam is illustrated. The study concludes that unbraced excavations with L/H ratios greater than 5 almost resemble plane-strain conditions. Slurry walls are better simulated in 3D FE models by dividing the plate element into discrete panels or by assigning anisotropic bending stiffness to the plate element. Finally, the presence of capping beam affects the behavior of cantilever walls resulting in reduction of deflections and redistribution of bending moments. INTRODCUTION Support of excavation (SOE) design practice ranges in complexity from conducting simple hand calculations to performing three dimensional numerical modeling depending on several factors among which is the geometry of the design problem. This paper addresses walls that are designed using numerical modeling, and discusses the factors governing the choice of the most suitable modeling approach. It has been believed for a while that modeling excavations using 2D numerical models would lead to a more conservative solution, which turned out to be incorrect in specific cases. This paper attempts to describe cases where 2D finite element modeling could be on the conservative side and other cases where it could be less conservative than the more complex 3D modeling.

Jan 1, 2018