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By Nasr Sheta

"After Hurricane Sandy, the stability of an earth slope in the Atlantic Highlands, New Jersey in the United States was deteriorating due to slumping soils and erosion from flooding. A slope stability evaluation indicated the slope did not satisfy the requirements of the local building code. A triple-tier, pile-supported and mechanically stabilized earth wall was designed and constructed to stabilize the slope. The construction was planned from a 3-m-wide roadway and, because of rough terrain and limited work space at the site, a cast-in-place drilled-pile construction was deemed impractical due to slow pile production. An alternative procedure was utilized by pre-drilling holes, and installing precast tip-and-shaft-grouted (PCTSG) piles, which extended to competent soils to improve slope stability. A grade beam, connecting the PCTSG piles along with soldier beams and concrete lagging were used to form the lowest tier of the slope stabilization, while the middle and higher tiers were built as mechanically stabilized earth. The stability of the proposed stabilization was analyzed using 2-D non-linear finite elements. After construction, monitoring of the wall continued for about 8 months to check its performance, and indicated lateral and vertical wall movements were less than 25 mm and 6 mm, respectively, indicating effective slope stabilization.INTRODUCTIONStabilizing earth slopes using piles to connect near-surface unstable soils to underlying stable ground masses has been investigated by many researchers, who presented various approaches to evaluate the contribution of the pile system towards improving the stability of the slope. Some of these approaches consider the piles as structural elements receiving forces from the upper sliding ground mass and transmitting these forces to the underlying stable one. The force from the top sliding mass is applied at between one third and one half of the pile embedment into the top sliding mass, Anagnostopoulos et al. (1990), Fukuoka (1977) and Matsui et al. (1988). The point of application of the sliding force was explored based on successful case histories while addressing the safety factors for both geotechnical and structural design, Vessely A. et al. (2007). The development of numerical analysis techniques utilizing the method of finite elements (FE) also enabled better analysis and design of slopes stabilized using piles. A FE-based approach was successfully utilized to design slope stabilization with target safety factor based on the shear and bending demands and the spacing of the piles, Pradel D. et al. (2010).After Hurricane Sandy in October 2012, the stability of many properties constructed atop earth slopes located along the coast of the Atlantic Ocean has become a concern due to storm-induced erosion. This paper presents the analysis, design and construction of a hybrid slope stabilization system utilized at one of these storm-impacted properties, which is located in the Atlantic Highlands, New Jersey in the United States. The subject property consisted of a two-story residential dwelling and a parking structure, and was built on top of an about 8-m-high earth slope having crest at about elevation 10 m (el 10) and toe at about el 2."

Jan 1, 1900

By Shyam Chengalath, Johan Jeansson, Magnus Hörman

Down-The-Hole (DTH) drilling usually uses compressed air to power the hammer. However, there are now DTH hammers on the market which instead of compressed air use high pressure water to power the hammer. There are several benefits with using water DTH compared to air DTH, which are discussed in more detail in this paper. From a physics point of view many of the benefits arise from the fact that water is an incompressible media and air is not. Energy consumption is roughly a quarter compared to air, resulting in lower carbon emission and a lower energy bill. In the case of water DTH the water leaving the drill bit in the hole is at a low velocity and ambient pressure. However, with air DTH the air leaving the drill bit in the hole is at a high velocity and high pressure. This means that the risk of damaging surrounding structures in sensitive areas such as urban environments and dams, is greatly reduced with water DTH. In this paper two cases where water DTH is used in jet-grouting applications are discussed in detail. As these cases show there is a clear improvement in productivity when using water DTH hammers.

Sep 1, 2022

By Rafael A. Rivera

"Since the dawn of construction, there has been a need for excavations, which sometimes need to occur below the groundwater table. Excavations in themselves are difficult enough, with the myriad of requirements, such as engineered support of excavations, considerations for stability and numerous other concerns. Excavations executed in rural landscapes can be accomplished easily without significant consideration to accessibility, adjacent properties or structures, and construction limits and deformations. However, all of these factors can have an impact on excavation considerations in an urban landscape. When digging below the groundwater table, these conditions, along with concerns associated with groundwater drawdown requirements, discharge limitations, groundwater contamination, property limits, adjacent buildings and subsidence concerns, can lead an experienced dewatering contractor to consider diverse installation methodology and equipment to allow construction to occur below the groundwater table.534 W. 29th St. New York, N.Y.There are many things that must be considered when constructing a new high-rise building within a small property footprint measuring 25 ft (7.6 m) wide by 80 ft (24.4 m) in length. When you take into account that the foundation needs to go several feet below the groundwater table and that there are two existing multistory buildings with shallower foundations on either side of the proposed structure, this task now becomes much more difficult. Consideration of geology, groundwater levels, depths of excavation and shoring for the excavation becomes critical to the success of the project. On a regular basis, dewatering contractors confront similar situations in congested cities where available real estate is limited.To minimize the negative impacts of construction dewatering, it is important to mitigate the potential effects of construction dewatering to the surrounding buildings, sidewalks, underground structures, tunnels, subways and other existing infrastructure. Such an instance occurred at the project located at 534 W. 29 St. in New York City. On this particular project, the required drawdown was greater than the typical 15 ft (4.6 m) of suction lift, so a vacuumed can pump system was utilized. The tubing was connected to a vacuumed perimeter dewatering well-point system, which is a predrainage system that is installed prior to the start of excavation for the underpinning of the adjacent structures and for the overall foundation. Each well-point, which was composed of a PVC pipe that was 1.5 in (38 mm) in diameter by 25 ft (7.6 m) long, was drilled to a depth of about 23 ft (7 m) using a hollow stem auger and was installed around the perimeter at a centerto- center spacing of about 7.67 ft (2.3 m). In lieu of a traditional perimeter collection header, and to allow for greater flexibility for the contractor, the well-points were interconnected to a modified vacuum can pump system utilizing ¾ in (19 mm) drop tubes that were “spaghetti” around the perimeter."

Jan 1, 2017

By Alper Turan

The use of aggregate pier foundation systems has become widespread as the engineering practice moves towards cost-effective ground improvement solutions that provide accelerated construction schedules. Increased bearing capacity, effective settlement control and potential for liquefaction mitigation are commonly acknowledged benefits of aggregate piers. This paper studies the mechanisms by which aggregate piers interact with each other and with the surrounding ground when excited by seismic loads. A particular emphasis was placed on the response of a raft foundation supported on a site improved using aggregate piers. Three-dimensional nonlinear finite element analyses were conducted using commercial software package, ABAQUS. Non-linear soil behaviour is modelled using a three-dimensional total stress-based bounding surface plasticity model, which is able to simulate stiffness degradation and damping increase in the soil. The soil stratigraphy considered in this study was a 30 m deep soil deposit that comprised a very stiff base layer and a shallow soft surficial clay layer. Ricker Wavelet time histories with different frequency contents are used as the excitation force in the analyses. Various area replacement ratios (ARR) for aggregate piers are studied for a square plan layout. The results presented in this study are considered to be of interest to researchers and designers in evaluating the seismic ground response of the sites improved using aggregate piers.

By Brian E. Ladd

"A load test program was performed on two auger cast piles constructed in the Inner Coastal Plain geology of North Carolina. Both test piles were installed through Coastal Plain deposits and into underlying Piedmont residual soils; one test pile was embedded into partially weathered rock (PWR). The recommended 100-ton design load was confirmed by a test program that included instrumenting the piles with strain gages. The two piles performed differently during the load tests due to the effect of embedment into PWR. Loading Test Pile No. 1, which was not embedded into PWR, to failure at about 230% of the design compressive load allowed for evaluation of the mobilization of the ultimate shaft and end bearing resistances. Mobilization pile resistance was evaluated by comparing shaft and end bearing resistances to top of pile deflection (d) normalized by the pile diameter (D). For Test Pile No. 1, the ultimate average shaft resistance was achieved at d /D of about 7.5% and ultimate end bearing resistance at d /D of about 9.5%. Test Pile No. 2, embedded into PWR, achieved a d /D of only about 4% at 200% of the design load and was not loaded to failure. Shaft resistance was mobilized at a different rate within each individual geologic layer, i.e. ultimate shaft resistance did not occur simultaneously for all geologic layers. As the available total shaft resistance was exceeded and end bearing mobilized, the unit shaft resistances reduced from the peak values. A modified Davisson offset using d /D of about 6.5% appears applicable for evaluating the ultimate capacity of auger cast piles in the Inner Coastal Plain.INTRODUCTIONAuger-cast-in-place (ACIP) piling was developed in the 1940’s and patented in 1956 (Neely, 1991). Since patent expiration in 1973, ACIP piles are abundantly used in the United States, particularly in the southeast. However, most literature addresses driven piles constructed in sand and clay with lesser discussion of drilled piles. Conventional design methodologies (a- method, ß-method, SPT or CPT correlations, etc.) are based on data derived from numerous projects in a great variety of geologies. O’Neil (2001) notes that there are significant levels of uncertainty in the “universal” databases as evidenced by coefficients of variation of 0.35 to 0.40 for geotechnical parameters (su, SPT-Nvalue, etc.) used to estimate pile capacities.There is a need to develop local databases developed from data obtained from load tests that measure shaft resistance and end bearing. This paper presents the results of load tests conducted on axially loaded auger-cast-in-place piles constructed in the Inner Coastal Plain geology of North Carolina. Shaft resistance, end bearing, and movements that initiated mobilization of these resistances are described. The information presented herein can be used to refine geotechnical correlations and parameters applied in auger cast pile design methodologies."

Jan 1, 2017

By Seyyed Mehdi Radeghi Mehrjou

It is important to study structures and their retrofitting techniques in order to avoid earthquake-induced seismic damage within countries that are prone to earthquakes. Todays, micro piles are employed as useful structural components for seismic behavior improvement. The present study analyzes inclined micro piles subjected to seismic loading by using the three-dimensional finite difference method (FDM). FDM assumes an idealized three-dimensional soil-micro pile model to perform logical behavior evaluation in the event of an earthquake. Linear and elastic micro piles and elastoplastic soil were employed in this study. The Mohr-Coulomb criterion was employed in the failure control of the micro piles. The micro piles were subjected to the 1978 Tubas earthquake records. The numerical results were compared to experimental data. The comparison revealed good agreement between the numerical results and experimental data. The inclined micro piles were found to sufficiently enhance soil strength under seismic loading, inducing smaller displacements than vertical micro piles. Furthermore, the soil and inclined micro piles showed salient interaction.

Sep 1, 2022

By Sara Moshfeghi, Seyyed Majdeddin Mir Mohammad Hosseini, Abolfazl Eslami

"Due to variety of current pile bearing capacity methods based on the cone penetration test (CPT), for optimum design, it is necessary to evaluate the performance of such methods in different geotechnical conditions. Geotechnical databases including piling and in-situ testing records have been recognized as useful tools for analysis, design and economical construction. In order to evaluate pile bearing capacity methods, AUT-CPT&Pile database has been compiled including 450 full scale pile load tests and CPT sounding records. This database consists of different pile types with a relatively wide range of geometries and various soil conditions. Forty three records of piles driven in sand deposits were then employed to evaluate effects of ultimate capacity interpretation criteria from load displacement diagrams. The Davisson offset limit criterion, the Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter were compared to estimated capacities from ten CPT based design methods currently used in practice. The Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter lead to reasonable results, the Brinch Hansen 80% criterion showed less scatter. For evaluating the accuracy and the precision of CPT-based methods, the results were compared to estimated capacities. Results of comparison indicate that the CPT-based methods mainly predict the pile capacity withreasonable accuracy.INTRODUCTIONAmong the different approaches of estimating the pile bearing capacity, in-situ tests, especially, the cone penetration test (CPT) are favored due to the cone similarities with piles in modes of installation as well as fast and continuous profiling. This trend is practically well established where deep foundations are to be constructed in soft to medium subsoil deposits (Eslami and Fellenius, 1997; Mayne and Niazi, 2009).Employing different design methods results in a wide range of values which complicates the selection of an appropriate one to determine the pile bearing capacity. Several studies by Briuad and Tucker (1988), Eslami and Fellenius (1997), Abu Farsakh and Titi (2004), Schneider et al. (2008) and Eslami et al. (2011) confirm disparity of different design methods predictions. Thus, for optimum design, it is necessary to evaluate and compare the performance of current methods.Geotechnical databases are known as helpful tools in research and practical applications for optimizing analysis and design and are mainly used for management and interpretation of data, evaluation of design methods, calibrating LRFD or ASD design factors, etc. Pile lateral and axial load tests are examples of databases in geotechnical engineering. A summary of several CPT and pile load test databases is presented in Table 1."

Jan 1, 2017

By Florian König

It is well known that the bearing capacity and stiffness of displacement piles may increase significantly with time, a phenomenon usually referred to as set-up. In cohesive soils the set-up is commonly explained by consolidation processes in which the dissipation of the excess pore pressures around the pile leads to an increase in effective radial stresses. Recent case histories show that set-up may also occur in sand over a period which exceeds by far the consolidation process. Therefore, other effects apart from the dissipation of excess pore pressures must contribute to this long-term set-up effect. This paper presents the results of a series of multiple pile load tests on prefabricated concrete piles which capture the effect of pile set-up empirically. The main characteristics of the set-up trend are shown with respect to soil type, pile dimensions and distribution over the pile length. Possible reasons for pile set-up like consolidation and stress relaxation after the end of driving are examined using a finite element model which simulates the pile installation process.

Jan 1, 2006

By Brain E. Ladd

A load test program was performed on two auger cast piles constructed in the Inner Coastal Plain geology of North Carolina. Both test piles were installed through Coastal Plain deposits and into underlying Piedmont residual soils; one test pile was embedded into partially weathered rock (PWR). The recommended 100-ton design load was confirmed by a test program that included instrumenting the piles with strain gages. The two piles performed differently during the load tests due to the effect of embedment into PWR. Loading Test Pile No. 1, which was not embedded into PWR, to failure at about 230% of the design compressive load allowed for evaluation of the mobilization of the ultimate shaft and end bearing resistances. Mobilization pile resistance was evaluated by comparing shaft and end bearing resistances to top of pile deflection (?) normalized by the pile diameter (D). For Test Pile No. 1, the ultimate average shaft resistance was achieved at ?/D of about 7.5% and ultimate end bearing resistance at ?/D of about 9.5%. Test Pile No. 2, embedded into PWR, achieved a ?/D of only about 4% at 200% of the design load and was not loaded to failure. Shaft resistance was mobilized at a different rate within each individual geologic layer, i.e. ultimate shaft resistance did not occur simultaneously for all geologic layers. As the available total shaft resistance was exceeded and end bearing mobilized, the unit shaft resistances reduced from the peak values. A modified Davisson offset using ?/D of about 6.5% appears applicable for evaluating the ultimate capacity of auger cast piles in the Inner Coastal Plain.

By Gustav Jahner, Michael Baltrusch, Norbert Hoffmann

Near the port city of Whitby in the north-east of England, Anglo American (AA) is setting up the deepest mine in the UK, which will have a depth of 1,500m. The purpose of the project is to extract and transport polyhalite, both underground, and to market it globally. As part of the construction works, BAUER Technologies Ltd, the UK subsidiary of BAUER Spezialtiefbau GmbH, constructed three different shafts using the diaphragm wall technique, with depths of up to 120m. In order to ensure the specified vertical tolerance of maximum 200mm, several measurement methods were applied, and the results were documented in a 3D model. Complex de-sanding plant technology and specially developed polymer products were adopted to regenerate the trench supporting bentonite-slurry.

Sep 1, 2022

By James M. Tantalla, Jr. Ellman

"Construction of the powerhouse for the Willow Island Hydroelectric Project, located at the Willow Island Lock and Dam, required a 120-ft deep temporary excavation inside the limits of a cellular cofferdam on the Ohio River side of the excavation and a soil-bentonite seepage cut-off wall on the landward side of the excavation. Stability analyses were performed for critical sections to evaluate the stability of the soil slopes and rock cuts using limit equilibrium, tension crack, and buckling analysis techniques. The stability analyses indicated adequate factors of safety through the landside embankment sections, and for the weighting berm soil slopes in front of the riverside cellular cofferdam. However, the results of deep-seated stability analyses through the rock supporting the riverside cellular cofferdam indicated marginal factors of safety for the 100-year flood condition. Consequently, the riverside portion of the excavation required enhanced stability measures, namely the installation of long, high-capacity rock anchors. Also, the dewatering system was modified to lower the site piezometric head to near the top of rock to improve the stability of the rock cuts.Thirty high-capacity rock anchors were installed on the upstream, riverside, and downstream sides of the cofferdam rock cut. The rock anchors consisted of multiple, seven-wire strands designed to provide the full-required design load at 60% of the strand capacity. Rock anchor loads varied from 1,968 to 2,074 kips. The maximum number of strands per anchor was 59. Bond lengths assumed an allowable bond stress of 100 psi based on the rock bond from pull-out tests.Project DescriptionAmerican Municipal Power, a nonprofit organization that owns and operates electric generation facilities for its member communities, has been in the process of constructing hydroelectric power plants adjacent to existing navigation locks and dams along the Ohio River. The Willow Island Hydroelectric Plant was recently completed on the West Virginia bank of the river adjacent to the US Army Corp of Engineers (USACE) Willow Island Lock and Dam. The plant is on the opposite river bank to the locks, and includes two turbine generating units with FERC rated capacity of 44MW at a 20-foot head differential. The Ruhlin Company of Sharon Center, Ohio was awarded contracts to construct both the cofferdam and the powerhouse. Construction began in mid-2011, and was completed in early 2016."

Jan 1, 2016

By Kevin R. Johnson, Matt Caskey, Bryan Plaskett

Working in urban environments presents unique logistical challenges beyond those typically associated with traditional geotechnical design and construction. These challenges can include constrained sites with limited access and laydown area, vibration concerns for adjacent structures, and the need to complete work within limited schedules. When challenging geotechnical conditions like variable bedrock elevations are present, the need to balance performance requirements with logistical constraints become the driving factor when selecting deep foundation systems. This paper focuses on the deep foundations used for a new elevated pedestrian bridge at a major health care facility in Tampa, Florida. In addition to the technical design requirements, the owner required a deep foundation system that could offer low vibrations, rapid production, and clean installation to limit impacts on their properties and the public roadway that separated them. The paper describes the project specific geotechnical and design conditions, describes Ductile Iron Pile design, and focuses on how installation of the system addressed the unique logistical challenges. In addition, the implementation of a full-scale load testing program to assess compression, uplift, and lateral design capacities is presented. This paper represents one of the few published references for Ductile Iron Piles on projects in the United States.

Oct 1, 2022

By Walter E. Vanderpool

Type 1B micropiles (Bruce and Juran, 1997) can be installed rapidly and efficiently. During an 85-day period, 536 micropiles were installed to depths of 61 meters within a site 41 meters by 43 meters. Their performance, as measured by load test, varied even where the materials, construction procedure, and installation technique were closely monitored and controlled. The variation in displacement, as measured by the standard deviation, exceeded 50 percent of the mean test-load displacement for all loads up to the maximum load applied (2670 kN). This study provides a statistical basis to predict variability with respect to the construction method, micropile materials, and installation technique. The variability of displacement at all test loads is a fundamental characteristic of this type of drilled deep foundation system.

Jan 1, 2002

By Francisco A. Flores, Rigoberto Torres

The Complementary Technical Standards of Mexico’s City Building Code do not mention the criteria to compute the bearing capacity of Steel H-piles. It is necessary to increase knowledge in using steel H-piles as foundation elements in very soft soils of Mexico City. Considering their applicability to reinforce structures as well as new foundations in confined spaces, this research is proposed to obtain the axial load capacity of piles at scale in laboratory. This paper describes the construction and testing of scale models in laboratory of steel H-piles to measure their axial compression and tension load capacity in the soft soils of Mexico City. Three types of piles were fabricated at scale. Tests were performed on individual piles and pile groups. Based on the axial load tests, the load-displacement curves are presented both in compression and tension. The analysis of the results is shown, and comments are given regarding the ultimate bearing capacity of piles. Recommendations are presented regarding the determination of the bearing capacity of these piles in the very soft soils of Mexico City.

Sep 8, 2021

By Manchanda H, Agarwal J.

The construction industry has one of the largest numbers of injuries compared to other industries. Thus, reducing accidents and determining construction risks are extremely important. One of the essential steps for construction safety management is hazard identification and risk assessment, since the most unmanageable risks are from unidentified hazards. While the urban rail transit systems are being developed rapidly in almost all major cities of India, adjoining Existing Building Structures and historic sites are facing possible threats of unexpected damages and accidents. The protection of these structures becomes one of the major challenges specifically when the infrastructure being developed involves construction of underground tunnels passing through old cities. The assessment of settlement induced damage on buildings during the preliminary phase of tunnel excavation projects, is nowadays receiving greater attention. Analyses at different levels of detail are performed on the surface building in proximity to the tunnel, to evaluate the risk of structural damage and the need of mitigation measures. The current paper presents current practices being adopted in India for prediction and excavation of tunnelling induced ground movement and building damage risk-assessment. The paper highlights empirical and numerical approaches towards predicting settlement induced damages on buildings during the tunnelling, detailed step by step methodologies for conducting building condition surveys, evaluating associated hazards, and adopting adequate building risk identification and mitigation methods. The paper also discusses associated technical and contractual challenges and highlights way forward to overcome them.

Sep 1, 2022

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 Lance Rasband, Richard Hanke

"Seattle Tunnel Partners (STP) started mining on Seattle’s SR99 tunnel on July 30, 2013, working slowly through a 15 ft (4.6 m) thick fiber-reinforced concrete headwall. Once through the headwall, the machine would move through roughly 400 lineal ft (122 m) of jet grout-improved soil at a rate slightly over 6 ft (1.8 m) per day. It was anticipated that once through the improved area, Bertha—the world’s largest tunnel boring machine—would move at a rate of 35 ft (10.7 m) per day. By the end of October 2013, Bertha had mined roughly 430 ft (131 m), averaging 4.73 ft (1.4 m) per day, and had begun mining within native soils. By the start of December 2013, tunneling reached the 800 ft (244 m) mark and Bertha averaged 12 ft (3.7 m) per day, achieving as much as 42 ft (12.8 m) of progress on some days. However, on December 6, 2013, Bertha began to stumble and all progress quickly came to a halt. Preliminary InvestigationInitial reports stated that an obstruction had stopped the machine in its tracks. Malcolm Drilling received an early morning call on Sunday, December 8, 2013, from STP to rapidly mobilize a Bauer BG-50 drill rig with crews to investigate what was hindering Bertha’s progress. Malcolm’s equipment and crews flew into action and were completely mobilized and operational by mid-week. The preliminary investigation involved installation of 10 deep dewatering wells to reduce the hydrostatic head within the ground around the machine and allow STP personnel to inspect the cutter head from within the shaft for presence of obstructions. By the close of December 2013, the wells were installed and the dewatering system was fully commissioned. STP crews were then able to inspect the cutter head and found small fragments of a steel pipe wrapped around the outside of the shield. The steel was apparently from an abandoned 10 in (0.25 m) diameter monitoring well casing previously installed by WSDOT (Washington State Department of Transportation) to monitor groundwater conditions for the design and planning of this very project. After the steel was cut out of the head and cleared from Bertha’s path, she attempted to move forward but was only able to manage a slow crawl"

Jan 1, 2015

By Christophe H. Locussol

D.C. United, the professional soccer team located in Washington, D.C., completed a 20,000 seat capacity stadium in July 2018 named Audi Field. The project initially considered a foundation system consisting of roughly 800 prestressed concrete driven piles configured in groups with pile caps. A value engineering alternative proposed in a design-build manner ultimately resulted in the use of 300 single element Auger Cast Piles (ACPs) for the foundation system. The ACPs ranged between 1.5 ft and 4 ft in diameter, were up to 85 ft in length, and were connected through a system of grade beams to accommodate large lateral induced loads. Limitations in conventional analytical methods were encountered during the structural design of the piles due to the complexity of the lateral loading and pile fixity conditions. An innovative approach using advanced finite element modeling that incorporated the framing effects of the grade beams was required to meet the strict movement criteria despite large lateral loads.

By Scott A. Walker, Gabriel J. Alcantar, Brian Zuckerman, Ramin Golesorkhi

"The new San Francisco 49ers Levi’s Stadium is part of the next generation of sporting facilities. Constructed in Santa Clara, Calif., the new structure has 68,500 open-air bowl seats and includes a 7- story tower housing more than 150 suites. The overall project includes the stadium structure, elevated open pedestrian walkways, commercial community space, three new pedestrian bridges and improvements to the adjacent light rail station. Sustainable design for the project includes a green roof, photovoltaic panel and a ground source geothermal system. Stadium-wide next-generation Wi-Fi capability is another feature. The design-build project team included HNTB (project architect), Magnusson Klemencic Associates (MKA, structural designer) and a joint venture of Turner Construction and Devcon Construction (TDJV, general contractor).During preconstruction, the 49ers’ original design team and the design-build team formed later worked together to facilitate communication and provide continuity. This helped to meet the project’s aggressive schedule. Working directly for the 49ers, with the design-build team, Treadwell & Rollo (T&R) served as the geotechnical engineer of record for the project from preliminary to final design and through construction. Although not contracted directly to TDJV, the stadium ownership encouraged direct interaction between T&R and TDJV and improved responsiveness to geotechnical issues during design and construction.Subsurface ConditionsThe new stadium lies within the Santa Clara Valley, a deep alluviumfilled basin resulting from historic movement on the active and potentially active strike-slip and thrust faults that bind the valley. The valley is filled with Holocene age (approximately 11,000 years old to present) alluvium, consisting of levee and basin deposits, with bedrock more than 750 ft (229 m) beneath existing ground surface. The stadium site is between two of the highly-active faults in California, the Hayward Fault 6.8 mi (11 km) northeast, and the San Andreas Fault about 11.8 mi (19 km) southwest."

Jan 1, 2014

By William G. Ryan, David S. Graham, Dan A. Brown, Rich A. Lamb, Paul J. Axtell

"The St. Croix River Crossing project on the Minnesota-Wisconsin border has been in the process of planning and public debate for two decades, with several changes in alignment. During the course of the earlier planning process in 1995, a drilled shaft load test was performed to obtain preliminary design information. There were some difficulties in maintaining stability within the weak sandstone bearing formation, and the measured axial resistance was relatively low. Subsequent experience by the Minnesota Department of Transportation with similar weak sandstones on the I-35W project suggests that improved construction techniques using modern drilling fluids may offer opportunities for improved performance. During final design in 2012 a second load test program was performed of a full scale test shaft constructed using polymer drilling fluids. The stability of the socket excavation in the weak sandstone appeared to be greatly improved and the measured axial resistance significantly higher.This case history illustrates the excellent performance that drilled shafts can provide in even relatively weak sandstone bedrock as well as the profound influence on axial resistance associated with the construction techniques used. The improved resistance values obtained by the new load test with more recent construction technology allowed the foundation scheme to be substantially optimized with respect to the number and size of required drilled shafts, reducing the size, cost, and risk of the coffercells and footings.IntroductionThe Minnesota Department of Transportation (MnDOT) has awarded the first phase of a bridge construction project that will cross the St. Croix River between Oak Park Heights, MN and St Joseph, WI. The first phase construction contract involves building the river pier substructures including groups of drilled shafts beneath each tower leg. A general location of the bridge project is provided in Figure 1.Prior to award of the construction contract, two separate design-phase axial load tests were performed on non-production drilled shafts with rock sockets. Both tests were static, bottom-up tests using the Osterberg Cell (O-cell). The first test was performed in 1995 when final design and construction was thought to be imminent. After years of public debate and literally, an act of Congress, design of the project was finally restarted and a second load test performed in 2012. The 1995 test was conducted on the Minnesota bank approximately 900 ft southwest of the St. Croix River bank. The 2012 test was conducted in the river about 2,100 ft northeast of the1995 test location. A plan-view of the project indicating the test program locations relative to the bridge alignment is provided in Figure 2."

Jan 1, 2015