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By Dominic Parmantier, Jason Page

"In the past, the designers of DSM have analyzed various failure modes and then specified a minimum unconfined compressive strength (UCS) for the soil-cement. The specified minimum UCS reflected the compressive stress in the soil-cement under design loads and an appropriate factor of safety. With the increased use of finite element analysis for the design of DSM applications where allowable strain as well as stress are considered, there is a growing trend for designers to specify a modulus and occasionally a tensile strength for the soil-cement in addition to the UCS. This paper compares the relationship of modulus and tensile strength to UCS for soil-cement from a recent DSM project with unique testing requirements. These results are compared to published data. The case is made that designers should utilize published relationships to characterize the required strength and stiffness by a single acceptance criterion: UCS.INTRODUCTIONAs the use of DSM has increased in popularity so has the use of service state deformation analysis in lieu of more traditional failure mode analysis. Most DSM designers are interested in the appropriate modulus values and occasionally tensile strength values of soil-cement as well as simply the unconfined compressive strength (UCS) of soil-cement.Although there are numerous published correlations between the UCS, tensile strength and modulus of soil-cement, some DSM project specifications are produced which have acceptance values for tensile strength, modulus, and UCS. If this specification of multiple strength properties is consistent with the nature of soil-cement, then there is really no harm except for the expenditure of client money on unnecessary testing. If however the multiple strength properties specified are inconsistent with the material properties of soil-cement, then the specifications can create the expectation that the DSM contractor can somehow create a custom soil-cement with tensile strengths and modulus characteristics which are unachievable.This paper presents a brief summary of a project in Burnaby, B.C. which specified minimum values for the tensile strength, modulus, and UCS of the soil-cement. A comparison of those test results to published correlations between the UCS and the tensile strength is presented. Additionally, a comparison of modulus derived from two different methods of testing is presented along with a comparison to published correlations between UCS and modulus for soil-cement."

Jan 1, 2015

By Ronaldo Luna, Donald Deardorff

"The use of load and resistance factor design (LRFD) is well documented since the 1960s for structural applications when it was first adopted into the American Concrete Institute Building Code in 1963 and was established for geotechnical applications by the Danish Geotechnical Institute about the same time under the name of Limit State Design (LSD).The Federal Highway Administration required all federally funded projects to use the LRFD method by 2007. Due to this funding requirement, recent LRFD research for geotechnical applications has focused on common bridge foundations (i.e., driven or drilled shafts), resulting in good documentation for design using these methods. Unfortunately, the practicing geotechnical engineer does not intuitively know how to create resistance factors for deep foundations systems that have design methodologies and installation techniques significantly different from driven or drilled shaft foundation systems.Helical anchors typically use semiempirical methods for preliminary capacity design and a torque correlation methodology during installation to verify required capacity. Here we provide basic information on the LRFD methodology for helical anchor design. Additionally, the First- Order Second Moment (FOSM) method is applied to a previous helical anchor study (Hoyt and Clemence 1989) to determine resistance factors for an ultimate tension capacity strength limit state.MethodologyThe concept of the LRFD method is to establish factors for both the load and resistance that account for uncertainties using probability theory. The factors increase the nominal load and/or decrease the nominal resistance such that the probability of failure is an acceptable value. LRFD also accounts for the effects of load combinations (dead, live, seismic, wind, etc.) by determining the probability of the combined occurrence. The general form of the LRFD equation used by American Association of State Highway and Transportation Officials (AASHTO) is:"

Jan 1, 2009

By Ganesh Deepak K., Anjana R. K., Dr. Kumar Pitchumani N., Rajasekharam R. M. V. M. S. S.

The Phase 2 of Chennai Metro is being introduced in the city to ease the dependence on the existing transportation systems. Phase 2 is a combination of underground and elevated metro stretches comprising of three corridors. The current study focusses on the underground stretch of Corridor 3 which has a total of 29 underground stations. Construction of the underground cut and cover stations results in ground movements, which in turn impact the structures adjacent to the excavations. The greenfield ground settlement can be evaluated with the help of empirical approach or an approach requiring finite element modelling (FEM). The paper compares empirical and FEM approaches with regards to ground conditions in Chennai. Further, with the predicted ground settlements, building damage assessment is performed. The damage category of a building is defined based on the estimated tensile strains. This paper also compares the building damage assessment with empirical method and finite element modelling.

Nov 1, 2022

By Patrick J. Hannigan, Seth Robertson, Rozbeh B. Moghaddam

The Top-Loaded Bi-Directional Test (―TLBT‖) and the conventional Bi-Directional Load Test (―BDLT‖) are full-scale static load test methods. In both methods, the test loads are applied bi-directionally to the deep foundation. The advantages of the conventional BDLT have been well established for cost efficient static load testing of deep foundations, particularly for large diameter, high-capacity drilled foundations. A conventional BDLT applies the bi-directional test loads using an embedded jack and bearing plates. The TLBT method also applies the bi-directional test load to embedded bearing plates but does so using reusable high-strength threaded bars attached to an above-grade hydraulic jack and load transfer assembly. The new TLBT method is well suited for load testing shafts of a moderate diameter, length, and nominal resistance or ultimate load. TLBT advantages include economic considerations resulting from the method’s reusable load application components and constructability considerations as it readily accommodates a center concrete tremie pipe or pump line location. This paper presents comparison results from full-scale load tests performed using both bi-directional load testing methods. Adjacent 3-foot diameter by 30-foot long BDLT and TLBT shafts were tested. Details regarding subsurface conditions and test shaft construction are included for the comparison of the TLBT and BDLT results. Corresponding test data and analyses for both test shafts are presented and discussed in detail. The BDLT shaft had a maximum uni-directional load of 240 kips at upper and lower bearing plate displacements of 0.5 and -3.8 inches, respectively. The TLBT had a maximum uni-directional load of 300 kips at upper and lower bearing plate displacements of 1.0 and -5.9 inches, respectively. These results as well as the load-transfer behavior and equivalent top loading curve results from the adjacent BDLT and TLBT drilled shafts are discussed. The paper also discusses the strain gage instrumentation on the TLBT load application bars and on the embedded bearing plates.

Oct 1, 2022

By Mohini Patel, Jahnavi Parmar, Pranav R. T Peddinti

Expansive clays pose a variety of geotechnical problems. Although the admixture stabilization is proven to address their problematic swelling and shrinkage characteristics, the influence of unsaturated condition on the engineering performance of these soils needs further research attention. In addition, highly saline soils with high organic content would further alter their performance. A similar soil stratum was encountered at the Gulf of Cambay, Bhavnagar district, India. High salinity in the in-situ expansive soil of basaltic origin and the prevailing unsaturated condition, enforces the engineers to look out for possible soil treatment methods. In this regard, the present work attempts to analyze the unsaturated behaviour of this soil when fly ash is used as an admixture. A comparative study for stabilized and unstabilized mixes is performed in terms of their unconfined compressive strength, electrical conductivity, swell characteristics and California Bearing Ratio.

May 1, 2022

By D. Barber, A. D. Miller, P. A. Bray

The project was to develop an area within the existing West County Wastewater Treatment Plant which would enable the construction of a new Raw Wastewater Pump Station (RWPS) with a footprint of approximately 85 feet by 190 feet and a foundation depth of about 82 feet below grade and a new Short- Term Detention Basin (STDB) with a footprint of about 80 feet by 130 feet and a foundation depth that varied from approximately 3 to 24 feet below grade.. The excavation support system had to be designed to withstand both normal and the 100-year flood elevations. A Reinforced Soil-Cement Wall (RSW)was chosen to provide a hydraulic barrier which consisted of a single row of soil-cement elements installed along the perimeter of the area to be excavated. Steel wide flange beams were installed on 4 foot centers to support construction loads and be resistant to the lateral forces of the soil and hydrostatic pressures. The RSW was installed to a maximum depth of 104.5ft using a triple-auger drill rig with mixing paddles with a 2ft key into weathered shale providing a cutoff wall consisting of 53,150 square foot of treated soil. The project was to provide the initial design of the excavation support for the pumping station excavation support system and groundwater cutoff. There was 534 linear foot of soil-cement-bentonite wall installed and 106 - 80 foot long W21 x 121 wide flange beams installed on four foot centers into the alignment of the wall. Each element was drilled down into the weathered shale to obtain groundwater cutoff. Derek R. Guthrie Water Quality Treatment Center Pumping Package is the site for a new pumping station that will service Louisville, Kentucky residents. After unplanned long term exposure into the winter, the effects of freeze thaw cycles were evident.

Jan 1, 2017

By Yazen Khasawneh, Osvaldo P. M. Vitali, Mohammad Nassim

The demand for renewable energy is growing as the conventional energy resources are becoming more limited and we are more conscious about the negative impact of conventional energy sources on the environment. Wind turbines technology is evolving in a fast pace, the towers are becoming taller, and the rotors are getting larger. The challenge is to maintain the Levelized Cost of Electricity (LCOE) as low as possible to ensure a sustainable and an economically feasible energy supply. Thus, the foundation systems for wind turbines should evolve to meet the increasing load demand, while reducing the LCOE. In this paper, an innovative foundation system for onshore wind turbines is presented. The new foundation system is the conventional P&H tensionless pier foundation (PHTP) with a reinforced concrete collar at the top of the pier. 3D FEM modeling was conducted to assess the benefits achieved by adding a collar at the top of the PHTP foundation. The numerical results show a significant performance enhancement of the proposed foundation system over the conventional PHTP foundation. The enhanced foundation system also has an economical advantage because the depth of the pier can be greatly reduced while maintaining a superior performance.

Sep 8, 2021

By Frank J. Purcell

“Down The Hole” (DTH) hammer drilling is often necessary to advance the casing during pile construction where the test bores have determined difficult drilling conditions with obstructions such as boulders, cobble and glacial till. The use of compressed air to operate DTH hammers in foundation drilling has been a contentious point in many regions of the world due to its potential to disturb the ground around the pile being constructed. There are many examples of damage to adjacent building foundations where compressed air exiting the pile being drilled disturbed the subsurface around the building’s existing piles. This paper looks at the use of compressed air in DTH hammer foundation drilling and the move towards controlling the exhausted air to avoid over drilling the pile, causing potential damage to nearby piles. Simulated models of air flow penetration into the soil of different configurations of drill bits are discussed to highlight design changes employed to better control the air during the drilling process. A case study of the construction of a water-tight pipe pile wall for a building’s underground parking structure is studied to demonstrate the potential of DTH hammer foundation drilling where the air is fully controlled.

Nov 1, 2022

By Rick Deschamps

"Fountain Slide is located approximately 10 mi (16 km) northeast of Lillooet, British Columbia, Canada, within the Coastal Mountain Range, and has been locally active since the 1970s. The project site is located near the base of the relic Tunnel Mountain landslide. The progressive movements have posed a significant challenge to British Columbia (BC) 99, the main north-south highway in the region. The slide began affecting the British Columbia Railway Company (BCR) tracks in the 1990s. In 2004, the Canadian National Railway Company (CN) acquired BCR and, during the next 11 years, undertook measures to stabilize the rail bed. Some of the measures undertaken include numerous track realignments, a shotcrete and soil nail wall, an anchored soldier pile-and-lagging wall, and adding a row of anchors to the wall. For many years, the measures had proved successful until mid-2014 when it was observed that the slide retrogressed uphill of the tracks. Since that time, the slide movements typically ranged between 5/32 and 0.4 in (4 and 10 mm) per day, leading to extreme distortion of the earth retention system and the need for frequent track realignment.In the spring of 2016, CN issued a request for proposals (RFP) for a designbuild solution with the expectations of: (1) a safety factor greater than 1.2, (2) considering only the currently identified retrogressive blocks that extend to about 200 ft (61 m) above the track; and (3) minimizing activities outside the current easement. It was also communicated that there was a possibility that a portion of the line may have to be abandoned if the proposed remediation was cost prohibitive.The fact that the existing slide was a small fraction of the relic slide was intimidating. The relic slide extended for approximately 1.0 mi (1.6 km) above the uppermost retrogressive block that was now affecting the rail line. Other areas of concern included:"

Jan 1, 2017

By Robert Alperstein, Nidal AbiSaab, Joe Pastore

"This paper describes the design and construction aspects of the foundation support for a 57-story building currently under construction in lower Manhattan. The site is located near the East River with subsurface conditions consisting of about 40-ft [12.2-m] of unsuitable historic fill and soft plastic clay underlain by about 130-ft [39.6-m] of dense sand resting on bedrock. A mat foundation supported on unsuitable soils improved by jet grouting was selected for the project. Design concepts and selection of the engineering properties of the improved and natural foundation soils are discussed. The results of quality control testing and methods to verify design parameters during construction are presented.INTRODUCTIONNew York City (especially Manhattan) is known for its skyline of high rise structures. The geologic conditions in the New York Metropolitan Area influence the selection of foundations and feasibility of high rise construction as noted by Horvath (2013). These conditions include varying depth and quality of bedrock, multiple glacial events during the Pleistocene Epoch, and the effects of human modifications to the subsurface environment. Clusters of relatively taller buildings are generally located in Lower and Midtown Manhattan where sound crystalline bedrock is at relatively shallow depth beneath the ground surface and shallow foundations rest on the bedrock surface. In recent years the use of more costly high capacity driven piles or drilled caissons and deep basements has enabled the high skyline to spread to other areas."

Jan 1, 2016

By A. Rod Kern, Michael A. McNicholas, Yaser Taheri

Deep foundations were required for construction of an 18,000 ft2 (1,672 m2) 4-story office building and an adjacent 23,750 ft2 (2,206 m2) 5-story parking garage in Queens, New York due to an existing uncontrolled fill layer ranging from 15-20 ft (4.6 - 6.1 m) in thickness beneath the building footprint. The geotechnical engineers for the project initially selected auger cast-in-place (ACIP) piles over driven piles to limit the impact of noise and vibrations on the surrounding neighborhood. Ultimately, drilled displacement piles (DDP) were installed since this method offered a more economical solution that would generate the required pile capacity with shorter drill depths and would also mitigate spoils volume. During installation of test piles by the geotechnical contractor retained for the foundation work, multiple unanticipated soil conditions were encountered that would adversely affect the constructability of the piles. The existing fill contained significantly more natural and manmade obstructions than expected and the underlying glacial soil became too dense to penetrate at shallower depths than anticipated. This paper discusses how these issues were overcome through pre-drilling and the use of detailed instrumented test pile data coupled with in-house engineering capability to proactively re-evaluate minimum pile lengths at any given location and keep the project on track. INTRODUCTION Geotechnical work in the New York City market presents soil conditions that can be highly variable and challenging due to the presence of uncontrolled urban fill placed over the native soils. Construction in this area can therefore pose many unforeseen challenges, even with detailed geotechnical analysis being performed at project sites. A case in point is a construction site in Queens, New York. The proposed site development consisted of construction of a 4-story office building with a footprint of 18,000 ft2 (1672 m2) and a stand-alone 5-level parking garage with a footprint of 23,750 ft2 (2206 m2), together with associated new pavements and utilities. The site is bordered by a mix of commercial buildings and residential properties on all sides. Depth of the uncontrolled nature of the fill extended up to 20 ft (6.1 m) below street grade. Given the significant cost associated with removal and replacement, deep foundations were recommended to bypass the unsuitable soils and support the structures at depth where good bearing material existed.

Jan 1, 2019

By Patrick J. Hannigan, Frank Rausche, Rozbeh B. Moghaddam

Large diameter open-end pipe piles are increasingly used as deep foundations to support heavy onshore and offshore structures. During the driving process, several factors such as subsurface conditions, hammer type, hammer efficiency, pile type, plug conditions, temporarily increased base resistance, and loss of shaft resistance have direct impact on the driveability of large diameter open-end pipe piles. In a uniform subsurface condition, the unit shaft resistance increases with depth. Consequently, more resistance is accumulated as piles penetrate to greater depths which results in higher driving resistance. However, according to the friction fatigue analysis, the greater the number of shearing cycles occurring on a soil segment along the pile shaft, the greater the reduction of its shear resistance. As a consequence, since upper soil layers are subjected to a greater number of blows than those at greater depths, they have a relatively lower resistance compared to what would be calculated with standard geotechnical analysis methods. As a result of this progressive and nonuniform loss of shaft resistance with driving, blowcounts tend to increase at a lower rate than expected from traditional analyses. This paper discusses one of the approaches to the driveability analysis with the geotechnical friction fatigue consideration. It also shows comparisons between predicted driveability obtained from wave equation analysis and field driving records. All analyses were performed for a 2.134 m (7.0 ft) diameter open-end pipe pile installed at a total depth of 192.90 m (554 ft). Two separate static resistance and wave equation analyses were completed for the case study presented in this paper: 1) Friction Fatigue analysis based on the recommendations of Alm and Hamre (2001), subsequently referred to as the FF model, and 2) Standard Driveability analysis based on soil set- up factors, hereafter referred to as the SD model in this paper. Results from analyses included the shaft resistance distributions compared to the result of the signal matching analyses determined from the pile dynamic measurement. Furthermore, predicted blowcounts were compared to observed blowcounts during the pile driving. The comparison analyses indicated a 54.4 percent resistance loss of the Static Resistance during Driving (SRD) due to the geotechnical friction fatigue corresponding to a 46 percent reduction in total resistance. The analyses also showed that average predicted blowcounts using the friction fatigue were 6.4 percent lower than measured blowcounts, whereas, the standard driveability approach showed 42.1 percent higher blowcounts compared to the blowcounts shown in the driving log values.

Jan 1, 2019

By Reinaldo J. Villa, Joshua C. Adams

The I-395/SR-836/I-95 reconstruction project is an $818-million design-build construction effort that includes construction of viaduct, segmental and signature bridges in Miami leading into Miami Beach in Florida. Based on the load testing performed during the design phase, the design-build team determined that conventional driven pile and drilled shaft foundations were not feasible for support of segmental and signature bridges. Due to the weak limestone formation and successful use of auger cast-in-place (ACIP) piles in the Downtown Miami area on commercial developments, ACIP piles were selected as a foundation system to support bridges. This is the first time in history where the bridges will be supported by ACIP pile foundations in an interstate highway in the State of Florida. The design build-team worked closely with the Florida Department of Transportation to develop requirements for the load test program. The paper will provide an overview of the geotechnical data collected, results of dynamic/bi-directional load testing performed on test piles, data collected, installation of piles, and lessons learned. The load test program included a total of fifteen test piles with dynamic, bi-directional, and lateral load testing on 30 and 36-inch diameter ACIP piles and instrumented with thermal integrity profiling wires.

Sep 8, 2021

By Martin B. Hudson, Kenneth S. Hudson, Gwendolyn Arreguin

A twin high-rise project site in Century City posed several foundation engineering challenges for the design team. One portion of the twin high-rise project site was required to utilize top-down construction in order to allow a driveway to remain open during construction of the project’s 40-foot deep excavation. The challenge was compounded by the need to utilize a mat foundation to support the high-rise construction and yet have temporary drilled shafts through the mat foundation area that would not create excessive differential settlement. This was accomplished by constructing a deck supported by eight drilled end- bearing drilled shafts with Osterberg load cells and five 7-foot-diameter end-bearing drilled shafts. The Osterberg load cells served to verify the capacity of each of the drilled shafts and preload the soils at the drilled shaft tips. The 7-foot-diameter shafts were constructed with bond breakers to prevent skin friction but instead mobilize end bearing (for settlement compatibility with the surrounding mat foundation). After the drilled shafts were placed, then top-down construction began beneath the driveway, leaving the driveway supported on the drilled shafts. Construction challenges included drilling of the shafts through previously abandoned tieback anchors from an adjacent parking structure basement, as well as cemented layers within the rock materials. The paper describes the use of the various analytical methods used to calculate capacities and check settlement compatibility, the construction and testing methods utilized, and the construction challenges encountered. INTRODUCTION Wood Environment and Infrastructure Solutions, Inc. (hereafter referred to as Wood) performed a geotechnical investigation for the New Century Plaza currently being constructed in the Century City District of Los Angeles, California. The New Century Plaza project consists of the construction of two new towers (designated as North and South Buildings) and the rehabilitation of the existing Hyatt Regency Century Plaza Hotel. The existing hotel tower is 15 stories in height above the existing grade and is underlain by four subterranean basement parking levels. The new North and South Buildings will stand approximately 46 stories in height above the existing grade to accommodate residential use. The new towers are planned west of the existing hotel. The site was previously occupied by the existing hotel subterranean parking structure and overlying podium structure, and a loading dock in the southwest portion of the site. The former western portion of the podium and subterranean parking structure west of the existing hotel building western edge were demolished to allow for new subterranean levels, a new podium structure, and the new towers. The lowest floor of the proposed subterranean level required excavation on the order of 35 to 80 feet.

Jan 1, 2019

By Patrick J. Hannigan, Frank Rausche, Rozbeh B. Moghaddam

The Top-Loaded Bi-Directional Test (“TLBT”) is a new method to apply bi-directional loads to a deep foundation element with the loading source located above the foundation head. In the TLBT reusable load assembly, loads are applied to the foundation using the R-System which consists of two stacked steel plates located at the geotechnical resistance balance point or at the foundation base connected to the load assembly via vertical elements. The top plate or the Shaft Bearing Plate (“SBP”) will transfer loads to the foundation upper portion, and the bottom plate or the Base Bearing Plate (“BBP”) will transfer loads to the foundation lower portion as well as the foundation base. At the surface, above the foundation head, a hydraulic jack is located between a Top Load Assembly (“TLA”), and the Bottom Load Assembly (“BLA”). The TLA and BLA are connected to vertical elements which are consequently connected to the R-system. As the jack is pressurized and expanded at the surface, the R-System plates are separated, and the foundation is bidirectionally loaded. This paper presents a brief description of the conventional Bi-Directional Load Test (“BDLT”) including benefits and limitations followed by the TLBT method introduction including its benefits and advantages over other testing methods.

Sep 8, 2021

By Douglas R. Hardin, Stanley L. Worst, Joanna Mason

A challenging earth retention project presented itself in Washington, DC in the backyard of the historic House of the Temple (The Scottish Rite of Freemasonry, Supreme Council 33°). Located at 15th St NW and S St NW, a forty-foot-deep underground basement was to be installed adjacent to the existing Temple, a historic Carriage House structure dating back to the 1800’s and across a narrow alley from a four-story brick apartment building. The unique geology of the site included typical urban fill overlying a mixture of loose alluvial soils underlaid by dense marine deposits of the Potomac Formation. The clay, sand and gravel of the Potomac included nested boulders up to three feet in diameter. Design of the earth retention system accounted for ground conditions, installation methods and estimated movement of the system and adjacent structures. Anticipated ground water and unanticipated water from leaky sewers also proved obstacles to overcome during construction. Soldier beams were installed using a variable momentvibratory hammer to minimize disturbance to the historic and sensitive structures. Monitoring of the existing structures included both seismograph and optical targets during installation of soldier beams and as the excavation progressed. Micropiles drilled into the Potomac Formation were a part of the permanent foundation for the new structure. This local case history will delve into the details of the successful design, installation, and performance of an earth retention system and micropiles in a historic and highly congested urban environment.

Oct 1, 2022

By M. Krzaninski, Y. Zou, A. Frost

The foundation solution for a data centre building in Sydney, Australia comprised two alternatives, the first of which incorporated the use of CFA piles founded in rock at approx. 27m depth to support column working loadings of approx. 7.5MN, and the second utilising rapid impact compaction with a raft foundation of 1.0m thick concrete slab. Soil conditions comprised 1m of fill over 3 to 4m of sands varying from loose to dense consistency, underlain by very stiff clays overlying the rock. A creative solution incorporating Rapid Impact Compaction to improve the loose soils in conjunction with a piled raft solution was proposed. Piles proposed under the raft were Atlas Drilled Displacement piles which offered advantages of displacement pile performance and savings in time and material costs. The piled raft solution was developed in consultation with the consulting structural engineer, combining the skills of the piling contractor and consulting engineer to the benefit of the project. This paper describes the development and design aspects of the piled raft solution adopted for the project.

Nov 1, 2022

By Karen Talbot, Noah Maier, Rob Jameson, Giuseppe Gaspari

A storage and drainage tunnel advancing below I-75 in Detroit, Michigan experienced sudden subsidence. The Tunnel Boring Machine (TBM) was damaged to the extent that its shield, cutting head and extensive interior components needed to be extracted and replaced along with several completed tunnel segments. The tunnel was 16 feet (4.9m) in diameter with crown over 79 feet (24m) deep at the time. The tunneling contractor immediately engaged their designers and specialty subcontractors to develop a scheme to access the machine and repair the tunnel. They required a shaft 99 feet (30m) deep, with unobstructed plan dimension of 50 feet (15m) to accommodate the large components that needed to be removed and replaced. This precluded the application of an internally braced excavation and instead earth support solutions focused on use of a compression ring. Since the completed tunnel section behind the TBM obstructed closure of the compression ring below its invert, this paper describes the innovative access shaft solution employed. A conventional compression ring was constructed using 5 feet (1.5m) diameter drilled shafts down to the tunnel crown. In front of, and to the sides of the tunnel heading, the secant shafts were extended to over 150 feet (46m) depth, creating a horseshoe of support extending 50 feet (15m) below the planned excavation invert. Larger diameter "King Pile" shafts were drilled immediately to either side of the tunnel, overlapped into each end of the secant "horseshoe". The king pile shafts, together with a heavily reinforced ring beam above the crown elevation, acted as a door frame to transfer hoop loads from the incomplete secant arc into reaction supports above and below the tunnel. These oversize king pile shafts were extended and socketed into rock over 70 feet (21m) below tunnel invert. Very tight installation tolerances were necessary to maintain secant shaft alignment to depths exceeding 150 feet (46m). The project operational, geotechnical, and quality data was managed and visualized using a custom GIS interface. This paper will present the design approach employed and review the construction and quality program selected to repair the tunnel.

Oct 1, 2022

By Dean Abbondanza

"Below grade foundation design has construction issues that above grade foundations do not. These cost factors are dependent on soil conditions and vary by region, but for the most part, the process remains standard.An innovative design concept using steel sheet piles as the permanent wall element changes the traditional cost and schedule for below grade foundations. The sheet pile application reduces dewatering requirements, does not require waterproofing on the vertical walls and eliminates the cast in place concrete wall structure.Foremost, this versatile application affords both Contractor and Designer the choice of two methods of construction; conventional bottom up or top down. The top down method not only provides the savings of bottom up, but also eliminates the cost of anchors while taking the foundation out of the critical path in the early stages of construction. CONVENTIONAL FOUNDATIONSINTRODUCTIONUS construction for a conventional below grade (BG) foundation is fairly standard. Design and install the shoring system, followed by dewatering (if groundwater is present), then excavate in stages with installation of anchorage as work proceeds to final elevation. The site is graded for a waterproofing system to be placed at the base. Once the base slab is cast; forms are set for the vertical reinforced walls. After curing , waterproofing is applied to the back side. The remaining levels are constructed until ground elevation is reached. The site is backfilled and the ground floor is cast. The foundation is now complete and work on the superstructure can now begin."

Jan 1, 2005

By Arash Khosravifar, Nason McCullough, Stephen, Milad Souri, Scott Schlechter, E. Dickenson

The results of five centrifuge models were used to evaluate the response of pile-supported wharves subjected to inertial and liquefaction-induced lateral spreading loads. The centrifuge models contained pile groups that were embedded in rockfill dikes over layers of loose to dense sand and were shaken by a series of ground motions. The p-y curves were back-calculated for both dynamic and static loading from centrifuge data and were compared against commonly used API p-y relationships. It was found that a significant reduction in ultimate soil resistance occurred in dynamic p-y curves in partially/fully liquefied soils as compared to static p-y curves. It was also found that incorporating p-multipliers that are proportional to the pore water pressure ratio in granular materials is adequate for estimating pile demands in pseudo static analysis. 1. INTRODUCTION Liquefaction-induced ground deformations can cause severe damage to pile-supported wharves and other waterfront structures. A common approach in analyzing the lateral behavior of piles against seismic loads is using the beam on nonlinear Winkler foundation (BNWF) or p-y spring analysis. One common p-y relationship for sand is the one proposed by the American Petroleum Institute, also known as the API sand model (API 1993). While the API sand model was originally developed for the static loading conditions, it is common to modify the API sand curves for the effects of cyclic loading. However, there is no consensus on how to modify the static p-y curves for the effects of liquefaction and pore water pressure generation in loose granular soils. In previous studies, p-y springs of piles in liquefying soils were back-calculated from case histories, centrifuge model studies (e.g., Wilson et al. 2000; Brandenberg et al. 2005; Abdoun et al. 2003), full-scale tests (e.g., Rollins et al. 2005; Chang and Hutchinson 2013), and numerical analyses (e.g., McGann et al. 2011). In general, these studies found the softening effects of soil liquefaction on p-y curves, as well as a hardening behavior attributed to the dilative response of the liquefied soil around the pile. However, these studies provide varying recommendations on how to modify the static p-y curves to capture this complex behavior. Some design guidelines propose softening the static p-y curves using p-multipliers (e.g., Caltrans 2012). Other studies propose an upward concave shape for p-y curves in liquefied soils (e.g., Franke and Rollins 2013; Chang and Hutchinson 2013).

Jan 1, 2019