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By D. V. Roberts

Approximately 800 private consulting engineering firms in America specialize in geotechnical engineering. The gross income from these firms totals about $500 to $600 million per year. Sixty-five to seventy-five percent of this geotechnical work is per­formed by consulting engineers that belong to the Association of Soil and Foundation Engineers (ASFE). This paper presents statistics concerning the business activities and functions provided by ASFE member firms. The procedures used in typical projects are described. The paper concludes with a summary of major trends which are impacting the American geotechnical practice today.

Jan 1, 2010

By James J. Tansey

A Deep Foundations Institute meeting with the University of Michigan at Ann Arbor in March of 1984 featured legal rights under Differing Site Conditions. A workshop conducted by the authors and Gerard Ittig, Esq. added to the value of the symposium. This paper will be of interest to your attorneys in any subsurface disputes.

Jan 1, 1985

By Robert L. Parsons

This paper describes the results of a detailed analysis of a loess deposit at the deep foundations test site established by the Kansas Department of Transportation. Multiple CPT, SPT, and pressuremeter tests were conducted as part of the investigation. This paper includes an evaluation of the effectiveness of common correlations used with the CPT, SPT when used for classification of loess and estimating its properties. Results show that common correlations must be used with caution as significant errors in estimation may result from using methods developed for other soil types. Laboratory testing included direct shear, triaxial, collapse, and consolidation testing, with many of the tests conducted on both vertically and horizontally oriented samples to evaluate anisotropic behavior. The results showed that strength properties could be considered to be isotropic.

Jan 1, 2009

By Mohammed Sakr

A Two-Section Helical Pile (TSHP) is a steel pipe with two shaft sections of different diameters and with one or more helix plates near the bottom of each shaft section. TSHPs are used regularly in western Canada as foundation pockets for single and double circuit distribution power line poles. The results of a comprehensive lateral pile load test program and the field monitoring of TSHPs installed in organic soil (muskeg) over soft clay are presented in this paper. A total of nine full scale lateral load tests were carried out, including seven tests using TSHPs with different diameters and embedment depths, and two tests using one-section helical piles. The prime objective of the study was to evaluate the lateral resistance of TSHPs installed into very soft organic soil (muskeg) overlying soft clay soils, to compare their lateral resistance relative to one-section helical piles and to compare the measured and the estimated lateral resistances using p-y curves. In order to provide sufficient soil data for analysis, the subsurface soil stratification was evaluated using two different techniques including; Cone Penetration Tests (CPT) and Portable Soil Probe Tests (PSPT). The two testing techniques were also compared and evaluated. This paper summarizes subsurface soil conditions, pile configuration, helical pile installation procedure, testing setup and results.

Jan 1, 2009

By Shachar Magali

This article describes two new concepts regarding the CFA (Auger Cast) piles. The first one, MALI Effect, is an approach to control the casting phase, while the second one, NETA Shear, is a technique which converts the drilling rig into a geo-mechanical tool. We look upon the system of the auger and the ground as a piston inside a cylinder. When concrete (grout) is pumped into that system, an up lift force is generated (We call that force MALI Effect). That up lift force reduces the needed tension in the pull up cable. By analyzing the tension force in the cable we detect the up lift force of the concrete. That pushup force is the product of the real concrete pressure at the bottom of the auger by the area of that bottom. As the area is known, the real pressure is accurately calculated. A control loop which is based on MALI Effect is very sensitive, precise, objective, reliable and easy to be used. All the process is based on pure real physical measurements. The system has no assumptions, no comparisons, no parameters, no zeroing and no adjustments. When we penetrate into the ground like a theoretical screw, for about a meter in depth, and then brake the main cable while rotating the auger, a set of forces generates. As the auger tends to keep penetration, but the cable holds it - a tension force develops (We call that force NETA Shear). Analysis of that tension force shows that it relates to the ultimate shearing capacity of the ground.

Jan 1, 2000

By Morgan L. Race, Matthew R. Glisson

"Most driven pile projects have plumbness limits from 0.25 in/ft (21 mm/m) to 0.5 in/ft (42 mm/m) to control bending stresses. For two projects, the project teams performed static load testing to evaluate performance of piles with sweep. One project, located in Grand Forks, North Dakota, used 9.625-inch (244-mm) diameter piles with a wall thickness of 0.395 inch (10 mm) and lengths ranging from about 130 to 160 feet (40 to 49 m). Measured pile sweep (lateral offset distance of the pile toe from the pile top) was between 12 and 17 inches (305 to 432 mm). Static load testing indicated that the piles could support the design load with axial deflection of less than 1 inch (25 mm) but only provided about 80 to 90 percent of the ultimate resistance at axial deflections of about 1.9 to 1.7 inches (49 to 43 mm), respectively. The other project, located in Shakopee, Minnesota, used 9.625-inch (244-mm) diameter pile but with a wall thickness of 0.352 inch (9 mm) and lengths around 50 to 90 feet (15 to 27 m). The measured sweep varied between about 20 and 63 inches (508 and 1,600 mm) for 9 of 214 piles driven at the site. Load testing indicated that these piles could provide the required design resistance with less than 0.3 inch (8 mm) of axial deflection and support the required ultimate resistance with about 0.5 to 0.6 inch (13 to 15 mm) to of axial deflection.INTRODUCTIONAnyone who has observed a significant number of piles has seen that, inevitably, the pile is not perfectly straight after driving. In spite of the best efforts of contractors, there are a whole host of reasons for piles to end up out-of-plumb or to have a curve, sometimes referred to as pile sweep. Most project specifications set limits for plumbness typically between 0.25 in/ft (21mm/m) and 0.5 in/ft (42mm/m) (USACE, 1991; PDCA, 2007; MnDOT, 2016; MoDOT, 2016). Closed-end pipe piles, including monotube or tapertube, are the only pile type that allow actual measurement of the final alignment of the pile.As Nadeem, et al. (2015) note, buckling failure of long, slender piles is the predominant mode of pile failure in soft soils. Pile sweep is just one source of buckling failure in long, slender piles. The nonlinear buckling analysis showed that increasing slenderness ratio and/or increasing degree of curvature decreases the loadcarrying capacity of a driven pile. Nadeem, et al. (2015) considered solid, steel pile with lengths from 24 to 66 feet (7.5 to 20 m), diameters from 9.75 to 26 inches (244 to 660 mm), initial bends from 2 to 6 inches (50 to 150 mm), and half- and quarter-sine shapes."

Jan 1, 2017

By Arash Khosravifar, Matt Steffan

An expansion of the City of Klamath Falls Wastewater Treatment plant required geotechnical seismic hazard evaluations and deep foundation design. The site is located on the shore of Lake Ewauna and is underlain by diatom rich lake deposits. Diatomaceous soils exhibit unique engineering properties that are not well understood. Cyclic Direct Simple Shear (CDSS) testing was performed on three undisturbed samples to evaluate cyclic and post-cyclic properties of the diatomaceous soils. Results from the CDSS testing indicated that the soils would not liquefy in the classical sense, though cyclic softening behavior was observed. The CDSS results were used to develop a Cyclic Resistance Ratio curve for the diatomaceous soil to compare with clean sand liquefaction curves. Seismic lateral pile capacities were developed using two approaches. One approach used conventional p-multipliers for liquefied soil and modified them to reflect expected excess pore pressure ratios. The other approach applied residual strength and fifty percent strain values from post-cyclic monotonic shear testing. A lateral spread hazard zone was identified along the Lake shoreline and reduced, seismic lateral pile capacities were recommended. The objective of this paper is to report the seismic design considerations for this project in a unique geologic and seismic setting. INTRODUCTION The engineering properties of diatomaceous soils have rarely been studied and the cyclic behavior under seismic loading is generally unknown. Some of the critical geotechnical uncertainties of diatomaceous behavior include potential for large consolidation settlement, influence of irrecoverable strains due to diatom particle crushing, shear strength (peak and residual), and cyclic properties. This paper presents results of cyclic shear testing, seismic evaluations and seismic lateral pile design in diatomaceous soils performed for the expansion of a waste water treatment plant in the city of Klamath Falls, Oregon, site of the largest recorded earthquake in Oregon’s history. The expansion consisted of adding six new facilities at the existing Plant including influent pump station (IPS) and headworks, aeration basin, tertiary treatment, and other buildings. The IPS/headworks and aeration basin will be founded approximately 15 feet below ground. The other buildings will be founded at grade. The existing facilities are supported by timber piles that penetrate the surficial diatomaceous soils and terminate on a hard underlying deposit. Figure 1 shows the site plan and proposed additions.

Jan 1, 2018

By Joseph T. Coe, Siavash Mahvelati, Alireza Kordjazi

This paper introduces recent advances in stress-wave NDT systems for use in assessments of in-service foundation integrity and drilled shaft construction. The primary results of the laboratory experiments are very promising, as the acquired image was capable of differentiating changes in pile cross section as low as 0.3 cm. The preliminary results with the same hardware components on a relatively large scale cemented sand model were also promising. A brief overview is provided of both systems including hardware, survey methods, and data processing techniques, followed by a discussion on application of the results to QA/QC of deep foundations. INTRODUCTION There are two main applications in which current QA/QC NDT technology fails to provide sufficient information regarding deep foundation conditions: (1) detection of flaws in outside cover concrete of drilled shafts and corrosion in steel piling; and (2) evaluation of anomalies beneath the bottom of drilled shaft excavations. Previous studies have demonstrated the capabilities of high frequency stress waves for geotechnical and foundation evaluation purposes (Lee and Santamarina 2005; Coe and Brandenberg 2010; Coe and Brandenberg 2012; Coe and Kermani 2016). Higher frequency waves can visualize smaller anomalous features at the expense of higher attenuation and smaller propagation distance. Therefore, the goal of this study was to advance the state of NDT practice by development of a prototype high resolution stress-wave imaging system as proof-of-concept. The equipment and hardware were modular, which allowed simultaneous development of two system configurations for application to in- service foundations as well as drilled shaft excavations during construction. Results are presented based on two large scale soil models. The first laboratory model simulated section loss in an in-service steel pipe pile and drilled shaft foundation (Fig. 1a). The second model simulated anomalous conditions beneath drilled shafts excavations as might be encountered in areas with significant karst (Fig. 1b). For both models, evaluation of foundation conditions relied on the propagation of small amplitude seismic stress waves using hardware similar to those described in Coe and Brandenberg (2010) and Coe and Brandenberg (2012).

Jan 1, 2018

By James S. Graham

Foundation pile driving hammers used in New York City in the past 100 years have been drop, steam, compressed air, diesel, and hydraulic. In 1992, the first hydraulic hammer in the New York City area was purchased by Norwalk Marine Contractors, Inc. from Junttan in Finland. It was bought because of its variable energy and ease of mobilization, not because of its higher transferred energy. Heller and Johnsen engineers instrumented hydraulic hammers on nine jobs. The measured transferred energy for the nine jobs was found to average approximately 80 percent. There is no clear consensus regarding the reasons for the hydraulic hammer being more efficient in delivering energy to the pile as compared to single-acting steam/air impact hammers. To minimize pile damage during installation, and to minimize footage overruns, an up-to-date version of the wave equation software that includes an efficiency value of 0.95 for hydraulic hammers is now used.

Jan 1, 2000

By Sanket Rawat, Ravi Kant Mittal, Vikash Prasad

"The understanding of the response of pile foundations under various types of loads is a necessary prerequisite to analyze and design them properly. Therefore, this paper highlights and compares the provisions available in Indian Standard IS 2911:2010 to estimate the capacity of laterally loaded pile foundation with the provisions available in different country codes and existing literature. Comparisons are made between the Indian standard method, Broms method and Matlock & Reese method for the analysis of laterally loaded piles due to popularity and prevalence of the later methods in design offices worldwide. This has been achieved using a parametric study on pile embedded in pre-consolidated clay and sand for both fixed head and free head case in terms of displacement and ultimate load capacity. It has been found that there are various limitations to the Indian Standard method associated with various cases such as short pile analysis, complete moment distribution etc. Therefore, suitable recommendations have been made on the basis of the above comparison to improve the accuracy of the design in Indian perspective. The proposed comparison and subsequent area of improvements will present the design engineers all across the globe, a broad sight of design specifications of laterally loaded piles.INTRODUCTIONPiles in groups are very often subjected to both axial and lateral loads. In the 1960’s, designers used to assume that the piles could carry only axial loads and the lateral load is to be carried by batter piles. However, later, a large number of load tests authenticated that vertical piles also can transfer lateral loads through shear, bending, and lateral soil resistance rather than purely acting as axially loaded members. Initial attempts to analyze laterally loaded piles used the finite-difference method, as described by Howe (1955), Matlock and Reese (1960), and Bowles (1968). Matlock and Reese (1956) used the finite difference method to get a series of non-dimensional curves to enable the user to input the appropriate curve with the given lateral load and estimate the ground-line deflection and maximum bending moment in the pile shaft. Later, Matlock and Reese (1960) extended the earlier curves to include selected variations of soil modulus with depth."

Jan 1, 2017

By Don C. Warrington

This paper is a survey of the various methods and research efforts by which the drivability of piles is determined. First, a brief outline of the basic theory and the important parameters for driving by vibration are presented. Then, a wide variety of methods by which the drivability of piles is determined are presented and discussed, with special emphasis on methods developed in the USSR. Each of these methods are examined as to how they take into account the various parameters of vibratory pile driving, such as eccentric moment, frequency, dynamic force, motor torque and power, vibrating and static weight, and other variables. Some relation of these methods of field data is presented as well.

Jan 1, 1989

By James Weaver

During the past 16 years, the authors have successfully used high-capacity rock anchors installed inside open-ended pipe piles, driven to bedrock, to provide uplift and overturning resistance for various structures including piers, bridges, power plant components and commercial buildings. These systems were ultimately used on the projects due to a combination of high uplift forces or overturning moments on the structures and the relatively poor subsurface conditions present at the sites. Other, foundation systems such as rock-socketed drilled shafts and spin fin piles were considered but were found to be economically prohibitive or not technically feasible.

Jan 1, 2011

By Douglas C. Brunot

Mabey Inc. is providing for the shoring design for the Naples bay Center project, located in Naples, FL. The excavation is approximately 374' long by 164' wide and is 27'-8" deep at the shoring line with a groundwater level six feet below present grade. The project Excavation is for a multi-use facility for residential and retail with underground parking. The shoring design will be incorporated into the foundation walls for the building. Mabey is using its pre-engineered Super Powerbrace Plus (SPP) wales and Mega Struts to support the excavation in two phases. The system design and the design of all the pre-engineered components are by Mabey. The foundation is supported on drilled shafts arranged with the building column grid. The excavation will be completed in two phases to allow for equipment mobilization and operation on a site with limited access. The construction sequence will begin with placement of the drilled shafts. The drilled shafts will also serve as the building columns. After the drilled shafts have cured, 630 AZ24-700 x 45 ft. long sheet piles will be installed. The sheets will be arranged in two phases, divided by a center row of piles. Since de-watering in south Florida is very expensive and often downright impossible prior to placing the seal slab, all the initial foundation and excavation bracing work will be completed with groundwater in situ. The entire excavation will be excavated to 5 ft. below ground surface to allow for the installation of the wale support brackets at 12 ft. on center, welded to the sheet piles. After the support brackets are installed, the SPP hydraulic wales and the Mega Strut hydraulic braces may be installed for both phases. Once the frames and struts are in place, Phase 1 excavation is completed, followed by Phase 2 excavation. The 4-ft. thick seal slab is then placed and cured in the wet. De-watering is now possible with the seal slab in place. Once the excavation is de-watered the leveling slab is placed and cured. The center row of sheet piles is then cut off at the top of leveling slab. With the leveling slab cured, the sheet piles have enough strength to support the excavation without the frames and struts near the ground surface. The permanent sheet piles are then seal welded for water proofing and the foundation walls are cast with the sheet piles. The design is modelled in 3D using REVIT to ensure accuracy of the design. The earth pressures are developed using Coulomb theory as there is a top frame and the frame and sheet pile are flexible and move to develop an active pressure wedge. Earth pressure uniform loads and loads from predicted surcharge are modeled in STAAD to determine load effects on the SPP frames and Mega Struts. Coulomb theory and Mabey’s structural model will be tested through monitoring with Mabey’s LIVEPin system. LIVEPin will be placed in struts for each phase of construction. The LIVEPin results will be calibrated with the structural model to determine actual frames forces and will also determine the actual earth pressures applied to the system from surrounding soil. Mabey has used the LIVEPin system in similar applications and this has helped us determine modelling accuracy.

Jan 1, 2018

By Jason N. Scott

CFA piling is a ?blind? construction process that relies heavily on the rig instrumentation to produce sound piles. If the data measured and recorded during construction can be made available to engineers and managers within hours after construction then there are many economic and quality control benefits that can be realised. A state of the art CFA instrumentation and data management process has been developed in the UK. The key components of the instrumentation, GSM data service and the central database are described. Many benefits to the business have been realised and, where possible, these are quantified.

Jan 1, 2006

By S. T. Kok

This paper presents a case study in West Malaysia for passive piles failure in very soft marine clay in open excavation. In this particular case, the thickness of the very soft marine clay ranges from 5 m to 7 m (16 ft to 23 ft) from the ground surface. Preliminary site investigation reported SPT ?N? value of zero for the very soft marine clay. The design was based on a deep foundation utilizing driven piles to support the superstructure. During pile cap construction, the piles were subjected to uncontrolled open excavation, inducing bending moment in the piles, resulting in some cracked and broken piles. Analyses were carried out using an existing three-dimensional finite element code with a non-linear soil model to predict the response of these piles during excavation. Finally, the predictions of pile responses during excavation were compared satisfactorily with the observed results.

Jan 1, 2009

By Rozbeh Moghaddam, William D. Lawson, Priyantha W. Jayawickrama, Hoyoung Seo, James G. Surles

"This study provides calibration of resistance factors (?) for design of driven piles to implement Load and Resistance Factor Design (LRFD) for bridge foundations using Texas Cone Penetration (TCP) Test data. The basic research approach was to compile a database of published full-scale load tests including projects from the Texas Department of Transportation’s (TxDOT) historical archive and projects from neighboring state DOTs. Load test results from neighboring states were leveraged by performing new geotechnical borings with TCP tests at the project sites. The final dataset consisted of 30 load tests performed on precast square concrete piles, with pile widths ranging from 356 to 508 mm and penetration depths ranging from 5.2 to 25.5 m, driven in soils. Ultimate capacities for each load test were interpreted based on Davisson, 5%, and 10% settlement criteria. These measured ultimate capacities were compared against predicted capacities estimated from TCP blow count values (NTCP) and design charts following the procedures outlined in TxDOT’s Geotechnical Manual. From the comparisons, statistical parameters of the biases (??= measured capacity/predicted capacity) such as mean and coefficient of variation were obtained. Resistance factors (?) for LRFD were then determined using Monte-Carlo simulations for each ultimate capacity criteria with the target reliability indices of 2.33 and 3.00.INTRODUCTIONThe Texas Department of Transportation (TxDOT) has used the Texas Cone Penetration (TCP) test since its development in the 1940s. The TCP test is an in-situ penetration test to characterize the materials encountered during geotechnical exploration. Texas currently maintains over 53,000 bridges in the National Bridge Inventory (FHWA 2016), and most of these bridges plus other transportation infrastructure in Texas are supported by foundations designed using the TCP test and its associated foundation design method. The Oklahoma DOT adopted the TCP test and foundation design approach in the 1970s, so the foundations for most of the 23,000 bridges in Oklahoma’s inventory were also designed using the TCP method. With this significant body of experience, the TCP method has been viewed as a straightforward, relatively easy-touse foundation design method that consistently yields safe, serviceable, economical, and maintainable foundations. TxDOT’s deep foundation design method is documented in the TxDOT Geotechnical Manual (TxDOT 2012) and currently employs the allowable stress design (ASD) approach. However, the Federal Highway Administration (FHWA) has mandated that the states begin to implement the LRFD method in place of the older ASD approach (Densmore 2000). This paper presents resistance factors at ultimate limit state (ULS) for design of driven piles using the TCP test, resulting from efforts to be in compliance with the FHWA policy."

Jan 1, 2017

By Harry G. Poulos

Ground movements can arise from a large number of sources and can have a significant effect on nearby piles and deep foundations. The loading of the piles by ground movements is a different mechanism to that arising from direct applied loading to the pile head, and consequently it is not generally possible to adequately analyze the effects of ground movements simply by applying some type of equivalent loading to the pile head. The main effects of ground movements are the development of additional movements, axial forces and bending moments in the piles, and thus the key design aspects are related to movements and to the structural integrity of the pile. However, the ultimate geotechnical load carrying capacity is generally not affected by the ground movements themselves. This paper will describe an approach to the analysis of ground movement effects on piles, considering axial and lateral movements separately. Some of the main features of pile response will be discussed for three specific problems involving ground movements: 1. Piles near and within embankments; 2. Piles near an excavation for a pile cap; 3. Piles subjected to seismic ground motions.

Jan 1, 2007

By James A. Schneider

Selection of resistance factors within Load and Resistance Factor Design (LRFD) requires accurate assessment of uncertainty and bias in load and resistance. To date, many studies have focused predominantly on the assessment of uncertainty, while the potential for bias appears to be the dominant factor in design for consistent levels of reliability under a variety of situations. Bias comes from factors which have been ignored in design method development but significantly influence resistance when extrapolating from conditions typical of databases to those at a given site. Uncertainty and bias can be quantified as the coefficient of variation and mean (or median) of a data set, respectively, for statistical assessment of load and resistance factors. This paper first presents an overview of statistical assessment of resistance factors, and then discusses factors that influence uncertainty and bias when extrapolating to situations outside of conventional databases of driven pile axial capacity.

Jan 1, 2009

By Alessandro Bertero, Dylan Pearson, Wesley Schmutzler, Matteo Bertoni

"The SR 83/US 331 highway is located in the Florida panhandle, where it connects the Walton County beaches to the I-10 corridor. The roadway is of vital importance to the economy of the area as well as its safety since it represents the primary hurricane evacuation route from southern Walton County. The Florida Department of Transportation (FDOT) decided to increase the number of traffic lanes from two to four and improve the geotechnical properties of the moderately deep, very loose foundation soils, that had affected the highway rideability for years. The soil mixing was selected as the method to meet the unique deep ground improvement challenges of the project. The design required that Shallow Mixing Method (SMM) be used to build a 10-foot thick platform that transferred axial load to the bottom soil layers through a series of Deep Mixing Method (DMM) columns. Upon completion over 8,300 SMM columns and 1,500 DMM columns had been installed, with no remedial work required. Also, only 1% of the almost 1,500 specimens tested did not meet the specification requirements. This paper will describe the challenges encountered and provide valuable information that may be useful for other future projects, including details not previously published.INTRODUCTIONThe counties of Walton and Okaloosa have been a very popular vacation destination for many ears. The 50-mile long coastline boasts beautiful, sugar-white beaches and waters the color of emeralds. The popularity of the area has been growing even further, over the last few years. A consequence of this phenomenon is a fast-paced increase of the traffic flow on the SR83/US331 highway, especially at the bridge that connects the Walton County beaches across Choctawhatchee Bay (Fig. 1) to the heavily traveled I-10 corridor. The highway plays a very important role for the area also as a commercial link and as the primary hurricane evacuation route from southern Walton County. The increase in traffic has produced higher travel time, when not a complete traffic paralysis, and exacerbated the issue of ground settlement where accelerated wearing of road foundation occurred due to the presence of very loose, moderately deep, soils, that had afflicted the highway for several years. The Florida Department of Transportation (FDOT) decided to put an end to these issues by increasing the number of traffic lanes from two to four and improving the geotechnical properties of the foundation soils. The Design-Build Maximum Price Request for Proposal (RFP) issued for the expansion of the Choctawhatchee Bay Bridge saw the participation of numerous D/B teams which produced various technical solutions. Among them, the FDOT selected the Skanska/Parsons Brinckerhoff (General Contractor) proposal which provided for the use of soil mixing as the ground improvement technology. The design/build team assigned Foundation & Geotechnical Engineering (Designer of Record) the ground improvement design which Treviicos South (Specialty Contractor) would execute."

Jan 1, 2017

By S. Ali Bastani, Ashley Varni

Design acceleration response spectra (ARS) are directly correlated with dynamic forces and estimated dynamic bridge displacements, which make them a critical aspect of dynamic bridge design. Nonlinear site response analyses are performed for a 1,400-linear-foot bridge site with a SC soil profile at the sides and a SF soil profile in the middle to evaluate the soil profile effects on the bridge analyses. One-dimensional seismic response analysis is commonly performed for site-specific response analysis. SHAKE or similar one-dimensional total-stress equivalent-linear approaches have been used since the 1970s. However, the equivalent linear method has deficiencies when the subsurface soils are susceptible to strain softening. Therefore, various assumptions are made when using the equivalent linear method by practitioners to estimate the SF soil profile site response. With recent advancements in constitutive models, effective stress models have become more popular. Although the effective stress models are generally more complicated and require additional input parameters, they shed further light on the liquefaction mechanism and its effect on the surface ARS. An equivalent-linear one-dimensional seismic response analysis and a non-linear effective-stress seismic response analysis, using DEEPSOIL, were performed to evaluate the ground surface ARS for a proposed bridge site in Orange County. The soil shear strengths were estimated based on cone penetration test results using empirical relationships. The shear modulus degradations (backbone curves) of soil layers were adjusted to match the estimated soil strength at failure. The ARS curves developed from each method were compared to determine the most suitable method for estimating a site-specific design ARS curve for a liquefiable site. Considering that the bridge abutments and the outer bents are founded in bedrock, while the middle bents are founded in liquefiable soils, ARS curves were created for each subsurface condition. Taking into account limitations of the structural analysis software, recommendations were made to combine the multiple ARS curves into a single ARS curve for the structural bridge design.

Jan 1, 2018