Ross W. Boulanger

Analysis of Bender Element Tests

A study is presented of potential errors in, and methods of interpreting, the results of cantilever-type, piezoceramic bender element tests for measuring the shear wave velocity of laboratory soil specimens. Interpretations based on the first direct arrival in the output signal are often masked by near-field effects and may be difficult to define reliably. Interpretations based on characteristic points or cross-correlation between the input and output signals are shown to be theoretically incorrect in most cases because of: (1) the effects of wave interference at the boundaries; (2) the phase lag between the physical wave forms and the measured electrical signals; and (3) non-one-dimensional wave travel and near-field effects. Interpretations based on the second arrival in the output signal are theoretically subject to errors from non-one-dimensional wave travel and near-field effects. Differences in Vs values obtained by the different interpretation methods are illustrated analytically and experimentally.

Nonlinear Seismic Soil‐Pile Structure Interaction

Analytical design tools for evaluation of soil-pile-structure interaction during seismic events are evaluated and modified. Several implementations of the “Beam on Nonlinear Winkler Foundation” (BNWF) method were used to predict results of centrifuge model tests of single piles in a soft clay soil profile. This paper shows that calculations from these computer codes can be sensitive to the details of the arrangement of nonlinear springs and linear viscous dashpots. Placing the linear viscous dashpots (representing radiation damping in the far field) in series with the hysteretic component of the p-y elements (representing the nonlinear soil-pile response in the near field) is shown to be technically preferable to a parallel arrangement of the viscous and hysteretic damping components. Preliminary centrifuge data is reasonably modeled by the numerical calculations using this implementation of damping, but additional field or physical model data are needed to fully evaluate the reliability of BNWF procedures.

Inelastic Seismic Response of Extended Pile-Shaft-Supported Bridge Structures

Nonlinear static and dynamic analyses were used to evaluate the inelastic seismic response of bridge and viaduct structures supported on extended cast-in-drilled-hole (CIDH) pile shafts. The nonlinear dynamic analyses used a beam-on-nonlinear-Winkler foundation (BNWF) framework to model the soil-pile interaction, nonlinear fiber beam-column elements to model the reinforced concrete sections, and one-dimensional site response analyses for the free-field soil profile response. The study included consideration of ground motion characteristics, site response, lateral soil resistance, structural parameters, geometric nonlinearity (P-Δ effects), and performance measures. Results described herein focus on how the ground motion characteristics and variations in structural configurations affect the performance measures important for evaluating the inelastic seismic response of these structures. Presented results focus on a representative dense soil profile and thus are not widely applicable to dramatically different soil sites.

Probabilistic Standard Penetration Test–Based Liquefaction–Triggering Procedure

AbstractA probabilistic version of the Idriss and Boulanger standard penetration test (SPT)–based liquefaction triggering correlation is derived using a maximum likelihood approach and an updated case history database. Measurement and estimation uncertainties in the cyclic stress ratio (CSR) and SPT (N1)60cs values and the effects of the choice-based sampling bias in the case history database are taken into account. The results of sensitivity analyses show that the position of the most likely triggering curve is well constrained by the case history data and that the magnitude of the total error term is also reasonably constrained. The most likely value for the SD of the error term in the triggering correlation is, however, found to be dependent on the uncertainties assigned to the CSR and (N1)60cs. The results of the sensitivity study appear to provide reasonable bounds on the effects of different interpretations on the positions of the triggering curves for various probabilities of liquefaction. Methods ...

CPT-Based Liquefaction Triggering Procedure

AbstractA probabilistic cone penetration test (CPT) based liquefaction triggering procedure for cohesionless soils is derived using a maximum likelihood method with an updated case history database. The liquefaction analysis framework includes revised relationships for the magnitude scaling factor (MSF) and for estimating fines contents from CPT data when laboratory test data are not available. The updated case history database and methodology for developing the liquefaction correlation are described. Measurement and estimation uncertainties, the potential effects of false positives and false negatives in the case history database, and the effects of the choice-based sampling bias in the case history database are accounted for. Sensitivity analyses showed that the position of the most likely triggering curve and the magnitude of the total error term are reasonably well constrained by the data. The sensitivity study provides reasonable bounds on the effects of different interpretations, from which probabil...

SPT- and CPT-Based Relationships for The Residual Shear Strength of Liquefied Soils

An evaluation of post-earthquake stability of earth embankments or slopes that contain, or are founded on, soils that may liquefy requires estimating the liquefied soil’s residual shear strength, Sr. Decisions regarding the need for expensive mitigation efforts, including ground improvement work, often hinge on the selected Sr values. This paper presents recommended SPTand CPT-based relationships for estimating the residual shear strength ratio, Sr/σ′ vo, of liquefied nonplastic soils in the field based on a review of prior case history studies, laboratory testing studies, and recent findings regarding void redistribution mechanisms. The recommended relationships provide guidance regarding the unavoidable task in practice of having to extrapolate beyond the available case history data. Limitations in the state of knowledge are discussed.

A low-compliance bi-directional cyclic simple shear apparatus

A new simple shear apparatus is described which can apply bi-directional simple shear cyclic and monotonic loading. Cylindrical specimens are placed in a pressure chamber so that confining pressure and back pressure can be applied. Bi-directional shear loads are applied to the specimens base, which is mounted on a series of two horizontal rolling tables which can be independently loaded in two orthogonal directions while preventing cap and base platen “rocking.” A computer-automated feedback-loop-controlled pneumatic servovalve system provides excellent control of loads and displacements. Displacement control during cyclic tests on softening specimens is improved by the inclusion of a parallel stiffness. Procedures and test results are presented for three different undrained cyclic simple shear loading conditions and for a strain-controlled monotonic loading condition.

Seismic Design of Pile Foundations for Liquefaction Effects

Procedures for the seismic design of pile foundations for liquefaction effects are presented with emphasis on the conditions relevant to bridges. Two local subsystems for a bridge are discussed in detail: (1) pile groups in laterally spreading ground away from the abutments and (2) pile groups at the abutments where the restraining or “pinning” effects of the piles and bridge superstructure can be advantageous. The recommended design procedures involve equivalent static analyses using beam on nonlinear Winkler foundation models. Guidance for these design procedures was derived from a combination of dynamic centrifuge model tests and associated nonlinear dynamic finite element studies. The design procedures, their basis, and other issues for design of bridges for liquefaction effects are discussed.

Examination and Reevalaution of SPT-Based Liquefaction Triggering Case Histories

AbstractA standard penetration test (SPT)-based liquefaction case history database for liquefaction triggering criteria is reexamined and reevaluated. The updated database incorporates a number of additional case histories, replaces prior estimates of earthquake magnitudes with current estimates of their moment magnitudes, uses improved estimates of peak ground accelerations when available, and includes a reexamination of the selection and computation of representative SPT (N1)60 values for most case histories. The approach used to select and compute representative SPT (N1)60cs values is illustrated using select case histories. The distribution of the case history data relative to the Idriss-Boulanger triggering correlation is examined for any bias with respect to various parameters and to identify the conditions that are, and are not, well covered by available case history data.

SOIL-PILE-SUPERSTRUCTURE INTERACTION IN LIQUEFIABLE SAND

Soil-pile-superstructure interaction in liquefiable sand is evaluated using dynamic centrifuge model tests and pseudostatic p-y analyses. Select recordings from a recent centrifuge test are presented to illustrate typical behavior with and without liquefaction in an upper sand layer. Pseudostatic p-y analyses of single-pile systems in two recent centrifuge model tests show that the apparent reduction in p-y resistance due to liquefaction was strongly affected by changes in the relative density of the sand and drainage conditions.