A dynamic beam on a nonlinear Winkler foundation (or “dynamic p-y”) analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests. The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 0.02 to 0.7g. The soil profile consisted of soft clay overlying dense sand. Site response and dynamic p-y analyses are described. Input parameters were selected based on existing engineering practices. Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events. Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated. These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems.

New liquefaction susceptibility criteria for saturated silts and clays are presented that are based on the mechanics of their stress-strain behavior and which provide improved guidance for selecting engineering procedures for estimating potential strains and strength loss during seismic loading. Monotonic and cyclic undrained loading test data for silts and clays show that they transition, over a fairly narrow range of plasticity indices (PI), from soils that behave more fundamentally like sands (sand-like behavior) to soils that behave more fundamentally like clays (clay-like behavior), with the distinction having a direct correspondence to the type of engineering procedures that are best suited to evaluating their seismic behavior. It is recommended that the term liquefaction be reserved for describing the development of significant strains or strength loss in fine-grained soils exhibiting sand-like behavior, whereas the term cyclic softening failure be used to describe similar phenomena in fine-grained...

Microbial-induced calcite precipitation (MICP), a novel bio-mediated ground improvement method, was explored to mitigate liquefaction-prone soils. Geotechnical centrifuge tests were used to evaluate cementation integrity and the response of MICP cemented sands to dynamic loading. The cementation integrity testing reveals a change in behaviour from ‘soil like' to ‘rock like', with an increase in treatment level. Results from dynamic testing demonstrate a clear increase in resistance to liquefaction of MICP-treated sands compared to untreated loose sand. The MICP sands were treated to varying levels of cementation (light, moderate and heavy cementation levels) and assessed using non-destructive shear wave velocity measurements. The centrifuge models were all subjected to ground motions consisting of sine waves with increasing amplitudes. Accelerations, pore pressures and settlements were measured in the soil during shaking, and the changes in soil behaviour and post-shaking shear wave velocity for soils prepared to different cementation levels are discussed. Increased resistance to liquefaction was demonstrated with a decrease in excess pore pressure ratios in the MICP-treated models, as well as in reduced post-shaking settlements; however, surface accelerations were amplified at heavy levels of cementation. A tradeoff between improving liquefaction resistance and minimising undesirable higher surface accelerations needs to be considered when designing the soil improvement level.

A 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...

Eight dynamic model tests were performed on a 9 m radius centrifuge to study the behavior of single piles and pile groups in liquefiable and laterally spreading ground. Pile diameters ranged from 0.36 to 1.45 m for single piles, and from 0.73 to 1.17 m for pile groups. The soil profile consisted of a gently sloping nonliquefied crust over liquefiable loose sand over dense sand. Each model was tested with a series of realistic earthquake motions with peak base accelerations ranging from 0.13 g to 1.00 g . Representative data that characterize the important aspects of soil–pile interaction in liquefiable ground are presented. Dynamic soil–pile and soil–pile cap forces are backcalculated. Directions of lateral loading from the different soil layers are shown to depend on the mode of pile deflection relative to the soil, which depends on the deformed shape of the soil profile, the pile foundation stiffness, and the magnitude of loads imposed by the nonliquefied crust. Procedures for estimating the total horiz...