Abstract
When evaluating the seismic performance of pile foundations in liquefiable soils, it is critically important to estimate the effects of cyclic ground displacements on the pile response. Advanced analyses based on the effective stress principle account for these effects in great detail by simulating the process of pore pressure build-up and associated stress-strain behaviour of soils. For this reason, the effective stress method has been established as a principal tool for the analysis and assessment of seismic performance of important engineering structures.
 In this paper, effective stress analysis is applied to a case study of a bridge pier founded on piles in liquefiable soil. The study examines the likely effects of liquefaction, cyclic ground displacements and soil-structure interaction on the bridge foundation during a strong earthquake. A fully coupled effective stress method of analysis is used to compute the dynamic response of the soil-pile-bridge system. In the analysis, an elastoplastic deformation law based on a state concept interpretation is used for modelling nonlinear behaviour of sand. The seismic performance of the pile foundation is discussed using computed time histories and maximum values of ground and pile displacements, excess pore water pressure and pile bending moments. The advantages of the effective stress analysis are discussed through comparisons with a more conventional pseudo-static analysis of piles.
Highlights
Soil liquefaction during strong earthquakes results in a nearly complete loss of strength and stiffness in the liquefied soil, and consequent large lateral ground movement
The seismic effective stress analysis and the pseudo-static analysis focus on different issues and play complimentary roles in the assessment of pile response in liquefying soils
The seismic effective stress analysis was used to examine in a rigorous manner the response of the strengthened pile foundation during strong ground shaking by considering the complex soil-structure interaction in liquefying soils
Summary
When evaluating the seismic performance of pile foundations in liquefiable soils, it is critically important to estimate the effects of cyclic ground displacements on the pile response. Advanced analyses based on the effective stress principle account for these effects in great detail by simulating the process of pore pressure build-up and associated stress-strain behaviour of soils. For this reason, the effective stress method has been established as a principal tool for the analysis and assessment of seismic performance of important engineering structures. The study examines the likely effects of liquefaction, cyclic ground displacements and soil-structure interaction on the bridge foundation during a strong earthquake. The advantages of the effective stress analysis are discussed through comparisons with a more conventional pseudo-static analysis of piles
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