Effect of ground motion characteristics on seismic response of pile foundations in liquefying soil

A three-dimensional Finite Element (FE) analysis is carried out to investigate the dynamic behaviour of pile foundations in liquefied soil using a fully coupled (u-p) formulation employed to analyze soil displacements and pore water pressures. The success of the u-p formulation is briefly discussed first, together with its application to various geotechnical problems. For the numerical analysis, a multi-yield-surface plasticity model is used to model the soil skeleton, and results obtained from the FE method are compared with centrifuge test data which shows excellent agreement with the observed pile and soil behaviour. The effect of the nature of the earthquake on pile performance has been studied using ten earthquake records scaled to different acceleration levels. It is found that the acceleration amplitude of the earthquake ground motion has a significant influence on the pile performance in liquefying soil. Moreover, it can be shown that the ratio of Peak Ground Velocity to Peak Ground Acceleration (PGV/PGA) of the earthquake ground motion is a better evaluation index to estimate bending moment and displacement of the pile than predominant frequency.