Seismic Lateral Response of Piles in Liquefying Soil

Abstract

Soil liquefaction is one of the major factors affecting the behavior of piles founded in seismically active areas. Although methods are available for seismic analysis of pile foundations, in many of them, the supporting soil is assumed to be an elastic material. Here a numerical model is presented which takes into account the reduction of soil stiffness and strength due to pore pressure generation and subsequent soil liquefaction, in addition to the material nonlinearity. Results obtained from the new method are compared with centrifuge test data and show excellent agreement with the observed pile behavior during these tests. To investigate the effects of soil liquefaction on the internal pile response, a parametric study is carried out for a range of material and geometric properties of the pile and surrounding soil. The effect of the nature of the earthquake on pile performance has been studied using 25 earthquake records scaled to different acceleration levels. It is shown that the “Arias intensity” and the natural frequency of the earthquake ground motion have a significant influence on the pile performance in liquefying soil. Existing elastic analysis methods for kinematic pile loading in layered soil deposits with soft and stiff layers are applied to the soil deposits with liquefying and nonliquefying layers. It is found that these simple design methods, which were derived assuming that the soil is a linear elastic material, do not predict bending moments accurately when nonlinear behavior of soil and effects of pore pressure generation are significant. Also a simplified limit equilibrium method proposed for the evaluation of bending response of single pile foundations subjected to lateral spreading is compared with the bending response obtained from the proposed numerical model. It is found that the limit equilibrium method, which is developed based on the centrifuge test results, does not give accurate results when the pile diameter and the thickness of the liquefied soil layer deviates from the values used for the centrifuge tests.