This study considers the motion of an end bearing single pile with lumped mass embedded in sandy soil deposit subjected to seismic liquefaction. An efficient finite difference model, whose accuracy was validated through experimental results, has been constructed to study the dynamic responses of piles under liquefaction. Effects of parameters such as soil and pile properties, and predominant frequency on dynamic response of pile are examined. Results reveal that earthquake predominant frequency, pile stiffness, soil relative density and soil-pile relative stiffness, can significantly affect the pile’s dynamic response, while pile material densities have negligible effects. Final results demonstrate that with increasing in pile stiffness, soil relative density and soil-pile relative stiffness, maximum moments in piles are increased while with increasing the earthquake predominant frequency, maximum moments in piles and depth of the liquefaction are reduced. Also, the depth in which the maximum value of moment, Mmax, occurs, depends only on the pile stiffness.

Introduction

When Pile foundations are exposed to intense dynamic transverse loads during earthquakes, soil–structure interaction (SSI) plays an important role in allocating the response of pile foundations to lateral excitation [1]. Recent observations after major earthquakes have shown that extensive damages and destructions are still likely to be happened to pile foundations. This problem is important particularly for pile foundations in loose saturated cohesionless deposits which are vulnerable to liquefaction and lateral spreading during seismic loading. Design procedures that have been developed for evaluating pile behavior under earthquake loading, have many uncertainties to be used for cases involving liquefaction. The performance of piles in liquefied soil layers is much more complex than that of non-liquefying soil layer as a result of the diminishing of stiffness and shear strength of the surrounding soil over time due to the increase of pore water pressure [2]. Lateral loads on piles are developed by the superstructure inertia as well as the soil movement induced by wave propagation through the soil. Inertial forces are the predominant forces before liquefaction and are mainly responsible for development of maximum bending moment near the pile head, whereas, kinematic forces which are predominant after liquefaction are responsible for the maximum bending moment observed at the interface of liquefiable and non-liquefiable layers [3]. However, consideration of the mentioned forces simultaneously, could lead to a more accurate analysis. This is due to the fact that the total forces are resulted from an inertial interaction from the oscillation of the superstructure and also a kinematical interaction from the soil deformation and motion. Tokimastu and Suzuki [4] believe that the peak pile bending moment in the pile with respect to natural period of structure and natural period of ground can be estimated by Square-Root-ofSum-of-Squares (SRSS) or algebraic addition of kinematic and inertial moment.