Seismic response of single piles in liquefiable soil considering P-delta effect

Abstract

Dynamic analyses of piles subjected to both vertical and horizontal loading under seismic conditions are of great significance to geotechnical and practicing engineers and the numerical methodology proposed in the present study fills the existing research gap. A finite difference based computer program FLAC3D is used to model a single pile and obtain the deflection and bending moment behaviour along the depth of the pile, under earthquake loading conditions in both non-liquefiable and liquefiable soil. The various earthquake motions considered in the current analysis includes 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj and 2011 Sikkim motions The bending moment is maximum at the interface of the liquefying and non-liquefying soil layers due to shear strain in the soil being discontinuous across the interface of the layers. The free field ground surface displacement is observed to initially increase with time, reaching the maximum at some instant during shaking and thereafter it remains constant with time, due to local failure of the liquefiable soil around the pile foundation. The combination of vertical load and lateral load on the pile top is varied to obtain the P-delta curves under dynamic loading conditions which are important factors for peak pile bending moment, when there is lateral spreading due to liquefaction causing displacement of the pile head, and inertial load from the superstructure is present. Hence a thorough evaluation of both horizontal and vertical inertial interactions and kinematic interactions due to free field motions, is necessary for considering the behaviour of piles in liquefiable soil and under combined loading situations.