Effect of soil nonlinearity and liquefaction on dynamic stiffness of pile groups

Determination of the behavior of pile groups under dynamic condition is a complex problem. The complexity becomes more intricate when the soil medium surrounding the piles behaves nonlinearly due to higher cyclic loading under dynamic condition. Further if the soil is saturated then the behavior of pile groups is also affected due to liquefaction. In this paper, nonlinear dynamic analyses of pile groups have been performed with and without generation of pore water pressure. A three-dimensional finite element soil-pile model has been developed with proper radiation boundary conditions. Frequency dependent Kelvin elements have been used for simulating radiation conditions at infinity. The numerical model and the process of computation have been verified with the established literature. For soil nonlinearity, work-hardening plastic cap model has been considered for further investigation. The pore pressure generation for liquefaction has been incorporated by two-parameter volume change model reported in literature. The effects of nonlinearity and liquefaction of soil medium on dynamic stiffness of single pile and pile groups have been investigated. Effects of frequency of excitation have been examined. It has been observed that the work-hardening soil plasticity and generation of pore water pressure has a significant influence on dynamic behavior of pile groups.