Strain effects on kinematic pile bending in layered soils

The kinematic bending of piles in two-layer soil is explored to account for soil stiffness degradation and associated damping increase with shear strain, a fundamental aspect of soil behaviour which is not incorporated in current simplified seismic design methodologies for pile foundation.A parametric study of a vertical cylindrical pile embedded in a two-layer soil profile to vertically-propagating S waves carried out in the time domain by a pertinent Beam-on-Dynamic-Winkler-Foundation (BDWF) model, is reported. Strain effects are treated by means of the equivalent-linear procedure which provides soil stiffness and damping ratio as function of shear strain level. Whereas the approach still represents a crude representation of the actual soil behaviour to dynamic loading, it is more realistic than elementary solutions based on linear visco-elasticity adopted in earlier studies. The paper highlights that soil nonlinearity may have either detrimental or beneficial effects on kinematic pile bending depending on the circumstances. The predictive equations for kinematic pile bending in visco-elastic soil recently developed by the Authors are extended to encompass strain effects. Numerical examples and comparisons against experimental data from case histories and shaking table tests are presented.