Response of pile groups in layered soil to dynamic lateral loads

This paper presents an analytical solution that provides the dynamic response of laterally-loaded pile groups with an arbitrary number of piles installed in layered soil. The solution allows modelling robustly pile-to-pile interaction effects via a new stress-based interaction factor, that considers the fact that soil displacements along the periphery of large-diameter piles of a group subjected to lateral loads will not be in-phase. Layered soil conditions are introduced in the solution by modelling wave propagation in the soil surrounding the piles with the popular plane-strain model and considering soil as viscoelastic material. These idealisations greatly simplify the formulation, at no expense of accuracy when considering loading of relatively stiff piles under serviceability conditions. The solution provides the Winkler modulus for each pile in the group as function of problem parameters that have direct phenomenological meaning, and allows direct calculation of the horizontal impedance of the entire pile group. The presentation concludes with results of a parametric analysis, to demonstrate the effect of considering layered soil conditions and the cross-sectional dimensions of the piles on the response of the group.