Analysis of a Single Pile under Vertical and Torsional Combined Loads in Two-Layered Nonhomogeneous Soil

Abstract

Pile foundations are inevitably subjected to combined vertical-torsional (V-T) loadings in offshore engineering contexts. This article proposes an analytical method for calculating the V-T response of a single pile in two-layered nonhomogeneous soil. First, the results predicted by this new method are validated against experimental data and found to be in good agreement. The behavior of a single pile under combined V-T loads is then subjected to a parametric study, exploring a range of dimensionless parameters related to the thickness of the top layer, the embedment depth of the foundation (or pile length), the relative pile–soil stiffness, soil profiles, and the level of vertical or torsional load mobilization. This reveals two interesting features of the behavior of a pile under combined V-T loads: (1) the loading path (loading sequence) has an effect on load response and deformation; (2) the length–diameter ratio, soil profile parameters, and relative pile–soil stiffness have a significant effect on the behavior of pile under combined V-T loads, but the top layer thickness has a minimal effect.