Modeling clay–pile interface during multi-directional loading

Series of multi-directional pot tests were conducted in soft clay to characterize the near field soil response during multi-directional soil–pile interaction (Mayoral et al. [19,22]). This experimental evidence has shown that nonlinearities associated with gapping and pile slippage during multi-directional cyclic loading of clay–pile interfaces lead to very complex force–displacement relationships. These relationships depend on the loading path and displacement history that affects the evolution of the soil stiffness. This paper introduces a simplified discrete model, which describes the variation of both the soil stiffness and lateral soil resistance of a model pile during multi-directional loading, to be used in the time domain. The model considers two limit deformation stages, and an interpolation damage like function to follow the gap evolution during the cyclic loading. The model parameters are obtained directly from uni-directional conventional p–y curves. Predictions for series of multi-directional displacement paths including circular, elliptical, figure 8 and parabolic were performed and compared to actual test data for these paths. For the cases studied, this approach is able to describe the evolution of the stiffness in the transition regime, accounting for the progressive formation of the gap around the pile, and to capture the trends, initial stiffness, peak and residual forces very closely.