Axial capacity degradation of single piles in soft clay under cyclic loading

A kinematic hardening constitutive model with von Mises failure criterion considering cyclic degradation was developed to analyze the cyclic axial response of single piles in saturated clay. After validation by comparison against published triaxial test results, this model was applied to a numerical simulation developed for computing the axial bearing capacity of a pile foundation subjected to a cyclic loading. The axial bearing capacity degradation of a single pile under different cyclic load levels and different cyclic load numbers was studied. It was found that the pile–soil system remains elastic at very low cyclic load levels, and the degradation of pile capacity happens when the cyclic load level increases. A higher cyclic load level after more cycles leads to faster degradation. In order to improve the computational efficiency, a simplified analysis method based on a simple nonlinear soil model is presented for the cyclic axial capacity degradation of single piles. The results calculated by this simplified analysis are consistent with those of the numerical simulation. Comparisons with laboratory test data suggest that both the finite element method and the simplified analysis method provide reasonable estimates of the axial pile capacity degradation of a single pile after cyclic loading.