Numerical Solution of Single Pile Subjected to Torsional Cyclic Load

Large structures, such as offshore platforms, wind turbine foundations, wide buildings, bridges, and railway granular embankments, are often supported by pile foundations. These structures are usually subjected to large cyclic loads (in axial, lateral, and torsional modes) arising from actions of waves, ship impacts, or moving trains. Significant torsional cyclic forces can be transferred to the foundation piles due to the eccentricity of the lateral loads. In the past, several theoretical and experimental investigations were carried out on piles under axial and lateral cyclic loads; however, study of the influence of torsional cyclic loads on pile foundations is rather limited. This paper presents a novel numerical model based on the boundary element approach to analyze the response of a single, vertical, floating pile subjected to torsional cyclic load. The nonlinear stress-strain response of soil is incorporated, and the pile material was idealized as elastic-perfectly plastic. The effect of progressive degradation of soil strength and stiffness under cyclic stress reversal is incorporated in the numerical method. Apart from predicting the degradation of torsional pile-soil interactive performance, the profiles for shear stress and angle of twist are also captured by the proposed solution. Validation of the model indicates the suitability and accuracy of the proposed solutions. The frequency, amplitude, and number of cycles play significant roles in torsional cyclic response of piles. The proposed model is also applied successfully to selected case studies on single piles under torsional cyclic loading, and important conclusions are drawn from there.