Numerical Solution of Single Pile Subjected to Simultaneous Torsional and Axial Loads

Torsional loads on pile foundations are induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twisting at the pile head but also reduces its axial capacity significantly with increased settlement of the foundation. Several theoretical and experimental investigations have already been carried out on piles under torsional load, as evidenced by the available literature on the subject, although contributions on the influence of combined torsional and axial loads on pile foundations are rather limited. This paper presents a novel numerical model (boundary-element method) to analyze the response of a single vertical floating pile subjected to simultaneous torsional and axial loads. The nonlinear stress-strain response of soil has been incorporated in the model by means of the hyperbolic model, whereas the pile material has been idealized as elastic-perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. Apart from predicting the load-displacement response and incremental angle of twist of piles under combined torsional and axial loading, the shear-stress profiles and the effect of vertical loads on the torsional capacity of the piles are some of the salient features captured by the proposed model. Validation of the proposed model by means of a comparison with existing models and experimental data indicates the suitability and accuracy of the solutions developed. The proposed model is also applied successfully to selected case studies on piles in clay, sand, and layered soil, and important conclusions are drawn. (C) 2014 American Society of Civil Engineers.