Numerical evaluation of effects of nonlinear lateral pile vibrations on nonlinear axial response of pile shaft

Axial and lateral dynamic pile analyses are generally handled separately; and consequently, dynamic soil reactions are assumed to be uncoupled. However, pure loading is rarely encountered as combined loading occurs in many situations (offshore piles, pile driving as well as pile groups and pile rafts). In this study, the effects of nonlinear lateral pile vibrations on the in-phase nonlinear axial pile response of a pile shaft are studied. New approximate nonlinear solutions for both axial and lateral pile behavior, developed from general elastodynamic equations, are presented. The solutions are obtained by extending the elastodynamic solution for plane strain cases with a view to model soil nonlinearity. Since axial soil resistance depends on the confining stress around the pile shaft, the effect of the lateral soil behavior on the confining pressure of the pile circumference is investigated and the axial soil reaction from coupled in-phase vibrations is derived. It is concluded that the axial unit shear strength significantly increases when lateral soil vibrations involve plasticity, which in turn results in an increase in the axial dynamic resistance of the pile shaft.