Modelling pile foundations under biaxial loading with a plasticity-based p–y methodology

Comparison of three-dimensional continuum finite element and p–y analyses illustrate the accuracy and efficiency of biaxial laterally loaded pile solutions obtained with a plasticity-based p–y methodology. The analyzed pile conditions correspond to a test pile founded in a stiff over-consolidated glacial till. The numerical analyses are first benchmarked against observed test responses for planar loading. Hypothetical cyclic pile responses are then investigated for two conditions with biaxial loading that produce anisotropic displacement responses due to the developing plastic foundation responses. The p–y model is based on a bounding surface plasticity theory facilitating analysis of loading in arbitrary directions relative to the pile axis. The three-dimensional continuum finite element model allows for the formation of a soil–pile gap in conjunction with an elastic perfectly-plastic Tresca soil model. The numerical analyses show that the p–y methodology captures the characteristic displacement and energy responses observed in the continuum analyses under biaxial loading with far less computational effort. Analyses demonstrate that significant anisotropic plastic responses may develop in simple cyclic biaxial loading conditions, perhaps rendering planar p–y model formulations inadequate with respect to a need to accurately predict responses and ensure they satisfy design performance criteria.