Torsional dynamic response of a pipe pile in homogeneous unsaturated soils

This paper proposed an analytical solution for investigating the dynamic response of a pipe pile subjected to a torsional harmonic excitation torque in unsaturated soils. Based on the wave equations of three-phase porous media, the capillary pressure and inertial coupling effect between water and gas phase are taken into account, as well as the influence of saturation degree on soil's dynamic shear modulus. The pile is modeled using one-dimensional elastic theory. The dynamic governing equations of outer and inner unsaturated soils are derived by virtue of the separation of variables method. Accounting for the boundary and continuity conditions of pile-soil interface, a closed-form solution for the torsional dynamic response of a pipe pile is derived in frequency domain. The proposed analytical solution is verified by comparing with the two existing solutions available in literature. Finally, a parameter study is undertaken to portray the influence on the dynamic response of a pipe pile.