With considering the difference between the horizontal and vertical mechanical properties of ground base

the torsional dynamic response of a pipe pile in transversely isotropic soil is investigated. Based on the stress-strain relationships of transversely isotropic material and soil-pile coupled vibration

differential equations and boundary conditions of the pile and soil are established. The solutions for the displacements of the outer and inner soil are obtained by Laplace transform and the variable separation method. The torsional response of the pipe pile is obtained based on the continuity conditions between the pile and both the outer and inner soil. The expressions of the complex impedance and velocity admittance at the pile head are obtained. The solution proposed in this paper is then compared with existing solutions to verify the validity. A parametric study is conducted to investigate the influence of the anisotropy of the outer and inner soil on the torsional vibration characteristics of the pipe pile.