Influence of soil plug effect on the torsional dynamic response of a pipe pile

The additional mass model is introduced to simulate the dynamic interaction of soil plug and pipe pile under small deformations and strains. In the additional mass model, the inertia and damping effect of soil plug, and the displacement phase difference between soil plug and pipe pile are taken into consideration. Based on the additional mass model, the analytical solutions of the torsional dynamic response of a pipe pile in the frequency domain are derived by utilizing the Laplace transform technique and impedance transfer function. The corresponding quasi-analytical solution in the time domain for a pipe pile subjected to semi-sinusoidal exciting force is obtained by using the inverse Fourier transform. A parameter sensitivity analysis of the additional mass model is conducted to determine the approximate range of the parameter values of the distributed Voigt model. The validity of the presented solutions is also verified by comparing the torsional dynamic behavior of the pipe pile calculated via the additional mass model with those based on the plane strain model. Utilizing the developed solutions, a parametric study is conducted to investigate the influence of the properties of soil-pile system on the torsional vibration characteristics of pipe pile.