Torsional dynamic impedance of a stepped pile based on the wedged soil model

Abstract

Stepped piles have been increasingly used as foundation elements for bridges and soft ground improvement in China. This paper derives an analytical solution of the torsional impedance of a stepped pile based on a wedged soil model. The accuracy of the developed solution is verified by degenerating the stepped pile into a straight pile. A parametric study is then conducted to investigate the influence of the wedged soil boundary and geometrical parameters on the torsional impedance of the stepped pile. A comparison between the present solution and the solution of a Voigt model is also presented. The findings demonstrate that the wedged soil boundary has a substantially influence on the torsional impedance for stepped piles with a short and stout upper pile segment. The difference in torsional impedance between the wedged soil model and the Voigt model is mainly reflected at high frequencies, while in a low frequency range these two solutions are almost identical, which is greatly divergent from the results of a vertical vibration case.