Theoretical investigation on characteristics of field reactions of saturated ground subjected to vibrations of inclined pile groups

Abstract

Inclined pile groups have been adopted in engineering practice (e.g. offshore wind turbines) to withstand strong horizontal environmental loads that are repetitive in nature. Field reactions including the additional stresses and excess pore water pressures are responsible for the cyclic degradation of foundation soil, which may induce the accumulative deformation and fundamental frequency shifting of the marine structure. In this study, a theoretical model incorporating an inclined pile group and a saturated half-space was established, wherein the pile and saturated soil were described by the E–B beam and Biot poroelasticity theories, respectively. The pile and soil were coupled through the receptance matrix, which was established at the pile–soil interaction points in the transform domain. The dynamic impedances of the inclined pile group are first obtained, and then the field responses, including stresses and excess pore water pressure in the saturated ground, are evaluated for different types of loads applied to the pile cap. The frequency response function and spatial distributions of the field responses were obtained for varying rake angle of pile and permeability of soil. It was found that the horizontal force induces the largest responses in the ground when compared to the vertical force and the overturning moment applied to the inclined pile group. It is beneficial to employ an inclined pile group to withstand the horizontal force and overturning moment because the foundation stiffness increases, and the additional stresses in the ground decrease with increasing rake angle.