Nonlinear 3D finite element analysis of suction caisson-tower-soil system subjected to horizontal earthquake excitation

Abstract

Suction caissons are widely used as a promising alternative foundation for offshore structures under variable offshore environments. In this paper, a three-dimensional finite-element model which takes into account soil inelasticity was used to study the seismic behavior of a suction caisson in clay taken from an offshore wind farm in the Hebei province of China. The results showed that the maximum acceleration of the soil increases with increasing depth. There is a distinct amplification for relatively low frequencies when seismic waves propagate to the mudline. It was assumed that the rotation center of suction caisson under seismic conditions was virtually existent. The rotation center was obtained by the proposed formula to explore the movement positions of the suction caisson. The time of the peak of lateral displacement of the lid did not synchronize with that of the changing direction of displacement of the rotation center, indicating that the displacement of the lid can not be a comprehensive assessment of the position state of suction caissons. The point mass at the top of the wind turbine tower was responsible for the increase of vibration amplitude of displacement. • In this paper, a three-dimensional finite-element model taking account of soil inelasticity was carried out to study the seismic behavior of suction caisson in soft clay. A 3D equivalent viscous-spring artificial boundary element is applied to eliminate the unnatural reflection wave generated on the boundary. • It is assumed that the rotation center of suction caisson under seismic conditions is virtually existent and it was obtained by the proposed formula to explore the movement positions of the suction caisson. • The time histories of lateral and vertical displacement were extracted for studying seismic behavior of the wind turbine tower under seismic loading.