Numerical simulation of the seismic liquefaction mechanism in an offshore loosely deposited seabed

As a natural foundation of offshore structures, the instability of offshore seabed foundations is the dominant factor for the failure of offshore structures in strong earthquake events. It has been reported that a great number of offshore structures have failed due to soil liquefaction of Quaternary loosely deposited seabed during several recent strong seismic events. At present, countless investigations on seismic wave-induced liquefaction in on-land soil have been conducted. However, investigations on seismic wave-induced seabed soil liquefaction in an offshore environment is limited. In this study, a coupled numerical model [fluid-structure-seabed interaction (FSSI)-CAS 2D] was utilized to investigate the seismic wave-induced liquefaction mechanism in newly deposited seabed soil. The advanced soil constitutive model PZIII was adopted to describe the nonlinear dynamic behavior of loose soil. In computation, the variation of void ratio e, and related variation of soil permeability is taken into consideration; and the hydrostatic pressure acting on the seabed surface, as a boundary condition value, is automatically updated based on seabed deformation. The numerical results indicate that a loose seabed could liquefy completely, and that seabed soil liquefaction initiates at the surface of the seabed, then progresses downward. It is also indicated that the advanced soil constitutive model, Pastor-Zienkiewicz Mark III (PZIII), is capable of describing the post-liquefaction behavior of loose seabed soil to some extent.