Dynamic responses of a transversely isotropic poroelastic seabed subjected to nonlinear random waves with emphasis on liquefaction depth

Abstract

Seabed instability is one of the important causes that lead to the failures of marine structures. Most previous works on seabed instability are limited to regular surface waves and linear random waves while nonlinear random waves are seldom touched. Hence, in this study, the hydrodynamic pressure of nonlinear random waves up to the second order is derived first. Then the analytical solutions of the dynamic responses of a transversely isotropic poroelastic seabed under the nonlinear hydrodynamic pressure are developed. The solutions are validated against analytical and experimental works in literature. The frequency response functions of pore water pressure, shear stress, vertical effective stress and horizontal effective stress are presented and discussed in the frequency domain. The influences of significant wave height, peak wave period and water depth on the dynamic responses and liquefaction depths of soil are analyzed in the time domain. The nonlinear random waves, linear random waves, linear regular waves and the second-order Stokes waves are compared in both time and frequency domains in terms of their influences on the dynamic responses and liquefaction depths of soil. The results reveal that the dynamic responses induced by second-order random waves are always greater than that induced by linear random waves, and much greater than that induced by equivalent linear waves and the second-order Stokes waves. The seabed may not liquefy under regular waves but does liquefy under random waves. Furthermore, the instantaneous liquefaction depths of soil caused by the second-order random waves are up to 23.5% larger than that induced by linear random waves. Therefore, the nonlinear random waves are recommended for the finite water depth use in engineering practice. In addition, the frequency-difference term plays an important role in soil liquefaction.