Numerical investigation into wave-induced progressive liquefaction based on a two-layer viscous fluid system

Based on a two-layered viscous fluid theory, a numerical model to capture the progressive nature of wave-induced liquefaction has been developed. Unlike the existing models, this model can consider the cyclic shear stress associated with vibrating liquefied soil layers and its effect on sub-liquefied soils during the wave-induced liquefaction. The reliability of this model is validated by simulating wave flume tests, which show a promising prediction when compared to analytical solutions, particularly after the onset of liquefaction where an increased amplitude in the oscillatory pore water pressure can be observed. The numerical results show that the moving characteristics of liquefied soil are similar to those of a water particle in the presence of surface water waves with the horizontal velocity being much greater than the vertical velocity. Unlike the model without considering the liquefied soil-induced cyclic shear stress, the proposed model predicts a prompt increase in residual pore pressure associated with the onset of liquefaction at shallow soil layers, which may change the curvature of residual pore pressure versus time in sub-liquefied soils from concave downwards to concave upwards at a certain depth. This phenomenon is consistent with many of the existing experiments for wave-induced seabed response and becomes more pronounced as the kinematic viscous characteristics of liquefied soil become more apparent, i.e., with a larger kinematic viscosity coefficient. Correspondingly, the cyclic shear stress induced by the vibrations of liquefied soil can accelerate the downward advancement of the liquefaction front and result in a larger depth of liquefaction.