A simplified quasi-static analysis of wave-induced residual liquefaction of seabed around an immersed tunnel

Evaluation of wave-induced soil response is particularly important for coastal geotechnical engineers involved in the foundation design for marine structures such as immersed tunnels, breakwaters, platforms etc. In this study, a finite element model for the wave-induced soil response around an immersed tunnel is developed, in which the seabed is treated as a porous medium and characterized by Biot's consolidation equations, while the tunnel is considered as a single-phase medium and behaves under a linear elastic law. A new conceptual pore-pressure buildup model is developed to investigate the wave-induced residual liquefaction around the tunnel due to the accumulation of pore pressures under cyclic shearing. The consolidation analysis of seabed foundation under the gravitational forces including the body forces of the structure is pre-assessed and incorporated. It is demonstrated from numerical results that the development of residual pore pressure is asymmetric in nature around the tunnel, which may result in the uneven liquefaction depth and deformation in the seabed near the bottom of the tunnel, thus compromising the stability of the structure. Parametric studies show that wave-induced residual liquefaction is more likely to occur in the shallow seabed with lower relative density and permeability under the wave loading with higher wave height and longer period.