Nonlinear dynamic simulation of offshore breakwater on sloping liquefied seabed

Offshore structures are generally vulnerable to strong seismic waves propagating through a loose seabed foundation. However, only limited attention has been paid to the seismic stability of composite breakwaters. In this study, a coupled numerical analysis is performed to study the seismic dynamics of a composite breakwater on a sloping loose seabed foundation under a seismic wave recorded during the 2011 Tohoku earthquake (M-L = 9.0) in Japan. Computation results show that the developed numerical model is capable of capturing a variety of nonlinear phenomena in the interaction process between offshore structures and their loose seabed foundation. Under seismic loading, the loose seabed foundation away from the composite breakwater becomes completely liquefied. Because of the presence of the structure, the seabed foundation beneath the composite breakwater is partially liquefied. The composite breakwater undergoes significant subsidence, translation, and rotation; meanwhile, large lateral spreading occurs in the sloping seabed foundation. This investigation demonstrates that an advanced numerical method is promising in realistic evaluation of seismic performance of offshore structures.