Seismic response of poro-elastic seabed and composite breakwater under strong earthquake loading

Abstract

The marine structures in offshore area, such as composite breakwater, are generally vulnerable to the strong seismic wave propagating through their seabed foundation. There are a lot of failure examples during the strong earthquake events in the world in the past 20 years. However, attention given to the seismic response of marine structures under strong seismic wave is limited. In this study, taking the dynamic Biot’s equation “u − p” as the governing equation for porous seabed foundation, the seismic response of a composite breakwater and its porous seabed foundation under the seismic wave recorded in the Japan 311 off the pacific coast of Tohoku earthquake (M L = 9.0) is investigated using a FEM numerical model. The numerical results indicate that the seismic response of composite breakwater is very strong in the earthquake process. The amplification of the input seismic wave occurs both in seabed foundation and composite breakwater; and this amplification is positively related to the buried depth of points. The horizontal seismic response is much strong than the vertical seismic response. The seismic wave induced excess pore pressure and effective stresses in seabed foundation vibrates; the vibration amplitude is also positively related to the buried depth of points. Under strong seismic loading, the surface region of seabed foundation could liquefy. The parametric study shows that the young’s modulus of seabed foundation has significant effect on the seismic response of composite breakwater.