Co-seismic and post-seismic behavior of a wall type breakwater on a natural ground composed of liquefiable layer

The tsunami disaster countermeasures such as breakwaters might be damaged or lose their capacity to resist tsunami after a strong earthquake. Therefore, not only the co-seismic behaviors of a breakwater and its foundation system during earthquake loading, but also the post-seismic behavior after the earthquake loading should be investigated and estimated for future tsunami preparation, especially when the foundation ground is composed of liquefiable layer, which may cause large amount of displacement to the breakwater. In this study, the co-seismic and post-seismic behavior of an existing wall type breakwater on a natural ground which is composed of nonuniform liquefiable layer and thick cohesive layer with low permeability is investigated using an effective stress-based soil–water coupling numerical method. In the calculation, the complicated nonlinear dynamic behavior of the foundation soil is described by an advanced elasto-plastic soil constitutive model. A real recorded seismic wave, which consists of a major shock and two aftershocks from the 2011 Great East Japan earthquake, is adopted as the input earthquake loading. The calculation results indicate that the used numerical method is capable of capturing the progressive liquefaction and consolidation process of the foundation soil, as well as the subsidence and differential settlement of the breakwater during and after earthquake loading. The influence of earthquake loading can significantly reduce the capacity of breakwater to resist tsunami which may arrive within 1 h after earthquake; therefore, anti-seismic design should be taken into consideration in future tsunami preparation.