Instability of caisson-type breakwater due to seepage and scouring of tsunami into rubble mound and seabed with earthquake, liquefaction and forward and backward waves

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Destabilization scenario of breakwater due to an earthquake and a tsunami was revealed. In the huge earthquake, after the large and long earthquake motion caused the liquefaction with increasing excessive pore water pressure, the breakwater was settled. The breakwater received tsunami force after the earthquake acted. The bearing capacity of the breakwater was loosed due to the decreased of the ground strength. Moreover we discussed on the performance of the breakwater by use numerical simulation result of tsunami inundation depth with damage level of the breakwater.Scours on the seabed due to tsunami causing reduction in bearing capacity of structures were examined by open-channel flow, overflow and seepage flow in rubble mound. During water flow, the vertically upward hydraulic gradient along with excess pore water pressure was generated in the saturated ground. The liquefaction-like phenomenon was observed in the ground.