In this study, we propose a new method for caisson breakwaters covered with wave-dissipation concrete blocks, which enables to evaluate cumulative maintenance costs including both ordinary maintenance costs (to raise work level of the blocks) and disaster recovery costs due to an extreme wave load. The method is based on a statistical model (Monte Carlo Simulation) calculating sliding distances of a caisson during its working life. This method can be effectively utilized for planning maintenance strategies, considering how the ordinary maintenance criteria for the settlement of the blocks affects the cumulative maintenance costs including information on both expected value and the its variations.

Coastal dikes were seriously damaged by tsunami of The 2011 off the Pacific coast of Tohoku Earthquake. The main cause of the damage was supposed to be scouring at the back slope toe. In this study, in order to estimate scouring landward of coastal dikes induced by tsunami overflow, a numerical model which introduced a geomorphological process into CADMAS-SURF/2D was developed. Then, the model was verified by comparison with experimental results. As a result, while numerical results may lead to underestimate width of scouring, the calculated maximum scour depth showed good agreement with experimental results. Thus, it was indicated that this model could be applied to estimate scouring at the back slope toe of coastal dikes.

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