Abstract
Most of coastal structures, especially coastal dikes were destroyed by the 2011 Tohoku Tsunami. It was reported that one a the most important causes was the failure of back slope due to scouring. It is assumed that understanding the relevance between external forces and structure types is important to study robustness of coastal dikes toward the tsunami. In this study, a numerical model using CADMAS-SURF/3D has been applied to consider mechanism of robustness and to make suggestions for design of coastal dikes. As a result, it was clarified that the weak points of coastal dikes were the scouring at the toe, and the negative pressure at the top of the back slope. To deal with these issues, it is considered to be effective to design the dikes without parapets to lower the overflow depth, and to make the back slope moderate to remove the negative pressure at top of the slope.
