Abstract
Many cases of structural damage have been reported after Tohoku tsunami earthquake. Among those cases, the failure of breakwater caused by the local scouring on gravel mound due to tsunami overflow can be selected as one of the typical structural damages. This study is intended to clear the characteristics of local scouring on gravel mound under several tsunami overflow conditions. Four cases of discharge and three kinds of gravel diameter were employed to investigate the characteristics of local scouring under tsunami overflow condition. Furthermore, this study proposed a horizontal plate which was introduced to reduce the local scouring. Numerical simulation was also conducted to investigate the flow pattern above the gravel mound and pressure distribution on proposed horizontal plate. This study revealed that the scales of local scouring, its depth and length, depend largely on both overflow discharge and gravel size. Based on the experimental data, this study proposed an equation that can estimate maximum scoured depth under different gravel diameter as well as several overflow conditions. The horizontal plate showed good performance in reducing the scale of local scouring. The length of horizontal plate affects the magnitude of vortices and the maximum scoured depth.
