Evaluation of Tsunami Force with Overflow on Breakwater

A tsunami force has unknown features due to its complexity, and makes it difficult to be predicted accurately. As a typical example, in the 2011 off the Pacific coast of Tohoku earthquake with huge tsunami, many breakwaters slid or fell down by the unexpectedly terrible damages caused by the tsunami. For effective design of coastal structures, achieving a correct prediction of the tsunami pressure should be an urgent subject. In the existing studies, the tsunami force F with an overflow is estimated by using a compensation coefficient a based on the hydrostatic pressure as: F = alpha rho gh. The compensation coefficient a is usually set as alpha = 1.1 for the front of the caisson and 0.9 for the rear of that constantly. However, in recent studies, it was found that Parameter a can be easily and randomly changed depending on the boundary condition, and unfortunately, estimation method of its effective has not been developed yet. To resolve this problem, in this study, hydraulic experiments targeting on tsunamis with their overflows on a breakwater are implemented to examine the variability of the compensation coefficient a. And from the experimental results, a simple and effective estimation method for the compensation coefficient a is newly proposed.