Calculation and hydraulic model experiments for the stable weight of rubble-mound considering the overflow and seepage flow

When The Tohoku-Pacific Ocean Earthquake occurred on the March 11th, 2011, harbor facilities such as breakwaters and tide embankments suffered serious damages from the Tsunami. The following three mechanisms are considered to be related to the collapse of the breakwater: 1) scouring of the mound due to overflow, 2) the horizontal force originated from the difference of water level between the sea side and the harbor side on the breakwater, and 3) reduction of bearing power of the mound induced by seepage flow. However, the mechanism of the instability of the rubble-mound by overflow and seepage flow induced by tsunami is not fully clarified. In this study, the formula to calculate the stable weight of rubble-mound was proposed in consideration of the overflow and seepage flow, and hydraulic model experiments were conducted on Kamaishi Bay breakwaters as the subject in order to confirm the effectiveness of the proposed formula. Using the results, the stability of the breakwater was evaluated from the geotechnical engineering point of view.