Stability of Wave-Dissipating Concrete Blocks of Detached Breakwaters Against Tsunami

In recent years, the risk of occurrence of tsunamis generated by near shore earthquakes, such as, Tokai, Tonankai, Nankai and off-Miyagi is considered to be higher than before, as well as off shore tsunamis traveling long distances, e.g., the 2010 Chilean tsunami. On March, 11th, 2011 the huge, devastating tsunami generated by The 2011 off the Pacific coast of Tohoku Earthquake attacked and damaged the east coast area of Japan. Tsunami forces onto vertical walls, such as seawalls, has already been studied in detail, e.g., Asakura et al.(2002) and Kato et al.(2006). In Japan, detached breakwaters made with wave-dissipating concrete blocks such as Tetrapods have been widely applied. However, the effects of detached breakwater on tsunami disaster mitigation have not been studied. In our study, hydraulic model tests have been systematically and carefully carried out using solitary tsunami waves to evaluate the stability of concrete blocks following the our previous study on the effect of detached breakwaters from the viewpoint of reducing run-up and wave pressure onto seawalls behind the detached breakwaters (Hanzawa et al., 2011).