EXPERIMENTAL STUDY ON SCOUR AND STABILITY OF BREAKWATER HEAD AGAINST TSUNAMI

<p> Coastal areas near cities with the potential for large tsunamis require improvements in facilities such as breakwaters. As an approach, the mechanism of the tsunami hazard in coastal structures has been widely studied, especially since 2011. However, most of the existing studies do not consider the 3D characteristics of the target hazards. In recent numerical/physical experiments on upright composite breakwaters, one such hazard has been newly revealed as the scouring of the mounds around the breakwater heads. This 3D mechanism should also be considered for the effective design of other types of breakwaters. In large wave conditions, breakwaters covered with dissipating blocks are often used instead of upright composite breakwaters. This type tends to have relatively large mounds. In order to maintain sufficient width of shipping lanes, the design of this type of breakwater often attempts to reduce the number of blocks around the head of the breakwater as much as possible. Given the recent understanding of the 3D mechanism of tsunami disasters, such a strategy may involve a fatal design. To avoid this, 3D experiments targeting the head of this type of breakwater are required to investigate the details of its failure processes. In this study, large-scale 3D experiments are carried out by targeting breakwaters covered with dissipating blocks, modeling a real port, under large tsunamis. The damage processes, including scouring around the head of the breakwater, is investigated.</p>