A STUDY ON STRUCTURES OF COASTAL DIKE THAT PERSIST DISASTER MITIGATION EFFECTS AGAINST TSUNAMI OVERFLOW

Abstract

 After the tsunami disaster induced by the Great East Japan Earthquake, there is a need to develop structures permitting the effectiveness of coastal dike on disaster mitigation, even when a tsunami overflows. The authors conducted hydraulic model experiments to reveal hydraulic conditions and scour process near coastal dike during tsunami overflow, and to study more resilient structures with scour protection at the landward slope toe of coastal dike and improvement of the landward slope armor. The results of the experiment showed that tsunami overflow caused negative pressure at the top of the landward slope and large velocity pressure rise at the landward slope toe, and that depth and width of scour landward of coastal dike increased with overflow depth. We found that it made coastal dike more resilient to tsunami overflow to install the landward slope armor made by interlocked blocks with notches at their top edges and bottom edges, and the foundation work and soil improvement at the landward slope toe.