Abstract
In the 2011 off the Pacific coast of Tohoku Earthquake, at many places, coastal dykes fully collapsed by deep over-topping tsunami deeper than the dyke height. In this study, the resistance of coastal dyke against deep over-topping tsunami current was evaluated by performing a series of model tests using constant-height water flow. The effects of the following factors were evaluated; the slope of upstream and downstream slopes; the thickness of surface gravel layers; the opening size between the slope protection panels; and the length of geogrid layers reinforcing the embankment; and the connection between the reinforcement layers and the panels. It was found that GRS coastal dykes having the following structures can exhibit high resistance against erosion of the backfill caused by deep over-topping tsunami current, thereby a high stability: the upstream slope is gentle while the downstream slopes is steep; the surface gravel layer is thick enough; the opening between the slope protection panels is small enough; and the geogrid layers are arranged over the full width of the embankment and the reinforcement layers are connected to the panels.
