Geogrid-based countermeasures against scour behind coastal dikes under tsunami overflow

Abstract

Following the Great East Japan Earthquake, a massive tsunami caused serious damage to coastal dikes. Local scour at the ground behind these dikes reportedly causes dike failures. It is important to reveal the scour process to establish methods for effective scour countermeasures. Herein, we focus on geogrids. To verify this proposal and examine its design, flume-model experiments were performed for non-liquefied and liquefied grounds behind coastal dikes. The results showed that the scour amount and area were reduced drastically when geogrids were present. Geogrids on the sand-bed surface changed the direction of overflow water. Thus, a scour hole developed away from a coastal dike model. Furthermore, geogrids exerted a scour-reduction effect even during liquefaction.