2016 年 4 巻 5 号 p. 88-92
In the Tohoku Pacific Ocean Earthquake in 2011, many coastal dykes were destroyed due to overflow of tsunamis which height were higher than the crown heights of coastal dykes. It is shown by previous studies that the GRS coastal dykes covered with crushed stone and panels are strong against overflow of tsunami. In this study, we studied the effects of slope inclination and the water flow inside of the dyke against overflow resistance of dykes. The height of the model dykes were 100 mm. Stepwise increasing water flow rate experiments and bore type water flow experiment with extremely high level of water rate experiments were conducted to the model dykes. The inclinations of slope used were 1:2 and 1:0.5. For performing the water flow through the model dyke, gaps between the panels were made with using paste plastic tapes. Followings were concluded in this study. (1) Effect of slope inclination: To improve the overflow resistance, inclination of seaside slope should be milder than 1:2 and inclination of landside slope should be steep as inclination of 1:0.5. (2) Influence of the water flow through the dyke: The water flow through the dyke has a large effect to the resistance of the dykes against overflow of tsunami, because if the water comes through the dyke, sand or embankment materials will be outflowed from the dyke.
