AbstractA lot of coastal dikes located along the Pacific Coast of Tohoku Region were severely damaged by the Great East Japan Earthquake Tsunami. In this study, hydraulic model experiments were conducted to understand characteristics of local scour at a landward toe of a coastal dike, which has been considered as a main cause of the failures of coastal dikes by the 2011 tsunami. A coastal dike model is fixed in a horizontal open channel with 4.5m length. Scouring of sandy bed behind the dike model under constant discharge is recorded by a video camera and temporal variations of sizes of the scour hole are extracted from the video images. In the experiments, two types of flow patterns, flow with hydraulic jump and submerged flow, were observed around the toe and it is found that the different flow types induce completely different processes of the local scouring, resulting in significant differences of scouring depths. Embedment of the landward toe induced the submerged-type flow to form deeper scour holes than those with a basic model of the toe without embedment. On the other hand, sheet-pile structure is found to be an effective measure against local scouring to delay start of suction of sand under the landward slope through the scour hole.
Kato, F., Y. Suwa, K. Watanabe and S. Hatogai 2012. Mechanism of coastal dike failure induced by the Great East Japan Earthquake Tsunami, Proceedings of 33rd ICCE, 9 pages.
Tokida, K. and R. Tanimoto 2012. Lessons and views on hardware countermeasures with earth banks against tsunami estimated in 2011 Great East Japan Earthquake, Proc. of the Int. Symp. on Engnieering Lessons Learned from the 2011 Great East Japan Earthquake, pp. 463-474, 2012.
Tanimoto, R. and K. Tokida 2012. Study on structure of dug pool eroded by tsunami flood and its tsunami reduction function, Int. Symp. on Earthquake Engineering, Vol.1, pp.143-150.