Abstract
It is important to know the threshold of the cross-section area of a beach to which a coastal dike and a seawall will come to suffer damage. Therefore, the actual conditions on coastal damage are investigated about 33 beaches in Japan and Thailand. Then, the marginal sizes of the beach required in order that those coastal facilities will not suffer damage to each incident wave are clarified. Moreover, since there are many cases that the fracture mechanism of the dike and the seawall in a sand area or a very shallow area cannot be explained by only the stability calculations of these facilities, scour and suction also need to be taken into consideration. Hence, a practical method of predicting the destruction of the dike or the seawall by using the wave overtopping rate to it and the net effective shearing resistance force in its sucking part is proposed. In addition, the availability of a countermeasure which strengthens the net effective shearing resistance force by using small stones as material of the sucking part is confirmed.
