2015 Volume 71 Issue 1 Pages 30-41
Since wave force becomes small when a coastal dike or a seawall is in the area shallower enough than the breaking water depth of large waves, the concrete covering of the dike or the seawall is not destroyed simply. However, if the scour in the front progresses owing to small waves acting repeatedly and the lowest edge of the front slope comes to be visible, since incident waves penetrate the body of the dike or the seawall from the lowest edge and the return flow by incident waves come to suck back-filling materials out of the body, the cavity in the body is enlarged by the suction, and the concrete covering come to be broken easily by weak waves.
In this research, the formula of Ioroi et al. to estimate suction rates for the dike and the seawall covered the front slope and the crown part with concrete is improved for handling simplification and expansion of the applicable extent. Next, diagrams to estimate easily front scour depths required for calculating suction rates are also improved. Furthermore, one method for estimating suction rates in the case that front water depths at the time of storm surges are unknown values is proposed. Then, the destructive mechanism of the dike and the seawall, and countermeasures to the suction of backfilling materials from those are also considered.