Mechanism of backfilling sand discharge from a gap under vertical revetment

Abstract

Coastal disasters such as sliding, settlement, and over-turning of coastal structures as well as subsidence of reclaimed areas occur due to toe scouring and backfilling sand discharge. In this study, the sand discharge mechanism from a gap under a vertical revetment without wave absorption and foot protection is investigated using hydraulic model experiments and newly developed numerical simulations. In the hydraulic model experiments, sand discharge and sinkholes similar to those observed in the field surveys are reproduced, and it is found that sand discharge is very sensitive to wave steepness and relative gap height. In numerical simulations, a comparison with the experimental data demonstrates the validity of the numerical methods. It is revealed that sand discharge tends to occur with an increase of the maximum seaward velocity just outside the gap under the revetment as well as the maximum volumetric strain inside the most offshore side of the sand inside the gap.