Backfilling configuration to improve tenacity of composite-type breakwaters

ABSTRACT Composite-type breakwaters are reinforced by piling rubble stones and constructing counterweight fillings (known as reinforcing embankments) behind caissons. Important performance requirements for breakwaters include minimal damage and high strength, even when the external forces exceed the design forces. In this study, the failure process and final state of breakwaters with reinforcing embankments are investigated via centrifuge model tests, and the cross-sectional configuration of the reinforcing embankment for improving the tenacity of breakwaters is determined. The results show that, in the overturning mode, when the number of rubble stones decreases, the reinforcing embankment deforms in accordance with the inclination of the caisson; subsequently, the caisson overturns and mounts onto the embankment. When balance is not maintained at that position, the caisson slides down the slope surface, resulting in catastrophic failure. A series of centrifuge model tests qualitatively show that placing more rubble stones adjacent to the caisson is less likely to result in such catastrophic failure. Furthermore, the stability of the breakwaters is evaluated via circular slip analyses, which demonstrate the importance of increasing the volume of the reinforcing embankment adjacent to the caisson in terms of the stability.