In the repair of damaged wave-dissipation works, the stability of wave dissipation blocks is expected to be improved by the use of blocks larger mass than the required mass in the initial design. However, although the wave-dissipation blocks used for the repair are larger than the mass calculated by the Hudson equation, the damage of the blocks has occasionally occurred near the crest of wave-dissipating works. This paper aims to elucidate the damage mechanism of wave-dissipation blocks used for the repair at the crest of wave-dissipating blocks of a low-crested seawall by conducting hydraulic model tests. It is found from the experimental results that the wave action in the vicinity of the discontinuity of the mass of blocks causes the block damage near the still water level.
In general, lifecycle cost of coastal structures is estimated as the total cost of the initial costs and the expected repair costs. Araki and Deguchi (2007) showed that the repair cost was reduced in the case where rubble stones with larger mass than the required mass in the initial design were used for repairing the detached breakwater body. This result is based on the assumption that the stability of the structure improved by using larger rubble stones. If stability of coastal structures is not improved despite such kind of repair method, damages will often recur and constant repair will be required and as a result, it might be that the total costs increase. Because frequency of damage and the repair costs are influenced by the change in the stability after the repair, high-accuracy evaluation of stability change is required. In addition, it is also essential that desired stability is ensured after the repair. In a practical case, wave dissipating blocks with larger mass than the required mass in the initial design are used for the repair of a low-crested wave absorbing revetment.