Abstract
In this study, the stability of backfilling stones under flat-type armor blocks with a circular hole against waves has been studied experimentally. The mechanism of displacement of the rubble backing under the flat-type armor blocks caused by wave actions is also examined extensively. According to the latest guidelines in Japan, it is recommended that the required mass of under layered gravels should be greater than 1/10 to 1/20 of the mass of a wave dissipating armor block. The covering flat-type block in this study has a comparatively large hole of circular shape at its center for reducing the uplift force and also saving the construction cost. It would be concerned that such covering blocks may cause displacement of the backfilling stones and finally result in the total failures of revetment works. In this study, supposing that the size of the backfilling stones is generally smaller than that of a circular hole on the covering blocks, the stability of such backing stones against waves has been examined extensively by the use of various median grain sizes of the backing. By referring to such experimental results, the displacement mechanism of the rubbles is also discussed precisely.
