Deformation of rubble mound breakwater, wave force on a rubble stone and run-up height were measured in the experiments to obtain fundamental data for establishing a design method where the change in profile of the breakwater is permitted. Characteristics of profile change, response of a rubble stone to waves and change in the hydraulic function of rubble mound breakwater with development of profile change were investigated. It was found that although the deformation profiles are classified into three types like deformation of sandy beach does, the characteristics of the deformation of rubble mound breakwater are different from that of sandy beach. Moreover it was found that there was no significant difference in run-up height on both initial and deformed profiles.
Profile of a rubble mound breakwater changes flexibly to form a stable profile according to the characteristic of incident waves, which is very unique character. At present, some existing stability formulas, for example Hudson formula, are used in designing rubble mound structures in Japan. Any displacement of rubble stone is regarded as the destruction of a rubble mound breakwater even though the hydraulic function of the breakwater to keep tranquillity behind them is maintained, because the stability formulas used in the design is based on static balance or experimental results under the condition of very small deformation. Thus profile change of a rubble mound breakwater is not practically permitted in the present design method. However a slight deformation of rubble stone does not always cause catastrophic reduction of the hydraulic function of the rubble mound breakwater. It is more reasonable for rubble mound breakwater to permit profile change provided that the hydraulic function originally expected to the breakwater is not lost after the deformation caused by very large waves that rarely occur.