Abstract
Stability of a composite breakwater which consists of a caisson and a rubble mound is discussed. Stability against sliding is conventionally estimated by the following formula, H=tanδ·V where V, H and tanδ are vertical load, horizontal resistance force and apparent friction angle between a caisson and a rubble mound. The value of tans used for design is 0.6 which is an empirical constant. From geotechnical point of view, this stability problem is equivalent to a bearing capacity problem of a shallow foundation subject to combined loads. By introducing macroscopic failure locus of a cassion-rubble mound system in 3-dimensional load spaceV-H-M/B, it can be easily explain that tanδ depends on loading conditions. Non-linear FE analysis is performed to evaluate a bearing capacity characteristic. The numerical results show that tanδ reduces owing to existence of a moment load around a base of a caisson. For breakwater problems, a horizontal component of wave loads also cause moment loads because they are working at some heights from the base. The importance of an applied height of a horizontal load is highlighted for rational estimation of sliding resistance of the breakwater system.
