A series of shaking table tests were conducted on composite breakwater systems under 30g centrifugal conditions. The emphasis was placed on investigating the mechanisms of seismic settlement of foundation ground, in particular of the contribution from the dispersion of mound rubble into the foundation soil. In-flight visual observation of the deformation process by a high-speed CCD camera showed the significance of cumulative vertical compression of foundation soils under cyclic loading. Pre- and post-shaking comparisons of weight of the rubble mound revealed that dispersion into the soil had occurred and contributed to caisson settlement
