Effect of Permeability on Stability of Rubble Bases

Abstract

The effect of permeability on the stability of homogeneous and multilayered rubble bases is investigated. The approach consists of theoretical modeling of the interaction of water waves with a caisson-type breakwater and its rubble foundation, and then employing predicted flow fields in a stability model to determine the required stone size. The permeability is shown to have significant effect on the stability. The results indicate that the stability increases with increasing the rubble-base permeability at intermediate water depths, and increases with decreasing the rubble-base permeability in shallow water. The armor-layer permeability has little effect on the stability at intermediate water depths, but in shallow water the permeability of the armor layer has little effect on the stability only for rubble bases of low core permeability. The significant effect of permeability on the stability implies a need for including permeability effects in hydraulic modeling. An analysis or scaling of experimental data without taking the effect of permeability into account may lead to confusing conclusions or just incorrect results, which is demonstrated on the basis of the laboratory results commonly applied in design.