The performance of high-density cubes in the armor layer of a breakwater was investigated through an experimental study. For this purpose, two different cross-sections, one with a conventional cross-section and one with a berm, were modelled in a wave flume. A total of ten tests were performed for both cross-sections. Different concrete densities of cubes and different placement methods were applied. The dimensions of the cubes with two different densities were the same for all tests to avoid potential scale effects caused by the dimensions of HD cubes. The experimental study showed that HD cubes were more stable than ND cubes; the characteristic wave height for HD cubes was 1.5 times higher than that of the ND cubes. The use of HD cubes may provide economic efficiency and enables a significant reduction of the concrete volume, transportation of material, and reduction of required construction area for manufacturing, etc. HD cubes in a single layer turned out to be very stable. However, only using HD cubes in a part of the armor layer or only used on the second (upper) layer caused a decrease in the stability of the armor layer, especially in comparison to the armor layers that fully consist of HD cubes. The performance of HD cubes was also evaluated by comparing the experimental results with the Van der Meer (1988) formula and the suitability of the stability number for HD cubes was discussed.

The stability number for rubble mound breakwaters is a function of several parameters and depends on unit shape, placing method, slope angle, relative density, etc. In this study two different densities for cubes in breakwater armour layers were tested to determine the influence of the density on the stability.