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.

In this study, the stability of cube armour units in the lower slope and berm of rubble mound breakwaters with a berm was investigated for irregular and regular placement methods. Cubes are simple and cheap in production. However, the design conditions for the upper slope and lower slope may differ depending on the water level of the dominant storm conditions. For the upper slope, relatively higher water levels are dominant. The berm has a reducing effect on the wave loading on the upper slope and therefore, it may be relevant to use cubes in the lower slope, in combination with rock in the upper slope. In this study, a regular placement technique named “the double pyramid placement method” was applied for cubes placed on the lower slope and the berm. This placement technique was compared with the irregular placement technique by performing experiments in a wave flume. As a result of this investigation, the regular placement method was found to be superior for the stability of cubes in the lower slope and berm of rubble mound breakwaters with a berm.

For the sake of overtopping, stability and economy, rubble mound breakwaters have been built with a berm in the seaward slope. Here, a breakwater model with cube armour units in the lower slope and a horizontal berm, and rock in the upper slope was tested experimentally. The purpose of the study was to investigate the stability of berms for two different configurations of the transition of armor units from the lower slope to the berm. Based on the test results, an effective configuration of cube units at the transition has been obtained.