First Tests on the Symmetrical Breakwater Armor Unit Crablock

Single layer concrete armor systems are being widely used nowadays in the design of rubble mound breakwaters. Recently, a new concrete armor unit has been developed and applied as single layer armor system in the repair works of one damaged breakwater at Al Fujeirah, UAE. It has a symmetrical shape, in contrast to most other units. Modern single layer concrete armor units that exist at this moment have design guidelines in terms of placement, stability and overtopping. However, because of lack of laboratory research and the little experience of using Crablock, no design guidance exists yet for this new single layer block compared to other existing one layer units. Being a new armor unit, the placement was investigated first. Then physical model tests were performed in a wave flume to come up with results on stability and wave overtopping. Furthermore, to determine the interlocking properties of armor units, pull tests were also conducted in this research. The placement tests showed that uniform placement was best achieved with a rectangular grid on a relatively small underlayer of rock. Test results on stability showed that longer waves affected the armor layer a little more, with more rocking and earlier start of damage. Packing density as well as placement pattern showed no influence on wave overtopping. The overtopping tests gave larger overtopping than expected, which might be due to the fairly steep 1:30 foreshore that gave a large ratio of significant wave-height from the time domain and the spectral wave-height.