Field Experiment to Check the Performance of New Wave Dissipating Block

Abstract

Verification of the damage coefficient of a newly developed wave dissipating block named Chi-block has been attempted via field tests. Usually, the concerned damage coefficient is determined via hydraulic experiments, and the block is used in the field without in-situ verification. The test breakwater was constructed in Marado, and 5-tonne blocks were installed in front of the breakwater having a 1:1.5 slope. In order to measure the movement of the block, a 3-dimensional acceleration sensor was installed in the block, and a pressure-type wave recorder was installed near the breakwater to measure the wave height causing displacement of the block. Seventy-three blocks were used in the experiment, and thirty acceleration sensors were installed amongst them. The experiment was conducted over the period starting from the beginning of May up to September 15, 2017 along the typhoon Talim hit Marado, thereby causing displacement of most blocks located near the water surface. It was observed that losses in the Chi-blocks occurred in the case of significant waves measuring 3.70-4.09 m in height, which is lower than 4.5 m calculated from the Hudson's formula with the damage coefficient 13. This is because the wave direction in the field was different from that observed during hydraulic experiments approximately normal to the breakwater. The waves in the field, however, hit the breakwater obliquely. The proposed field experiment demonstrates that the acceleration sensor monitoring system installed within wave-dissipating blocks is useful in verifying the damage coefficient and performance of the concerned blocks.