Revetment breakwaters on reclaimed coral sand have demonstrated vulnerability to seismic damage during strong earthquakes, wherein soil liquefaction has been identified as a substantial contributor. Based on the results of three centrifuge shaking table tests, this study investigates the characteristic seismic response of revetment breakwater on reclaimed coral sand and the influence of soil liquefaction. The basic mechanical properties of reclaimed coral sand were measured using undrained triaxial and hollow cylinder torsional shear tests. The centrifuge test results indicate that liquefaction of coral sand can result in significant displacement and even failure of revetment breakwaters, encompassing: (a) tilting, horizontal displacement, and settlement of the crest wall; (b) seismic subsidence in the foundation and backfill. The liquefaction consequence of the reclaimed coral sand increased with a decrease in soil density and rise in sea water level (SWL). Post-earthquake rapid reinforcement measure via sandbags is found to be effective in limiting excess pore pressure buildup in foundation soil and structure deformation under a second shaking event. Based on the test results, the effectiveness of current simplified design procedures in evaluating the stability and deformation of breakwaters in coral sand is assessed. When substantial excess pore pressure generation and liquefaction occur within the backfill and foundation coral sand, the pseudo-static and simplified dynamic methods are inadequate in assessing the stability and deformation of the breakwater.

To date, numerous coral sand revetment breakwaters have been constructed in oceanic regions to resist wave impact and scour. However, frequent earthquakes significantly threaten their stability, especially during mainshock-aftershock sequences, where aftershocks can further exacerbate the risk of damage or collapse. This study proposes a reinforcing countermeasure, i.e., geosynthetics reinforced soil technique, to mitigate seismic deformation and enhance the resilience of revetment breakwaters against earthquakes. A series of shaking table tests were conducted on coral sand revetment breakwaters to examine the effect of geogrid reinforcement on their seismic performance under mainshock-aftershock sequences. Additionally, the reinforcement mechanism of geogrid was elucidated through supplementary cyclic triaxial tests. The results indicate that acceleration amplification intensifies during aftershocks, while geogrid reinforcement mitigates this detrimental effect. The inclusion of geogrid also decreases the buildup of excess pore water pressure (EPWP) under mainshockaftershock sequences. Coral sand shear dilation results in the generation of notable negative EPWP within revetment breakwaters, and more significant negative EPWP oscillation, compared to the aftershocks, is observed in the mainshock. Additionally, geogrid decreases the maximum cumulative settlement in reinforced revetment breakwaters by over 54 % compared to unreinforced structures. The cumulative damage induced by aftershocks exacerbates the damage to coral sand revetment breakwaters, leading to the emergence and rapid progression of lateral displacements. Nevertheless, geogrid reinforcement mitigates this adverse effect and prevents the formation of plastic slip planes, thereby altering the deformation pattern of the revetment breakwater subjected to mainshock-aftershock sequences. Overall, geogrid reinforcement is found to be highly effective in enhancing the stability of coral sand revetment breakwaters against mainshock-aftershock sequences and holds promising applications in infrastructure construction in coral sand island and reef areas.