Dynamic responses of rubble mound breakwaters reinforced with geogrid-wrapped slopes and sheet piles under sequential earthquake loading

Rubble mound (RM) breakwaters are widely used to protect coastlines from sea wave actions; however, past seismic events have exposed their vulnerability to catastrophic failure, most often driven by foundation soil instability. Despite the critical importance of this problem, experimental investigations on the seismic behaviour of RM breakwaters remain limited. This study addresses that gap through a series of shake-table experiments aimed at elucidating earthquake-induced failure mechanisms and developing effective countermeasures. The study proposes two reinforcing techniques to enhance the seismic resilience of RM breakwaters by employing sheet piles embedded in the foundation soils and geogrids integrated into the breakwater mound. The breakwater slopes were wrapped with geogrid facings on both sides of the mound. Sequential foreshocks and mainshock loadings were applied at the model's base. The reinforced models were compared with a conventional RM breakwater with respect to settlement, horizontal displacement, acceleration amplification, excess pore water pressure, and overall deformation. The geogrid-wrapped face-sheet pile configuration exhibited an 85% reduction in settlement and an 80.1% decrease in horizontal displacement under mainshock conditions. Also, 3D profile analyses and numerical simulations further clarified failure mechanisms. Finally, the developed breakwater models proved resilient under the applied earthquake loading.