Effects of duration and acceleration level of earthquake ground motion on the behavior of unreinforced and reinforced breakwater foundation

This paper describes an effective reinforcement technique for foundation of breakwater in order to provide resiliency to the breakwater against earthquake and tsunami related compound geo-disaster. As reinforcing measures, the technique uses gabions and sheet piles in the foundation of the breakwater. A series of shaking table tests were performed to evaluate the effectiveness of the technique under different earthquake loadings, and comparisons were made between conventional and reinforced foundation. The results of these tests reveal the advantages of the reinforcing foundation technique in terms of reduction in settlement and horizontal displacement of the breakwater during the earthquake loadings. Duration and level of acceleration of earthquake loadings had significant impacts on the settlement and horizontal displacement of the breakwater. It was found that one of the reasons of settlement of the breakwater is lateral flow of foundation soils during earthquake, and the sheet piles could reduce the lateral flow. The excess pore water pressures could be reduced significantly during earthquake due to the reinforcing technique. Numerical analyses were also performed to confirm the effectiveness of the technique, and to determine behavior of the reinforcement-soil-breakwater system during the earthquakes.