Seismic performance assessment of a pile-supported wharf retrofitted with different slope strengthening strategies

Pile-supported wharves may be subjected to severe damage during major earthquakes. As such, efficient strategies for retrofitting wharf systems are needed. In this study, we investigate the seismic performance of a pile-supported wharf retrofitted by the following three conventional slope strengthening strategies: i) improving the ground with a soil-cement mixture, ii) driving pin piles near dike toe, and iii) creating an underwater bulkhead system using sheet piles. Effectiveness of the three retrofit schemes is assessed comprehensively. First, seismic response of the as-built and retrofitted pile-supported wharf is investigated. Subsequently, performance of the retrofit strategies in mitigating the seismic vulnerability is thoroughly investigated by comparing component and system-level fragility curves. It was found that: (1) overall, the strategies are effective in mitigating the seismic response and in reducing the seismic fragilities of the wharf system; (2) the performance of the retrofit measures varies at the structural component level, as a retrofit measure may have an isolated local negative effect for a certain structural component. In this regard, an appropriate retrofit strategy should be identified based on specifically defined retrofit purposes; and (3) as implemented, the soil-cement mixture performed best (in lowering the system seismic fragility), followed by the pin pile, and lastly the sheet pile.