기후변화에 대응하기 위한 항외곽시설 설계기준 개정에 관한 제언

설계 충실도 지수와 피복석 공칭지름 변화에 따른 파괴확률 변화율을 중심으로

This study aims to develop an amendment to the design guidelines for the outer port facilities based on quantitative indexes to address harsh wave conditions due to climate change. To this end, the author first looked into the in situ data of damage to outer port facilities collected in about a dozen major ports in Korea, where the outer port facility has failed in fulfilling its intended disaster prevention against typhoons over the last decade. In doing so, the design fidelity index, a quantitative index that can rationally determine the scope of reinforcement of outer port facilities, was developed based on the specified failure mechanism. The design fidelity index evaluates the degree of loss of armoring rocks, erosion of main body of breakwater, displacement of cap-concrete, lee side damage by overtopping, and scouring near the toe, which are the primary failure mode of the outer port facilities, and displays these damage extents of each of 5 primary failure mode in polar coordinates. Among the various failure modes mentioned above, scouring near the toe has been found in most outer port facilities, and as a result, the current design practice like whether to install scouring-prevention work is determined based on the limit depth for the incipient sediment motion needs to be revised. Numerical simulation shows that with sediment motion triggered by harsh water surface displacement in the standing waves formed in front of vertical type breakwater being accounted for, the robustness of scouring prevention works, which takes the maximum scour depth as the maximum wave height, could be secured. In addition, among the various quantitative indexes that can provide information concerned with how robust or vulnerable the outer port facilities would be by adjusting design waves return period, it turns out that the increasing rate of failure probability associated with the unit change in the nominal diameter of armoring rocks could provide most promising results.