기후변화 효과를 고려한 케이슨 방파제의 시간 의존 성능설계
Time-dependent Performance-based Design of Caisson Breakwater Considering Climate Change Impacts
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초록
케이슨 방파제의 설계는 구조물의 기능을 유지하면서 일정 피해를 허용하는 성능설계를 권장한다. 하지만 기존 성능설계 방법은 기후변화로 변화된 해양 환경을 설계에 반영하기 어려워 구조물의 수명 동안에 안정성을 보장할 수 없다. 따라서 본 연구에서는 대표적인 기후변화 효과인 해수면 상승과 파고의 증가를 고려한 시간 의존 성능설계를 수행하여 케이슨의 기대활동량과 파괴확률을 산정하였다. 특히, 해수면 상승과 파고의 증가가 시간의 함수로 표현되어 케이슨 활동에 대해 시간 의존 파괴확률을 계산하였다. 개발된 방법을 일본 동해안에 위치한 Hitachinaka항 동방파제에 적용하였다. 해수면 상승보다 파고의 증가가 구조물의 안정성에 훨씬 큰 영향을 주는 것으로 분석되었는데, 이는 해수면 상승 폭이 구조물 전면 수심에 비해 상대적으로 아주 작기 때문이다. 또한 설계자들의 실제적인 관심사인 기후변화에 의한 케이슨 단면 폭의 변화를 산정하였다. 구조물의 설계수명이 커질수록 단면 폭의 증가가 컸으며, 현재 폭이 약 22 m인 Hitachinaka 방파제 케이슨은 기후변화 효과인 파고의 선형 및 포물선 증가에 의해 단면 폭이 각각 0.5m와 1.5m 내외로 증가된다.
Abstract
During the past decade, the performance-based design method of caisson breakwaters has been developed, which allows a certain damage while maintaining the function of the structure. However, the existing method does not consider the changing coastal environment due to climate change impacts so that the stability of the structure is not guaranteed over the lifetime of the structure. In this paper, a time-dependent performance-based design method is developed, which is able to estimate the expected sliding distance and the probability of failure of a caisson breakwater considering the influence of sea level rise and wave height increase due to climate change. Especially, time-dependent probability of failure is calculated by considering the sea level rise and wave height increase as a function of time. The developed method was applied to the East Breakwater of the Hitachinaka Port which is located on the east coast of Japan. It was shown that the influence of wave height increase is much greater than that of sea level rise, because the magnitude of sea level rise is negligibly small compared with the water depth at the breakwater site. Moreover, investigation was made for the change of caisson width due to climate change impacts, which is the main concern of harbor engineers. The longer the structure lifetime, the greater was the increase of caisson width. The required increase of caisson width of the Hitachinaka breakwater whose width is 22 m at present was about 0.5 m and 1.5 m respectively for parabolic and linear wave height increase due to climate change.
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