방파제의 변천과정 분석을 통한 설계방안 연구

Abstract

Breakwaters are constructed outside of ports and allow some wave overtopping and displacements. Also, they are progressively settled to optimal shapes through trial and error for a long time. For example, in Europe they usually adopt rubble mound breakwater type for long time. On the contrary, caisson type breakwaters reinforced with wave dissipation blocks are mostly adopted in japan. In comparison, composite breakwaters with various shapes of slit caissons and rubble mound are recently evolved in Korea. In this study, I have studied the changes of structural sections of vertical breakwaters in Korea for the advisable design processes of breakwaters, and I recommended the advisable design processes in the long term by analytical review from the latest design. The results of this study are as follows.

1. I figured out typical sections of breakwaters from construction report of breakwater during the Japanese colonial era. 1) In the early stage of breakwater construction in Korea, a rubble mound breakwater type(Mukho port, 1929 ~ 1932) and a composite type breakwater with solid blocks(south breakwater in Busan port, 1919 ~ 1927) were constructed. 2) North breakwater in Busan port(1936 ~ 1940) was constructed with solid block composite type on very soft ground by partial replacement with riprap method in order to prevent settlement.

2. Composite breakwaters with caissons have features as follows. 1) Composite breakwater constructed with caissons in Korea was introduced in the Mukho port(1937 ~ 1945) first. 2) The first case of caisson type composite breakwater designed by Korean engineer was the inner north breakwater in Pohang new port(1968 ~ 1973).

3. In case of reinforcing the existing caisson type composite breakwater for stabilities, the rehabilitation method was covering by stacking up wave dissipation blocks on the outside of existing caissons.

4. The results of analytical review show that there were drastic changes between before and after the year of 1999 when alternative design bidding and design build bidding system were adopted by the Korean government. The changes are as follows. 1) Design wave heights have gradually been increased, and the reason was formed to be the heightened deep sea waves. 2) Relative design wave heights(H1/3/h) changed to 0.6 ~ 0.7 from 0.5 in 1970s. It means design wave heights are overestimated compare to water depth. 3) Design water level has adopted the high water ordinary spring tide before the year of 1999, but it is being increased competitively by bidders because of additional consideration of an anomalous sea level after 2000. 4) Relative crest heights of breakwaters were investigated into 0.6 ~ 0.7 before 1999, but these increased to 1.0(mean) ~ 1.26(maximum) after 1999. 5) Cap concrete were generally formed to simple rectangular shape before 1999, however after 1999 the shapes of cap concrete have been changed to various shapes like stairs, and etc. As a result, those cap concrete shapes attract citizens to come in and enjoy fishing, watching ocean, and etc. 5. In conclusion, I recommended advisable design processes for breakwaters based on the result of the analysis of problems caused by change features of Korean breakwaters.

1) It is necessary to estimate deep sea waves periodically by the government for surrounding seas around Korea. Also, the data from the estimation of deep sea waves should be adopted to alternative design bidding or design build bidding systems as well as projects directly ordered by government.

2) It is necessary that high water ordinary spring tide(or approximate highest high water level) should be adopted for the design water level in case of general port facilities which is not seriously affected by surges due to storms or high pressures.

3) When we decide the structural types of breakwaters, the top priority to select should be the rubble mound type, and then vertical caisson or solid block type reinforced with wave dissipation blocks in front of composite type of caisson and rubble mound should be considered. In addition, if wave reflection does not dominate water state in deep water depth and high wave areas, solid caisson is mostly advisable for the breakwater structure.

4) For the relative crest heights of breakwaters, 0.6 is mostly advisable in case of large waters in the back of breakwaters.

5) For the safety, placing berthing facilities right behind the breakwater and waterfront facilities for citizens on the top of breakwaters should be avoided as much as possible.

I hope that the data and the results of this study would be used for rational design of breakwaters in Korea. In addition, I hope that port engineering will be more developed through more reasonable design processes by widening and deepening studies and researches.