Compiled and reported by: Li Zeng-Wang
After the first foundation pile of the main section of Kinmen Bridge, which is 2.5 meters in diameter, was erected despite the challenge of digging through hard granite rocks in March 2018, Taiwan’s first steel cofferdam was completed in the sea on the early morning of July 16, 2018, which symbolizes another breakthrough of the arduous construction.
According to the press release of the Freeway Bureau, MOTC, in areas alongshore where the seabed is less than 6 meters deep, the pier foundation of Kinmen Bridge across the sea between Kinmen and Little Kinmen can be built through the double-wall sheet pile cofferdam; in areas where the seabed is more than 7 to even 20 meters deep, sheet piles can no longer be practicable. Therefore, the pier foundation of Kinmen Bridge was first built through the steel cofferdam. The maximum size of the steel cofferdam is 29 meters × 23 meters × 5 meters (length × width × height), which is used for the main section, and the minimum size of the steel cofferdam is 7.5 meters × 7.5 meters × 2.5 meters, which is used for the approach section. A total of 11 piers were erected for the main and side sections in the widest trench area and 15 piers were erected for the approach section through the steel cofferdam.
First, foundation piles were coated with steel tubes as support in the sea. Second, the steel cofferdam assembled on land was hung above the foundation pile with 24 steel rods. Third, 12 jacks were used to gradually descend the rods to the designed undersea height. Last, divers installed the bottom plate of the cofferdam and the blanking plate between the foundation pile coated with a steel tube at 3~9 meters below the sea, filled them with concrete (1.5 meters in thickness), and then drained seawater from the steel cofferdam.
After seawater was drained from the steel cofferdam, 6 coated steel tubes and 4 anti-floating steel tubes were used to resist more than 1000 tons of buoyancy and wave impacts twice a day. In case of water seepage from the steel cofferdam, divers had to dive to the bottom of the steel cofferdam and find and seal the leaks. After confirming that no more leakage inside the steel cofferdam was taking place, construction workers could remove coated steel tubes, band foundation reinforcements and pour concrete. The construction process was complex, and construction workers had to stay alert to the leakage of seawater inside the steel cofferdam. After construction workers made all-out efforts and eliminated difficulties around the clock, the first P15 steel cofferdam was finally completed on the early morning of July 16, 2018.
It took 2 months to complete the first steel cofferdam from mold assembly to concrete pouring. Construction workers carefully carried out each step and recorded all the problems as a reference for the subsequent construction of the steel cofferdam, and gradually shortened the construction time.
As of July 15, 2018, 16 foundation piles of the main section (2.5 meters in diameter) and 22 foundation piles of the side section (2.0 meters in diameter) have been erected. Contractors improved the overall construction efficiency and results by extending the original working area of 2 foundation piles to 5 foundation piles. The superstructure segment prefab workshop at Singda Harbor in Kaohsiung is under construction now and is expected to fabricate segments in August. The overall construction of Kinmen Bridge has been effectively improved
The Freeway Bureau, MOTC indicated that construction workers continued to make all-out efforts in the face of ever-changing challenges and were confident of completing the construction of Kinmen Bridge in 2021.