Construction crews finished laying the first pier foundation for the Kinmen Bridge yesterday, the National Freeway Bureau said, adding that it is confident that the bridge would be finished by 2021.
The bridge would connect Greater Kinmen and Lieyu, also known as Little Kinmen), the two main islands in the county, the bureau said.
It would span a strip of sea whose bed is on average 7m below the surface, it said, adding that in some areas the seabed is about 20m below the surface.
The geological complexity has made it impossible to lay the pier foundations using steel sheet piles, so the construction crews used the steel cofferdam method, the bureau said.
This was the first time the method was used by the bureau to lay a pier foundation, which took two months to complete, it said, adding that it should be able to lay the other pier foundations faster.
The bureau in March laid a foundation pile on granite.
The bureau yesterday explained the challenges of applying the steel cofferdam method.
The crews first installed jacketed steel pipes as a support base before beginning the construction, it said.
They assembled the steel cofferdam on land before lowering it to a designated depth using 12 large hydraulic jacks, the bureau said, adding that divers worked 3m to 9m below the sea surface to install bottom boards for the cofferdam and seal the plates between jacketed steel pipes.
Crews then pumped in concrete to form a 1.5m-thick bedding at the bottom of the cofferdam before pumping out the seawater trapped inside the structure, it said.
The cofferdam had to withstand buoyancy of more than 1,000 tonnes and tidal effects twice per day, the bureau said, adding that the crews installed six jacketed steel pipes and buoyancy-resistant steel piles to reinforce the structure.
Divers were kept on standby during the construction in case seawater leaked into the cofferdam, it said.
The bridge project has been criticized for “only surfacing during elections.”
The Legislative Yuan’s budget center has said in a report that the project had several issues, such as low budget implementation efficiency and construction delays.