Changxing Island Cofferdam Dock Construction, Phase 1
About The Project
After extensive technical research and economic evaluation, it was decided that our steel sheet piles were the best foundation solution for the purposes above especially given the overall layout of the dock and harsh underwater terrains. Specifically, our steel sheet piles were used both to construct the retaining cofferdams, as well as providing the excavation and structural support.
Zhongchuan (中船), shorthand for the China Shipbuilding Corporation (中国船舶工业 总公司), is a docking company in Changxing Island. OSP was commissioned to engage with what is by far the largest docking project in the history of China. OSP in particular was in charge of supplying steel sheet piles for the 1st to 4th docks.
The 1st and 2nd docks are located in the Yangtze River, which is host to naturally harsher water conditions. Conditions were therefore extremely unfavourable towards alternative foundation solutions. All 4 relevant docks were situated on soft soil conditions.
The two relevant dimensions for sheet piles we provided are 98 x 30m and 128 x 30m; both were arranged side-by- side at a distance of 28m. Excavation depth was 14.78m, calculated based on highest water levels experienced.
What we see is an enclosure is made with PU32 steel sheet piles (each being 31m
in length), which results in a total of 5 fencing support systems.
The 1st and 2nd dock positions
In order to further enhance the stability of the dock against winds and waves, the outer as well as eastern and western sides are supplemented with an additional row of AU16 steel sheet pile (each being 16m in length) 3m apart from the original row. As the entire foundation pit is located on an underwater slope, it is necessary to make the mud surface elevation levels on the outer side of the walls consistent in
order to maintain the balance of the surrounding load throughout the entire enclosure.
The slope is divided into two levels, but the sand at the 8.00m elevation is further heightened by 4.00m in the southwest side of the 1st dock as the slope there is much steeper.
Foundation pit formed via PU steel sheet piles
Construction began in December 2005, and was successfully completed by December 2006. The largest horizontal displacement experienced throughout the project was 40mm, while the largest vertical displacement experienced was 30mm.
From our observations, deformation of steel sheet piles occurs most heavily at the surface of the excavation, with sheet pile being pushed to a maximum of 15cm inwards. This is all within the allowable range, and alongside the fact that the underwater slope protection is not compromised through erosion, satisfies overall stability requirements for the project.
Solving stability issues
Overall, this project capitalizes on the strengths of steel sheet piles to solve stability issues normally encountered by other foundation solutions in water-based projects. OSP in particular with its proprietary technology and experience in foundation solutions specializes in addressing deformation control and sealing requirements to ensure water-tightness. Besides being much more appropriate for foundation dock construction application-wise, using sheet piles has various other benefits. These include the naturally slimmer profile of sheet piles occupying a smaller area of water, thus reducing impact of construction on nearby water channels; additionally, faster installation of sheet pile means shorter construction periods and higher cost-savings overall.