Tony Gee has produced a cost-saving alternative design of an immersed tunnel structure to carry the Central-Wan Chai Bypass over the existing MTR Tsuen Wan Line (TWL). The alternative design combines five separate box structures of the original design into one single structure, 120 metres long, 47 wide and 10 high. The structure is supported on two rows of bored piles along each side of the TWL tunnel. Tony Gee’s design permits the tunnel installation to be carried out in one phase and substantially reduces the impact on marine traffic in the Victoria Harbour and the risk of damage to the TWL.
The structure will be precast in a dry dock in China close to Hong Kong waters from where it will be towed to the site and ballasted with seawater to sink it onto the bored pile supports.
A 3D model of the structure, generated using Microstation software, was used to simplify the mass and buoyancy calculations. Subsequently, this model was integrated with finite element stress analysis program, SOFISTiK, which was used to determine the structural stresses under temporary towing and permanent conditions.