Western Harbour Tunnel - Hong Kong's quickest cross-harbour traffic route

Construction

Reclamation

The landfalls of West Kowloon Peninsula and Sai Ying Pun were constructed on areas of reclamation. At Sai Ying Pun the reclamation was placed in 1988 and no long-term settlements are expected. The West Kowloon reclamation was placed in 1993, using pumped marine sand. Future settlements are not expected to be significant. Settlement points have been established and ongoing monitoring continues.

Sai Ying Pun Cut-and-cover Tunnel

Top-down construction within diaphragm wall was used at Sai Ying Pun due to the limitations of space. The top roof slab was constructed between the two walls and central steel piles were driven to support it until the dividing wall could be constructed. The base slab was then placed, supported by shear keys into the diaphragm walls.

One of the major concerns was the control of water seepage through the diaphragm walls and the roof and base slabs. Precast wall panels were erected along the diaphragm walls leaving a 400 mm gap. Half round drainage channels have been provided at the top of the profile road barrier between the wall and the panel and these were drained at intervals into the road drainage system.

West Kowloon Cut-and-cover Tunnel

The cut-and-cover tunnel linked the immersed tube to the open approaches and the toll plaza area. It was constructed on newly reclaimed land by the conventional bottom-up method, using a temporary cofferdam with diaphragm walls and steel cropping. The open approach structure was constructed in an open-cut, using a cement bentonite cut-off wall. The base slab structure was up to 2 m and was designed to resist the uplift pressure and floatation generated by the ground water in the reclamation site.

Immersed Tube Tunnel

Construction of the immersed tube units took place using steel shutters in a controlled way, and by employing good concrete curing and quality control. Crack widths were specified to be less than 0.2 mm. As soon as the units were confirmed in a final position, the alignment holes were projected with hydraulic jack to draw the two units together to create an initial seal to the rubber gasket. The water between the two units was then pumped out and the unbalanced hydrostatic pressure forced the units together and compressed the rubber gasket into a watertight joint. Once the unit was in position and was supported on temporary vertical jacks at its pre-end, sand was then pumped into the space below the unit to provide a permanent foundation. The main trench was then backfilled. Protected rock armour was then placed on top of the units to prevent damage.

Reference :

Thomas Telford Limited - Journals on Line. "Civil Engineering Special Issue : Hong Kong International Airport, Part 2: Transport Links / November 1998 - Paper 11526 Western Harbour Crossing, Hong Kong - a successful BOT model"