THE advanced section of a 1.2-kilometre 'immersed tube' to form the new sub-harbour link for the airport railway is ready to be towed into Victoria Harbour.
The 80-metre advanced tunnel unit will form the initial link between the Central and Wan Chai reclamation site and the sub-harbour tunnel itself. The tunnel will link up with the Kowloon reclamation site for the new airport railway terminal.
This first connecting section of the tunnel is budgeted for under the $1.8 billion Central and Wan Chai reclamation scheme. The tunnel proper has a separate budget of $600 million.
The advanced tunnel unit was pre-cast from concrete on a special semi-submersible 100-metre barge at Siu Sai Wan, Chai Wan.
The barge will be towed by tugs into the harbour, carrying the tunnel unit and a pump house which will be used to provide cool water for the air-conditioning for the harbour-front buildings.
Ballast tanks in the barge will be filled, allowing the tunnel unit to float, and the barge will then be removed in its semi-submerged position before being re-floated.
Tanks inside the tunnel section itself will then be filled allowing it to sink to the bottom of the harbour. Once in place it will be moved by a complex system of jacks on the sea bed. Divers will monitor the positioning.