First tunnel 'tube' section for harbour

PUBLISHED : Friday, 09 September, 1994, 12:00am
UPDATED : Friday, 09 September, 1994, 12:00am

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.

The advanced unit, which is wide enough to allow for two trains, will be visible on its barge in the harbour for several days before the sinking operation takes place.

The operation of moving the section is scheduled to start this weekend, but may be delayed until Monday or Tuesday.

Vessels using the harbour have been notified of the movements of the tunnel unit.

'Buoys will be put in place and vessels warned to keep out of the area. This shouldn't cause any problems but we will monitor the situation,' said a spokesman for the Marine Department.

Bryan Reid, Senior Resident Engineer in charge of the advanced tunnel section said: 'The unit will jut out from the new sea wall about 30 metres when it is in position and will form the link with the immersed tube project itself - that will create the link with the Kowloon side site.' The sections of the immersed tube itself will be laid, 120 metres at a time, beginning in April next year.

The work will be co-ordinated with the Western Harbour Crossing project, the new road tunnel link.

The project is scheduled to finish by the end of June 1997.