Tunnel crossing underway

PUBLISHED : Thursday, 28 October, 1993, 12:00am
UPDATED : Thursday, 28 October, 1993, 12:00am

WORK on the Western Harbour Crossing at the Hong Kong landfall site of Sai Ying Pun is in high gear as the Nishimatsu Kumagai Joint Venture begins civil works on the ventilation shafts.

Built inside a 38-metre-diameter circular diaphragm wall, the shafts will be sunk to a depth of about 40 metres.

Work is nearing completion on the installation of the bentonite batching plant and slurry pits at Sai Ying Pun. Four bentonite storage pits are being built, each with a 300-cubic-metre capacity.

The excavation shafts will be pumped full of the bentonite slurry, a syrupy material that keeps the walls from caving in. As the concrete is pumped in, the bentonite is displaced, recaptured and reused.

A reinforced cage is pushed down into the slurry, and then tremie (underwater) concrete is poured. This is heavier than the slurry and forms the diaphragm wall.