Monday, August 13, 2012

Services tunnel overcomes obstacles

Straits Times: Sun, Aug 12

While building the Common Services Tunnel, the mammoth infrastructure tube that funnels power lines, water pipes and telecoms wires to Marina Bay buildings, the Urban Redevelopment Authority (URA) hit a rock wall - literally.

Beneath the surface of the reclaimed land lay a 1.5km-long breakwater, made up of tightly packed stones, that dated back to colonial times. To build the tunnel, contractors had to break it up and extract the rock, a mammoth task that took six years from 2006 and innovative construction methods.

For its efforts and for the Common Services Tunnel itself, the URA team received a Ministry of National Development Minister's Team Award last week.

The Common Services Tunnel is an extensive custom-built underground network under the Marina Bay area housing pipes to deliver chilled water for cooling buildings, as well as power lines and other utilities. It saves land and does away with the need to dig up the ground to add more infrastructure or access underground cables.

Ms Ng Bee Theng, URA's deputy director of its development coordination department, said that Marina Bay is a high-density area and because government land is sold in stages, "there would be a lot of digging each time a development comes up".

Planning began in 1998 and construction started in 2001, with the first stems of tunnel finished in 2006. Today, some 4km is completed, with another 1.7km of tunnel in Marina South to be done by 2014. To date, $800 million has been pumped into the project.

Buildings served by the tunnel include Marina Bay Sands, One Raffles Quay and Asia Square.

One of the biggest challenges involved removing the old, buried breakwater off the former Clifford Pier. "We knew it was there, but we thought it would be easily broken like other seawalls," Ms Ng said.

But its huge stones, some weighing 20 tonnes, were too tightly packed and sometimes as deeply as 20m underground. Conventional methods would mean digging up the earth and removing the buried stones one by one.

Instead, the construction team ended up building support structures called cofferdams around sections of the wall, pumping them full of seawater, and using a clam-shell attachment to grab the rocks and work them free in the resulting earth and water slurry.

Besides the breakwater, there are also pier and wharf structures and seawalls buried beneath the surface, and some parts of the tunnel had to cut under existing MRT lines.

In general, building the tunnel is not unlike the work of tunnelling for expressways or MRT lines, said URA project management deputy director Loo Pak Chai.

The Common Services Tunnel may one day stretch up to 20km, though Ms Ng said future extensions depend on planning of the area and its vicinity.

It is not the only below-ground infrastructure. The 48km-long first phase of the Deep Tunnel Sewerage System runs 20m to 55m underground to channel sewage to a Changi plant. Singapore Power has also planned a 35km network of tunnels, 60m below the surface, to house high-voltage transmission lines. An 18.5km tunnel will run from the north of the island to the south while a 16.5km tunnel will criss-cross east to west.

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