Undersea tunnel built by end 2012, part of 5km long Marina Coastal Expressway

By Royston Sim, The Straits Times, 7 Apr 2012

A 420M undersea tunnel for motorists - the first of its kind here - will be completed by the end of this year.

The first stage of the tunnel, which dives 20m under the sea, has been successfully built.

It is part of the 5km-long Marina Coastal Expressway, which is on track for completion by the end of next year, promising motorists a smoother ride to the Marina Bay area.

With a price tag of $4.3 billion, it is the most expensive expressway built here in terms of cost per kilometre.

The new expressway will link the East Coast Parkway (ECP) and Kallang-Paya Lebar Expressway (KPE) with the Ayer Rajah Expressway in the west.

With five lanes in each direction, it will be able to carry 10,000 vehicles an hour in each direction.

Once it is open, drivers can expect a smoother ride to the Marina Bay area, which is expected to see heavier traffic.

Major developments in the area include the Marina Bay Sands integrated resort, Gardens by the Bay and a new financial centre. An international cruise terminal will also be built there, along with future residential developments.

Drivers who are not headed downtown can also use the new expressway to bypass the Marina Bay area. It will have a total of nine entry and exit points to the ECP, Marina Boulevard, Central Boulevard and Maxwell Road.

The new expressway will also allow a portion of the ECP just after Benjamin Sheares Bridge to be downgraded to a network of normal arterial roads to serve the area.

Work started on the new expressway, Singapore's 10th, three years ago.

Building what is considered the largest and most complex road construction project here is an engineering feat. It features 3.6km of tunnel and 1.4km of surface road, depressed road and a viaduct.

Building the undersea tunnel is especially challenging. Engineers had to ensure temporary walls were strong enough to withstand the force of the discharge from the Marina Barrage, located 130m from the excavation area.

At its peak, the Marina Barrage discharges 2,000 cubic metres of water per second - the volume of more than 50 Olympic pools every minute.

Conducting wide and deep excavations for tunnels in reclaimed land with soft marine clay also proved a challenge.

For both problems, construction crews used robust pipe piles to support tunnel excavations, which proved effective in limiting ground movement.

Soft clay was also strengthened by injecting cement grout.

For safety, more than 5,000 monitoring instruments have been installed along the entire project to track temporary wall movements, ground settlement, soil water pressure and adjacent structures, such as the barrage.

About 13.1ha of land will be reclaimed in total at Marina Wharf and Marina East for this project - the equivalent of about 17 football fields. To date, 90 per cent of that 13.1ha has been reclaimed.

Auditor Wilfred Lim, who lives in Hougang, takes the KPE to work now. With the new expressway, he expects a quicker drive to his office in Shenton Way. Said the 26-year-old: 'The new expressway should provide a more direct route when I need to drive to work.'