Why the Marina Coastal Expressway, one of Spore's most ambitious road projects, is now costing $4.3 billion
Venessa Lee Today Online 22 Jan 11;
One of Singapore's most ambitious road projects is being built on land described as being like "toothpaste" and "peanut butter".
The Marina Coastal Expressway (MCE), a 5km, 10-lane artery through which will flow the traffic lifeblood of the new Marina Bay downtown, runs through land reclaimed in the 1970s and 1980s. There are, said Mr Chuah Han Leong, director of the MCE with the Land Transport Authority, "very thick and deep layers of soft marine clay present. The ground is like toothpaste."
This soft terrain is partly why capital costs have ballooned some 70 per cent from initial estimates to $4.3 billion today, with about 10 per cent of the new expressway completed.
Until plans for the 21km North-South Expressway (NSE) were announced on Wednesday, the MCE was Singapore's most expensive road (the NSE is estimated to cost between $7 billion and $8 billion). And no wonder, with engineers having to grapple with not only the challenge of excavating in old reclaimed land, but also reclaiming - and building on - new land from the sea, as well as digging a 420m stretch of tunnel under the very seabed, in a first for Singapore.
In 2007, it was estimated the MCE would cost $2.5 billion to build. "The contract sum to date is about $4.3 billion," Mr Chuah revealed to Weekend Today - another slight increase from the $4.1 billion reported when work on the MCE began in April 2009. He attributed the cost hike to construction prices and the "very challenging ground conditions".
It has had some wondering if the new expressway is worth its price tag. Based on benefit-cost ratio calculations, Mr Chuah said, the tangible benefits of the MCE - such as the reduced travelling time for highway users - outweigh the construction costs by more than a factor of one.
For one, the MCE will optimise the potential of the Marina Bay area, serving as a vital link from the new financial centre, integrated resort and other developments to the rest of the island. Slated for completion by the end of 2013, it will link the East Coast Parkway and Kallang-Paya Lebar Expressway in the east, to the Ayer Rajah Expressway in the west.
And while they could have built a viaduct for less than the cost of a tunnel, a viaduct - a long elevated roadway - would prevent the land from being fully utilised. "If you build underground, you can use the land on top for other purposes," added Mr Chuah.
As for whether it'll be a smoother drive, motorists might like to know that "about 10 (ERP) gantries" are being built in anticipation, but "will only be activated when needed", when traffic flow is less than optimal.
MOSTLY MADE UP OF TUNNELS
Tunnels make up 3.6km of the 5km length of the MCE. At one stretch, a tunnel lies about 12m above an MRT tunnel, said Mr Chuah.
Professor Yong Kwet Yew, an LTA adviser and civil engineering academic at the National University of Singapore, said the soft clay on which the MCE stands is "like peanut butter" and that it was "certainly one of the most challenging projects in the world".
Excavation can take place at a depth of 25m, the equivalent of eight storeys. The soft clay can extend downwards more than twice that - up to 59m. By comparison, in constructing the KPE, the depth of the soft clays averaged only 20m.
To improve the ground, cement grout is injected to stiffen the clay, a process that is "about 90-per-cent completed" said Mr Chuah. Temporary walls are erected to support the large tunnel excavations, with massive pipe piles driven as deep as 85m (over 25 storeys) underground. Such safety measures are what have pushed costs up, said Mr Chuah.
Prof Yong, who chaired an investigation panel on the collapse of the Nicoll Highway, said that following the 2004 disaster, the designs of temporary safety structures must have the same "factor of safety" as permanent structures.
In addition new land, about 12 football fields' worth, is being reclaimed from the sea in the Marina Wharf area. The process involves filling the sea bed with sand and earth that compresses the soft material - like "squeezing water out", Mr Chuah said.
It takes "decades" for reclaimed land to fully settle, at a rate of 50mm or 100mm a year; even the land on which ECP is built is "still settling today", he noted, stressing that this was of no danger to the public.
Nor does reclaimed land have to lie fallow for a time before being put to use, said Mr Chuah and Prof Yong. With the MCE, said Mr Chuah: "We can't wait for the land to compress. So we do the section of the road here on piles." This foundation of piles ensures the road does not shift even when the ground does.
What about tremors from quakes in neighbouring countries, such as those felt here in recent years? These "have not affected the MCE in any way", said Mr Chuah, while Prof Yong said they would "not be a problem even when the whole structure is finished".
The challenge of digging under the sea
by Venessa Lee
First, they tunnelled under a river to build the Kallang-Paya Lebar Expressway. Now, Singapore's road engineers are digging away at a more formidable challenge: Building a tunnel under the sea.
The experience of building part of the KPE under the Geylang River has proved helpful to the work on the Marina Coastal Expressway, which in one section runs below the sea-bed parallel to Marina Barrage.
"It's an extension of our existing technology ... (In terms of scope) when we crossed the Geylang River, it was 120m wide. Now, we are crossing a distance 420m wide," said MCE director Chuah Han Leong.
Building out in the open sea, as opposed to the sheltered waters of a river, is naturally tougher. "Then we have to cater for the effects of the barrage," said Mr Chuah. The double-piled temporary walls have to be impermeable and strong enough to withstand the barrage's maximum discharge of "more than 50 Olympic-sized swimming pools every minute". To prevent the sea bed from being eroded, rock-filled wire-mesh cages were placed on the sea bottom.
Once in operation, emergency and evacuation plans for the tunnel will be similar to those for the KPE, said Mr Chuah. Escape staircases leading up the ground are placed at 500m-intervals. Cross-passage doors will allow evacuation from one bound of the tunnel to the other. "There are also incident detection cameras and electronic signs in the tunnel to help to manage incidents." Venessa Lee
Vision of a tunnel
- The MCE's 420m undersea tunnel lies about 130m from the Marina Barrage.
- It is being built in two parts. Stage 1 on the Marina East side will be completed in the middle of this year.
- In stage 2, water will be diverted to flow above the completed section, which will be sealed off, then work will begin on the tunnel on the western side.
The fate of the ECP ... and the Benjamin Sheares Bridge
The East Coast Parkway has long been the fast route to town and westward for residents in the east.
But when the Marina Coastal Expressway opens, part of the ECP - including the Benjamin Sheares Bridge with its sweeping views over the bay - will be downgraded from an expressway to an arterial road.
The result: The land adjoining the ECP can be put to optimal use. As an arterial road, traffic junctions can be put in; roads can be reconfigured in a more rectangular grid, "in such a way whereby you optimise the land parcellation", said Mr Chuah Han Leong.
"Currently the land parcels are all sort of cut off by the ECP ... that's the strategic value of the MCE. It allows you to redevelop that land."
As to speculation that the iconic bridge, which opened in 1981, could be torn down, Mr Chuah emphatically said there "will be no change".
