Sinkholes are part of rapid urbanisation: Experts

They urge more preventive steps; LTA says roads checked regularly
Daryl Chin Straits Times 19 Mar 13;

ROADS in Singapore are checked for potholes, cracks or other physical defects regularly, said the Land Transport Authority (LTA) yesterday.

Highways and major roads, for instance, are inspected every two weeks, and smaller roads every eight weeks. Inspections are also carried out immediately when members of the public call in, added a spokesman.

It was explaining its procedures for road maintenance, following queries from The Straits Times on the sinkholes that have appeared in recent months.

Experts say that sinkholes are part and parcel of the rapid urbanisation that Singapore is undergoing, and existing measures could be tightened to prevent any incidents.

There have been four cave-ins in three areas so far this year.

Two of them - one in Woodlands Road last Saturday, and one in Keppel Road in January - were caused by burst water pipes, the authorities said.

A sinkhole also appeared in Clementi earlier this month. Four days after it was filled in, the road gave way again. The LTA is still investigating this.

The lane-wide depression in Woodlands appeared next to a construction site for the MRT's Downtown Line 2. Experts say sinkholes are caused by several factors, including water pipe leakages, excavation works and rainwater, which may erode the sand and silt underground.

When the soil matter directly beneath the roads trickles to deeper cavities and the surface collapses, a sinkhole forms.

It does not help that Singapore has a complex network of utility lines such as power cables, water pipes and sewage lines running underground at depths of 3m to 6m.

"Older infrastructure works may not be exact to what's on a map, and contractors sometimes have to pin down exactly where these lines run, and isolate or divert them properly," said Associate Professor Leong Eng Choon from the Nanyang Technological University's School of Civil and Environmental Engineering.

Working on water pipes can be tricky as they are held together by joints, which may leak when moved even slightly.

Singapore's highly built-up environment also makes erosion, which happens gradually underground, harder to detect until the sinkhole appears.

The train network is set to double over the next 17 years, with two new lines and three extensions. On its part, the LTA said it conducts engineering assessments, which check the geological properties on the ground and can take several years, before the start of any road or rail construction.

It also looks out for any unexpected ground movements around the project when works are carried out.

Mr Chong Kee Sen, vice-president of the Institution of Engineers Singapore, said the current framework is already comprehensive. "Whatever regime you put in, such incidents are bound to happen. The key issue lies in how fast we deal with it," he said.

But Prof Leong said there is always room for more stringent site investigations before and during works.

Motorists, too, have become more aware.

Flight steward James Chua, 31, said he has been paying more attention to the roads.

He said that with construction works taking place everywhere, drivers not only need to keep an eye out for other vehicles, but also check whether the road itself is sound.