Tanjong Katong sinkhole: PUB to call for safety time-out to review sewer works similar to incident site

SINGAPORE: The site where a sinkhole appeared in Tanjong Katong on Saturday (Jul 26) is adjacent to an active PUB worksite involving the construction of a 16m-deep shaft connecting three existing sewer lines, the national water agency said on Sunday.

Providing a timeline of what happened, PUB said that a concrete component in the shaft failed at around 5.50pm on Saturday. 

At around the same time, a sinkhole formed on the adjacent road, causing a vehicle to fall in.

PUB said it was still not clear what contributed to the failure of the component, known as a caisson ring. A caisson, from the French word for "box", is a watertight retaining structure that allows water to be pumped out, keeping the work area dry.

"The shaft has been backfilled to stabilise the surrounding ground," said PUB.

As a precautionary measure, the agency will call for a time-out to review and ensure the safety of similar sewer construction works across Singapore.

PUB also said that the sinkhole has been filled with liquefied stabilised soil to further stabilise the area, after which works to reinstate the road will begin. 

Tanjong Katong Road South between Mountbatten Road and East Coast Parkway (ECP) will be closed until further notice for repairs, the Land Transport Authority (LTA) said on Sunday. 

Bus services 36 and 48 have been diverted.

The sinkhole is about 2m to 3m deep and as wide as two lanes of the road.

According to PUB, the driver who fell in managed to exit the vehicle on her own. She was rescued by workers within five minutes and taken conscious to Raffles Hospital. 

Water was later seen filling the sinkhole.

"The damage to the water pipes had contributed to the filling of water in the sinkhole. This ceased once the mains were shut off," PUB said.

The agency began pumping water out of the sinkhole from 9.45am on Sunday, and this was completed by 1.20pm.

The vehicle that had fallen into the sinkhole was retrieved at 2pm.

There were also water supply issues in the area after the sinkhole opened up, with 18 households affected from about 6pm on Saturday.

Preliminary findings suggest that the water mains may have been damaged as a result of ground movement associated with the sinkhole, said PUB.

The affected pipes were isolated and the water supply was fully restored by 2.30am on Sunday.

PUB said it is working closely with the Building and Construction Authority (BCA) and LTA to oversee the repair efforts and to investigate what contributed to the incident.

It said on Sunday night that it was analysing the results of a ground-penetrating radar scan that was carried out to assess the surrounding area.

In an update on Monday morning, PUB said the ground-penetrating radar scan and analysis were still ongoing.

"Engineers from BCA have checked and affirmed that nearby structures, including One Amber condominium and the landed homes across the road, are not affected by the incident," said PUB.

Motorists and commuters are advised to plan their routes in advance and expect possible delays during the weekday peak periods.