Tanjong Katong sinkhole: PUB calls for safety time-out to review similar sewer works across Singapore

PUB said they will be calling for a safety time-out to review and assess sewer construction works similar to the Tanjong Katong incident on Saturday (July 26). 

A sewage shaft failure was identified as the cause for the sinkhole which formed at Tanjong Katong Road South and swallowed a black car that day, said the agency in a statement issued on July 27 night. 

The car's driver, who managed to exit the vehicle on her own, was then rescued by workers at the site and later taken to hospital by the Singapore Civil Defence Force.

According to the national water agency, a caisson ring at a PUB worksite at Tanjong Katong — where a 16-metre deep shaft was being built to connect three existing sewer lines — was observed to have failed at about 5.50pm on July 26. 

A sinkhole formed on the adjacent road at around the same time. It is still not clear what contributed to this failure, the agency added.

A caisson ring refers to a large, watertight cylinder that is sunk into the ground and filled with concrete as a foundation for other structures.

The shaft has been backfilled to stabilise its surrounding ground and a ground-penetrating radar (GPR) scan and analysis is being carried out to assess the surrounding area, PUB said.

Surrounding structures unaffected: BCA

Engineers from the Building and Construction Authority (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, it added.

PUB began pumping water out of the sinkhole from 9.45am on July 27 and this was completed by 1.20pm. The car that had fallen into the sinkhole was retrieved at 2pm.

The sinkhole has been filled with liquefied stabilised soil to further stabilise the area, after which road reinstatement works will commence, said PUB.

The portion of Tanjong Katong Road South between Mountbatten Road and East Coast Parkway will remain closed to facilitate ongoing repair works, the agency stated, advising motorists and commuters to plan their routes in advance and expect possible delays during the weekday peak periods.

"We seek the public's understanding and apologise for the inconvenience caused. Further updates will be provided on the progress of works and when the affected road can be reopened," said PUB.

Road to be repaved after testing: Goh Pei Ming

MP for Marine Parade GRC Goh Pei Ming said in a Facebook post on Monday that the Land Transport Authority (LTA) will carry out tests to ensure there are no air pockets in the soil before repaving the road.

He explained that the backfilling of the cavity has been completed, and the teams are currently compacting the ground further.

"Besides additional radar scans, the tests will include a series of drilling probes up to 20m deep. This testing and analysis work will take some time," Goh said.

"I understand residents are keen to know when the road can be reopened. I think it is best we give the agencies the time to be doubly sure the road is safe before we reopen."

He added that he's glad to see the agencies coming together and working closely to restore normalcy safely and expediently. 

"To our residents, thank you for your patience and understanding," he said.

Goh also said that when he returned to the site on Monday morning to check on the traffic situation — especially as parents send their children to the nearby schools and residents head to work — traffic was smooth aside from some localised traffic buildup along Mountbatten Road.

"Good that LTA deployed a number of Vehicular Messaging Systems, and worked with MOE to notify parents early on the traffic diversions. Many parents also left home earlier to cater more time to send their children," said Goh.

Water supply disruption

At about 6pm on July 26, some 18 households experienced a disruption to their water supply. 

Preliminary findings suggest that the water mains may have been damaged as a result of ground movement associated with the sinkhole. The affected pipes were isolated, and water supply was fully restored by 2:30am on Monday, said PUB.

PUB added that the damaged water pipes had led to water filling up the sinkhole. Videos of the incident showed water gushing and completely submerging the car which had fallen in.

This stopped once the water mains were shut off, said PUB.

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bhavya.rawat@asiaone.com