PUB to call for 'safety time-out' to review safety of similar sewer construction works across S'pore after Tanjong Katong sinkhole incident

A gaping sinkhole opened up on Tanjong Katong Road South on the evening of Jul. 26, leading to a car plunging in and multiple lanes being cordoned off for more than a day.

Following the incident, national water agency PUB gave an update to the media on the recovery works on Jul. 27 at 10:10pm.

They said that they are working closely with the Building and Construction Authority (BCA) and Land Transport Authority (LTA) to oversee the repair efforts and to investigate what contributed to the sinkhole incident.

To ensure public safety, PUB said they have also worked closely with LTA and the Singapore Police Force (SPF) to cordon off the affected area and restrict access to traffic and pedestrians.

Caisson ring in shaft failed at PUB construction site around the same time the sinkhole formed

PUB shared that sewer-laying works are ongoing at the PUB construction site adjacent to the site of the sinkhole.

The works at the site involve the construction of a 16m deep shaft to connect three existing sewer lines, they said.

At around 5:50pm on Jul. 26, around the same time when the sinkhole was formed, a caisson ring in the shaft under construction at the PUB worksite was observed to have failed.

It is still not clear what contributed to this failure, PUB said.

The shaft has since been backfilled to stabilise the surrounding ground.

A ground-penetrating radar (GPR) scan was also carried out to assess the surrounding area and results of the scan are still being analysed.

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, PUB added.

Safety time-out for similar sewer construction works

Following the formation of the sinkhole, a disruption to water supply occured at around 6pm, affecting 18 households.

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

The damage to the water pipes had contributed to the filling of water in the sinkhole.

Water stopped filling the sinkhole once the mains were shut off, PUB added.

PUB began pumping water out of the sinkhole at 9:45am on Jul. 27, completing the process by 1:20pm.

The vehicle that had fallen into the sinkhole was retrieved at around 2:00pm.

To stabilise the area, the sinkhole was filled with liquefied stabilised soil (LSS), after which road reinstatement works will begin, PUB said.

As a precautionary measure, PUB said they will be calling for a safety time-out to review and ensure the safety of similar sewer construction works across Singapore.

Road to remain closed

To facilitate ongoing repair works, Tanjong Katong Road South between Mountbatten Road and East Coast Parkway will remain closed, PUB said.

Motorists and commuters are advised 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," they said.

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Top photos by Aiman Nadzri/Mothership