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Tanjong Katong sinkhole located next to 16m-deep shaft at PUB worksite

The sinkhole on Tanjong Katong Road South on Saturday (26 July) developed at the same time that a structure “failed” in an adjacent shaft, national water agency PUB has revealed.

As a result, it has called a safety time-out on similar sewer construction works across Singapore.

Source: Goh Pei Ming 吴培铭 on Facebook

Shaft at adjacent PUB worksite to connect 3 sewer lines

In a Facebook post late on Sunday (27 July) night, PUB said the sinkhole is adjacent to an active PUB construction site.

Sewer-laying works are ongoing at the worksite.

The works involve the construction of a 16m-deep shaft to connect three existing sewer lines.

Tanjong Katong sinkhole formed at the same time as caisson ring failure: PUB

At about 5.50pm on Saturday, a caisson ring in the shaft “was observed to have failed”, PUB said, adding:

It is still not clear what contributed to this failure.

A caisson ring is a structure meant to be watertight, used during wet ground conditions to keep the excavation area dry.

At “around the same time”, the sinkhole formed, swallowing a passing car, PUB added.

Source: SGRoad Blocks / Traffic News on Telegram

Sinkhole filled with water as 2 water mains were damaged

The sinkhole quickly filled with water, partly due to the damage caused to two water mains in the incident.

Photos showed water spraying out from the sinkhole.

Source: SGRoad Blocks / Traffic News on Telegram

After the mains were shut off, the water stopped, PUB said.

Tanjong Katong sinkhole caused 8.5-hour water supply disruption: PUB

As a result of the sinkhole, water supply in the neighbourhood was disrupted for about 8.5 hours.

It started at about 6pm, with 18 households affected, PUB said, adding:

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

PUB isolated the affected water mains and water supply was fully restored by 2.30am.

Water pumped out of sinkhole, car lifted out

From 9.45am on Sunday, PUB began pumping water out of the sinkhole, finishing the job by 1.20pm.

The car was then lifted out from the sinkhole at 2pm, PUB said.

The sinkhole has been filled with liquefied stabilised soil. Once the area is stabilised, road reinstatement works will commence.

Source: Goh Pei Ming 吴培铭 on Facebook

Additionally, a ground-penetrating radar scan was carried out to assess the surrounding area. Its results are still being analysed.

PUB calls safety time-out

As a precaution, PUB will call a safety time-out across all similar sewer construction works in Singapore.

This will enable the safety of these works to be reviewed, it said.

PUB is working closely with the Land Transport Authority and Building and Construction Authority (BCA) on both repair works and investigating the cause of the sinkhole.

Water pipe burst the night before sinkhole: Residents

Some residents had told the media that a water pipe had burst in the area after midnight on Saturday, more than half a day before the sinkhole developed.

A netizen who posted a comment on Minister for Sustainability and the Environment Grace Fu’s Facebook post said she took a video of a large plume of water gushing out from the road at 1.30am.

Source: Christine Mei Yee on Facebook

A family told Channel NewsAsia that they were awoken after midnight by the sound of water spraying out from a work site at the junction of Mountbatten Road and Jalan Seaview, which is across the road from the site of the sinkhole.

A resident of One Amber condo said she saw what appeared to be a “huge fountain” of at least one storey high at about 1am near the junction.

Video clips posted by SG Road Vigilante on Facebook showed the road flooded due to the water.

Source: SG Road Vigilante on Facebook

Another depicted a rubbish bin floating on the deep waters.

Source: SG Road Vigilante on Facebook

BCA engineers have confirmed that nearby structures, including One Amber and the landed homes, are not affected by the incident, PUB maintained.

Also read: Migrant workers rescue woman from Tanjong Katong sinkhole, receive widespread praise

Migrant workers rescue woman from Tanjong Katong sinkhole, receive widespread praise

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Featured image adapted from SGRoad Blocks / Traffic News on Telegram and Goh Pei Ming 吴培铭 on Facebook.