Written Reply to Parliamentary Questions on the Sinkhole Incident at Tanjong Katong Road South

Questions:

To ask the Minister for Sustainability and the Environment (a) what is the cause of the sinkhole in Tanjong Katong Road South on 26 July 2025; (b) whether any party has been penalised for its formation; (c) what are the lessons learnt; and (d) what is done to prevent a similar incident from happening again.

To ask the Minister for Sustainability and the Environment (a) what was the mode of structural failure of the caisson ring at the Tanjong Katong Road South sewer shaft site; (b) whether the failure was due to material, installation, or design deficiencies; (c) what structural integrity checks are mandated for such caisson rings; and (d) whether the failed caisson ring had passed all inspections.

To ask the Minister for Sustainability and the Environment (a) when will the independent panel’s findings on the sinkhole that appeared on Tanjong Katong Road South on 26 July 2025 be released; (b) who are the panel members; (c) whether any preliminary findings can be shared; and (d) what measures are in place to periodically check the structural integrity of nearby roads and buildings.

To ask the Minister for Sustainability and the Environment (a) whether an update can be provided on the cause of the sinkhole which occurred on the evening of 26 July 2025 along Tanjong Katong Road; and (b) what additional measures will be taken in future to prevent or minimise the occurrence of such sinkholes in the vicinity as well as on all our roads generally.

To ask the Minister for Sustainability and the Environment (a) when will the independent review of practices and safeguards pertaining to the sinkhole incident on 26 July 2025 at Tanjong Katong Road South be completed; (b) what is the frequency of sewer shaft inspections to ensure their continued structural integrity; and (c) whether any additional measures have been made by the Ministry to ensure workers’ safety at similar worksites.

To ask the Minister for Sustainability and the Environment what are the pre-emptive measures taken to ensure that PUB job sites will not be at risk of sinkhole formation.

Answer:

1 The Building and Construction Authority (BCA) is conducting an independent investigation under the Building Control Act. MSE has also convened an internal investigation to look into the cause of the incident and how we can prevent similar incidents from happening in the future. MSE’s internal investigation panel comprises four senior members from the MSE Family agencies with the requisite professional and technical expertise.

2 Since 2024, PUB’s contractor had been conducting sewer laying works beside Tanjong Katong Road South. The works involved the construction of a 16-metre-deep shaft, which is a temporary structure made up of multiple layers of reinforced concrete caisson rings. On 26 July 2025, at approximately 1750hrs, the contractor’s workers observed the failure of one of the caisson rings. This led to soil flowing into the bottom of the shaft. At around the same time, a sinkhole formed along a section of Tanjong Katong Road South which was adjacent to the worksite. Following the incident, to ensure public safety, PUB, in consultation with BCA and the Land Transport Authority (LTA), performed safety assessment checks on the roads around the sinkhole. No abnormalities were detected. The affected road sections along Tanjong Katong Road South were then progressively re-opened from 2 August.

3 At this time, investigations into the incident are still ongoing and it would be premature to draw any conclusions. Given the complexity involved, the investigations are expected to take several months.