Cause and Actions Taken for Sinkhole Formation at Tanjong Katong Road South in July 2025

Mr Gerald Giam Yean Song asked 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.

Ms Gho Sze Kee asked 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.

The Building and Construction Authority (BCA) is conducting an independent investigation under the Building Control Act. The Ministry of Sustainability and the Environment (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.

Since 2024, the Public Utility Board's (PUB) 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 5.50 pm, 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, 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 reopened from 2 August 2025.

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.