Tunnelling Works that Led to Cave-in at Bukit Brown Tomb

Assoc Prof Daniel Goh Pei Siong asked the Minister for Transport with regard to the ground cave-in at a historic tomb within Greater Bukit Brown (a) whether the contractor had knowledge of ground conditions and exercised adequate supervision of tunnelling operations; and (b) how does LTA ensure that machine operators are adequately trained and experienced to handle tunnelling in historic, ecologically-sensitive and built-up areas.

Mr Khaw Boon Wan: The localised depression was caused by a combination of mixed ground conditions and poor judgment on the part of the machine operator. The correct protocol, which the operator failed to follow, is to stop tunnelling and consult the on-site Tunnel Manager or Senior Tunnel Engineer. The errant operator has been replaced.

Tunnel boring requires specialist skills. LTA only appoints machine operators with at least five years of experience. LTA also requires the contractor to conduct soil investigation before tunnelling to understand the ground conditions. Thus, depressions of such scale and magnitude are rare. Nevertheless, LTA will be enforcing even stricter controls and supervision going forward.