ROAD CAVE-INS FROM MRT TUNNELLING WORKS

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ROAD CAVE-INS FROM MRT TUNNELLING WORKS: * * *

53.

Mr Cedric Foo Chee Keng asked the Minister for Transport if he will provide the number of road cave-in incidents from MRT tunnelling works since 2005; and (b) whether a safety review has been conducted to prevent future cave-in incidents.

Mr Raymond Lim Siang Keat: Since 2005, there have been four incidents of road subsidence from MRT tunnelling works. Other than the Cornwall Gardens incident in May 2008, there were two other incidents at North Buona Vista Road and Telok Blangah Road. In all four cases, LTA took swift recovery actions within a day.

I would like to reassure Members that LTA has instituted a strict regime of safety processes for all their projects, including those which involve tunnelling works. Before any

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physical work is started, LTA's engineers would carry out an extensive investigation into the nature and composition of the soil, search building records for details of the safety condition of nearby buildings, and inspect ground conditions and buildings in the area. During construction, LTA installs and monitors a range of instruments to detect any early signs of soil movement or possible damage to nearby structures. If necessary, they will carry out soil conditioning work to strengthen the ground. A Tunnel Task Force Committee, comprising senior LTA officials, tunnel specialists from the construction industry and geotechnical engineering consultants, oversee and review all of LTA's tunnelling operations to ensure safety. In addition, LTA regularly consults an International Board of Advisors (IBA), made up of world-renowned engineers and academics, to review the technical aspects of the tunnelling with particular emphasis on safety.

Going forward and as a precautionary measure, LTA has undertaken a comprehensive safety review and tightened its tunnelling specifications, which are technical requirements imposed on all tunnelling works. For example, the revised specifications require soil investigation holes along the tunnel route to be drilled more frequently, every 25 metres compared to the earlier requirement of 50-75 metres. It has also added more early warning devices to detect any abnormal movement of soil. In addition, LTA has added technical refinements to the tunnel boring machines, to improve ground stability during tunnelling. These improvement measures, which are part of LTA's continuous efforts to improve safety practices, reduce the risk of encountering unexpected soil conditions and road subsidence from tunnelling.