Mr Cai Yinzhou asked the Acting Minister for Transport (a) what proportion of Singapore's rail network is built on marine clay; (b) what long-term measures are in place to manage "tunnel squatting" across the rail network; (c) what other portions of rail network are scheduled for maintenance related to ground settlement; and (d) how advanced geotechnical monitoring is integrated into rail maintenance regimes to ensure structural integrity and minimise service disruptions.

Mr Jeffrey Siow: Around 10% of our underground rail tunnels run through marine clay.

Rail tunnels are regularly inspected for defects including for tunnel squatting. Tunnel segments that are more likely to be affected are subject to enhanced monitoring, including the use of advanced instruments, laser profilers and high-definition image scanners.

The current works are focused on the tunnels between Paya Lebar and Mountbatten stations. Should further works be needed on other parts of the network, the public will be informed early. 

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