LTA begins wtrengthening of circle line tunnels to counter ground deformation

Singapore’s Land Transport Authority (LTA) has initiated a targeted strengthening programme for two Circle Line tunnels where progressive ground deformation, known as tunnel squatting, has been identified. The phenomenon is linked to underlying marine clay and can affect long-term tunnel performance if left unmanaged. Decade-long monitoring enabled LTA to pinpoint three localised sectors between Stadium and Paya Lebar stations that require intervention.

Construction of the Circle Line began in 2002 and progressed through phased openings from 2009. Its delivery demanded extensive technical effort to manage difficult ground conditions across the alignment. Specialised methods were required near Promenade and Nicoll Highway stations, where variable soils introduced stability concerns, and blasting was needed near Mountbatten to remove deep reinforced concrete and steel piles. Tunnelling was also executed through complex underground corridors containing existing MRT tunnels, sewerage systems and utility networks, which required precise control and, at times, manual excavation to safeguard adjacent infrastructure.

The current programme involves sequentially closing each affected tunnel section to install steel plates along the interior circumference. Assessments confirm that train operations can continue safely while works progress across the combined 450 metres of tunnel. LTA has drawn on international benchmarking from cities such as Shanghai, Taipei, Busan, Barcelona and Lisbon to refine the strengthening methodology. Service adjustments will occur during engineering hours, and commuters are encouraged to plan additional time during peak periods.