North-South Corridor enters 'most technically demanding' phase with tunnelling 1m beneath MRT line
Construction of Singapore's North-South Corridor has entered its most technically demanding phase, with tunnelling taking place as close as 1m beneath the operational North-South Line at Novena. The Land Transport Authority said ground conditions have been more challenging than expected, requiring a
SINGAPORE – Construction of the North-South Corridor (NSC) is entering its “most technically demanding” phase, as engineers contend with hard rock formations, tunnelling just a metre above an operational MRT line and the assembly of Singapore’s longest viaduct, the Land Transport Authority (LTA) said on Saturday (Sep 12).
Spanning more than 20km, the multi-modal corridor is designed to improve connectivity between the northern region and the city, serving towns such as Sembawang, Yishun, Ang Mo Kio, Toa Payoh, Novena and Rochor. The project comprises an 8.8km elevated viaduct and a 12.3km underground tunnel section. Construction has been ongoing since 2018 and will be completed in phases, with the viaduct section expected to open from 2027.
At Novena, the corridor’s tunnel passes both above and below the North-South Line, with clearance as close as 1m. The southbound tunnel crossing above the line has been completed using the tunnel box pushing method, but as excavation progressed on the northbound tunnel below the line, fractured rock and groundwater inflows were encountered. LTA said these ground conditions could not be fully identified in advance. A more controlled mining method is now being used, with the tunnel excavated in smaller, separately supported sections alongside additional rock removal, grouting and monitoring.
At Nicoll Highway, the NSC tunnel has to pass over existing Circle Line tunnels, with clearances of only about 1.5m to 2.5m. Given the proximity and the presence of soft reclaimed ground, LTA is using specialised pipe roofing and ground improvement measures. In the Thomson area, hard rock formations and large boulders encountered during excavation have required extensive controlled rock blasting and changes to the design of earth-retaining systems.
The 8.8km viaduct, about 40m wide and roughly 19m tall, will be Singapore’s longest. More than 6,000 precast elements have to be fabricated, transported and installed, with major segment installation carried out mainly during four- to five-hour off-peak windows at night. Foundation works at some locations, including Gambas Avenue and Woodlands Avenue 8, have taken longer than anticipated due to utility diversions and adverse ground conditions. With more than 90 per cent of foundation works completed, construction is moving into launching large viaduct segments across existing roads and above an operational MRT line.
LTA said the impact on residents is expected to ease as construction progresses, with heavy foundation works completed and most upcoming works carried out underground beneath live traffic, cutting noise and the need for multiple traffic diversions. The authority said it will update on the project’s completion timeline in due course and continues to engage business owners affected by hoardings and noise barriers, including in areas such as Novena.
