Singapore’s massive North-South Corridor project is facing a series of unexpected underground obstacles, with engineers encountering harder rock, large boulders and groundwater seepage that have complicated construction in several key areas.
The Land Transport Authority (LTA) said the challenges were discovered as excavation progressed, particularly around Novena and Thomson. Earlier ground investigations were limited by live traffic, existing utility networks and operating MRT infrastructure, making it difficult to fully determine underground conditions before construction began.
In Novena, workers found a mixture of hard rock and softer material where more uniform clay had been expected. The northbound tunnel has proved particularly challenging because it is being built beneath the operational North-South MRT Line, with the tracks only about 1m above the excavation area.
Groundwater seepage has added another complication because it can weaken the excavation area. To reduce the risk of ground movement and protect the MRT tracks, engineers changed their approach and are now excavating the tunnel in smaller sections rather than digging across its full width at once.
Each section currently advances by about 2m, compared with roughly 3.3m achieved when the southbound tunnel was constructed using a box-jacking technique.
Thomson has presented a different problem. Hard rock was found around 10m closer to the surface than anticipated, while large boulders had to be removed before reinforced concrete wall panels could be installed. Work that normally takes about a week can now take more than four weeks in some areas.
Further north, construction of the NSC viaduct has also been affected by complicated utility diversions involving gas, water and telecommunications lines around Gambas Avenue and Woodlands Avenue 8. In some locations, rock was found to be higher and harder than expected, delaying foundation work and consequently the installation of columns and viaduct segments.
Despite these difficulties, LTA said more than 90 per cent of the northern viaduct’s foundation works have been completed. The remaining major works include installing viaduct sections above MRT tracks and major road junctions, with some operations restricted to four- to five-hour overnight windows to minimise disruption.
LTA has not confirmed that the newly discovered conditions will push the project’s completion date further. The authority said it is monitoring construction progress and will provide an update on the timeline when appropriate.
The 21.5km North-South Corridor is one of Singapore’s largest transport infrastructure projects. It comprises an 8.8km viaduct, about 400m of ground-level roads and a 12.3km underground road tunnel, connecting the northern part of Singapore to the East Coast Parkway.
The corridor was originally expected to be completed in 2027, but Covid-19-related disruptions pushed completion to 2029. LTA currently plans to open the northern viaduct between Admiralty Road West and Lentor Avenue in 2027, followed by the tunnel section from Lentor Avenue to the East Coast Parkway in 2029.
Once completed, the project is expected to improve north-south connectivity while freeing up existing surface roads for wider pedestrian and cycling paths, bus-priority measures and community spaces.
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