SINGAPORE – Construction of the North-South Corridor (NSC) has hit unexpected ground conditions at Novena and Thomson, complicating works as the project enters its most complex engineering phase, the Land Transport Authority said.

In Novena, tunnelling crews encountered a mix of materials, including hard rocks, rather than the more uniform and softer clay material previously anticipated. This caused a change in construction method.

In the Thomson area, the hard rock layer was closer to the surface than expected and large boulders were also found. This slowed progress because more work was needed.

At a media briefing on Sept 8, LTA said that such conditions were fully detected only during excavation. Earlier investigations had been constrained by live traffic, utility networks and existing MRT infrastructure.

Ground conditions are among the challenges adding to the complexity of construction, which is being carried out close to operational rail lines, major roads, utility lines and densely built-up areas.

Asked if these engineering challenges would delay the completion of the corridor, a spokesperson said LTA is monitoring the progress of the works and will give an update on the completion timeline in due course.

LTA had previously announced that the NSC would be ready in phases from 2027, with the northern viaduct from Admiralty West to Lentor Avenue and the road tunnel from Lentor Avenue to East Coast Parkway to be ready in 2029.

During the media briefing, LTA detailed the challenges encountered in Novena, where the road tunnel is being built directly above and below the operational North-South MRT line.