SINGAPORE — One of Singapore’s biggest transport projects has run into something engineers could not fully see from the surface: unexpectedly hard rock, huge underground boulders and water seeping through the ground — in some places just metres from operating MRT infrastructure.
The Land Transport Authority (LTA) has revealed that construction of the 21.5km North-South Corridor is facing complicated underground conditions in several sections, particularly around Novena and Thomson, forcing engineers to modify excavation methods and slowing some stages of work.
But despite the setbacks, authorities have stopped short of announcing another delay to the multibillion-dollar infrastructure project.
Asked whether the latest engineering problems could affect the corridor’s opening schedule, LTA said it was monitoring progress and would provide an update on the completion timeline in due course.
That answer puts renewed attention on a project already stretching across more than a decade of planning, construction, diversions and disruption.
What engineers found beneath Novena
The challenge is particularly delicate in Novena.
Engineers working on the NSC road tunnel expected relatively uniform and softer clay in parts of the area. Instead, excavation uncovered a more complex mixture that included hard rock formations.
The location makes those conditions even more difficult.
A section of the NSC tunnel is being built around the existing North-South MRT Line, which must remain operational while construction continues. The southbound road tunnel above the railway has already been completed, but work on the northbound tunnel beneath the MRT line has encountered harder mixed rock and underground water seepage.
Water seepage is especially important to control because it can affect soil stability and increase the risk of ground movement during excavation.
And there is very little room for error.
According to LTA, active rail infrastructure is only about 1 metre above part of the excavation area.
That proximity forced engineers to rethink how they dig.
Instead of digging the whole tunnel, crews are taking it piece by piece
Rather than excavating across the entire width of the tunnel at once, crews are now opening smaller sections progressively.
Each section is excavated, monitored and stabilised before workers move to the adjoining area.
The new approach is slower but gives engineers tighter control over movement in the surrounding ground — an important safeguard with operating train infrastructure so close by.
Each excavation step now advances the tunnel by about 2m, compared with roughly 3.3m achieved while constructing the southbound tunnel using a different technique known as box jacking.
Box jacking involves using powerful hydraulic systems to push a prefabricated rectangular tunnel structure through the ground.
The change illustrates why major underground projects in densely developed cities can encounter problems that cannot always be completely mapped before construction begins.
LTA said earlier site investigations were limited in some locations because engineers had to work around live roads, extensive utility networks and existing MRT infrastructure.
Thomson produced another surprise underground
The geology caused a different headache farther north around Thomson.
There, crews found that hard rock was located about 10m closer to the surface than engineers had anticipated.
Large boulders also had to be removed before reinforced-concrete wall panels forming part of the tunnel structure could be installed.
That has dramatically changed how long some jobs take.
A wall-panel installation that would typically require around a week can take more than four weeks under the more difficult conditions.
The obstacles are consistent with the unusually varied geology engineers have long known lies beneath the NSC route.
Engineering consultancy Mott MacDonald, which has worked on several major civil contracts for the corridor, previously described the project as particularly challenging because its route passes through everything from very soft marine clay to extremely hard granite — while simultaneously navigating MRT lines, utilities and dense urban development.
The problems are not confined to underground tunnels
At the northern end of the project, where much of the NSC runs on elevated viaducts, construction teams have also faced complicated utility diversions involving water, gas and telecommunications infrastructure, particularly around Gambas Avenue and Woodlands Avenue 8.
Some areas also contained harder and higher rock formations than anticipated.
That slowed foundation work, which in turn affected the construction of columns and viaduct segments that depend on those foundations being completed first.
There has nevertheless been significant progress.
LTA deputy group director for the North-South Corridor Ang Pui Boon said more than 90 per cent of foundation work for the northern viaduct has been completed.
The focus is increasingly shifting to installing viaduct segments over major junctions and MRT infrastructure.
Those operations often have to take place during narrow four- to five-hour overnight windows to minimise disruption to motorists, bus passengers and train operations.
Years of construction have already tested residents and businesses
The engineering challenge is only one side of the story.
For communities along the route, construction has meant years of road diversions, dust, noise, altered pedestrian routes and changing bus access.
A CNA report in June found residents and businesses in areas including Novena, Woodlands and Yishun describing prolonged disruption from the works. Some businesses around Thomson Road said construction barriers had affected visibility and customer traffic, while residents complained of vibration, noise and constantly changing routes.
LTA told CNA that it has used measures including noise barriers, enclosed work areas, machinery mufflers and dust controls, and expects noise to decline as heavy foundation works wind down and more activity moves underground.
Current LTA road notices show that construction is still affecting traffic across multiple parts of the alignment, including long-running closures and diversions around Gambas Avenue, Marymount Road and Thomson Road.
Why Singapore is building the corridor in the first place
The North-South Corridor is far more than another expressway.
Originally conceived as the North-South Expressway, it was redesigned in 2016 as Singapore’s first major integrated transport corridor intended to combine road capacity with public transport, cycling and pedestrian infrastructure.
The 21.5km route stretches between Singapore’s northern region and the city and serves areas including Sembawang, Yishun, Ang Mo Kio, Toa Payoh, Novena and Rochor.
It includes an approximately 8.8km viaduct and a 12.3km underground tunnel.
Once vehicles are moved onto the viaduct and tunnel, LTA plans to repurpose sections of the existing surface roads for wider pedestrian paths, cycling routes, bus priority measures, greenery and community spaces. The Ministry of Transport estimates that road space equivalent to roughly 30 football fields could ultimately be freed for those uses.
LTA has also said bus commuters travelling from the north toward the city could eventually save up to 15 minutes with the corridor and its bus-priority measures.
So, is the North-South Corridor still opening on time?
For now, the official timetable has not formally changed.
LTA’s current project page says the NSC is scheduled to open in phases.
The elevated viaduct between Admiralty Road West and Lentor Avenue is targeted for 2027, while the remaining tunnel section between Lentor Avenue and the East Coast Parkway is targeted for 2029.
Those dates already reflect an earlier delay.
The project was once expected to be completed earlier, but COVID-19 disruptions pushed construction back by more than a year. The Ministry of Transport subsequently adopted the phased 2027-to-2029 opening schedule.
What the latest disclosures change is the level of uncertainty surrounding the remaining construction.
Unexpected geology does not automatically mean the 2029 deadline will slip. Large infrastructure projects routinely adapt their engineering methods as excavation reveals conditions that boreholes and preliminary surveys cannot completely capture.
But LTA’s decision not to reaffirm the final completion date when specifically asked about the new challenges is significant.
The authority says it is monitoring progress.
Until it provides its next timeline update, the rocks and water beneath Novena and Thomson have turned what looked like an engineering problem into something thousands of Singapore commuters, residents and businesses will now be watching closely: whether Singapore’s longest transport corridor can still reach the finish line on schedule.
Leave a Reply