Nothing stops. The city keeps going while you rebuild it.
Beneath the ordinary hum of Singapore's traffic, engineers spent years threading new infrastructure through a city that could not pause — boring tunnels under live viaducts, stacking passages vertically where no horizontal room remained. On July 12, three new Circle Line stations open, completing a loop that required not the suspension of urban life, but its careful accommodation. It is a quiet testament to the discipline of building in a world already fully occupied.
- A tunnel boring machine had to pass directly through the foundation piles of a live, traffic-bearing viaduct — with no option to close the road above.
- Engineers transferred the viaduct's entire structural load onto new micropiles using hydraulic jacks, then removed the original piles to clear the tunnel's path — a process that took eight months while vehicles passed overhead unknowing.
- At Prince Edward Road, proximity to high-rise foundations and the viaduct left no room for conventional parallel tunnels, forcing a vertical stacking solution with machines working within three meters of existing buildings.
- Underground road crossings were solved by installing a steel pipe roof to stabilize the ground, allowing smaller borers to excavate beneath open, undisturbed streets.
- When Prince Edward Road, Cantonment, and Keppel stations open July 12, 23 additional trains will progressively enter service, expanding both capacity and network resilience.
On the Keppel Viaduct, traffic moved as it always does — cars and trucks in the ordinary rhythm of the city. Beneath them, unseen, a tunnel boring machine was completing Singapore's Circle Line loop. The challenge was not merely geological but civic: nothing could stop, and yet everything had to move.
The most demanding problem lay between Cantonment and Keppel stations, where the tunnel's path ran directly through the foundation piles of two viaduct piers. Closing the road was not an option. Instead, engineers drilled new micropiles alongside the route and used hydraulic jacks to gradually shift the viaduct's load onto them. Once the original piles were relieved of weight, they were removed, and the boring machine passed through the space they had occupied. The operation took eight months in 2021. Drivers above never knew.
At Prince Edward Road, the constraints were spatial rather than structural. Hemmed in by high-rise offices and the viaduct itself, there was no room for the standard side-by-side tunnel configuration. Engineers stacked the tunnels vertically instead, with boring machines working within three meters of the nearest building's foundations. Connecting the platforms to street level meant crossing beneath busy roads — solved by first installing a protective roof of steel pipes underground, then excavating beneath it while the roads above remained open and undisturbed.
When the three stations open on July 12, the Kim Chuan Depot will expand alongside them, enabling 23 additional trains to enter service progressively. The completed loop is less a triumph over the city than a demonstration of how to build within it — working around what exists, disturbing as little as possible, and keeping everything moving throughout.
On the Keppel Viaduct, traffic moved as it always did—cars and trucks passing overhead in the ordinary rhythm of the city. Beneath them, in the dark, a tunnel boring machine was carving through the ground to complete Singapore's Circle Line loop. It was a feat of coordination that required stopping nothing while moving everything: the viaduct's weight, the tunnel's path, the city's flow.
Three new stations—Prince Edward Road, Cantonment, and Keppel—will open to the public on July 4 for preview, then enter full service on July 12. Their construction involved a series of engineering problems that had no simple answers, each one solved by rethinking how to work in a city where space is finite and nothing can truly stop.
The most visible challenge was the tunnel between Cantonment and Keppel. It had to pass directly through the pile foundations of two viaduct piers—the long columns drilled deep into the earth that hold the structure's weight. The Land Transport Authority could not close the viaduct. Traffic had to keep moving. So engineers drilled smaller micropiles alongside the planned tunnel route and used hydraulic jacks to gradually transfer the viaduct's load from the original piles to these new ones. Once the old piles were no longer bearing weight, they were disconnected. The tunnel boring machine then excavated through the space where they had been. The entire procedure took about eight months in 2021. Vehicles passed overhead throughout, unaware of the work below.
At Prince Edward Road station, the problem was different but equally constrained. The site sat close to high-rise office buildings and the Keppel Viaduct itself. There was no room to build the station in the conventional way—two parallel tunnels running side by side. Instead, engineers stacked the tunnels vertically, one above the other. The tunnel boring machines came within three meters of the nearest building's foundations, working in the narrow margin between what existed and what could not be disturbed.
Connecting the platforms to the station exits required tunnels to run beneath busy roads. Engineers could not simply excavate from above; that would mean closing streets, diverting traffic, moving utilities. Instead, they installed a protective roof made of heavy steel pipes underground to stabilize the ground above. Smaller boring machines then worked beneath this roof, excavating the passage while the road remained open and undisturbed. The Land Transport Authority noted that this approach avoided traffic disruption, kept underground utilities in place, and minimized disturbance to the surrounding area.
When the three stations open on July 12, the Kim Chuan Depot will also expand. The depot extension will allow the system to house and maintain more trains. Twenty-three additional trains will be rolled out progressively, giving the Circle Line the capacity to serve more passengers and providing the network with greater resilience.
The completion of the loop represents not just an addition to Singapore's transport system, but a demonstration of how to build in a place where every meter of space is claimed, where nothing can stop, and where engineering must work around the city rather than asking the city to work around it.
Notable Quotes
This avoided traffic disruption, diversion of underground utilities and minimised disturbance to stakeholders— Land Transport Authority, on the protective roof method used beneath roads
The Hearth Conversation Another angle on the story
How do you move a viaduct without closing it?
You don't move it. You move what's holding it up. They drilled new micropiles next to the old ones, used hydraulic jacks to shift the weight over, then removed the originals. The tunnel went through the space where the old piles had been.
That sounds incredibly precise. What happens if something goes wrong mid-transfer?
That's why it took eight months. They had to monitor constantly. But the real risk was never the transfer—it was the tunnel boring machine working three meters from a building's foundation. One miscalculation and you're into someone's structural support.
Why stack the tunnels vertically instead of side by side?
Because there's nowhere else to put them. The buildings are too close, the viaduct is overhead. You work with what you have. Vertical stacking meant they could fit the station in the space that existed.
And the roads—they couldn't close those either?
No. So they built a steel roof underground first, stabilized the ground above it, then bored beneath it. The road never knew anything was happening.
It sounds like every decision was constrained by what couldn't move.
That's Singapore. Nothing stops. The city keeps going while you rebuild it.