Metrolinx announced that the Highway 401 and 409 Rail Tunnel project has reached a significant milestone by achieving ‘substantial completion.’

Without disrupting the constant highway traffic above, the project has reached substantial completion and crews are wrapping up the final touches. The twin tunnel will support future service increases on the Kitchener line. Take a look at all the work leading up to this significant milestone.  

Toronto Tunnel Partners, consisting of EllisDon and STRABAG, has been constructing the twin tunnels, less than three metres underneath the Highways 401 and 409, without disrupting the 21 live traffic lanes directly above.

This work is part of the GO Expansion program, which will transform the Kitchener line from a rush hour commuter service to a more convenient transit experience with two-way, all-day rail service.

“The project is a significant achievement and provides key infrastructure for the Kitchener line,” said Franca Costantino, Metrolinx senior manager of the project delivery team.

“The tunnels will eventually help get more commuters off the roads and onto public transit, improving quality of life for many people.”

Crews started construction on the twin tunnels in the summer of 2019 by using auger boring to support the ground above where the tunnel would be excavated. This involved inserting large metal tubes into the top of each future tunnel to form a canopy, to support the structure before excavation started. Next, crews began digging out the tunnels and removing dirt, rock and debris. About 73,500 m3 of material was hauled away – an amount so large it required approximately 8,000 dump trucks.

By January of this year, both tunnels were completely excavated.

The team used the sequential excavation method (SEM), a construction method that provided a safe and versatile option for tunnelling underneath live lanes of traffic. The top half of the tunnels were excavated first followed by the bottom. As crews dug out a section of dirt, they also applied shotcrete – concrete sprayed on the newly excavated surface – to maintain the structure of the tunnel as the crew proceeded deeper inside.

For tunnel two, it was a little different – after careful planning, it was hollowed out by digging from each end and meeting in the middle. When the digging finally reached the median, the only way to breakthrough to the other side was to cut open a three-quarter inch thick steel wall with a torch. It took three days of focus to cut and remove sections with an excavator.

The next phase of major construction, and performed under a separate contract, will include track installation, signalling and communications infrastructure.

Featured image: A cast in-place machine being positioned to enter tunnel one. It creates a smooth surface inside the tunnels as it travels from one end to the other. (Metrolinx photo)

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