Crews have reached another milestone in the new rail passage in the heart of some of the busiest highway traffic in Canada – 100 per cent excavation in tunnel two. Since March, heavy machinery has been digging through rock and debris in the second tunnel. We get the dirt on how this was done on the Highway 401 and 409 Rail Tunnel project, including new videos.
There’s light at the end of the tunnel – or middle of the tunnel in this case.
When construction crews began digging in tunnel two of the Highway 401 and 409 Rail Tunnel project, it wasn’t as straightforward as many would assume. A carefully thought out plan determined the best way to hollow out the tunnel, which was to dig from both ends and meet in the middle, starting with the top half of the tunnel.
This work is part of building a twin tunnel structure underneath 21 live lanes of traffic, and supports GO Expansion on the Kitchener line. When complete, the tunnels will accommodate future track, enabling more frequent, two-way, all-day train service.
To ensure the proper supporting structure is in place during excavation, only the top half of the tunnel is emptied first. This was competed by digging the first section from the east portal to the median and then proceeding with the second section from the west portal to the median.
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.
With the top portion of the tunnel fully excavated, the next step was to start removing the earth from the bottom of the tunnel and working from the ends towards the centre again.
Why was there a steel wall in the tunnel?
Earlier in the project, multiple interlocking steel sheets were driven into the ground in between Highways 401 and 409 creating a square work area, at the median (mid-point). The sheet pile wall was installed before the tunnel was constructed. The area enclosed by these walls was then excavated, making a small work area below the highway. The sheet pile walls allowed workers in the newly made work area to auger bore pipes which provided support for the tunnel structure – find out more about this innovative technology here.
To facilitate safe excavation of tunnel two, work began at the east portal to allow for construction to continue at tunnel one at the west portal to be completed. Working at the separate portals provides enough space for crews to maneuver and remove any large obstructions from the tunnels.
Achieving 100 per cent excavation in tunnel two is another major milestone and brings the project closer to completion. When finished, the new infrastructure will help increase capacity on the rail corridor, delivering better, faster and more frequent GO train service to surrounding communities.
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Story by Teresa Ko, Metrolinx senior advisor