Tunnel excavator


Highway 401-409 project finishes second tunnel excavation

See the video as crews reach another milestone on the 401/409 tunnel project.

Feb 11, 2021

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.

A workman walks through a tunnel.

The tunnel excavator moving into position to start the final phase of tunnel two 100 per cent excavation. (Metrolinx photo)

A tractor works inside a tunnel.

A mini excavator clearing the finer excavator material and preparing the area for the tunnel excavator. (Metrolinx photo)

The tunnel is seen with smashed concrete.

The tunnel excavator exiting the tunnel after the initial phase of the 100 per cent excavation. (Metrolinx photo)

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.

Image is a graphic showing how digging happens in the Highway 401 and 409 tunnel.

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.

a tunnel with concrete in the middle.

Crews start opening up the steel wall by cutting through to the west portion of tunnel two. (Metrolinx photo).

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.

A worker stands in the tunnel.

Concrete obstruction from the existing bridge structure shown on the right. (Metrolinx photo).

See the videos – Highway 401 and 409 Rail Tunnel project completes excavation in tunnel two

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.

For more information or sign up for e-newsletter updates click here.

by Teresa Ko Metrolinx communications senior advisor