Clearing the way for the Scarborough Subway Extension launch shaft construction

Teams have begun preparing the tunnel boring machine (TBM) launch shaft site for major construction work, bringing the Scarborough Subway Extension another step toward reality. Let’s dig in.

It’s almost launch time for construction on the Scarborough Subway Extension.

The 7.8-km extension of TTC Line 2 subway service will provide seamless, reliable transit to key areas in Scarborough, and is expected to serve over 105,000 riders daily. The first visible step toward that seamless rapid transit experience involves creating an entry point for the equipment that will dig the new subway tunnel – the launch shaft for the tunnel boring machine. Crews are now on the ground, preparing that launch shaft site.

Last month, Metrolinx and Infrastructure Ontario announced that they had identified Strabag as the successful bidder that would design, build and finance the tunnel for the project. Now, Strabag has started some on-the-ground work that is bringing project plans to life.

Two Launch Shafts To One

Image shows a map of route
The refined proposal for construction of the Scarborough Subway Extension, including the direction of drilling for the tunnel boring machine. (Metrolinx image)

Late last year, the teams working on the extension fine-tuned the tunneling approach for the project, going from two tunnel launch shafts to one. The single launch shaft required for the project, where the tunnel boring machine will eventually begin tunnelling, will be constructed at the northeast corner of Sheppard and McCowan.

Image is a graphic showing the location of the launch shaft.
Here is the location of the launch shaft site for the Scarborough Subway Extension (Metrolinx image)

Before construction can begin on the launch shaft, there are a few things that need to be taken care of to prepare the site for the excavation that will take place as the tunnel is dug out.

Handling Hazardous Material

On May 4, 2021, demolition crews begin to dig in and through. (Metrolinx photo)

The existing buildings on the site are being demolished, but first the interiors of the buildings were thoroughly inspected and hazardous materials were removed.

“Removal of hazardous materials before demolishing these buildings keeps workers on the site safe and prevents these materials from dispersing into the nearby community,” said Walter Trisi, construction director for the Scarborough Subway Extension.

Utilities connected to the buildings like power, water, natural gas and telephone lines also had to be disconnected to allow for a safe demolition and to prevent any utility service disruptions in the local community. This involves a tedious coordination effort with different utility providers who have services in the area.

Demolition

After all these preparations were complete, it was time for the excavators to begin demolishing the buildings.

After the buildings are fully cleared away, crews will then begin the process of grading the site to make sure that the ground is level and safe before shaft excavation can begin.

Some areas will also be paved to create an internal road network that will be used to move equipment and materials easily across the site.

Crews can then begin the process of secant pile drilling. This is a process where deep holes are drilled into the ground and the holes are then filled with concrete and steel to create a water-tight barrier. These concrete and steel columns hold soil and water in place so that excavation for the launch shaft can begin safely.

“We’re very excited that work is underway at this launch shaft site,” said Trisi. “We’re working closely with Strabag on their construction plans and approach so that we can get this subway extension built as soon as possible,”

As construction officially begins on the project, Metrolinx will continue to keep the community informed about progress and what to expect during every phase. Visit the website for the latest project information and updates, where you can also sign up to receive email updates from the project.

So, even as experts prepare to go below, things are really looking up on the new route.

Story by Joshua Patel, senior advisor, subway program.