Image shows inside a tunnel

Local manufacturer to help hold back the weight of the earth along the Scarborough Subway Extension

As construction for the new Scarborough Subway Extension continues at the tunnel launch site, teams are already partnering up with a local manufacturer to build the giant concrete rings that will line the tunnel and help keep the earth below Canada’s biggest city at bay.

Sophisticated engineering is everywhere you look in a subway project, and for the Scarborough Subway Extension, you don’t have to look very far. The project’s tunnelling contractor, Strabag, has partnered up with an experienced local manufacturer to build tunnel liners for the project.

While tunnel boring machines (TBMs) attract most of the excitement when tunnels are being built, tunnel liners just might be the unsung heroes of tunnel construction. The liners are the concrete rings give the tunnels their structure, and they’re critical in keeping them safe and keeping the TBMs moving. These precast pieces of reinforced concrete are designed to support the earth and resist pressures from the soil, rock, and water that surround the tunnel.

CSI Tunnel Systems, a leading precast concrete manufacturing company, has been selected to produce these important pieces of the project. They were chosen because of their experience and knowledge manufacturing these types of products for other big projects. Their manufacturing facility is in Whitby, which is only about 30 kilometres from the tunnel launch site.

Want to know more about the Scarborough Subway Extension? Then just go here.

CSI Tunnel Systems have confirmed that approximately 50 local jobs have been created at their facility to manufacture the tunnel liners for the Scarborough Subway Extension.

Big Work

Teams will build a whopping 3,500 rings, or 28,000 individual tunnel segments, that will line the project’s single tunnel.

Reinforced with steel, each tunnel lining ring weighs in at roughly 132,000 pounds, the average heft of 10 adult elephants. A single ring is made up of eight individual concrete segments that are connected together by bolts and dowels.

Image shows large concrete quarter-circles, piled on one another.
Precast tunnel liner segments that were used on the Crosstown (Metrolinx photo)

The individual pieces will be brought to the tunnel launch site at Sheppard and McCowan by truck and will then be lowered underground to the TBM for installation. As the TBM advances underground, concrete segments will be positioned around the tunnel to form rings, with a special part of the TBM called a ‘segment erector.’ These pieces are then bolted together to form the lining, or frame, of the tunnel.

Image shows inside a tunnel
A completed tunnel for the Crosstown, with tunnel lining rings bolted together to create the wall of the tunnel (Metrolinx photo)

The tunnel liners will also help push the TBM through the earth – the TBM pushes on the tunnel lining to propel itself forward. All 3,500 rings will be installed to complete the single tunnel for the project.

Name The TBM Contest

As materials are manufactured and the TBM begins its journey from Germany, Metrolinx is also inviting the community to submit name ideas for the mighty machine that will build the tunnel for the project. Visit the contest page to submit name ideas until Nov. 18.

The Scarborough Subway Extension will provide quick and seamless transit for those travelling within Scarborough or heading into and out of the downtown core, putting 34,000 jobs within a 10-minute walk from the three new stations. For more information about the Scarborough Subway Extension and to contact the project team, visit