The Eglinton Crosstown West Extension project is making rapid progress following the completion of six kilometres of tunnels that make up the western segment of the line, stretching from Mississauga’s Renforth Drive to just west of Scarlett Road in Etobicoke.

This massive feat was achieved by twin tunnel boring machines (TBMs) Rexy and Renny, as well as through an efficient construction technique that meticulously installed more than 52,000 pre-cast reinforced concrete liner panels (called segments) as the tunnels were being dug out.

Let’s take a closer look at how the walls of these tunnels were built.

Concrete puzzle pieces

Think of each tunnel segment as pieces of a massive, three-dimensional jigsaw puzzle. The segments interlock to build thousands of sturdy rings that create a continuous wall, forming the tunnel’s structure. 

To create each segment, concrete is first poured into a mould that is custom shaped to the diameter and curve of the tunnel. The mould vibrates to remove air pockets before it is left to set. It then goes into a kiln to cure before it is removed from the mould and inspected.

This method allows for higher quality control through visual inspections and quality checks. For an infrastructure project of this scale, ensuring each part meets strict standards is essential to ensure durability and reliability of the tunnel.

Building a tunnel, one ring at a time

The process of building with pre-cast segments is as interesting as it sounds.

Here’s how it works: as the TBM digs through the earth, it leaves an empty cylindrical space behind. In this space, crews place a ring of pre-cast concrete segments. Once one ring is securely in place, the TBM advances, and the team repeats the process, ring by ring, segment by segment.

The tunnels were dug using TBMs then manoeuvred into place to form the tunnel wall. Using pre-cast concrete wall segments offers many advantages for a project like the Eglinton Crosstown West Extension, as each segment is designed in advance to support the weight of soil, roads, and buildings above. And because the segments were manufactured ahead of time at a facility in Whitby, construction crews could focus on assembly rather than heavy-duty fabrication.

While tunnel boring machines were used to tunnel the western segment of the line, we’re using another method – the sequential excavation method – to dig the tunnels between Jane Street and Mount Dennis Station.

What’s next for the Eglinton Crosstown West Extension?

Now that the twin tunnels are complete on the western end of the line, work is underway to prepare sites for the construction of the elevated segment, which will run between Scarlett Road and Jane Street, along the north side of Eglinton Avenue West before transitioning back underground. Work is also underway to prepare for tunnelling on the second tunnelled portion of the route, which will run from just east of Jane Street to Mount Dennis Station. This is where the extension will connect to the future Eglinton Crosstown LRT service. 

Earlier this fall, an important procurement milestone was reached when a request for proposals (RFP) was issued for the Stations, Rail and Systems (SRS) contract for the Eglinton Crosstown West Extension. Included in this package of work is the construction of all seven new stations, fitting the tunnels and 1.5-kilometre elevated guideway with track and signals, and installing and commissioning communications, ventilation, and other support systems.

Once complete, the extension will create a continuous rapid transit line that stretches from Scarborough, through midtown Toronto, and into Mississauga.  To keep up with progress on construction, follow the Eglinton Crosstown West Extension on Instagram, X, and Facebook.