The Edmonton North Light Rail Transit Tunnel project is a 3.3-kilometer (approximately 2-mile) extension of the existing light rail network in Edmonton, Alberta. Flatiron was a subcontractor on the project for construction management team North Link Partnership, a joint venture of SNC-Lavalin Group and Graham Infrastructure.

Flatiron was responsible for the construction of two twin tunnels. The twin northbound and southbound tunnels begin near the location for the new MacEwan Station, run underneath 101st Street and through a sub-basement of the Epcor Building, before continuing on to the existing Churchill Station for a total length of 875 meters of tunnel. Each tunnel is about six meters in diameter, but the tunnels are egg shaped, a bit taller than they are wide.

The first 11 months of the project consisted of tunnel excavation. Crews worked 24 hours a day, seven days a week, to stay on schedule, completing work in early November 2012. Crews then worked on lining the tunnel with concrete. During excavation, the tunnel was lined with shotcrete to provide temporary stability. To permanently line the tunnel, crews applied waterproofing over the shotcrete, installed rebar, and then placed concrete. Concrete for the lower half of the tunnel (called the invert) was installed first. The crews used a monorail system, installed in the roof of the tunnel, to transport the invert form incrementally down the tunnel. A separate system was used for the arch (or upper half) of the tunnel lining. Each completed segment of concrete lining is approximately 12 meters long, and the project had a total of more than 250 separate concrete placements.

Crews faced the challenge of having only one entrance to the project site, making managing people, equipment and material more difficult than other types of work. The final work on the project included constructing the transitions between the tunnels and the station at the end of the line. Flatiron’s portion of the work was completed in June 2013. The North Link Partnership installed the power, signaling and rail systems to open the line to the public in spring 2014.