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A Little Tunnel Vision Can Be a Good Thing

Workers finish surfacing a diamond inside a tunnel while constructing a portion of the new North LRT Extension in Edmonton, AB.

There’s nothing like building three diamonds and six switches in a tunnel to reshape your views about track construction logistics.

There are the usual overhead clearance and emission issues. Throw in a significant pre-assembly step, limitations on track accessibility, equipment restrictions, and live traffic with curious onlookers on the nearby platform, and the situation calls for … well, a type of tunnel vision, where you ignore the periphery activity and focus on the central issues.

Fortunately, the PNR RailWorks team faced with receiving, assembling and installing special track inside the Churchill “cavity” in Edmonton, Alberta, was ready for the rigor of the exercise. Working as a subcontractor to North Link Partnership, a joint venture partner by SNC Lavalin and Graham Construction, PNR RailWorks was working in a tunnel near Churchill Station to construct a portion of the new North LRT Extension.

With materials sourced from abroad by the joint venture, including steel components from the Czech Republic and ties from Spokane, Wa., crews first pre-assembled the 87-metre section of track, featuring six switches and three diamond crossovers, in Edmonton’s Cromdale Yard to make sure it came together properly. They then disassembled the track section and transported the materials inside the tunnel over existing track on a flatcar provided by Edmonton Transit. With the new materials inside, they demolished the existing track and re-reassembled and installed the new track work inside the tunnel. They worked much of the time near live traffic on adjacent track.

Garry Potrebenko, site superintendent, marvels at the complexities. “In my 30 years of railway experience, I have been involved in the construction of only nine diamond crossovers, which are considered the elite of special track work. Only three of those were in tunnels, and they were all engineered as hoisting locations for access to build the tunnel. Or they were right beside a hoisting access spot; then the roof was built over it later, after the bulk of the construction was completed. In this particular case, we were building a diamond crossover for the new line and building two extra switches and two extra diamonds into a diamond crossover, while keeping traffic operating on one track.”

Initially, Garry envisioned his crews hauling materials in on trucks, offloading it, and then reloading it onto push cars during a four-hour overnight window. But making arrangements with Edmonton Transit created efficiencies. By using Edmonton Transit’s equipment, PNR RailWorks avoided double-handling materials. Crews gained further ground when Edmonton Transit was able to open up additional hours for materials transmission.

Gaining track time was a good thing, because once inside the narrow confines of the tunnel, with about 4 metres from pillar to pillar and about 4 metres of overhead clearance, crews couldn’t use conventional equipment to dig or place assembled panels. Instead, they relied on mini-excavators and skid steers to prepare the ground and lay rail.

PNR RailWorks wrapped up the first part of the contract ahead of schedule, which Garry attributes to a skilled core group that he relies on for multiple projects, plus workers hired from the local area. “This was all due to their hard work and effort,” he says. “They’re the ones that put in all the long hours and made the sacrifices to make it happen.”

In fact, when it was apparent the job was ahead of schedule, PNR RailWorks identified the opportunity to move forward and tackle the 2013 portion of the contract.  The future work called for changing out all the rail in a segment of the tunnel and would necessitate shutting down the line again.  Crews believed the shutdown could be avoided.

Although skeptical about whether PNR RailWorks could pull off the additional work under time constraints, North Link Partnership and Edmonton Transit agreed to the attempt.  “If we slipped on our revised schedule,” Garry explained, “we would store the strings along the right of way and complete the rail change next year as originally scheduled.”

But PNR RailWorks didn’t slip.  Drawing on labor from Calgary and Edmonton as well as the Holland Company, the company finished welding rail strings ahead of schedule and then received the go-ahead to complete the rail change-out. 

“It’s sure nice,” Garry said afterward, “to work for an organization that can pull in such talented and experienced work forces to get so much more accomplished than ever imagined.”

Work on the remaining three portions of the contract, plus additional embedded track crossing work, will continue through the end of September. The project is part of Edmonton’s North LRT Extension, a light-rail expansion northwest from downtown Edmonton to the Northern Alberta Institute of Technology.