Piling Canada

Ground Control

Written by Jim Chliboyko
March 2015

Keller Foundations’ role in Toronto’s new underground transformer station

When the construction of Toronto’s new downtown transformer station was announced, what was arguably the most amazing thing was the news that it was to be the city’s first downtown transformer station built since 1955. The power being routed through the new transformer station will not only supply Toronto’s financial district, but will give the existing infrastructure a bit of a break and an opportunity to get some maintenance done on the rapidly aging Windsor Transformer Station, a half-kilometre to the north.

Toronto Hydro’s estimated $195-million new station – located by the John Street CPR Roundhouse, a block or so away from both the CN Tower and Rogers Centre (the SkyDome) – is seen as the next step in strengthening the city’s electrical infrastructure. The company points out on its website that the population of the downtown area increased by 50 per cent in one five-year period alone (2006 to 2011), adding to increased electrical demand, and adding to the pressure on the Windsor station. The new station will add 144 MVA of capacity.

Occasionally, the transformer station is still referred to as the Bremner Transformer Station, though it’s recently been renamed the Clare R. Copeland Transformer Station (after a former chair of the Toronto Hydro board, who only just left the position in 2013 after 14 years as chairman). The area in question is at the southwestern corner of Rees and Lakeshore. It’s actually part of Toronto’s municipal parks system, known as Roundhouse Park, and the Roundhouse itself is considered a National Historic Site of Canada.

Isherwood Geostructural Engineers designed the shoring component of the project. Carillion Construction Inc. won the general contractor bid and, in turn, they selected Keller Foundations to perform the shoring and foundation work for the station.

When Ontario-based Keller Foundations project manager Graeme Smart was asked what the challenges on the project were, he replied, “I would say the complexity of the physical location of the site, the irregular shape of the site and an aggressive schedule.”

In terms of sheer numbers to do with shoring, Smart said, “The plan consisted of 425 vertical shafts for the secant wall, all one meter in diameter, and ranging from 40 to 60 feet in length. The site had two levels of rock anchor tiebacks, 187 of them total for 2,600 lineal meters of tiebacks. We used two Liebherr LB 28 hydraulic drill rigs with segmental casing to install the secant wall, and Klemm 806-3D drills for the tiebacks.”

Multiple five-person crews were on site for the installation of the secant wall with Keller forces increasing in numbers when the schedule called for tieback installation work to begin while the secant work was still ongoing.

It’s not only a tricky place to build such a station, but the Clare R. Copeland Transformer Station added a few new wrinkles to a typical hydro-related build. First, it’s only the second underground transformer station ever built in Canada. This particular transformer station will be the equivalent of four stories underground. Secondly, the place is so crowded that one particular historical building, the Roundhouse’s machine shop, had to be carefully and painstakingly dismantled in order to be properly rebuilt after the station was completed. (The machine shop will eventually contain some of the equipment for the station; the dismantling will give it the chance to be properly upgraded before it is repurposed.)

The site also had a few surprises in store for the crew.

“If you look at the history of that site, apparently there’s an old sunken ship around there. We did hit an obstruction on the east wall at the south end of the site,” said Smart, who added that they never found out the exact source of the obstruction. This is not unprecedented; parts of the Commodore Jarvis, an old wreck that had been destroyed by fire in the early 20th century, were unearthed during the construction of the Air Canada Centre.

“It was a tough process to drill within inches of the existing Roundhouse,” said Smart. “We had to avoid and dodge, weave through the Roundhouse foundation, which is driven timber piles. No one was sure of the condition of those existing timber piles or exactly where they were located.

“To get to depth, we had to drill our tiebacks past and in between those existing timber piles. We knew roughly where these piles would be. Essentially, we would probe ahead with our casing, and then rely on the experience of our drillers to alert us if they were hitting some kind of obstruction.”

And then the crews discovered that on the south side of the site, there was an old seawall.

“There were actually no records of it, no workaround,” said Smart. “Basically, we had to core our way through that seawall.”

As the site was less than a half-kilometre from Lake Ontario (to the south), water was always an ongoing concern. The station was built within what is commonly referred to as a concrete bathtub.

“There was a big emphasis on making sure that our secant piles were straight and we achieved proper overlap to ensure the water was sealed off. All fillers for the secant wall were sealed in the rock,” said Smart. “There was major waterproofing on both the walls and the floorslab,” said Smart. “We also installed 345 vertical tie-down anchors, double-corrosion protected, and chemical grout as a further preventative measure for any potential seepage into the slab.”

By August, the Keller team was virtually complete with only some chemical grouting still to do on a handful of tie-down anchors. When Piling Canada talked to Smart in mid-summer, he said, “We are essentially 99.5 per cent done. We started April 2013, on site. We wrapped up the vertical drilling in September 2013. The drilling and installing of tiebacks and tie-down anchors were completed earlier this year.”

Being a large project having to do with electrical infrastructure meant that there were some other considerations with which to deal, including drilling nine-foot-diameter holes in rock.

“Because it is a transfer station, there was a huge amount of tunneling,” said Smart. “We installed two manhole shafts to service the tunnel from a foundation perspective. We did a total of four large diameter shafts, two for Carillion and two more for the tunneling company for rescue shafts further down Lower Simcoe Street.

“We used our [Liebherr] LB 36 hydraulic drill rig to install the large-diameter rescue shafts. The largest hole was a 108- inch shaft drilled to 120 feet; 100 feet of that was rock. That hole took us five days to drill.”

At this point, with the job almost finished, there should be no further surprises – seawalls, the potential of finding ancient ships – for the Keller Foundations crew, only the satisfaction of being able to contribute to such a major part of Toronto’s infrastructure.

“I would say, from a new structure perspective, it’s a very important project, a much-needed project,” said Smart.

The new transformer station is due to go online by the end of 2014. 🍁

Category: Projects

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