Whole new world underground for TTC crews constructing Vaughan Metropolitan Centre Station

Yorkregion.com
Sept. 4, 2014
By Sean Pearce

From the surface, it doesn’t look like much.

When you step on to the site of the future Vaughan Metropolitan Centre Station, which will act as end-of-the-line for the Toronto York Spadina Subway extension, it doesn’t appear all that different from any number of other construction projects on the go across the GTA.

It’s a hub of activity, certainly, with bulldozers moving earth and workers in hard hats and reflective vests wielding tools and barking orders, but there’s nothing going on that, at first glance, sets it apart from the various work sites dotting the Hwy. 7 corridor running through the City Above Toronto.

All of that changes, however, as you approach the trench.

Stepping toward the edge reveals sheer, shored-up walls stretching dozens of metres down into the earth. Steel supports, along with conduits and utility pipes, stretch across the gaping maw’s expanse while scores of tradespeople labour below.

Much like an iceberg, the ground level serves as little more than a hint as to the scale of what’s going on beneath the surface.

The number of people working on the site varies from day to day, explains TTC engineer Charlie Raymond, who serves as assistant construction site manager, explaining that as many as 200 may be toiling away during our tour. A naturally soggy area, the site is kept dry through the use of a massive cut-off wall, which is one metre wide, 28 metres deep, and a little under 2,000 metres long.

The wall is made of a cement-bentonite mixture as the bentonite helps to slow the penetration of water. Raymond notes the wall is the largest in use in Canada.

Construction of the wall was made possible through the use of special equipment brought in from Germany, engineer and director of third party planning and property Joanna Kervin says, explaining once the area is back-filled, the wall will be removed to let the water table settle once more.

Even after the cut-off wall is gone, the concrete pads at the very bottom of the subway tunnels and the station itself will be anchored in place to prevent them from being lifted up by natural moisture in the years to come, Kervin adds.

Before descending a set of temporary steel stairs into the trench itself, Raymond draws attention to a partially built structure, what will be the north-side emergency exit, rising out of the ground nearby. He goes on to say there will also be a second emergency exit built on the south side of Hwy. 7.

That’s because those on the south side of Hwy. 7 will be able to walk to the subway station, as well as access York Region Transit and Viva service, via an underground passage, Kervin says. The tunnels running to and from the new station will also allow access for future development surrounding the site, she says, adding a SmartCentre office building being built on an adjacent parcel of land will take advantage of that very feature.

“That’s very good news and a really great start,” Kervin says, expressing hope other development will follow. After all, anything that brings more people to the area will no doubt equate to greater ridership for the subway extension.

At the bottom of the stairs sits an enormous concrete pad that will, one day, serve as the concourse level for the new station. Despite its depth and the gloomy sky above, the feature remains bathed in sunshine and Kervin explains that the plan calls for the finished station to have skylights overhead so natural light can still reach this level once construction is completed.

Standing here also gives you a good view of the gigantic steel I-beam running beneath Hwy. 7 that allows the six-lane regional route to bridge the trench’s expanse while work continues unhindered below. The I-beam is one of two found on the site, Kervin says, pointing out the other a short distance beyond that runs beneath a private road on Toromont property south of Hwy. 7. Securing the private road on Toromont’s land and keeping it accessible was an important measure to ensure the business could keep operating during construction, she says, noting the company has been very co-operative throughout.

Down another few flights of temporary stairs leads to another concrete pad that will serve as the subway platform itself. You won’t be able to catch a train here for at least two more years and the walls and floor are still bare concrete, but it’s already taking shape.

Running on either side of the platform are two concrete trenches where the tracks will be laid at some point next year if all goes according to plan, Kervin says. Climbing down into the future track area, she points out where the cross-track will eventually be and draws attention to the two tunnels beyond. It was here, just last year, that two massive tunnel-boring machines, Yorkie and Torkie, emerged to complete their sections of the extension.

Yorkie and Torkie were two of the four machines involved in the project. During tunnel work, the boring-machines dug their way through up to 45 metres of earth every day, Kervin says, adding 1.4 million cubic metres of dirt was excavated during the process.

On either side of entrances to the tunnels workers busily weld together massive lattices of re-bar. A construction project of this size, this station alone will stretch 550 m in length, requires massive amounts of concrete, Kervin says, explaining concrete pouring sometimes begins in the early hours of the morning and then spans virtually the entire day.

When it’s all finished, the Vaughan Metropolitan Centre subway station will have consumed about 55,000 cubic metres of concrete, Kervin says. The entire project will necessitate around 400,000 cubic metres of concrete - enough to build 10 CN Towers.

The area near the tunnels’ mouths is also where a drop shaft will be maintained even once the rest of the station is covered over and filled in Kervin says. It is here the tracks, other finishing materials and even vehicles will be lowered in to complete the project, she continues.

Heading back toward the northern section of the future station, Kervin notes that the pedestrian tunnel will also feature the potential for small shops and kiosks to open, establishing something of a mini-PATH in the area. The station, itself, also has a tail track beyond the main track, which is there to help facilitate any future extensions of the subway to the north.

As the tour draws to a close and we climb another set of temporary stairs to reach the surface-level concrete pad atop which will sit the future subway entrance, Kervin explains Downsview Station also incorporated a tail track for the same purpose, although the actual expansion had to deviate slightly from what was envisioned at the time of its construction. All of the stations, and indeed much of the 8.6-km extension, has brought with them challenges to overcome, Kervin says, but all of that will be worthwhile when the project becomes the first new stretch of subway to open in more than a decade.

“I think the end result will be fantastic,” she adds.