Canadian Consulting Engineer

Downsview Park Station

March 1, 2014
By Mary Van De Gevel, AECOM

In a previous age, transit stations only needed to connect riders between different transit modes — subway, train or streetcar — operating as part of a single transit system. Today, however, the need to improve transit mobility...

In a previous age, transit stations only needed to connect riders between different transit modes — subway, train or streetcar — operating as part of a single transit system. Today, however, the need to improve transit mobility between urban and suburban areas is leading to the integration of services between multiple transit operators. As a result, a new kind of station is required, one that can handle more complex patterns of rider movement and transfer.

Multi-modal stations play a significant role in Toronto’s new 8.6-kilometre-long rapid transit project, the Toronto-York Spadina Subway Extension (TYSSE). Running from Downsview Park in northwest Toronto, through York University, and terminating north of Highway 407 at the Vaughan Metropolitan Centre Station, the TYSSE is the first Toronto Transit Commission (TTC) subway line to cross a City of Toronto boundary. Direct connections with other regional transit services will include GO Transit, York Region Transit, and Brampton Transit, as well as other modes of TTC service, including buses and light rail.

Downsview Park Station is one of five new stations on the line that feature a multi-modal design. It was designed by AECOM (lead architect and lead engineer) with input from Aedas (architecture), and Parsons Brinckerhoff (engineering). The same team is responsible for the Highway 407 Station.

Downsview Park Station is located at the north end of Parc Downsview Park, a 2.4-kilometre-square urban park currently undergoing a $40-million redevelopment. (The existing “Downsview Station” near the park will be renamed “Sheppard West Station.”)

Entrance pavilions flank railway line

With a total building area of 3,648 square metres, the new station is being built where the TYSSE tunnel intersects with the above-ground CN/GO rail line, which runs from Toronto’s downtown Union Station to Barrie’s Allandale Waterfront Station.

The station allows riders a direct interchange between the GO Transit and TTC services by being situated immediately below the existing railway line. This proximity is an important component of the station’s function as a multi-modal station, but it also involved accommodating more challenges in the structural engineering.

On one hand, the station requires open spaces, column-free areas and openings in the structure to allow light and the free flow of riders. Yet, the station also needs to be strong enough to support being built below an active railway line.

Two surface-level entrance pavilions built on either side of the rail line allow riders to access and exit from the station. The pavilions consist of a single level configuration of glazed curtain walls and sloping steel columns. Curved steel beams support a green roof system, and spread footings provide support from below. The footings are on the native soils founded approximately 1.2 metres below grade.

Underground multi-unit box

The entrance pavilions are structurally independent of the station’s underground portion, which consists of a two-level station box. The concourse level is at a depth of 6.9 metres. Designed to allow riders passage between the separate entrance pavilions below the rail line, the concourse level includes the fare control equipment and collectors’ booth for the subway. It also provides space for the station’s non-public services and staff rooms.

To meet the station’s electrical energy needs — lighting, equipment and safety systems, as well as traction power for trains — a separate electrical substation is integrated into the grade level west entrance pavilion.

The 13-metre deep subway platform level includes two tracks with a 10.3-metre wide, 152.4-metre long rider platform. The platform is oriented parallel to, and positioned directly below, the concourse level.

The GO train platforms, which are being designed as a separate effort under the direction of GO Transit, are expected to be operational when subway service begins.

Creating open space that’s easy to navigate

Creating intuitive circulation paths for riders was one of the station’s critical design objectives. Given the different streams of users — subway riders, GO Transit riders and non-rider pedestrians — the station required architectural features, like large, column-free spaces and openings for natural light, to make the transfer between systems efficient and hassle-free.

While these open design features allow riders to make informed decisions when moving around and within the station, they also required a more advanced structural configuration than is typically involved in the engineering of traditional station boxes.

The station box here is actually made up of six units separated by contraction joints. Units 1 and 6 consist of a two-level reinforced concrete box configuration with intermediate concrete columns and beams. Units 2 and 5 consist of a two-level reinforced concrete box with struts at the concourse and ground levels. Intermediate columns are built only between the base slab and concourse level. Units 3 and 4 consist of a two-level reinforced concrete rigid-frame configuration with intermediate concrete columns and beams, while transfer beams at concourse level support some concrete walls above.

From the surface-level pavilions down to the concourse and platform levels, 20- and 23-metre long reinforced concrete beams,1.8-metres wide x 1.6-metres deep, are used to help create large openings. In other units, where the structure is required to carry the load of trains operating above ground, 10-metre long 2-span beams, 1.5-metres wide x 1.6-metres deep, with twin 1.5-metre diameter columns, are used with 16-metre long T-beams, 2.6-metres wide x 1.4-metres deep, to create the rigid frame to resist the train loads. The concrete strength for all the beams is 35 megapascals.

Another challenge involved creating large open spaces in the structure for natural light was dealing with the earth pressures and buoyancy forces due to the location’s high water table. Approximately 250 micropiles were installed throughout the station to resist these uplift forces. The micropiles are 11.5 metres in length and consist of a 63-mm diameter high strength threaded bar as the core, with a 180-mm diameter x 6.3-mm thick steel casing filled with 30 MPa Portland cement grout.

Vertical circulation

Supporting the station’s strategy for rider movement are its vertical circulation elements. Aside from the elevators, the same elements also act as the primary means of egress during an emergency. Each pavilion entrance incorporates one set of stairs, two sets of escalators and an elevator. The elevator from concourse level to platform level is of a “walk-through” design, which is preferred by the TTC. The elevators from the entrances to the concourse level are of a “single entry” design, to ensure that the passengers entering the elevator from ground level arrive at the unpaid area of the concourse level.

Acoustical issues

Another aspect of sharing space is managing the acoustic challenges of operating subway service underneath a railway line. The station’s public announcement system is an important part of the overall emphasis on rider wayfinding. At the same time, it is important to ensure that the station’s ambient noise does not interfere with the optimal rider experience.

Noise and vibration from the GO Trains running above, however, posed a challenge. In response, a ballast isolation mat, consisting of high quality resin bonded rubber with a protection layer of non-woven geo-textile to avoid ballast penetration, was installed onto the station box’s concrete substrate. This solution will help reduce train pass-by noise and will not interfere with the intelligibility of the paging system.

When complete in 2016, the station will serve as a site of convergence and connectivity, seamlessly integrating the TYSSE and GO
Transit rail line services, ensuring riders move safely and efficiently between the different transportation modes.cce

Mary Van De Gevel is a project manager at AECOM in Markham, Ont.

Client: Toronto Transit Commission

Architects: AECOM with Aedas

Engineers: AECOM (David LeBlanc, P.Eng., Leslie Martin, P.Eng., Mark Cavanaugh), with Parsons Brinckerhoff (Richard O’Brien, P.E.)

Contractor: Aecon


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