Construction Methods

The subway will be constructed using tunnel boring machines, with “cut and cover” construction around Scarborough Centre Station and to facilitate connection to Kennedy Station.


Emergency Exit Buildings

These exits are required to evacuate passengers from the subway tunnel in the event of an incident or emergency. The building houses a stair case which connects from the tunnel to the surface. Emergency exit buildings are required at a maximum spacing of 762 metres along the subway alignment (8 buildings are required for the SSE).


Tunnel Ventilation Structure

A structure is required to provide fresh air to the subway tunnel and to remove smoke in the event of a fire. This includes powerful fans moving large volumes of air. One structure is required at the midpoint between Scarborough Centre Station and Kennedy Station. A second structure will be north of Scarborough Centre Station at the tail track.


Traction Power Substations

These are electrical substations that convert electric power from Toronto Hydro to an appropriate voltage, current type and frequency to supply the Subway with traction current. The locations for traction power substations on the TTC subway system are typically at subway stations. Due to the distance between Kennedy Station and Scarborough Centre Station, two “stand alone” traction power substations are required along the subway alignment. A third traction power substation will be located at Scarborough Centre Station.


Underground Construction

Single Large Diameter Tunnel

Most of the Scarborough Subway Extension is planned to be constructed using a single large tunnel boring machine (TBM) (10.7 metre diameter) to accommodate tracks in both directions. Other recent TTC subway projects (such as the Toronto-York Spadina Subway Extension and the Sheppard Subway) were constructed using twin TBM (about 6 metre diameter tunnels). Eglinton Crosstown LRT (Metrolinx project – currently under construction) also uses twin TBM (6.5 metre diameter). Single large diameter tunnels have been constructed for several subway lines in Europe, Asia and the Middle East. In Canada, this type of tunnel is being used for the Vancouver Evergreen Line (10 metre diameter), which is currently under construction. The key benefit of the single large diameter tunnel is that it minimizes the areas that must be constructed using cut and cover construction, such as crossovers, resulting in reduced construction disruption at the surface level.


Tunneling Work Sites


What is a Tunnel Mobilization Site?

Tunneling requires “mobilization” sites. The key functions of the mobilization sites are:

  • Launch or maintain the tunnel boring machine
  • Temporary storage of concrete tunnel liner segments
  • Temporary stockpiling and haulage of excavated soil
  • Storage of other equipment and material
  • Location of construction trailers


Tunnel mobilization sites require an area of approximately 10,000 m2 (1 hectare), and are proposed at two locations:

  • Scarborough Centre Station
  • Vicinity of the McCowan Road and Ellesmere Road intersection


Smaller construction sites are required at the tunnel boring machine extraction shaft locations, which are proposed to be located at:

  • North end of the Scarborough Town Centre
  • East of Kennedy Station


McCowan/ Ellesmere Tunnel Mobilization Site

Due to the area required, the McCowan/Ellesmere site will require on the following:

  • Temporary use of a section of the Frank Faubert woodlot (to be replanted at the end of construction); or
  • Acquisition of privately-owned property at the south-west corner of the intersection (Esso gas station and Ellesmere Road plaza or Esso gas station and Stanwell Drive houses)

Further discussions with property owners, and City of Toronto Parks, Forestry and Recreation and Transportation Services are needed to recommend the property for the McCowan/ Ellesmere tunneling mobilization site.




Scarborough Subway Alignment heading north from kennedy station to Scarborough Town Centre
These are electrical substations that convert electric power from Toronto Hydro to an appropriate voltage.

Emergency Exit Building along the Sheppard Subway


Most of the Scarborough Subway Extension is planned to be constructed using a single large tunnel boring machine.

Vancouver Evergreen Line, Tunnel Boring Machine

“Alice” – 10 metres diameter


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