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Digging the Tunnel: The full scoop

October 21, 2013
Feature Stories

Underground LoaderOttawa is bustling with Construction activity these days.

As the City works hard to renew existing infrastructure and pave the way for our future growth and prosperity, many residents are feeling some impacts of construction. This is particularly true when it comes to getting around downtown.

You may be pleased and surprised to discover that the construction project with the biggest benefit to our future mobility—the Confederation Line transit tunnel—will actually have one of the smallest construction impacts on residents and businesses.

The Confederation Line tunnel, which is currently under construction, is 2.5 kilometre in length, running underneath the downtown core. It will include three new underground Light Rail Transit (LRT) stations:

  • Lyon Station – under Queen Street between Kent and Lyon;
  • Parliament Station - under Queen Street between Bank and O’Connor;
  • Rideau Station – under Rideau Street at the Rideau Centre and Byward Market

The tunnel is being carved through the bedrock by three machines called “roadheaders.”

[caption]Sequential Excavation Method

An image of the sequential excavation method that will be used to dig the Confederation Line transit tunnel under downtown. Credit: Rideau Transit Group. 


The Digging

Each roadheader is approximately 20 metres long and weighs 135 tonnes. The roadheader uses a cutter head to cut through the stone and carry away the debris. The cutter head includes a large rotating drum covered in metal teeth (called pics) that grind the stone and a loading device that carries the debris from the rock face to a conveyer belt at the back of the machine.

Even though the pics are made out of very tough tungsten carbide, they will wear down and need to be replaced. It will take approximately 50,000 pics to carve out the entire 2.5 kilometre tunnel.

Each roadheader will work 24 hours a day, Monday to Saturday and carve out an average of three metres of tunnel per day.

[caption] Sandvik Mining and Construction

The Sandvik MT720 tunnelling roadheader. Credit: Sandvik Mining and Construction



As the roadheader cuts out the tunnel, special underground loaders will carry the debris to one of the three exits:

  • the Western Tunnel Entrance at Lebreton Flats;
  • the Central Shaft near Queen and Kent; or
  • the Eastern Tunnel Entrance near Waller and Laurier Avenue East.

Debris will be stored in the tunnel overnight and is scheduled to be removed during day-time, non-peak hours using approximately three to five trucks per hour.

The Impacts

Most residents won’t experience any impacts from tunnel construction. Most of the work is taking place approximately 15 meters underground, and the roadheader machines cause less noise and vibration than other tunnelling methods. That said, there are some activities related to tunnel construction that you may notice on the surface. These include:

  • Short term explosive blasting will occur at two of the tunnel access points:
  • The movement of construction equipment and excavated material at the east, west and central tunnel entrances will cause minimal traffic impacts.

Small, localized lane and sidewalk closures will begin to occur in 2015, as we begin construction of station entrances and vent shafts.

[caption] Rideau Transit Group

An illustration of sequential excavation under a busy street. Mining will occur at an average depth of 15 metres and will have little impact on the surface. To ensure we are minimizing impacts on the public, all material extraction and transport is scheduled to occur during daylight, non-peak hours. Credit: Rideau Transit Group.


The Results

Downtown Ottawa will be transformed. By moving rapid transit underground, we will reduce congestion and create additional surface capacity for improved streetscapes that are more cycling and pedestrian friendly.

Transit will be faster. A ride from Blair station to Tunney’s Pasture will take less than 24 minutes, saving cross-town transit commuters 10 to 15 minutes each day and offering a more competitive and attractive to commute for those interested in getting out of their cars.

Transit will be more reliable. Rapid transit users will no longer have to contend with foul weather, congestion, accidents and 14 traffic intersections across the downtown core.

On opening day, trains will run every three minutes and fifteen seconds during peak periods. As demand grows, this could be increased to as little as a minute and forty-five seconds between trains.

Learn More:

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