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Tunnel dig: Three years for 3.2 km

It will take up to three years to complete the 3.2-kilometre transit tunnel through Ottawa’s downtown.

It will take up to three years to complete the 3.2-kilometre transit tunnel through Ottawa’s downtown.

Most of the $735-million tunnel from Bronson Avenue and Campus Station will be dug out by a tunnel-boring machine.

The machine would likely be launched from the parking lot north of Scott Street and the tunnel liners could be fed in from that site. It would also be a temporary dump site for rock removed from the tunnel.

“There would be a fairly high level of activity in that area for likely two and half to three years for the construction of the tunnel and the underground stations,” said project manager David Hopper, an engineer from Delcan Corp.

The machine digs its hole like an earthworm, explains Hopper. It uses jacks to eat into the rock about 1.5 metres at a time and pushes crushed rock out of the tunnel on a conveyor. Depending on the type of rock, the machine could dig up to 10 metres per day.

As the boring machine plods forward, concrete liner rings are installed in the newly dug out sections, essentially creating a completed tunnel along the way.

Although the tunnel is being built 30 metres below ground to minimize impact on utilities and building foundations along the route, Hopper said there will be some surface work done to build ventilation for the stations.

 
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