Quote:
Originally Posted by MalcolmTucker
Thanks to the depth of the stations for the most part. Tradeoffs for everything.
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The stations are actually fairly shallow. In the CBD, the station concourses are only a few metres below the surface. The roof of the tunnel in most places is directly beneath the municipal utility level.
Further east near the canal it gets deeper; Rideau Station is about 20 metres below the surface. Even that's not particularly deep.
The reason why Ottawa is able to bore out such a shallow tunnel with minimal disruption at the same time is because Ottawa basically won the geology lottery. Shallow, softish bedrock starts only a few metres below the surface in Ottawa's CBD.
The city also chose Queen Street for the CBD alignment; this reduces interference with underground parking lots and such.
Earlier on in the process before the EA was finished preliminary plans called for a tunnel diagonal to the street grid cutting between Albert and Slater streets which required a much deeper tunnel, almost 40 metres. (This is probably why you're under the impression that Ottawa's tunnel has deep stations).