OLRT Constructors - Dragados, SNC-Lavalin and EllisDon
— April 2019
Tender design, preliminary and full detailed design including execution drawings for the mined twin track running tunnel, three mined station caverns and access shafts.
Ottawa's Confederation Line runs from Tunney's Pasture in the west to Blair station in the east, is 12.5 km long and includes 15 stations. The central piece is a 2.5 km long tunnel, running under the central business district of the city, including 3 underground stations. The twin track running tunnel and 3 underground stations were designed using the mined construction method in order to minimise surface disruption. The underground stations are located adjacent to existing, sensitive and historic buildings and required detailed risk mitigation measures during design. An innovative engineering solution involving a tailor-made excavation sequence and permanent tension ties spanning the cavern was developed.
The geology varied between competent limestone and fractured shale. A soft ground section included variable glacial till deposits of sand, silt and clay layers and a groundwater table close to ground surface.