Owner
City of Ottawa
Client
OLRT Constructors - Dragados, SNC-Lavalin and EllisDon
Cost
$2.1 billion CAD
Timeframe
March 2012
— April 2019
Services performed
Tender design, preliminary and full detailed design including execution drawings for the mined twin track running tunnel, three mined station caverns and access shafts.
Description
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.
Geology
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.
Location
Ottawa, Canada
Highlights
- 3 large mined caverns & twin track running tunnels located mainly in limestone rock mass
- Sensitive urban environment in close proximity to existing infrastructure
- Minimum impact on buildings and basement by tailored excavation sequence
Downtown station located between high-rise buildings
Downtown station construction sequencing including tie-backs