Downtown Ottawa Transit Tunnel - TunnelTalk
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Plan for LRT under downtown Ottawa Jan 2010
Paula Wallis, TunnelTalk
Twin 3.2km (2 mile) tunnels and four underground stations are the cornerstone of a Can$2.1 billion light-rail (LRT) project moving forward in Ottawa, Canada.
Last week (January 13, 2010) the Ottawa City Council approved the recommended plan and directed staff to being an expedited, maximum six-month, environmental assessment process on the Downtown Ottawa Transit Tunnel (DOTT) that could get Provincial approval by May of this year.
The underground works are part of an ambitious plan to remove transit buses from the city center. Phase 1 of the new electrified grade-separated project includes about 12.5km (7.8 miles) of LRT between Tunney's Pasture and Blair Stations, primarily on the existing Transit way corridor. Thirteen stations have been identified, including the four underground stations to serve the downtown and the University of Ottawa Campus (Fig 1). Each station is designed with a center platform of 180m (590ft) long to accommodate four-car LRT trains to begin with and six-car trains in the future.
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Fig 1. Preferred alignment of Ottawa's LRT line with the tunnel segment in the yellow area

The recommended plan also includes a LRT maintenance and storage facility in the vicinity of St. Laurent, south of the Queensway. LRT trains will enter the underground section at the western portal of the twin tunnels, located east of Le Breton Station near Brickhill Street and run through the downtown core area, veering southeast to re-surface south of the Campus Station (Fig 1).
According to the City's functional design documents, an EPB TBM is anticipated to excavate the twin tubes through varying ground conditions. The tunnels will be excavated at a depth of about 30m to 35m (98ft - 114ft) to avoid impacts to building foundations and utilities and clear the Rideau Canal. Cut-and-cover will be limited to the west and east tunnel portals and to construct entrances to the stations and the vent shafts. The three downtown stations will be excavated using conventional methods from within the tunnels, and all of the excavated material will be hauled out to the LeBreton work site. The Campus Station will be constructed using the traditional open cut excavation.
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Depth of tunnels and section of an underground station

The TBM will be launched from the west portal between LeBreton Station and Bronson Avenue and will progress to the east tunnel portal located south of Mann Avenue.
According to Dennis Gratton, a senior project manager with the city, the preliminary geotechnical studies indicate substantial groundwater issues. "The majority of the alignment is in limestone, with the section from Rideau Station to the Campus Station in Sandy Till," said Gratton. Preliminary studies also indicate three inactive faults cross the tunnel alignment in the downtown core that will likely affect the quality of the bedrock and the hydrogeological regime. More detailed testing of the geotechnical and hydro-geological conditions will be advanced in the preliminary and detailed design phases.
Consulting firm Delcan Corporation is the prime consultant on the project with Halcrow as the tunnel planning and design expert.
A total of 130 properties will be needed for the project, including 50 owned by the City, 50 owned by the Federal Government, 10 by the Provincial government and 20 privately owned properties.
As the planning phase moves into environmental review, funding of the $2.1billion project has been called into question. The estimated cost includes property acquisition, design, project management, construction, vehicles and contingency. The underground segment is anticipated to cost $735 million. The surface works are expected to cost
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Fig 2. Piechart of cost breakdown

$540, with another $515 million for the maintenance facility and trains, $160 million for acquisition of property, public art and insurance, while $100 million will be set aside for contingencies and $50 million for the project office (Fig 2).
The Premier of Ontario, Dalton McGuinty recently committed Can$600 million to the project, but has stated that any cost overruns would be borne by the residents of Ottawa. If Canada's Federal Government also commits $600 million, Ottawa would have to come up with $900 million for the project. This is $200 million more than the one-third share it was hoping to cover. The City is in the process of identifying funding sources.
The DOTT is Ottawa's first project to take advantage of a June 2008 change in provincial law that allows projects to build on past planning decisions to advance transit projects through an expedited environmental assessment process. "We can complete the environmental assessment (EA) process in less time because the planning study addresses many of the issues we would normally address during the EA", said Gratton. Once the Environmental Project Report is submitted, the Ministry of the Environment has 35 days to make a decision. If no decision is render at the end of 35 days the project is considered approved. While the Province is expected to approve the DOTT environmental assessment by May, the Federal environmental assessment process, which requires more design details, is expected to be complete in early 2011. If all goes well, construction could begin in 2012 and take three years to finish.
Downtown Ottawa Transit Tunnel

           

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