With the first construction blasts taking place in September and progress moving well along schedule, crews excavating the shaft and tunnel for Ottawa’s new light rail tunnel can vouch for how extremely cold this winter has been.
The winter weather conditions have been the most challenging aspect of the project, says Humberto Ferrer, deputy project director of Rideau Transit Group (RTG) the consortium building Ottawa’s new light rail line. With the project’s three roadheaders arriving on site and being assembled this fall, it was a cold start to the city’s biggest project on record, which reached the 10 per cent excavation mark in early February. In the between months temperatures dropped as low as -17 of (-27oC) on some days.
"We started in December, and those were the most difficult conditions," Ferrer says. "In early December it was very cold. We’ve made a significant investment in our facilities to keep workers warm at the front, and apply shotcrete.
"Once we get deep into the tunnel and all facilities are built we’re not going to be affected by the winter," he says, optimistically. But he also points that cranes stop working around -25oC, and frozen pumps can’t remove water from the tunnel. While much of the equipment is capable of working in cold weather, not the extremes of -29oC, as seen this year.
Despite the cold weather troubles, the project is moving along well. Once the surface level facilities are completed, progress is expected to pick up even more with 24-hour mining, and hopefully warmer weather next year.
Running 12.5km, the 13-station line includes a 2.5km tunnel through the city’s downtown to address a transit bottleneck (Figure 1). The tunnel’s west portal will be located east of LeBreton Station, and there will be three underground stations (Downtown West, Downtown East, and Rideau) before the east portal located north of Campus Station. Each underground station will have platforms 150m long on each side of the tracks.
Key players in the planning and development phases include a preliminary geotechnical program by Delcan Corporation as part of the environmental assessment, Golder Associates performed a detailed geotechnical and hydrogeological investigation as part of the preliminary engineering program and Capital Transit Partners (CTP, a joint venture of Morrison Hershfield Limited, Jacobs Associates, STV Canada Consulting Inc, and URS Canada Incorporated) for the preliminary engineering program.
The City of Ottawa issued an RFQ in July 2011 and later that October announced a shortlist of three consortia. RTG won the CAD 2.1bn (USD 2.13bn) contract for the 12.5km line in late 2012, finalising the contract in February 2013. The Confederation Line has been procured as a Design-Build- Finance-Maintain (DBFM) project. The city is requiring RTG to provide private financing of up to CAD 400M (USD 361) of the construction costs to stand behind overall contract performance, and to maintain the system for at least 15 years.
Deputy city manager for the City of Ottawa, Nancy Schepers is pleased with the decision to use a public-private-partnership (P3) for procuring the Confederation Line. "What was really affirming for me was that the use of a P3 model, it really proved out that the proponents really apply innovation in preparing their proposal, and that’s a real benefit to the owner."
Another advantage has been transferring as much risk as possible to the contractor. "We weren’t sure that that could happen," she says, adding, "We constructed our proposal to allow for flexibility to try and get 100 per cent risk transfer, and we were successful. That was affirming because we thought we had done our homework."
Antonio Estrada, CEO of RTG, says the P3 allows the construction partners to provide more innovation in their construction solutions. "A good example of this is the tunnel. The solution for the downtown section of the Ottawa LRT at the beginning was cut and cover, but we proposed a tunnel, which is much less disruptive," he explains.
"This proposal was key in our offer and this way of building the downtown section in a tunnel is an advantage to the city and all the stakeholders."
Start up
RTG has chosen to use three Sandvik MT720 roadheaders for the excavation of the tunnel. Assembly for the machines started in mid-September 2013 with the first starting mining on November 8, at the West Portal moving east toward Lyon Station.
For tunnelling there is one shaft and two portals: East, which is 75m long by 12m wide, and West, which is 90m long and 12m wide. At the Central shaft, measuring 22.5m long by 14m wide and 18m deep, tunnelling will move east.
Ferrer explains the geology changes between each location though the West portal and the Central shaft are more similar. Blasting was used to excavate the overburden and rock in both of those, and in contrast, there is clay at the East portal.
"We’ve got shoring systems to embed in the rock and then we excavated the rock in the West portal and the Shaft," he says, adding, "In the East portal because the section of rock we have is much less [than the others], we used the roadheader to excavate the rock."
Each roadheader has a cutting profile of 9.1m in width and 6.6m in height, and each cutterhead contains 78 picks made from tungsten carbide.
"There are six different types of support that we are doing. Five for the running tunnel and one when we are below the umbrella and below portal of tunnel in the soft ground in beginning of tunnel," Ferrer explains. In the soft ground, 60m, RTG are doing two headings and then the bench.
The final lining is not yet confirmed, and isn’t required until 2015. RTG is still considering all of its options. Ferrer says there will be some shotcrete, and as much as 95 per cent of it is likely to be cast in place. The route is expected to be in service by May 2018.
Ottawa underground
Once the Confederation Line is in operation, construction on a second phase is planned to extend the light rail west. Part of the 22km-long alignment could include tunnelling, and the project is in the environment assessment phase.
"In terms of what [the] council has approved. There are certainly some sections that will be underground," Schepers says. "Now, will that be tunnelling in the traditional sense, or cut or cover it’s really too early to tell."
It’s very likely Ottawa will bid the work through another P3. Referring the procurement process for the Confederation Line, she says, "you can’t assume you know how the work will be addressed by the proponents and nor should you in the P3, to get the innovation."
In addition to any potential LRT tunnelling in Ottawa, the City will be undertaking a Combined Sewer Storage Tunnel (CSST) as part of its Ottawa River Action Plan to prevent sewer run-off into the Ottawa River. While the project and specific details of the tunnel are still in the planning stage, it is estimated at CAD 15M (USD 13.5M).
As well, the city announced in November 2013 it has partnered with the Province of Ontario on an engineering feasibility study for a tunnel to divert truck traffic congestion in select parts of Ottawa. Currently, 2,600 trucks travel daily through the neighborhoods in the study.
"We want to have strong transportation links between Ontario and Quebec but not at the expense of our nation’s capital," said Ontario Transportation Minister Glen Murray.
The proposed tunnel would eliminate non-local trucks from the core of the city, and is an option that has been previously discussed, but dismissed without any in-depth technical analysis. The city cites an example that "previous interprovincial crossing studies focused on the need to provide additional car capacity through this corridor. However, as the National Capital Region continues to emphasize investments in public transit and alternate transportation modes, providing additional car capacity becomes a lesser priority."
This technical study will cost approximately CAD 750,000 (USD 677,000) and should be completed within 12 months. If the study finds the truck tunnel feasible, a subsequent environmental assessment study would be implemented.
