Canadian Consulting Engineer
Tunnelling projects hit snags in Niagara Falls, York Region and VancouverEngineering
Three important tunnelling projects in Canada have hit snags recently, showing how difficult it is to predict condi...
Three important tunnelling projects in Canada have hit snags recently, showing how difficult it is to predict conditions for these types of projects.
At Niagara Falls, Ontario Power Generation is digging a third tunnel to carry water from the Falls, under the town and to the Sir Adam Beck generating station in Queenston. The 10.4-km. tunnel is supposed to be completed by 2009, but it looks as though it will be delayed by at least a year because of unexpectedly harsh conditions.
Last summer Ontario Power Generation reported that they were encountering unstable rock and soils under the St. David’s Aquifer. By September 2007, crews had excavated 1,350-metres of tunnel, less than half of what was hoped. Then this March, OPG reported there were further delays. Strabag AG, the contractor, has a $600-million fixed-price contract to complete the work and wants to realign the tunnel.
Strabag is using “Big Becky,” the world’s largest tunnel boring machine (TBM) to dig the tunnel, which is 14.4 metres in diameter and constructed with a 600-mm thick unreinforced prestressed concrete lining. It is 140-metres deep, parallel to the existing twin tunnels built in 1955, but deeper. The intake is under the existing barrage dam, and will send an additional 500 cubic metres per second of water to power the Beck generating station. Hatch Mott MacDonald and Hatch Acres are owner’s representatives on the project. Designers are Morrison Hershfield and ILF of Germany.
Across the other side of the country in Vancouver, work on the Seymour-Capilano twin tunnels being dug by Bilfinger Berger below Grouse Mountain has been halted half way. The 7.4-kilometre tunnels are to carry water between the Capilano reservoir to a water treatment plant in Seymour, as part of a massive water supply project by the Greater Vancouver Regional District. Bilfinger Berger, which has a $100-million fixed price contract, halted the work in January after falling rock prompted safety concerns. A new safety plan was prepared by Metro Vancouver, but the contractor refused to recommence work.
In late May, Metro Vancouver terminated its contract with Bilfinger Berger and is said to be in discussions with the two contractors who were also in the original bidding. It’s estimated that the work will now cost twice as much to complete. Golder Associates and Hatch Mott MacDonald were the tunnel engineers, and the overall project Seymour-Capilano Filtration Project is being managed by Pacific Liaicon, a subsidiary of SNC-Lavalin.
Lastly, a tunnel boring machine digging part of the “Big Pipe” York-Durham Sewer System north of Toronto is stuck underground going nowhere. McNally and Aecon are the contractors for the 9-kilometre Langstaff trunk sewer, which they were excavating 22 metres below ground. According to reports, 1,800 cubic metres of mud poured into the tunnel, forcing workers to run to escape. They had to sprint almost two kilometres to the entry point, leaving the 10-metre tunnel boring machine and 50 metres of trailing equipment stranded underground at a point east of Dufferin Street, north of Highway 407. The tunnel was sealed, and an insurance probe is to determine what caused the failure. The problem is expected to delay the project by a year. Tomislav Hrkac, project manager for York Region, says they are now planning how to dig a shaft to recover the TBM and in the meantime a new TBM will start excavating from the opposite end from Bathurst Street.
The Langstaff sewer is part of a massive sewage system being constructed to carry waste from York Region to a treatment plant on Lake Ontario in Pickering.