Niagara Tunnel breaks through

47-ft diameter TBM breaks through on Niagara Tunnel

47-ft diameter TBM breaks through on Niagara Tunnel

This spring the world’s largest hard rock TBM at over 47 ft in diameter broke through on the 6.4 mile Niagara Tunnel Project. Ontario Power and Water commissioned the project as a third tunnel to convey water from the Niagra River for hydropower generation. The tunnel was plagued with major hurdles, including the difficult Queensland Shale unit which caused massive overbreak issues. The tunnel project was a favorite topic of a very entertaining blogger Harold Asmis at Ontario Geo-fish. He had a very wry and pessimistic view of the project and loved to chronicle the many challenges and tribulations faced during the tunnel construction. I tried to keep a running list of his blog posts on the topic of the Niagara tunnel. But regardless of the technical and financial challenges, the completion of the tunnel represents a significant engineering accomplishment! [Source: Tunnel Business Online. Image: Tunnel Business Online]


  1. Yes, technology helps to overcome the adverse ground conditions; TBM is a better and faster solution than the conventional D & B; would be glad to know reasons of time and cost over runs, if any, while driving the TBM through. thnks.

  2. There is a bunch of information on the Ontario Geofish blog and you can start with my [url=]attempt at indexing it[/url]. He’s a rock mechanics guy with experience working for Ontario Power. He’s very entertaining to read as well. I don’t know of any official sources of information on the overbreak and cost overruns. But the Queensland Shale is a highly disturbed rock mass and the tunnel alignment goes through an area where the principal stress direction is horizontal, not a very good combination for tunneling.

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