The Niagara Tunnel Project

Ontario Power Generation’s Niagara Tunnel Project includes the planning, design and construction of a 10.2 km long, 12.7 m internal diameter tunnel and associated facilities to divert an additional 500 m3/s of water from the Niagara River upstream from the Horseshoe Falls to the existing Sir Adam Beck generating stations near Queenston. The design / build contractor, STRABAG Inc, used the world’s largest hard-rock tunnel boring machine (14.44-m diameter) to excavate the tunnel. Construction of the tunnel includes initial support provided by steel ribs, wire mesh, rockbolts and 150 mm (nominal) of shotcrete, and final lining comprised of an impermeable polyolefin membrane and 600 mm of cast-in-place, unreinforced concrete.

The concrete liner is cast in 12.5 m blocks using separate invert (lower one-third) and arch (upper two-thirds) operations that are currently in progress. Subsequent contact and pre-stress grouting operations will lock the concrete liner into the host rock and ensure that the tunnel liner remains in compression under all operational conditions. Reinforced concrete intake and outlet structures will incorporate the isolation gates and efficient transitions required to minimize head losses. When operational, the Niagara Tunnel will deliver enough additional water to increase average annual energy output from OPG’s Sir Adam Beck stations by about 1.6 billion kilowatt-hours – enough to supply 160,000 Ontario homes with clean, renewable hydroelectric power.

Click for more details:2012 Mar 27 IMechE-CCB Rick Everdell

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