Ontario Power Generation: Power Generation: Hydroelectric Power: New Projects : Niagara Tunnel Project

November 2011 Update
At the intake site, where water will enter the tunnel above Niagara Falls, work continues on disassembly and removal of the Tunnel Boring Machine (TBM). In late August, using a 300 tonne crane, the first of Big Becky's six 60-tonne cutterhead segments was safely lifted to the surface from the intake channel previously excavated in the Niagara River bed. By early September, all four of the cutterhead's outer segments had been lifted to the surface and work continues on removal of the various TBM components.

There are six major sections that comprise the cutterhead of the Tunnel Boring Machine (TBM). Each piece weighs about 60 tonnes, requiring a 300-tonne lift capacity crane to get the job done. The crane will remain on site until it is replaced in November by a larger crane needed to lift and remove Big Becky's 80-tonne main beam. Discussions have begun with the Niagara Parks Commission regarding remediation of the lands near the inlet, including a display of all or part of the cutterhead.

At the outlet end, near the Sir Adam Beck generating stations, work continues on the outlet structure that will incorporate the emergency closure gate and will direct the water flowing through the tunnel into the canals that feed the stations. To construct the complexly shaped outlet structure, the workers install formwork and rebar, and place the concrete in several stages. This work is complicated by the need to keep construction traffic moving in and out of the tunnel while the reinforced concrete outlet structure is being built.

Inside the tunnel, work continues on tunnel crown restoration, installation of the upper two-thirds of the permanent concrete liner, and the grouting needed to permanently secure the concrete lining to the surrounding rock. Installation of the upper two-thirds of the permanent liner has progressed beyond 4.6 km. The tunnel crown restoration is an operation that involves installing rock bolts, wire mesh, steel forms and concrete to fill the area at the top of the tunnel, where excess rock broke away during the tunnel mining. This work has progressed to about 5.3 km, which is just over half way along the tunnel.

STRABAG's plan for repair and reinforcement of the tunnel crown support through the area where initial reinforcements and rock fell in July has been accepted by the Ministry of Labour. Installation of the additional rock bolts, wire mesh and shotcrete is underway from both the intake and outlet ends of the affected area.

August 2011 Update
While the tunnel mining (TBM excavation) was completed this spring, there are still a number of activities over the next two years to complete the tunnel construction.

At the intake site where the water will enter the tunnel above Niagara Falls, preparatory work to disassemble and remove the Tunnel Boring Machine (TBM) continues. In the coming months, all of the TBM parts will be removed and most will be scrapped. The TBM cutterhead will be preserved, and discussions have begun to determine the best location to display all or part of the cutterhead.

At the other end of the tunnel, workers are busy building the concrete outlet structure that will incorporate the emergency closure gate and will provide a smooth transition for the water flowing out of the tunnel and into the canals that feed water to the Sir Adam Beck hydroelectric stations. This massive structure will be made from reinforced concrete. Workers are now building the structure formwork, installing the rebar and pouring concrete. When completed the outlet structure will be approximately 30 m long, 20 m wide and almost 40 m high.

Inside the tunnel, work continues on the upper two-thirds of the permanent liner, tunnel crown restoration, and grouting. Installation of the upper two-thirds of the permanent liner has progressed to beyond 3.6 km. The tunnel crown restoration is an operation that involves installing rock bolts, wire mesh, and concrete to restore the area at the top of the tunnel, where excess rock broke away during the tunnel mining. This work has progressed to just beyond five km.

On July 2 about 1,000 cubic metres of shotcrete, steel ribs, wire mesh and loose rock fell from the tunnel crown at about six km from the outlet portal. There were no workers in the area at the time and no one was injured. Under order by the Ministry of Labour, STRABAG (the constructor) immediately restricted access to the affected area in the tunnel and began an investigation into the cause.

The investigation, by STRABAG's engineering consultants, identified the cause as a unique geotechnical condition that does not occur at other locations along the tunnel route. A thin layer of relatively brittle Power Glen shale in the tunnel crown buckled under the high horizontal stress and overloaded the rockbolts. Ongoing surveys to monitor convergence (inward movement of the surrounding rock into the tunnel excavation) will permit STRABAG to identify any other areas of concern along the tunnel and reinforce the initial support (with more or longer rockbolts, additional shotcrete, etc.) to prevent another similar incident. STRABAG's plan to repair the affected area is under review by the Ministry of Labour.

As a result of the July 2 incident, work on the invert concrete (lower one-third of the tunnel lining) has been temporarily stopped until remedial work at the fall of ground is completed.

May 13, 2011 Update
Big Becky breaks through. View the news release and photos on the right side.