Case Studies: Current Projects
Largest Hard Rock TBM Assembled Onsite
- Machine Type: Main Beam TBM
- Diameter: 14.4 m (47.5 ft)
- Tunnel Type: Hydroelectric
- Tunnel Length: 10.4 km (6.5 mi)
- Owner: Ontario Power Generation (OPG)
- Contractor: Strabag AG
- Location: Queenston, Ontario, Canada
Project Overview
The Niagara Tunnel Project is an ambitious project to tunnel 10.4 km (6.5 mi) from the Sir Adam Beck Generating Complex to above Niagara Falls. The new tunnel will increase the power supply for owner Ontario Power Generation (OPG) by 150 MW and will help to bolster the current power system, which is close to exceeding its capacity during peak months.
OPG awarded the construction contract to Austria-based Strabag AG, who chose a 14.4 m (47.5 ft) diameter Robbins Main Beam TBM to bore the tunnel. The setup also includes a 105 m (345 ft) long back-up system, which will transport 1.7 million m3 (2.2 million cubic yards) of muck over three years via conveyor belt.
The tunnel is located predominantly in Queenston shale with some limestone, dolostone, sandstone and mudstone up to 200 MPa (29 ksi) UCS. The rock along the tunnel bore path is known to have high in-situ stress and there is potential for squeezing ground. An initial rock support lining of wire mesh, steel ribs, rock bolts, and shotcrete will be installed as the TBM advances. After tunnel excavation is completed, an in-situ placed concrete lining will be installed, and the final lining will include a waterproofing membrane system to ensure that water does not seep from the tunnel into the rock and cause swelling.
The Main Beam TBM, the largest hard rock TBM in the world, was assembled onsite in under 12 months -- ahead of a tight delivery schedule. The onsite assembly is considered unprecedented for such a large TBM. The TBM began boring in September 2006.
The Main Beam TBM is the also first ever to utilize back-loading 20-inch cutters, which increase cutter life and reduce cutter changes in hard rock. Both 19-inch and 20-inch cutters can be installed in the cutterhead. The machine has a cutterhead thrust of 18,462 kN (4,150,422 lb) and a maximum torque of 18,670,000 N-m (13,770,285 lb-ft).
Updates of this project will be posted as boring continues.
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