Closely following the news of the contractor award to Strabag AG for the 10.4km long Niagara Tunnel Project (T&TNA, September, p5) comes the announcement that Robbins has been chosen to supply the TBM – at 14.4m diameter, claimed to be the largest hard rock TBM in the world.

The new 12.5m id tunnel will be used to divert water from upstream of Niagara Falls to the Sir Adam Beck hydroelectric generating station. The TBM is due to be delivered in 12 months, with boring scheduled to begin in the autumn of 2006. Plans call for TBM excavation to be finished just two years later by the end of 2008.

The open, hard rock TBM will use Robbins floating gripper design and powered by a 4,725kW variable frequency drive that can be increased to 5,040kW. Robbins said Strabag had decided to use 20″ cutters mounted in a back-loading cutterhead, introduced by Robbins with a claimed 35-40% ring wear volume than 19″ cutters, although 19″ cutters can also be used without modifying the cutterhead.

Geology along the alignment consists of limestone, sandstone, shale and mudstone. The majority of the rock varies in strength from 100 to 180MPa, although some sections are as low as 15MPa.