Assembly works are progressing on schedule for the 14.4m diameter Robbins TBM for the Niagara Tunnel Project (T&TI, November 2005, p11) in Canada, claimed to be the world’s largest diameter hard rock TBM.

With boring scheduled to begin this year, the supply programme was tight for Robbins following project award late last year. To meet the delivery schedule and to reduce overall construction costs, Robbins opted to build the TBM onsite rather than its more usual practice of pre-assembling such a machine in one of its workshops first. In early July, the status of the build was that the main drive, cutterhead support, gripper assemblies and rear support had all been assembled onsite. With hydraulics, electrics and cutterhead all due to be finished in July, it is hoped that the machine can be tested with boring commencing this month.

Mike Kolenich, project manager for Robbins onsite, said of the approach: “It’s saving us a lot of time on the schedule.” T&TI was told by Robbins that project contractor, Strabag AG, had expressed its satisfaction with the onsite TBM build and had every confidence in Robbins to meet its schedule.

Strabag was awarded the design and build contract by Ontario Power Generation, (OPG), in 2005 to build a 10.4km long tunnel upstream from the Sir Adam Beck Generating Complex to above Niagara Falls, connecting to the intake shaft. The TBM, dubbed “Big Becky”, will bore an expected 15m advance per day, excavating 1.6Mm3 of rock along the length of the tunnel. The schedule calls for the TBM excavation to be completed in two years, by the end of 2008.

The alignment geology 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.

The open, hard rock TBM will use Robbins’ floating gripper design and be powered by a 4,725kW variable frequency drive that can be increased to 5,040kW. The TBM will use 20” cutters mounted in a back-loading cutterhead.