On July 22, 2015, a 3.5 m (11.5 ft) Robbins Main Beam TBM began a new chapter in its 
storied 32-year career. Originally built for the Terror Lake project in Alaska, the veteran machine has been used all over the world, most recently in Hong Kong. Including its new 6.3 km (4.0 mi) long tunnel for the Mid-Halton Outfall in Ontario, Canada, the machine will have bored nearly 30 km (18.6 mi) of tunnels since 1983.
The machine’s latest endeavor will not be without challenges. The rebuilt TBM has been beefed up for high-capacity tunneling in hard rock. Geology is expected to consist of laminated shale with interbedded limestone and siltstone layers and a maximum rock strength of 120 MPa UCS. “We have kept this a simple, streamlined Main Beam machine, but we modified the cutterhead with larger muck buckets, so material can be moved through it faster,” explained Robbins Project Manager Lynne Stanziale. In addition the TBM was outfitted with fully modernized VFDs, electronics, and high-capacity gearing and motors. The back-up system was also modified to make it more mobile through two 130 m (427 ft) radius curves that the TBM will have to navigate, one in each direction.
“The concept of using refurbished TBMs bears great opportunities for value-for-money constructors,” said Christian Zoller, Commercial Project Manager for contractor STRABAG. “Our TBM ‘Peggie’ is evidence of that–when well-maintained and professionally refurbished, the lifespan of these machines is extensive. We’re pleased to see that our client Halton Region has the forward-oriented mindset that allows STRABAG to provide its renowned high level of skill and quality, paired with the good value for money that a refurbished TBM yields.”
Contractor STRABAG, who has had several projects in Canada including the epic Niagara Tunnel project, is in charge of the works. In addition to the tunnel, STRABAG had to construct two deep shafts for the launch and exit of the TBM. The scheme involves two sections of tunnel designed to carry treated effluent water from a treatment plant in Oakville into Lake Ontario. The completed system will upgrade water treatment capacity in the Halton Region of Ontario.
The TBM was launched from a 12 m (39 ft) diameter, 62 m (203 ft) deep shaft and is ramping up production, having excavated over 300 m by early September 2015. “An ongoing challenge associated with the tunneling on this project is the requirement to drive the TBM downhill for the first 4 km (2.5 mi) of the tunnel. Keeping the water that infiltrates the tunnel from flowing directly to the cutterhead requires significant effort,” said Terry McNulty, Technical Project Manager for STRABAG.
Management of water inflows is not the only challenge. A portion of the drive will curve to run directly under Lake Ontario for 2.1 km (1.3 mi), though the tunnel is deep enough that it will remain in bedrock. Once the machine has completed its final bore under Lake Ontario, it will be backed out of the blind heading and removed from an 8.0 m (26 ft) diameter shaft in a local park.
“We can already see the potential performance that this TBM will have, once fully assembled and tested. We look forward to the continued support and cooperation with our partner Robbins on this endeavor,” said Zoller. Though the TBM has only recently started up, crews are moving forward with a plan to line the tunnel with mesh panels and ring beams if necessary. A cast-in-place liner will follow on after tunneling is completed in August 2017.