A refurbished veteran Robbins Main Beam TBM is launched for the 6.3km-long Mid-Halton Outfall project in Ontario, Canada.
The 3.5m diameter machine, which was originally built for the Terror Lake project in Alaska in 1983, has been used all over the world, most recently in Hong Kong. By the time it completes its latest challenge it will have bored nearly 30km of tunnels.
The machine’s latest endeavor will not be without challenges. The rebuilt TBM has been uprated for high-capacity tunneling through hard rock. Geology is expected to consist of laminated shale with interbedded limestone and siltstone layers and a maximum rock strength of 120MPa UCS.
“We have kept this a simple, streamlined, Main Beam machine, but we modified the cutterhead with larger muck buckets so that material can be moved through it faster,” said Robbins Project Manager Lynne Stanziale. In addition, the TBM has been outfitted with fully modernized VFDs, electronics, and high-capacity gearing and motors. The back-up system has also been modified to be mobile enough to cope with two 130m radius curves that the TBM will have to navigate, one in each direction.
“The concept of using refurbished TBMs has great opportunities for value-for-money constructors,” said Christian Zoller, Commercial Project Manager for contractor Strabag, which holds the excavation contract. “Our TBM, ‘Peggie,’ is evidence 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 us to provide the good value for money that a refurbished TBM yields.”
Strabag has completed a number of projects in Canada, including the epic Niagara Tunnel project. In addition to the tunnel, the contractor has been required to excavate two deep shafts for the launch and reception 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 in July from a 12m diameter x 62m deep shaft, and is ramping up production, having excavated more 300m as of early September 2015. “An ongoing challenge associated with the tunneling on this project is the requirement to drive the TBM downhill for the first 4km 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 itself for a distance of 2,100, although the deep alignment will ensure that the TBM remains in the 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 8m diameter shaft located 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. Alhough 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.