Paula Wallis, TunnelTalk

Client procurement of four new EPBMs and the segments for the lining system is designed to get a head start on a new 15km stretch of 3m i.d. sewer infrastructure for The Regional Municipality of York, located immediately north of the city of Toronto.

The estimated $520 million Southeast Collector Sewer (SEC) contract is scheduled for tender in early January 2010 after a lengthy process of acquiring the necessary Environmental Assessment approval from the Province of Ontario. In advance of the tender, York Region has purchased four new LOVAT 3.6m EPBMs to excavate the 15km tunnel (Fig 1).

Fig 1. SEC alignment and its 13 shafts (in blue)

“This is the first time we have undertaken a purchase of machines in advance of the general contractor's tender call,” said Wayne Green, Project Manager for the owner. “In addition to the TBMs, we also have tenders out for the segmental liner system. We want to have the machines, material and equipment ready to go to work when we award the tunneling contract.” York Region plans to novate the four TBMs and the segmental liner contracts to the successful contractor(s), with the plan to have all four machines operating concurrently. Bids for the liner contract close next Tuesday (September 1, 2009).

Hatch Mott MacDonald and AECOM are responsible for various components of the tunel design on the design-bid-build project that includes 13 shafts. The launch shafts for the four TBMs are identified as Shaft 1, Shaft 4, Shaft 6/7 and Shaft 10, where two machines will be launched in a westerly and southerly drive from large shaft 10 location. The contractor will determine the order of the launches.

With purchase of the machines, the client has specified vacuum lift for the segment erector systems and tail grouting. “In most cases, it is the contractor's preference whether to tail grout or liner grout,” said Green. “However we specified tail grouting for these new machines to maintain a good grout seal as the machines move forward.” Grouting throught the segments was the method employed on the project’s Langstaff Tunnel contract that suffered a major collapse on May 2, 2008 (Ref 1).

TBMs ordered similar to this used on other projects

Ground conditions anticipated along the tunnel alignment consist of glacial tills both, plastic and non-plastic, sands, silt, gravel and clays. Cobbles and boulders of various sizes are also expected. “For this particular project we chose a profile that allows us to stay mostly in the Newmarket Till so we have some very good soil conditions to work with," said Green. “At the very start of the job, we excect some surficial water-bearing sands. As we progress from high to low, we go into a very tight till and move back into water bearing layers towards the end of the project in the Finch Ave area.”

Several contractors are known to be interested in bidding the work including McNally Inc who has completed five major tunneling projects for York Region since 2000. This includes the Langstaff Tunnel and the ensuing collapse and recovery. Tunneling work on that delayed contract is coming to a close this week (August 28, 2009), some 10-months passed the original finish deadline of November 5, 2008.

The new SEC trunk sewer pipe is part of York Region’s $800 million, 14-segment sewer network. The one-pass segmentally lined tunnel will carry sewage from York Region to a treatment plant in Durham Region in the southern part of the City of Pickering. Expanding and building the new sewer collector is necessary to service planned and approved growth for both regions.

References

TBM recovery reveals the unexpected - TunnelTalk, Aug 2009
Buried EPBM recovery in Toronto - TunnelTalk, Aug 2008