Local contractor Foraction, Inc., headed the excavation of the 4km-long tunnel with a TBM launch in December 2014. Roger Lepinay, Equipment Manager for Foraction, Inc., said the ground was "almost ideal", with a few difficult sections.
"Below Montreal there is mostly thinly bedded limestone, with some shale and intrusive igneous dykes," said project geologist Brigitte Gagné for company Exp Service Inc. While the limestone averaged 100-150 MPa UCS, rock in the intrusives ranged from 100-300 MPa. The dykes were as small as 1m wide and as large as 100m. The contractor was able to successfully navigate these sections despite the varying rock strengths.
Even with geologic challenges including some water inflows and over-break in small sections, the contractor was able to achieve advance rates of up to 38m per day in two shifts of 9.5 hours each, according to Robbins. Much of the ground was self-supporting, though the contractor installed rock bolts every 2.5m into portions of the tunnel crown, while mesh, rock bolts, and steel sheets were used in the sections of unstable rock.
The Rosemont reservoir was built in 1960 to increase water supply to the city and a geotechnical study for the tunnel was carried out in 1977. However, other major infrastructure projects soon took priority and the project was placed on hold. By 2010, the population of the city had increased dramatically and problems with the existing reservoirs put the project back on the fast track. The large reservoir that sat idle for decades will now be used to improve much of the city’s water supply.
As of mid-January the contractor is working to ready the tunnel for installation of the carrier pipe, consisting of 2.13m I.D. pre-stressed concrete cylinder pipe (PCCP). Crews will then grout the pipe in place in preparation for the Rosemont Reservoir to come online.
