McNally/Aecon JV recently completed a challenging 6.8km bore, as part of the 9th Line & 16th Avenue trunk sewer tunnel in Greater Toronto, Canada.
A 3.5m diameter Lovat TBM was used to bore through the tills, silty sands, silty clays, and coarse sands, while under tremendous water pressure – at times, engineers were up to 50m below the water table.
Following a tool-change, McNally/Aecon will bore another 7.2km on the design-build contract: 3.6km with the same machine (“the front of the machine is as good as the day as it went into the ground” – Tim Cleary, McNally area manager); and 3.6km with a 2.4m diameter Lovat TBM.
A total of 15.6km will be constructed as part of the US$520M project in York Region, in the northern suburbs of Toronto. 1.52km will be lined to a diameter of 1.7m, while the rest will have an i.d. of 2.7m. The contract also includes two mining shafts, two exit shafts, and six access/drop shafts. Extensive dewatering has made full-face TBM-excavation possible. Primary support is in the form of steel ribs and lagging. Unreinforced concrete was poured once tunnelling was complete.
