The Rebecca Trunk Wastewater Main Construction project comprises 4.05km (13,287 ft.) of microtunnel (MTBM) construction including a total of 14 microtunnel drives (12 rock drives & 2 mixed face drives) varying in length from 165 m (540 ft.) to 403 m (1,325 ft.) located in Oakville, Ontario. Twelve of the drives are curved in part based upon requirements to limit impacts to existing utilities, protected trees, and existing structures, minimize easement requirements, maximize clearance beneath environmentally sensitive creeks, and connection locations required to decommission existing pumping stations. The rock drives are located primarily within the Georgian Bay Formation (Upper Ordovician) which comprise shales with interbedded Siltstone and Limestone ("hard layers"). The mixed face drives comprised of Georgian Bay Formation and Glacial Till. All drives are below the water table. Design considerations include provisions for swelling Shale, interbedded Limestone & Siltstone ("hard layers") within the softer Shale, high horizontal stress, areas of limited ground cover (less than 0.4 MTBM diameters), curved and composite curved alignments (minimum radius of 430 m/1,410 ft.), and pipe requirements including provision for grout ports (for lubrication during jacking and grouting after jacking), and watertight gaskets. Construction requirements include a continuous lubrication system, an automated guidance system; and an MTBM equipped with rear loading cutters, a crushing chamber, and a minimum required overcut. The paper presents the design approach taken and the requirements placed within the Contract Documents for the project. Construction commenced in December 2015.
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