Cole Engineering was retained by the Regional Municipality of Halton for the detailed design, contract administration and inspection of 4.2km long microtunnel project comprised of 2.5km 1200mm ID and 1.7km 1350mm ID pipe construction. The Rebecca Trunk Wastewater Main project includes a total of 14 microtunnel drives (12 rock drives & two (2) mixed face drives) varying in length from 160 meters to 395 meters. Twelve of the drives are curved or composite curves 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 remove existing pumping stations offline.
The rock drives are located within the Queenston Formation and Georgian Bay Formation, 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 included provisions for swelling Shale, interbedded hard layers (Limestone & Siltstone) 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 meters), and pipe requirements including provision for grout ports and gaskets/watertightness.