Making a Solid Choice: Tunnel Crossing Optimization under the Credit River

Stantec is working with the Region of Peel on the design of the Lakeshore Road Trunk Sewer to divert flows from GE Booth Water Resource Recovery Facility (WRRF) to the Clarkson WRRF. The sewer will be constructed from Jack Darling Memorial Park approximately 3.3 km, then crossing the Credit River and continuing an additional 1 km to Elmwood Avenue. Understanding the geology at this important crossing location is key in the design and construction of the project, driving the depth of the tunnel and appurtenances. Initial desktop geotechnical information and historic field investigations in the vicinity of the crossing indicated that there was a risk that the subsurface bedrock valley was deeper under and east of the river than to the west, extending under the east riverbank and adjacent public library resulting in mixed face tunneling at the originally planned elevation. Stantec undertook a comprehensive geotechnical field investigation followed by an evaluation of mixed face tunneling vs. deepening the sewer, so that it would remain in rock. The evaluation concluded that deepening the sewer had the most benefit to the Region from an overall construction, cost, and operations viewpoint.