Case Study: Region of Peel (City of Mississauga), Ontario - Cooksville Creek Trunk Sanitary Sewer Diversion Using TBM Tunnel Methods

The existing Cooksville Creek Trunk Sanitary Sewer (Cooksville Creek TSS) servicing the downtown core of the City of Mississauga, Ontario, Canada, in the Region of Peel, was nearing its capacity limits and had shown signs of experiencing surcharge events in 2005. To address this issue, a portion of the Cooksville Creek TSS sanitary flows were diverted to the nearby Canadian Pacific Railway Trunk Sanitary Sewer. The diversion strategy redirects a peak flow of 1020 L/s (36 cfs) and involves the construction of approximately 2.0 km (1.25 miles) of 2400 mm (8 ft) diameter tunnel using Tunnel Boring Machine (TBM) tunnel construction methods to accommodate a 1200 mm (4 ft) diameter trunk sewer. This case study details a number of the project design challenges including: sewer and tunnel alignment and profile, tunnel design considerations, corrosion protection measures, sewer ventilation, maintenance hole design and construction, sewer pipe material selection, and construction sequencing.