Tunnel Project to Address Toronto’s Overflow Issue


Construction is underway on a 10.5-km (6.5-mile) tunnel beneath Toronto that will prevent combined sewer overflows from entering Lake Ontario and the Don River. Michels Canada and Tunneling operations are partnering with Jay Dee and C&M McNally on the joint venture expected to be completed in 2024.

The 6.3-metre (20.6-foot) diameter Coxwell Bypass Tunnel is being mined through hard rock 50 metres (164 feet) deep by “Donnie,” a 115 metre (377-foot) long tunnel boring machine (TBM) that weighs nearly 1,000 tonnes.

The tunnel and TBM are accessed by five major shafts and 12 drop shafts. During construction, the TBM’s rotating cutter head will break up shale bedrock to create the tunnel. The rock spoils will be transported by conveyer belt to the back of the machine, transported to the entry shaft, lifted to ground level and taken by another elevated conveyor belt to a pile on the site’s edge. As the TBM advances, it will systematically place precast concrete segments into rings to line the tunnel.

When completed, the tunnel will capture, store and transport a mix of overflow rainwater and sewage to a treatment plant before its eventual release in Lake Ontario. PLCAC Member, Michels Canada Co., is proud to assist the City of Toronto with the largest and most significant stormwater management program in the city’s history.