Coxwell Sanitary Trunk Sewer, By-Pass Sewer Tunnel

Coxwell Sanitary Trunk Sewer, By-Pass Sewer Tunnel

Tunnel Segments, Maintenance Holes & Steel Connection Elbows

The Coxwell Sanitary Trunk Sewer (CSTS) built in the 1950s, services 750,000 residents and conveys 400 million litres of wastewater per day to Ashbridges Bay Treatment Plant. The CSTS is the most critical trunk sewer section in the City of Toronto. During a condition assessment, it was discovered that approximately 60m (200’) of the trunk sewer was damaged and there was a high potential for a blockage to develop should there be further deterioration or a collapse of the sewer. CSTS has no redundancy to allow for re-routing of flows in the event of an emergency, such as a significant blockage or collapse of the sewer.

The City of Toronto selected a design build approach to construct a 510m semi-circular tunnel, 2.7m in diameter, around the damaged area of the sewer. The connection of the existing sewer to the by-pass was to be completed during live flow conditions.

We manufactured tunnel segments which were used in the Earth Pressure Balance Tunnel Boring Machine (EPB TBM) to bore and construct the segmented concrete tunnel. Tunnel segment installation started in late 2010 and the tunnel was completed in 2011. We manufactured maintenance holes designed for deep burial and the resulting hydrostatic forces. Additionally, we made steel entry and exit elbows for the permanent connection of the old sewer line to the new tunnelled section.

The contractor encountered construction difficulties at the 42m deep exit shaft due to unstable ground conditions and an abandoned, buried sewage pumping station. After several methods to try and stabilize the ground, the live connection was finally completed on February 22, 2013 in early morning.