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Preventative Rehabilitation of the Fairfield CTS to allow undermining for the Eglinton Crosstown LRT


Metrolinx, a Government of Ontario Agency, is currently undertaking construction for the Eglinton Crosstown Light Rail Transit (ECLRT) project which is, in total, 19 km long, 10 km of which are constructed in tunnels.

Eglinton Avenue, a major arterial road in Toronto, accommodates four (4) lanes of traffic. The area has been developed approximately 100 years ago. The ECLRT tunnels run primarily under the Eglinton Avenue Right of Way (RoW) and are passing under significant existing infrastructure including trunk brick sewers which have been deemed to be at risk of failure due to losing ring compression as a result of ground settlement due to the tunneling operations. As a precaution, to mitigate the risk of catastrophic failure, these brick sewers were lined using Cured in Place Pipe (CIPP).

One tunneled section passes directly under the Fairfield Combined Trunk Sewer (CTS) – a 1200 mm (48 inch) diameter brick sewer consisting of two or three ring brick cross sections (depending on depth), likely constructed in a hand mined tunnel. The undermined section of the sewer varies in depth from ~7 m to near ~21 m (to invert). A jet grouted station headwall had to be constructed in the upper reaches of the sewer, creating a sub-section where differential settlement would occur. It was therefore anticipated that the Fairfield CTS would likely loose compressive ring forces and collapse catastrophically.

The City of Toronto (the City) requires CIPP liners to be designed to the “Fully Deteriorated State”, meaning that the host pipe will not provide/contribute any structural support. The City had, due to the high risk impacts from failure (100’s of flooded basements), mandated that a Safety Factor of 3.0 be used for the design. The depth of the sewer, high water table and restrictions on the Structural Dimension Ratio of CIPP liners meant that the Safety Factor could not be achieved in the design using a single pass liner installation.

Relining of combined sewers requires approval from the Ministry of the Environment and Climate Change (MOECC) to ensure that relining does not cause additional combined sewer overflows. The City’s model showed significant flows surcharging in the upper reaches of the sewer. An extended period of flow monitoring and calibration was required to confirm the existing and projected hydraulics to show how the sewer would perform following relining.

The hydraulic capacity of the sewer was in the range of up to 2.3 mᶟ/s. Given the depth of the sewer of up to 20 m, bypass pumping the full capacity of the sewer was deemed not economically feasible; this would have required a long-term full closure of Eglinton Avenue and significant excavation to allow pumping access to the sewer.

This paper summarizes how these challenges were addressed using an innovative way to minimize flooding and construction risks.

Conference Paper Details

Session title:
Utilities Management
Rüsch, P.
Jacobs, M.
Tunio, I.
Construction, Maintenance and operations