Toronto’s Future, Flood-Protected: Engineering Excellence Beneath the City

As part of Toronto’s long-term Basement Flooding Protection Plan, the Fairbank Silverthorn Storm Trunk Sewer System (FSSTSS) is a transformative infrastructure project designed to protect more than 4,500 properties from flooding. Now, the project has received a major industry award recognizing the team’s innovative engineering, technical excellence and strong commitment to minimizing disruption in the community.

Led by the City of Toronto and the EBC Bessac Joint Venture (EBJV) team, the project’s award-winning phase, Contract 2, involved the construction of a 2.4-kilometer (~1.5 mile)-long, 4.5-meter (~14 foot)-diameter storm sewer tunnel, buried as deep as 45 meters (~147 feet) beneath Toronto. 

Threading through tight urban corridors with curves as sharp as 120 meters (~393 feet), the tunnel required a highly specialized approach. The team worked with Bessac to develop a custom Earth Pressure Balance Tunnel Boring Machine (EPB TBM) featuring a double-articulated shield and an 18-meter (59-foot) screw conveyor capable of navigating the tunnel’s complex geometry.

A defining moment came when the team encountered an unexpected face instability during the construction of a back gallery. With the TBM already on site and the original launch method no longer viable, the team quickly re-engineered the strategy. In just three months, they modified the TBM to launch umbilically — an extraordinary feat that required redesigning the screw conveyor, thrusting system and muck handling operations, all while staying on schedule.

The team also introduced a novel logistics system at the 46-meter (~148 foot) deep launch shaft. Using hydraulic rail switches, sliding tables and car movers, they managed muck removal and segment delivery without locomotives — keeping excavation on target despite the mid-project pivot.

To reduce surface disruption, the team reimagined the construction of adits, the access points that connect the tunnel to the surface. Rather than traditional large-scale excavations, they used pre-cast jacked round pipes from drop shafts, allowing for earlier road reopenings and faster restoration of residential driveways.

These innovations not only kept the project on track but also demonstrated a deep commitment to reducing community impact — an essential factor in the award recognition. 

While Contract 2 is complete, the broader FSSTSS initiative continues. Contracts 3 and 4 are now under construction and will carry the momentum forward over the next three years. Together, these efforts represent a bold step toward a more resilient Toronto, where infrastructure meets ingenuity to protect communities for generations to come.