Toronto, Canada — In a major step toward improving urban flood protection, the Fairbank Silverthorn Storm Trunk Sewer System (FSSTSS) has earned significant industry recognition for its engineering excellence and community-first construction approach. The award-winning Contract 2 of the project is part of Toronto’s long-term Basement Flooding Protection Plan, designed to protect over 4,500 properties from severe flooding events.
Led by the City of Toronto and the EBC Bessac Joint Venture (EBJV), the project features groundbreaking tunneling technology and innovative construction strategies that set new standards for urban infrastructure.
Engineering Achievement Underground
Contract 2 involved the creation of a 2.4 km (1.5-mile) storm sewer tunnel, 4.5 meters (14 feet) in diameter, buried up to 45 meters (147 feet) beneath Toronto’s surface. Designed to navigate sharp curves and tight urban corridors, the tunnel required custom-built engineering solutions.
A bespoke Earth Pressure Balance Tunnel Boring Machine (EPB TBM) was developed with:
- A double-articulated shield
- An 18-meter (59-foot) screw conveyor
- A system capable of navigating complex geometry underground
Innovation Under Pressure
An unexpected face instability during back gallery construction forced the team to redesign the launch strategy. Within three months, the TBM was modified to launch umbilically — an extraordinary engineering pivot that included:
- Redesigning the conveyor and thrusting system
- Reworking muck handling operations
- Achieving all modifications without delaying the schedule
At the 46-meter-deep launch shaft, a new logistics system using hydraulic rail switches, sliding tables, and car movers allowed muck removal and segment delivery without locomotives — maintaining productivity despite the mid-project shift.
Minimizing Community Disruption
To reduce surface impacts, engineers reimagined how adits (access points) were constructed. Instead of traditional large excavations, they used pre-cast jacked round pipes from drop shafts, enabling faster road reopening and quicker restoration of residential driveways — a key factor in earning industry recognition.
Looking Forward
While Contract 2 is now complete, Contracts 3 and 4 of FSSTSS are underway and will continue over the next three years, marking Toronto’s commitment to building a resilient, flood-protected future driven by innovation in infrastructure.
