COMBATTING RECURRING FLOODING THROUGH ADVANCED WATERWAY MANAGEMENT

The Fairbank Silverthorn Storm Trunk Sewer System represents a transformative investment in stormwater infrastructure for the City of Toronto. Valued at approximately $400 million, this critical initiative is designed to combat chronic flooding while modernizing aging infrastructure originally constructed in the 1950s.

Spanning four city wards, Toronto St. Paul’s, Eglinton–Lawrence, Davenport, and York South, the project delivers a comprehensive waterway management solution. At its core is a three-kilometre-long, 4.5-metre diameter storm trunk sewer, supported by 17 kilometres of collector sewers and 320 inlet control devices, including maintenance holes, catch basins, headwalls, and interconnected piping.

Once complete, the system will significantly strengthen the area’s resilience to extreme weather events by:

• Providing flood protection across a 140-hectare catchment area
• Reducing basement flooding risks for more than 4,645 homes
• Benefiting over 12,500 residents
• Preventing approximately 40 million litres of annual combined sewer overflows into Black Creek and surrounding waterways

Funded by the City of Toronto with support from the Government of Canada, this project represents a long-term commitment to sustainable water management and community protection.

THE CHALLENGE

The Fairbank Silverthorn community has experienced repeated flooding over the past decades, with major storm events in 2000, 2005, and 2008 exposing the limitations of the existing combined sewer system.

Addressing these recurring issues required more than capacity upgrades and demanded a resilient, forward-looking solution capable of managing increasing storm intensity within a dense urban environment. The project called for deep tunneling through complex ground conditions, installation of large-diameter infrastructure in soft soils, and execution within tight timelines while minimizing disruption to surrounding communities and maintaining strict safety standards.

THE SOLUTION

To support this large-scale waterway management initiative, DECAST supplied precision-engineered Precast Concrete Tunnel Liner (PCTL) segments designed for high-performance tunneling applications.

With a 4500 mm internal diameter and 5000 mm external diameter, each ring was composed from six pieces. The system was designed and engineered to deliver both structural integrity and long-term hydraulic efficiency.

Gasketed joints ensure watertight performance, preventing infiltration and exfiltration, which are critical for protecting surrounding soils and nearby waterways. Integrated features such as bolt pockets, alignment indicators, and grouting sockets enabled efficient installation and consistent assembly within the tunnel environment.

Manufactured in a controlled facility setting, each segment achieved exceptional dimensional accuracy, consistent concrete quality, and durability required for long-term stormwater conveyance.

Key Product Features

• Six segments per ring forming a complete structural unit
• 4500 mm internal diameter / 5000 mm external diameter
• Average 1300 mm ring width
• Gasketed joints for watertight performance
• Integrated features: Bolt Pockets, Alignment Indicators, and Grouting Sockets

INSTALLATION & EXECUTION

Tunneling operations began on May 8, 2023, with the launch of a 270-tonne Earth Pressure Balance Machine (EPBM) from a 40-metre-deep shaft at Fairbank Memorial Park. The TBM is approximately 80 metres long when assembled, advancing through soft ground conditions while installing precast segments in real time.

A continuous, synchronized process of excavation, segment placement, ring assembly, bolting, and grouting ensured steady progress and high productivity. On October 2, 2024, the machine successfully broke through the extraction shaft, marking a major milestone in the project.

 Installation Process

1. Excavation and TBM advancement
2. Segment lifting and positioning
3. Ring assembly (six segments per ring)
4. Ring closure and bolting
5. Grouting of annular space
6. Continuous cycle progression

In total, 2,410 metres of tunneling were completed, with approximately 1,850 rings installed by EBC Bessac, specializing in large-scale tunneling and underground projects. Operations achieved an average production rate of 10.5 rings per day (approximately 13.6 metres), supported by continuous weekday operations.

MANUFACTURING EXCELLENCE

DECAST maintained a production rate that exceeded installation demand, ensuring a consistent and reliable supply of segments to the project site. With limited on-site storage, segments were strategically staged at our Stouffville facility and delivered in sequence to align with tunneling operations.

This delivery approach optimized the sites efficiency while reducing congestion and handling requirements. The use of PCTL’s has resulted in many benefits to the project, some of which are listed below.

Enhanced Safety

• Reduced on-site labor exposure
• Minimized interaction with active excavation zones
• Controlled, repeatable installation process

Environmental & Community Benefits

• Reduced surface disruption compared to open-cut methods
• Lower noise and impact within surrounding neighborhoods
• Efficient tunneling minimized environmental footprint

Quality & Performance

• Factory-controlled production ensured precision and consistency
• Watertight gasketed joints enhanced long-term system integrity
• Smooth internal bore reduced friction and improved hydraulic performance

The Fairbank Silverthorn Storm Trunk Sewer System demonstrates DECAST’s ability to deliver engineered solutions that directly address recurring flood challenges while supporting sustainable waterway management.

Through advanced precast technology, coordinated logistics, and engineering expertise, DECAST has contributed to a resilient infrastructure system that protects communities, preserves local waterways, and supports the City of Toronto’s long-term stormwater management strategy.