Helical Piles Support Structures at Switching Station

The owner of a large live switching station located in Toronto required a cost-effective foundation solution for the support of towers, equipment skids, cable trays and lightning masts. The soil conditions throughout consisted of loose fill in which conventional footings would not be sufficient to withstand the loading of the proposed structures. In addition, there was a possibility of contaminated soil. Stringent deflection criteria and installation tolerances were required to support the sensitive nature and final design of the structures.

EBS Geostructural was chosen because of their design-build capabilities and their ability to work closely with Hallex Engineering Ltd. (structural engineers) and the geotechnical engineers to provide a complete foundation solution with Helical Piers. Helical Piers are a deep foundation system that supports or resists compression, tension and lateral loads. With end-bearing Helical Piers, loads are transferred down a shaft onto helical bearing plates and into load bearing soil.
Applying torque to the shaft installs the helical pier. The helices minimally displace the soil; therefore no vibrations or spoils are created during installation. A compressed construction schedule required quick mobilization and the use of EBS’s in-house design team

A Chance® Helical Pier installation was chosen for the following reasons:
• Minimal vibrations and spoils from the installation of Helical Piers made it possible to work in close proximity to existing live hydro equipment
• There was tight access for installation equipment including overhead obstructions
• Minimal excavation was required to support the proposed structures
• Installation continued in the winter months (unaffected by cold temperatures)

Helical pier depth ranged on site from 10 metres (32 feet) to 15 metres (50 feet) from grade. Various pieces of equipment and installation methods were utilized. Load capacities ranged from 130 kN to 800 kN in compression and 90 kN to 400 kN in tension depending on the application and the owner’s requirements. The exterior of the pile was grouted for additional capacity and protection against stray currents inducing corrosion in the helical pier. Several compression, tension and lateral load tests were completed for the owner and consultants to verify the capacity of the helical piers. The construction of the superstructure could continue immediately upon the installation of the helical piers.

Compression Load: 890kN (200 kips)
Tension Load: 845kN (190 kips)
Depth: 10 to 18 metres
Total Number of Helical Piles: 108