NWIC Upper Plateau Separation
Client:
City of Calgary
Location:
Calgary, Alberta
Year:
2023–2024
Project Scope
Whissell Contracting Ltd. served as the prime contractor on the Northwest Inner City (NWIC) Upper Plateau Separation project — the largest project undertaken by the firm in the preceding three years and one of the most technically complex microtunnelling projects in North America. The project was designed to mitigate chronic storm flooding in Calgary's inner-city northwest communities by separating combined sewer flows and routing stormwater to the Bow River via a new dedicated trunk system.
- Installation of a 765 m curved-alignment microtunnelled storm trunk using 3.4 m internal diameter jacking pipe with 328 mm thick concrete pipe walls — the largest diameter microtunnel in North America at the time of construction
- Construction of launch and reception shafts to support tunnelling operations
- Construction of a new outfall structure on the Bow River
- Installation of a storm siphon and associated outfall infrastructure
- Coordination with ENMAX for utility crossings throughout the alignment
- Full traffic accommodation, environmental protection measures, and community interface management
Challenge & Mitigation
The curved tunnel alignment, combined with the unprecedented pipe diameter and wall thickness, required highly specialized equipment configuration and continuous monitoring to maintain line and grade through the arc. Coordination with ENMAX for live utility crossings along the alignment added significant complexity to the tunnelling program. Whissell's team developed detailed shaft sequencing and tunnelling protocols to manage ground movement risks and maintain zero-settlement tolerances throughout the operation.
Value Add Solution
Whissell's in-house tunnelling expertise and self-performance model allowed the team to maintain direct control over the critical path tunnelling operations. By managing the microtunnelling scope directly rather than subcontracting, Whissell was able to respond rapidly to ground condition variability and maintain schedule integrity on what was, at the time, a record-setting installation in North America.
