Northwest Inner City Upper Plateau Separation Project
Summary
In response to major flooding events in the early 2010s, the City of Calgary identified the need for a new 3.4‑meter (11.2 ft) tunneled stormwater trunk sewer. This system will intercept runoff collected from higher elevation communities, referred to as the Upper Plateau, separate it from the stormwater system of the lower-lying community of Sunnyside, and convey it to discharge on the north side of the Bow River immediately adjacent to downtown Calgary.
- 3.4-meter-diameter (11.2 ft), 765-meter-long (2,510 ft) microtunneled stormwater trunk sewer
- Largest pipe diameter installed by microtunneling in North America at time of project completion
Scope of Work
Delve Underground, as a subconsultant to Associated Engineering, led the design of the shafts and tunnel. During construction, we performed quality assurance reviews for the tunnel lining and shaft structures, as well as daily reviews of geotechnical instrumentation data for the protection of nearby infrastructure and tunnel boring machine (TBM) data to monitor tunneling progress.
Challenges & Innovations
The interface with the urban environment was identified as a major risk for the underground scope of the project. A feasibility study of alternative alignments and trenchless methodologies was performed, with the preferred methods recommended for detailed design.
For each option, Delve Underground identified and analyzed temporary works and ground improvement areas (jet grouting for shaft construction, TBM launch structure), and permanent structures (initial and final lining requirements for tunnels, shafts, and permanent storage facility). Construction methods and constructability were assessed, including TBM, microtunnel boring machine (MTBM), roadheader, open-cut, horizontal directional drilling, and pipe jacking.
The microtunnel was completed in 12 weeks and advanced through weak sedimentary bedrock (mudstone of the Paskapoo Formation), a mixed-face zone, and coarse granular channel fill soil. At the time of completion, this was the largest diameter microtunnel in North America.