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Big Lake Offsite Sanitary Gravity Portion (W14) Project

The Big Lake development and Winterburn industrial areas in northwest Edmonton are growing quickly and required upgraded sewer infrastructure to meet increased demands projected to reach 13 MLD by 2024. The City of Edmonton contracted with Â鶹´«Ã½ to design 2.3 km of 1,200 mm gravity sewer.

Previous projects in this area were highly challenging with schedule delays and difficulty maintaining grade due to extremely poor ground conditions, including a near ground water table, wet sand, peat layers, and the potential for flowing silt and hard cobbles. The alignment crossed two high-traffic roads and Anthony Henday Drive on-ramps. Schedule was also a concern, as sewage from the development would have to be hauled by truck until this sewer was in service.

We used microtunneling to install a combination of Hobas and Flowcrete pipes at depths from 4 m to 11 m, with Permalock casing pipe for the road crossings. Microtunneling allowed the alignment to be shifted from off the road to the center of 199 Street, eliminating soft ground staging and providing better access for maintenance. Hobas is resistant to H2S attack, a condition expected to be prevalent in the initial years of operation with minimal upstream development contributing flow. In the areas with the poorest ground conditions, a switch to Flowcrete Pipe was made to combat buoyancy. Flowcrete is a concrete pipe with an integrally cast FRP liner (addresses corrosion concerns).

To our knowledge, this is the first installation of Flowcrete pipe in North America.