Establishing Thoughtful Design Plans
For generations, the First Nations, or aboriginal, communities have found a home within the area’s vast landscape, using the land for hunting, fishing, trapping and more. Consulting with local populations to identify areas of significant importance, including sacred sites, to avoid disturbing their way of life is crucial step in the planning process. The same amount of intense scrutiny goes into protecting endangered species’ habitats and abiding by environmental conservation regulations. Developing design plans — creating custom routes around restricted areas while limiting environmental impacts — plays a significant role in achieving stakeholder approvals and maintaining community relations.
Within the plan itself, the main design consideration for completing work in northern Canada is the performance of materials — because, at frigid temperatures, many will fail. For this region, all structural steel, including bolts, nuts and hardware, is required to undergo a Charpy impact test to determine energy absorption, or the amount of energy absorbed by a material during fracture, and identify notch toughness. As a rule of thumb, project teams typically request the minimum acceptable value at a specified temperature to meet the Canadian Standards Association requirements. Additionally, the Association of Professional Engineers and Geoscientists of Alberta requires licensed structural engineers have experience working in Canada or similar extreme cold weather environments. Understanding the material property changes in cold environments help them deliver designs that consider environmental constraints and will perform at temperatures reaching minus 40 or 50 degrees Celsius.
Another requirement is a design that’s quick to erect. Depending on the voltage of a transmission line, for example, structures can extend farther than the traditional 250-meter range at 230-kV class, minimizing the number required within a nontraditional design. For AltaLink’s Christina Lake Area Development Project in Northern Alberta, the Burns & McDonnell transmission line team suggested using tubular steel H-frame structures, about 350 meters apart, instead of lattice steel towers because they would take less time to install: one day, rather than a week to build on-site. Though they could have required larger foundation build-up, H-frame structures helped AltaLink meet its in-service date for a new 22-kilometer (km) double-circuit 240-kV transmission line and 240-/138-kV greenfield substation. Guy wire — tensioned cable that adds stability to freestanding structures — will do the trick, too, and installation of the structure mast and guy anchor happens faster compared to a self-supported lattice steel tower.
Foundations, and their lasting performance, are heavily considered in these scenarios as well. Concrete, for instance, isn’t easy to find or work with at temperatures drastically below freezing. In fact, it isn’t allowed unless there’s a heating source nearby to properly install and protect the concrete structures. To address the muskeg, or low-lying marsh made of decomposing organic material, in Northern Alberta, helical screw pile foundations are commonly used. Made of a series of strong columns inserted underground, this foundation is easier to install in softer terrain and provides protection from permafrost as it naturally creates separation between the frozen ground and structure.
To penetrate the shale in Ontario, however, a series of micropiles — consisting of small, high-strength steel casings — can be installed and secured with a steel pile cap, reinforcing the structure base connection within difficult ground conditions.
After establishing a durable design — by evaluating the most economical and effective material, structure and foundation options for the specified field condition — the focus turns to defining the safest approach for the fastest construction. This not only considers stringent Canadian laws but also the safety of the entire project team.