By Rhiannon Russell
Structural problems at the Ross River School are likely a result of a miscalculation of the soil’s moisture content when the building was constructed in 1999, according to the company that installed its underground cooling system at the time.
“We believe that the soil was much drier than was anticipated and so the degradation goes deeper … and that’s what causing the movement of the school,” said Bill Watt, vice-president of Arctic Foundations of Canada Inc.
The building was constructed on permafrost. If soil is moist, it takes longer to thaw out because it holds more latent heat — heat that allows water to turn to vapour. If it’s dry, though, there’s a lack of latent heat and the thaw extends deeper into the ground.
Temperature monitoring equipment has shown that despite a thick layer of frost under the school in the winter, in the summer, it thaws out, said Watt. “And it thaws out to a much greater depth than was ever anticipated. The only explanation for that is that the soils are much drier than what was anticipated.”
Two geotechnical reports by EBA Engineering Consultants Ltd. completed in 1998 show that moisture content readings were taken from 30 soil samples. To determine ground conditions, the company drilled four holes into the permafrost and excavated one test pit to determine the potential for frost heaves.
Both reports recommended a thermosyphon system be installed to freeze the ground in the wintertime, when heat from the building would otherwise cause it to thaw.
The Ross River School has been plagued with structural issues, including cracks in the walls and sloping floors, since shortly after it opened in the fall of 2001. In 2015, it closed for five months and the whole building was relevelled.
In May of this year, after a series of earthquakes, an engineering company assessed the school and recommended it be relevelled again this summer, at an estimated cost of about $1.2 million.
This month, two engineering firms stated in a memo to the Yukon government that the building is structurally safe to occupy, but “continued foundation movements (heaving and settlement) have affected the functionality of the school” and “further remediation is needed as part of a long-term strategy to ensure the continued structural safety of the school.”
At the time of construction, Watt’s company was hired to install the system underneath the school. He describes thermosyphons as a “passive refrigeration device,” because they don’t require power.
Instead, they rely on a cyclical process of evaporation and condensation. A refrigerant — carbon dioxide, in the case of the Ross River School — is added to the system’s radiators. Vapour condenses on the cold pipes and the condensate runs back down into the piping underground.
“What happens is that the heat that goes through the floor of the building will boil the liquid carbon dioxide, change it into a vapour, then the vapour goes back to the top and condenses,” Watt explained.
The system only works in the winter. The idea is that it freezes the ground enough to remain frozen in the summer. During the warmer months, a thick layer of gravel — what’s called a “thaw-stable material” — helps to contain any heat coming from the building.
“We’ve done hundreds of installations all across the Canadian Arctic and this is the only one that we’ve run into this kind of a problem with,” Watt said.
In 2006, as it was clear the ground was not remaining frozen throughout the summer, Arctic Foundations returned to install more thermosyphons around the perimeter of the building. “I think that helped somewhat but it didn’t completely resolve it,” he said.
While the school is set to open on time at the end of August, work on the building will have to be ongoing, according to engineers’ assessments.
One proposed solution is adding refrigeration devices to cool the ground in the summer months. In hindsight, Watt says, this type of system should probably have been installed in the first place.
“That’s the only solution that I can think of,” he said. “If it’s thawing out in the summertime, then cool it in the summertime.”
A March 2017 report includes a loose estimate from Arctic Foundations for the installation of these devices to the existing thermosyphon system — $500,000.
At a press conference earlier this month, Highways and Public Works Minister Richard Mostyn said the government would focus on stabilizing the ground underneath the school first, rather than trying to fix the structure.
“It doesn’t make sense to relevel and then deal with the ground because as you deal with the ground, you change the conditions and the school has to be relevelled again,” he said.
The structural engineer who wrote the May report, as well as a geotechnical engineer hired by the government, support this approach, Mostyn said.
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