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Drilling into permafrost study
Researchers seek method to keep ground frozen during road construction

Evan Kiyoshi French
Northern News Services
Published Saturday, November 22, 2014

Keeping permafrost frozen is the focus of a study underway near the legislative assembly.

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The Department of Transportation is performing a permafrost study outside the legislative assembly. - NNSL file photo

Territorial construction crews run into difficulty when excavating frozen ground, said Christian Nesrallah, project officer for the Department of Transportation, because - once disturbed - it tends to turn into a liquid.

"It can be as bad as water,"said Nesrallah.

Dealing with permafrost during construction is extremely costly, said Rod Hildebrant, general manager for NW.T Construction. He said thermosiphons - tubes directing cold air down into the ground - have been installed in the ground around the legislative assembly to keep the ground beneath it safely frozen. He said planting similar convection tubes beneath territory highways could help to prevent their decay after they have been paved.

"Permafrost is a long-term thing,"he said. "As soon as you disturb permafrost it starts there. It begins to melt. It doesn't always happen right away. But you can see it over on Deh Cho Boulevard ... where parts of the road have sunk."

Hildebrant said the cost of rehabilitating disturbed permafrost to a point where work can continue is high, and easier said than done.

Permafrost is a problem for city builders, said Wendy Alexander, acting-manager of public works and engineering. She said she hadn't heard of the test system under construction near the legislative assembly, and can't comment on cost-savings that could result if the test system proves successful, however she did add that dealing with permafrost is expensive.

"We have run into permafrost on other jobs - and it is costly,"she said. "Generally, you don't want to disturb permafrost."

The goal of the research project is to see if passive convection tubes - tubes directing icy-winter air underground into the permafrost - will help to keep it super-cooled throughout the winter, Nesrallah said, allowing road crews to excavate without fearing the earth will turn into a soupy mess. If the project proves effective and feasible, Nesrallah said, the technology could be used throughout the territory. Drilling began two weeks ago and finished up this week, said Nesrallah. Installation of the test system will be completed this week, he said.

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