Adding cold air to permafrost may cure Yukon’s degraded highways.
But the solution comes with a steep cost – about $1 million per kilometre.
Yukon’s Highways and Public Works is looking for long-term solutions to the frost heaves that plague the Alaska Highway between Destruction Bay and the Alaska border.
Battling melting permafrost is the biggest struggle.
The government has called it a threat to northern Yukon highways.
The 200-kilometre stretch between Destruction Bay and the Yukon border is the most affected because of its underlay of ice-rich permafrost, said Robin Walsh, a government transportation engineer.
With warmer temperatures, the permafrost melts and disrupts the road’s foundation and surface.
The Dempster Highway is also plagued with an underlay of permafrost, but because the temperatures are cooler there, it’s not melting and causing as much distress, said Walsh.
“But if climate change continues, as some of the models are predicting, we could see similar distress on highways such as the Dempster in several years from now.”
There is no good, permanent and affordable solution, he said.
“There are techniques out there, but they’re all very expensive and some of them aren’t particularly practical.”
The air-convection system is being tested at Beaver Creek.
In the winter, the cold air is inserted below the highway’s surface through ducts.
Because the cold air is denser than the warm air, it sinks to the bottom of the embankment and displaces the warm air.
The heat is removed from the foundation of the embankment through a natural convection process, allowing the permafrost to stay frozen during the summer.
So far, the results have been successful, said Walsh. But the tests need to continue for several more years to ensure effectiveness.
Each year, this stretch of the Alaska Highway costs about $30,000 a kilometre to repair, not including snow removal.
That’s $6 million for the 200-kilometre stretch between Destruction Bay and the border. On most permafrost-free stretches of highway, repairs average about $4,000 per kilometre, said Walsh.
Since 1977, more than $1.8 billion has been spent rebuilding and maintaining the Alaska Highway through the international Shakwak Agreement. As part of that deal, Washington has contributed $400 million building the North Alaska Highway and Haines Road.
The US funding has to be regularly approved by Congress.
The million-dollar question for Yukon’s Highways and Public Works is whether to continue with its routine repairs, or implement an expensive but permanent solution.
A combination of the two would be the most effective, said Walsh.
More intensive maintenance needs to be paired with these new systems.
“They would only be suitable for very localized applications. So maybe you have a stretch that’s 500 metres long that’s really distressed. You could address that with air convection techniques.”
“Those distresses need to be repaired in order to make sure the highway remains safe for people to travel on.”
Alaska has been much more effective in maintaining its highways.
That’s in part due to the amount of money Alaska puts into its roads.
But the biggest difference between the Canadian and American side of the highway is the Alaskan section’s age.
“Scientific studies indicate when you destabilize this ice-rich permafrost, it takes roughly 40 years to reach a state of equilibrium and to stabilize again, so they’re sort of through that 40-year cycle in Alaska with their part of the highway,” said Walsh.
“Permafrost has been a problem on the north Alaska Highway since the day it was built during the Second World War and it’s typically been addressed through maintenance over the years, heavy-duty maintenance.”
But the Destruction-Bay-to-the-border section was reconstructed between 1992 and 2002. That began when Public Works Canada devolved the highway to the territory.
Reconstruction disturbs the stability of the permafrost and adds heat to the foundation, creating more melting.
It will be another 22 to 32 years before that cycle is complete.
For now, the Yukon government is providing additional funding to repair this stretch.
The government is not announcing the budget because it is in the tendering process, said Karla Ter Voert, spokesperson for Highways and Public Works.
Usually, Yukon uses its own maintenance crews for highway repairs, but because there is so much work to do this year, the government will contract out the work, said Walsh.
Contact Larissa Robyn Johnston at firstname.lastname@example.org