Warmer Winters Forcing Engineers to Rethink Technologies to Chill Permafrost Under Roads

Apr 1, 2016

Rethinking road-building in a warming Arctic  …

Rush-hour traffic if often heavy on Thompson Drive. Most vehicles move along at a brisk pace, probably over the speed limit, along the street that cuts through a permafrost-ridden area just south of the University of Alaska Fairbanks campus.

The smooth flow of traffic may be at least partly due to the smooth pavement on Thompson Drive, which does not suffer from the humps and dips common to most roads built over permafrost in Alaska’s Interior.

Melting permafrost beneath Alaskan roadways creates a sort of roller-coaster surface.
Credit Alaska Department of Transportation and Public Facilities

“And that’s really what’s probably our single biggest maintenance problem with the roads in the Interior of Alaska – thawing permafrost,” says Jeff Currey a materials engineer with the Alaska Department of Transportation.

Currey says Thompson Drive showcases technologies that keep permafrost beneath the roadbed frozen. That prevents the settling that occurs when it thaws, which creates a surface more like a roller-coaster than a roadway.

“Thompson Drive was sort of a poster child for a lot of the permafrost technology,” he said.

Thompson Drive features two technologies. One is a thermosyphon system that uses tubing filled with liquefied carbon dioxide. It’s buried under the roadway and helps transfer cold from the surface to permafrost several feet below.

“These are intended to either slow down thawing or prevent thawing or, theoretically, supercool the permafrost to make it more stable,” Currey said.

Jeff Currey, a materials engineer with the Alaska Department of Transportation, explains how the air-circulating embankment behind him helps preserve permafrost under and around Thompson Drive and Tanana Drive on the University of Alaska-Fairbanks campus. Technologies used on those and other roads built over permafrost were pioneered by Doug Goering, a UAF College of Engineering professor.
Credit Tim Ellis/KUAC

The other technology is the air-circulating embankment, which uses grapefruit-size rocks buried underneath the roadbed and along the shoulders to enable circulation of cold air from the surface to sink to the permafrost layer and warm air from that level to rise to the surface.

“That is a more cost-effective solution,” he said.

Currey says both technologies have worked well since Thompson Drive was built 13 years ago. But he and other engineers now believe they’re going to have to come up with new solutions – because of climate change.

“If the winter temperatures aren’t as cold as they used to be, then these technologies will become ultimately less and less effective over time,” he said.

Next week: Transportation engineers consider strategies on adapting permafrost-preserving technologies to the warming climate of the circumpolar north.