Paved divots, asphalt crevasses, chuck holes, nature’s speed bumps. Call them what you want, “frost heaves,” are the seasonal bane of every Maine driver.
An undeniable, if unwelcome sign of spring, frost heaves — an upward swelling of soil occurring where there are seasonal freezing and thaw cycles — create everything from minor annoyances to major hazards on roads from Kittery to Fort Kent.
“You need three things to create a frost heave,” said Clifton Curtis, assistant highway maintenance engineer with the Maine Department of Transportation. “You need frost-susceptible soil like clay, moisture, and freezing temperatures, [and] Maine has all three so I guess we are a winner.”
While drivers and road maintenance crews only see the rises and falls of the frost heaves on the road, Curtis said there is a lot going on under the surface to create the road condition.
“Water gets into what is under the road and when that water freezes it expands [and] as the winter goes on more water is drawn in. It freezes and the soil rises, pushing up the road,” Curtis said. “When the soil starts to thaw in the spring, some areas will thaw faster, causing the soil to retract and that part of the road will drop, creating what we call ‘frost heaves.’”
To avoid frost heaves, according to Dr. Melissa Landon, associate professor of civil and environmental engineering at the University of Maine, the best bet is to build roads over soil that does not trap water which can then freeze in the winter.
“In areas where sand is present like on [Route 9] the Airline where part of the road is built on a glacial esker, which is basically a big pile of sand, you often won’t see frost heaves,” Landon said. “You are mostly going to see them where the soil beneath the road is the type that traps and holds moisture, like clay.”
The only solution to mitigating or eliminating the frost heaves, according to Curtis, are removing the frost-susceptible soil, removing the water or keeping the road from freezing.
“We try to tackle the first two,” he said. “We try to remove or eliminate as much water as possible getting on or under the road [and] the critical part is drainage, drainage, drainage.”
That is why, Landon said, the surfaces of Interstate 95 and the Maine Turnpike are for the most part free of frost heaves.
“They are engineered and built with a good soil base and drainage and taken care of to prevent water from collecting,” she said.
That type of road construction and maintenance is ideal, Curtis said, but comes at a cost.
“Rebuilding a mile of the interstate the range is $8 million to $10 million per mile,” he said. “Compared to [a road like] Rt 2 in Bangor to rebuild would be somewhere between $3 million and $5 million [per mile].”
For the most part, those who deal with Maine’s roads agree frost heaves are simply something to be dealt with every spring.
“They are basically the spring time speed bumps,” said Don Guimond, Fort Kent town manager. “Are they an issue? Sure, but are they something that are simply going to go away? Not in this environment.”
The best strategy, according to Guimond, is to remember frost heaves are out there usually from March into May and plan your drive time accordingly, as driving over one at excessive speed can damage a vehicle’s alignment or even cause the operator to lose control.
After a few bumpy months, Guimond said, the ground is completely thawed, the soil settles back into place and the roads are again smooth and frost heave-free.
“The best strategy when it comes to frost heaves is slowing down,” Guimond said. “It works.”
As for the rise and fall of frost heave topography in residential driveways, the same strategies apply — try to mitigate by bringing in sand or gravel before construction. And, when all else fails, wait them out.
By building up a potential roadbed or driveways with a more gravel-type soil, Curtis said less water is trapped and the effects of freezing and thawing are mitigated — to a point.
“In a lot of areas the road turns into a big bowl [because] the shoulders are still frozen but the road bed is thawing and sinking below the level of the shoulder or areas that are not thawing as quickly,” he said. “It takes a period of time for all the water caught under the road to thaw allowing the road to even out so we can drive across it without spilling our coffee.”
To help drivers not get caught by surprise, Curtis said the MDOT places thousands of temporary warning signs for frost heaves or bumps this time of year.
“Just go slow when you see a sign because you don’t know how deep or tall the frost heave is going to be,” Curtis said. “The last thing you want is to bottom out or tear out your exhaust.”