The Lincoln Journal Star reports that frost boils seemingly can devour the wheels of a truck, immobilize a car or all but sink a road grader. In short, they can make a gravel road impassable.
They’re created when frost in the gravel roadway melts in spring but can’t drain away because of frozen ground below, experts said. The soggy roadbed eventually heaves, softens and fails.
The mud below the gravel and limestone on top of the road basically liquefies, like it has been whipped in a blender, said Ron Bohaty, road maintenance superintendent for county engineering.
The county has had a few frost boils in the past, Bohaty said, but this spring there have been several dozen areas with the liquefied mud. Sometimes drivers can detect frost boils because the ground goes up and down as vehicles pass over. Sort of like driving on a sponge, he said.
This year’s frost line is 36 inches (91.4 centimeters) below the surface on many county roads. The county can do little more than close affected roads until the road frost thaws and the muddy muck above it dries.
But not everyone pays attention. On warmer days some people go beyond the barricades and their vehicles just sink and high-center, Bohaty said.
A frost boil is a problem “you learn about in college engineering classes and hope never happens to you,” said the Lancaster County engineer, Pam Dingman.