Lancaster County engineering staff has run into a new wrinkle in the many problems created by the very long, wet winter — frost boils in gravel roads.
Frost boils can devour the wheels of a truck, immobilize a car, sink a motor grader and basically make a gravel road impassable.
Frost boils are created when frost in the gravel roadway melts in the spring but can't drain away because of frozen ground below it. The soggy roadbed eventually heaves, softens and fails, leaving ruts and maintenance headaches for county road crews.
The mud below the gravel and limestone on top of the road basically liquefies, like it has been whipped in a blender, explains Ron Bohaty, road maintenance superintendent for county engineering.
This year’s frost line is 36 inches below the surface on many county roads. And until that thaws out and the mud above it dries, the county can do little more than close off the road so motorists don’t get stuck.
County trucks get stuck putting more gravel on the road and there isn’t much gravel left, said Bohaty.
The county has had a few frost boils in the past, but this spring there have been several dozen areas with the liquefied mud, Bohaty said.
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Researching online, staff discovered that some road crews in North Dakota use an auger to put salt into a hole. The hole gives the moisture in the roadway a place to drain and the salt helps melt the frost line.
Engineering staff are trying the auger method in several locations.
Sometimes you can tell there is a frost boil because the ground goes up and down as you drive over it, like driving on a sponge, Bohaty said.
The engineering office has set up barricades to keep people from driving into frost boil areas. But not everyone pays attention. On warmer days, people get beyond the barricades and the car just sinks and high-centers, Bohaty said.
Frost boils are the kind of theoretical failure, “you learn about in college engineering classes, and hope never happens to you,” said Lancaster County Engineer Pam Dingman.
But this has been a very bad winter, so bad that even her longtime employees can’t think of a worse winter, Dingman said.
The county is also low on rock and hoping to get a response to a rock bid early this week. And the department is low on dry dirt, needed to make repairs on some of the closed bridges and culverts. A district supervisor has put dirt in an empty salt dome to keep it out of the rain and help it dry, Dingman said.
In addition to frost boils, the shoulders on gravel roads are often very soft and many roads are basically one lane.