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      Ground heave and spring thaw cause bumpy roads

      Itâ??s been a winter for the books with record low temperatures all across the Upper Peninsula.

      Civil engineering associate professor at Michigan Technological University, Ralph Hodek, said the unusually frigid temperatures have created a problem below the surface: a deepened frost line.

      â??The average since 1948 is a total of 1,700 freezing degree days,â?? said Hodek. â??This year, at the Houghton County Airport as of yesterday, we were already at 2,500.â??

      And itâ??s not over yet.

      Houghton County Road Commission highway engineer, Kevin Harju, said this year, the frost line is an estimated two feet deeper than usual.

      â??Typically, our frost line gets down around 60 inches. There are probes and the state trunk line that we can check, and this year, itâ??s over 80,â?? said Harju. â??Thatâ??s as deep as the probes go down, so weâ??re not sure if itâ??s farther than that. Chances are it is.â??

      Harju said the road commission tacked on an additional half million dollars over last year to keep up with the weather, and that doesnâ??t include the cost it will take to repair roads this spring. He said repairing one mile of road can cost up to $250,000.

      He also said his crews know which roads are historically hit the hardest during the spring thaw; however, this winter has caused some roads, which typically survive the thaw without much crumbling, to begin to break.

      â??Severe frost heaves show up relatively fast,â?? he said. â??Weâ??ve actually experienced some frost heaves in areas that we havenâ??t seen in the past, which is unique, but thatâ??s just because the depth is deeper.â??

      Hereâ??s how it happens: over the winter, ground water is seeped up toward the surface and is frozen into â??water lenses.â?? Because water expands as it freezes, these water lenses heave the ground upward.

      Hodek said the problem lies in the fact that thawing occurs from the top down.

      â??As the ground thaws from the top down, we have an excess of water beneath the pavement, and that water cannot drain downward through the frozen ground,â?? explained Hodek. â??Rather, it has to move upward, and you can see that on some of the county roads where the alligator cracks are wet.â??

      â??You have a frozen layer deep down with water trapped on top of it, and water has no place to go,â?? added Harju. â??Itâ??s like driving over a big, for example, like a water bed.â??

      The result is a bumpy road.

      These bumps, however, are expected to straighten out with the passing of the season, though they wonâ??t ever be exactly they way they were when constructed.

      â??After weâ??ve thawed the ground completely, the water can start draining downward, and this is the time that the roads will start to stiffen up again,â?? said Hodek.

      Hodek estimated the spring thaw would need to last about two to three weeks to do as little damage to roadways as possible.

      The Houghton County Road Commissionâ??s top priority is keeping their roads as intact as possible, according to Harju. For this reason, he said, the road commission enforces weight limits on roadways.

      Harju added itâ??s too high a price to repair entire roadways to afford a quick thaw.

      â??Just be patient,â?? said Harju. â??Itâ??s going to be a long spring, I think.â??