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Manholes aren't sinking -- frost is lifting the streets around the city

A manhole cover on the 600 block of 25th Avenue Southwest that's several inches below street level. Tribune photo by Gary Miller

WILLMAR -- People driving around Willmar's rougher-than-usual streets this spring are seeing a demonstration of the tremendous power of water and ice.

Many have probably noticed that many manhole covers in the city seem to be sinking.

That is what it looks like, but the manholes don't rise or fall with the weather, because they extend below the frost line, said Willmar Public Works Director Ron Gilbertson.

Those deep holes around some manholes are actually caused by the street surface rising and falling as frost works its way out of the ground.

"This year's been a huge problem with the streets lifting," he said Tuesday afternoon.

City crews have been working to even out the driving surface by filling in the holes with cold mix on top of a layer of paper, he said.

It's common to see the manhole issue every spring in some wetter areas of the city, but this year, it's all over town -- "five times more than we typically have," Gilbertson said. "We think it's because of all the moisture we had last fall."

Another spring problem is the frost heaves creating bumps and dips in driving surfaces. Those, too, are worse than usual this year, with some streets becoming "really wavy."

Once the frost is gone, "the streets go back to where they were before." Then city workers will have to return to remove the cold mix to even things out again. It's all part of their annual maintenance work, Gilbertson said.

People will know when the frost is finally coming out of the ground, because they will see water seeping up through cracks in the roads, he said.

The pothole patching crew was working its way around town on Tuesday, too, Gilbertson said.

"We're trying to catch up with potholes," he said, but recent rain and subsequent freezing hasn't made their job any easier. The freeze-thaw cycle through the winter and spring causes weak spots in asphalt to pop out.

The crew tries to keep the main thoroughfares patched and then works through the rest of the town one area at a time, he said.

Linda Vanderwerf

I cover education issues for the West Central Tribune and have worked for the paper since 1995. I have worked in journalism since 1981.

Follow me on Twitter: @lindavanderwerf

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