MnDOT seeking fix for Minnesota highway sliding down hillside
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A state highway in western Minnesota will remain closed into next year as officials create a plan to stop it from sliding down a hillside.
State Highway 67 at Upper Sioux Agency State Park southeast of Granite Falls, Minn., has been closed since April 4. That's when cracks started to form in the pavement along a slope above the Yellow Medicine River.
Parts of the roadway have now shifted as much as three feet and are still moving.
"(We were) seeing about an inch of movement per day at the beginning," said Cody Brand, a soils engineer with the Minnesota Department of Transportation's District 8. "It's starting to slow down to slightly less but it is still moving. We're recording movement at about 50 feet below ... the pavement surface."
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Those measurements come from instruments and test borings as deep as 100 feet along the hillside. MnDOT also has gathered information about the soil and groundwater.
"We're calibrating a soil stability model using the soil descriptions that we recorded with the borings. We're putting in data that's coming in about groundwater depth and locations of movement," Brand said. "And so using that model we're going to determine the forces that are acting on the hillside and then be able to start designing what it'll take to resist those forces."
Brand said river erosion at the base of the slope, as well as abnormally high rainfall, may be to blame for the slope failure.
He said the road has been graded on its current alignment since the 1940s, with no previous recorded problems along that hillside.
While the exact plan to address the problem is still being developed -- the highway is slated to remain closed into 2020 — Brand said crews likely will need to penetrate the layer moving 50 feet beneath the road "and tie the roadway into something stable beneath that." The highway closure is slated to extend into 2020.
A detour is in place around the closure, using State Highway 23, State Highway 274 and County Road 18. Highway 67 is open from Granite Falls to the Upper Sioux Agency State Park visitor center, but campers must use the detour to go from the visitor center to the park's Yellow Medicine Campground.
Park manager Jeremy Losinski said earlier this year that what's usually a brief drive between the two has become a 16-mile detour.
"It essentially splits the park into an east and west district," he told MPR News in May.
