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Story County Iowa Box Culvert & Wall

Challenge

To address increasing traffic counts, deteriorating pavement conditions, and safety concerns, the Iowa Department of Transportation wanted to transform the interchange of U.S. Highway 30 and Interstate 35 in Story County, Iowa, by building a new crossover bridge. The engineering firm managing production of the new crossover bridge needed design assistance with a retaining wall at a widened lane under the Dayton Avenue structure and replacing an existing box culvert at a relocated exit ramp.
 

Solution

Because the exit ramp at the interchange of U.S. Highway 30 and Interstate 35 crosses a creek, Shive-Hattery designed plans that included a new 10-foot-wide by 11-foot-tall double box concrete culvert to be installed.
 
Another exit ramp at the interchange of U.S. Highway 30 and Interstate 35, which crossed underneath the existing crossover bridge, was being widened to include an additional roadway lane. In order to widen this exit ramp, a retaining wall needed to be designed and placed underneath the existing Dayton Avenue bridge. After considering limited headroom and the soil conditions, Shive-Hattery chose to design a 172-foot-long soil nail retaining wall that uses grouted tension-resisting steel elements (nails) to stabilize the embankment.
 

Impact

By replacing an existing box culvert with a new 10-foot-wide by 11-foot-tall double box concrete culvert, the interchange of U.S. Highway 30 and Interstate 35 can safely cross the nearby creek. The soil nail retaining wall stabilizes the existing embankment and allows for an appealing aesthetic exterior.
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