Construction of unique Y-shaped bridge pier foundations tested by IDOT

Updated Sep 20, 2017

Iowa Department of Transportation (IDOT) officials say the construction of Y-shaped pier foundations for the Interstate 74 span over the Mississippi River is a bit unique, which is why people gathered to watch construction workers pour 136,000 pounds of concrete into a “mock pier” built to test the procedures and materials that will be used for the real piers, the Quad-City Times reports.

“It’s such a unique pier that, before we do 60-plus of them, we want to make sure we’re doing it properly,” IDOT project manager Cedric Wilkinson told the news agency, explaining that it doesn’t usually conduct this type of test. “We want to make sure all this concrete flows through the rebar,”

The piers include reinforced steel that crosses others to form the Y shape, a design created especially for the I-74 bridge. But because the shape is so unusual, particularly the intersecting steel, builders wanted to test it first. The 15 sets of piers — one each for the westbound and eastbound spans — will be built in downtown Bettendorf, with another 10 sets built in Moline from the river to 7th Avenue. Plus, 15 sets of piers will be built in the river, requiring their own testing.

Friday’s test cost $64,000, according to the Iowa DOT, which is 0.2 percent of the $30.1 million contract awarded to Civil Constructors of Freeport, Ill., for construction of the bridge as it crosses downtown Bettendorf.

“It’s a good insurance policy, in my opinion,” Danielle Mulholland, the I-74 project manager with IDOT, told the news agency.

Six truckloads of concrete were used for the pour. The forms around the piers will be kept in place for five to seven days, after which inspectors will look for gaps and test the internal temperature to ensure the concrete doesn’t set too quickly. Additional tests will ensure the form is withstanding the upward pressure of the concrete’s weight. After testing is complete, the test span will be torn down.

The real piers will have a cap to provide a base for the bridge steel and decking, which will also have to be tested, Wilkinson said. Construction of the new I-74 bridge is expected to take three and a half years, but the bridge is being designed to last 100 years.

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The YouTube video below shot by Quad-City Times shows being poured into the test piers.