Precast Concrete Expedites Completion of U.S. 20

Header image is courtesy of Iowa DOT. Gallery photos are courtesy of Hancock Concrete.

Building or expanding a major highway is grueling and time-consuming work. Long before the first piece of heavy equipment shows up or the orange barrels appear, there is years of behind-the-scenes work including design, surveying, environmental reviews, funding models, public hearings and support campaigns, right of way acquisitions, bid letting, partner selection, etc. Only then can construction begin. The analogy of the iceberg is apropos.

However, once a project clears all those hurdles and construction begins, the work typically moves forward until the road is complete. Typically. Unless we’re talking about the expansion of U.S. Highway 20 in Iowa. Although the cross-state route was planned in phases, nobody could have predicted just how much time would pass between the start of the first phase and the end of the last. The project’s first segment opened to the public in 1958. The final segment, named the “final 40,” didn’t open until 2018.

Photo courtesy of Iowa DOT

Finishing the final 40 was a challenge due to topographical and site issues, but the Iowa DOT’s planning made accelerating the timeline from nine down to three years possible. To do so required many contractors working in harmony, as well as allowing an alternate from cast-in-place to precast concrete box culverts.

“I think the DOT is receptive to alternative construction methods to expedite projects and reduce costs, provided we get the performance and results that we are expecting,” said Steve McElmeel, resident construction engineer for the Iowa Department of Transportation. “In general, I believe precast type box culvert construction to be much faster as opposed to cast-in-place and can provide a good product.”

The state awarded part of the job to Ames Construction, which then turned to Hancock Concrete to manufacture the boxes. Hancock has 50 years of precast box culvert experience and the equipment and expertise to handle such a job.

Photo courtesy of Iowa DOT

“All along the DOT was concerned about the timeline because they had 40 cross road boxes to build in phases,” said Bill Adams with Hancock Concrete. “That many cast-in-place boxes would have taken considerably longer to build so for the contract that Ames Construction took, six days before that letting, the Iowa DOT added precast as an alternate to cast-in-place. Ames asked the DOT to allow as much precast as possible on this job.”

The culvert installations were anything but typical, and each required custom engineering. There were fill heights of up to 40 feet, bends to follow creek alignments and differential soil settling, to name a few issues. McElmeel said to his knowledge burying precast box culverts that deep was a first for the DOT, as was the use of precast box culverts in such challenging conditions. Hancock used a computer-generated load resistance factor design to dictate wall thickness, steel content and mix design for each site. The resulting box culvert segments vary in size and some are mitered or cambered for potential differential settlement.

The company then handed off the designs to Lake View plant manager, Eric Ortner, who worked with his crew to make them a reality in the shortened time frame.

“We have a fair amount of equipment for all of our operations, but Eric got equipment from our other plants on a regular basis for this job,” Adams said. “We worked two full Iowa winters making those boxes so they were ready for the subsequent construction seasons. It was a real task for Eric, but they did it and Eric’s attitude about the things we throw at him now is if ‘I can get through U.S. 20, I can get through anything.’”

Photo courtesy of Iowa DOT

The precast culverts met the deadlines and came in handy during some excessively wet springs that put a damper on most other construction activity. In total, contractors installed more than 10,000 linear feet of culvert during the project. The Iowa DOT plans to monitor soil settlement and resulting culvert settlement uniformity as well as inspect some of the boxes and survey elevations in 2023 to assess in-service performance over 5-6 years. This assessment will inform future decisions on similar job sites.

In the short term, McElmeel said the success of the project may lead to the DOT expanding the allowable use of precast box culverts, and it has already put in place a new policy that allows a single line of precast box culverts to be used where estimated settlements are less than 12 inches. In the past, it was limited to six inches.

Adams, a lifelong resident of the area, said he is thankful for the final 40 miles are complete as the Sioux City area has been growing. He was also impressed with how well the project went.

“We were lucky to get the job and lucky to be able to work with the contractors we worked with,” he said. “It took such a concerted effort from contractors. The DOT, Peterson Contractors, C.J. Moyna & Sons, Ames Construction, Dixon Construction, Godbersen-Smith and others did a lot of work and not only handled it, but they shined.”