Washington County's Buried Bridge

Washington County’s buried bridge project represents a proven infrastructure solution that delivers lasting value to the community. By replacing an aging, restrictive structure with a galvanized steel buried bridge, the county restored safe, reliable access for residents and the surrounding agricultural network. This strong design offers quick installation, long-term durability, and environmental benefits, demonstrating how innovative engineering can strengthen a rural community and support the heavy work of modern farming.

A new buried steel bridge in Washington County, Iowa, has replaced a narrow 1966 one-lane structure that carried a 15-ton weight limit and forced farmers to make lengthy detours. Seeking a solution that improved access while controlling costs and minimizing environmental impact, county engineers evaluated multiple alternatives and, after learning about short-span steel systems at the NACE conference, selected an open-bottom buried bridge as the most effective option. The final design incorporates 80 feet of galvanized steel structural plate with 15" × 5.5" corrugations set on simple spread footings. Its open-bottom configuration preserves the natural streambed, maintains hydraulic performance, and reduces debris accumulation while providing an unobstructed passage for fish and wildlife. The surrounding soil contributes to load distribution and offers natural insulation, enhancing durability in Iowa’s freeze-thaw climate. “It took us about two and a half days to put it all together,” said Pete Hammes, superintendent of Iowa Bridge & Culvert LC, in Washington, Iowa. “We had to put two concrete footings in with keyway for the panels to sit in, and then the riprap. After that, we put the bridge plank in across there to work off of and put the sections together. “We used excavators, a long reach excavator to set everything in place. Typically, we'd use a lattice boom crane. But, because there's power lines, we thought we could get by with excavators where we could get underneath them. So, that's what we used, a regular excavator and then a long reach. I think each piece was near 400 to 500 pounds.” The resulting two-lane structure eliminates previous width and weight restrictions, allowing modern farm equipment to travel directly through the corridor. Local residents have quickly recognized the improvement, and the county is now considering buried bridge solutions for future applications.