Needing to replace a set of bridges on Interstate 15 in Cedar City, the Utah Department of Transportation (UDOT) came up with an innovative plan to keep traffic moving by building one bridge offline, using it during construction and then sliding it into place southbound.

“This was a fun project,” says Tyrell R. Wood, Resident Engineer during construction with UDOT in Cedar City. “The reason we did this the way we did was to keep the traffic moving and free flowing.”

The project replaced the northbound and southbound bridges over East Nichols Canyon Road. About 30,000 vehicles cross the bridges daily, about 15,000 in each direction.

Consulting engineer Klophaus & Associates designed the structures and Perkins Engineering designed the roadway portion of the $10.5 million project. The structures have been designed to enable expansion to three lanes as future traffic demands.

“That will save money in the future,” Wood says. “We know that’s going to occur.”

Wadsworth Brothers Construction of Draper, Utah, received the contract to rebuild both bridges and work began in July 2021. “The project went smoothly,” says Linn Bogart, Senior Project Manager for Wadsworth Brothers. “It was a successful project.”

The company, founded in 1991, began as a bridge builder. It has since expanded to one of the largest commercial construction firms in the region. It continues to build bridges and other heavy highway projects in Arizona, California, Idaho, Nevada, and Utah.

“It was a pleasure working with this crew,” Wood says. “They were an extremely good contractor.”

The new steel-girder bridges are supported on steel H-piles driven to as deep as 75 feet in places to reach solid rock. Crews attached a hammer to a crane to place the piles into the ground. An inspector watched and counted each hammer blow and recorded how far the hammer blow moved. When it reached specified driving criteria, the team knew it had the strength to support the bridge. The piles are topped with concrete pier caps.

“We had to keep going until we found good, hard soil,” Wood says. “It was done quickly and efficiently. When they had a problem, we talked about it and worked it through together.”

The bridges are on a skew, so they are not level on all four corners. Every corner of the bridge has a different elevation

“The way it was angled, it was an extremely complex design,” Wood says. “The designers took numerous precautions in the design process to make sure they got it right. And during the construction process, we double and triple checked everything to make sure we had that bridge exactly where it needed to be. I am proud to say when we were done, we were within a half of an inch. It was built precisely to the plan.”

The I-15 project began in July 2021 with crews building a new bridge in the median between the northbound and southbound lanes. This center bridge, built about 1-foot from the existing southbound bridge, required the use of temporary shoring and soil nail walls, Bogart says.

During the second phase, northbound traffic shifted to the new bridge, crews demolished the old northbound structure and built a new bridge in its place. Northbound traffic was then shifted to the new northbound bridge.

Southbound traffic was then placed on the center bridge, while crews demolished the old southbound bridge and built the foundations for the new southbound structure, which was serving as the temporary bridge in the median of the interstate. “It was an innovative approach to build the bridge in the center,” Bogart says.

The project consumed 234,034 pounds of coated reinforcing bar and 1,534 cubic yards of concrete.

Crews maintained two lanes of traffic on I-15 throughout the project during daytime hours. The speed limit was reduced. However, East Nichols Canyon Road was closed for safety of drivers during the entire construction season, with detours available nearby. Crews then reconstructed the local road. “Construction proceeded more quickly than if we had left it open,” Wood reports.

Once the foundations were ready, crews pulled the 1.15-million-pound center bridge into position to carry southbound travel, during a nine-hour closure of the interstate on the night of July 13, 2022.

“First we had to break the bridge free,” Bogart reports. That required removal of the Styrofoam between the asphalt and approach slabs with chainsaws. Once it was gone, the bridge immediately started moving.

The process entailed the use of Williams steel rods and large hydraulic jacks to pull the bridge into place, along with Teflon plates or slider pads, and Dawn dish soap.

“I know it sounds crazy, but that’s what we are calling the secret ingredient,” Wood says. “It has the best lubrication quality of almost anything for this type of application.” Bogart explains that Dawn is more environmentally friendly than an oil-based lubricant.

Crews moved the bridge in two and a half hours. “It was a great partnering effort on the part of the department and the contractor to be able to do that,” Wood adds.

Bogart agrees, saying, “the team worked really well together. The state supported us in every aspect of the work, and they were in the trenches with us. The department also did a good job with distribution of public information and public involvement.”

The department invited local officials and several students and professors from the Southern Utah University’s Engineering and Construction Management program to observe the slide on site.

“We were thrilled to have students from Southern Utah University join us to observe the bridge slide,” says Sharice Walker, UDOT Project Communications Manager. “As a student, there's nothing quite like seeing your field of study in action. We hope it was an inspiring and educational experience for our next generation of construction professionals and something they will remember every time they drive over that section of the interstate.”

Traffic now flows in both directions on the new bridges. “It was really good to build this job the way we did it,” Wood concludes. “It was rewarding.”

Photos courtesy of the Utah Department of Transportation