The process to replace the pair of 60-year-old bridges carrying Illinois 2 over the Rock River in Rockton began with a push.
At the start of the project, the southbound bridge was shoved more than 40 ft. closer to its northbound twin.
Doing so created a temporary workstation, also called a tramway, allowing the contractor to demolish and replace both structures more safely and efficiently. Normally with such projects, a temporary structure is built in the river.
This approach is being monitored for its potential time and cost savings on other projects as IDOT is in the midst of the busiest construction period in its history.
For bridge projects like this, a temporary structure is typically built from scratch and torn down at the end of construction, a process that takes time and can leave the work zone susceptible to flooding.
"The process to rebuild the Illinois 2 bridges poses less intrusion in the river as the tramway is high above it," said Matt Hardt, District 2 construction engineer. Conventional methods would create a temporary tramway in the river using barges and causeways built out of crushed stone. The causeway and tramway would be removed once the structure is completed.
"These temporary tramways and causeways would have been susceptible to river level fluctuations with potential for lost time if they were overtopped by flooding," Hardt said. "The use of an elevated tramway allowed both structures to be built from a single tramway and was not susceptible to river level fluctuations."
Built in 1965, the bridges carry 8,550 vehicles daily across the river between Rockford, Rockton, South Beloit and Beloit, Wis. The structures had exceeded their design life, with a weight limit of 26 tons for a single vehicle and 40 tons for a combination vehicle. Helm Civil was awarded the project with a $25.3 million bid.
Construction began in early 2024 to move the 3-million-lb., 588-ft.-long southbound span in place for its last chapter serving the public.
The effort would require building temporary supports in the river between the bridges and installing slide rail columns that will move the bridge to the center. The bridge was then lifted onto machine skates, which eased in rolling it to the supports.
A set of hydraulic rams pushed the bridge to its new location, moving the structure 8-10 in. at a time in 30-second intervals. Once the tramway was established, work shifted to demolishing the piers of the old southbound bridge and constructing its replacement.
The effort, which took place over 12 hours, was one that had previously never been done in Illinois, let alone in much of the United States, said Mahmoud Etemadi, Illinois highways and roads construction leader of Bloom Companies, which provided engineering services for the project. Etemadi was previously the bridge maintenance engineer for more than 26 years at IDOT's District 2, where the project is located.
"It's innovative and something they have never tried before," Etemadi said of Helm Civil of Freeport, the contractor for the project. "There have been structures smaller than this that were done, but this was a big, big thing."
The new southbound bridge opened to traffic in June. Work is under way to replace the northbound bridge, which is expected to be completed by the end of this year, when the last of the old southbound bridge will be removed after being pressed into special duty the last two years.
