Demolition of the I-74 Mississippi River bridge is a big, complex task

For years, people in the Quad-Cities have awaited demolition of the old Interstate-74 bridge between Bettendorf and Moline.

It’s not that people here hate the bridge, although the narrow road width and nearly non-existent shoulders gave some drivers the shakes. It’s just that its demise would mean the new bridge, in the planning stages for decades, would be complete.

Also, anticipation of the span’s demise in some quarters was driven by the prospect that it would be imploded; that once the new bridge was opened, the old twin bridges might be brought down in a spectacular crash of steel, concrete and dust.

Alas, it was not to be. Iowa DOT officials said last year there would be no big implosion.

Instead, crews are undertaking more nuanced methods, if that’s the right word to describe the demolition of two spans that include 16 million tons of steel, piers that plunge into the Mississippi River bed and large towers and accompanying suspension cables that rise high above the road surface.

Despite the lack of one big implosion, however, the intricacies of dismantling the bridge while simultaneously limiting environmental effects and maintaining safety for work crews, river traffic and drivers traversing the new I-74 span nearby is no simple – or boring – task.

Since last September, planners, engineers, laborers, carpenters, ironworkers and electricians, among others, have methodically toiled to dismantle the spans, one built in 1935 and the other finished in 1960. (Helm Group, whose corporate base is in Freeport, Ill., has the $23.3 million demolition contract.)

From a distance, the bridge doesn’t look that much different. But up close, the changes are visible.

A chunk of the span on the Bettendorf side of the river is gone.

The concrete decking over the river also has been taken out, while roughly 4 million tons of steel have been removed, according to a recent estimate.

Still, there is plenty of complex work left to be done.

Because of the proximity of the new bridge and the interrelation among the different spans that make up the old I-74 bridge — there are actually four different “bridge types” that make up the structure – extra planning and care must be taken to limit movement of the old bridge while its various pieces are removed.

“It’s all interconnected so when you start removing a bridge like this, you actually have to engineer how you’re going to remove it. It’s a very complicated process,” said George Ryan, who is the I-74 corridor manager.

For example, steps had to be taken to balance removal of concrete and steel to limit the movement of the bridge towers.

“Those towers will move,” Ryan said.

Protecting the environment

In addition, on the Moline side of the span, they could not let steel pieces hit the water because of the presence of mussel beds, so they had to work from barges. This also is where there are fairly shallow areas of the river.

Officials have estimated 1.2 million mussels, including endangered species protected by federal law, are in the I-74 bridge footprint. A significant number of the mussels have been removed, beginning with a big effort in 2016, but a large number remain.

“We’re trying to minimize the impact to those mussels and the river in general,” said Scott Gritters, fisheries biologist with the Iowa Department of Natural Resources. “Any of those features of the bridge, if we blow it up or tear it down, could drop on the mussel bed itself, and we’re trying to do our best to minimize those impacts to that bed.

The mussels also carry benefits for the river.

Mussels filter plankton and bacteria out of the river, Gritters said, which help the entire system.

“They’re kind of like a mini-sewer treatment plant,” he said.

Taking down the towers

As the steel is removed, it is cut up into smaller pieces, then taken by local recyclers.

The demolition contractor is allowed to sell the steel to recyclers, a practice that lowers the price of the bid and the cost to taxpayers, Ryan said.

“It’s pretty high value steel,” he says.

This summer is when the more dramatic task of demolishing the signature green towers and suspension cables is expected to take place.

The contractor’s intent is to use explosives to take down the towers and suspension cables, and it will be done one bridge at a time.

Ryan said the use of explosives, which must meet state and federal requirements, will involve a coordinated effort among the contractor, the U.S. Coast Guard, Corps of Engineers, Environmental Protection Agency, the Department of Natural Resources, the Iowa and Illinois DOTs and the cities of Moline and Bettendorf.

The contractors’ plan is under review, Ryan said, but commercial and recreational traffic along the river will be shut down then, while it is anticipated vehicular traffic on the new I-74 bridge will be shut down, too.

It’s estimated closures of the new bridge would last about an hour at a time.

There is likely to be a great deal of public interest in this part of the operation, so more information will be released later.

Explosives also will likely be used to remove select support piers. Others will be removed by hydraulic methods, with those in the Mississippi taken down to a point two feet below the bottom of the river.

Traffic closures also are anticipated when those explosions take place.

Not all of the piers will be removed. Two piers on the Illinois side of the river will be left so as to minimize disruption to the mussel habitat. Navigation lights will be installed on the piers to aid boaters.

The demolition also involves an underwater survey to ensure all the debris is removed, along with a final cleanup along the riverbanks. Completion of the project is expected in mid-2024.

After that, the span that once carried an average of 74,000 vehicles per day will be gone. The tall green towers that graced the skyline here for decades will fully give way to the twin basket handle arches on the new span that now are a prominent architectural feature in the Quad-City skyline. (The new bridge fully opened a little more than a year ago.)

Preserving history

Still, not all of the old I-74 bridge will be lost forever.

A two-foot long section of cross frame from the span built in 1935 was donated in 2021 to the Putnam Museum and Science Center in Davenport, where it has been on display in the museum’s local history exhibit. The I-74 bridge team is also coordinating with the cities of Moline and Bettendorf about preserving pieces of the old bridge, perhaps to go to local museums. Those discussions are in the early stages.

The piece moved to the Putnam was donated after the museum reached out to the bridge team looking for photographs, said Nora Moriarty, curatorial project coordinator at the museum.

The exhibit with the bridge piece is currently closed for renovation. But when it reopens, the section of bridge will be back on display, Moriarty said.

“The previous I-74 bridge is something that just about every Quad-Citizen has driven across and is a part of our lives living here,” she said. In addition, preserving pieces of the old bridge causes us to remember that our heritage isn’t just something that exists in the past. “It helps remind people they’re living history every day,” Moriarty said.