Quad Citians who hoped to send the old twin-span Interstate 74 bridge off with a big bang will get their wish – not once, but twice this summer.
Representatives of demolition contractor Helm Group told members of the Rock Island Rotary Club on Tuesday, May 30, that the groundwork is being laid to prepare the bridge for the series of charges that, once detonated, will drop the two central towers that remain on the eastbound span.
No date has been announced yet, but the event is widely expected to take place soon.
Consultant Mark Brandl, of HNTB, and Helm Group’s Tom Schebler, project engineer, joined Chris Snyder, Helm Group’s project manager, at the Rotary lunch to talk about the history of the bridge and the painstaking bridge demolition efforts involved so far.
The trio also provided the broad strokes of a tentative schedule that will treat the public to two separate bridge detonations – or more accurately series of detonations – designed to drop trusses and cables on parts of the remaining eastbound and westbound spans this summer.
Following their presentation, the trio dashed off Tuesday to a meeting with federal, local and multi-state agencies and stakeholders whose input is required before the first blast can take place.
Among them are the Coast Guard, Department of Natural Resources, U.S. Fish & Wildlife Service, Environmental Protection Agency, local and federal highway officials, and the railroads. Even the Federal Aviation Administration is involved since the bridge is in an approach corridor for one of the Quad Cities International Airport’s runways.
“Roll call there probably takes longer than it does here,” Mr. Snyder quipped about that day’s demolition meeting to the large group of Rotarians gathered to hear the presentation.
The presentation at the Quad Cities Botanical Center in Rock Island came some eight months after the Helm Group began the complex and painstaking demolition of the old green bridge that itself required meticulous engineering and execution.
When demolition began in September 2022, the Iowa DOT said then “We know you want to see the old bridge go out with a BANG. But we’ve decided to dismantle the majority of it piece by piece. At this time, the contractor is only planning to use explosives on select areas of the bridge.”
Now that time has nearly come, though the exact date remains unknown.
“The blast date is still being kept internal at this point,” Mr. Schebler said when contacted by the QCBJ after the afternoon multi-agency meeting. “I know that there will be a press release coming out very soon with the date and other information.”
In the meantime, he said, there are still demolition details that need to be addressed by the Iowa Department of Transportation, which managed the construction of the new Interstate 74 Bridge and now the demolition of the old one.
What comes next
Even though they couldn’t give a date, the demolition experts willingly shared with Rotarians what’s likely to happen on demolition day and what’s taken place so far.
A series of charges will be placed on the cables and towers to remove the suspension cables and towers of the eastbound bridge only, Mr. Schebler said. That process for truss removal will then be repeated on the westbound suspension span, which means a second blast of the suspension cables and towers will take place in late summer.
When it happens, it will have taken all of the past eight months to get to this point, and Quad Citians have had a front-row seat throughout the process.
Consider that even before demolition could begin, Mr. Schebler said, Helm Group had to scan the river to ensure that none of what they would be taking down ends up in the river permanently. Those scans are helping experts identify what doesn’t belong in the water so that it can be retrieved later.
In the case of areas where rare mussels were found on the Moline side of the river, Mr. Schebler said, “we’re not allowed to retrieve any pieces that are in the water so they’re ensuring that doesn’t happen.”
Because of the environmental restrictions, the Helm Group couldn’t have any temporary operations in the area where mussels could be impacted. So to stabilize the structure while it was being removed, the contractor sank a barge with a big tower until it could be moved under the bridge, then pumped out water until that tower supported the structure.
Actual bridge demolition began with deck removal which involved using a massive saw to cut the concrete deck into 4-foot by 12-foot slabs to be picked up with excavators and hauled to Bettendorf where concrete was separated from rebar, “munched up” and recycled.
Balance has been an issue throughout the demolition of the hanging bridge spans so engineering consultants worked to counterbalance the removal. That included stacking 400 deck panels on the main suspension span. Even so, the towers moved as much as a foot in either direction during the process.
Demolition plans evolve
According to Mr. Snyder, the current bridge demolition plan evolved dramatically over time.
The original plan, he said, was “to blast the entire suspension span with the trusses and everything into the river during the winter.”
Helm Group didn’t like that so much material would be going into the river and because crews would have just 48 hours to remove it all, doing it that way “was really tricky,” he said.
Instead, planners opted for the piece-by-piece removal and the two series of detonations expected to happen this summer.
“We tentatively had a date already set before the flood hit,” Mr. Snyder said of the initial explosion. “Then our operations got impacted by it just as much as any boating operation out there. So we had to move that back purely because of the flood.”
What can viewers expect when the demolition does come?
“We’re out there right now doing a lot of the prep work on it,” he added. “When you blast a structure, you can’t just attach charges and hit the button. That’s not going to work. You have to get down to as little spaces and angels as possible, if that makes sense, for your charges to hit that steel right.”
Workers have detailed drawings to guide them, but the work is still “nerve wracking” since placement is critical, Mr. Snyder said.
What to expect on D-Day
On demolition day there will be several detonations, starting with setting off a few blasting caps underwater to scare away the fish, Mr. Snyder said. That will be followed by a series of detonations that will bring down the targeted cables and towers.
To viewers it will sound like “one big explosion,” he said. “There is a time sequence, but it’s pretty quick. You might catch it with your eye but it will seem like one blast.”
Despite all that’s involved, the nearby new Interstate 74 Bridge is likely to be closed for only an hour. “What we really need is 15 minutes,” Mr. Snyder said, adding “that doesn’t mean cleanup. We’ll be there clearing a lot longer.”
What specific date it all will happen isn’t known yet, but Mr. Snyder said blast time must be between 7 to 9 a.m. on a Sunday. When the exact window is identified, the demolition contractor will set up a “global detour” that will send I-74 traffic around to Interstates 80 and 280 and a local detour that is likely to send vehicle traffic down River Drive to the Centennial Bridge.
Interstate 74 is expected to be closed to vehicles and pedestrians for an hour and river traffic will be closed for 24 hours because crews will be in the area immediately following the blast.
Coordinators also are working to ensure that river features such as the Channel Cat water taxi will be disrupted as little as possible.
Who gets to do the honors? A licensed blaster subcontracted by Helm Group sets and detonates the charges.
That first blast will be on the eastbound lane only, Mr. Snyder reminded his audience. When the westbound lane follows later, that blast will be far less dramatic, he added.
