COOK — The Cook City Council voted Tuesday to spend up to $209,137.95 to stabilize a massive hidden void beneath the public library’s concrete floor, an unexpected structural failure discovered during flood renovation work this fall.
The void, which reaches depths of more than two feet in places, left the slab without enough support to meet building code. SEH engineer Benjamin Wolf determined the most viable fix is to inject closed cell foam under the slab to rebuild the lost support. The council also agreed the deteriorating sewer line running beneath the same floor must be replaced before the foam work can begin.
Contractors uncovered the void earlier this fall while cutting into the concrete to run plumbing for a new bathroom, a step in the ongoing repair from the June 2024 flood. In a Nov. 5 report to library director Crystal Whitney, Wolf said the void ranged from about a foot to more than two feet deep and left the slab without the uniform support needed to safely bear load.
Wolf spoke to the council by phone Tuesday and walked members through what the foam process will entail. He described it as a multi-day operation in which the contractor drills into the slab and injects expanding foam in controlled lifts so the material cures properly and does not put unintended pressure on the floor or utilities.
“They actually drill some relatively small holes maybe in the neighborhood of a five-eighths or three-quarter inch drill bit hole,” Wolf said. He added that the small diameter allows the contractor to adjust drill points as needed.
“If those were to encounter rebar, it’d be easier to relocate them slightly to miss rebar,” Wolf said.
He emphasized the need to preserve the existing reinforcing steel.
“Once this foam is installed, the slab will be supported uniformly. I think it’s a very good idea not to take out that rebar that really at the moment is functioning as a structurally reinforced slab,” Wolf said.
“Do you do any inspection on this as they’re applying this?” Mayor Dan Manick asked. “I truly believe some of the voids are 28 inches. That could be many, many layers. So, is somebody going to inspect this to make sure that they’re putting down the appropriate thickness in each layer, allowing it to fully cure?”
Wolf confirmed that SEH has staff available to monitor the process.
The projected schedule for the work remains tentative. Wolf said he will confirm it with the contractor, but he does not expect the job to happen in a single day.
“Just with the sheer volume the foam that needs to be installed in this circumstance, I’m thinking maybe a couple days for that process,” he said. “My guess would be three days.” Wolf also told the council that winter conditions are not a barrier.
“So long as the building is heated, I don’t see any issue,” he said.
One advantage of the closed cell foam system is longevity. Wolf said foam protected from sunlight does not degrade quickly.
“This would be applied below the slab, so it’s protected from UV degradation. It would have a service life of effectively 40 to 50 years,” he said.
The product also carries a contractor warranty that limits settlement to no more than one quarter inch for five years. If settlement exceeds that, the installer must re-level the affected area at no cost.
Still, monitoring matters. Wolf suggested preserving a few of the existing access holes cut by contractors so the city can periodically insert a camera to confirm the slab has not shifted. He noted that most of the library’s carpeting uses removable squares, making those checks easier.
“We can identify some locations where those tiles would not get permanently glued down and would allow that to be observed in the future,” he said.
But the sewer line under the floor turned out to be just as pressing as the void itself. City maintenance supervisor Tim Lilya, who inspected the line earlier, told the council the pipe was in poor shape.
“We see the condition it’s in. We see the water still sitting in that,” he said.
“We probably are dealing with old cast all the way from the alley into the building,” Councilor Ron Bushbaum said during the discussion, and Lilya agreed. Once the foam is injected, replacing that pipe later would be extremely difficult.
“If it was something you wanted to replace, I think now would be the time rather than potentially having to do it in the future,” Wolf said.
Council members agreed. Lilya was directed to find a contractor immediately and noted that the work will likely need to be done as time and materials allowed rather than a firm bid, since the conditions under the slab are difficult to estimate. The council authorized Lilya to proceed with whichever contractor is able to take on the work at a reasonable rate.
Wolf also underscored the importance of protecting both water and sewer lines during the foam process. Although the written proposal from the subcontractor lacked specifics due to the rush of preparing it, Wolf said the requirements from SEH’s earlier assessment still apply.
“It is part of the requirements to locate them and also protect them,” he said.
Doing so may require drilling a few additional observation holes so the contractor can see the utilities as the foam rises. Wolf said SEH will also request the contractor’s technical submittals before work begins to ensure the city and engineers understand the lift thicknesses, cure times and proper installation techniques.
Along with that oversight, Wolf recommended a pre-installation meeting that brings together general contractor Lenci, DBS, SEH, and city staff. The purpose would be to walk through the sequence of work and clarify how utilities will be located and protected.
While Tuesday’s meeting resolved the technical path forward, it left the financial side still emerging. The city will cover the cost for now out of reserves and liquor store funds, while continuing to explore whether any reimbursement or matching opportunities exist. Council members noted that much of the library’s earlier flood renovation costs may be eligible for state disaster reimbursement, although the void repair itself is not tied directly to the flood.
For now, the goal is to keep momentum. The sewer line replacement must come first, and interior work by Lenci continues while the foam contractor prepares for installation. With the building heated and accessible, the city hopes to have the stabilization completed before winter deepens.
The full repair, including both the sewer line and the void fill, is expected to push the total investment in the library’s restoration close to three quarters of a million dollars when flood work is included, Manick said. Council members acknowledged the weight of that number but agreed the fix could not be deferred.
As Councilor Liza Root put it near the end of the discussion, the library remains central to Cook’s downtown identity, and ensuring the building rests on solid ground is part of safeguarding that role for decades to come.