Marine batteries to power the sensing equipment placed on top of the piers.
The Wisconsin Department of Transportation (WisDOT) northeast region in Green Bay held a news conference on Oct. 3, to release findings regarding the Leo Frigo (I-43) Bridge. Pier 22 on the bridge’s east side sank 2 ft. (.61 m) on the morning of Sept. 25, causing the deck to sag and the bridge to be closed to traffic indefinitely.
WisDOT reported that the investigation is ongoing, but the bridge deck and Pier 22 appear to be in good shape. The inspection reportedly revealed that pilings for Pier 22 that are located 8 ft. (2.4 m) below the bottom of the concrete footing had buckled, apparently due to corrosion. The experts on the investigation team believe this corrosion was caused by a combination of the soil composition at this location and the rise and fall of the water table.
“Through careful research, soil analysis, observation, measurements, and such, we determined that the soil around Pier 22, particularly the pilings, was such that it contributed to corrosion of the piling, and the piling eventually buckled, causing Pier 22 to settle two feet,” said Kim Rudat, communications manager of WisDOT’s northeast region. “We feel reasonably sure we know why it happened, and that’s why we’re moving ahead to come up with a fix. But I can say that part of the research is [that] obviously we’re looking at all the piers along the bridge and taking soil samples throughout the length of the bridge just so we feel comfortable as to the area that we’re isolating that we’re going to be addressing the fix.”
Rudat added that the investigation has involved several consultants, including Federal Highway Administration (FHWA) staff and WisDOT staff, both from the region and from the state capitol of Madison.
“We will finish our investigation towards the end of next week,” Rudat said on Oct. 4. “As for what the fix will be, we should be announcing that in the next…certainly several weeks…and how long that’s going to take, we can’t speculate.”
As far as funding for repairs, Rudat said that WisDOT expects assistance from the FHWA, and that she is certain that state funds will be involved, as well.
“But as our governor said, we’re going to fix this, we’re going to fix this right, and we’re going to fix this safely, and we’re going to open this up as quickly as we can,” Rudat said.
It was reported on Oct. 4 that FHWA did determine that repairs to the bridge were eligible for funding under the Emergency Relief Program.
“It does not appear…that there is anything that the state could have reasonably done to have anticipated or avoided this failure,” Federal Highway Division Administrator George Poirier said.
The funds will reportedly cover 100 percent of the emergency repairs within 180 days of the bridge closing. After that, a 90 percent federal share would be paid for the repairs. The preliminary estimate for repairs is $50 million.
Rudat added that the current detour for the bridge involves taking Highway 172 from I-43 across to U.S. 41. Local traffic also can get across the river at several bridges in Green Bay.
The sagging in the bridge was originally noticed by a motorist at about 4:51 a.m. on Sept. 25. The Brown County Sheriff’s Department was notified, and WisDOT was contacted at 5:30 a.m. that the bridge would be closed. A bridge inspector from WisDOT soon determined that a 400-ft. (122 m) span was sagging across all four lanes of the structure.
“The Wisconsin DOT believes this bridge was designed and built properly,” Rudat said. “This has nothing to do with the design or the building of the bridge. This soil condition was there before we started the bridge, and it is not a similar soil condition as what runs along the majority of the bridge, and we feel — at least from what we’ve seen — the majority of the pilings are as good as the day they were driven in. Piling buckling like this is extremely unusual.”
The department believes there is no danger of the bridge collapsing. WisDOT is monitoring bridge movement with a Memsic VG 350. The equipment has been placed on the tops of three piers (21, 22, and 23), and is powered by marine batteries in protective cases. The equipment sends signals to a computer to record data. Any detected movement triggers a horn to sound an alarm to workers. Only a half inch (1.27 cm) of new movement was reported late Oct. 3.
Regarding other bridges in the area, Rudat said that WisDOT is not doing any testing.
“We feel confident that our bridges are sound,” he said.
But according to Dr. John Luczaj, geoscience chair in the Department of Natural and Applied Sciences at the University of Wisconsin — Green Bay, corrosion is definitely an issue for this pier, and likely others nearby.
“There are several layers that could be potentially corrosive,” Luczaj said. “One of them is a buried forest layer called the Two Creeks Buried Forest. It’s kind of a famous place [with] 13,000 year-old spruce forest material that got buried by a glacial advance. That’s in the middle of this stack of material, and if you excavate or you drill through this, and pull out the wood pieces, they’re just coated with sulfur, so it’s kind of a prime material for the potential corrosion of things like steel. In addition to that, a lot of the glacial settlements, at least in the region, have a lot of sulfide mineralization in them, and as we all know, when you have sulfides like pyrite in your aggregate material it can cause sulfuric acid to be produced when you weather it, and that can cause corrosion as well.”
Another potential problem Luczaj noticed deals with water.
“The biggest change geologically in the region has just taken place in the last six years, and that is the recovery of the deep aquifer system,” he said. “What we’ve got is this 100 and some feet of clay, and then about a hundred feet of dolomite. Both of those are on top of sandstone aquifers, and for the last 80 years or so, people have really pumped a lot of water out of the deep aquifer, so these clays were relatively dry. But six years ago, they shut off a lot of the wells in our region. They stopped pumping 12 million gallons of water per day in central Brown County — they switched to surface water as part of a pipeline — ultimately because of radium in the deep aquifer and the EPA said you had to treat it or you had to get a different source — and we’ve got so much water out here, we just chose a different source.”
Luczaj continued that the result was that the water levels in the deep confined aquifer rose dramatically —150 to 200 ft. (45.7 to 61 m) in some places. He also added that before Green Bay was developed, the water was under artesian conditions, so if a hole were drilled, water would just flow out at the surface.
“When this bridge was installed in 1980, the level of the water in the deep aquifer was low enough that the gradient for water to go was downward and they didn’t have any reason to transmit much water from the surface,” he said. “But now, the water levels are within about 20 to 30 feet of the surface, and so the deep aquifer has the potential for water to flow upward. We know the dolomite layer, this bedrock, is fractured. I can take you to quarries and show you pictures — there are fractures everywhere. However, the glacial sediments here are generally not, they’re a really good confining layer for the deep aquifer, and so any water pressure that would be below and could be transmitted through could basically go into a sand and gravel layer that’s right at the base of all these plates. So you can really increase the pore pressure, and you know what happens to clays when you increase the pore pressure and get them wet. Instead of being wet and strong, they become slippery and weak —or have the potential to. So if there was any topography on the bedrock surface, and you have increased pore pressures and changing material properties, there’s always a potential for slippage.”
About the Bridge
The Leo Frigo Bridge was originally constructed in 1980, and was named for Leo Frigo, a former cheese company president who founded a food pantry for the poor in Green Bay.
It has 51 support piers over its 8,000 ft. (2,438 m), and is the second longest bridge in Wisconsin.
Currently, it carries about 40,000 cars a day over the Fox River on Interstate 43. Repair of the substructure was completed in 1988. The bridge was last inspected in Aug. 2012, and was not on the list of 60 deficient bridges in the state, according to WisDOT. It underwent asphalt, joint, and pin replacement in 2012 and 2013.