Earlier this summer, DOT engineers were finally able to see what caused the bridge to sink.
"It's amazing that the structure still stood after September 25th after seeing that," said project manager Tom Buchholz, referencing a picture of a corroded steel piling.
Sixteen feet below ground, highly corrosive soil ate into a handful of the steel pilings holding up some of the bridge's piers. Hydraulic jacks were used to lift the sagging portion and concrete shafts were placed at five piers to stabilize the bridge.
"We put a very robust system in there that will last a very, very long time," aid Buchholz. "The bridge is safe."
But the work is not over. Engineers say slight corrosion was also found on a few other piers, but not anywhere near as bad. That's why they installed eight probes to monitor the corrosion at different locations to see if it gets worse and at what rate.
"Really to measure the areas where we saw corrosion last fall," explained Buchholz. "It's not nearly to the extent of pier 22 but to measure that rate and then we can use that information to see if we have to fix anything in the future."
It's the first time a system like this has been used in Wisconsin. State bridge inspectors say they've learned a lot from this project and are now looking into the soil conditions surrounding other bridges across the state.
"We haven't found any of the similar situations," said Scot Becker, Director of the Bureau of Structures. "But we're looking to see if the ingredients are there."
Those monitoring probes will be checked at least every two years. A 2,000 page final investigation report is expected from WisDOT this fall.
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