Kimball Street bridge piers at risk

The sun sets behind the Kimball Street bridge in downtown Elgin. (James Jordan•BocaJump)By Ted Schnell • BocaJump

The Elgin City Council is preparing to embark on a detailed look at the city’s bridges after the discovery of scouring that has exposed the pilings on the 10 piers of the Kimball Street bridge, which sparked a “below acceptable” rating of the bridge by the state.

Assistant City Manager Rick Kozal said Monday the exposure of the pilings does not place the bridge in any imminent danger. But it does require the city to increase the scope of its work for its annual bridge inspection and maintenance program to determine how the city will address the issue and to determine if there are broader concerns regarding the other bridges in Elgin.

Any remedy for the problem will be tackled later as a separate project. According to the city, the additional work – a scour assessment and countermeasure design – will provide the city with bid specifications to address the issue.

Bridge scour is caused by rapid currents that remove sand and rocks from the river bottom around the base of bridge abutments and piers, according to the U.S. Geological Survey, which lists scour as one of the three main causes of bridge failure.

At the Kimball Street bridge, the scouring around the 10 piers is occurring mainly on the southern side of the bridge toward the Kimball Street dam.

“We’re performing additional engineering services to determine the extent of the scouring on this bridge, and that will make a determination  as to what the level of remediation will be necessary,” Kozal said, adding the additional services are part of a proposed amendment to the city’s original 2010-11 bridge inspection and maintenance program contract with Collins Engineers Inc. The additional services carry a $73,544 price tag

While there is no imminent threat from the scouring, Kozal did note that the staff’s documentation of the issue to the City Council does note that if the piers are not corrected and the scouring continues unabated, it could eventually force the closure of the bridge.

“But we’re at that point yet,” he said.

Under the proposed amendment, the extended bridge scour study and related work is supposed to be completed by Dec. 31.

Kozal said Collins Engineers Inc. were to find danger from the scouring is more imminent, the city would be advised immediately.

Under its original agreement, staff documents indicate Collins Engineering conducted an above-water inspection for 14 Elgin bridges and construction management for maintenance work on 13 bridges. Above-water inspections include inspection of the bridge deck, support beams and pier probing for any undermining. Construction management includes contract document preparation, field observation for maintenance and repair work based upon the inspections. The original engineering services agreement cost $92,233.38, and the contract was awarded by the City Council on May 26, 2010.

The pier probing inspection at the Kimball Street bridge indicated considerable scour in the 10 piers, which triggered a “below acceptable” ranking by the Illinois Department of Transportation.

That sparked a request by IDOT for the city to prepare an action plan to remedy the problem and ensure the bridge’s safety, and that is what the study is supposed to include.

But IDOT also wants the city to evaluate two other bridges – the Shales Parkway and Eagle Road bridges – for scour.

Separately, IDOT is requiring the city to update its bridge inventory data to include the new Bowes Creek Boulevard and South Street bridges the city recently accepted, and to create an electronic bridge file containing inventory data for all of the city’s bridges, in compliance with the Federal Highway Administration’s National Bridge Inspection Standards.

The contract amendment with Collins Engineers Inc. will cost the city $73,544.34. Of the total, $20,463.93 will fund geotechnical and survey work, $39,791.72 will fund scour analysis and countermeasures design, $8,958.12 will fund electronic bridge file work and $4,330.57 will fund administrative costs. Monies for the work will come from the city’s riverboat revenue funds.

Following is a list of Elgin’s 20 bridges and what they cross: