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Underwater bridge inspections help ensure safety above

Scuba gear is not a standard tool for engineers. However, a federal mandate requires bridges crossing more than 20 feet of water to undergo underwater inspection every five years. So every five years it’s time for a deep dive into Illinois’ waters.

Specially trained divers, many of whom are engineers contracted by IDOT, regularly explore the depths to primarily check for scouring, the leading cause of bridge failure. Scouring is soil erosion surrounding bridge foundation elements such as pier footings, columns, piling and abutments.

Divers typically conduct routine inspections in the fall when water levels are at their lowest, comparing groundline elevations to those previously recorded. Low visibility poses a challenge as few bodies of water in Illinois offer more than a couple of feet of visibility—even with the aid of lights. Given the murky and dark conditions, inspections are typically tactile, with the diver relying mainly on the sense of touch to detect potential defects, foundation exposure, undermining and scouring.

If a structural- or safety-related deficiency is discovered that could pose a threat to the traveling public, IDOT’s Critical Finding Procedures are put into play. In these situations, inspectors would immediately contact the Bureau of Bridges and Structures and the appropriate bridge program manager to discuss the observations and develop an agreed-upon action plan. In the most serious situations, the inspector lead has the authority to close a bridge with local or state police assistance. Thankfully, this is extremely rare.

For more information on underwater inspections, watch On Location: Lacon Bridge.