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June 20, 2014 1:50 PM, EDT
Inspectors Confirm Dirt Pile Caused I-495 Bridge Piers to Buckle
DelawareGovernor/Flickr

Federal Highway Administration inspectors have confirmed earlier suspicions that a 50,000-ton pile of fill dirt placed adjacent to the I-495 Christina River Bridge site in Wilmington, Delaware, caused a buckling of four of the bridge’s 37 piers that led to its closing earlier this month.

“The FHWA has determined that the damage was initiated by a force external to the damaged element of the bridge — that external force being a large amount of soil adjacent to the bridge,” said a letter from FHWA Division Administrator Mary Ridgeway, sent to the Delaware DOT.

The I-495 bridge, which bypasses Wilmington, was closed June 2 after a tip. A subsequent inspection revealed that four of its support columns were tiling 4 degrees.

Ridgeway said that each of the pier foundations was excavated to determine the condition of the bridge’s piles, which were not corroded or fractured. However, the four concrete pile caps in question were found to be cracked, FHWA said.

“The piles were found to be under stress and unsuitable for support of an in-service structure in all four piers,” the letter said.

Ridgeway said the bridge “appears to have been properly maintained and inspected,” and that the state DOT likely could not have foreseen the problem.