Sagging bridge

A span on the Leo Frigo Memorial Bridge in Green Bay, Wis., dipped across all four lanes, prompting its closure. (Jim Matthews / Associated Press / September 25, 2013)

Engineering experts worked through the weekend to investigate why a major bridge in Green Bay, Wis., began to sag last week, prompting its indefinite closure.

On Sunday, crews finished placing movement sensors on three of the Leo Frigo Memorial Bridge’s piers, or support pillars, including pier 22, state Department of Transportation spokesman Mark Kantola told the Los Angeles Times.

It was pier 22 that settled Wednesday morning, causing a 400-foot span of roadway to visibly dip and prompting motorists to call 911. The Interstate 43 bridge's contours posed an immediate hazard and had the potential to send drivers airborne, according to another Department of Transportation spokesman, Kim Rudat.

Installing the network of sensors, which sound an alarm if any movement is detected, clears the way for investigators to safely examine pier 22, its neighboring piers and the bridge’s underside, Kantola said.

Before Sunday, investigators had tested the soil underneath other sections of the bridge, trying to ascertain the composition of the earth and looking for clues as to why the ground may have settled, Kantola said.

"The bridge needed a lot of fill because of the wet area underneath," said Kantola, adding that wood chips were among the materials used to fill in the area around the piers when the bridge was built in 1980.

"What else was used? We're trying to find out through soil testing," Kantola said.

Crews are also combing through engineering plans for the bridge and are reaching out to engineers that worked on the design, Kantola said.

Officials have yet to pinpoint a cause for the earth’s settling. Determining why subterranean settling occurred probably would entail a longer investigation than most bridge repairs, Rudat said.

Officials would not estimate possible costs or offer a timeline. But on Friday, Gov. Scott Walker issued an executive order declaring the bridge’s condition an emergency, clearing the way for the Federal Highway Administration to fund the first 180 days of repairs, according to a statement by the governor’s office.

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matt.hamilton@latimes.com

Twitter: @MattHjourno