As a temporary fix, workers are erecting steel-truss support towers under the sagging Leo Frigo Bridge on Interstate 43 in Green Bay, Wis., and lateral supports at the top of the damaged pier as investigators continue their examination of the 8,000-ft structure.
Lunda Construction Co. of Black River Falls, Wis., started work Oct. 14 to put up two pairs of support towers on each side of Pier 22 and 55 ft away from its base. The pier sank 2.5 ft in late September and early October, prompting the Wisconsin Dept. of Transportation to shut down the bridge (ENR 10/14 p.22).
The support towers are designed to stabilize the bridge and to prevent additional sagging in the deck, WisDOT said. The cost is about $1.5 million and completion is planned for early November. Lunda was the general contractor when the bridge was built in the late 1970s.
The pier pilings corroded, causing them to buckle, the pier to sink and the bridge to sag, the department said. Repairs will cost an estimated $50 million.
Mike Oliva, professor of civil and environmental engineering at the University of Wisconsin-Madison, calls such temporary support "essential action."
"The buckled piles now are relying on lateral earth pressure from the soil surrounding them to prevent further buckling and settlement," Oliva says. "This creates a predicament because any further excavation or work around the piles could cause further buckling."
In a separate job, WisDOT has contracted Wiss Janney Elstner Associates Inc., one of the firms hired to help investigate the bridge, to construct a series of lateral supports at the top of Pier 22 and three others at a cost of about $80,000.
The department has not yet said when the bridge will reopen. Depending on the solution selected, it likely will be several months, especially as winter begins to affect construction, Oliva says.
"The piles below the sunken pier might be reclaimed, but it will be difficult," he says.
With temporary supports, corrosive soil could be removed and the integrity of the piles examined.
"If just the top corroded portion of the piles are buckled then it would be possible to jack the pier back up into position and pour a new structure below reaching from the top of the uncorroded and unbuckled length of pile to the original pile cap below the pier," he says.
However, "This is a long shot," Oliva adds. "The alternative looks like removal of the pier, driving new piles, and rebuilding the pier."