A Delaware bridge that carries part of a major East Coast transportation artery has been closed indefinitely after several support columns shifted nearly two feet out alignment.
The Delaware Department of Transportation announced an emergency closure Monday (June 2) of the six-lane Interstate 495 bridge that carries 90,000 vehicles daily over the Christina River in Wilmington.
The state's Transportation Secretary, Shailen Bhatt, told reporters that the closure was "going to be a pretty significant traffic event for the Northeast region."
After a preliminary analysis, engineers said the bridge was not at risk of collapsing, adding that while the bridge could hold its own weight, it could exceed capacity under a full traffic load.
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The bridge that carries I-495 over the Christina River in Wilmington, DE, is closed indefinitely while crews try to figure out why four pairs of support columns shifted.
The 4,800-foot-long structure, identified as Bridge 1-813, was built in 1974 and features a concrete deck on steel beams. The bridge was last inspected in October 2012, and showed no deficiencies, according to DelDOT.
Officials said four of the 37 pairs of vertical reinforced concrete columns that support the bridge were leaning; the worst is 4 percent out of its vertical alignment.
The shifting columns have also caused the concrete pier caps to move, resulting in a height difference of about one foot between the bridge deck's barrier walls.
"This is a very serious situation that we're glad we caught in time," Bhatt said.
Bhatt said he has assembled a team of experts from DelDOT, the Federal Highway Administration, engineering consulting firms, and the University of Delaware to investigate, monitor and determine the next steps.
Tilt monitors were installed Monday evening to measure any additional movement, but data collected from the sensors over a 12-hour period were inconclusive, DelDOT said Tuesday (June 3).
DelDOT's contractor, AECOM, is working with the agency's bridge design consultant and geotechnical experts to figure out possible reasons for the bridge's movement.
So far, engineers have floated two possible sauses: settling and compacting of soft soils under the bridge, or corrosion of steel pilings 140 to 160 feet below the surface.
Pennoni Associates has been inspecting the overall bridge, and no other distress to the structure has been found, DelDOT said.
Calls Come In
DelDOT received a report late Friday (May 30) about an anomaly with a column and sent an inspection crew Monday morning. According to the Associated Press, the Friday call came from an engineering firm working on an unrelated project.
"It didn't come to us as like an emergency call," Bhatt said, explaining why a crew wasn't sent out until Monday.
According to ABCNews.go.com, the call came from two employees of a private geoscience consulting company who first noticed cracking in the soil around a large dirt pile near the leaning columns.
Engineers are trying to determine if the dirt pile could be related to the bridge shifting.
"We don't know what the effect of that weight is," Bhatt said. Officials are also unsure where the dirt came from and how long it has been there.
"This is a very serious situation that we're glad we caught in time," said the state's Transportation Secretary, Shailen Bhatt.
A DelDOT equipment operator also sent a notification Monday morning after noticing the concrete barrier on the road surface shifting.
"When we got the appropriate information that there was a significant event going on, we closed the bridge out of an abundance of caution," Bhatt said, according to DelawareOnline.com.
Bracing for Stability
The transportation agency and AECOM are now designing a temporary brace, including shoring up and leveling the deck.
"Once we feel the structure is stable and able to hold a live load, then, and only then, can we open it to traffic," DelDOT's chief engineer, Robert McCleary, told DelawareOnline.com
Bhatt said DelDOT was working with FHWA to determine if the bridge was eligible for federal emergency relief funding.