With a massive mound of dirt being removed from underneath a closed interstate bridge in Delaware, the columns that were tilting seemed to have rebounded slightly, officials said Monday.
As the dirt was being removed over the weekend, sensors indicated columns moving back very slightly toward their original alignment. That finding bolsters the theory that the weight of an estimated 50,000 tons of dirt that a contractor dumped next to the Interstate 495 bridge over the Christina River contributed to moving underground soils. The result was four pairs of bridge columns tilting in the direction of the dirt mound.
Officials ordered the emergency closure of the bridge a week ago when they saw that the columns were tilting and do not know how long it will take to make it safe for vehicle traffic again.
But a local businessman called 911 almost two months ago to report that concrete barriers separating the bridge's northbound and southbound lanes, which are supposed to be level with each other, had separated in elevation by as much as a foot.
Separately, a geotechnical engineer working in the area on an unrelated project notified transportation officials on Thursday, May 29, that the bridge columns appeared to be tilting. Officials did not send out an inspection team until the following Monday.
Delaware Department of Transportation officials have yet to provide records requested under the Freedom of Information Act regarding their response to the two notifications they received about the bridge.
Meanwhile, a state environmental official said Monday that testing of samples from the dirt pile showed no dangerous contaminants. Tim Ratsep, administrator of the state environmental agency's Site Investigation and Restoration Section, said test results showed only low levels of polyaromatic hydrocarbons, or uncombusted carbon, which he said is typical of soils next to roadways because of asphalt.
The soil testing results cleared the way for environmental officials to approve storage of the dirt on a developer-owned parcel of land on South Market St. in Wilmington.
With completion of the dirt removal Monday, engineers are turning their attention to shoring up the bridge, which typically carries about 90,000 vehicles a day on the I-495 bypass around Wilmington. Crews are installing brackets and post-tensioning bars on the columns to tie them together and stabilize them.
In addition to tilt sensors on the bridge columns, crews also are installing sensors to monitor underground soil movement.
An underwater inspection of the first pier in the water on the south end of the bridge was scheduled for this week, weather permitting. Officials said no deformation or movement has been detected on the pier above the waterline.
With traffic being shunted from the I-495 bypass onto already congested Interstate 95 through downtown Wilmington, officials warned of the nighttime closure of a section of I-95 northbound for repaving starting Tuesday night. Transportation officials said road already had been milled for repaving before the bridge closing, and that repaving must be done now because the milled asphalt surface has degraded under heavier traffic volumes.