By Jan Carabeo and Pat Loeb
WILMINGTON, Del., (CBS) — Delaware highway engineers are studying a bridge on Interstate 495 to determine what is causing it to tilt and how to fix it. That portion of the highway remains closed in the meantime and it could be a while before it reopens (See Previous Story).
DelDOT made it very clear today that this is just day two of what will likely be a very long process.
Engineers are only in the early stages of this investigation. The findings presented today are preliminary.
But what we know right now is four pairs of those support columns are rotating causing tilting.
And a big pile of dirt may be one of the reasons why.
DelDOT busy taking a close look at four pairs of support piers on Tuesday.
Pier 12 in the worst shape. Engineers saying it’s tilting four percent out of vertical alignment.
The question now — is why.
“This is the sort of thing that is a defcon five for a transportation system,” said DelDOT Transportation Secretary Shailen Bhatt.
Officials say the bridge showed no sign of trouble the last time it was inspected in October 2012 but inspectors this week found four piers under the bridge tilting, causing the roadway to list eastward. Engineer Paul Moffitt says the initial theory is that the marine sediment in the soil beneath the bridge may be compressing.
“Any kind of movement or compression in that material would induce stresses onto those piles. The piles would be designed to resist that however if we would have large magnitudes of movement, you could end up moving the pile group,” said Moffitt.
As engineers explained how these piers on the I-495 bridge in Wilmington are supposed to work, they also offered some possible causes of the problem, starting with the fact that this bridge stands in a flood plain.
“That soft soil is very compressive or settlement-prone,” said Moffitt.
There could be a corrosion potential involved.
Then there’s this, a huge pile of dirt.
DelDOT is still trying to figure out how long its been here and how much it weighs.
In the meantime, officials have asked the contractor to move it while engineers determine the next step.
Officials say they’re studying at options temporarily shoring up the piers but until they can, they fear the bridge will not support traffic so the road will remain closed.
“The pier can support its own weight, however it cannot support full traffic load,” said Engineer Harry Rocker.
The bridge needs temporary support and until then it’ll remain closed, creating a traffic jam.
“Everywhere I go is a detour,” a driver said.
“Since I’ve gotten here it’s been a mess,” another driver said.
This bridge sees about 90,000 vehicles a day. DelDOT could not give a timeline when the span would re-open.
It’s still assembling a team to figure out the exact cause and that could take weeks.
And it’s still unknown if the columns are still moving.
DelDOT is planning daily updates.
Due to the I -495 Bridge closure and related congestion on all major and secondary roads in and around the City of Wilmington, DART bus routes will be experiencing delays of up to 20 minutes during the Wednesday morning rush hour.
Additional buses will be sent out when delays reach over 30 minutes.