The southbound lanes of the I-495 bridge spanning the Christina River in Wilmington, DE could be open as soon as Labor Day this year, and the northbound lanes would be opened several weeks after that, announced DelDOT Secretary Shailen Bhatt today, at a briefing held today.
"The timeline that we are announcing today is only possible because we have acted quickly to mobilize firms and personnel that have a proven track record of reopening critical transportation infrastructure under deadline pressure," Bhatt said. "As of today, the people, materials and equipment needed to reopen the I-495 bridge is on its way to Delaware from across the United States."
Design for the project is being managed by AECOM. Construction will be performed by J.D. Eckman, Inc. The two firms have a history of successful collaboration of rapidly reopening other bridges on the U.S. interstate highway system, including structures on I-95 in Philadelphia and Wilmington, DE.
The plan to reopen the bridge to traffic calls for the construction of new concrete-filled shafts down to bedrock beneath the columns that have tilted out of alignment. These shafts will create a stable surface above the underlying unstable soil. The concrete shafts will be tied together with a reinforced concrete grade beam. Temporary jacking towers would be erected on the grade beam to restore the bridge's superstructure to its original position, and lift the weight off of the existing, rotated piers. Once the bridge has been rendered safe for traffic, permanent new concrete columns will be erected taking the place of the jacking towers.
The first phase of construction to re-open the bridge is estimated to cost $20 million, while the cost of the permanently fixing the problem is not yet certain, said Bhatt said.
There were a number of options considered for reopening the bridge, Bhatt said.
"We first looked at just shoring up the existing bridge, but that option was quickly ruled out because of the poor soil conditions. Another idea was to fully reconstruct this section of the bridge. That option would've put us at an early 2015 opening, which was not a viable option given the traffic volume the bridge normally carries."
Bhatt said it became immediately clear that the most expeditious way to make the repairs was to bring in the contractor early, so that from day one the firm that will fix the bridge is working side-by-side with firm who designed the structure. "We didn't want to lose time by designing something on paper that a contractor couldn't build in the field. Work will proceed 24 hours a day, seven days a week until the bridge is reopened," he said.
Regarding potential causes and when the problem was first detected, Bhatt said, "A lot of the questions we're receiving right now are about what caused the bridge to tilt, whether it should've been closed sooner, and when did DelDOT know about the tilt. I want to be clear that we will do a thorough analysis of agency actions and the causes that led to this situation. We will do so in a transparent manner by sharing our findings publically. However, the major focus of our efforts as an agency right now is to get this bridge reopened as safely and quickly as possible."
Some details about the project:
- The plan will stabilize and re-align a 400-foot section of the 4800-foot-long bridge.
- DelDOT believes damage is isolated to this area for the following reasons; the entire bridge has been inspected and doesn't show signs of tilting or deflection, outside of the area supported by the four sets of columns that are leaning. No corrosion was found in the existing steel piles supporting the columns
- The geology of this area is important
- The layers of soil are comprised from top to bottom of approximately 6 feet of dredge spoils, 100 feet of accumulated organic material and a layer of clay and densely packed sand on top of bedrock.
- These layers are very compressible, and very saturated, making the construction of an entirely new support structure on bedrock necessary.