BATON ROUGE, La. – Stability issues of the soil surrounding the Chef Menteur Pass bridge on U.S. 90 east of New Orleans will delay completion of emergency repairs, the state Department of Transportation and Development announced today.
The project, originally set for completion by Saturday (April 15), is now expected to be completed within two to four months, or by August, at more than double the cost, according to Gill Gautreau, DOTD structures and facilities maintenance administrator.
The contractor, Coastal Bridge, is adding additional rip-rap, or rocks, to slow the foundation’s deterioration while the movement is being monitored in order to determine the best remediation approach, according to Kim Garlington, DOTD pavement and geotechnical design services engineer.
Wave action from hurricanes Katrina and Rita resulted in scouring, or the washing away of soil around the bridge supports, which destabilized the piers on the Chef Pass bridge, explained Brian Buckel, DOTD District 2 construction engineer. The original $1.3 million emergency project included replacing several spans on each side of the bridge with longer, 120-foot girder spans. The contractor began fabricating the new spans in February and then moved them to the site to replace the failing spans.
However, crews noticed a tension crack in the ground and DOTD’s Geotechnical Services section investigated by installing instrumentation in the slope. Possible deep-seated movements are being monitored to determine the extent of the slide.
Garlington said, “This is a very deep channel, and the material at the top of the slope is very susceptible to scouring. The slope is trying to move out toward the channel.”
Garlington said initial plans are to fix the toe of the slope using the rip-rap; the rocks add weight to help prevent additional sliding. Then, she said, DOTD is considering using four even-longer girders, about 200 feet each, on the New Orleans side, or southwest end of the bridge to reach a stable portion of the bank.
Gautreau added that the cost of the additional work is estimated at about $1.6 million to fabricate and install longer spans on one end of the bridge; heftier bents (groups of pilings with a cap on which the girder sits); additional stone; and additional demolition.