Belle Chasse Bridge and Tunnel Replacement

The Belle Chasse Bridge and Tunnel in Louisiana, infamous for causing traffic delays along LA 23, is finally being replaced by a modern long-span bridge. A GeoEngineers team led by Associate Geotechnical Engineer Larry Sant is providing foundation design and other geotechnical services for this ambitious project.

Although the Belle Chasse Bridge and Tunnel have carried LA 23 traffic across the Gulf Intracoastal Waterway for more than 50 years, they have been plagued by regular closings for most of that time. Northbound traffic came to a halt whenever the vertical-lift bridge opened for a passing ship, and southbound tunnel traffic had to contend with frequent flooding and maintenance closures.

“It’s pretty rare to have a tunnel in Louisiana,” Larry says. “They nicknamed it the carwash because it leaks so much.”

The aging bridge and tunnel will be replaced by a 3,300-foot fixed-span bridge carrying both north and southbound traffic via four travel lanes. The $169 million project is a public-private partnership (P3) between the Louisiana Department of Transportation and Development (LA DOTD) and the Plenary Infrastructure Belle Chasse Consortium, a large team of consultants and contractors. It’s the first P3 of its kind in Louisiana history.

Designing and testing foundations for a long-span bridge in soft Louisiana soil is no easy task, especially since the bridge would be supported by a combination of precast prestressed concrete piles and relatively large 48-inch diameter steel pipe piles. Geotechnical recommendations are usually validated by on-site testing, which can cause construction delays because of the long set-up times in these soft clay soils. To streamline the process, the GeoEngineers team completed a combination of test piles and dynamic testing (PDA) to provide early-acceptance criteria for production piles. With our testing and analysis, the contractor doesn’t need to wait for set-up to complete testing before piles can be approved.

The GeoEngineers team also is contending with United States Army Corps of Engineers (USACE) regulated flood-control T-walls and levees on either side of the intracoastal waterway. Fortunately, our staff have a lot of experience working with the USACE and its regulations. To satisfy USACE requirements, Larry and the team evaluated how settlement, stability, pile driving vibrations and other construction activities might affect the flood walls.

GeoEngineers’ scope of services—including foundation design and testing, settlement analysis, slope stability and interaction analysis for USACE flood wall systems—is already about three-quarters complete. The new bridge is expected to open in 2024, although demolition of the old tunnel and bridge will take an additional year.

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