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Audubon Bridge

Situation:

Crossing the Mississippi River by ferry has been the only choice north of Baton Rouge, Louisiana since the Civil War. But the ferry was unreliable, slow and a drag on development.

The State of Louisiana invested over $400 million to construct a new bridge spanning the Mighty Mississippi to spur economic development and improve transportation in this important industrialized part of the state.

Challenge:

The challenge was to connect St. Francisvillle to New Roads, Louisiana by constructing the longest cable-stayed bridge in North America, with the main span stretching 1583 feet across the Mississippi River. Audubon Bridge Constructors, a joint venture of Flatiron Construction, Granite Construction and Parsons Transportation Group, submitted the winning bid for overall construction.

SPX Power Team was selected to supply lifting jacks, hydraulic pumps and hydraulic hoses for several aspects of bridge construction, including the cofferdams needed to build the original footings for each tower. Richard Dudgeon supplied the hydraulic jacking design and equipment.

Solution:

The design called for two towers rising 520 feet above elevation, with each tower positioned on a pylon constructed on top of 21 eight foot (8') diameter drilled shafts. Pier footings were built in the Mississippi River but as close to each side as possible to minimize problems with barge traffic in the navigational channel.

Flatiron determined that a cofferdam was needed at each pylon site to withstand a potential high water mark of 80 feet and protect workers as they constructed the footings on the riverbed 40 feet below the top of the river. Conventional sheet pile cofferdams were ruled out as too costly, so a precast concrete cofferdam was used to withstand the river and protect the construction team.

Process:

Modular units were cast on-site in small, manageable sizes for easy transport and erected using a crane. The cofferdam was constructed in sections above the water and then, using hydraulic cylinders and pumps from SPX Power Team, lowered 47 feet in 2 to 4 inch increments into the river. A unique combination of 48 separate 1-3/4" diameter threaded rods, and Power Team hydraulic jacks sandwiched between steel beams were used to slowly lower these cofferdams into place.

SPX Power Team furnished 200 Ton, 150 Ton, and 55 Ton jacks, along with 10,000 PSI hydraulic pumps. Over 22,000 feet of hydraulic hose was utilized since the hydraulic operation station was located outside of the cofferdam.

Result:

Construction of the cofferdams commenced with the erection of precast panels in November, 2008 and successfully concluded with dewatering upon placement of a final 3,000 yard concrete seal slab in May, 2009. In the Spring of 2011, the ferry was shut down due to dangerously high water levels of the Mississippi River, and the James Audubon Bridge was opened in what the Louisiana Department of Transportation called an emergency opening. The bridge provided uninterrupted access for commuters across the river.