The gate leaves, which were fabricated at Shaw Global in Delcambre, La., are 42 ft tall and have an arc length of floodgate shield that is approximately 103 ft, says Larry Haser, vice president of operations management for Shaw Environmental & Infrastructure, Baton Rouge, the prime contractor.

The gate leaves arrived on site May 8 and are to be set in-the-wet, rather than inside a dry cofferdam. The contractor began pulling sheet piles to re-flood the cofferdam on May 10.

Installing the 550-ton gate leaves will be “very tricky,” Zillmer says, since each leaf must be attached at the pintle on the bottom, the thrust block in the middle and the hinge block near the top with a 1/8-in tolerance.

Massman will use a 600-ton crane and a 700-ton crane to move the gates from the transport barge to inside the flooded cofferdam. “The gates will be moved into final position using a system of push boats, winches and guides,” Haser says. “When accurately positioned, they will be sunk into final position in a controlled manner.”

 The gate structure foundation is supported by 478 steel pipe piles that are 154 ft long and driven to a tip depth of -178 ft. “When we built the barge gate next to it, using 2-ft-diameter square piles, we noticed a lot of movement,” Zillmer says. So instead of using the planned, 3-ft-dia. concrete square piles for the sector gate foundation, the contractor switched to 3-ft-dia. circular steel piles to reduce displacement.

Last July, Shaw’s subcontractor, TMW, a joint venture of Traylor Bros., Evansville, Ind., Massman and Weeks Marine, Cranford, NJ, drove the pilings during 6 p.m. to 6 a.m. navigation closures. “We only have four piles out of tolerance, and only by inches,” Zillmer says. “That’s quite an accomplishment for driving at night, underwater.”  

The cofferdam is larger than a football field: 163 ft by 383 ft, Zillmer says, and required a 10,251 cubic yard tremie slab. “It is one of the largest, continuous underwater concrete pours ever,” he says.

C.J. Mahan Construction Co., Grove City, Ohio, made the 58.5-hour continuous pour last October. “We had concrete truck operators from all over the country supplying the 160 CY per hour pour,” Zillmer says.

The 8-ft sill on top of the slab required 12 pours, each over 1,000 cu. yd.

At the end of April, the contractor was placing the last lifts on the thrust gates, ringwalls and abutments in preparation for the gate placement. “It will only take about four days to put the gates in, but we’ve planned 13 days in the schedule to accommodate wind and weather,” Zillmer says.