Construction is beginning on the largest design-build civil works project in the history of the U.S. Army Corps of Engineers, a $695-million barrier designed to protect New Orleans from storm surges similar to that generated by Hurricane Katrina, which inundated the low-lying city in 2005.
The Inner Harbor Navigation Canal Lake Borgne Surge Barrier Project is a massive job designed to block hurricane storm surge, by 2011, from entering the funnel-like confluence of the IHNC, Mississippi River Gulf Outlet and Gulf Intracoastal Waterway, deemed the Achilles’ heel of the Greater New Orleans Hurricane and Storm Damage Risk Reduction System.
Test piles are being driven for a 7,490-ft-long, 24-ft- to 26-ft-tall, braced concrete barrier wall. The wall is the central component of the roughly two-mile-long project. It also includes a sector gate 150 ft wide by 16 ft deep with a bypass barge gate of the same dimensions at the intracoastal waterway, as well as a 56-ft-wide by 8-ft-deep navigable sector gate at Bayou Bienvenue. Rock-reinforced T-wall-style floodwalls will form transitions to the bankside levees and the gated structures. “This will be the most robust structure you’ve seen in this area,” says Lt. Col. Victor Zillmer, the Corps’ resident engineer for the project.
Shaw Environmental & Infrastructure Group, Baton Rouge, was to break ground on Dec. 4. “This is a different application of this system for a floodwall,” says Charlie Hess, senior vice president of operations for Shaw. “These are usually built as breakwaters, but the batters provide extra strength for the differential head you get with storm surge.”
Hess says plans call for the wall to be constructed of 1,284 concrete cylinder piles 66-in. in diameter, 144 ft long, and driven to 130 ft. “The concrete barrier wall runs from the south transition across MRGO to the Bayou Bienvenue sector gate,” Hess says. “That section is 3,432 ft long and includes 588 piles. The north wall, from the Bayou Bienvenue structure to the GIWW structure, is 4,058 ft long and includes 696 piles.”
The wall will be braced on the protected side by 660 steel-cylinder batter piles, placed every second plumb. The 36-in.-dia steel piles will be driven to 230 ft. Skyline Steel Inc., Armorel, Ark., is supplying the steel, and Berg Steel, Royal Oak, Mich., is doing plate fabrication and rolling it into 40-ft sections, Hess says. Final welds to join sections will be done at Shaw Global, Delcambre, La.
An estimated 2,600 square concrete closure piles will finish the joints in the round plumb piles. The square piles will be bolted together with concrete poured to fill voids, says Ron Elmer, the Corps’ IHNC branch chief. The top of the plumb piles will be fitted with rebar and filled with concrete down to 85 ft. That will provide a tie-in to concrete deck caps, which top off the structure and create an access roadway. “Each of the 300 caps is 17 ft long, 6 ft tall, 12 ft wide and weighs an estimated 96 tons,” Elmer says. A parapet wall on the surge side brings the structure to its final contract elevation.
Part of Shaw’s contract is to provide advanced measures to block surge on the intracoastal waterway by the 2009 hurricane season, which begins on June 1, 2009. The contractor anticipates completing installation of the wall, if not the cap, by then.
The contract for the caps will be “on the street soon,” says Hess. The next solicitation after that will be for construction of an earthen dike to partially fill MRGO, raising the depth from 40 ft to 15 ft. The dike, whose dimensions have not yet been released, will consist of a fill-rock perimeter and an interior of geotextile fabric topped with sand. “We are basically filling in the hole and driving piles through it,” Elmer says.
Shaw’s first task on site is to move shoreline protection and dredge for access. The spoil will be used to raise 205 acres of marsh by 5 ft for “enrichment” that will eventually settle, Zillmer says.
Production on the 11,566 16-ft-long segments of concrete-cylinder piles is already under way at Bayshore Concrete Products Corp., Cape Charles, Va., and Gulf Coast Pre-Stress Partners Ltd., Pass Christian, Miss. The segments will be pieced together and post-tensioned once the test pile results are analyzed, probably by mid-March, Elmer says.
Gulf Coast Pre-Stress has the lion’s share of the 60% of casting work already awarded for the piles. By the end of November it had 2,400 sections awaiting the Corps’ final length specifications. “It will be the end of January before we actually start putting pile together,” says Mike Spruill Jr., the head of cylinder pile production at Gulf Coast Pre-Stress. “We will add about 30 more people and be in peak production when the Corps gives us the specs for the lengths. This is the biggest cylinder-pile job we’ve ever had.”
Despite the large size of the job, Spruill says his company has sufficient equipment, such as stressing jacks and cable pushers, on hand because it had already geared up for another big current contract—it would have been its largest contract—supplying pre-stressed piles and girders for the Interstate 10 Twin Spans project over Lake Pontchartrain. “We had all this equipment because we thought the Twin Spans would use cylinder piles, but they didn’t,” Spruill says.
To spin the cylinder piles, a steel cage is constructed and inserted into steel forms. A head gasket fixed with rubber tendon ducts is inserted into the cage and form to create gaps in the “spun” concrete where the post-tensioning steel will be threaded, explains Spruill. “Then we lay down the forms and torque all the tendon ducts to 90 lb per ft,” he says.
The forms are transported via dollies to the spinning machine and laid down. Low-slump concrete is fed into the forms while they are spinning; centrifugal force throws 4.75 cu yd of concrete into the cylinder pile. “We use zero-slump concrete so we can get a good stick to the form,” Spruill says.
Once the forms come out of the spinner, they are stood up and set to cure for an hour, then steamed for four hours. After five hours, they have reached 4,000-psi strength and the forms are stripped.
“That’s a pretty short amount of time for concrete to get to 4,000 psi,” says Spruill. “Then we lay them down on carts and line up all the holes. There are 32 stressing tendons in a 66-in.-dia pile.” To connect the 16-ft lengths, a second round of half-inch special strand is threaded through, making a total of 64 strands in each full-length pile.
To store the growing supply of cylinder-pile sections, GCP has already poured a 55-ft by 900-ft slab and is pouring another, says Mike Spruill Sr., president and CEO. The company also is in the process of acquiring 10 adjacent acres to add storage to its existing 110-acre site.
Spruill Sr. says he plans to bid on the caps and “every piece we possibly can” of the IHNC storm-surge barrier. “Before Katrina, a lot of structures were smaller,” Spruill Sr. says, by way of explanation for his company’s post-Katrina growth from $32 million annual sales in his best year to $92 million in 2007.
Spruill Jr. says the company has previously manufactured cylinder piles this large for other projects, but never in this quantity and for this application. “This will be the largest floodwall prevention project we’ve ever done,” Spruill says.