Engineers investigating canal levee and floodwall failures in New Orleans are going back to the toolbox after crews pulling sheetpile at one breach site found that non-invasive tests, which indicated the pilings were 7 feet too short, were wrong.

Seven pilings pulled Dec. 13 from either end of the site of a 455-ft breach of the 17th Street Canal that opened in Hurricane Katrina were found to have  been long enough to pass the specified elevation of 17 ft below sea level. Two different nondestructive tests had showed them to extend only to -10 ft.

“One of the things we wanted to find out is if the nondestructive parallel seismic tests are valid for treating the rest of the system,” says Col. Lewis Setliff, the U.S. Army Corps of Engineers officer in charge of restoring the city’s storm defenses to Category 3 hurricane level of protection. “This sort of testing is important so we can suppress some speculation and make adjustments on facts and science,” Setliff says.

Both the Corps and a team from the Louisiana State University Hurricane Center, Baton Rouge, La., had independently performed seismic tests on the pilings using different technologies and come up with similar results; that the pilings were short. But when the piles were pulled they ranged from 23 ft, 31⁄8 in. long to 23 ft, 77⁄16 in. long—all long enough to reach the design elevation.

The results vindicated the work Boh Brothers Construction Co., New Orleans, the contractor that sank the piles 15 years ago. “We did it exactly in accordance with the plans and specifications that were given to us when we bid, and that’s what you are going to see when it is pulled,” predicted Robert S. Boh, president and CEO, in the hour before the first pile was drawn.

The proceedings also included removal of the concrete floodwall cap, 10 ft on either side of the breach. Four-ft-sq test sections were cut from each. The samples will be sent to a third-party laboratory for testing. “Coupons” also were cut from the pulled steel for similar analysis.

“We are testing everything to eliminate possibilities,” Setliff says. Other investigators are studying soil conditions. They will be on the scene during the next step of the breach repair, which involves excavation of the emergency limestone wall that Boh constructed after the levee failed.

For now, Setliff says that the Corps is applying some lessons from analysis conducted to date, including that design improvements are needed at transitions between the earthen levee and other materials, and that inverted T-walls  would be better than I-walls at reducing scour when levees are overtopped.

“We are also looking at where utilities run through levees,” Setliff says. “We have to take a holistic look. This is the beginning of a long investigation. It’s part of finding out what went wrong.”