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SHORT SHEETED -- SONAR SHOWS 17TH STREET CANAL PILINGS ARE SEVEN FEET SHALLOWER THAN THE CORPS CLAIMED |
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by Bob Marshall Sheet Piles Too Short for Safety, Experts Say, by Bob Marshall November 10, 2005 Sheet piling supporting the failed floodwall on the 17th Street Canal extends just 10 feet below sea level, 7 feet shorter than the Corps of Engineers has maintained, a team of investigators said Wednesday, strengthening earlier findings that faulty design and construction played a role in the canal breaches that flooded much of New Orleans during Hurricane Katrina. An LSU forensic engineering team, working in conjunction with the state attorney general's office, began examining the levee foundation with ground sonar Wednesday. The first reading was taken about 150 yards south of the break that allowed water from Lake Pontchartrain to inundate the city. Soil borings the corps consulted as it designed the walls in the early 1990s indicated pilings would have to be driven at least 40 to 50 feet deep before reaching soil strong enough to support the wall, investigators have said. "By going down just 10 feet, the piles are anchored in peat, the weakest layer of all the soils below the levee and the canal," van Heerden said. A copy of the final review set of design drawings for the project obtained by The Times-Picayune showed the pilings on the New Orleans side of the canal were to be driven 10 feet below sea level, while those on the Jefferson Parish side were 6 feet below sea level. But the corps has said the piles were actually driven to 17 feet below sea level before the concrete caps were added. Because the corps has refused to release final design drawings and other documents, researchers have been trying to solve what they call "the mystery of the sheet piles." But even with the sonar measurements, it still is unclear which government entity is responsible for the pilings. Newspaper reports from the period show the Orleans Levee Board first used sheet piles on the canal after the 1947 flood. After Hurricane Betsy slammed the city in 1965, the board drove 18-foot pilings to raise the canal floodwalls to 9.4 feet above sea level. But according to the engineering section of the Orleans board, in 1988 those pilings were pulled as part of work done by the New Orleans Sewerage & Water Board, and new pilings were driven. The length of those piles is not a part of the public record, and the Sewerage & Water Board did not answer requests for details on that work. "The corps keeps saying the piles were 17 feet, but their own drawings show them to be 10," van Heerden said. "This is the first time anyone has been able to get a firm fix on what's really down there. "And, so far, it's just 10 feet. Not nearly deep enough." |