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Floodwall's shallow pilings called 'design flaw'
New Orleans -- When the Army Corps of Engineers started to design a floodwall on the 17th Street Canal here in the early 1980s, deep probes found what geologists viewed as a potentially weak layer of peat soil about 15 feet below sea level in the area where the wall collapsed during Hurricane Katrina. Yet in building the wall, Corps officials acknowledge that they did not drive the steel pilings -- the main anchors for the structure -- any deeper than 17 feet. Several outside engineers who have examined the designs say the decision not to hammer the pilings deeper and into firmer ground left the support for the floodwall dangerously dependent on soil that could easily have washed out under the immense pressure from the floodwater. And members of a team of experts from the National Science Foundation say it now seems likely that this simple failure probably led to the collapse of the walls on the 17th Street and London Avenue canals, which flooded the main parts of the city. Corps investigators say they have just started going through 235 boxes of the agency's records that could shed more light on why the engineers believed the design was safe. And outside investigators say they would like to examine more of the records before deciding what caused the break. Robert Bea, an engineering professor at UC Berkeley who has examined the soil data for the National Science Foundation, said the decision not to drive the piling deeper was "a design flaw." He said he and others in his group believed it was the most likely reason that the floodwaters broke through, shoving parts of the walls and the earthen levees beneath them as far as 35 feet into nearby neighborhoods. Walter Baumy, the chief engineer for the Corps' New Orleans district, said, however, that the problem was "a little more complicated than just saying that there's a 5-foot-deep layer of peat in there." "What's probably more important is, how did we account for it in the design?" Baumy said. "Or did we properly address it?" He added, "We need to step back and review our design and see if it was done properly at that time." The teams from the National Science Foundation and the American Society of Civil Engineers visited the breach sites and plan to release a preliminary report in early November. Posted by: Steve 2005-10-24 |
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