The steel sheet piles anchoring 450 feet of floodwalls on the 17th Street Canal in New Orleans are too close to underground sand, so the U.S. Army Corps of Engineers will bolster them with up to six feet of rock and clay.
Tests showed that the bottoms of the sheet pile walls were within two feet of layers of underground sand, said Col. Richard Wagenaar, commander of the corps’ New Orleans district.
“This is a lesson learned from Katrina,” he said. “Our geotech sampling located a sand stratum that’s within five feet of the tip of the sheet pile, and that’s like an alarm that goes off.”
Underground sand from prehistoric beaches proved too unstable a foundation for the London Avenue Canal levee during Hurricane Katrina, which breached levees along three drainage canals and flooded most of New Orleans and parts of East Jefferson Parish.
Some yards in Gentilly, where the London Avenue Canal is located, wound up under six feet of sand.
Safety standards adopted since the storm require the tips of sheet pilings to be at least five feet above sand.
Analyses indicated that even without reinforcement, the floodwall in that region wouldn’t fail under six feet of water – the limit before the Corps closes new storm surge floodwalls between the canals and Lake Pontchartrain, district chief engineer Walter Baumy said.
“What we’re doing is actually adding insurance,” he said.
Information from: The Times-Picayune, www.timespicayune.com
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