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We knew the flood control walls rested on peat.
Wet with flood waters, they slid sideways, free of all moorings.
Who decided 20 feet was deep enough for the pilings?
Jerry Nelson, 2011

Sliding Away on Wet Peat

The levees at 17th Street and London Avenue had 20 foot steel pilings topped with concrete walls. Unfortunately, below 20 feet lay a layer of peat which becomes very slippery when wet. At the 17 Street and London Avenue Canals, the entire earth embankment rolled as much as 35 feet into the city before tipping over, steel pilings, concrete wall slabs and all, to pour mud and the contents of Lake Pontchartrain into the city.

The wall was higher than the water, but so what?

"These levees did not overtop, yet they failed anyway," said Peter Nicholson, an engineering professor at the University of Hawaii at Manoa and the leader of the American Society of Civil Engineers (ASCE)investigating team. The ASCE team was comprised of civil engineers from across the nation, and computer modelers from the Louisiana State University Hurricane Center.

"Nothing beats a full-scale field test, and this was a full-scale field test," said Gordon Boutwell, president of Soil Testing Engineers Inc. and another member of the ASCE investigating team. "Some structures did the job they were supposed to, but some were total failures -- and those you can't just leave alone. And you can't expect to just stack them higher and walk away."

The Army Corp of Engineers first detected the conveyor-belt peat layer in the 1980s. Laboratory tests were performed on its properties in 1988. It's about time the Corp considered piles driven down 40 feet, not 20, for peat's sake.

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