FOR
PEAT's SAKE !!
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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