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March 11, 2006

levee investigation

nope the experts

 still aren't on to em





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Weak clay soils 

combined with tilting concrete storm walls 

caused the failure of the 17th Street levee 

during Hurricane Katrina,

 according to an Army Corps of Engineers 

investigation released Friday.

The corps' first official findings 

 do not indicate whether 

they resulted from defects

 in design or construction,

the wall withstood less force

 than it should have.

  A 465-foot section of the 17th Street levee

 was breached Aug. 29, flooding the Lake View section

 of New Orleans.

 Breaches occurred on two other major canals

 in New Orleans;

 the analysis of those failures is incomplete.

As the 17th Street Canal

 filled up with water 

from the surges that inundated Lake Pontchartrain,

 the top of the wall on the canal

 began to deflect or tilt

 toward the neighborhood 

and away from the canal, 



The tilting of the concrete wall

 opened a gap between the soil

 and steel-sheet pilings 

that had been sunk 17 feet 

into the ground. 

The water raced into the gap

 and to the bottom of the sheet piling,

 exerting heavy pressure 

along the entire height

Despite those intense pressures,

 the levee should have remained standing,

 other storm walls in New Orleans 

suffered similar deflection 

during Katrina and did not fail.

But the soil was weak 

in ways the corps did not anticipate.

 The soil directly under the levee

 was compacted and strong, 

the result of the massive weight 

of the levee and storm wall 

sitting over the foundation for decades.

 However, at the toe of the levee

 in the backyards of residents

 living near the storm wall, 

it was comparatively weak. 

As the water pushed 

against the steel sheet piling,

 it caused the entire foundation

 of the levee to slide backward

 toward the homes,



 the gap also compromised 

half the strength of the levee.

 The gap negated any strength 

that would have come from 

the canal side of the levee.

At the 17th Street levee,

 the failure did not occur 

in a layer of organic peat,

 as earlier surmised.