This story, headlined "Soft soils under levee sank city," was originally published Oct. 15, 2005. It is being republished for the 20th anniversary of Hurricane Katrina as part of The Times-Picayune's Pulitzer-winning coverage.

WASHINGTON — Soil tests indicate that a soft, spongy layer of swamp peat underneath the 17th Street Canal floodwall was the weak point that caused soil to move and the wall to breach during Hurricane Katrina, an engineer who has studied the data says.

"The thing that is remarkable here is the very low strength of the soils around the bottom of the sheet pile" base of the floodwall, said Robert Bea, a geotechnical engineer at the University of California, Berkeley, who examined the test results. Bea is a member of the National Science Foundation team that is studyin

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