The New Orleans Times-Picayune, being printed again in New Orleans on Saturday the 15th, reported that engineer Robert Bea of Cal Berkeley and also of the National Science Foundation, says that the walls which failed on the 17th Street Canal and the London Avenue Canal did so because beneath their foundations was a layer of peat. This layer was weak. Bea was asked by the newspaper to interpret findings on a Corps of Engineer website, which the Corps was not willing to interpret. The findings were from borings into the soil beneath the walls.
Bea reckons that the extraordinarily weak peat allowed the walls to slide sideways under pressure, because the base of the walls' sheet pilings was either above on in the layer of peat.
In one boring, the sheer strength of the soil at 27 feet down is just one tenth of the strength just 8 feet further down. At 70 feet the sheer strength is 0.6 tons per square foot, 30 times the value at 27 feet.
It seems unlikely that the peat layer, giving its size laterally and vertically, could have been missed by pre-construction borings.
Did the contractor know the peat was there? Did the Corps of Engineers know?
If so, who reasoned that it would not matter? I do not know.
Saturday morning links
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