Repeatedly it has come to light that the Corps of Engineers ignored crucial data that caused the floodwall failures that flooded New Orleans.
I have to admit… This time they didn’t ignore any data, they just made it up instead.
The key to learning why the 17th Street canal floodwall failed during Hurricane Katrina may lie more in what designers didn’t do, than in what they could have foreseen, experts now say.
Lost in the controversy swirling around a government panel’s comment last week that the designers of the floodwall could not have anticipated the combination of forces that brought the structure down was its finding that one of the main triggers for that failure — extremely low soil strengths under the toe of the levee — would have been detected had the design team done soil borings in that area, an official with the Army Corps of Engineers said Thursday.
Had the weakness at the toe of the levee been included in the analysis system used by the project designers, “The factor of safety would have been (low enough) to where they would have changed the design,” said Reed Mosher, a researcher at the corps’ Engineering Research and Development Center in Vicksburg, Miss., and a member of the corps-sponsored Interagency Performance Evaluation Task Force that is investigating the failures. The options considered would probably have included a T-wall, or a much larger levee, he said. …
Review team members said the designers did “few if any” soil borings at the toe of the levee, a finding John Greishaber, acting chief of the engineering division at the corps New Orleans district, said was not normal. He said his office normally required designers to take borings at the center line as well as at the toe of levees.
They didn’t even do soil samples at the toe of the levee?!?! So how did they figure out the soil strength there for their calculations?
Greishaber said when borings aren’t made, engineers can estimate the soil strengths at the toe of a levee.
Engineers use a standard formula for estimating the soil strengths at the toe based on the known strength of soils at the center line of the levee, where the soil strengths are highest. That means soil borings at the toe usually aren’t necessary unless the center line values are below a certain threshold, task force members said.
And that is where the designers made obvious mistakes, said J. David Rogers, a professor at the University of Missouri-Rolla who is a leading expert on levee failures and a member of a National Science Foundation investigation into the disaster.
“Looking at their calculations on the slope stability analysis, they used the same high figure from the center of the levee and projected it out to the toe, without any diminution in value,” Rogers said. “That was one of the first things we picked up when we started working on this.
“When we tried to find out what factor they used for diminution with increasing distance from the toe, it didn’t appear they used any. They were using maximum strength all the way to the toe. That’s the part everyone will take issue with.”
They used the same soil strengths where the levee was 6 inches high and where the levee was 10 feet high. You don’t need to be an engineer to know that 10 feet of mud is stronger than 6 inches. They just made up data as they went along.
So why didn’t this obvious flaw headline the Corps’ report released last Friday?
“Our position on this is that, very simply, whoever did the design just did not consider this particular mechanism,” said Link, the University of Maryland Senior Fellow who is head of the corps-sponsored Interagency Performance Evaluation Task Force. “We, IPET, made no value judgment whether it should have been considered or could have been considered.
In other words, “We were hoping nobody noticed.” – It gets better…
When task force panelists and corps engineers were asked if that meant the design systems used by the engineers of the day could not have foreseen this type of failure, they answered “yes.” [cough lie cough -ed]
Link said that while the individual components of the failure are well documented as concerns for engineers doing stability analysis of levees and floodwalls, the combination of those factors coming together at the same time is not.
That is pure spin. The Corps failed to account for probably about a dozen factors. They are trying to make that case that ALL DOZEN needed to happen at the same time to doom the floodwalls. We know that is not true. The tests they ignored in 20 years ago proved that. What the Corps is actually saying, if you read thru the spin, is that they made so many mistakes they shouldn’t be held accountable.
This is not the first time they’ve used the “Don’t blame us, we’re stupid” line of defense.
For a few days after the storm, the Corps was running around on T.V. saying that all the levees failed for different reasons. Until people like myself pointed out that if an engineered structure failed for multiple reasons then -by definition- it means the engineers screwed up multiple times. They dropped that line of spin.
When I first heard the floodwalls failed well below their design specifications, I was in disbelief. Now that we know the sheer randomness of the design process I’m now not sure how they held up as long as they did.