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New Tests Damn Corps of Engineers Design

There has been a controversy brewing in New Orleans over the length of the sheet pilings under the floodwalls that gave way. Sonar tests indicated that while the Corps' plans called for the sheet piles to go down to 17.5 feet below sea level, they were apparently only 10 feet down.

Rather than speculate, they yanked a "good" section (term used euphemistically) section of the wall out the ground and measured the sheet pilings.

First section of flood wall met specs, but was design flawed?

NEW ORLEANS (AP) -- Four sections of steel sheet piling pulled from the ground Tuesday during an inspection of a failed New Orleans levee appeared to meet design specifications for size and depth, contradicting earlier tests.

The sheet pilings were removed as part of an investigation into why the flood wall at the 17th Street Canal failed, contributing to floods that covered 80 percent of the city when Hurricane Katrina struck on Aug. 29.

The findings were significant because initial testing by sonar had indicated the piling was only driven to about 10 feet below sea level.

If the flood wall was built to specifications, the next question will be whether the design was faulty.

Brig. Gen. Robert Crear of the U.S. Army Corps of Engineers said the length of the first section removed varied from about 23.5 feet to 23.6 feet. About six feet of the sheet piling was above sea level, leaving 17.5 feet or more below sea level -- in accordance with design specifications. Three other sections were of similar size and depth, officials said.

LSU computer models showed that even if the pilings had gone to 17.5 feet below sea level as design documents said they should have, they still would have failed because the canal ran deeper and seepage into the ground still could have undermined the flood wall.

To be sure there, neither answer (10 ft pilings or 17.5) was going to be GOOD news for the Corps. But if the pilings were 10 feet they could claim they "only" failed to manage the contractor... The Corps was holding its breath hoping for 10 foot pilings so they could point to the contractor(s).

From these results it looks like the contractors built it EXACTLY the way the Corps designed it. One of the last scapegoats the Corps had has left the barn.


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Comments (11)

Do you know if they sonar'd... (Below threshold)

Do you know if they sonar'd the "good" sections prior to puling them out? If they did then we (they) would have a refence for how accurate their sonar data was. Maybe the conditions were such that it only read 10' but was actually 17.6'...

Just a thought.

I'm not a civil engineer, b... (Below threshold)
Cousin Dave:

I'm not a civil engineer, but what the heck, I'll play one on the Internet...

I can't help but wonder if all of that length below the water level did more harm than good. Could it have actually caused the piling to float up out of the ground? When I lived in Florida, they always told people to keep their swimming pools full during hurricane season, because the water in the pool would help keep a rising water table from floating it out of the ground.

So it sounds like New Orlea... (Below threshold)
TJIT:

So it sounds like New Orleans may be surrounded by levees that will fail long before they reach their design rating.

Lovely news for everyone who has moved / is moving back to New Orleans.

>Do you know if they sonar'... (Below threshold)
Paul:

>Do you know if they sonar'd the "good" sections prior to puling them out?

Yes. Why the sonar was not accurate. I do not yet know why.

----------
>I'm not a civil engineer, but what the heck, I'll play one on the Internet...

[as long as you qualify it as such have fun!]

>I can't help but wonder if all of that length below the water level did more harm than good. Could it have actually caused the piling to float up out of the ground? When I lived in Florida, they always told people to keep their swimming pools full during hurricane season, because the water in the pool would help keep a rising water table from floating it out of the ground.

Nope. (sorry but) you ain't even in the ballpark on this one. You keep your pool full because if the water gets underneath an empty pool then the pool turns into a boat and pops out the ground.

The sheet piles don't displace any air.

You may now resume whatever it is really do for a living. ;-)

(I'm not a CE either but I can handle that question ;)
------------------------------

>So it sounds like New Orleans may be surrounded by levees that will fail long before they reach their design rating.

GIVE THAT MAN A CEEEEGAR.

From these results it lo... (Below threshold)

From these results it looks like the contractors built it EXACTLY the way the Corps designed it.

That isn't what the report said! I quote:

"The issue here isn't structural, or the piles," Seed said. "The issue here is the foundation," meaning the earthen material in the levee beneath the flood wall.

Seed said a preliminary analysis of soil borings taken near the breach indicate that the strength of the soil, which included sand and peat, was "very low."

The poor quality of fill material is what doesn't match spec and where the contractor probably cut corners. I have hypothesized that this could have happened at night, coordinating with road construction, but while the Corps wasn't looking.

That said, the Corps' own drawings, showing sheetpile depth "Varies 10-17'" are damning in and of themselves. And you'd think they would at least have had the wit to line with plastic tarp a canal that had been dredged lower than the sheetpile design depth! Arrggghhh!

So, let the people of NOLA ... (Below threshold)
Mrs. Davis:

So, let the people of NOLA contract to have it designed, built and paid for themselves next time.

Solomon2:The soils... (Below threshold)
Paul B.:

Solomon2:

The soils suspected of being problematic are native materials down at or below the tip of the pilings, not fill which was probably limited to the earthen levees at the top of the piling. The quality of those native soils, the strength they could be counted on to provide, and the potential for undermining by seepage, would have been key design issues for the sheet piling system. Although there may still be room for contractor misconduct, they really can't be blamed for the presence of those soils.

Mrs. DavisBecause ... (Below threshold)
Paul:

Mrs. Davis

Because Louisiana is robbed of the oil revenue all the other states in the union get, LA has bought and paid for the levees about 10 times by now. Please get some eduation for shut the hell up.

Paul B., Enginee... (Below threshold)
doctorj:

Paul B.,
Engineers have to plan there designs with the ground support at the locale in mind. If this design wasn't suitable for our local soils, another design should have been used. The local news today is investigating the possibility that dredging of the canal 12 years ago may have been a factor. I guess we will have to wait and see.

Solomon2 That is E... (Below threshold)
Paul:

Solomon2

That is EXACTLY what the report said.

The issue was the depth of the piles. That issue was resovled. Period. Your quote backs that up...

"The issue here isn't structural, or the piles," Seed said. "The issue here is the foundation," meaning the earthen material in the levee beneath the flood wall."

In other words it was built to spec.

So we go back to design... (incluing soil strength)
----------------

Now if you wan to talk about ANOTHER issue being the fill, we can do that. The problem with your grand theory is that the mud you are talking about has been there for decades before the floodwalls were build.

Remember the floodwalls were only build less than 10 years ago.

---------
And finally:

I have hypothesized that this could have happened at night, coordinating with road construction, but while the Corps wasn't looking.

In the middle of a residential neighborhood? um No. If they were moving fill in at night, the neighbors would have had a cow. There were already disputes about the work they were doing.

Remember, this is LITERALLY in people's backyards.

Sorry dude that one's a no go.

And to think that Trent Lot... (Below threshold)
Tom:

And to think that Trent Lott saw to it that in the disaster package there are funds to build a museum for the COE.




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