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Floodwalls in Swampy New Orleans `Like Putting Bricks on Jell-O'
Newhouse News ^ | 11/10/2005 | John McQuaid

Posted on 11/10/2005 9:28:36 AM PST by Incorrigible

Floodwalls in Swampy New Orleans `Like Putting Bricks on Jell-O'

BY JOHN McQUAID

When the Texas construction firm AquaTerra Contracting began work on an Army Corps of Engineers hurricane protection project on New Orleans' West Bank, it encountered a serious problem: Its floodwalls wouldn't stand up straight in the mushy soil.

AquaTerra workers tried driving steel sheet piling down to the 55-foot depth the design required for the walls' foundation, company CEO Clay Zollars said. But the piling began to lean inward.

Zollars said the corps decided to nearly double the depth of the steel foundation to 105 feet. That didn't work either.

"Before we completed the wall, it began to lean and sink also," Zollars said. "The pilings were inadequate. The corps corrected that by installing some additional reinforcing steel in the concrete, but the wall still is leaning."

The top of one section of the 10-foot wall is more than a foot off the vertical, he said. AquaTerra is seeking $5 million it says the corps owes it for the extra work on the $11.1 million contract. Corps officials won't comment on the case because of the dispute.

The problems illustrate one of the basic obstacles to building reliable levees -- or any heavy structure -- in south Louisiana: It's a swamp.

Questions about soil are at the heart of investigations into why some of New Orleans' levees breached during Hurricane Katrina. Investigators say poor foundation conditions almost certainly led to the breaching of floodwalls along the 17th Street and London Avenue canals in New Orleans, flooding large parts of the city. The walls broke without being topped, suggesting a design or construction flaw. Layers of soft soils and organic matter under the wall foundations were not able to withstand the underground pressures generated by high waters in the canal, engineers say.

"They were struck with a bad situation, and they made a poor choice with those floodwalls, trying to put a structural wall on plastic soils. It's like putting bricks on Jell-O. There isn't a lot of support," said J. David Rogers, a veteran forensic engineer at the University of Missouri-Rolla who specializes in dam and floodwall failures.

What is unclear is how the corps and its contractors went forward with designs that some engineers now say appear fundamentally flawed. A team of engineers at the University of California at Berkeley studying the levee failures said that the corps' design standards do not seem to have accounted for all the soil uncertainties, raising questions about the design of the entire levee system.

The challenges of building floodwalls in weak, wet soils are well-known to engineers. A corps design manual warns that "by their very nature, floodwalls are usually built in a flood plain which may have poor foundation conditions."

Unexpected problems with weak soil have cropped up before. The AquaTerra case resembles a 1990s dispute concerning the 17th Street Canal floodwall. Segments of that wall also tipped off-center when the concrete wall sections were poured, requiring additional work and sparking a legal tangle. As with AquaTerra, the corps left the leaning walls in place.

A slightly tilted wall wouldn't necessarily be a safety hazard, engineers say, and it's not clear if the 17th Street Canal floodwall's early problems are directly linked to its ultimate failure.

Mississippi delta soil is notoriously unpredictable, both in composition and the ways it responds to stress. It's squishy and wet, with alternating layers of sand, silt, soft clays and peat, imbedded with the odd shells and decaying organic matter such as cypress trees.

Engineers must figure out how to imbed stable structures in this gumbo that will remain upright and withstand occasional extreme pressures from hurricane storm surges, winds and waves.

To do that, they depend on a delicate balancing of the forces of friction and gravity.

Floodwalls, skyscrapers, homes and other structures are typically built on steel or concrete piles imbedded in the earth. They get some support from the bottom tip of the structure, the way legs hold up a table. But most of the work is done by friction. Pile foundations are held immobile by friction between the soil and the surface of the pile. Long piles offer more security because they have more surface area and generate more total frictional force. Multistory buildings in downtown New Orleans are anchored by concrete friction piles extending hundreds of feet below the surface.

But a foundation is only as strong as the soil it's built in, and in engineering terms, strength is the soil's ability to resist forces acting on it and remain in place.

The area around the breached canals was swamp before it was drained or filled to make way for the city's residential expansion in the early decades of the 20th century and after World War II. Before Katrina inundated it, it looked like any neighborhood. But a completely different landscape lurks just under the surface.

"If you fly over the LaBranche Wetlands (upriver from the city), you will see wet and dry areas, areas with vegetation and areas with none," said David Lourie of Lourie Construction, a New Orleans-based soil engineering firm. "If you imagine some of that occurring at depths of 50 or 100 feet underground, that's what we've got in New Orleans residential areas."

Forces acting on the swamp for hundreds of years before humans decided to make it livable deformed it in peculiar ways, Lourie said, creating an unpredictable underground terrain.

"Through the passage of time, changes in Gulf water levels, changes in river flows, some of those (soil) surfaces were eroded or cut away," he said. "There were natural variations in the surfaces. They weren't all flat like a tabletop. You can have variations block to block. ... On one block you are over the center of a channel, and you could be only a block away and not over the same channel."

That means the requirements to anchor a foundation can also vary block by block. That's why detailed soil testing is essential before building a levee, or any big structure, to identify exactly what's below ground.

Documents show that in the 17th Street and London Avenue floodwalls, original soil borings were done about every 300 feet. It's not clear if there were later surveys that collected more data, but investigators say the soil surveys could have missed spots of soil weakness, and that could have created unidentified weak points in the walls.

In designing a wall, engineers weigh not only structural questions, but also issues of expense versus the high cost of failure.

Floodwalls "must be designed for the most economical cross section per unit length of wall, because they often extend for great distances," a corps design manual says. "Added to this need for an economical cross section is the requirement for safety. The consequences of failure for a floodwall are normally very great since it protects valuable property and human life."

Engineers say that the corps standards required an unusually low safety factor for the floodwalls, perhaps a remnant of a time when most levees protected sparsely populated rural areas, not cities and suburbs. A higher safety factor would require stronger walls -- and cost more.

Nov. 10, 2005

(John McQuaid can be contacted at john.mcquaid@newhouse.com. Bob Marshall contributed to this story.)

Not for commercial use.  For educational and discussion purposes only.


TOPICS: Business/Economy; Editorial; Government; US: Louisiana
KEYWORDS: katrina; louisiana
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Count on engineers to make honest assessments about the viability of floodwalls in Mississippi River soil around a major metropolitan area.

Alas, when will politicians ever listen.

1 posted on 11/10/2005 9:28:37 AM PST by Incorrigible
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To: Incorrigible

No insurance company in their right mind is going to be issuing any more policies in low lying NO.


2 posted on 11/10/2005 9:30:20 AM PST by Semper Paratus
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Comment #3 Removed by Moderator

To: Incorrigible

It was the engineers trying to get out the information about the Challenger. Politicians failed to listen then. I wonder if we should start electing more engineers to political office. They seem to be connected to the real world.


4 posted on 11/10/2005 9:33:08 AM PST by saganite (The poster formerly known as Arkie 2)
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To: Incorrigible

How about a floating swamp? Rebuild the city on stilts, or we could have the Venice of the South. Oh, well, they've probably already thought of that. However, the Dutch have new ideas about reclaiming land from the sea that might bear looking into.


5 posted on 11/10/2005 9:34:27 AM PST by hershey
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To: Incorrigible

Level the place. Make it for business and shipping lanes only. Build homes OUTSIDE of the city of N.O. and smarten up. Sick of paying taxes and funding this sin hole for nothing. Besides...it's too "French" for my taste.


6 posted on 11/10/2005 9:35:20 AM PST by My Favorite Headache ("Scientology is dangerous stuff,it's like forming a religion based around Johnny Quest and Haji.")
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To: Incorrigible
Would it be cheaper to create an enormous concrete raft and build the city on that? Water rises, city rises. Water leaves, city comes back down to earth.

Or relocate New Orleans a little to the West. Like, in Texas.

7 posted on 11/10/2005 9:35:25 AM PST by ClearCase_guy
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To: Incorrigible
AquaTerra workers tried driving steel sheet piling down to the 55-foot depth the design required for the walls' foundation

I keep reading about "sheet-steel pilings". How long is steel going to last while buried in a swamp?

8 posted on 11/10/2005 9:35:36 AM PST by wideminded
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To: saganite
"I wonder if we should start electing more engineers to political office. They seem to be connected to the real world."

I doubt you could get them to run. And given the engineer's propensity for truth, I can't see any of them winning.

9 posted on 11/10/2005 9:37:24 AM PST by Wonder Warthog (The Hog of Steel)
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To: Semper Paratus

Any fool knows that a building {or dam} is only as strong as its foundation. Put cement on top of swamp and water will go under the cement collapsing the cement wall. Even my 11 year old grandson can understand this.


10 posted on 11/10/2005 9:37:37 AM PST by USS Alaska (Nuke the terrorist savages - In Honor of Standing Wolf)
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To: wideminded

Ssshhhhhh! It will last ... long enough.


11 posted on 11/10/2005 9:38:08 AM PST by ClearCase_guy
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To: Incorrigible

Maybe just a big pile of money will hold back the flood water. Just keep adding more.


12 posted on 11/10/2005 9:38:39 AM PST by JustAnotherOkie
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To: Incorrigible
Count on engineers to make honest assessments about the viability of floodwalls in Mississippi River soil around a major metropolitan area.

The problem is always that political and business leaders never like what engineers have to say and force a solution with a small fraction of the needed resources.

Sometimes, the solution is acceptable. Many times, clueless leaders just manage to produce crap. Sometimes, no matter how much effort you put into educating them, they still make the worst possible decisions.

13 posted on 11/10/2005 9:39:14 AM PST by hopespringseternal (</i>)
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To: Incorrigible

Jello would be a better foundation than much of what NOLA sits on.


14 posted on 11/10/2005 9:40:42 AM PST by SWAMPSNIPER (LET ME DIE ON MY FEET IN MY SWAMP, ALEX KOZINSKI FOR SCOTUS)
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To: hershey

In a way, it is a city on stilts. You should see them driving the piles for a multistory building there....


15 posted on 11/10/2005 9:43:39 AM PST by Knitting A Conundrum (Act Justly, Love Mercy, and Walk Humbly With God Micah 6:8)
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To: Incorrigible

"Listen, lad. I built this kingdom up from nothing. When I started here, all there was was swamp. Other kings said I was daft to build a castle on a swamp, but I built it all the same, just to show 'em. It sank into the swamp. So, I built a second one. That sank into the swamp. So, I built a third one. That burned down, fell over, then sank into the swamp, but the fourth one... stayed up! And that's what you're gonna get, lad: the strongest castle in these islands." -- Monty Python and the Holy Grail.


16 posted on 11/10/2005 9:45:38 AM PST by Ingtar (Understanding is a three-edged sword : your side, my side, and the truth in between ." -- Kosh)
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To: Semper Paratus
No insurance company in their right mind is going to be issuing any more policies in low lying NO.

I was just at an insurance seminar for the AE community (Architectural/Engineering) and a geotechnical engineer complained he was having a very difficualt time getting insurance for their firm which does mostly dam work. Very high risk, and the premiums easily could put you out of buisness.

BTW, expect a few insurance companies to go under as a result of Katrina.

17 posted on 11/10/2005 9:45:53 AM PST by finnman69 (cum puella incedit minore medio corpore sub quo manifestu s globus, inflammare animos)
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To: jeffers; Brilliant; Gumdrop; nuconvert; visitor; Barnyard; carola; 1903A3; babble-on

PING!!!


18 posted on 11/10/2005 9:47:52 AM PST by Bigun (IRS sucks @getridof it.com)
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To: Incorrigible

Oh, oh! It can be done, but at what cost? Leave the part that is on high ground, but no development in the swamp areas except in small increments. Cheaper for the government to buy out the landowners and let them settle elsewhere.


19 posted on 11/10/2005 9:50:20 AM PST by RobbyS ( CHIRHO)
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To: Incorrigible

Good report. Having lived and worked as an architect in Houston 20 years ago I know all about soil plasticity(up to 20% expansion)from sedimentary deposits. I live in my native Montana now but am working on my FLOOD ROAD concept/table sized model, in response to Katrina. I thought of this 4 years ago after the flood in Des Moines : buoyant road panels, 20' x 20', piano-hinged on the landward side, dead man anchors on the river/sea side. The rising flood water naturally lifts the panels up into a vertical seawall, then back down into a roadway again as the waters recede. No sandbagging needed, no power requirements; natural forces do all the flood water containment work for you. Will video tape it in action and send to GOVERNORS of coastal states. I've already sent it to state transportation depts : no response as you would suspect. W=P


20 posted on 11/10/2005 9:51:06 AM PST by timer
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