Pile of mud may be clue to levee failure (‘Heave' points to structural problem, not levee topping)

http://www.nola.com/newslogs/tporleans/index.ssf?/mtlogs/nola_tporleans/archives/2005_10_04.html#084767 ^ | October 04, 2005 | John McQuaid

[Maria S]

A child's clubhouse, built about 25 years ago by a civil engineer for his son, provides another clue pointing to possible design or construction flaws in the structural failures that breached two canal floodwalls and inundated the city during Hurricane Katrina.

Engineer Gus Cantrell, 60, and son Daniel Cantrell, 33 &150; now a structural engineer himself &150; returned to the family's Pratt Drive house last week for the first time since Katrina struck. They discovered the old clubhouse sitting a few feet from its original location next to the London Avenue canal levee &150; on top of a pile of mud and silty sand about 8 feet high.

The Cantrells believe that extreme pressure from high water pushed soil under the base of the floodwall away from the canal and upward in an arc, something known as a heave. That appears to have raised a mound of earth into the back yard under the clubhouse. The wooden clubhouse's base is now even with the edge of the house's roof, Daniel Cantrell said.

[jeffers]

Thanks for the ping.

I saw an aerial image of the 17th Street Canal before the levee failed in which there was a a construction barge just southeast of the Hammond Highway bridge, but I can't locate it now.

In any event, I've looked for the barge in the post storm imagery and have been unable to spot it, inside or outside the levees. It could have been removed prior to the storm, it could be well upstream now, or it might have gone through the breach and sank. Given the similarities between the London Canal breaches and the 17th Street Canal breaches, I am currently operating from the assumption that the construction barge played no part in the 17th Street Canal breach. (Not to be confused with the grain barge located on the wrong side of the breach east of the Industrial Canal, which probably didn't cause that breach either.)

As to dredging being a cause of the failures, it is mathematically possible. It depends on how close to the sides of the canal they dredged and the exact structural cross section details of the levee/floodwall. Given that the CoE would almost certainly have supervised the dredging, and that I've yet to see gross stupidity on the part of the CoE, I rate the likelihood of dredging being a direct or contributory factor in the 17th Street Canal breach as being very low.

[Sunnyflorida]

"300 ft. of property has to be condemned on either side of the canal"

My concern pretty much. However if you take 300 feet on either side of the levee there is not much of a canal left. One of the most expensive parts of public works projects is taking of land through eminent domain. In KELO the city is taking the land to get more taxes. When you take land for roads, bridges and levees you are shrinking the tax base and getting people POed. I'm sure this had to be a consideration.

http://www.nola.com/hurricane/images/nolalevees_jpg.jpg

Looking at the above map you can see that it is likely that thousands of parcels of private property would have to be given up to build nice thick "Dutch" levees.

That is the minimum. The real problem is no matter how good the levee the chance of a small break and the catastrophe that a small break creates MANDATES redundant systems. This requires massive land taken off the tax rolls.

This is the real problem faced in NOLA (after people finally figure that what got wet must come down.) The proper outcome is a whole new land use map.

[Sunnyflorida]

" $809,000 to correct the problem"

I don't buy it. There is no way a few million would be enough to build a proper levee system. This is tin-foil land with a political agenda. Levees fail no matter what. They just do.

[Sunnyflorida]

Canals in low-lands are necessary for port operations and drainage. Ever been to Florida?

[Sunnyflorida]

jeffers, good call.

Plus drainage pipes need to be cleaned from time to time. Surface draining is much less expensive.

[Bigun]

I don't buy it. There is no way a few million would be enough to build a proper levee system.

You are right about that but that is NOT what we are talking about here!

The contractor putting in this levee (for millions) recognized the fact that the substrate (the material upon which the levee was to be built) was not sufficient to hold the weight to be placed upon it in several locations and so informed the Corp. of Engineers in writing of this fact. At the same time, the contractor requested a change order in the amount of $809,000 to correct the substrate problem before proceeding. (This $809,000 would have been in addition to the monies already in their contract for the job.)

The request for change order was denied and the levee was built on top of the known substandard substrate material!

[Sunnyflorida]

Ok, I do not find it odd that once a project gets going the Corp is not going to easily make changes. My take on the Corp is that it spends too much time dealing with lawyers and not enough engineering. Best news I heard in a long time is the proposal to change the "Endangered" Species Act. We have one nasty little bugger on that list in Florida is not even NATIVE to the United States of America. It would be as if some dope Down-under proposed protecting the cane toad - that bugger is the destructive and nasty pollution machine known as the West Indian Manatee. That particular feral species has all kinds of impacts on Corp related projects.

If you look at the excellent work of jeffers and a couple of nola.com maps and consider the history of the area there is no doubt that the things had to fail. The whole system looks hopeless to me.

[Constitution Day]

FYI...for your list?

A child's clubhouse, built about 25 years ago by a civil engineer for his son, provides another clue pointing to possible design or construction flaws in the structural failures that breached two canal floodwalls and inundated the city during Hurricane Katrina.

[Fierce Allegiance]

Civil Engineer Ping List:

Thanks for the ping, CD.

I have been involved in levee strengthening projets on the American River, specifically in Sacramento where a backhoe digs a trench approx 3-4 wide, and almost 100 feet deep. The trench is backfilled with a soil/cement/bentonite tokeep the water on the proper side. Here's a backhow used in the project. BTW, this work runs about 3-5 million per mile of levee.

[Fierce Allegiance]

Backhoe, not backhow.

[Sunnyflorida]

Cool tool.

I stand by my opinion that the problem with the Corp is not techinical or financial. These guys are engineers turned into lawyers.

If they get a project and people let them alone (fat chance) the project will be fine.

I'd bet a manatee steak (the other, other white meat) that down under the controversy is some meddling politician or EIR.

[jeffers]

I like that, with a grout curtain being impractical and steel being steel with its affinity for oxidation and corrosion in salt environments.

Can you backfill under pressure, as a slurry that sets up later, or do you have to keep the trench unwatered until you've backfilled it?

[Fierce Allegiance]

In order to keep a trench like that open, it is filled with a bentonite slurry that has a higher density than water. That keeps hydrostatic pressure working outward on the trench walls.

When the backfill material is placed, it is dumped at the top of the trench and it slides down a ramp of unexcavated material or previously placed backfill in such a way that it does not drop through the liquid slurry and separate as it reaches the bottom.

Glancing through Google, this reference seems like a fairly decent one. If this doesn't answer all your questions, let me know.


http://www.tceq.state.tx.us/comm_exec/forms_pubs/pubs/rg/rg-282_189585.pdf

[Fierce Allegiance]

Sometimes in lieu of a slurry trench, a jet-grout wall or soil mix wall is used. Those consist of overlapping vertical cylinders, and on deep holes, if the alignment isn't perfect (With in one half of a percent) the wall/curtain is flawed and will not perform as necessary. The slurry trench is guaranteed by the nature of excavation to provide 100% coverage, and long as the backfilling method is done correctly

[Robert A Cook PE]

The huge diameter of a pipeline equal in area to the canal would be very difficult (expensive) to build. But supporting the height of a concrete pipe is also difficult: you can't bury it: it's already below water level (burying the pipe wold just make pumping all that water much more difficult, and mean easily 3-8 times the diesel power and pump capacity). Also, the pipe can't be supported structurally by the loose muck and mud.

Canal (at lake level, with locks/ports to adjust for changing river levels) is the only practical means. Once you pump it "up" out of the city into the lake, (which is slightly "uphill" from the ocean), the water flows to the sea naturally and at no expense.

[Robert A Cook PE]

Big Dig (in Boston) used that parts of that technology: But not everywhere. Expensive.

[gridlock]

But what is the velocity of water flow in the canal? I don't think the cross sectional area of a pipe would have to be nearly as large, because a pipe can operate at much higher velocities.

At some point, however, you have to trust the engineers who have been scratching their heads over this problem for the last couple hundred years or so. To my mind, the best solution involves either condemnations of large areas in order to build proper earthen dikes, or a decision to not build in these areas at all.

[gridlock]

Hey, dude! You might want to check out Post #29...

[Ditter]

At the beginning of the flood it was supposed to be because of 2 barges knocking the levee down. Was that story not true or is this a different levee?

[jeffers]

Got it, thanks.

I was interested because there is a chemical plant here that had contaminated the surrounding area and they were looking into similar technologies to prevent the contaminants from further leaching out and affecting the groundwater and the surrounding neighborhood. They were looking at a curtain some 200 feet deep, surrounding the plant, which is roughly a mile square in area.

To All, bentonite can be considered, for non-engineering purposes, to be "clay", which may help in understanding the technology under discussion.