posted
Who said anything like that, pH? All I did was contradict that the city of New Orleans was "just fine". Clearly it was an unhealthy city, whether or not it was on the mend. I'm speaking in terms of its government. That doesn't make it unworthy of help.
Posts: 17164 | Registered: Jun 2001
| IP: Logged |
quote: But I won't say it any more, because you're not being rational and that's fine, but I refuse to keep repeating myself.
*grin* Sure, if you can't actually counter an argument, descend to calling it irrational and running away. I'd be annoyed at the pathetic name-calling if it wasn't proof that you've run out of cogent ripostes.
Posts: 26077 | Registered: Mar 2000
| IP: Logged |
The levee pilings in the levee were SEVEN FEET too shallow according to the Design Specifications. This is evidence of *criminal* corruption from contractors back in 1993. At least one or two engineers should *lose* their licenses over this and the contractors should be jailed.
I think it's safe to say there was severe corruption. Engineers have been brainwashed that they live in the "public trust". For a supervising engineer from a contractor to allow this sort of henious deviation from the design plan, there has to be systemic corruption.
posted
Well, speaking from experience, an engineer might design a system, but there are several layers of incompetence between "design" and "build"
Posts: 880 | Registered: Nov 2005
| IP: Logged |
posted
I know *exactly* what the government will and won't allow when it comes to infrastructure in the State of Illinois (which itself is pretty darn corrupt) My boyfriend is directly involved with watchdogging contractors so that they *do* follow the design specifications.
Some of the blame may be on the Army Corps of Engineers because they didn't have a licensed civil engineer standing there supervising, because you need to constantly badger the contractors to do it right. However the contractors contracted the job in the first place. Theoretically you *shouldn't* have to stand over their shoulders of every minute of the day to make sure it is done right. If they don't do it right they are in breach of their contracts!
posted
Oh, there's still lots of screwups by the engineers. I'll have to dig up some of the articles I've read, but one problem was the inadequate level of testing that was done for design. There was not enough soil borings done to adequately determine the length of sheetpile necessary. The soil stratigraphy is pretty variable in New Orleans with a lot of muck and other weak soils.
The article I read said that borings were done about every 300 feet. Even if you base your design on the worst case condition, your betting that there wasn't something even worse between them.
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
posted
Shoot, Engineers screw up every day. *I* happened to actually wake up and come to work this morning, for example.
Posts: 880 | Registered: Nov 2005
| IP: Logged |
posted
Okay, I know I'm a little late with this, but I have a few words to say about insurance companies. I am a property and casualty insurance actuary for a large insurance company. I have worked primarily on mobile home insurance and renters insurance, both kinds that would be needed in case of a hurricane. My primary job as an actuary is to make sure the rates are adequate to cover our losses, expenses, and provide profit, as well as ensure that the rates are not excessive. Each state has laws about what insurance can and can't do to rates. With homeowners, renters, and mobile home insurance, the company may not raise an individuals rates based on that individual's experience. Your homeowners does not go up because you filed a claim. I can't say the same thing about Auto, because I don't work with that type of product. We are a company and our purpose is to make a profit. We are also now a publicly traded company, so it is doubly important to make a profit. Because we insure people against "acts of God", I am required to be conservative in my analysis of our experience. The insurance industry is highly regulated. Because we are conservative, some years we have more profit than we plan. Some years(like this year and last year) we have much less. The cushion must be built in to keep the company viable and our customers insured.
Regarding the flood insurance comment earlier: As far as my company is concerned, if the wind blows your roof off and rain gets in, it's caused by the hurricane. If it is storm surge(or a wall of water) then it is flooding. Folks, if you are in a coastal area, get flood insurance! I recommend everyone in the state of Florida who lives on the ground floor get flood insurance. I know it's more money, but if you get hit by a hurricane, then can you afford not to have it? We are in for more storms next year, I'm sure. I also have experienced hurricanes--I live in Miami.
Posts: 77 | Registered: Feb 2005
| IP: Logged |
quote:I recommend everyone in the state of Florida who lives on the ground floor get flood insurance.
Well, not everyone, but certainly the coastal areas and people in flood prone areas. In fact, I thought that the banks required them to carry flood insurance.
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
posted
Smittg I *am* an engineer. Not a PE yet though. I'm not a civil engineer but I have a Freudian affinity to them.
Zgator. I believe there should have been an engineer at least signing off to the correct material as the pilings were driven in. That is Steve's job. He samples the quality of concrete and asphalt leaving plants, and if it is at a bridge deck they supervise the material quality going in. They have another engineer supervising at each site to catch whether the contractor tries short on materials. The steel girders and rebar are approved in similar fashion.
So yes, mistakes are made, but if they catch the contractors, the contractors are *forced* to eat the cost and fix it, depending on how egregious the screwup is. There is a bit of bridge deck on a main thoroughfare near the O'Hare airport that is going to have to be completely redone at the contractors expense because the contractor out and out lied on their material QC reports.
In this particular case it wasn't caught before the pour, but shortly therafter, as the state engineers reviewed the contractors submissions and realized that the report data below the first page was totally screwed up.
AJ
(In other words there should have been a PE either from the Corps or the Contractor standing there *watching* as the girders were driven in. If the girders were indeed half the length they were supposed to be (though now they are saying they weren't) it should have been obvious from a visual inspection.
posted
Perhaps in the case of regulary homeowners, but I don't think that those in mobile homes or who rent are required. In any event, it behooves everyone to know exactly what their insurance covers and what it doesn't.
The reason I say everyone, is what if it rains more than the ground can take. If it seeps into your house, than it is considered flooding and not covered by regular homeowners. Florida has a very high water table and, as recent experience has shown, the middle of the state is not safe from strong storms. When Katrina came through South Florida, there were some non-flood zones that were flooded. I guess I'm just saying to be conservative and be prepared when it comes to insurance. It may be very painful paying the premium, but it's sure worth it when you have a loss. And if you are familiar with your policy, you know what claims will be covered and what will be denied. It will give you some ammo to fight with, if need be.
Can you tell I feel strongly about this? Posts: 77 | Registered: Feb 2005
| IP: Logged |
posted
I don't have flood insurance, but I live on the second floor in Dallas, Texas. I feel okay about that. I have insurance for everything else, though. If I am offed, then my brothers get money for college. No one tell them.
Posts: 26077 | Registered: Mar 2000
| IP: Logged |
posted
Oh--when I said everyone, I meant everyone in Fla. I think you're okay on the second floor in Dallas. Posts: 77 | Registered: Feb 2005
| IP: Logged |
posted
seespot, I agree you should be conservative. Most homeowners probably don't know enough about their area to know if it's flood prone or not. But there are many areas of the state that don't have a high groundwater and have free draining soils. In fact, that pretty much describes the conditions you need for citrus groves.
I do see what your saying, though. There are entire communities in Central Florida that struggle to stay above water.
AJ, I was actually referring to the testing that was done prior to design to determine what size and length sheetpile was necessary. From what I read, the spacing they used didn't even meet what I would consider the standard of care for a wall in Florida and our soils are generally much more consistent. Ask Steve how far apart he would space borings for something like this. They used 300 feet. I would say 100 feet, but hindsight's a grand thing.
edit: Oh, and I disagree that a PE needs to be in the field checking everything the Contractor does. They need to be watched by an experienced technician who is under the responsible charge of an engineer, but I don't think an actual engineer needs to be there. I don't know about where you are, but engineers are in too short a supply to have in the field verifying things like depth of piles
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
posted
Unfortunately state contractors are too dishonest to not be babysat. Perhaps not always a P.E., Steve actually isn't one yet, but a PE guarantees more honesty than anything else. Cause they know they are legally responsible and if something goes wrong it is their head.
I don't think *everything* needs to be checked and sometimes spot checking is sufficient. (For example if they are putting in a curb instead of a bridge). However in the cases of Dams (which is what a levee is) and Bridges, *absolutely*. A PE should be on site around whenever any construction of import is happening. (There is always an IDOT PE present on major interstate rebuild projects, around the clock. If the contractors are there, a state PE is there.) In the case of major work on bridges a Structural Engineer has to be present too.
If that's what it takes to keep contractors honest and insure public safety, so be it.
quote:(In other words there should have been a PE either from the Corps or the Contractor standing there *watching* as the girders were driven in. If the girders were indeed half the length they were supposed to be (though now they are saying they weren't) it should have been obvious from a visual inspection.
This would absolutely be required in a Navy Facilities Engineering Command Project. I don't know that it always gets done, but it's clearly required by the regulations. I've never gotten the impression that the Corps had more relaxed rules.
There are construction criteria that exist solely so that things can be inspected properly. For example, there are bolts in steel construction that have to include a special kind of washer, not for holding power, but because deformation of the washer is a reliable indicator of torque. 10% of those bolts are checked by a P.E. in certain types of construction.
Pre-made concrete door lintels have to have reinforcing on both the top and the bottom, even though they add nothing to the strength of the top (concrete is very strong in compression, weak in tension, so a concrete span supported at the ends needs reinforcement in the lower section where it would tend to pull apart). The rebar in the top is there just in case the lintel gets installed upside down.
Anytime I've seen pile driving, I've seen engineers on site every day taking measurements.
Posts: 26071 | Registered: Oct 2003
| IP: Logged |
quote: But I won't say it any more, because you're not being rational and that's fine, but I refuse to keep repeating myself.
*grin* Sure, if you can't actually counter an argument, descend to calling it irrational and running away. I'd be annoyed at the pathetic name-calling if it wasn't proof that you've run out of cogent ripostes.
Actually, your arguments WERE addressed, and you kept repeating the same points and questions, almost word for word, as if nothing had been posted to address those points in your posts. When are you going to address the rebuttals to your posts?
*knock* *knock* *knock*
The lights are on, is anybody home?
Posts: 337 | Registered: Nov 2005
| IP: Logged |
quote:Anytime I've seen pile driving, I've seen engineers on site every day taking measurements.
Then you definitely haven't been watching pile driving in Florida. That is one of the main things I do - design the pile foundation, determine what criteria is required before the Contractor can stop the pile, etc. You absolutely do not have to have an engineer, much less a PE, on site checking that criteria when they drive the piles. You need someone who has been trained in doing that, but they don't have to have a degree. I'm registered in the state now to train people how to do that.
I or one of the other engineers is on hand if a problem arises, but we're not out there full time. Who in the world would actually do the engineering work if we were always out in the field babysitting contractors?
Same with the bolt. You don't have to be an engineer to check that, you just have to be trained properly. In Florida, we have threshold inspectors that handle that under the responsible charge of a PE.
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
Regarding the flood insurance comment earlier: As far as my company is concerned, if the wind blows your roof off and rain gets in, it's caused by the hurricane. If it is storm surge(or a wall of water) then it is flooding. Folks, if you are in a coastal area, get flood insurance! I recommend everyone in the state of Florida who lives on the ground floor get flood insurance. I know it's more money, but if you get hit by a hurricane, then can you afford not to have it? We are in for more storms next year, I'm sure. I also have experienced hurricanes--I live in Miami.
One of the issues in Mississippi is the fact that the homes there were damaged by wind AND the storm surge. Many of these homes were not 'coastal' but were miles inland. This storm surpassed the standard set by Camille many times over. The houses further inland were not considered to be flood risks.
There is litigation right now about whether the Insurance companies can refuse to pay anything when there is both wind damage AND a storm surge, as happened along the entire gulf coast from south of New Orleans through Mississippi. Pine trees were snapped off well above the storm surge, proving that the force of the winds were at least a major factor in the damage. The contention is that the storm surge was PART of the destruction, and finished the homes off, but it did not cause ALL of the damage. Paying all or nothing when a storm surge to finishes the destruction of the homes AFTER the wind has damaged the homes first just doesn't seem fair. So the State of Mississippi stepped in and sued.
I live in Florida. I am literally in the middle of the state, but only a couple of miles from a river. When we bought our home I asked about flood insurance. We were told that being in a designated flood plain is a requirement for whether you can buy Federal flood insurance. So we couldn't get Federal flood insurance since we were not 'in a flood plain.' Buying it on our own was too expensive.
Posts: 337 | Registered: Nov 2005
| IP: Logged |
[snip] If the girders were indeed half the length they were supposed to be (though now they are saying they weren't) it should have been obvious from a visual inspection.
AJ
According to the link posted above (and on NBC Evening News this evening, showing the engineers pulling the metal sheets out of the ground) the depth specifications were correctly followed. The specs actually were exceeded by 6 inches. At this point (and that could change) it looks like there were design flaws. Perhaps the stability of the ground was not correctly assessed. It is still being investigated.
Had the Levees held, life could have gone back to normal in most of New Orleans. The deep water Canal which was created by the Corps of Engineers (called Mr.Go) would still have flooded the area south of New Orleans ... most of St. Bernard and Plaquemines Parishes ... but the flooding would have been substantially less.
Oh well, if wishes were horses...
The fact is New Orleans flooded, and we are left the the clean-up and rebuilding. If the government doesn't help restore the wetland buffer then the locals will do what they can. And pray that next year's Hurricanes go somewhere else.
From what I saw on the news during the waiting game in watching for where Rita was going to hit, Houston has a serious flood potential too. Had Rita not gone into western Louisiana, Galveston and Houston would have been dealing with what New Orleans is now dealing with.
And by the way, as someone who has dealt with a lifetime of Hurricane seasons, I can tell you why they didn't evacuate sooner. You really have no idea where Hurricanes are going until the last 24 - 48 hours, and even then they can turn at the very last minute - literally.
Last year Charlie was heading straight for Tampa/Clearwater, and along the way it took a sharp turn into the Peninsula at Punta Gorda, at least a hundred miles south of there. Tampa got showers, and Punta Gorda was wiped. That is why many people watch and wait - you may actually endanger yourself by evacuating INTO the storm's path.
Posts: 337 | Registered: Nov 2005
| IP: Logged |
quote: The floodwall on the 17th Street Canal levee was destined to fail long before it reached its maximum design load of 14 feet of water because the Army Corps of Engineers underestimated the weak soil layers 10 to 25 feet below the levee, the state's forensic levee investigation team concluded in a report to be released this week.
quote:Several high-level academic and professional investigations have found that the sheet piling used in the design to support the floodwalls was too short for the 18.5-foot depth of the canal. In addition to holding up the concrete "cap" on the walls, the sheet piling is supposed to serve as a barrier preventing the migration of water from the canal through the porous soils to the land side of the levee, an event that rapidly weakens the soils supporting a wall and can cause it to shift substantially.
The corps has long claimed the sheet piling was driven to 17.5 feet deep, but Team Louisiana recently used sophisticated ground sonar to prove it was only 10 feet deep.
Van Heerden said Team Louisiana's latest calculations prove investigators' claims that a depth of 17 feet would have made little difference. He said the team ran the calculations for sheet piles at 17 feet and 16 feet deep, and the wall still would have failed at a load of 11 to 12 feet of water.
Investigators have been puzzled by the corps' design since it was made public in news reports. They said it was obvious the weak soils in the former swampland upon which the canal and levee were built clearly called for sheet piles driven much deeper than the canal bottom. It was not a challenging engineering problem, investigators said.
quote:From what I saw on the news during the waiting game in watching for where Rita was going to hit, Houston has a serious flood potential too. Had Rita not gone into western Louisiana, Galveston and Houston would have been dealing with what New Orleans is now dealing with.
Yes! I can't remember when it was exactly, but in the decade I lived in Houston we did get one really bad storm that flooded the city. It wasn't the intensity of Katrina or Rita but it left the city in water for days, if not weeks. I remember the big controversy was a basement full of animal test subjects that drowned. Took them forever to pump the water out of all the parking garages.
quote:And by the way, as someone who has dealt with a lifetime of Hurricane seasons, I can tell you why they didn't evacuate sooner. You really have no idea where Hurricanes are going until the last 24 - 48 hours, and even then they can turn at the very last minute - literally.
Again, dead on! With Rita I spent 48 hours on the phone begging my friends in Houston to leave. Then I woke up one morning, checked the weather channel and saw that it had taken a big turn west and my town, in West Louisiana, was now in Rita's path. Suddenly, I was the one who needed to evacuate and the storm was going to be hitting land in a matter of hours.
Besides, if anyone saw the Houston evacuation of tv, you saw how bad that was. The same thing happens in New Orleans. Alot of my neighbors never evacuate because they're more afraid of being stranded in their cars on the highway when a hurricane hits. When my family evacuate for Dennis, it took them 12 hours to drive to Lafayette which is usually 2 hours away. And this was with them leaving days before landfall
Posts: 1733 | Registered: Apr 2005
| IP: Logged |
posted
Yeah, plus, a lot of people CAN'T evacuate because they can't get off work or whatever just because a hurricane MIGHT hit. Not to mention the expense of gas or plane fare and a hotel. You've gotta go really, really far away to make sure you're safe. You can't just evacuate willy-nilly.
However, I have evacuated three times in the past year and a half. The difference is that I'm a student, and the university doesn't want to be held responsible for having class and trying to make students stick around with the possibility of a hurricane. And I've got my parents as financial backing. And I generally leave town at very strange times, if I'm driving. I have no problem with driving all night if it means I can get to where I'm going in five hours instead of twenty-four. Oh, and we totally evacuated the "wrong way" for Katrina. Straight to the Florida panhandle. Everyone else went to Houston and told us we were nuts for going to Florida because "hurricanes ALWAYS hit there." We got to Tallahassee in five hours. They took over twelve just to get CLOSE to Texas.
When I was in high school, we never, ever evacuated. Not once. We didn't live near the coast, but it was also very rare for families who did to evacuate, and if they did, it was always last-minute. We did get a lot of school cancelled, though. And we never had to make up the days, unlike college, where we had Saturday classes last year because of Ivan.
posted
zgator, your link is from Nov 30th. They've exhumed the pilings showing that they were actually 17 feet, since then. I don't know why the sonar tests say it was only 10 feet if this is so. Someone is wrong somewhere either way.
I'm more lenient on the "design flaw" stuff, with the subsurface soils, given that it was a category 4 hurricane.
quote:Then you definitely haven't been watching pile driving in Florida.
Nope. Just on navy bases.
quote:That is one of the main things I do - design the pile foundation, determine what criteria is required before the Contractor can stop the pile, etc. You absolutely do not have to have an engineer, much less a PE, on site checking that criteria when they drive the piles. You need someone who has been trained in doing that, but they don't have to have a degree. I'm registered in the state now to train people how to do that. I or one of the other engineers is on hand if a problem arises, but we're not out there full time.
I didn't say they were there full time. Just every day at least once.
Posts: 26071 | Registered: Oct 2003
| IP: Logged |
posted
zgator. I believe I addressed this above. I'm ok, with someone besides a PE checking, and I'm ok with spot checking. However I *do* think you bear some of the responsibility if someone you trained makes a major mistake since you were the PE training them. I don't think you bear the blame if the guy you train is crooked. But I also think that since the guy you train is getting paid considerably less and *isn't* a PE it's easier to become corrupted.
And I just plain don't trust state contractors any further than I can throw a backhoe.
posted
Oh, yeah, and my 2 cents - on the electrical side, a PE usually delegates field work to underlings he trained - the guy that signs off on our work (apparently I was too much a perfectionist) doesn't have a degree. It surprises me how few EE's go after a PE - it seems a lot easier than the ones the civvies take
Posts: 880 | Registered: Nov 2005
| IP: Logged |
posted
AJ, on the above article about the levees, I was focusing more on the fact that even at 17.5 feet, they still weren't deep enough - even for the Cat3 storm they were designed for. It was a serious design flaw. But some other things I've read now say that the Corp wasn't initially responsible for them anyway. They basically took ownership of them at some point.
Sorry if I was snarky about the PE issue. It's a matter of trust. I have technicians working under me that I trust. The ones that haven't shown they can handle the responsibility don't do that level of work. If you don't have field techs you can trust, going out once a day or even twice a day won't matter.
And I don't disagree in the slightest that I'm still responsible. Anything they do, I still sign off on the paperwork.
We actually have a bigger problem with our trained guys getting hired away by CEI firms rather than them being corrupted.
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
Yes, the date on that article you are quoting is November 30, 2005. The article is old news, written before the completion of the excavation this week.
In this case at least, the sub contractors were doing exactly what they were supposed to do and then some. In the end I suspect they will call it 'human error' and use the new data to contruct the levees more effectively. Hopefully.
Not that that will help anyone who suffered from the mess after the levees broke.
Posts: 337 | Registered: Nov 2005
| IP: Logged |
posted
zgator, I've just heard way too much about the incompetency of some of the testing agencies (in IL) that the contractors subcontract to for their QA. And how hard it actually is to strip their testing license (not a PE).
Not to mention the hundreds of tons of asphalt and concrete that gets "misplaced" in the Chicago area. (I think it was a total of 71 dump trucks full). And the Feds keep a wary eye on Chicago. I don't think they've been keeping that close an eye on Louisiana, unfortunately.
As far as the design issue, that's considerably different. I wonder what sort of geological data was available to the original designers, and if it was perhaps *old* back from the 50s or so. But they couldn't squeeze out the pennies in the budget from the bureaucrats to do the new surveys. As long as those engineers can show that they followed reasonable design practice for the time, from the data they had I'm ok. I'm worrried about a bunch of butt-covering within the Corps of Engineers itself though. Not particularly a good thing for actually addressing engineering issues.
quote:Evidence points to man-made disaster Thursday, December 08, 2005
[snip] The levee system's design dates to the 1950s, when understanding of hurricane risks and flood dynamics was primitive compared to today. The system was never built to take a hit from the most powerful hurricanes, storms in Categories 4 or 5 on the Saffir-Simpson scale. The levees were designed by congressional mandate to fend off floodwater heights -- up to about 11 or 13 feet, depending on location -- that Category 1 or 2, and some Category 3 storms would kick up.
But the investigations show that the levees did not live up even to that billing. When Katrina's storm surge rolled in from the Gulf of Mexico before dawn Aug. 29, the huge dome of water followed a path up the Mississippi River and then along the Mississippi River-Gulf Outlet (the infamous "Mr. GO") into Lake Borgne.
In a matter of hours, the sheet of water -- (the hurricane's storm surge) reaching 25 feet high at some locations -- moved relentlessly north and west, pouring over the tops of and eroding large stretches of levees surrounding Chalmette, clearly exceeding their design capacity.
When the surge reached New Orleans' southern edge along the Gulf Intracoastal Waterway, it caused as much as five miles of the 17.5-foot tall levee there to disappear, creating a back door for water into eastern New Orleans.
Water pushed west through the waterway into the Industrial Canal, where it met water already rising from storm surge that had entered Lake Pontchartrain. The water topped levees on both sides of the canal, causing walls to fail on the east side, flooding the Lower 9th Ward, and leaking through smaller levee breaks and a pump station on the west side, flooding the rest of the 9th Ward.
Breaches by design
Later that morning, as surge rose in Lake Pontchartrain, floodwalls along the 17th Street and London Avenue canals breached, even though the water was well below their tops. Investigators say those breaches shouldn't have happened. Observational data and computer modeling indicate that storm surge entering the canals from the lake reached heights ranging from 9 to 11 feet in the 17th Street Canal and 11 to 12 feet in the London Avenue Canal. The walls were 13.5 feet high or higher along much of the two canals and were designed to withstand water rising to 11.5 feet.
Investigators say the walls broke when floodwater, pushing through the soft, porous earth under the steel sheet pile foundations, started moving the soil. In the 17th Street Canal, one breach opened on the east side, and in the London Avenue, two breaches occurred. Water poured into the Lakefront area and moved south, inundating much of central New Orleans over the course of the day and night.
Engineers say some systemic design problem -- not merely a localized fluke -- caused the breaches because walls gave way in two canals and some walls appear to have been close to breaching at other points.
While it's easy to second-guess after a disaster, outside engineers say the depth of the sheet pile foundation appears too shallow. A survey by Team Louisiana, the state-sponsored forensics group, found -- and the corps confirmed last week -- that the sheet pile depth was about 10 feet below sea level in the breached areas at both canals, much shallower than the 18.5 foot below-sea-level depth of the canals and 7 feet shorter than the corps thought. (NOTE: An assumption now proven to be incorrect.)
Modjeski & Masters, the firm that designed the 17th Street canal wall, said last week it had initially recommended a 35-foot depth for the piling on the 17th Street Canal, then shortened it at the corps' behest, but the firm offered no documentation to back the claim.
Soil and safety
It's still unclear exactly what went wrong, though engineers suggest the soil's resiliency was overestimated. New Orleans soil is swampy and mushy, with alternating layers of peat, clay and sand. Along the length of a floodwall it varies wildly in consistency and strength. Along both canals, a layer of peat -- the weakest and spongiest of soils -- lies directly under breaches a few feet below the base of the sheet pile. Along the London Avenue Canal, coarse sand underlay the peat and now lies throughout nearby residential yards and homes, another layer of weakness, the engineers said. "Those are the kinds of subsurface conditions that lend themselves to having weak pockets or stronger pockets, and Mother Nature will always find the weak pockets," said Joseph Wartman, a Drexel University geotechnical engineer studying the levee failures. "What makes levee design and engineering so challenging is you can have a system that's many, many miles long and you only need the weakest 150 feet to rupture for the whole system to fail." Another factor in the breaches, one with national implications, is the low safety factor used in constructing the levee banks and floodwalls. A safety factor is a kind of cushion that engineers include in a structure's design to ensure it can withstand all the punishment it's designed to take, plus a little more. Corps standards for levees and floodwalls date back decades, officials say, and were intended to protect sparsely populated areas, not cities and billions of dollars of infrastructure. The safety factor of 1.3 used in the designs is significantly lower than those used in structures with similarly large-scale tasks of protecting lives and property. With data from soil borings spaced at more than 300-foot intervals along the canals, engineers could develop only a fragmentary picture of what is underground. They were supposed to account for that uncertainty. That is typically done by raising the safety factor or by making conservative estimates of soil conditions. [snip] http://www.nola.com/search/index.ssf?/base/library-91/1134028092231650.xml?nola
I read an early article about the soil movement in the Times Picayune. In at least some of the levees soil moved sidewards, weakening the levees. A Local engineer noticed this in his own backyard. A small storage shed he had personally built in his yard 'floated' on the moved soil. The shed was not flooded, but his home was flooded. He brought that to the attention of the engineers researching the causes of the levee failure. I'm not an engineer so I don't remember the terminology involved for that effect.
Posts: 337 | Registered: Nov 2005
| IP: Logged |
posted
The Corps built "Mr. Go" for the occassional deep draft 'extra large' ship that could not use the Mississippi River. It was built very deep, and very straight, and it was rarely used.
"Mr. Go" caused many problems during and after it was built. Mr. Go is blamed for salt water intrusion into the marshes, and is believed to have accelerated their erosion. Katrina's storm surge siphoned straight up that canal, and was amplified by it.
At this time the Corps has agreed to stop dredging the canal. many locals want the canal to be filled to prevent future problems like this flood.
Posts: 337 | Registered: Nov 2005
| IP: Logged |
quote: With data from soil borings spaced at more than 300-foot intervals along the canals, engineers could develop only a fragmentary picture of what is underground.
In my professional opinion, that interval is too long. I can't think of any project I've worked on where the borings were greater than 200 feet. I would think 100 feet would be more appropriate for what they know (or don't know) that they're dealing with. At least when dealing with a FS of only 1.3. For geotechnical engineering, that is a very, very low number.
Of course, this is all said with the benefit of hindsight. I have no idea what the standard of care was back then.
Wow, AJ, that's scary. I understand contractors wanting to save a buck through cost cutting. But when they know it could endanger people, that's just ... wrong.
Posts: 4625 | Registered: Jul 2002
| IP: Logged |
Printer-friendly view of this topic
![[Wink]](wink.gif)
Apologize to those poor, misunderstood engineers
![[Smile]](smile.gif)
![[Frown]](frown.gif)
