That's exactly the point. The soil profile should have made it obvious that they should drill deeper. The sheet piles ended in the middle of a pocket of peat soil, a mixture of decaying biological matter. The canal bottom was 18 feet deep and the piles were only driven to 17 feet. The Engineering firm that did the soil samples called for a depth of 35 feet but was overuled by the ACof E. Corps engineers in Vicksburg, Mississippi questioned the designs, but the local Corps project leader again overuled. Water seeped under the piles and eroded away the base of the levee. The levees were not overtopped. I have talked to several witnesses who said the water level was a couple of feet below the top of the wall just before they broke. I am talking about the 17th street canal levee that is about 2 miles from my house. I am sitting in a 1 bedroom apartment as I type this because my home and everything that I worked 30 years to earn was destroyed when that levee broke. Perhaps it is too strong to say the feds destroyed my city but it is hard to amagine it was the best thing to happen to New Orleans. An investigating engineer from LSU called it the worst Engineering failure in the nation's history. I'll tend to take his word for it.
Saints fan, your row is a hard one to hoe. I'm sorry for your loss--I hope you had insurance--but that can't bring back cherished possessions, a neighborhood, a way of life.
In America, we somehow assume we are immune to natural disasters, and we are not.
Looking back, I apologize if my remark about this being the best thing for NO in the long run seems aloof. I realize how it must sound to one who has suffered your losses.
But I would be lying if I said I did not mean it. I think this storm will ultimately wash away the power of corrupt NO politics, although it will take time. NO could not thrive on tourism and Mardi Gras alone. It will be built better and smarter then before, and the lessons learned the hard way may well save many lives in the future due to improved readiness and experience in such a disaster.
Concerning the canal walls, if it wasn't overtopping that caused the scour, then the wall was in the process of failing under design conditions. My own view is because the overtopping was not necessarily the culprit(it is the easiest explanation but not necessarily the correct one)there was a problem in the side to side connections of the piling. Once breached, the water kept widening the opening,then the rushing water undermined the piling on both sides, causing the collapse. The collapse was continuous in one area for about 300 feet-that width of the opening equalized the forces, which left the rest of the piling on both sides of the breach intact. The wall did not fail in all locations--but it only takes one.
Had Katrina hit has a Cat 5, the same result could well have occurred, as the entire wall on both sides was now out of design limits and factors of safety
The investigation has not been complete, and the forensic engineering examination must be thorough and objective. I don't think that has happened yet. We have a lot of theories by non objective parties in CYA mode.
Regardless, that doesn't change your situation. You have seen the destruction that nature can do, in spite of man's efforts to contain its forces. I hope that you will look to future optimistically, as to do otherwise will make you stuck in a past that can never be again. My best to you and yours.