Uh Oh I'm getting on my soap box again so I'll shut up. It is apparent that Focht3 and I are not going to fully agree on these issues. I would love to hear from some other engineers, their thoughts on slope stability and cohesion. Not that I don't thoroughly enjoy reading Focht3's thoughts.
There is so much to learn and so little time. And of course there are always those people who love to let you know that you don't know squat. Too many engineers rely entirely too much on "cohesion" with no appreciation for what causes it to occur. A very bad, sad circumstance. A good posting - your description of the K 0 test failure by increasing the back pressure is very interesting. While I find the test of intellectual interest, I have yet to find a practical need for it.
Why was it run this way?
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What do you mean by an "adobe" soil? Is this a CL material with a substantial silt content? As a side note, you described the stress path plot as a p-q; did you mean p-q' effective stress plot? I am very comfortable with the concept of "cohesion" created by negative pore pressures, and recognize that this is the likely cause of most of what we call "cohesion. Two specific causes come to mind: mild cementation, and the effect of soluble salts in the sample and pore water.
Both of these can occur in a natural setting, but be destroyed unintentionally in the lab. Remember that you use distilled water in your triaxial tests in fact, all "normal" geotechnical tests use distilled water in accordance with ASTM. The distilled water is slightly acidic due to the presence of CO 2 , and will dissolve some cementation bonds in alkaline soils. And the absence of dissolved salts in the distilled water will cause some salts to be leached out of test samples, affecting their behavior.
In these cases, the tests can show no cohesion while it actually occurs in the field.
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But the criticism of PhDs is not always for this reason. My biggest complaint with most PhDs is that they expect their "book learning" is a perfect substitute for field experience. It most certainly is not. This knowledge requires one to get hot cold, wet, bug bitten, etc. I know too many PhDs that think they are "above" this kind of experience. Karl Terzaghi called this part of a geotechnical engineer's work the "observational method.
Terzaghi recommended this approach as the principal method of dealing with large construction projects.
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As long as some PhDs maintain this attitude, their education has been long, expensive, difficult - and incomplete. And their judgement is potentially flawed. In the words of a Hindu friend of mine, "PhD no sacred cow. I got you going. I will try to answer your questions sequentially: I realize that apperant cohesion can be caused by things other than negative pore pressure caused by dilation or partial saturation or cementation. I also know that I have allot to learn! It is a fat clay CH. It is not a Ko test. It was a project meant to implament a model for slope stability by the USGS and we were hired to do the testing.
Whether it ever gets implemented I don't know. Probably not due to the difficulty of the testing procedures. The total stress pq plot is not very usefull in my opinion. I would rather remain anonymous. That way I can vent and make an ass of myself without losing clients. They are doing the research.
They understand testing and soil mechanics. You may have been correct in Terzaghi's time but not now.
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I find just the opposite. I find most engineers lacking a basic understanding of soil mechanics and testing and rely upon practical experience too much! I think the pendulum has swung. But I have to admit and remain humble in the fact that I am not an engineer and know less than you. I probably should not be scolding anyone but myself. The only problem is that I have engineers asking me how to interpret our test results!
That is scary. You my friend are much more knowlegeable than I, but I could still teach you a thing or two about testing and soil mechanics and I am sure you could teach me a thing or three about all of the above. My question to you is: do you think that you have more to learn?
I have got to lay off these eggnog and brandies! And I have no doubt that you could teach me a few things - I get "wound up" sometimes; not angry, just animated. I understand your position on PhDs. I did not mean to malign them all; just those that think that education trumps experience. It doesn't - you need both.
You also need to apprentice with a really good geotechnical engineer in order to make the best use of your education and experiences. Please keep in mind that I have had opportunities to disagree with a few PhDs on a professional plane; you might not be too surprised to learn that I am thorough and win quite a few of these disagreements.
I even had one of my well known grad school professors effectively "surrender" when I challenged his analyses and arguments during a litigation assignment about 10 years ago. I find that the claim of "experience" without an adequate technical argument to support their position is usually a smoke screen for ignorance Regarding adobe: I'm very cautious about local soil descriptions.
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In particular, the term "caliche" has caused me a lot of indigestion over the years. Just wanted to know what you meant by the term. On the use of subscripts, underlines, bold text, etc. TGML is proprietary to these forums and allows you to format your posts, enabling bolding, italicizing, and so on, as well as typing in color and changing your text alignment center, right alignment.
Re: Ph. Asked him about cost and installation; he said that they teach the theory but doesn't know anything about the cost or installation problems. This is the problem with a lot of professor types - not the practising Ph. They love their degree. Red Flag This Post Please let us know here why this post is inappropriate.