Monday, February 1, 2010

Slope Stability

Yesterday I was reading Rock and Gem and in one of the articles the author mentioned what books he felt were a must to have in your library (from a rockhound perspective I believe). Interested, I looked up one of the books he mentioned; Mineralogy for Amateurs, by John Sinkankas. He said that he used it quite a lot for reference, and sometimes to return to when he had forgotten certain aspects about a mineral. I did a quick search for the book, as it is an older publication, to find initial searches were at about 70.00. So I checked ebay, although my account is quite rusty these days, and found a copy for 50.00 with the buy it now option. The book reviews on it (book) at amazon were pretty good, and the seller had a good rep so I bought it. Since I was already on the ebay site and hadn't checked it out in awhile, I did a quick search for other Geology publications.

This was when I found a listing for training papers from the USCE (army corp of engineers) being sold via CD by a guy in Australia. Now why would a guy from Australia be selling US training documents? Finding that odd I mentioned it to Husband. The CD came with pdf files with topics ranging from structural integrity to soil testing procedures. I thought 10.00 wasn't a bad price for what was listed, and the sellers rep was okay. Husband asked what the publication number was from the documents, because he could get them for free. Hmmm. Free? There wasn't a publication number, but I figured if this guy had access to these publications I should be able to find them too. After a quick search and 2 link clicks later I hit the mother load!!!! I found so many publications that I ended up downloading PDFs for several hours. (Took me so long because I was reading them after I downloaded them- lol). I felt as if I had robbed a candy store! It was nice reading these publications mainly in part because it enabled me to use what I have already learned in a classroom and apply that knowledge towards a practical application. As without the background knowledge you wouldn't really understand what some of the publications were referencing. (e.g. mohr/coulomb strength envelopes, poisson's ratio, sheild's diagram, reynold's number,..etc).

One of the publications I really liked can be found here. There is a perfect example of rotational slides/slope failure on page 20. Appendix C (p.57) has a listing of the corresponding mathematical formulas. Page 71 fig. C-10 was really interesting to me because while I had applied the mohr circle in structural geology, it was more in terms of determining the probability of failure for rocks under stresses related to tectonic forces.  I like this diagram because it brought to light other applications of this process. Page 72 mentions 'The Simplified Bishop Method' of which I am unfamiliar with, but this document was well written and had an abundant array of visual diagrams. Figure C-11 offers a visual of the equation for the Bishop Method, whereas another new (to me) method terms the 'Force Equilibrium Method/Modified Swedish Method'. This latter method is depicted in fig. C-12 (p. 75) . These modifications opened up my mind to where I won't be so apt to think I have to stick to the canned equations we learn in classroom environments. Not that it is ever projected that we have to do such, there is only so much time in one semester so professors cannot introduce all methods available. I just never thought about the possibility of modifications, hence, this made me see the forest through the trees so to speak.

Shear strength characterization is described in detail starting on p. 98. The use of a modified Mohr-Coulomb diagram is explained from which I will quote:
"Several different forms of modified Mohr-Coulomb diagrams can be used. All modified Mohr-Coulomb diagrams are based on the fundamental relationship between the principal stresses and the Mohr-Coulomb shear strength parameters, c' and φ' or c and φ.

Referring to Figure D-5 and the triangle formed by points, def, the following expression can be written:

Equation D-3 can be rearranged to obtain a number of different relationships between the principal stresses and the shear strength parameters, c and φ. Two of the most useful forms of Equation D-3 and the resulting modified Mohr-Coulomb diagrams are described in the following text......." (p.106, USCE).

That is about the meat and potatoes of the publication, I just wanted to share my excitement in finding such wonderful publications. There are a few others I found that are really interesting, and once I have a chance to read through them I will write about it. I have always just loved the Mohr circle, it was the one thing on exams in structural geology I could whip through quickly and get 100% correct. There is something about using a compass and drawing tangent lines that brings out the best in me I guess. Now if I could just get that one thing in structures that I am horrible at mastered, I will be a happy camper. Hope you enjoyed my Monday "show and tell".

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