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Soil Friction Angle
- Thread starter kxa
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No. And there should not be, although I have to admit that I did develop an expert system that did things like that back in the 1980s, with intention of preserving the knowledge of an old guy (older than oldestguy) with about 40 years of lab experience. Fortunately or unfortunately, a lot of that effort was lost due to changes in computers that meant it can be made to run only on certain antique machines. :~/
There are many published tables of typical values, but those can lead you astray if you are not asking the question that they answer.
There are many published tables of typical values, but those can lead you astray if you are not asking the question that they answer.
First to agree with dgillette!
Just to add to the discussion: To do geotechnical engineering requires subsurface exploration, sampling and laboratory testing. It also requires some understanding of the proposed construction and the loads/stresses conveyed to the subsurface. With that said, to develop correlation to laboratory testing parameters JUST from the boring log data could be negligent. It's like describing a person by looking at their back - just not the whole picture. The boring log shows the details of the subsurface as you collect samples. If knowing the friction angle is the relavent parameter, then run the lab test. Correlation would then just not be needed. If friction angle is not important, I guess you could guess - but what's the purpose? Then again, maybe you want consolidation characteristics, undrained shear strength or some other parameter. . . .
The boring log is just one dimension to the needed data. Trying to gleen the entire image from that has been attempted, but results may be misleading.
¡papá gordo ain’t no madre flaca!
Just to add to the discussion: To do geotechnical engineering requires subsurface exploration, sampling and laboratory testing. It also requires some understanding of the proposed construction and the loads/stresses conveyed to the subsurface. With that said, to develop correlation to laboratory testing parameters JUST from the boring log data could be negligent. It's like describing a person by looking at their back - just not the whole picture. The boring log shows the details of the subsurface as you collect samples. If knowing the friction angle is the relavent parameter, then run the lab test. Correlation would then just not be needed. If friction angle is not important, I guess you could guess - but what's the purpose? Then again, maybe you want consolidation characteristics, undrained shear strength or some other parameter. . . .
The boring log is just one dimension to the needed data. Trying to gleen the entire image from that has been attempted, but results may be misleading.
¡papá gordo ain’t no madre flaca!
GeoPaveTraffic
Geotechnical
I agree with both dgillette and fattdad. I would go one further than fattdad and say that using just the boring log data WOULD instead of could be negligent.
The new Cviltech shoring program allows you to input N values and it generates phi, c unit weight etc. I have played with the function but , end up assigning my own parameters instead. If you know something about soils it can be helpful to select values.
However it does show that with only a little knowledge, you can generate numbers to design problems with the "right" software.
However it does show that with only a little knowledge, you can generate numbers to design problems with the "right" software.
theCorkster
Geotechnical
The nexus of geotechnical engineering is knowing when to:
1) know that the field data is suspect; and
2) know when the laboratory data is suspect.
It does seems that more often than not, the geotechnical's cummulative experience with formations that he's familiar with, which in my case grows with each experience, is considered by some to be less than valuable.
One wonderful geo-professor told me that after he received and reviewed his laboratory results, if the results did not fit with his expections of the parameters in question, he'd send it back to the lab be run again.
The old IBM adage of "GIGO" goes along with "caveat emptor."
When I started in the early 1970's I asked the same questions and got just about the same answers. THECORKSTER dispite the tone, got it right. Experience is the guide and is, without doubt, the most valuable experience. You should have someone in your place of work who can pass on that valuable experience and knowlege.
Colleagues - dgillette, jdmm, theCorkster et al have hit the important point that bothers me immensely - that younger engineers (who may not be getting the lessons of mentors' experiences) are blindly following computer programs and defaults without knowing if it is the gi part of gigo. This is something that we must all fight against - even though there are programs out there now for just about every conceivable computation, I still do my back-of-envelope estimate for the ballpark first - and the use of sensitivity analyses (varying Su values for a given problem with resultling FoS) are so very important - and something that might not be considered as much today in light of "point" analysese.
BigH, I cannot agree more, to spot check and learn to recognize the order of magnitude of where you should be cannot be overstressed as the computers are dumb animals, and no matter how good the software is, there is always a chance for a bug somewhere.
However, it does not have to be a bad thing, and being a proponent of the use of computer programs, I encourage the smart use of computer to develop this "feel" of what to expect, conduct the "sensitivity" analysis etc... because the time saving and the knowledge learned in invaluable.
However, it does not have to be a bad thing, and being a proponent of the use of computer programs, I encourage the smart use of computer to develop this "feel" of what to expect, conduct the "sensitivity" analysis etc... because the time saving and the knowledge learned in invaluable.
Touma08 - computers are a boon to the profession - buy you apparently use it correctly. You have not been blinded; but you see so many posts on this site where engineers do not even know ANYTHING about the parameters they are inserting into the computer program. THAT, as may be said, is very scary.
Absolutely. I once had a discussion with a city engineer in the States, and when he ran out of answers, his answer was: I know that we have equations and computer programs available to us. I plug a number and I get a number to use. People with such an attitude do indeed scare me as they do not have the desire to question / investigate, and that is scary.
all the best.
all the best.
i agree with the thread here, but feel that there is not enough testing of the friction angle. that was about the easiest test we did in soils lab, so why not just run the direct shear box test more often? it combines with the compaction test nicely, so you get both your baseline compaction data and the soil friction angle. be careful, the friction angle depends on the stress level so make sure you use normal forces compatible with your anticipated use.
"Be careful, the friction angle depends on the stress level so make sure you use normal forces compatible with your anticipated use."
mudman54 has pointed out something that I have seen forgotten or misunderstood many times.
It's especially true if there are fines in the material, and be especially careful if the material being tested in DS is partially saturated (e.g., at Proctor OMC), because the capillary tension creates pseudocohesion that is lost if the material becomes saturated.
DRG
mudman54 has pointed out something that I have seen forgotten or misunderstood many times.
It's especially true if there are fines in the material, and be especially careful if the material being tested in DS is partially saturated (e.g., at Proctor OMC), because the capillary tension creates pseudocohesion that is lost if the material becomes saturated.
DRG
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