Mohr-Coulomb Failure envelope - help please
Mohr-Coulomb Failure envelope - help please
(OP)
Hi all,
I am stuck in my attempts to calculate M-C envelope as well as uniaxial strength parameters from example stress data:
Sigma_1 (psi) Sigma_3 (psi)
0 -892
Any tips on how to get started? FYI, I am not an engineer but am familiar with the principles of some of it. Thanks in advance.
I am stuck in my attempts to calculate M-C envelope as well as uniaxial strength parameters from example stress data:
Sigma_1 (psi) Sigma_3 (psi)
0 -892
Any tips on how to get started? FYI, I am not an engineer but am familiar with the principles of some of it. Thanks in advance.





RE: Mohr-Coulomb Failure envelope - help please
I'm afraid you don't have the kind of data you need. Looks like all you have is an unconfined compression test.
(BTW - the convention in soil mechanics is compression is positive stress.)
DRG
RE: Mohr-Coulomb Failure envelope - help please
Sigma_1 Sigma_3
0 -892
8850 0
14925 1000
20900 2000
30900 3000
62887 6000
I need to find the tensile strength, compressive strength, shear strength, internal friction and angle of failure by rewriting the equation somehow.
Any ideas?
RE: Mohr-Coulomb Failure envelope - help please
Start by assuming the tensile strength is pretty darned close to zero. It is a rare project indeed that requires any attention to tensile strength at all. (I can recall once in ~23 years of practice, and that was a situation where tensile strength would be a problem if too high!)
Then, check the units. They don't look like plausible psi numbers. Also, verify that those are effective stresses and not total stresses.
Next, draw the Mohr circles for the data pairs. (Don't bother trying to rewrite the equation.) If you don't know Mohr circles, you'll have to look it up. I don't want to explain here - it would take too long.
Finally, get a basic soil-mechanics text book and see how to interpret strength parameters from the Mohr circles, and to verify that they make sense with respect to the nature of the soil, overburden stresses, etc. This is much too complicated to explain here. Better yet, find a geotechnical engineer to do this.
Bon chance!
RE: Mohr-Coulomb Failure envelope - help please
RE: Mohr-Coulomb Failure envelope - help please
RE: Mohr-Coulomb Failure envelope - help please
RE: Mohr-Coulomb Failure envelope - help please
RE: Mohr-Coulomb Failure envelope - help please
s1 s3
0 -6
61 0
103 7
144 14
213 21
434 41
very high S1