Ilight
Civil/Environmental
- Dec 2, 2018
- 10
Hey everyone:
For a typical CU triaxial test, I can't seem to get my head around why the effective failure envelope corresponds to the long-term drained effect for a clay sample.
Let's say the confining stress is Sigma 3 and the deviatoric stress is DeltaSigma, hence total stress sigma1 = sigma3 + DeltaSigma and minor principle stress sigma3 stays constant. Then to develop the effective stress Mohr circle, excess pore pressure measured from the shearing stage would need to be subtracted from total stress.
Now from my understanding, excess pore pressure will dissipate completely in the long term, hence u=0, if that's the case, shouldn't the total stress mohr circle represent the long-term drained effect? I.e: effective sigma 1 = total sigma 1 - u, with u =0.
I feel I've missed something trivial yet critical, but can't seem to grasp
Also for the drained shear strength obtained from CD and CU test (T'=c'+a'tan@'), is the a' value used in the equation similar for both tests (assuming same confining stress)? Because for CU test, the effective stress Mohr circle is offset by pore pressure U from the total stress Mohr circle.
Pretty standard stuff, help would be much appreciated xD
For a typical CU triaxial test, I can't seem to get my head around why the effective failure envelope corresponds to the long-term drained effect for a clay sample.
Let's say the confining stress is Sigma 3 and the deviatoric stress is DeltaSigma, hence total stress sigma1 = sigma3 + DeltaSigma and minor principle stress sigma3 stays constant. Then to develop the effective stress Mohr circle, excess pore pressure measured from the shearing stage would need to be subtracted from total stress.
Now from my understanding, excess pore pressure will dissipate completely in the long term, hence u=0, if that's the case, shouldn't the total stress mohr circle represent the long-term drained effect? I.e: effective sigma 1 = total sigma 1 - u, with u =0.
I feel I've missed something trivial yet critical, but can't seem to grasp
Also for the drained shear strength obtained from CD and CU test (T'=c'+a'tan@'), is the a' value used in the equation similar for both tests (assuming same confining stress)? Because for CU test, the effective stress Mohr circle is offset by pore pressure U from the total stress Mohr circle.
Pretty standard stuff, help would be much appreciated xD