Geotechnical Mohr Circle
Geotechnical Mohr Circle
(OP)
Hi I am trying to develop Mohr circle. I Have deviator stress which is (sigma 1 - sigma 2)/2. I also have three confining pressures for one sample. Can someone tell me whether confining pressure is sigma 1 or sigma 3?





RE: Geotechnical Mohr Circle
Andy Machon
RE: Geotechnical Mohr Circle
Sigma 2 is the same as sigma 3 in atriaxial cell.
Sigma 1 is increased above sigma 3 by applying a 'deviator' stress in the vertical (axial) direction by loading the top of the sample.
Sigma 1 - Sigma 3 is the deviator stress.
(Sigma 1 - Sigma 3)/2, half the deviator stress, is the radius of Mohr's Circle and if Sigma 1 is the deviator stress at failure it is the shear strength.
In an unconfined test, Sigma 3 is zero so the shear strength is half the uniaxial compressive strength.