What Does Mogi-Coulomb Criterion Mean?
The Mogi-Coulomb criterion is used in wellbore stability analysis, understanding rock strength under true triaxial condition. It is found that the intermediate principal stress (σ2) influences the ultimate strength of a rock.
Alternatively, in the Mohr-Coulomb criterion, only the maximum (σ1) and minimum (σ3) principal stresses are considered and it is assumed that the intermediate stress (σ2) has no influence on the strength of a rock.
Trenchlesspedia Explains Mogi-Coulomb Criterion
The Mogi-Coulomb criterion equation takes into account the intermediate stress as well as the intersection of the line axis, represented as Toct and the line inclination.
The strength parameters for both a and b relate to the cohesion and friction angles of triaxial compression and uniaxial compression.
Toct = a + bσm,2
When ignoring the intermediate stress and utilize solely the Mohr-Coulomb criterion, the overall rock strength may be greatly underestimated. Conversely, some believe the Mogi-Coulomb criterion greatly overestimates overall rock strength.