Estimation of cohesion and internal friction coefficient using a modified Mohr-Coulomb failure criterion.

During uniaxial compression testing, the sample fails macroscopically in the form of longitudinal splitting. This indicates that, although only axial load was applied, internal tensile forces caused the sample to fail. In the classic Mohr-Coulomb failure criterion, these tensile forces are not taken into account and the minimum principal stress is considered to be zero. In our modified Mohr-Coulomb failure criterion, we assume that during a uniaxial compression test, tensile stresses are generated in the rock, causing the specimen to fail. Under this assumption, it is possible to extend the stress state during a compression test into the tensile range. The hypothesis is that during a uniaxial compression test, failure is also determined by the tensile strength perpendicular to the load axis. Based on Mohr-Coulomb theory, it is now possible to determine the cohesion and internal friction coefficient from this stress state, knowing only the compressive and tensile strength of the rock.

This method has been tested for various rock types with known values for cohesion, internal friction coefficients, and tensile and compressive strength. Our method provides a good estimate of the intrinsic rock properties.

We present the theoretical basis for our modified Mohr-Coulomb failure criterion and its applicability to various rock types.