Determination of the ultimate tensile strength of rocks by the unaixial compression test data

Based on the hypothesized material-independent relationship of the normal and shear stresses on the plane of shear, the authors have plotted an envelope of Mohr’s circles, that represents a rock strength condition in the compression stress domain. The relation of the maximal principal stresses extends to the tension domain as a hyperbola, and its parameters can be obtained only in the non-uniform triaxial compression tests. The hyperbolic equation derived provides, in particular, the ultimate tensile strength of rocks.