Analysis of the stress ratio of anisotropic rocks in uniaxial tests

The effect of structural discontinuities on the progressive failure process of anisotropic rocks should be paid particular attention. The crack damage stress σcd, also considered as the yield strength, and the relationship between σcd and the uniaxial peak strength σucs of anisotropic rocks for different orientations θ of the isotropy planes with respect to the loading directions were investigated theoretically and experimentally. A theoretical relation of σcd/σucs with the function of the shape parameter m was established. Additionally, uniaxial compression tests of shale samples were conducted for several inclinations θ. The test result of σcd/σucs was close to the theoretical value for a given orientation. Furthermore, both experimental results and theoretical solutions of σcd/σucs were independent of the inclination θ while σcd and σucs were strongly affected by θ. The strength ratio σcd/σucs may therefore be an intrinsic property of anisotropic rocks and could be used to predict the failure of rock samples.