Experimental investigation on anisotropic characteristics of carbonaceous slate under uniaxial compression

To explore the anisotropic characteristics of layered carbonaceous slate, uniaxial compression tests were carried out on five groups of carbonaceous slates (each group has three specimens) with different bedding angles (β = 0°, 30°, 45°, 60°, 90°). In combination with acoustic emission location monitoring technology, the anisotropic characteristics of the slates were quantitatively and qualitatively analyzed from five aspects (mechanical properties, energy evolution, damage evolution, macroscopic cracks, and fractal dimension). The results show that the peak strength and elastic modulus of the slates first decrease and then increase with the increase in β. In addition, when β increases from 0° to 90°, the dissipated energy ratio increases nonlinearly, while the elastic energy ratio decreases nonlinearly, and the variation of the residual energy ratio is small. Specifically, the dissipated energy accounts for more than 95% of the total energy when β is 90°, indicating that the damage is the most intense under this condition. In addition, with the increase in stress, the damage anisotropy shows a decreasing trend, but the anisotropy evaluated by fractal dimension increase gradually. Furthermore, the macroscopic crack anisotropy index (M) first increases and then decreases with the increase in β, and when β is 30°, M reaches its minimum value. Finally, the failure modes of the layered slate are tension-splitting (0°, 90°), splitting-shear (30°), and shear slip failure (45°, 60°).