Mechanical Testing and Crack Expansion Law of Heterogeneous Rock under Different Angle Crack Conditions

Based on the geological data of the Mu Gong Coal Mine in Guizhou Province and the specific engineering characteristics observed on-site, this study analyzed the influence of crack length, width and angle on the mechanical parameters of the surrounding rock composite specimens. The crack propagation behavior and failure characteristics of the composite specimens were investigated, providing a basis for tunnel support design. The experiments showed that as the crack length (10-30mm) and width (1.5-3mm) increased, the elastic modulus, peak strength and peak strain of the composite specimens gradually decreased; moreover, as the crack inclination angle (30°-60°) increased, the inclination angle of the crack at 45° was a turning point, with the elastic modulus, peak strength and peak strain initially decreasing and then increasing. Finally, a composite mechanical model was constructed to explore the instability mechanism of the composite specimens, and the instability process was divided into five stages.