The Influence of Joint Inclination and Opening Width on Fracture Characteristics of Granite under Triaxial Compression

Abstract

Based on conventional triaxial compression tests, the influence of joint inclination (α) and opening width (t) on rock strength, deformation, and failure mode will be analyzed. Combining particle flow discrete–element (PFD) analysis, the fracture mechanism of jointed rock will be further investigated from the perspectives of microscopic crack evolution and energy conversion. The results show that as α increased, its peak strength (σc) presented a U-shaped change of first a decrease and then an increase, and it reached a minimum at approximately 60°, and its elastic modulus (E) exhibited an approximately linear monotonic increasing trend, and the ability to resist deformation gradually increased. For joint specimens with different opening widths, the strength and E exhibited similar evolution, and both decreased with the increase in opening width. As α increased, the failure mode changed from single inclined plane shear failure to an X-shaped conjugate inclined plane shear failure, and the increase in t resulted in a wider fracture zone. During rock failure, the number of microcracks accumulated in an S-shape, and its mutation point was consistent with the elastic, plastic, and failure characteristic points of the stress–strain curve. As the α angle enlarged, the external driving energy (Ew) first decreased and then increased, the ratio of dissipated energy (Ed) to Ew (Ed/Ew) decreased and tended to become stable. In triaxial compression, the frictional energy consumption of the microstructure surface accounted for ≤5%–20% of the total input energy, which indicated it should be considered during the analysis of fractures.