Analysis of dynamic fracture of granite after uniaxial recompression predamaged by high confining pressure cyclic loading based on acoustic emission

As the mining industry continues to mine deep, the safety and stability of deep rock masses (such as pillars) in a complex geostress environment become increasingly important. By selecting granite as the object, a uniaxial compression experiment was designed for predamaged specimens prepared under high confining pressure cyclic loading. The porosity, secondary uniaxial peak strength, and the dynamic fracture characteristics of saturated granite before and after predamage test in the whole process were obtained by nuclear magnetic resonance (NMR) and acoustic emission (AE) analyses. The porosity increment of granite before and after high confining pressure cyclic loading test indicates that the granite has different degrees of mesoscopic damage. The high confining pressure cyclic loading in predamage experiment makes the granite release a stronger energy signal when it ruptures, but the higher the number of cycles, the weaker this energy signal. The stress-strain curve can be divided into four stages: I, II, III, and IV, the fracture mode of natural saturated granite is tensile crack-tensile crack-tensile crack-mixed crack, and the fracture mode of saturated granite after predamage changes into tensile crack-shear crack-shear crack-mixed crack. The distribution range and rise and fall of CV(r) have a certain symmetry with the b-value. The reference value of predamaged saturated granite is CV(r) = 1.2.