In this paper, we have examined the crack formation of weathered granite by monitoring acoustic emissions (AE) under uniaxial compression. Except for the uniaxial compressive strength (UCS), the thresholds have been determined for crack closure, crack initiation and crack damage, respectively. Moreover, the relationship has been preliminarily established between the AE energy and the rock damage variable. Compared to the deformation and failure characteristics of unweathered granite, the uniaxial compression strength and the elastic modulus of weathered granite are significantly decreased. Additionally, the acoustic emissions are consistently observed in the stage of original crack closure and loading-induced crack initiation followed by crack formation. The crack volumetric strain is an indicator for the crack closure and crack initiation, while the bulk volume strain is an indicator to the crack damage threshold. In elastic phase, AE signals are mainly caused by the micro-damage, while in plastic phase, AE signals are attributed to the plastic deformation. The AE cumulative parameter curves describe the damage evolution process, including the damage initiation and damage development for the weathered granite. The b-value of AE accompanying rock-fracturing is estimated, and oscillates between 1.0 and 1.7 on a long-term decreasing background, indicating a close correlation with the alternate occurrence of clustering. Of particular interest is that the two PZTs are appropriate for monitoring acoustic emissions under uniaxial compression.

The propagation and coalescence of numerous discontinuous joints significantly contribute to landslide instability during excavation unloading. The tip expression of stress intensity factors of two collinear unequal length cracks in a typical rock mass under unloading conditions was calculated based on the superposition principle and fracture mechanics to determine the meso-influence law of intermittent joint interaction in the slope under the action of excavation. The effects of many factors on this interaction were also analyzed theoretically. Unloading tests were conducted on rock-like specimens with two collinear unequal length cracks in addition to numerical simulation and theoretical analysis. The results show decreased interaction between the two cracks with increased crack distance, increased influence of the main crack on a secondary crack with increased length of the main crack, and decreased influence of the secondary crack on the main crack with decreased length of the secondary crack. Wing tensile cracks first appear at the tip of flaws, and the propagation of these cracks occurs with the generation of secondary tensile cracks and shear cracks during unloading. Propagation and coalescence between cracks lead to tension and shear mixed failure of a rock bridge, and tensile cracks appear near the unloading surface. The axial initiation and peak stress of a crack increase with increased flaw distance, and the theoretical calculations were confirmed by lateral unloading test results.