Evolution of mechanical properties and acoustic emission characteristics of granite with normal stress under true triaxial shear test

Shear failure is a typical failure mode of surrounding rock in underground excavations. The mechanical properties and damage evolution characteristics of rock under true triaxial shear conditions are essential for stability evaluation and monitoring, however, remain insufficiently explored. To investigate the influence of normal stress on the shear mechanical properties and failure mechanisms of rock under true triaxial conditions, the shear experiments of granite subjected to varying normal stresses while maintaining constant lateral stress were carried out using the true triaxial shear experiment system. Combined with changes in acoustic emission(AE) signals during rock shear deformation, the influence of normal stress on the macroscopic strength, deformation and mesoscopic damage process of granite under true triaxial shear conditions were analyzed. The results indicate: (1) Within the test stress range, the peak shear strength, residual shear strength, crack initiation stress, and crack damage stress demonstrate a nearly linear increase with rising normal stress. (2) An increase in normal stress is associated with the rise of cumulative AE ringing counts and cumulative AE energy. (3) As normal stress increases, the proportion of shear cracks within the sample proportionately grows, thereby restraining normal expansion deformation; consequently, the peak normal dilation decreases with normal stress. The research can provide a new basis and reference for the stability analysis of deep geotechnical engineering.