The influence study of normal force on the crack propagation of granite and the b-value of acoustic emission

As the basic medium for various underground tunnels and slopes, rock stability has become a key issue in field of underground engineering research.Engineering rock masses are more prone to complex shear failures.In addition to the stress boundary conditions, it is also closely related to the damage scale and fracture distribution.Based on the acoustic emission technology, the rock shearing experiment under different normal force has been carried out.A research on the distribution and expansion of fracturing has been conducted, and the precursor feature information of the rock final instability has been obtained.The results demonstrate that there exists positively correlated with normal force and shearing force and the angle of echelon crack; the echelon crack is the main crack which is produced by the main shearing force, and the local scale of pinnate is generated by the secondary shearing force; the suddenly decreased of b-value means that some higher-energy crack has been occured during the rock shearing process; the continuous and abnormal lower b-value can be regarded as an effective precursor of rock shearing failure.