Acoustic Emission Characteristics and Failure Prediction of the Granite with Orthogonal Cracks under Compressive Loading

Abstract

Natural joints existing in rock significantly affect the stability of long-term served subsurface engineering. In this paper, granite specimens with two orthogonal cracks were made for uniaxial compressive tests. The acoustic emission monitoring (AE) and digital image correlation techniques were employed to record the acoustic events and cracking of rock. The stress, ring-down count, and cumulative ring-down count of AE during the tests were obtained. The b-value of AE was calculated based on the magnitude and number of AE events. The relationship between the b-value and rock cracking for the specimens with orthogonal cracks was discussed. Further, the effects of orthogonal cracks distribution on the b-value and rock cracking were investigated. Experimental results show that the specimens with orthogonal cracks would undergo multiple cycles of energy accumulation-release-reaccumulation-rerelease under the uniaxial compression. For the specimens with orthogonal cracks, the b-value of AE was volatile but generally decreased until complete failure. Every cracking event during the loading made the b-value drop and then the reaccumulation of energy made the b-value increase or stable. The specimen with orthogonal cracks was more prone to initial cracking than the intact rock. The orientation of cracks had effects on the b-value evolution and crack patterns. The b-value reaching about 1.5 can be used as the failure precursor of specimens with orthogonal cracks.