Correlation between shear induced asperity degradation and acoustic emission energy in single granite fracture

Abstract

Shear induced asperity degradation and gouge formation significantly affect the mechanical and fluid flow behaviors of single rough rock fractures, but the asperity damage process during shear has not been entirely understood and requires further investigation. In this study, direct shear tests were performed on the artificial and natural fractured granite specimens, respectively. The evolution of asperity damage during shear was monitored using acoustic emission (AE) technique, and the asperity degradation zones and damage volumes caused by shear were evaluated with the 3D blue light scanner. The correlation between the asperity degradation and AE energy was examined. The results show that there is a strong correlation between shear stress and cumulative AE energy in both artificial and natural fractures. AE events are scattered in the pre-peak stage but are localized around the fracture surface in the post-peak stage. The shear induced asperity damage is represented well by the clusters of AE events with large amounts of energy, which initially occur after the shear entering the post-peak stage. Their distribution conforms to the destruction locations of surface asperities. The proposed new method of calculating AE b-values based AE energy is more suitable to predict the surface damage characteristics in the artificial and natural granite fractures. The consistency between AE energy and shear induced damage volume of asperities is found when the detection area increases up to a certain range of about 25 mm.