Estimation of cracking and damage mechanisms of rock specimens with precut holes by moment tensor analysis of acoustic emission

Abstract

This work presents an experiment on the acoustic emission (AE) of coarse grain granites with two square-shaped precut holes under uniaxial loading. Studies were carried out on the temporal–spatial evolution behavior of micro-cracks by AE mechanisms with the use of the simplex location method and the moment tensor theory, with further analysis in comparing the numerical simulations using the software RFPA$^\mathrm{2D}$ (Rock Failure Process Analysis). The results show that during the loading process, from beginning to rock failure, shear-mode micro-cracks are prominent, constituting more than 60 % of the total events; next most common are tensile-mode micro-cracks a less than 35 % of the total events. Variations of micro-cracks of the three modes during the loading process have the same increase tendency, i.e. fewer were generated in the initial loading stage, with a rapid increase when the stress values are between 40 and 60 % of the peak stress, and a rate dimunition before rock failure. It is observed that the tensile stress concentration is prone to appear at the tops of the two holes in the form of tensile type cracks, while the shear stress concentration usually appears at the bottom in the middle region of the specimen in the form of shear type cracks. The findings of the present work may serve as guidance for the prevention of roof and floor collapse in the stope exploration of mines.