Cracking mechanisms in granite rocks subjected to uniaxial compression by moment tensor analysis of acoustic emission

In underground engineering structures, rock mass stability is influenced by the excavation with the stress concentrated at the roof and side wall. In this paper, acoustic emission (AE) technique and moment tensor (MT) analysis were both applied to study the behavior of coarse-grained granite samples, containing an inverted U-shaped opening, which were subjected to uniaxial compression. The resolved micro-crack types were presented in terms of their spatial–temporal evolution and change in their proportions throughout the tests. The AE hypocenter locations were calculated using the Simplex algorithm and the micro-crack fracture modes were assessed using the MT analysis. AE events, in most of the cases, were prone to cluster in zonal areas from the top to the bottom of the samples. Micro-cracks were classified to shear, mixed-mode and tensile cracks. Shear-type cracks, accounting for almost 60% of total number of AE events, were dominant, compared to the tensile-type cracks. Moreover, shear micro-cracks were predominantly observed at the sidewall whereas tensile micro-cracks were dominant at regions around the roof of the inverted U-shaped opening.