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Under the influence of many factors, including complicated geological condition, high stress environment and strong disturbance by blasting, rock mass failure, and in some cases, dynamic failures would occur. Therefore, it is important to investigate and to understand rock mass stability during mining. In this study, Modified Omori Law (MOL) was applied to analyze the acoustic emission (AE) and microseismic (MS) sequence power-law attenuation characteristics in the laboratory and in situ. The MOL parameters, during the period of constant stress at lower stress level was much different with that at higher stress level, can reflect the stress level in rock. Before failure of the two rock specimens, the MOL is not applicable, indicating that the rock was close to the critical instability state. During the mining process, rock mass would be strongly disturbed by blasting. The AE sequence monitored from a ramp near the stope, and the MS sequence monitored from the whole rock mass near the stope all exhibited distinct power-law attenuation characteristics. The changes of MOL parameters, i.e., p, c and A, are very complex and related to many factors and it should cooperative analyze the three parameters to evaluate rock mass stability during the mining process.

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.