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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.

Under high stress and blasting disturbance, the failure of deep rock masses is a complex, dynamic evolutionary process. To reveal the relation between macroscopic failure of deep rock masses and spatial-temporal evolution law of micro-cracking within, the initiation, extension, and connection of micro-cracks under blasting disturbance and the deformation and failure mechanism of deep rock masses were studied. The investigation was carried out using the microseismic (MS) monitoring system established in the deep mining area of Ashele Copper Mine (Xinjiang Uygur Autonomous Region, China). The results showed that the failure of the deep rock masses is a dynamic process accompanied with stress release and stress adjustment. It is not only related to the blasting-based mining, but also associated with zones of stress concentration formed due to the mining. In that space, the concentrated area in the cloud chart for the distribution of MS event density before failure of the rocks shows the basically same pattern with the damaged rocks obtained through scanning of mined-out areas, which indicates that the cloud chart can be used to determine potential risk areas of rocks in the spatial domain. In the time domain, relevant parameters of MS events presented different changes before the failure of the rocks: the energy index decreased while the cumulative apparent volume gradually increased, the magnitude distribution of microseismic events decreased rapidly, and the fractal dimension decreased at first and then remained stable. This demonstrates that the different changes in relevant MS parameters allow researchers to predict the failure time of the rocks. By analysing the dynamic evolution process of the failure of the deep rock masses, areas at potential risk can be predicted spatially and temporally. The result provides guidance for those involved in the safe production and management of underground engineering and establishes a theoretical basis for the study on the stability of deep rock masses.

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.