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To clarify the influence mechanism of initial defects on the internal crack evolution law and damage destruction of cement superfine tailings backfill(CSTB), uniaxial compression and simultaneous acoustic emission (AE) tests were carried out on CSTB with different degrees of internal initial defects constructed by doping with different contents of doping agent(DA), and the AE b-value, amplitude fractal dimensional time series characteristics and three-dimensional distribution law of AE events of CSTBs were analyzed in this paper. The research shows that the doping of DA caused the fluctuation and jump of the CSTB b-value to be significantly enhanced, and the b-value showed two jumps in the loading process. The fractal characteristics of CSTB with different DA doping are better, and the fractal dimension D-value and b-value both show a rapid decreasing trend in the preparation process of the specimen for the occurrence of overall unstable failure. The admixture of DA increases the number of initial defects and non-homogeneity within the CSTB, making the generation of 3D localization points of AE events somewhat random. The results of the study can help to better analyze the unstable failure process of the backfill in the mine hollow area and carry out the corresponding support work. [ABSTRACT FROM AUTHOR]

During the construction of underground projects, different types of rock are often in a cyclic state of loading and unloading. Therefore, cyclic fracturing experiments have been carried out on metamorphic sandstone, slate and granite from one mine site. Based on the basic parameters of acoustic emission (AE), the damage processes and damage precursor patterns of different types of rock samples are analysed. The results of the study show that there is basically no AE signal generated during the unloading phase of the first two cycles of loading, and less acoustic emission signal is generated in the loading stage. In the experimental process on different types of rock samples, when the value of CV(r) (standard deviation of the ratio between rise time, amplitude and mean frequency of acoustic emission parameters) is larger, it can be considered as large-scale crack dominance, and as small-scale crack dominance when the value of CV(r) is small; also, CV(r) values are more accurate than AE b-values in determining the pattern of cracking within a rock sample. With different internal crack development during cyclic splitting, we can focus on the changes in the AE loading energy ratio and CV(r) values before damage destabilization occurs. The Felicity ratio, CV(r) value and loading energy ratio can be used in combination in practical engineering to improve the accuracy of determining rock stability. [ABSTRACT FROM AUTHOR]