Damage evolution process and damage precursor law under cyclic splitting action of different types of rocks.

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]