Study on crack dynamic evolution and damage-fracture mechanism of rock with pre-existing cracks based on acoustic emission location

The acoustic emission (AE) location technique is used to characterize the entire progressive failure process of rock with preexisting cracks. The mechanical properties, AE characteristics, crack dynamic propagation process, failure modes and damage-fracture evolution rules are studied for prefabricated rock samples with different crack inclination angles under uniaxial compression. The results show that the peak strength and elastic modulus first decrease and then increase with increasing crack angle. AE events exhibit different characteristics with changes in stress. In the initial compaction and elastic deformation stage, the AE activity is not obvious; when microcracks form in the rock sample, the AE count increases; after entering the crack stable growth stage, the AE activity becomes significant; during the period of unstable crack propagation to rock failure, the AE activity is extremely active. The AE location can well accurately reflect the crack initiation position, propagation direction and surface orientation in the rock. AE location can well reflect cracks initiation position, propagation direction and space surface shape in the rock. For intact samples, microcracks are first generated at the ends of the sample and extend internally along the loading direction until they coalesce and form macroscopic cracks; for precracked samples, microcracks appear first at the tips of the prefabricated crack, and extend outward at a certain angle, while the microcracks are mainly concentrated around the preexisting crack, with a small number of microcracks distributed at both ends of the sample. With increasing the crack angle, the rock failure mode changes from splitting failure to tension-shear mixed failure and finally to single shear failure. The AE positioning results are in good agreement with the observed macroscopic failure of the rock samples. The damage variable based on AE counts divides the rock damage-fracture evolution process into four stages, and the initial damage and damage rate of the rock sample with a crack angle of 45° are the largest.