Moment Tensor Analysis of Acoustic Emissions for Cracking Mechanisms During Schist Strain Burst

Acoustic emission (AE) location technique and moment tensor analysis were used to evaluate the temporal–spatial evolution and damage of micro-cracks of schist during true triaxial compression and strain burst tests. The results show that the AE locations coincide with the macroscopic cracks for true triaxial compression while they are scattered during unloading strain burst tests. A shearing concentration occurs at the bottom of ejection position, but a tensile zone is located in the fracture plane of the ejection block. The ratios of shear and mixed-mode micro-cracks to total micro-cracks for true triaxial compression are both larger than those for strain burst. However, the strain burst has more tensile micro-cracks. Additionally, the damage caused by tensile micro-cracks for a strain burst is larger than that for a true triaxial compression. Moreover, for strain burst, the difference of damage between shear and tensile micro-cracks is in direct proportion to the loading rates after unloading.