Estimation of cracking and damage mechanisms in rock under triaxial compression by moment tensor analysis of acoustic emission

In highly stressed conditions, the excavation damaged zone induced by stress redistribution and disturbance must be evaluated after tunnel excavation. Therefore, the deformation and fracture characteristics of rock must be investigated. In this study, the fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by moment tensor analysis, as well as by the moving point regression technique, both of which were applied to acoustic emission (AE) and strain data obtained from triaxial compression tests. Damage thresholds before the peak strength of rock under triaxial compression were determined by the moving point regression technique using acoustic emission data. The results showed that damage thresholds, except the crack closure stress, increased linearly with confining pressure. The results of the moment tensor analysis showed that shear failure was a major microscopic failure mechanism of rock under triaxial compression. In addition, shear failure became more dominant as the confining pressure increased. In this analysis, the expression of the damage magnitudes in each AE source as relative crack volumes leads to accurate prediction of macroscopic failure mechanisms, as well as major failure planes in the rock. In addition, the orientation of the macroscopic failure plane could be estimated by the orientational distribution of microcracks.