Anisotropic damage characterisation by integrating moment tensor inversion and P wave velocity monitoring

The determination of anisotropic damage variables for underground space engineering is still challenging since the microcracking behaviour cannot be directly monitored, even under laboratory environment. In this study, we aim to determine the anisotropic damage tensor through moment tensor inversion of acoustic emissions integrated with continuous P wave velocity measurement. Two different damage variables (micromechanical damage and fourth-order damage tensor) are formulated in this study based on different hypothesis and monitoring technologies. The second-order micromechanical damage tensor is first back-calculated using the moment tensor inversion and supported by the continuous P wave velocity measurement in rock triaxial test. On the other hand, fourth-order damage tensor is based on P wave velocity measurement in different directions among rock specimens. In addition, the presence of a non-diagonal component of both damage tensor was observed, even under principal stress directions. This confirms the rotation of the eigenvector of the damage tensor as well as the close relationship between the direction of the microcracks and microcracking behaviour inside rock samples. We also noticed that the direction of the second-order damage tensor is closely related to the eventual failure plane, even before the catastrophic failure of rock samples.