Rock anisotropic damage characterisation and its evolution model by integrating acoustic emission tomography and ultrasonic monitoring

With the exploitation of deeper underground resources with harsh working conditions and significant geotechnical issues, it is challenging to quantify the damage evaluation (especially anisotropic damage) of stressed rock materials. The insufficient understanding of anisotropic damage inside rock may result in unexpected hazard potential in rock engineering. However, most of the current acoustic emission (AE) data analysis is limited in the isotropic stage and AE-based damage characterisation has not been well integrated with the continuum damage mechanics. Therefore, by adopting multiple monitoring technologies such as ultrasonic wave velocity measurement, active AE location and passive AE tomography, the paper investigated the anisotropic damage characteristics of Gosford sandstone samples under triaxial compressive tests. Multiple parameters including AE event location, P wave velocity and AE energy were used to correlate microcracking with the internal rock damage during the loading process. The anisotropic damage variable was determined using the heterogeneous P wave velocity field obtained from passive AE tomography, based on both linear and non-linear stress strain relationships. The damage evolution is further investigated following the frameworks of thermodynamics and continuum mechanics. This study casts light on laboratory-scale anisotropic damage identification, which further improves the understanding of anisotropic damage evolution inside rock materials.