Effect of thermal damage on strain burst mechanism of brittle rock using acoustic emission

Abstract

Influence of thermal damage on strain burst characteristics and damage stress of granitic rocks were investigated in a series of strain burst tests. Granite samples were exposed to various temperatures ranging from 25°C to 150°C. A true-triaxial loadingunloading system was used to replicate in-situ stress condition taking into account creation of excavation process. During true-triaxial loading-unloading process, damage evolution of the rocks was examined using Acoustic Emission (AE). While the damage at the onset of Critical Strain Burst Stress (CSBS) was found to be around 35% in relation to cumulative AE hits, the damage starts at about ∼15% according to the analysis based on cumulative AE energy at temperature 25°C. This suggests that damage evaluation with cumulative AE hits is inaccurate as it does not account for the size of the micro cracks which is related to the AE energy. Based on AE energy approach, thermal damage caused an approximately 55% decrease in the onset of strain burst stress when the temperature increased from 25°C to 100°C. A gradual increase was observed at temperatures 100–150°C but it was still less than that of at room temperature which showed more intense strain burst behaviour.