A Comparative Evaluation of Stress-Strain and Acoustic Emission Methods for Quantitative Damage Assessments of Brittle Rock

The purpose of this study is to identify the crack initiation and damage stress thresholds of granite from the Korea atomic energy research institute's Underground Research Tunnel (KURT). From this, a quantitative damage evolution was inferred using various methods, including the crack volumetric strain, b value, the damage parameter from the moment tensor, and the acoustic emission (AE) energy. Uniaxial compression tests were conducted, during which both the stress-strain and AE activity were recorded simultaneously. The crack initiation threshold was found at a stress level of 0.42-0.53 sigma (c), and the crack damage threshold was identified at 0.62-0.84 sigma (c). The normalized integrity of KURT granite was inferred at each stress level from the damage parameter by assuming that the damage is accumulated beyond the crack initiation stress threshold. The maximum deviation between the crack volumetric strain and the AE method was 16.0 %, which was noted at a stress level of 0.84 sigma (c). The damage parameters of KURT granite derived from a mechanically measured stress-strain relationship (crack volumetric strain) were successfully related and compared to those derived from physically detected acoustic emission waves. From a comprehensive comparison of damage identification and quantification methods, it was finally suggested that damage estimations using the AE energy method are preferred from the perspectives of practical field applicability and the reliability of the obtained damage values.