Direct acoustic emission (AE) monitoring and micromechanical damage modelling of the Himalayan sandstones under conventional triaxial loading: petrographic integration and model advancement

This study presents a direct contact-based acoustic emission (AE) monitoring approach to quantify rock damage under triaxial compression loading. With its application on five geologically diverse Himalayan sandstones to capture damage evolution using three AE parameters: event counts (E_AE), ringdown counts (R_AE), and energy (U_AE). The study reveals an inverse relationship between rock strength and critical damage: higher-strength rocks exhibit a lower magnitude of AE-based critical damage (d_AE)_c and vice versa. Moreover, the (d_AE)_c to the sandstones decreases exponentially with increasing confining pressure (σ₃). A generalized exponential regression model was proposed to predict critical damage using σ₃ and experimental AE-based damage based on E_AE, R_AE, and U_AE, achieving R² values of 0.58–0.91, 0.61–0.99, and 0.57–0.97, respectively. Among these, R_AE and U_AE-based models demonstrated superior predictive accuracy compared to E_AE. The derived critical damage was integrated into a modified AE-based micromechanical model, which was evaluated through 72 simulation scenarios accounting for variations in σ₃, AE parameters, and sandstone types. The model effectively captured regional geological variability, σ₃ influence, and nonlinear stress-strain behaviour, including pre- and post-peak responses, Class II-Class I failure mode, and hardening–softening transitions. Additionally, the study introduced a multivariate regression framework that links petrographic indices with critical damage under varying confinement. Results identify P_d, GAR, and P_c as the most influential features for R_AE-based modelling. These offer a new pathway to connect rock microstructure with mechanical behaviour. The findings advance the microcrack-driven damage constitutive model and provide a predictive tool for safely designing underground structures.