Identification of acoustic emission precursors for strainbursts in dry and saturated sandstone under true triaxial transient unloading

Abstract

Groundwater is a key factor influencing rockburst in underground engineering. Identifying how water alters precursory signals is essential for reliable prediction and mitigation. Using a self-developed true triaxial rockburst system integrated with high-speed camera (HSC) and acoustic emission (AE) monitoring, we investigated water effects on sandstone rockburst processes, failure modes and AE evolution, clarified microscopic water-induced weakening mechanisms, and developed a multi-parameter coupled AE precursor model incorporating critical slowing down (CSD) and Ib value theory. Results show saturated sandstone exhibits significantly reduced rockburst strength, ejected fragment mass and peak AE energy compared to dry samples, with a distinct AE energy "quiet period" prior to instability. Among the investigated indicators, the Ib value and Variance (Var) provided clearer precursor responses in the present tests. Based on Var based warning, the precursor time for saturated sandstone occurred at 475 s, which was 45.7% earlier than that for dry sandstone. The proposed AE multi-parameter integrated early warning framework is preliminary and requires further validation; within this dataset, it indicated that the warning interval for saturated sandstone was advanced by 2.15% compared with dry conditions. These findings offer effective AE-based indicators for rockburst early warning and support water-assisted risk control in deep underground engineering.