Study on Mechanical and Acoustic Emission Characteristics of Unloading‐Induced Rockburst in Granodiorite Using a Grain‐Based Model

ABSTRACT To well understand the crack evolution and failure mechanisms of strain rockburst, the present study simulated the rockburst processes under nine unloading rates. A discrete element grain‐based model (GBM) was adopted, coupling with acoustic emission (AE) monitoring. The results show that the unloading rate minimally affected the overall fracturing sequence: initial micro‐tensile crack dominance, followed by accelerated micro‐shear crack growth, leading to macro‐fracture formation. However, rock strength exhibits a non‐monotonic dependence on unloading rate, decreasing rapidly initially and then gradually increasing. This strength fluctuation correlates strongly with a rapid decrease followed by a gradual increase in the proportion of intragranular micro‐cracks (tensile and shear). Furthermore, under low unloading rates, the failure mode is mainly shear macro‐fractures without V‐shaped pits, and it transits to pronounced V‐shaped pit formation under high unloading rates. As the rate increases, the specimen failure mode changes from tensile‐dominated to shear‐dominated strain rockburst. Throughout rockburst process, the proportion of tensile failure in AE events gradually decreased but remained the dominant micro‐failure mode. The onset of rockburst is consistently marked by a sharp increase in AE events associated with compaction failure. Notably, a distinct AE “quiet period” precedes rockburst initiation at low unloading rates; this quiet period diminishes and becomes less probable as the unloading rate increases.