<p>Compaction-induced fragmentation dynamics of broken coal samples (BCS) exert governing control over goaf geomechanical integrity and multiscale void topology reconfiguration under stress-activated compaction regimes. We systematically characterized this process through particle gradation experiments integrated with real-time acoustic emission tracking, revealing key mechanisms controlling particle breakdown. The compaction process demonstrated three characteristic stages: Initial self-adjustment stage dominated by particle rearrangement, subsequent active broken stage with intensive fragmentation, and final elastic compaction. A stress–strain model incorporating particle size effects effectively characterizes the broken stage compaction behavior. Analysis revealed that larger BCS exhibit enhanced fragmentation intensity with higher AE energy release, yet require lower stress to achieve equivalent strain levels. Temporal AE patterns showed delayed signal initiation in coarse particles compared to finer counterparts. AF-RA parameter analysis delineated evolving failure modes: shear-dominated cracks prevail during initial compaction, transitioning to tensile-dominated fractures in the active crushing stage, with larger particles retaining greater shear components. This stage-dependent fracture behavior underscores the complex interplay between mechanical loading and granular material response in BCS systems. The observed particle size dependence of shear crack formation suggests scale effects in stress transmission and energy dissipation mechanisms during compaction processes.</p>