Compressive-shear damage and acoustic emission response of grouted concrete in fault zones: Coupling effects of aggregate content and particle size

Understanding aggregate effects within fault fracture zones is crucial for assessing fault reactivation risks in grouted deep coal mines. This study investigates the compressive-shear damage mechanisms of grouted concrete specimens with varying aggregate contents (20%, 40%, 60%) and particle sizes (1–5 mm, 6–10 mm). Uniaxial compressive-shear tests were monitored synchronously using digital image correlation (DIC) and acoustic emission (AE). Additionally, a calibrated PFC2D discrete element model, incorporating matrix, aggregate, and interfacial transition zones, elucidated the mesoscale mechanisms. Results indicate: (1) peak shear load decreases linearly ( R 2 >0.86) with increasing aggregate content, dropping 64.3% from 20% to 60%, driving a transition from brittle to plastic failure; (2) AE b -value evolution tracks progressive damage, while damage rate k exhibits contrasting size-dependent trends; (3) macroscopic failure modes are synergistically controlled by aggregate size and content; and (4) numerical simulations validate the mesoscale mechanical origins of this brittle-to-plastic transition. These findings reveal the micro-mechanical mechanisms of anisotropic failure and re-strengthening in grouted fault materials, offering vital geological insights into stress evolution and instability precursors during fault reactivation.