Study on the failure mechanism and acoustic emission characteristics of cemented gangue backfill under load-gradation synergy

• Investigated the mechanical properties of Cementitious Gangue Backfill (CGB) under the synergistic effects of gangue grading and compaction pressure. • PFC simulation of crack propagation in CGB compression under combined grading and compaction pressure. • Acoustic Emission-Based study on pre-failure characteristic parameters of CGB: Synergistic effects of grading and compaction pressure. Backfill mining is vital for ground control, and backfill strength is crucial for safety. Gangue particle size distribution significantly influences the strength of cemented gangue backfill (CGB). Using Particle Flow Code in 2D (PFC2D) modeling, this study analyzes CGB's mechanical response under different gradations and compaction pressures. Key findings are: (1) Both gradation index and compaction pressure significantly affect CGB strength. Strength increases with compaction pressure, with 10 MPa specimens showing the highest strength. The optimal gradation index for maximum uniaxial compressive strength was 0.5. (2) Under compression, cracks initiated at aggregate edges, with smaller aggregates (0-5 mm) failing first. Tensile damage dominated, leading to macroscopic failure. Force chains weakened post-failure on the fracture surface. (3) Acoustic emission (AE) parameters showed distinct phases. Before peak stress, sudden jumps in cumulative ring counts and Rise Angle / Average Frequency (RA/AF) values (point "F") served as failure precursors, with multiple points indicating multi-stage failure. b-value fluctuations reflected unstable crack propagation, with sudden drops and rises signaling the interplay of micro- and macro-cracks. (4) AE precursors consistently occurred between 80% and 98% of peak stress. The b-value was best for early warning, while the RA/AF value was more suitable for short-term failure prediction.