The uniaxial mechanical properties and damage mechanism of layered surrounding rock-backfill composite

In underground mining, common issues include surface subsidence and tailings accumulation. To address these issues, the layered tailings cemented filling technique is frequently utilized. The coupling of the filling body with the surrounding rock constitutes a complex mechanical support system. Additionally, the layered structure enhances the stress distribution and deformation patterns within the rock-filling composite. Consequently, to investigate the structural stability of the rock-filling composite under various filling durations, a layered composite model was developed using PFC software. The mechanical properties and macro-micro failure characteristics of the composite were analyzed, while the damage evolution mechanism was investigated using acoustic emission (AE) monitoring and dissipation energy theory, allowing for the prediction of composite failure. The results show that, compared to single-fill composites, double-fill and triple-fill composites exhibit peak strength reductions of 30.8% and 37.2%, respectively. Cracks in single-fill composites initiate at the interface with the surrounding rock, propagating and expanding until macroscopic failure ensues. When the stress reaches approximately 90% of peak stress in composites with different filling times, a sharp increase in AE events is observed, indicating composite failure. The research findings hold significant theoretical and engineering value for underground mine filling.