Compaction characteristics and lump crushing behavior of homologous gangue powder grouted uncemented backfill

The homologous material system is a green backfill technology that utilizes mine-derived associated solid wastes to prepare filling materials in situ, with minimal or no introduction of exogenous components, thereby achieving a closed-loop "mining-beneficiation-backfill" paradigm. Backfill systems using gangue powder as the primary material can provide effective support for underground caving zones while offering significant advantages in cost and sustainable mining. In this study, an integrated mold for filling, curing, and loading was independently designed, and confined compression and acoustic emission (AE) tests were conducted on gangue powder slurries with varying particle sizes and concentrations. The stress-strain responses under confined compression, AE ring-down counts and spatial localization, and fractal dimensions of crushed gangue were systematically analyzed, and the cause of the qualitative transformation in slurries around 100 mesh was discussed. The results show that: (1) At 6 MPa, the backfill specimens reach 83%-88% of their maximum strain, which can be regarded as the structural yield critical point of this material. (2) The maximum strain depends solely on the post-filling porosity and is inversely proportional to both the slurry concentration and the mesh size (i.e., finer particles lead to lower strain). (3) The backfill strength is influenced by multiple interacting factors; generally, finer particle sizes and higher concentrations yield higher strength. However, when the concentration exceeds 50%, slurries with particle sizes larger than 100 mesh suffer from reduced fluidity, resulting in decreased backfill strength. (4) The 100 mesh threshold represents the point of qualitative change in gangue powder slurries. The underlying mechanism is the competition between force fields: as particle size decreases, the gravitational force on particles diminishes following a power-law, while short-range repulsive forces increase exponentially. Research on homologous material systems is an essential step toward addressing increasingly complex backfill environments and provides valuable guidance for backfill scheme selection and strength prediction.