Compaction Deformation and Acoustic Emission Characteristics of Crushed Gangue with Different Lithologies in Goafs Under Wetting Conditions

The compaction deformation and load-bearing behavior of crushed gangue in the caved zone of goafs directly affect overburden movement, fracture evolution, and stability evolution. To clarify the compaction deformation mechanism of crushed gangue under wetting conditions in goafs, confined compression tests coupled with synchronous acoustic emission (AE) monitoring were carried out. Sandstone and mudstone crushed gangue were selected as the research objects, and Talbot gradation indexes of n = 0.2, 0.4, 0.6, and 0.8 were adopted. The effects of lithology, particle gradation, and moisture condition on compaction deformation, particle-structure adjustment, and AE response were systematically analyzed under dry and short-term wetting conditions. The results show that: (1) the confined compression process of crushed gangue exhibits pronounced nonlinear strain-hardening behavior and can be divided into rapid compaction, slow compaction, and stable compaction stages. Water dripping shifts the stress–strain curves toward the higher-strain side and significantly enhances the compression deformation of mudstone, indicating a stronger wetting response of mudstone than sandstone. Meanwhile, water dripping reduces the equivalent compressive stiffness of crushed gangue. (2) Particle gradation affects the compaction response by modifying the proportions of coarse and fine particles and the initial pore structure. With increasing Talbot gradation index n, the proportion of coarse particles increases, resulting in more pronounced skeleton collapse, localized particle breakage, and secondary filling by fine particles, and the final compression deformation generally increases. After wetting, the final strain of mudstone samples with different gradations concentrates within 0.32035–0.33439, indicating that the control of water-induced softening on mudstone compaction deformation is stronger than the gradation effect. (3) AE results indicate that the compaction process of broken rock can be divided into a flow sliding deformation stage, a fracture deformation filling stage, and a compaction elastic deformation stage, corresponding, respectively, to particle sliding and rearrangement, particle breakage and pore filling, and structural stabilization and consolidation. Water action affects damage evolution by modifying particle contact conditions, promoting fine-particle migration, and facilitating structural adjustment. Among them, mudstone exhibits a more pronounced wetting response, whereas sandstone maintains relatively higher structural stability. The findings provide a reference for analyzing overburden movement, predicting residual subsidence, and evaluating stability in water-influenced goafs.