Study on the synergistic bearing characteristics and fracture evolution mechanisms of rock-like backfill specimens

The mechanical properties and fracture characteristics of goaf following tailings backfilling are crucial for exploiting deep resources. This study investigates the bearing characteristics and cracking behavior of hollow specimens and rock-backfill specimens with different diameters under uniaxial compression. The study examines the fracture evolution process driven by energy and analyzes the time-varying characteristics of acoustic emission (AE) parameters during loading. The results indicate that tailings backfilling enhances the peak strength and elastic modulus of the specimens, with the maximum increases being 38.87% and 66.41%, respectively. However, it does not alter the overall trend, which remains negatively correlated with the hollow diameter. As the diameter increases, the surface crack network phenomenon in hollow specimens gradually weakens. Rock debris transitions from small spalled and ejected pieces to larger spalled fragments. The crack propagation morphology of rock-backfill specimens exhibits a V-shaped distribution. The final failure mode of the specimens is a tensile-shear mixed failure, with shear failure being predominant. The internal backfill primarily exhibits shear slip failure. The input energy and elastic strain energy of the specimens are positively correlated with variations in mechanical parameters. Tailings backfilling reverses the trend of dissipation energy changes in the specimens compared to hollow specimens. At peak time, the dissipation energy of rock-backfill specimens with diameters of 25 mm and 30 mm is 2.4 and 2.09 times greater than that of the hollow specimens, respectively. The AE b-value of the rock-backfill specimens exhibits a secondary reduction phenomenon, and this phenomenon appears earlier as the diameter increases. The fluctuation in the RA value is substantial, indicating more severe stress release and crack propagation coalescence. As the diameter increases, the proportion of shear cracks initially increases and then decreases; however, the change range is more gradual in rock-backfill specimens, with a variation of about 4.25%. This study is of great significance for understanding the synergistic bearing behavior and fracture mechanisms of tailings backfill in the goaf.