Abstract: To reveal the damage evolution and fracture mechanism of rock-backfill composite structure in mine stope under frequent stress disturbance, a series of multi-stage increasing-amplitude fatigue tests and post-test CT scanning were carried out on rock-backfill combination with four different cement-tailings ratios. The results indicate that: 1) Deformation, stiffness degradation, damage propagation, and failure pattern of the rock-backfill combination are influenced by the cement-tailings ratio. Volume expansion increases, while the secant modulus initially rises and then decreases as the cement-tailings ratio decreases from 1:4 to 1:12. 2) An irreversible axial strain-based cumulative damage evolution model was proposed, which aligns well with the experimental data. For rock-backfill combinations with cement-tailings ratios of 1:4 and 1:8, the cumulative damage exhibits a two-stage increasing pattern, characterized by an initial steady rise followed by a sudden increase. Conversely, for rock-backfill combinations with cement-tailings ratios of 1:10 and 1:12, an inverted S-shaped damage accumulation pattern is observed, featuring a clear three-stage progression of initial, steady-state, and accelerated increase. 3) Decreasing the cement-tailings ratio transforms the rock-backfill combination samples from mixed tensile-shear failure to tensile failure. Post-test CT images depict the mesoscopic fracture evolution pattern of the rock-backfill combination, which comprises shear fractures in the backfill, tensile fractures along the rock-backfill interface, and tensile-shear fractures in the rock. The study suggests that implementing “flexible backfilling” can help mitigate disasters like rock spalling and collapse. These results offer a theoretical foundation for optimizing mine filling ratios and ensuring the safe extraction of deep mineral resources.

Key words: rock-backfill combination, cement-tailings ratio, fatigue disturbance, damage fracture, CT scanning