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.