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.
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