Macro-meso Mechanical Properties And Fracture Evolution Mechanisms Of Backfill-Rock Under Triaxial Effect

The backfilling method in deep metal mine not only faces the complex engineering conditions of "three highs and one disturbance",but also the interaction mechanism between rock and backfill is yet to be studied in depth.This study aims to reveal the damage mechanism of the rock and backfill combination under comlex triaxial action.Utilizing cylindrical specimens with both rock and backfill,this research carried out in-depth research on the coupled macro-meso mechanical properties,energy dissipation characteristics,and fracture evolution mechanisms.The testing combined laboratory mechanical tests,acoustic and visual monitoring,theoretical analysis,numerical simulation and other technical means.The results provide new insights and strategies for the stability in deep mining under complex paths.(1)The uniaxial and triaxial compression tests were carried out for different configurations of rock and backfill.The relationships between confinement,backfill/rock volume fraction and critical macro mechanical properties were quantitatively characterized.The significant strain softening characteristics of the backfill-rock specimens were revealed and a damage strength model of it was established.(2)Combining energy dissipation theory,acoustic emission monitoring and high-resolution nondestructive CT scanning technology,the spatial and temporal evolution of fracturing was analyzed to reveal the mechanisms governing interface friction between the two materials under mechanical-only loading.(3)Based on the nonlinear constitutive characteristics of the backfill-rock structure,numerical simulations,and triaxial compression cyclic loading and unloading tests,the dissipation energy and the percentage of shear microcracks were found increase with the increase of the number of loading cycles,and they exhibit similar trends under different stress conditions,the influence of volume fraction and loading and unloading rate on the elastic-plastic transformation characteristics of rock-fill composite was revealed.(4)Through the triaxial hydro-mechanical coupling cyclic loading and unloading tests,the deformation and seepage characteristics were determined at both microscopic and macroscopic scales.Based on water diffusion and mechanics theory,the damage index,which can characterize the degree of acoustic fracture,was defined and verified.Finally,the evolution of the pore-crack hydraulic conductivity and saturation properties during the damage process was revealed.(5)Flac3d simulations were used to study the evolution of stress and failure characteristics under the hydro-mechanical coupling.The influence of pore pressure on the dynamic deterioration response of tip cracking is discussed.A nonlinear damage constitutive model under seepage flow-stress coupling effect is constructed based on the evolution of pore damage.The influence of permeability pressure and confinement on the damage mechanism of the backfill-rock structure was revealed,and the suggestions for improving the stability of deep backfilling method quarries under complex stress paths were proposed.The paper has 115 figures,20 tables,and 256 references.