Experimental Study On Environmental Effects Of Gangue Backfilled Body In Underground Coal Mines

In recent years,solid wastes backfilling mining technology such as gangues has been widely popularized and applied.After backfilled into the goaf,gangue will be in a relatively closed environment infiltrated by mine water for a long time.There are physical and chemical reactions in the interaction process of gangue with mine water,which not only deteriorate the bearing and compressive mechanical properties of gangue,but also make heavy metal elements precipitated from gangue diffuse and migrate within the area of goaf floor,resulting in potential pollution risk of groundwater environment.In this dissertation,based on the interaction of gangue with mine water as the springboard and comprehensive use of research methods such as literature investigation,theoretical analysis,experimental test and numerical simulation,etc,the mechanical properties of instantaneous compression and creep properties of gangue under the effect of aqueous chemical solutions was tested,and the constitutive model of gangue considering creep damage under the hydro-physico-chemical effect was established.The deterioration mechanism of the mechanical properties of gangue is revealed from the perspective of micro-domain morphology,pore structure and mineral composition.Seepage relationship of gangue eroded by aqueous chemical solutions in the process of bearing compression were analyzed in mechano-hydro-chemical coupling environment,and spatially distributing feature of concentration of heavy metal elements in gangue in backfilled body was ascertained based on the precipitation characteristics of heavy metal elements in static immersion test,while the controlling method and technology system for environmental effect of heavy metal elements in gangue backfill was proposed.The following are the main innovative results achieved:(1)As the effect of 5 factors,lithology,particle size grading,pH,solid-liquid ratio and soaking time on the instantaneous compression mechanical properties of gangue under the action of aqueous chemical solutions was tested,the experiment for creep characteristics of gangue soaked at different times was carried out with test method for step loading.Then with hydro-chemical damage variable,the evolution law of instantaneous compression mechanical properties of gangue with hydro-chemical damage was characterized,and the constitutive model of gangue considering creep damage was established and model parameters were identified.(2)The micro-morphology and fracture mode of gangue particles eroded by hydrochemical solutions systematically were studied by scanning electron microscope(SEM)test.Based on element spectrum and test results of XRD pattern,association of local element spectrum and mineral composition alteration with chemical reaction of gangue under the action of aqueous chemical solutions was elucidated,and damage mechanism for macro mechanical effect of gangue eroded by aqueous chemical solutions was revealed.(3)The evolution characteristics of porosity during compression deformation of instantaneous and creep were analyzed,and the coupling governing equation in the mechano-hydro-chemical multi-field environment was constructed.Then,the space distributing character of pore in the process of bearing compression deformation of gangue under seepage action were studied,and the dynamic evolution law of deformation and seepage characteristics in heterogeneous gangue was revealed.(4)The relationship of separated concentration of the heavy metal element with the lithology,particle size grading,pH,and solid-liquid ratio under the action of aqueous chemical solutions was indicated.Moreover,the temporal and spatial distribution laws of the release-migration of the heavy metal elements in coal gangue backfill were indicated,and the controlling method and technical system for environmental effect of the heavy metal elements in coal gangue backfill were proposed.