Research On The Damage Properties Of Composite-Excited Coal Gangue-Slag Backfill Under Different Loading Conditions

Coal mining companies discharge large amounts of coal gangue into the environment.Due to the untimely disposal,the coal gangue spontaneously ignites,causing serious environmental pollution and potential safety hazards.The coal gangue after spontaneous combustion has a certain pozzolanic activity.If a new type of cemented paste backfill can be developed based on the paste filling technology and the excellent properties of spontaneous combustion coal gangue,it will be of great significance to the disposal of solid waste and the green mining of mines.When the cemented paste backfill is pumped into the goaf,it deforms or even destroys under the action of in-situ stress,and its damage evolution law is not yet clear.Based on the research method of the combination of laboratory test and theoretical analysis,the paper uses the spontaneous combustion coal gangue in Fuxin area as the test raw material,and uses the strength activity index test method to determine the optimal grinding time of coal gangue.Taking the ground coal gangue and slag as the cementitious material and the sieved coal gangue as the aggregate,the optimal mixing ratio of the coal gangue-based cemented paste backfill was obtained by the response surface method and the satisfaction function method.The strength formation mechanism was analyzed using SEM-EDS and FTIR characterization methods.Through conventional uniaxial compression tests,the deformation characteristics and the damage characteristics of cemented paste backfill in different compression stages are analyzed.Based on the deformation characteristics of different stages,a segmental damage constitutive model with the end point of the initial compaction stage as the critical point is established.Through the uniaxial cyclic loading and unloading test,combined with the digital image correlation method,the damage evolution law of cemented paste backfill under loading and unloading conditions was explored.Research indicates:(1)With the increase of grinding time,the pozzolanic activity of coal gangue increases continuously.Too long grinding time will cause coal gangue powder to agglomerate and reduce the degree of reaction with cement.The optimum grinding time of coal gangue is 30 min,and the pozzolan activity index is 70%.(2)The optimal mixing ratio of coal gangue-based cemented paste backfill: the mass concentration is 82.58%,the alkali content is 2.93%,the slag content is 30%,and the fine gangue rate is 52.92%.SEM-EDS analysis results show that the strength of cemented paste backfill is due to the formation of C-S-H gel and C-A-S-H gel.The results of FTIR analysis showed that there were H-O-H,Si-O,Si-O-T(T is Si or Al)bonds in the product,which was confirmed with the SEM-EDS analysis results.(3)The horizontal displacement,vertical displacement and maximum shear deformation of the cemented paste backfill under conventional uniaxial compression conditions increase with the progress of the test,and the damage degree increases continuously.A segmented damage constitutive model is established with the end point of the initial compaction stage as the dividing point,which can effectively describe the development process of the stress-strain curve in the uniaxial compression state.(4)Under the condition of uniaxial cyclic loading and unloading,the horizontal displacement,vertical displacement and maximum shear deformation of the cemented paste backfill increase continuously with the increase of the number of cycles,and the final failure form is Y-shaped cross failure.(5)Under the condition of uniaxial cyclic loading and unloading,the elastic strain,total strain and unloading modulus of the cemented paste backfill increase with the increase of the number of cycles,while the plastic strain first increases,then decreases and then increases slowly with the increase of the number of cycles.The total energy generated by the external load on the cemented paste backfill,the elastic strain energy stored in the cemented paste backfill,and the dissipated energy increase with the increase of the number of cycles.The energy consumption ratio increases with the increase of the number of cycles,and the growth rate is gradually accelerated.The larger the energy consumption ratio,the more serious the damage of the cemented paste backfill.The paper has 39 figures,22 tables,and 100 references.