Study On Mechanical Properties Of Filling Paste-Collapse Roof Composite Backfill Under Local Filling Condition

Filling mining is a mining method that comprehensively considers resource efficiency and environmental impact.It can effectively prevent surface subsidence and water and soil loss caused by mining.It has the advantages of high resource recovery rate and small impact on ecological environment.In order to solve the common problems caused by coal mining,such as coal pressure under three conditions,surface subsidence and waste accumulation,from the perspective of coal mine economic benefits and natural environmental protection,this paper puts forward the method of partial filling mining in the stope to control the bending subsidence of overburden,so as to form an effective supporting structure,inhibit the development of fracture zone and control surface subsidence.In this paper,by means of partial filling,the roof strata collapse and develop to the surface of contact paste.The composite bearing structure composed of artificially filled paste cementation materials and naturally collapsed roof rocks supports the overburden.Theoretical research and production practice show that this filling method can make full use of the fragility of loose rock when the roof collapses and strengthen the support performance of the roof.Compared with other filling methods,this filling method can also reduce the filling cost,simplify the filling process,reduce the amount of filling materials,improve the filling speed,minimize the impact on production and improve the production efficiency.The main research contents are as follows:In this paper,in order to meet the needs of partial filling process,the coal gangue fly ash cemented paste specimen is improved by using additives and changing the distribution ratio.The effects of fly ash content,cement content,sand ratio(the percentage of fine sand in the total mass of gangue sand)and the amount of early strength agent on the properties of the specimens were comprehensively analyzed according to the multi factor orthogonal experiment.The study shows that the paste material with 8%cement,15%fly ash,40%sand ratio and 82%mass concentration of 1.2%early strength dose meets the requirements of the filling and mining construction technology of the experimental mine.In the self-made closed steel cylinder container,the loose gangue is used to simulate the mechanical properties of the direct roof collapse rock block.The influence of multi factor variables on the gangue properties is analyzed through different lithology gangues(sandstone,mudstone,shale),different continuous grading(0.3～0.7),and different loading rates(0.5kn/s～2.0kn/s),so as to provide a basis for simulating the mechanical properties of the roof collapse rock block.The composite load-bearing structure was built with loose gangue and paste specimens,and the stress displacement curve and displacement time curve of the filling structure were recorded.The mechanical characteristics and stability of the composite loadbearing structure were studied through the mechanical experiments of composite filling with different filling ratios.The FLAC3D numerical simulation experiment is used to simulate the stress characteristics of the composite bearing structure under different filling ratios(the ratio of filling height to mining height)in the actual stope,study the stress,deformation and failure laws of the composite bearing structure under the condition of partial filling in the goaf,and analyze the instability range of the goaf filling body in combination with the mechanical experiment results.Combined with regression analysis,the correlation model between filling ratio and instability range is established,and the specific filling ratio without instability is predicted by spssau software.UDEC software is used to simulate the influence of different direct roof thickness,direct roof strength and filling body strength on the development of overlying rock fractures in the actual stope,and the stress characteristics of the surface of the paste filling body and the development height of the water conducting fracture zone of the overlying rock are obtained.The research shows that the change of filling condition parameters within a certain range will not make the fractures develop to the overlying rock aquifer,which is mutually corroborated with the results of the regression model,The applicability of partial filling mining in specific working conditions is verified.