Deterioration Characteristics Of Gypsum Ore Rock In Water And Stability Of Goaf

During the mining process,the action of groundwater and seasonal rainfall leads to the existence of long-term leaching or alternating wet and dry processes in the leftover gypsum ore columns.Water-rock action makes the mechanical properties of gypsum rock deteriorate,which will easily lead to the reduction of the bearing capacity of the ore column,and may cause a large collapse of the roof plate in the mining area when the bearing capacity is insufficient to support the overlying rock load.Therefore,it is of theoretical significance and application value to investigate the deterioration characteristics of gypsum rock under the interaction of water and rock.In this paper,a gypsum mine rock in Jingmen is used as the research object to investigate the fine and macroscopic deterioration characteristics of gypsum rock under the action of water rock and its influence on the stability of the quarry area.The main research contents and conclusions are as follows:(1)The density,mineral composition,and mineral distribution characteristics of gypsum rocks were investigated by density testing,X-ray diffraction analysis,and EDS energy spectrum analysis.Preliminary understanding of the physicochemical properties of gypsum rocks.(2)The fine structure of gypsum rock under water-rock interaction was analyzed,and it was found that the crystal structure of gypsum rock in a dry state was dense and the crystal surface was smooth;water-rock interaction,inter-particle cementation weakens,cracks and pores increased,and water-conducting space expands continuously.In addition,the fine pore structure of gypsum rock under the action of water rock has fractal characteristics,and the pore fractal dimension of the specimens all show different degrees of increase compared with the dry state.(3)Longitudinal wave velocity tests,uniaxial compression,and triaxial compression tests were used to study the deterioration of physical and mechanical parameters of gypsum rocks under long-term water immersion.The results show that the rate of deterioration of the physical and mechanical parameters is faster in the early stage of water immersion,and the rate of deterioration decreases with the increase of time.The deterioration effects of each physical and mechanical parameter under water immersion are ranked as follows: modulus of elasticity > cohesion > uniaxial compressive strength >longitudinal wave speed > internal friction angle.(4)Longitudinal wave velocity tests,uniaxial compression,and triaxial compression tests were used to study the degradation of physical and mechanical parameters of gypsum rocks under the action of dry and wet cycles.The results show that the rate of deterioration of the physical and mechanical parameters is faster in the early stage of water immersion,and the rate of deterioration decreases with the increase of time.The deterioration effects of each physical and mechanical parameter under the action of dry and wet cycles were ranked as follows: modulus of elasticity > uniaxial compressive strength > cohesion > longitudinal wave velocity > internal friction angle.(5)FLAC3D numerical simulation software was used to establish numerical models for different pillar sizes and analyze the distribution of stresses,displacements,and plastic zones in the gypsum mining hollow under dry,submerged,and wet-dry cyclic conditions,and initially determine the stability of the mining hollow under dry,submerged and wet and dry cyclic conditions.And based on the destabilization damage mechanism of the ore pillar,the safety coefficients of different pillar sizes under the action of dry,submerged,and dry-wet cycles were calculated,and the calculated results were in agreement with the numerical simulation results.