| The environmental risk and coal pillar stability in the process of storing high salt mine well water in underground reservoir of coal mine restrict the popularization and application of this new underground water conservancy project.In view of the difficulties of the underground reservoir in the process of establishing coal seam mining,such as unclear evolution law of fissure water channel,unclear evolution law of coal seam group mining on groundwater migration and water seepage diffusion field,and lack of quantitative characterization methods for damage and failure of coal pillar dam,Multi-efficiency method was adopted to study the possible environmental risks in the storage of thick salt water in underground reservoirs of gently inclined coal seam group and the stability of coal pillar dam,and the following research results were :(1)It reveals the weakening effect of different concentrations of high salt mine well water on mechanical properties of coal and rock medium and the deterioration mechanism of coal and rock crack propagation.The strength,elastic modulus,fissure evolution and water distribution characteristics of coal samples soaked in mine water with different moisture content,number of dry-wet cycles and salinity were analyzed.The test results showed that: The mechanical parameters of water-bearing coal samples,such as compressive strength and elastic modulus,have a negative linear decreasing relationship with water content,a negative exponential relationship with the number of dry and wet cycles,and a linear decreasing relationship with the salinity of mine water.With the increase of mine water salinity,the main mineral composition represented by calcite generally shows a decreasing trend,and the overall structure of coal sample surface begins to loosen,and small impurity fragments gradually appear,and there are chlorate and chloride crystals attached.When the salinity exceeds 5.0%,the surface of the coal sample presents flake or block fracture,and there are cavitation erosion caves.At the same time,compared with the dry coal samples,the surface micro-fissure sizes of coal samples soaked by mine water with different degrees of salinity are increased in different degrees.(2)The coupling mechanism between high pressure concentrated salt water in underground reservoirs and fractures in surrounding rock of reservoirs is clarified,and the evolution characteristics of mining-induced fracture network under the action of water-force coupling are revealed.A new fluid-structure coupling similar simulation material with low strength,large deformation and water resistance was developed,and a fluid-structure coupling physical simulation experiment system for coal seam group mining was constructed.The spatio-temporal evolution law of mining stability of repeated mining strata in gently inclined coal seam group was analyzed.Study slowly inclined coal seam group of goaf surrounding rock(including roof,isolated coal pillar and base plate)deformation,stress distribution and displacement of structure fracture and fracture characteristics of surrounding rock of the mined-out area delamination crack and fracturation mutual conduction,and extended to K4 aquifer between K3 aquifer and goaf seepage path does not appear obvious,It shows that the mining of coal seam group has little influence on K3 aquifer,and then the boundary range of surrounding rock fracture development in goaf and its influencing factors are mastered.(3)The time-space evolution characteristics of seepage field and concentration field under the condition of concentrated brine storage in underground reservoir of coal mine are revealed,and the diffusion influence range of concentrated brine storage in underground reservoir is mastered.Numerical simulation method is used to analyze the diffusion law of concentrated brine seepage field and concentration field under water storage condition.The results show that both of them mainly diffuse upward through the fracture fracture at the boundary of goaf,and the seepage field mainly diffuses to the K4 aquifer and the overburden fracture in the upper small range,and has no influence on the K3 aquifer.However,under the action of dead weight,the diffusion rate of the concentration field decreases significantly after 10 years of water storage.After 40 years,the concentration field begins to spread to the K3 aquifer,but the influence is limited.After 50 years,the relative concentration is only about 0.1-0.3.(4)The stability evolution law of coal pillar dam body of underground reservoir in gently inclined coal seam group is revealed,and the minimum width of coal pillar to maintain the safe operation of underground reservoir is defined.The stability evaluation mechanical model of coal pillar dam of underground reservoir of gently inclined coal seam group is established,and the influence law of water content,salinity,coal seam dip Angle and buried depth on the inelastic zone of coal pillar dam is analyzed.Combined with the hydrogeological situation of Lingxin Coal mine,the design width of the overall width of coal pillar dam is determined to be43.5～57 m: The unbalanced deformation characteristics and progressive failure behavior of coal pillar dam body of underground reservoir in gently inclined coal seam group under the action of high salt mine well water were studied,the evolution law of plastic zone of repeated mining of coal seam group was analyzed,the development characteristics of coal pillar damage zone under the mining condition of side coal seam of underground reservoir was explored,and the depth of coal pillar crack propagation under hydraulic action was studied.The minimum width of coal pillar is guaranteed when coal seam is mined on the side of underground reservoir. |
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