Characteristics Of Mining Failure And Permeability Evolution Of Coal Rock Pillar At The Boundary Of Closed Coal Mine

In recent years,with the structural adjustment of the energy supply side,the implementation of the national policies of shutting down wells to reduce production and eliminating backward production capacity,coal mining has gradually become centralized and precise.A large number of unproductive mines that do not meet the national safety and ecological environment standards have been closed,resulting in a significant reduction in the number of mines and the formation of a large number of closed or abandoned mines.With the continuous rise of the underground water level in the closed coal mine,the accumulated water in the goaf flows to the adjacent production mine by destroying the coal and rock pillars at the mine boundary,posing a serious threat to its safety in production.The closed coal mine has become a dangerous source of major accidents in China’s coal mines.Therefore,the systematic research on the stress distribution,fracture development and permeability evolution law of coal and rock pillars at the mine boundary under the superposition of mining on both sides of the stopes not only plays an important role in ensuring the safety production of adjacent mines,but also has very important theoretical significance and application value for the prevention and control of closed coal mine disasters and ecological environment protection in China.This paper takes Liuqiao coal mine in the closed coal mine of Huaibei Mining Area as the research object,adopts mathematical statistics,theoretical analysis,similar material simulation,numerical simulation and on-site monitoring and other methods and means,on the basis of analyzing the stress distribution,plastic evolution and fracture development of the coal and rock pillars at the mine boundary under the action of mining on both sides of the stope,systematically studies the mining failure laws of coal and rock pillars at the mine boundary with different widths,and conducts destructive zoning of the mining affected areas,The vertical and horizontal permeability evolution law and zoning characteristics of the damage affected area under the action of mining superimposition are analyzed,the calculation model of lateral seepage flow of mining overburden is established,and the dynamic evolution characteristics of groundwater flow field in Liuqiao coal mine in the study area are simulated considering the dynamic changes of water inflow and seepage flow of the mine boundary,which provides a scientific basis for the prevention and control of water disasters in Hengyuan coal mine,an adjacent production mine.The main achievements are as follows:(1)The failure law of coal and rock pillar at the boundary under the superposition of mining on both sides of the stope is systematically studied.Based on the geological model of coal rock pillar at the boundary of closed coal mine,the similar material model and numerical model of the mining effect of coal rock pillar are constructed,and the stress distribution characteristics of coal rock pillar with different widths under the influence of mining are analyzed,that is,the stress state changes from saddle shape to pointed arch shape when the width of coal pillar is gradually narrowed,and the stress value is about twice as large as that of single side mining;The deformation evolution law of coal and rock pillar is studied,that is,the vertical displacement of coal and rock pillar increases gradually when the width becomes narrower,and the displacement of coal wall is greater than the middle of coal pillar;The development characteristics of coal and rock pillar fractures increasing and connecting under the narrowing width are summarized.The failure zones of coal pillar in the mine boundary are divided,and the calculation model for solving the width of coal pillar in different areas is established.(2)Based on comprehensive analysis of stress,deformation and fracture development characteristics of coal rock pillar and rock mass in goaf after mining on both sides of stopes,the mining damage area is divided into 3 zones and 6 zones,which are respectively the highly developed zone of collapse zone damage(Zone I-1),the moderately developed zone of collapse zone damage(Zone I-2),the moderately developed zone of fracture zone damage(Zone II-2),the slightly developed zone of fracture zone damage(Zone II-3)Moderately developed area of coal and rock pillar damage(III-2 area)and undeveloped area of coal and rock pillar damage(III-4 area).Through the analysis of the leakage characteristics of the drilling fluid,the rationality of the development zoning of the pores in the mining damaged rock mass is further verified.(3)The evolution law and distribution characteristics of overburden permeability under the action of mining superimposition are studied.By analyzing the evolution law of vertical and horizontal permeability of overburden under the action of mining superimposition during the progressive process of working faces on both sides of the coal pillar in the mine boundary,and considering the influence of horizontal and vertical fractures on permeability,the permeability zoning of adjacent stopes in the mine boundary is divided into four zones:seepage multiplication zone,seepage recovery zone,seepage weakening zone and seepage superimposition zone.The coal and rock pillars are respectively seepage weakening zone and seepage constant increasing zone from bottom to top,The overburden in goaf is divided into seepage multiplication area and seepage recovery area from bottom to top.(4)The prediction model of groundwater level rise in Liuqiao coal mine is established,which reveals the characteristics of groundwater level rise in closed coal mines with dynamic changes of mine water inflow and mine boundary seepage.Through the simulation and analysis of the dynamic evolution characteristics of groundwater flow field in the study area,the results show that the groundwater level rises rapidly in the initial period after the closure of Liuqiao coal Mine,and the difference between the old empty water level and the water level of the underlying recharge source is reduced with the passage of time,and the water level rises slowly.The difference between the prediction model results of groundwater level rise in Liuqiao coal mine and the actual monitoring results of mining space method and mine water level observation hole is not large,the maximum relative error is 1.9%,which verifies the accuracy of the prediction model of water level rise.(5)The control mechanism of the width and strength of coal pillar on the permeability of coal and rock pillar at the mine boundary is analyzed.The numerical model of lateral seepage of coal and rock pillar under mining is established using COMSOL software.The coal and rock pillar is divided into three regions according to the horizontal seepage rate.On this basis,the prediction model of seepage flow of coal and rock pillar is established,with the maximum relative error of 5.06%,which verifies the accuracy of the prediction model.Figure[100] Table[16] Reference[251]...