| The Neogene sand gravel aquifer is generally developed above the coal measure strata in the western mining area of Changcheng No.3 Coal Mine,which directly covers the coal measure strata at the shallow part of the mining area,bringing potential safety hazards to the shallow mining of coal seams 3,5 and 9 in the mining area.Therefore,based on the analysis of the engineering geology and hydrogeological data of the mining area,combined with the experimental data,the paper studies the relevant properties of the aquifers,aquifers and oxidizing zone,and determines the mining level under the water body and the type of coal seam roof overburden;Study the overburden failure law of coal seams 3 and 5 under the condition of close coal seam mining,and analyze the relationship between overburden failure and coal seam dip angle under the condition of large mining height.Using empirical formula,engineering analogy,neural network and numerical simulation,the development height of "two belts" of each coal seam under the conditions of close coal seam mining and high mining height is obtained,and the height of safe coal(rock)pillar of each coal seam is finally determined.According to the research of the full text,the following main achievements have been obtained:(1)According to the borehole exposure,the thickness of the upper Neogene sandy clay relative water resisting layer in the western mining area is 141.51～214.83 m,with an average of 186.05 m.The thickness gradually becomes thinner from north to south.On the whole,the thickness in the west is larger than that in the east,but it is generally uniform,with little change.The aquiclude effectively blocks the direct recharge of the upper Quaternary water to the lower aquifers.The thickness of sand gravel aquifer in the lower part of Neogene in the western mining area is 7.80m～24.95 m,with an average of 13.67 m.In the overall scope of the western mining area,its development trend gradually decreases from west to east.On the whole,the thickness distribution of the aquifer is relatively stable,and the shallow part of the mining area is directly covered by the coal measures.(2)According to the pumping test,the unit water inflow of sand gravel aquifer in the study area q=0.01903L/(s.m),the permeability coefficient k=0.1229 ～ 0.1333m/d,which is a weak water rich aquifer.According to the Code for Retaining and Mining Coal Pillars in Buildings,Water Bodies,Railways and Main Roadways,the mining level in the western mining area is determined to be Grade II,and sand proof safety coal(rock)pillars need to be reserved.(3)According to the drilling exposure in the western mining area,the overburden of the coal seam in the study area is mainly sandy mudstone,siltstone and fine sandstone.According to the comprehensive analysis of the test data of the compressive strength of bedrock and bedrock weathering zone,it is determined that the overlying strata of the coal seam are of medium hard type.(4)According to the variation law of coal seam dip and coal thickness in the mining area,the numerical models of mining in the south and north wings of the mining area are established respectively.The simulation results show that the interaction law of the close separation mining of Coal Seams 3 and 5,that is,the mining of Coal Seam 5will quickly break the stress balance after the mining of Coal Seam 3.The partial overlap of the caving zones of Coal Seam 5 and Coal Seam 3 will lead to the secondary destruction of the overburden,and increase the damage height of the plastic zone of the overburden.At the same time,under the condition of large mining height,the damage range and height of coal seam overburden increase;In addition,the higher the coal seam dip angle is,the smaller the overburden failure height is.According to the characteristics of overburden failure,the "two belt" heights of coal seams 3,5 and 9 in the western mining area are simulated.(5)In view of the problems such as multiple influencing factors and complex failure mechanism of overburden deformation and failure,the BP neural network and GRNN neural network in machine learning are used to establish a neural network model of "two belts" development height by comprehensively considering the influence of multiple factors such as mining method,lithology,dip angle and mining height,and the prediction results of the two models are comprehensively compared.It is concluded that the prediction accuracy of GRNN model is slightly higher than that of BP network,It reflects the advantages of GRNN model in dealing with nonlinear problems.Considering the mining conditions of close distance coal seams and high mining height coal seams,by comprehensively using empirical formula,analogy method,neural network,numerical simulation and other methods,it is concluded that the roof caving zone heights of coal seams 3,5 and 9 in the west are 22.0m,32.24 m and 27.89 m in the south wing and 18.0m,20.0m and 27.89 m in the north wing respectively;The height of the water conducting fracture zone is 45.80 m,95.00 m and 76.00 m in the south wing and 44.64 m,45.00 m and 76.00 m in the north wing respectively.Finally,it is determined that the vertical heights of the safety coal(rock)columns for sand control in Coal Seams3,5 and 9 are 31.0m,50.24 m and 42.89 m respectively in the south wing;The north wing is 27.0m,29.0m and 42.89 m respectively.Through the research of this paper,the safe coal(rock)pillar height of coal seams 3,5 and 9 is determined,which provides an important theoretical basis for the prevention and control of coal mine water disasters.Figure [41] Table [42] Reference [84]... |
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