Study On The Law Of Movement And Deformation In Mining Under Collapsible Loess Surface With Different Moisture Content

The mining areas in the west of China are rich in coal resources and the surface is covered with collapsible loess extensively.Due to the collapsibility of loess,the surface movement and deformation law caused by coal mining are quite different from the general geological conditions,especially the influence on the green ecological environment construction of mining area is particularly significant.Taking the collapsible loess with different water content as the research object,this paper systematically studies the surface movement and deformation law of mining under the collapsible loess with different water content by means of theoretical analysis,geotechnical test,numerical simulation and similar material simulation.The research can provide some reference value for the prediction of surface movement and deformation in the collapsible loess covered mining area and the green mining of coal.The main research results are as follows:(1)Based on the probability integration theory,the law of surface movement and deformation and crack development of the mining loess is analyzed;Based on the surface movement deformation data of coal seam mining in loess covered area,a prediction model of surface probability integral parameters for mining in loess-covered areas is constructed using BP neural networks.The model takes geological mining conditions as the input layer and probability integral parameters as the output layer.The result of the example test shows that the model prediction error is less than 10%,which proves the reliability of the prediction model based on BP neural network.(2)By testing the mechanical properties of collapsible loess with different moisture content,the research results show that when the moisture content increases from 11.3%to 23.3%,the shear strength decreases by about 50%?60%,and the cohesion,internal friction Angle,compressive strength and deformation modulus decrease by 64.9%,42.0%,70.3%,and 38.9%,respectively.It shows nonlinear attenuation and gradually gentle trend.(3)Using FLAC3D numerical software,the influence of moisture content of collapsible loess layer on probability integral parameters of mining surface was simulated and analyzed:when the moisture content increased from 11.3%to 23.3%,the surface subsidence coefficient increased by 6.8%,the horizontal movement coefficient increase by 5.7%,the deviation of inflection point increase by 3.7%,and the tangent of the main influence angle decrease by 5.9%.(4)Through two similar simulation experiments of collapsible loess layers with different water content,the influence of loess water content on the surface movement deformation and probability integral parameters was compared and analyzed.After the water content of the collapsible loess increases,the mining subsidence extremum increases by 4.5%,the inclination extremum increases by 10.3%,the horizontal movement extremum increases by 6.3%,and the horizontal deformation extremum increases by 5.2%,the curvature extremum increases by 8.9%The experimental phenomenon verifies the surface movement and deformation law of mining under collapsible loess soil with different moisture water.(5)Based on the simulation results,the calculation expression of probability integral parameters based on moisture content is given by linear fitting.The probability integral theory is used to analyze the change law of surface movement and deformation index under different water content collapsible loess:with the increase of moisture content from 11.3%to 23.3%,the subsidence extremum,horizontal displacement extremum,horizontal deformation extremum and curvature extremum increase;The inclination extremum increases first and then decreases,and reaches the maximum value when the moisture content is 14.3%.