Mining Subsidence Analysis Of Inclined Coal Seam Based On Key Layer Theory

For a long time,the surface subsidence caused by underground coal mining has caused varying degrees of damage to the surface buildings in the mining area.After coal seam mining,the process of surrounding rock and surface movement is a very complex physical and mechanical process.Compared with the near horizontal coal seam,the subsidence caused by inclined coal seam mining is more difficult.Therefore,in order to minimize the negative impact of inclined coal seam mining,it is necessary to study the laws of internal and surface movement and deformation of weathered rock after inclined coal seam mining.In this paper,theoretical derivation and numerical simulation are combined to study the movement and deformation of overlying strata,surface and key strata in goaf under the condition of inclined coal seam mining.The main contents and results are as follows :(1)Taking the movement and deformation of hard rock in bending zone caused by longwall mining method in inclined coal seam as the research object,combined with the key layer theory and thin plate small deflection bending theory,the movement prediction model of key layer in bending zone in inclined coal seam mining was established by using the semi-inverse solution method in elastic mechanics.(2)Taking the geological conditions of a mining area in Guobei as the background,the three-dimensional numerical model of inclined coal and rock strata was established by using the finite difference software FLAC3 D,and the distribution laws of stress field,displacement field and failure field of coating rock strata in goaf under different propulsion degrees were analyzed.The results show that when the coal seam mining reaches a certain stage,the maximum value of horizontal stress and vertical stress no longer changes significantly,but stabilizes near a value.With the advance of the working face,the internal displacement field of the mined-out area expands continuously,and the displacement field above the mined-out area is similar to the inclined ‘torch’.When the advancing distance of coal seam is close to the length of short axis in goaf,the maximum height of grazing rock failure field stops to expand upward,and the short axis in goaf size limits the maximum development height of plastic zone.(3)The monitoring line is set on the main section of the surface strike and dip to monitor the surface subsidence and horizontal displacement.The results show that when the coal seam is mined to 250 m,the surface subsidence occurs.With the advancement of the working face,the surface subsidence value and the influence range are increasing,and the whole is moving downhill.(4)The monitoring lines are set at the surface of the key strata and at the position of 20 m above and below the key strata to monitor the subsidence and movement trend of the key strata in the direction and tendency,and the theoretical calculation results are compared with the numerical simulation results.The results show that the coupling degree of the calculation results near the center of the key layer is good on each profile,and the coupling degree of the calculation results near the boundary of the key layer is general,and the maximum error is 110 mm.In the tendency of each section,the settlement coupling results of the key layer are better,but the position of the maximum subsidence point is different.The maximum subsidence point of the key layer calculated by the theory shifts more to the downhill direction,and the results are more realistic.With the increase of the thickness of the key layer,the maximum value of surface subsidence decreases gradually.When the thickness increases,the decrease of surface subsidence value is larger than that when the thickness decreases.As the key layer is close to the surface,the settlement of the surface gradually increases,and the surface soil layer plays a role in digesting the subsidence of the main key layer.