Study On Development Law Of Mining Ground Fissure Based On Breaking Theory Of Uneven Load Beam Structure

Underground mining caused serious deformation of the surface of the earth,destroying the local ecological environment,including destroying the construction,affecting the growth of crops,causing landslides,debris flow and other geological disasters.Shanxi is the main coal production base in the central and western regions.More than 80% of the coal mines are in the mountainous area.The most notable feature is that the overlying bedrock is thin,and the thickness of the overlying loess layer is large.The destruction of overlying rock and surface is serious under the condition of thin bedrock and thick loess layer.Therefore,it is of great significance to study the law of overlying rock fracture and surface crack formation in the process of coal mining under this condition.On the basis of engineering geology,rock mechanics and mining engineering,the UDEC software is used to simulate the 2212 working face of the Hezhai coal mine in Jinnan branch of Yangquan Coal Group,which isdivided into 5 stages with the monthly mining progress of the Hezhai coal mine as the space-time scale unit.The break form of overlying rock in the mining process and the law of surface movement and deformation in this process are studied to reveal the formation mechanism of the overlying rock fracture and the surface crack in the coal mining under the thick and thin bedrock geological conditions in the mountain area.Using the "beam" structure in rock mechanics to explain the mechanism of overlying rock fracture,the structure of a solid supported beam fixed in the coal wall at the end of the basic top is considered as the structure of a solid supported beam at the two ends.The structure of the cantilever beam before the basic top period is seen as a cantilever beam with one end suspended in the coal wall and the geological condition of the thick loess and thin bedrock in the mountain area.The fracture form of overlying strata in lower coal mining is studied.Combined with the relationship between the overlying rock fracture and the surface crack,the “Overlying rock fracture-Surface crack”prediction model is established,and the example is verified and analyzed,and the following results are obtained.(1)In this study area,the mining conditions of the thick loess layer,thin bedrock and the basic top are the only key strata,and the UDEC numerical simulation software is used to study the deformation law of overlying rock and surface movement during the mining process.In the early stage of mining,the basic top and overlying strata produced small deformation and did not spread tothe surface.With the development of mining,the basic roof collapsed because of the failure to load the overlying strata pressure.The overlying rock fracture extended to the surface,the surface of the surface was seriously deformed and the step cracks were produced at the overlying rock fracture.(2)Based on the theory of "beam" structure of rock mechanics,the old roof of the thick loess layer and the thin bedrock under the geological mining condition is regarded as the beam.The structure of the solid supported beam and the cantilever beam under the uneven distribution load are adopted to study the initial fracture and the periodic fracture regularity of the basic top respectively,and the law of overlying rock fracture more in line with the undulating surface is obtained.(3)Under the geological and mining conditions of thick loess and thin bedrock in mountainous areas,the “Overlying rock fracture-Surface crack”prediction model is established on the basis of the law of overlying rock fracture and the formation mechanism of the surface step shape crack under the uneven distribution load.(4)The “Overlying rock fracture-Surface crack”prediction model is applied and analyzed.The results of the numerical simulation are compared with the measured data,and the position and size of the fracture are in good agreement,and the effectiveness of the “Overlying rock fracture-Surfacecrack”prediction model is verified,and it is a coal mining area under similar conditions.Table cracks are expected to provide reference.