Prediction Of Mining Subsidence And Study On The Law Of Overlying Rock Movement In Near Horizontal Coal Seamunder The Condition Of Insufficiency Mining

The main research object of this paper is the near horizontal coal seam in Yulin region.The purpose of this paper is to study the surface subsidence,the law of the movement of overlying strata,the movement track of the surface point,the starting distance and the terminating distance under the condition of insufficiency mining.In order to provide theoretical support for the prediction of surface subsidence and the law of movement and deformation of overlying strata under the condition of insufficiency mining of near horizontal coal seam.Through collecting the relevant data of the Yulin region,the meteorological,hydrological and stratigraphic conditions in this region are understood,and the general law of the mining subsidence and the general method of subsidence prediction are also studied.On the basis of this,the maximum value of surface subsidence under the condition of insufficiency mining is calculated by using the traditional probability integral method,and then use the FLAC3 D software based on the finite difference method to simulate the maximum surface subsidence under the mining condition.By comparing the calculation results of the two methods,the paper analyzes the similarities and differences of subsidence prediction under the condition of insufficiency mining.Secondly,in the FLAC3 D numerical model,the monitoring points of the different horizontal surface of the overlying strata are set up,and the law of the movement of the overlying strata up the goaf is analyzed by the subsidence value of the monitoring points during the dynamic mining.Finally,according to the horizontal and vertical displacement of the surface monitoring points,the trajectory of the surface points is obtained,and the starting distance and the stopping distance are determined.The maximum subsidence value calculated by the probability integral method is 5333 mm,and the maximum horizontal moving value is 1979 mm.The maximum subsidence value obtained by the finite difference method is 2259 mm,and the maximum horizontal moving value is 943 mm.In the same mining period,the subsidence rate of the surface is the least,which is0.4m/time,and the subsidence rate of the roof of the coal seam is the largest,which is 3.6m/time.The time of the maximum subsidence rate at the roof of the coal seam is earlier than the maximum subsidence rate at the surface.The caving zone in the "upper three belts" of the overlying rock is about 239 m below the surface,and the fracture zone is within the range of 179m~239m below the surface,and the bend zone is located in the range of 179 m below the surface.Bythe lengthening model to simulate the mining of coal seam under limited mining conditions,the starting distance of the surface point is 200 m and the terminating distance is 1500 m.The results calculated by the probability integral method are two times larger than the results of the finite difference method of the numerical simulation when the surface subsidence is predicted under the condition of insufficiency mining of the near horizontal coal seam.Because the two methods are all defective in calculation,so we need to compare the actual observation data of the surface after mining,and combine the results of the two methods to further determine the prediction of the surface subsidence under the condition of insufficiency mining.It is significant to determine the distribution range of the "upper three belts" by studying the subsidence value on different horizontal surfaces,which provides a new method for studying the law of the movement of the overlying rock.Through the study of the moving trajectory of the surface point,the paper innovativelyputs forward the termination distance of the stop movement of the surface point,and forms a complete theoretical system with the existing starting distance,which has important theoretical significance.