Study On The Law And Prediction Of Surface Movement And Deformation In Fully Mechanized Coal Mining

In the past three decades,China's annual coal output has consistently ranked first in the world.With the improvement of coal mining methods and more advanced roof management methods,the area of goaf and ground subsidence caused by coal mining is increasing year by year.Mined-out subsidence not only causes direct loss of life and property,but also causes a series of social and ecological security problems,including further deterioration of the living environment,destruction of natural landscapes,grassland degradation and desertification.Therefore,it is urgent and realistic to study the mechanism of ground subsidence in the goaf.Taking Longde Coal Mine in Yushen Mining Area,Shaanxi Province as an example,the internal rock mass stability and surface movement and deformation after multi-layer coal slicing are studied.The methods used are as follows:First,analyze the strength of the roof and coal pillars in the goaf from the perspective of mechanics,and then use the probability integral method to predict the maximum surface subsidence displacement after repeated mining of multi-layer coal,and then use FLAC^3D software to analyze the internal rock mass stress changes in the process of repeated mining of multi-layer coal,predict the maximum surface subsidence displacement,and analyze the reasons for the difference between the results of the two methods.The main research results are as follows:(1)Based on structural mechanics,the strength of the roof and coal pillars in the goaf is analyzed,and the results are as follows.After the first mining,the roof of the 2^-2 coal seam working face was damaged and collapsed,and the coal pillar was basically stable.After the second mining,the roof of 3^-1 coal seam working face was damaged and collapsed,and the coal pillar was in an unstable state of bearing limit.(2)Based on the probability integration method to calculate the results of surface movement and deformation,the results are as follows.The duration of the surface movement process after mining the 2^-2 coal seam is about 1.12 years.The duration of the surface movement process after mining the 3^-1 coal seam is about 1.39 years.After the 2^-2 coal seam and the 3^-1coal seam are all mined,the maximum surface subsidence value is 5.5m.(3)Based on the simulation results of Flac^3D,after all multi-layer coals are mined,different subsidence monitoring curves appear along the coal seam's direction and inclination.Stress concentration occurs in the roof and sidewall coal pillars of the goaf,2^-2 the maximum tensile stress appears at the roof position of the goaf,3^-1 the maximum compressive stress and the maximum shear stress appear at the position of the coal pillar on the sidewall of the goaf,The coal pillars of the 2^-2 coal seam goaf are stable,and the coal pillars of the 3^-1 coal seam goaf have shear failure.The maximum accumulated surface subsidence is 3.51m,which is different from the 5.5m calculated by the probability integral method.The reason is that the overlying strata formed rock beams after the first mining of the 2^-2 coal seam,which delayed the caving zone and the water-conducting fracture zone to the surface.During the development process,the surface subsidence speed and subsidence displacement are therefore reduced.