Numerical Simulation Of Overburden Movements In Fully-mechanized Caving Mining Of Extremely Thick Coal Seam

The study of dynamic failure law of overburden strata plays an important role in rational planning and safe production of coal mines.On the basis of a large amount of field data and extensive investigations,the 8012 working face of extra-thick coal seam in Tashan coal mine is determined as the research object.Combining field data,theoretical analysis and numerical simulation,the overburden movement law of fully mechanized caving mining face in extra-thick coal seam was analyzed from three aspects:stress of surrounding rock,overburden movement law of "three zones" and mechanism of overburden breakage.8102 fully mechanized caving mining face in Tashan coal mine is carried out by using FLAC3D numerical simulation software.After advancing the working face,the distribution regularity and characteristics of stress,displacement and plastic zone of overburden rock were analyzed.The distribution law of stress,displacement and plastic zone of overburden rock were also revealed under different coal seam thickness and the influence of burial depth,mining height and working face width on the movement law of overburden rock under large mining height were studied,which provided a theory for the overburden movement in fully mechanized caving mining of extra-thick coal seam in Tashan Coal Mine.On the basis of this,the following conclusions were drawn:(1)The strata pressure obviously occurs after the advance of the cut hole to 40 m.With the advance of the working face,the vertical displacement of the strata above the coal seam increases dramatically at 30 m in front of the mining face.This is because the influence of mining.(2)When the working face is conventional mining,the maximum height of the plastic zone is 35 m,the plastic zone in front of the working face is 30 m,and the plastic zone of the coal seam roof is basically the same as the advancing of the working face.The failure form of the plastic zone in the roof is mainly tensile failure.(3)The maximum stress in surrounding rock changes obviously before and after top coal caving.When the thickness of coal seam is less than 20 m,the maximum stress in surrounding rock of working face basically remains unchanged.When the thickness of coal seam is more than 20 m,the maximum stress in surrounding rock of working face changes obviously and increases in a parabolic form,while the maximum stress curve of surrounding rock before top coal caving is in a saddle shape under different thickness.(4)The larger the mining height of large mining height,the larger the variation range of stress field,and the smaller the peak stress;The buried depth is closely related to the stress field,and the peak stress field increases with the buried depth;The width of working face has a significant effect on the stress field,and the peak stress field increases with the width of working face.Compared with the traditional mining height,the plastic zone of the large mining height working face is wider,and shear failure is the main factor.