Overburden movement and surface damage characteristics of non-pillar mining in shallow extremely-thin seam
In order to explore the difference between the overburden migration and surface damage in the shallow extremely-thin coal seam non-pillar mining by roof cutting and pressure relief mining and the conventional coal pillar retaining mining,based on the key stratum theory and the shallow extremely thin coal seam in Zichang mining area,the formula for calculating the critical value of the hard rock breaking distance and the overburden caving height is obtained.Combining with 3DEC numerical simulation and field tests,the characteristics of overburden migration and surface damage in shallow extremely thin coal seams under the conditions of non pillar mining and coal pillar retaining mining are compared and analyzed,and the heights of the two overburden zones in extremely thin coal seams are determined.The results show that when the mining face reaches 60m,the development height of the two zones is basically stable.When the mining face is larger than 60 m,the cracks in the overburden behind the working face gradually close from cracks,and the crack area moves forward with the mining face,and the height of the two belts is stable at 24.6～27.7 m;compared with the conventional coal pillar retaining mining,the overburden under the roof cutting and entry retaining mining without coal pillar is continuously moving and deformed,which can effectively repair the overburden cracks and surface damage cracks caused by the discontinuous movement and deformation on both sides of the coal seam mining face,and eliminate the overburden cracks on both sides of the coal pillar in the adjacent working face section under the conventional coal pillar retaining mining method.The results are verified by field observation.
NETL
NSTL
万方数据
