Numerical Simulation Research on “Three Zones”Distribution Rule in Overlying Strata of Fully Mechanized Working Face in Upper Protective Seam with God-side Entry Retaining

Studying the development characteristics of fractures in overlying strata after the extraction of protective seam is the premise of mastering the normal distribution height ofvertical three zones,the stress distribution law of overlying strata and the range of pressure- relief distribution. Combined with present mining situation of the medium- long- interval upper protective seam of the coal seams group in Qidong Mine,stimulation evolution was carried out on the displacement and stress distribution of the overburden strata in the mining process of No. 6135 fully- mechanized face by using Flac~(3D)software. By analyzing the failure law of the overburden strata,it was concluded that after the mining of 61 coal seam,the biggest caving height was 7. 1 m,the development height of mining fissure zone was 30. 1 m,the stress was in a distribution state with small top and large bottom just like a bell shape,and a pressure relief protection law appeared along the dip and strike of the protective seam,all of these provided technical support for mine safety and efficient production.