The Movement Of Upper Strata And The Pressure Behavior Of Close Distance Coal Seam Mining

This paper is based on the background of western mining area of Hongyang No.2 mine,study the law of overlying strata movement and rock pressure change in close-up coal seam mining,theoretical analysis,numerical simulation,in-situ monitoring are used.The stability analysis of roof and floor in mining face is carried out in this paper firstly,according to fracture mechanics model,the roof stability of 1201 working face in close-up coal seam mining is studied,according to the law of floor depth failure,the failure depth of the bottom of 1201 working face is studied,the roof stability of 1301 working face is studied based on the bulk-block model;Then through numerical simulation,according to the actual engineering geological conditions of western mining area of Hongyang No.2 mine,The movement and displacement of the overlying strata,the stress distribution and the support pressure distribution of working face under different advancing distances are analyzed;Finally,according to the monitoring data of rock pressure,the laws of strata behavior in the process of face advancing is studied.Through the above research methods,the main conclusions are drawn:(1)Simply the initial fracture of basic roof as four edges clamped mechanical model,simply the periodic fracture of basic roof as three edges clamped and one side simply supported mechanical model,according to the calculation,the initial fracture distance of basic roof of No.12 coal seam is 16.8m,the period fracture distance of basic roof is 13.9m;according to the theory of floor depth failure,the failure depth of the bottom is related to mining thickness,cohesion and internal friction angle of coal,concentration factor,mining depth,calculation shows that the floor failure depth of No.12 coal seam is 2.12 m.According to bulk-block model,analyze the stability of lower coal seam roof,conclude the instability of the roof block in the lower seam is proportional to the vertical stress on the block,and inversely proportional to the horizontal stress,especially affected by the inclination of the fracture surface of the block.(2)For close-up coal seam mining with thin interlayer spacing and without basic roof structure,The initial pressure is caused by the instability of the bulk block structure,which is caused by the gradual increase of the vertical stress on the block,The periodic pressure is caused by the breaking of the upper basic top and the breaking of the basic top of the lower limb;In addition to stress concentration on both sides of the work face,when the upper coal seam is mined,in the middle of the mined out area,the stress area formed by the collapse rock formation will be formed,when the lower coal seam is pushed to a certain distance in the working face,there will be "stress rising areas-decompression zone-extrusion stresszone-decompression zone-extrusion stress zone-decompression zone-stress rising areas”.(3)For close-up coal seam mining with thin interlayer spacing and without basic roof structure,when the lower coal seam is mined,the initial pressure step of the working face is close to the periodic pressure step,the initial pressure and periodic pressure of the lower coal seam are smaller than those of the upper coal seam.