Dip angle effect of coal seam on crack propagation rule of compacted area at fully-mechanized rise mining face

In order to study the dip angle effect of the coal seam compacted area in the fully-mechanized rise mining face，the physical similarity simulation test and theoretical analysis were combined to study the cracks in the overburden compacted area under different coal seam dip conditions. According to the height of the compacted area，the collapse angles and the width of the compacted area，the study of fracture evolution law has established a dip effect model of the evolutionary coal seam dip in the compacted area. The results showed that with the increase of the dip angle of the coal seam(0°<15°<30°)，the average pressure step was gradually reduced(12.5 m>11.6 m>10.4 m),the abscission layer of rock was increasing. At the same time，the numerical value of the abscission layer of rock and the local concentration of the floor stress were used as the basis for determining the boundary of the compacted area. It was concluded that the height of the compacted area increased with the increase of the dip angle of the coal seam. The curve composed of the slope value of the height fitting straight line of the compacted area showed a gentle，steep and gentle change rule. This meant that the compacted area had little difference in height at the initial stage of formation，but it would rapidly increase the height difference and maintained the state of the large height difference when the working surface was advanced to 55-65 m. What’s more，the collapse angles of the working face side and the cut-off side showed an increasing and decreasing trend with the increase of the coal seam dip angle. Then，based on the evolution of the height of the compacted area and the collapse angles，a simplified model of the compaction zone was established，and the mathematical expression equation of the width of the compacted area increased with the dip angle of the coal seam. Finally，based on the theory of mining fracture ellipse belt，combined with the experimental results，the mathematical equation of the compacted area of the mining fracture elliptical belt affected by the dip angle factor of coal seam was established，which provided a reliable theoretical basis for accurately located the gas enrichment area in the up-dip working face of coal mining.