Effect of elevation angle of coal seam on top-coal caving law in fully-mechanized top-coal caving mining face during topple mining

In order to further study the dynamic variation law of coal seam dip angle and the influence mechanism of top coal loss and rock mixing in the topple mining,No.34201 working face of Jinggong No.3 mine of Pingshuo Group was taken as the research background. Based on the geological and production technical conditions of the site,a numerical model of the inclination angles of 0°,13°,23° and 33° was established by using the numerical simulation software PFC2D. The displacement field and contact stress of the top-coal,the boundary of top-coal and top-coal displacement staring point were analyzed. Using fish language programming to record the particle number and inversion of the drawing body,the distribution law of the top-coal loss space occupancy is obtained. Finally,the flow law and recovery of top coal under different coal caving steps are simulated on the spot. The results show that the dip angle increases the migration of the top-coal to the side of the goaf,so that the interface of the coal shovel is convex toward the goaf,and the top-coal draw body develops ahead of the top beam of the support,and the displacement of the top-coal starts. The point moves forward,and the displacement range increases with the dip angle; the sparse zone of the stress chain near the coal inlet is semi-circular,and increases with the dip angle within a certain range,showing an expanding trend,and the coal body is enhanced in the vicinity of the coal inlet. It is beneficial to top-coal recovery; when the dip angle is too large,the top-coal is difficult to release,the top-coal loss is increased,and the loss range is mainly located in the upper middle part of the coal seam; compared with other angles,the top coal recovery rate is the highest when the inclination angle is 13°. 83.6%,which is consistent with the above conclusions; statistical simulation data show that the top-coal recovery rate under the current geological conditions using the two mining and one caving is the best,and has been verified in the field application. The research results of the thesis provide a basis for determining the reasonable parameters of the vertical inclined fully-mechanized top-coal caving mining and improving the recovery rate of the top-coal.