Study on reasonable mining and caving ratio in fully-mechanized top-coal  caving mining of coal seam with large thickness variation coefficient

Based on the characteristics of large variation of coal seam thickness on strike and dip of the fully mechanized caving test surface of Jiulishan Mine，and the thickness in the middle is thick and thin on both sides，two groups of numerical simulation tests were carried out at a typical slope changing position of coal seam，two sets of numerical simulation tests were carried out on the coal seam where the coal seam changed from one direction to the other，and a reasonable mining and caving ratio was proposed and verified by field tests. The experimental research results show when the mining height of the constant mining height group increases，the number of top-coal dropped coal particles remains in a constant value range，and the change of mining height has little effect on the recovery ratio of top-coal. With the increase of mining-caving ratio，the number of discarded coal particles first increased and then decreased，and the top-coal discharge first decreased and then increased，and the change of mining and mining and caving ratio has great influence on the recovery ratio of top-coal. The comparison results between the two groups of tests shows that:in the process of coal thickness increasing gradually，combined with the recovery ratio of mechanical mining，there is a high mining and mining and caving ratio intervals range of 0.9-1.1; Linear influence requires specific analysis for specific coal thickness. The field test results of the top-coal recovery rate on the test surface by the top-coal migration tracker show that the recovery ratio is 85.7% under the condition of 1∶1 mining and mining and caving ratio. The top-coal on site has a high degree of fragmentation. The middle and lower head coals are thin and broken，resulting in a high recovery rate of the lower top-coal. Top-coal leaks from the coal wall. The engineering practice shows that after adopting 1∶1 mining and caving ratio，the parameters optimization can reduce the process coal loss to the greatest extent，and the fully-mechanized top-coal caving process has strong adaptability to the continuous change of top-coal thickness. The recovery ratio of fully mechanized caving face reaches 90%，and the recovery of more top-coal is about 8 100 tons. It has realized safe，efficient，scientific and accurate mining recovery，and laid a theoretical and practical foundation for the transformation of mining methods and the popularization of fully-mechanized top-coal caving technology.