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| Experimental study on top-coal breaking and moving rules during fully mechanized top-coal caving mining in extremely thick coal seam#br# |
| LYU Huayong1，2，WANG Zhaohui1，2，TANG Yuesong1，2，ZHANG Lingfei1，2，LIU Fei1，2，ZHANG Yaning1，2 |
(1. College of Resources and Safety Engineering，China University of Mining and Technology(Beijing)，Beijing 100083，China；
2. Top-coal Caving Mining Research of Coal Mining Industry，China University of Mining and
Technology(Beijing)，Beijing 100083，China)
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Abstract In order to achieve safe and efficient underground mining of extremely thick coal seam above 20 m，a fully mechanized top-coal caving mining method after extracting the middle slice in extremely thick coal seam was creatively proposed. The similar simulation test with a large scale of 60∶1 was performed to study breaking and moving characteristics of top-coal，displacement and vector fields of top-coal，and support load effects of the fully mechanized top-coal caving mining after extracting the middle slice in extremely thick coal seam above 20 m. The results show that，during the stage of pressure relief mining，the top-coal collapse shape is approximately trapezoidal，the breaking and instability of the stepped top-coal cantilever beam structure above the support have a periodic effect，the displacements of the upper，the median and the lower of the top-coal decrease in turn，and cutting top press support accident occurs after the first weighting of the main roof. During the fully mechanized top-coal caving mining stage，the short cantilever beam structure is finally broken into a loose structure and the total displacement of the median top-coal is greater than that of the upper top-coal. Due to supporting effect of the support structure，vertical cracks occur obviously in the lower top-coal，and the thickness of the top-coal affected by the support is approximately 10 cm. The evolution characteristics of the displacement and vector fields of the top-coal are in consistent with the experimental results. The research results lay a theoretical foundation for the development of mining technology of extra-thick coal seams above 20 m in China.
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