Abstract: The two key issues concerning safety mining in caving coal with weak thin bedrock are the development law of mining-induced fissure and variation regulation of support load. This paper uses physics simulation, theoretical analysis and field measurement to further research the two problems centered on the fully-mechanized caving face in thin bedrock area of Zhuxianzhuang coal mine. The result shows that weak thin bedrock is rich in clay minerals. The bedrock is liable to disintegrate and expand because of weathering under the chronicle impact of groundwater, effectively resisting the development of mining-induced fissure. The fissure-mining ratio in the top coal caving ranges from 3.6 to 5.4. The crack developing height of the breakage is much less than the normal thickness of the bedrock, and the thinner the bedrock is, the more obviously resisted the height of the fractured zone is. The bedrock’s mechanical property will be greatly weakened under the weathering. Without basic roof bearing layer in the roof, the working resistance of support is much less than the rated working resistance. The roof weighting step is far less than that of normal bedrock, and therefore the phenomenon of weighting is not obvious.

Key words: thick seam, weak thin bedrock, support load, fully mechanized caving mining, mining-induced fissure