Abstract: The mining-induced fractures in roof and floor are the origin of a series of mine disasters. Thus, the research on the development and evolution law of the fractures has great significance to the mine disaster prevention. To study the closing mechanism of mining-induced fractures in overburden aquifuge and the associated influencing factors, several research means, including the ultrasonic imaging technology, mineral composition measurement and expansibility experiment are introduced in this paper. The results show that the expansion rate of the overburden aquifuge shows direct proportion to the  montmorillonite content (including mixed minerals of Illite and montmorillonite) and its distance to the coal seam roof. Meanwhile, when the overburden structure is not suffered a severe damage, if the expansion rate is greater than the development rate of fracture, the mining-induced fracture can be closed effectively. Finally, the research result has been successfully verified by the penetrability evalution of coal mining under water body at Xin’an Coalfield and the water-preserved mining at Shendong Mining Area, and has achieved a good application effect in practice.

Key words: overburden aquifuge, fracture closing mechanism, mine water inrush prevention, mining under water body, water-preserved mining