Abstract: In order to obtain the law of instability and caving for large-span cut-hole roof with thin bedrock in depth during mining, the cut-hole of 1105 great mining height face in Zhaogu No. 2 Coal Mine has been taken for research background. Separate type displacement monitoring instrument of deep roof and separate type bolt (cable) condition monitoring instrument, whose sensors were arranged in goaf and secondary instruments were moved outside, have been adopted for the first time to real-timely monitor the deformation and failure laws of cut-hole roof and dynamic changes of bolt (cable) supporting force during mining. The mechanical model of breakdown destabilization of large-span cut-hole roof has been constructed and the mechanical mechanism of instability and the mechanism of caving of roof has been expounded. The results indicate that the instability and caving form of cut-hole roof is manifested as instantaneous fractures of high-horizon roof in twice. Instability and caving horizon of roof is over 6 m. After the completion of the first fracture, the roof will form hinge structures with certain self-stability. With continues propulsion of coal face, the secondary fracture occurs and then the roof completely collapses. The deformation rate can reach 5.3-19.4 mm/min during the first roof fracture. Accompanied by anchorage invalidation of the bolt, deformation rate is relatively small during the secondary fracture, which is about 2.6-7.2 mm/min.

Key words: large-span cut-hole, thin bedrock roof, instability and caving, span