Abstract: In order to determine safe roof blasting thickness of a VCR stope in Fankou mine， a mechanical ultimate-bearing analysis model of roof blasting under complex boundary condition (three sides fixed and one side supported) was constructed， the relationship between bearing capacity and roof blasting thickness was derived， and the minimum roof blasting thickness was calculated as 4. 6m. Accordingly， numerical simulations of blasting roof stability under various thicknesses were carried out to obtain the changing law between indexes (plastic zone volume， maximum vertical displacement and safety coefficient) and thickness. Research results show that safety indexes change obviously and plastic zone develops into complete connection when roof blasting thickness decreases from 5m to 4m， which proves the rationality of mechanical analysis. Referring to safety coefficient of similar mines， safe roof blasting thickness is revised as 6~7m. In practice， the fact that the blasting roof of 6. 5m thickness keeps safe all the time indicates that the results fit well with actual situation.

Key words: VCR mining method, roof blasting, boundary conditon, plastic limit analysis, numerical simulation