Abstract: Research status of current roof safe thickness of mined-out area were analyzed. Taken Qidashan iron mine as an example, roof stability of underground hidden mined-out area under loading was analyzed by using FLAC^3D and RFPA, and the relationship between safe roof thickness and span length under loading was simulated. Numerical results show that safe roof thickness and span length of underground mined-out area of Qidashan iron mine was close to linear relationship. In the practical project, the safety factor of 1.3 times of calculated minimum roof thickness should be considered. It provides theoretical guidance for roof and pillar safety of Qidashan iron mine.

Key words: Mined-out area, FLAC3D, RFPA, Numerical simulation, Roof safe thickness