Abstract: For the comprehensive analysis of complex goaf roof stability, the method combining classical mechanics and numerical simulation is adopted. With simply supported beam theory, load transfer intersection line theory, and ratio of span and thickness equation, the goaf roof instability critical parameters are theoretically calculated. The FLAC3D numerical simulation software is utilized to give a study of the surrounding rock stability. Results indicate that the goaf is instable when the roof structure parameters are all higher than the instability critical parameters; according to the goaf roof stability numerical simulation analysis, the roof central displacements are larger than the pillar lateral displacements with a maximum of 4.7 cm；the goaf roof minimum principle stress is near to the tensile stress; plastic zones are distributed to varying degrees in the goaf roof, floor and pillars, especially widely distributed in the pillars, showing that the goaf surrounding rock is in poor stability and the goaf is obviously instable. Reasonable measures should be taken in time to deal with the goafs. As it shows, the numerical simulation with FLAC3D, which can comprehensively evaluate the instability factors of the goaf, and truly reflect the state of goaf surrounding rock stress-strain and plastic distribution, has widespread applicability.

Key words: goaf roof instability, numerical simulation, goaf surrounding rock, minimum principle stress, plastic zone