Abstract: The dressing-plant of the Chengchao iron mine is located on the deep ore-body,and surface subsidence may be caused with combination of two mining methods to cave the orebody between -430 m and -500 m.Mining model is established on the basis of numerical analysis theory,and the excavation process of the model is simulated by using finite difference software FLAC3D.Surface subsidence regularity is obtained according to the simulation to predict the relocation of dressing-plant and propose appropriate preventive measures according to different situations.The results reflect that the influence of underground mining on the subsidence of dressing-plant area is large,thus affecting the normal production of dressing-plant and the safety of workshop buildings.The general rules of the relationships between the surface subsidence of dressing-plant area and the horizontal distance to cave deep ore-body have been carried out.It is recommended to relocate the dressing-plant.

Key words: Combined mining, Finite difference method, Numerical simulation, Surface subsidence