Abstract: Dahongshan iron mine which uses sublevel caving method without sill pillar has three extra-large mined-out area, the displacement of overburden and surface subsidence will lead to ground pressure and geological disasters, like rolling stones in open stope, air-blast wave in the underground stope, mud-rock flow in surface and underground, and so on. In order to monitor the natural caving height and displacement of overburden and subsidence range and displacement of surface, we use many means of monitoring methods, like multi-channel microseismic monitoring system, non-contact displacement monitoring system, handheld GPS device, total-station instrument. We obtained a lot of data after two years of monitoring; these data show that the natural caving height of overburden is between 1 090 m and 1 060 m elevation, the total settlement of observation point in +1 090 m tunnel is 1 350 mm, the subsidence range of surface is within the scope of the designed surface displacement based on traveling angle 75°, the maximal total vertical and horizontal displacement in surface is 1 779 mm and 948 mm, the deformation of overburden and surface is stable and controllable, there is no disaster occurred at present.

Key words: extra-large mined-out area, surface subsidence, overburden ground pressure, microseismic monitoring, displacement monitoring