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.