Based on the geological conditions

underground mining situations

as well as the status of cracks and ground surface deformation of Chengchao Iron Mine

a cantilever beam mechanical model is proposed. The bottom-up tubular collapse in the deep rock mass causes the horizontal tectonic stress release which favors the bending fracture deformation and destruction of the NWW-trending joints. This model can explain the formation of four zones in the deep rock mass: rupture zone

the transition zone of rupture to deformation

the deformation zone and the undisturbed zone. In such a mode

it inevitably leads to different deformation areas on the ground surface related to the different zones in the deep rock mass. So the mine surface is divided into four related areas: cumulative deformation area

crack-producing area

crack-extending area

and crack-closing area. As mining progresses

four zones of the deep rock mass will gradually extend downward

while four areas of the ground surface deformation will gradually expand outward.