Based on the geological conditions, underground mining situations, as well as the status of cracks and surface deformation of Chengchao Iron, a cantilever 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 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 surface deformation will gradually expand outward.

1 Introduction

With the rapid development of the national economy and the demand for mineral resources is increasing, the size of the underground resources development is gradually increasing and the depth of mining continue to extending. Land surface deformation and rock mass movement caused by Iron ore underground mining is a very complex system engineering problem, which has been studied by many scholars. Zhu Jiaqiao [2], Xi Renshuang [3] and Huang Pinglu [4] all view that Chengchao's land surface deformation and geological disasters are controlled by NWW-trending joints. Zhu Jiaqiao [2] believed that the surface deformation failure modes of Chengchao Iron is dumping type tensile failure. Xi Renshuang [3] believed that the main deformation of Chengchao Iron is the form of goaf ladder in the east main well area. Huang Pinglu [4] believed that the driving force of rock deformation comes from the horizontal tectonic stress release of Chengchao's collapse pit wall rock. The mechanism of footwall crack deformation in Chengchao Iron is as follows: the adjustment of the tectonic stress field caused structural surface through fractures and dislocation after the formation of the underground mined area from east to west. Deep rock mass deformations are divided into four zones by Chen Congxin [5–7]: rupture zone, the transition zone of rupture to deformation, the deformation zone, and the undisturbed zone. Rock deformation and failure process is divided into four stages by Bai Weiwei: underground goaf formation stage, the top of the goaf rock slump stage, rock mass deformation stage and rock mass unloading rupture mobile stage.

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