Characteristics of Discontinuous Surface Deformation Due to Mining in Hard, Thick Bedrock: A Case Study

Abstract

Coal mining at Zhaizhen coal mine has resulted not only in continuous deformation of the surface but also discontinuous deformation such as surface cracking and step subsidence. The discontinuous deformation of the surface causes serious damage to the environment, cultivated land and surface buildings in the mining area. This study summarizes and studies the characteristics of discontinuous surface deformation in the western mining area of Zhaizhen coal mine and analyzes the mechanisms by which it occurs. The discontinuous surface deformation is caused by two main types of mechanism. The first results from the characteristics of the overlying strata. Specifically, the bedrock layer is thick (230–260 m) and hard, while the topsoil layer is loose and thin (4–8 m). The loose topsoil layer is not thick or strong enough to absorb the deformation of the hard, thick bedrock, and cracks develop at the surface. The other main cause of discontinuous surface deformation is dislocation at faults and folds under the influence of mining. Moreover, repeated coal mining aggravates the discontinuous surface deformation. In order to effectively control this deformation, fully mechanized mining with gangue filling was adopted in mining area No. 7 of Zhaizhen coal mine and the corresponding surface deformation was monitored. The results show that the gangue-filling method effectively controlled the discontinuous surface deformation and resulted in a maximum surface subsidence with a trend and tendency of 206 mm and 209 mm, respectively and no surface cracks or step subsidence at the surface.