Study on Discontinuous Deformation Law and Mechanism of Repeated Mining Surface Ground

In order to have the discontinuous deformation law of the surface ground in the geological development area under the repeated mining conditions, the s ite observation, theoretical analysis and other means were applied to the study on the discontinuous deformation phenomenon of the surface ground under the repeated mining conditions above Zhaizhen Mine.The results showed that the discontinuous deformation of the surface ground above Zhaizhen Mine was mainly concentrated in the west part of the minefield.Along the geological structure development and the coal mining face in a certain angle, the crack depth was not deep, the crack width was ranging from 300-600 mm, the crack length was ranging from 320-2 143 m and the sinkage of the benches was ranging from 0.4-2.4 m.The special overburden strata st ructure, low depth and thickness ratio and the activation of the geological structure caused by the mining would be the important conditions to the discontinuous deform ation caused in the west part of the minefield.The surface ground cracking and bench subsidence phenomenon were affected by the special overburden strata structure and the miming and thickness ratio and the activation of the geological structure caused by the mining would be the induction factors to cause the discontinuous deform ation of the surface ground.