Abstract: Based on a survey of the distribution of in situ structural planes and surface cracks and an analysis of surface deformation monitoring data, a case study is performed in Chengchao Iron Mine to investigate the influence of the structural planes on the surface deformation in the mining zone. The results show that, under a large horizontal stress condition, the structural planes of rock mass can change the surface tensile deformation distribution and the failure pattern, and intensify the deformation of rock mass. In areaⅰ(i.e., the area on the eastern of section Ⅲ), the toppling-sliding deformation is formed along NNW structural planes within the outermost crack, and the surface deformation is featured mainly with rapid deformation; the bedding deformation occurs along NNW structural planes outside the outermost crack, and a linearly stable development of surface deformation prevails; In the stage of toppling failure, the deformation in this area is mainly dominated by horizontal displacement of rock mass. In areaⅱ(i.e. the area on the western of section Ⅲ), under the north-south horizontal stresses caused by mining subsidence, the rock masses are separated into parallel blocks, resulting in rapid surface deformation. In some local regions, some parallel blocks mentioned above fails in a toppling way along NNW structure planes under the west-east horizontal stresses.

Key words: mining engineering, underground mining, surface deformation, deformation monitoring, structure planes