Abstract: According to the history and current situation of ground caving-in in the eastern Chengchao Iron Mine, a 3D surface model of ground caving-in was reconstructed with the help of a 3D laser scanning technology. Furthermore, the ground subsidence contour map and the accumulative subsidence basin were obtained by combing with Surfer program. It showed that the initial ground caving-in points were mostly distributed in the marble area and the wall rock alteration zone. It is found that the ground caving-in area was a zonal distribution from east to west. Moreover, the situation of ground caving-in in the north was more severe than in the south. The terrain and landform of the ground caving-in area show similar glacier landscape features, such as the horn and blade ridge. According to geological conditions, underground mining situations and monitoring data of cracks and ground surface deformation by the 3D laser scanning technology, it is considered that underground mining is an internal cause and geological condition is an external cause for ground caving-in. The combined effect of these two factors led ground caving-in to appear mostly in the marble and surrounding rock alteration zone area for the first time. After the emergence of ground caving-in, a high level horizontal tectonic stress was released. As a result, rock mass, which was cut into a cantilever beam-plate by NE-trending joints, was broken. Through the analysis of the mechanical model of a cantilever beam-plate, the scope of fractured rock mass reached up to 172 meters wide. The fractured rock mass produced toppling-sliding failure along the sliding surface. Therefore, this mechanism of mechanical expansion makes the scope of ground caving-in wider, and finally forms a large ground caving-in basin in the eastern Chengchao Iron Mine.

Key words: underground mining, metal mine, three-dimensional laser scanning technology, mechanism of ground caving-in, mechanical expansion mechanism, cantilever beam-plate model