Analysis of the surface subsidence induced by sublevel caving based on GPS monitoring and numerical simulation

This paper describes a case study of the surface subsidence induced by sublevel caving without sill pillars in the Maogong Iron Mine, China. A comprehensive analysis based on GPS monitoring and numerical simulation is proposed and used to analyze the surface subsidence characteristics and damage range. GPS monitoring results showed that the vertical displacement reached 40.3 mm at the JC5 monitoring station and was accompanied by ground crack development. According to the in situ surface subsidence monitoring data and numerical calibration model results, the corresponding critical horizontal strain and angular distortion due to the surface subsidence were estimated as 1.5 × 10−3 and 2.0 × 10−3, respectively. The numerical results showed that the center of the surface subsidence was located in the hanging wall of the orebody, which changed to its far end with increasing mining depth. In the early surface subsidence stage, macro-tension cracks developed in the hanging wall rock mass, and the slabbed rock mass then collapsed into the cave through rotation and/or translation failure. With increasing mining depth, there will be unfilled goaf in the underground, and the rock mass will gradually collapse under high mining-induced stress concentration. Accumulation of caved rocks and the bulking effect result in slow surface subsidence. Notably, surface collapse will not occur suddenly in Maogong Iron Mine, and potential secondary hazards mainly small landslides in the hillside.