Numerical Simulation of Overburden Deformation Mechanism and Surface Settlement Characteristics Induced by Underground Coal Mining: A Case Study

Underground mining in mountainous regions presents a significant geological hazard, characterised by the occurrence of land subsidence and movement of overlying strata. To aggrandise the theory of mine rock mechanics, we conducted a systematic investigation into the deformation and failure mechanisms of overlying strata as well as the patterns of surface subsidence in mountainous regions. With the method of engineering mechanics and theoretical analysis, supplemented by the universal distinct element code (UDEC) numerical simulation, the mining status of Songzao mine was simulated effectively. Herein, the results revealed that the nonlinearity of the overlying strata failure field occurred during mining, as evidenced by an increase in the failure field when the coal approached the seam roof. The subsidence curve of the underlying lower strata exhibits an inverted trapezoid pattern, while that of the overlying upper overburden displays a funnel-shaped trend. Additionally, the upward transmission displacement velocity was significantly attenuated due to the shielding effect exerted by the key stratum in the overburden, resulting in a greater spatial separation from the underlying strata. The critical stratum fractures as the working face advanced to 120 m, subsequently leading to an increase in vertical displacement and cessation of surface subsidence. The surface subsidence value and speed, however, exhibited a gradual increase as the coal seam mining progressed. Due to the influence of mountain surface landforms, the subsidence value of convex landforms surpasses that of concave landforms, thereby expediting the rate of subsidence and resulting in geological hazards.