The evolution characteristics and disaster-causing mechanism of goaf collapse in the southern coalfield of Shenyang

Underground coal mining causes ‘damage–fracture–instability’ of the overlying rock in the stope, resulting in movement and deformation of the mined rock mass that eventually extends to the surface, posing serious threats to buildings, transportation, pipelines, etc. To study the evolution rules of the overlying rock and disaster-causing mechanisms after coal seam mining, this paper analysed the surface subsidence of the West 1st District of Linsheng Coal Mine in the southern coalfield, Shenyang, China. Continuous models were initially used to analyse seven mining times in the coal mine. The overlying rock and surface displacement evolution rules were analysed, and then discrete models were used to further study the rock mass deformation and damage mechanism and rules for surface subsidence caused by coal mining. The results showed that the mining of inclined coal seams has a smaller impact on the surface in the shallower direction of the coal seam, but a larger impact on the surface in the deeper direction of the coal seam, as the deeper coal seam mining causes longer tensile fractures cutting the surface. The vertical surface displacement polyline caused by the mining of the upper coal seam with smaller inclination angle and shallow burial depth was slightly symmetrical on both sides, and the surface subsidence caused by each mining was small. In such cases the rock strata disturbance, including tensile and shear fractures and the associated large-scale rock mass subsidence, caused by the coal seam mining is restricted to localized areas. When mining the lower coal seam with a large inclination angle and great burial depth, affected by the surface deformation that had occurred, the surface displacement value becomes larger and appeared asymmetrical like a parabola. The subsidence range at the end of the mining area with greaterburial depth was larger, as additional fractures are formed across the upper rock mass above the coal seams, eventually causing larger areas of rock mass subsidence. The discrete model can more realistically simulate the deformation and damage characteristics of the rock mass, and its simulated maximum surface settlement value caused by rock layer rupture and instability was greater than that of the continuous model. This study will provide a theoretical basis for monitoring, early warning, prevention, control and treatment of geological hazards in coal mining subsidence areas.