CONTROL EFFECT OF THE EXTREMELY THICK NEOGENE BOTTOM CLAY ON THE HEIGHT OF CAVING ZONE IN THIN BEDROCK MINING AREA BY NUMERICAL SIMULATION

To investigate the control effect of unevenly thick bottom clay on overburden movement and failure during mining of coal seam No.3 in the Shanxi Formation within a thin-bedrock outcrop area covered by extremely thick Neogene strata at the western Zhaolou Coal Mine, the geological and hydrogeological conditions of the study area were systematically analyzed. Six generalized mining models with discontinuously uneven bottom clay and one model with continuously uneven bottom clay were established. A three-dimensional engineering geological numerical simulation model was then constructed. The simulation results indicated that, under identical conditions, the presence of a certain thickness of bottom clay significantly reduced the maximum height of the caving zone, maximum vertical stress, and maximum vertical displacement, with a turning point observed at a bottom clay thickness of 8 m. The findings reveal the intrinsic mechanism by which the absence of bottom clay greatly increases the risk of water and sand inrush during mining, whereas a certain thickness of bottom clay can effectively dissipate mining-induced stress concentration and deformation energy, thereby restraining the development of the caving zone height.