Spatiotemporal distribution and evolution mechanisms of land subsidence in areas with combined coal mining and groundwater extraction

Land subsidence in areas with combined coal mining and groundwater extraction is characterized by multi-source induction, multi-field coupling, and multi-stage transfer, making its formation and evolution mechanisms particularly complex. Taking the Xuchang Coal Mine as the study area, this paper systematically investigates the spatiotemporal distribution patterns of land subsidence. A numerical calculation method for land subsidence in combined coal-groundwater extraction areas is proposed, and a corresponding hydro-mechanical coupling model of the study area is established. On this basis, the intrinsic subsidence mechanisms of such combined extraction areas are elucidated, and their future evolution trends are quantitatively predicted. The main conclusions are as follows: (1) Coal mining typically induces subsidence with large magnitudes and high rates, whereas groundwater extraction generally produces relatively small magnitudes and low rates. (2) The contributions of inducing factors to land subsidence exhibit spatiotemporal variability. Coal mining accounted for an average of 62.4% of the total subsidence in the study area during 2018–2020, while groundwater extraction accounted for an average of 37.6%. (3) The plastic zones mainly develop in weak surrounding rocks or at stress-concentrated interfaces between adjacent mined-out working faces. (4) No new large-scale subsidence funnel will form in the study area over the next five years under current conditions. This research can serve as a reference for similar engineering practices.