Abstract: With most open-pit mines in China approaching depletion, an increasing number of operations are transitioning to underground mining. The rock-mass movement and slope-stability problems induced by underground extraction beneath previously mined open pits have become a serious threat to nearby buildings and transportation infrastructure. Excavation of coal seams beneath the pit floor may lead to damage to surface structures and highways. In this study, numerical simulations were conducted for several mining schemes in the Xixi open-pit mine to obtain the surface deformation after extraction in four mining panels. The extents of potential damage were delineated using three indicators: surface tilt, surface curvature, and horizontal deformation. In addition, the safety of highways surrounding the mine boundary was evaluated with reference to roadbed design specifications. The results show that backfill mining significantly reduces surface subsidence and horizontal displacement, effectively confining the deformation zone within the open-pit boundary. This approach enhances the safety of surface structures and provides guidance for highway construction around the mine. The method has been endorsed through expert review and holds substantial economic significance for both the mining group and the city of Fushun.

Key words: Goaf Deformation, Numerical Simulation, Damage Extent, Subgrade Stability