Physical Similarity Simulation of Overburden-Slope Deformation and Fracture Evolution Under Sequential Highwall-Mining Excavation at Different Chamber Heights

To reveal the evolution of overburden movement, slope deformation, and fracture damage during highwall mining, a physical similarity model was established based on the geological conditions of the Heishan Open-Pit Mine, Xinjiang. The excavation extended through the model thickness and was idealized as a continuous slot. Different chamber heights were considered to simulate the extraction of Coal Seam 13-2 and the subsequent mining of the overlying Coal Seam 9. Overburden and slope displacements, fracture-area ratio, and fractal dimension were analyzed using the MatchID-2D digital image correlation method, displacement monitoring, and fracture image processing. The results show that deformation initially concentrates in the chamber roof and lower overburden and subsequently propagates toward the slope toe and surface, exhibiting distinct stage-dependent and spatially differentiated characteristics. As the chamber height increases, overburden subsidence, slope-toe displacement, fracture-area ratio, and fractal dimension all increase. During the extraction of Coal Seam 9, displacement continues to accumulate within the previously formed deformation zones, accompanied by further propagation and coalescence of existing fractures. The results characterize progressive local damage and spatially coordinated deformation within the model. These findings improve understanding of overburden-slope deformation and fracture evolution under the investigated conditions.