Impact of Underground Coal Mining Subsidence on Surface Soil Pore Structure: 3D Visualization and Quantitative Analysis

ABSTRACT Underground mining‐induced subsidence significantly damages soil structure, leading to surface ecological degradation; however, the characteristics of soil microstructural changes under this disturbance remain poorly understood. This study systematically analyzes the three‐dimensional (3D) pore structures in surface soils (0‐60 cm) from different subsidence disturbance units (fissure units, non‐fissure units, and undisturbed units) using x‐ray computed tomography (CT) and image analysis. The results show: (1) Porosity increased by 7.42% in the non‐fissure unit and 19.25% in the fissure unit compared to the undisturbed unit; (2) Volume expansion of large‐diameter pores (> 3 mm) was the main driver of increased porosity; (3) Fractal dimensions rose by 5.35% and 8.23%, while tortuosity increased by 12.59% and 20.74% in the non‐fissure and fissure units, respectively; (4) Ellipsoidal pores showed the most significant changes in number and volume, serving as a key characteristic of the complexity of the pore network; and (5) Fissure units exhibited the highest pore connectivity, as evidenced by the Euler number, connected porosity, coordination number, and pore node parameters. Correlation analysis revealed that subsidence‐disturbed soil pore structures are largely dependent on connected pores. 3D visualization further confirmed that soil pore structures evolve toward looser, more complex, and more interconnected states under subsidence. This structural change disrupts soil function, potentially leading to vegetation degradation and exacerbated subsidence. Based on these pore structure characteristics, an ecological risk classification framework and targeted restoration strategies were proposed. These findings deepen the understanding of ecological degradation mechanisms in subsidence areas and provide theoretical guidance for ecological restoration in mining regions.