Experimental investigation and analysis of void evolution and CO2 seepage characteristics in broken rock

To elucidate void-structure evolution and CO 2 seepage characteristics of broken rock masses during goaf compaction, confined compaction tests were conducted on broken argillaceous sandstone with different particle-size gradations and filling weights, while CO 2 seepage tests were performed at a fixed filling weight of 4.8 kg under different axial stress levels using a fractured rock mechanics–gas permeation testing system (FRM-GPTS). The results show that single-sized samples have higher initial porosities (0.490–0.541) than continuously graded samples (0.448–0.458), with porosity generally increasing as particle size decreases. Compaction proceeds through void compression, void filling, and void compaction, accompanied by progressive energy accumulation, particle breakage, and pore restructuring. At 25 MPa, deformation and breakage generally increase with particle size; at 4.8 kg filling weight, the relative breakage ratio increases from 36.33 to 66.35%. Continuously graded samples exhibit lower deformation and breakage because of fine-particle filling and skeleton-supporting effects. CO 2 seepage shows pronounced non-Darcy behaviour, with permeability decreasing continuously with increasing axial stress and decreasing porosity. Single-sized samples exhibit higher permeability (564.2–658.6 mD) than continuously graded samples (415.8–461.5 mD). These results reveal a coupled evolution mechanism of compaction deformation, particle breakage, pore restructuring, and seepage attenuation, providing an experimental basis for evaluating CO 2 storage capacity and migration in coal mine goafs.