Study on Water Seepage Characteristics of Coal under Triaxial Stress Based on Computed Tomography Reconstruction and Three-Dimensional Printing

Coal seam water injection is a crucial technique for mining disaster prevention, and its effectiveness depends on an understanding of precise seepage mechanisms. Current three-dimensional (3D) printing methods cannot accurately replicate coal’s complex pore structure, leading to unreliable seepage results. Through computed tomography (CT) 3D reconstruction and 3D printing technology, we prepared gypsum samples that precisely mimic natural coal’s internal structure and then conducted uniaxial compression and triaxial seepage tests to analyze fluid–solid coupling characteristics. The results show that (i) the stress–strain curves of 3D printed samples were similar to those of natural coal samples, and the mechanical parameters were close to each other; (ii) the permeability of 3D printed coal samples gradually decreases and stabilizes with the increase of axial and circumferential pressures, while the seepage volume increases linearly; (iii) the initial permeability of the 3D printed samples is similar, but the slope of permeability decrease increases with loading rate; and (iv) the permeability changes conform to the power law function and monoexponential decay function, with R2 higher than 0.94 and 0.99, respectively. This work has provided a new repeatable experimental method for the study of coal seam water injection and a reliable means for improving the coal seam water injection seepage theory.