Abstract: Grouting is a crucial technique for treating rock fractures in goafs, but it still faces challenges in predicting diffusion patterns and controlling the process; thus, optimization is needed to improve efficiency and effectiveness. As a case study, actual rock fractures in a grouting project for an underlying goaf in Jincheng City, Shanxi Province were used. A fracture model with controllable roughness was constructed, and transparent epoxy resin rough fractures were fabricated by 3D printing. And then, a self-developed visual experimental platform for rough fractures was established to analyze the diffusion characteristics, range, and grouting rate considering different grout concentrations, fracture roughness, grouting pressures and grouting rates, revealing the grouting diffusion mechanism with combination of grout concentration, fracture roughness, and grouting input conditions. And also, the phase interface theory was applied to characterize the diffusion pattern, and the fractal dimension was proposed to describe corresponding diffusion pattern under different conditions. The correlation between actual filling rate and filling capacity was explored, with “actual filling ratio” used as an index for grout filling capacity in rough fractures. These investigations show that grouting diffusion exhibits different patterns depending on grouting pressure, fracture roughness, and grout rheology, with grouting rate and grouting pressure as primary controlling factors and diffusion regulated by rheology and fracture morphology. Furthermore, faster grout diffusion leads to more irregular diffusion contours, which hinders complete filling of complex fracture networks, so the actual filling ratio can explain effective grouting in the fractures considering the combination of high-concentration grout and high grouting pressure. Additionally, a proposed numerical model for rock fracture grouting was established, verifying the reliability of the experimental results. The above achievements provide scientific supports for optimizing grout mixture design, grout hole spacing, and grouting pressure, solving corresponding parameter selection in traditional grouting methods for rock fractures grouting.

Key words: visualized experiment, grouting, rough fractures, grout diffusion, actual filling rate