Mechanism of grout-flowing water displacement in orthogonal rock fractures

Fractures are the primary pathways for fluid flow in rock masses, and they commonly occur as interconnected networks. Rock grouting is a process in which flowing water is displaced by grout. Since rock fracture networks are formed by a large number of crossed fractures, it is of great significance to study the displacement of grouts under the action of flowing water for designing effective grouting schemes. In this study, a rough orthogonal fracture model was established using three-dimensional reconstruction, and a laboratory visualization grouting test was conducted. We developed a numerical orthogonal fracture model using COMSOL Multiphysics to investigate the effects of fracture roughness, the grout-to-water flow rate ratio, and inlet–outlet configurations on the grout–water displacement process. After validation, the experimental and simulation results suggest that grout primarily fills well-connected channels. Grouting pressure rises rapidly after injection and stabilizes once most water is displaced. Efficient mixing at intersections yields more consistent grout volume fractions across branches. Displacement efficiency is governed by the dominant flow channels. If the conventional parallel-plate model is used, which ignores fracture surface roughness, the grouting pressure may be underestimated by more than 30%.