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%.