In subsurface engineering

grouting is an important measure to seal or strengthen fractured rock mass and reduce groundwater flow. Understanding the grout flow in rock fractures is significant to improve the grouting efficiency. The influence of grout material property on the grouting process in rock fractures saturated with a resident fluid is studied by visualized experiments. We present an experimental phase diagram of pattern formation and elucidate the relevant microscopic mechanisms. The experimental results show that the injection velocity and mass fraction in the grout significantly influence the displacement patterns in rough fractures

which is different from the displacement behavior with Newtonian fluid. During the displacement

the formation of different patterns is attributed to the local viscosity heterogeneity induced by the coupling effect of shear-thinning behavior and the spatial variability of fracture apertures. Decreasing injection velocity or increasing the mass fraction would stabilize the fluid-fluid interface and increase the area of initial stable region. The narrower aperture region of the fracture can only to be partially filled (with a low filling rate) by the polymer solution

except under the condition of very low flow rate and high mass fraction. The grout filling rate exhibits non-monotonicity with respect to flow rates. The displacement efficiency is significantly affected by displacement patterns

and thus we propose a theoretical model based on the interface stability analysis to elucidate the mechanisms behind the transition of displacement patterns. This work improves the fundamental understanding of grout flow in rough fractures and can provide a reference and technical guidance for evaluation and control of grouting efficiency in engineering practice.