Analysis of grout radial propagation in water-saturated rough-walled rock fractures

Understanding the propagation behavior of cement grout in rough-walled fractures is crucial for predicting its effectiveness and design of optimal grouting schemes. To investigate radial propagation of cement grout in saturated rough-walled fractures, a water-cement grout two-phase flow model in rough-walled rock fractures is developed using the phase field method, Herschel-Bulkley model, and mass and momentum conservation equations. Then, the established model is validated against analytical solutions and rough fracture grouting tests. Subsequently, the sensitivity of grout propagation versus grout rheological properties, injection pressure and fracture geometry is analyzed. Simulation results reveal that the increase in water-to-cement ratio (W/C) and injection pressure can enhance the filling rate and flow rate of cement grout in rough-walled fractures. Nevertheless, regardless of adjusting W/C and injection pressure, there is a maximum filling rate for a certain fracture that cannot be exceeded. An increase in the relative standard deviation (RSD) of fracture aperture may promote preferential paths' formation to facilitate better penetration by the grout; although, excessive RSD may enlarge areas where it is difficult for grout to penetrate effectively. Additionally, the fracture shear direction significantly affects the propagation direction of cement grout, with preferential propagation occurring perpendicular to the fracture shear direction. Finally, the comparison between the rough-walled fracture model and smooth parallel-plate fracture models from previous research indicates that the smooth parallel-plate models might overestimate the grout filling rate by about 30 %, while significantly underestimating the grout flow. These results provide valuable insights for more accurate predictions of grouted penetration ranges and for optimizing rock grouting methods such as real-time grout control (RTGC).