Nonlinear flow characteristics of cement grout in fractures with varying geometries

The interplay between the non-Newtonian rheology of cement grout and fracture geometry exerts a critical influence on grout penetration efficiency and reinforcement performance in fractured rock masses. This study conducts a systematic investigation of the nonlinear flow behavior of cement grout in both tensile and shear fractures, utilizing theoretical analysis and numerical simulations across a range of fracture structures, apertures, and roughness levels. To capture the complex flow characteristics accurately, the Bingham-Papanastasiou model is employed as the rheological framework. Results reveal that fracture roughness intensifies flow field heterogeneity, particularly within shear fractures. Due to the influence of yield stress, grout exhibits more pronounced channelization compared to water. At high flow rates, the interaction between yield behavior and inertial forces induces notable nonlinear flow phenomena. In this regime, a modified Forchheimer equation offers superior predictive capability across fracture types. The evolution of grout flow is characterized by a three-stage process sequentially dominated by yield stress, viscous forces, and inertial forces. The critical Reynolds number (Re_c) for both fracture types are identified, and the effects of fracture geometry on nonlinear flow are quantitatively evaluated via the non-Darcy coefficient. These findings contribute valuable theoretical insights into the mechanisms governing grout flow and inform the optimization of grouting design parameters.