Dynamic water grouting in fractured coal mass: Experimental and numerical study on granule deposition characteristics and sealing efficiency

It is challenging to control the concealability and roughness of the fracture grouting process in a water-rich environment, which makes it difficult to directly observe the grout diffusion and deposition process as well as evaluate the sealing effect. Consequently, the water-blocking mechanism remains unclear. To address this issue, this paper utilized 3D printing technology to create a transparent rough fracture model based on the random midpoint displacement method and fractal theory. Additionally, an independent water grouting test system was developed to perform dynamic water grouting tests under various working conditions. The computational fluid dynamics and two-phase flow approach (CFD-TFM) is employed for numerical simulation to ascertain the slurry diffusion patterns and deposition effects at various time intervals throughout the grouting operation. Uniaxial compression and direct shear tests were conducted to evaluate the mechanical behavior of the grout-consolidated specimens. The results indicate that the rough fracture produced by the 3D printing process exhibits effective visibility, allowing for the observable trend of grouting flow. The experimental phenomena categorize the distribution pattern of dynamic water grouting into three types: cross-section water plugging pattern, comet type, and elongated streamline type. The slurry flow trend and particle deposition effect described by the CFD-TFM method are consistent with experimental observations, and all three forms—cross-section type, comet type, and slender streamline—are evident. The concrete results indicate that the particle deposition effect follows the order: cross-section type > comet type > slender streamline. Pressure monitoring data reveal a decreasing trend from the moving water inlet to the outlet boundary. As the distance from the grouting hole increases, the drop in sensor pressure values becomes less pronounced, resulting in reduced grouting deposition. These research findings provide a theoretical basis for the design of grouting reinforcement engineering.