CFD Simulation to Study the Grouting Behavior in Rough-Walled Fractures

In rock engineering projects such as dam and tunnel, rock grouting is performed to increase strength and reduce leakage of the rock mass. In rock grouting, grout materials, typically cement slurry, is injected in rock mass. For jointed rock mass, the cement slurry is considered to flow through the rock fractures as fractures are significantly more permeable than the rock matrix. Although several numerical and experimental works have been conducted to understand the filling and penetration behavior of grouting into rock fractures, the fracture is oftentimes assumed to be a parallel slit, while the aperture of actual fracture is not constant, and exhibits roughness. In this paper, the influences of fracture roughness on the penetration and filling behavior of the cement slurry are investigated through numerical simulation. This is achieved by simulating the grout flow in an idealized sinusoidal fracture with computational fluid dynamics approach. The combined effect of pressure, water-cement ratio, and roughness of the fracture are examined through parametric studies. Based on the simulation results, the insights regarding the penetration behavior and filling behavior of the cement slurry in rough-walled fractures are obtained. 1. INTRODUCTION In rock engineering projects such as dam and tunnel construction, grouting is performed to increase strength and reduce permeability of the rock mass (Utuski et al. 2013). In grouting, grout materials, typically cement slurry, is injected in rock mass. For jointed rock mass, the cement slurry is considered to flow through the rock fractures as fractures are significantly more permeable than the rock matrix. The measure of the effectiveness of grouting is typically expressed by the penetration length of cement slurry. Therefore, understanding the penetration behavior of the cement slurry is crucial for the grouting design. Gustafson and Stille (1996) estimated the stop distance of cement slurry by solving a force balance equation assuming the cement slurry to be Bingham fluid that is characterized by the shear strength and viscosity. This theory was further developed as a criterion that is applicable in the practical application of grouting design. Although the criterion has been applied extensively in practice, this theory is based on the simplified assumptions that the fracture is a parallel slit, while the aperture of actual fracture is not constant, and exhibits roughness. In terms of the effect of fracture roughness on the fluid flow, previous research has shown that the roughness of fractures has significant effects on the flow behavior of water. However, the influence of roughness on the flow behavior of cement slurry has not been examined in detail.