Today, grouting is used as an aid in ground improvement in most civil and mining projects. Groutability and grout penetration depth are subjects that are considered in grouting operation. As discontinuities compose the main paths for fluid flow in jointed rock mass, geometric characteristics, such as joint aperture, spacing and orientation, affect the grout flow. On the other hand, fluid flow in joint is a hydromechanical process and the state of applied stress on joint affects the fluid flow. Knowledge of these parameters has advantages in prediction of grouting results (grout penetration and intake). Unlike water (Newtonian fluid), stable cement-based grout usually acts as a Bingham fluid. In this study the effect of important joint geometric characteristics on grout intake and penetration depth was simulated hydromechanically using the UDEC code. The gained results show that grout intake and penetration depth increase as joint aperture and normal stiffness increase and in-situ stress decreases. Increase in joint spacing does not have any effect on penetration depth but decreases the grout intake. The effect of joint orientation on grouting process is strongly dependent on in-situ stress state.
Presence of fractures in rock mass decreases the rock mass strength and stiffness and increases its permeability. Grouting is one of the commonly adopted methods that are used to improve the rock mass quality. Groutability and grout penetration depth are two main factors for design of grouting operations. Several parameters affect the groutability and grout penetration depth. Knowledge of these parameters is technically and economically useful for optimum design of grouting. Since, the permeability of intact rock, as compared to joints, is very low, the discontinuities are main paths for grout flow in jointed rock mass. Accordingly, the joint characteristics including aperture, spacing and orientation influence the grout flow and grout intake and penetration depth. Moreover, various fluids have different flow behaviour (i.e. rheology). Unlike water, which behaves as a Newtonian fluid, cement-based grout is a non-Newtonian fluid. Bingham fluid model is the most appropriate model for cement based grouts. Based on Bingham fluid model, the effect of joint geometric characteristics was investigated analytically and numerically by many researchers, [1, 2, 3, 4, 5]. In most of these studies, grout flow was modeled only hydraulically, while fluid flow in joints is a hydromechanical process and the state of applied stress on joint also affects the fluid flow. In this study the effect of important joint geometric characteristics on grouting process was simulated hydromechanically.
Rheological models are used to characterize the fluid flow and deformation. These models describe the relation between shear stress and strain rate of fluid. Fluids are either Newtonian or non-Newtonian, rheologically. In Newtonian fluids, relation between shear stress and shear strain rate is linear (Fig1).