Grouting is a widely used method to seal and/or reduce permeability of fractured rock masses around underground structures. However, the filtration and penetration mechanism of cement-based grout have not been clarified sufficiently yet due to complicated physical and chemical processes of grouting. Therefore, the grout material and injection parameters such as injection pressure and water/cement ratio (W/C) are usually determined empirically by technical experts at the injection site. In this paper, for better understanding of the penetration and filtration mechanism of cement-based grout through rock fractures, the two-dimensional numerical model of coupled Computational Fluid Dynamics and the Distinct Element Method (CFD-DEM) was developed and the effect of rock fracture roughness on the filtration and penetration mechanism was numerically investigated. The simulation results clearly shows that the effect of surface roughness of rock fracture on the movement of cement particles and the amount of injected cement particles is significant.
Grouting is a widely used technique to seal and/or reduce permeability of fractured rock masses around underground structures. Recently, the efficient and effective grouting has been required from environmental and economical points of view. So far, different injection techniques and new grout materials have been developed to inject more grouting material (cement) in shorter time (efficient and effective grouting). For example, grout with high water/cement ratio (W/C) is injected under low injection pressure (HTLP method) (Mutoh 1999) and/or injection pressure is changed dynamically (so-called dynamic injection) (Aoki et al. 2006). In addition, superfine spherical silica and silica sol are commonly used to inject into narrow fractures and/or low-permeability layer.
However, the filtration and penetration mechanism of cement-based grout have not been clarified sufficiently yet due to complicated physical and chemical processes of grouting such as pressure-dehydration, consolidation, bleeding, clogging, absorption, sedimentation, condensation and etc. Hence, the selection of grout material and injection parameters such as injection pressure and W/C is usually determined empirically by technical experts at the injection site.
In this paper, for better understanding of the penetration and filtration mechanism of cement-based grout through rock fractures, the two-dimensional numerical model of coupled Computational Fluid Dynamics and the Distinct Element Method (CFDDEM) was developed. The fluid flow governed by Navier-Stokes (N-S) equation and particle movement were solved by finite difference method and DEM, respectively. The interaction between fluid and particles was evaluated using immersed boundary (IB) method. In the simulations, to investigate the effect of surface roughness of single rock fracture which commonly characterized by JRC (Joint Roughness Coefficient) on the injection mechanism and the amount of injected cement particles into rock fracture, the simulation model was created based on the measurement data of actual rock fracture by 3-D laser scanner.
