# A State-of-the-Art Review on the Study of the Diffusion Mechanism of Fissure Grouting
## 2 Current Status of Research on Grouting Materials
### Current Status of Research on the Percolation Effect on Slurry Diffusion in Fissured Media  
Due to the assumption of too many conditions in theoretical formulae and the large error in the real working conditions, with the gradual development of slurry diffusion theory, the influence of slurry gravity, the flow pattern of slurry, the time-varying viscosity of slurry, the percolation effect of slurry particles, and the zig-zag effect of slurry diffusion paths on the theory of infiltration grouting are constantly revised, thus making the theory of infiltration grouting more and more accurate. [PERSON] et al. [60] independently developed a visualized test system for micro-fissure grouting, and it was found that during the grouting process of micro-fissured rock, the percolation effect of the cement slurry has a significant influence on the grouting effect. [PERSON] et al. [61] used a central combination test (CCD) to investigate the effect of grouting pressure and soil mass fractal dimensions on the diffusion of cement slurry, considering the percolation effect. They discovered that as the grouting pressure increased, the viscosity as well as the effective diffusion radius of the leachate increased and then decreased. In addition, they found that the larger the soil's fractal dimension, the smaller the effective diffusion range of the slurry. [PERSON] et al. [62] established the consolidation and diffusion mechanisms of compressible intelligent synchronous grouting material based on the percolation effect according to the composition characteristics of lightweight intelligent synchronous grouting material. The results show that the percolation effect has a significant effect on the consolidation and diffusion of grouting materials. [PERSON] et al. [63] established a differential control equation for slurry filtration diffusion based on the laws of mass conservation, solute transport, and mass transfer principles. They provided analytical solutions for constant pressure and constant flow rate grouting filtration diffusion and revealed the influence mechanisms underlying the filtration effect on the pore structure of the porous medium, the viscosity of the slurry, and the distribution of diffusion pressure. [PERSON] et al. [64] studied the influence of the percolation effect on the porosity, permeability, and slurry flow rate of an injected medium using the Kozeny-Carman model. [PERSON] et al. [65] established a theoretical model for the three-dimensional front infiltration diffusion of cement slurry based on the law of mass conservation, the linear filtration law, and the permeability continuity equation. They found that the viscosity of the slurry had a significant impact on the filtration effect and the effective diffusion distance of the slurry. Specifically, their study revealed that the filtration effect became more pronounced with increasing slurry viscosity, leading to a shorter effective diffusion distance for the slurry. This suggests that controlling the viscosity of the slurry is an important factor in optimizing the grouting process and achieving the desired grouting effect. [PERSON] et al. [66] constructed a cement slurry diffusion model in spherical pores based on the law of mass conservation and the linear filtration law. Their investigation revealed that the filtration effect induces a gradual increase in the permeability resistance of the grouting medium, leading to a progressive rise in grouting pressure over time. [PERSON] et al. [67] utilized the flow-solid coupling mechanism and PFC2D particle flow numerical simulation technology to conduct a numerical simulation study on the transport of slurry particles in porous media and the coupling of slurry and a porous skeleton during the grouting process. Their study used the FISHTANK function library and FISH programming language embedded in PFC2D 6.0 software to carry out the numerical simulation calculations.