# Experimental Study on Grouting Visualization of Cover Layer Based on Transparent Soil
## 5 Discussions
In this paper, systematic tests are carried out under a wider range of pressure gradients (0-200 kpa), and the boundary conditions are more strictly controlled. In addition, most existing studies (such as [PERSON] et al. (2016), 2016; [PERSON] et al. (2024), 2024) focus on the final diffusion form of grouting, but pay less attention to the dynamic evolution in the diffusion process. In contrast, through continuous image acquisition and time-series analysis, this paper reveals the unstable evolution process of the slurry flow front, which provides a more comprehensive time-domain perspective for the understanding of the diffusion mechanism. It is worth noting that under the model box pressure set in this study, the slurry diffuses in a \"T\" shape, and its asymmetric shape can be derived from the self-organization effect of microstructure or the local path difference in random media. When the slurry forms a dominant flow in a certain direction, it often continues to expand along the path, showing a certain randomness in the flow direction. This phenomenon reflects the microstructure difference of the medium, rather than the artificial layout deviation on a large scale. During the experiment, to facilitate the outflow of pore fluids, the top of the model box was designed as a permeable boundary that prevents sand migration, thereby creating a boundary condition different from the fixed sides and bottom. Additionally, due to limitations in the structural strength of the model plates and the sealing performance of the interface bolts, complete sealing could not be achieved, imposing an upper limit on the internal grouting pressure. Due to the material strength of the acrylic model box, the top was not fully closed during the test, but a pressure boundary was set. This causes the slurry to diffuse upward along the weak part under the action of pressure difference, which conforms to its basic diffusion characteristics. In addition, it should be pointed out that the model is more suitable for revealing the evolution trend and mechanism of the diffusion process than for accurately predicting the numerical results at the actual engineering scale. This paper focuses on the preliminary exploration of the diffusion behavior of single-hole grouting under typical working conditions. The test is based on a single condition, and systematic repeated tests have not been carried out to verify the universal repeatability of the diffusion pattern. The current results only represent a representative diffusion form under the test conditions. In the future, a series of repeated tests will be carried out in combination with different grouting pressure conditions, particle grading types, and random initial structures to further verify and expand the scope of application of the diffusion form, and to further explore the diffusion form and mechanism of grout in the overburden. Therefore, the conclusions drawn in this study are primarily intended to reflect the trends and mechanistic characteristics of grouting behavior. For practical engineering applications, these findings still require validation through field experiments and large-scale numerical simulations.