# Experimental Study on Grouting Visualization of Cover Layer Based on Transparent Soil
## 5 Discussions  
Compared with traditional grouting test methods ([PERSON] et al., 2023) ([PERSON] et al., 2023), where the diffusion distance and morphology of the grout can only be assessed after the process is complete and the grout has solidified ([PERSON] et al., 2020) ([PERSON] et al., 2020), dynamically display the diffusion shape and the movement of the grout front in real time. Therefore, transparent soil grouting tests offer significant advantages for investigating grout diffusion mechanisms in cover layers. Although the preliminary test results are obtained through the transparent soil grouting test, there are still some problems in the research:  
Transparent soil experiments are typically conducted at a reduced scale ([PERSON] et al.,2023) ([PERSON] et al., 2023). Boundary and scale effects have consistently posed challenges in transparent soil testing. It is difficult to fully satisfy the third law of similarity in all aspects of the test, inevitably resulting in similarity errors ([PERSON] et al., 2023) ([PERSON] et al., 2023). Nevertheless, conducting experiments under conditions that satisfy the primary similarity criteria can still achieve the intended research objectives. In this study, the model box was designed with dimensions five times the slurry diffusion distance observed in pre-experiments, aiming to minimize boundary effects. Unlike [PERSON] et al. (2014) (2014) who used a small cylindrical plexiglass model container with a size of 180 mm \(\times\) 180 mm and a height of 265 mm, this paper introduced a large model box with a size of 700 mm \(\times\) 700 mm \(\times\) 40 mm to more accurately capture the spatial diffusion characteristics of slurry in the overburden. In contrast, [PERSON] et al. (2024) (2024) ignored the influence of model boundary on slurry morphology in their simulation, and their model box design did not consider the sensitivity of mixed oil transparency to temperature changes, which may lead to a decrease in visibility of transparent soil. In addition, [PERSON] (2024) did not consider the water precipitation effect of cement slurry in the grouting test. Due to the water analysis caused by the particle settlement of slurry in the setting process, the additional water will reduce the visibility of transparent soil, thus affecting the accurate judgment of the slurry expansion process in the model box. On the other hand, most previous studies (such as [PERSON] et al., 2023 ([PERSON] et al., 2023)) used uniform particle-size particles to simulate the overburden, ignoring the effect of particle gradation in natural soil on grouting behavior, which may lead to misjudgment of slurry diffusion in actual projects. In this paper, through the configuration of transparent soil and the introduction of the actual particle size distribution, to explore and simulate the flow  
Figure 7: Transparent soil velocity fields at different times (mm/s). law of slurry in the complex pore channel closer to the actual working condition. Thus, the experimental results are closer to the field conditions, and the engineering applicability of the study is improved. Although [PERSON] et al. (2024) (2024) used a similar visualization method in the study of transparent soil grouting, the flow medium they used was tracer materials such as water flow or dye flow, which failed to reflect the real flow characteristics of the slurry. In order to more accurately simulate the diffusion behavior of Bingham fluid in the overburden, a slurry with a low water separation rate and high stability is selected in this paper. Compared with ordinary cement slurry or dyeing water flow, the grouting material selected in this paper has more obvious advantages in visual effect and authenticity of flow behavior. Although [PERSON] et al. (2016) (2016) used similar PIV technology in the study of the grouting diffusion model, the grouting pressure range in their test was small (60 kpa), and the effect of hole wall constraint on diffusion morphology was not considered.