# Experimental Study on Grouting Visualization of Cover Layer Based on Transparent Soil
## 2 Visualization Grouting Test System  
### Test Materials  
(1) Transparent soil materials  
To better observe the grouting process in the cover layer, this study uses fused quartz sand particles with high transparency and stable properties to simulate the cover layer. Inits semi-transparent state, the material allows visibility up to 250 mm ([PERSON] et al., 2024) [13], meeting the requirements for tracking slurry diffusion and observing formation deformation. In this experiment, fused quartz sand produced by Jiangsu Welfare Fucai Factory, Lianyungan, China was used as the transparent soil matrix. Its main chemical component is silica (SiO\({}_{2}\)), with a refractive index of 1.458. Relevant parameters are provided in Table 1.  
Although the transparent soil (fused silica sand and mineral oil) used in the experiment is different from natural soil in physical and chemical composition, its particle size, particle grading, dense state, and slurry compatibility are controlled in the range close to the actual sand soil layer ([PERSON] et al., 2016) [7]. In the experiment, geometric, dynamic, and material similarity criteria based on similarity theory were used to control key parameters (such as particle size distribution and permeability coefficient) to maintain the similarity of diffusion behavior of the experimental system as much as possible ([PERSON] et al., 2016) [12]. The prototype particle size distribution of the model was derived from the dam foundation cover layer of the Xiabandi Water Conservancy Project in Xinjang Province. This paper selects the sand and soil of the glacial water accumulation layer in this stratum as the ground to be injected. According to the sample preparation requirements outlined in the Standard for Geotechnical Test Methods (GB/T 50123-2019) [14], the maximum particle size of the test soil must be less than one-fifth of the sample's characteristic dimension. The test materials consisted of fused quartz sand particles ranging from 0.1 to 5 mm, categorized into five size intervals: 0.1-0.2 mm, 0.2-0.5 mm, 0.5-1 mm, 1-2 mm, and 2-5 mm. Based on the material gradation characteristics, the original grading was optimized using a combination of the equal-amount replacement method and the elimination method, aiming to minimize the impact of scale reduction on grading properties. The scale reduction process involved two steps: first, the similar grading method was applied to reduce the scale by two-thirds; then, the equal-amount replacement method was used to further reduce the scale to a maximum particle size of 5 mm. Following the screening test and gradation curve fitting, the uniformity coefficient was determined to be 5.38, and the curvature coefficient was 1.13. The grading curves of the test materials before and after scale reduction are shown in Figure 1a,b. Industrial #15 white mineral oil (manufactured by Morunke Company, Shanghai, China) and isomeric dodecane (from Chukyo Company, Nagoya, Japan) were selected as pore fluids and mixed in a volume ratio of 5:1, based on the refractive index calculation method outlined in the literature ([PERSON], 1984) [15]. The resulting mixture is a colorless and transparent liquid at room temperature (25 \({}^{\circ}\)C). The refractive index of the mixture, measured using an Abbe refractometer, is 1.458. After being mixed with fused quartz particles, the mixture exhibits good transparency, as shown in Figure 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Particle Specific** & **Maximum Dry** & **Maximum Void** & **Minimum Dry** & **Minimum** & **Average** & **Average** \\
**Gravity** & **Density** & **Ratio** & **Density** & **Porosity Ratio** & **Density** & **Porosity Ratio** \\ \(d_{\mathbf{s}}\) & \(\rho_{\text{max}}/(g/\text{cm}^{3})\) & \(e\) & \(\rho_{\text{min}}/(g/\text{cm}^{3})\) & \(e\) & \(\rho/(g/\text{cm}^{3})\) & \(e\) \\ \hline
2.30 & 1.72 & 0.84 & 1.50 & 0.53 & 1.61 & 0.685 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Basic physical and mechanical parameters of transparent soil particles.