## 2 Experimental Design
### Experimental Equipment  
The grouting model test system, as shown in Figure 2a, mainly consists of four major components, namely the grouting equipment, test bucket, measurement system, and data image processing system. The grouting equipment mainly includes the grout pump, grout delivery pipelines, and grouting nozzle, as shown specifically in Figure 2b. The test bucket is made of organic glass and has a diameter of 350 mm (for ordinary sand) and 200 mm (for transparent sand), with a wall thickness of 10 mm and a height of 500 mm. The measurement devices include soil pressure gauges, pore water pressure gauges, displacement sensors, charge coupled device (CCD) cameras, and slab laser emitters. The data processing system includes digital image processing software and data analysis software. The arrangement of surface displacement meters is shown in Figure 2c, with four surface displacement meters positioned at different horizontal distances from \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \begin{tabular}{c} **Specific Surface** \\ **Area (m\({}^{2}\)/kg)** \\ \end{tabular} & \begin{tabular}{c} **3 d** \\ **Flexural** \\ **Strength (MPa)** \\ \end{tabular} & \begin{tabular}{c} **3 d** \\ **Compressive** \\ **Strength (MPa)** \\ \end{tabular} & \begin{tabular}{c} **28 d** \\ **Compressive** \\ **Strength (MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Initial Setting** \\ **Time (min)** \\ \end{tabular} &
\begin{tabular}{c} **Final Setting** \\ **Time (min)** \\ \end{tabular} \\ \hline P\(\cdot\)O 42.5 & 356 & 5.4 & 27.8 & 49.6 & 176 & 232 \\ Standard & \(\geq\)300 & \(\geq\)3.5 & \(\geq\)17.0 & \(\geq\)42.5 & \(\geq\)45 & \(\leq\)600 \\ \hline \hline \end{tabular} Note: the standard is the Chinese standard.  
\end{table} 
Table 1: Performance parameters of P\(\cdot\)O 42.5.  
the center of the grouting hole to measure the corresponding surface displacement. As shown in Figure 2d, laser speckle images of transparent particles are obtained using the CCD camera. For the purpose of elucidating the overall deformation characteristics of the overlying transparent sand during the grouting process, the following definitions are made: the analysis plane is taken as the laser section, with the bottom of the transparent sand serving as the X-axis, the grouting center as the origin, and positive towards the right (\(-0.1\) to \(0.1\), unit: m); and the Y-axis is represented by the height of the transparent sand, with the positive direction upwards (0 to 0.3, unit: m). Displacement vector maps are obtained through image processing, where displacement upwards is defined as positive. The direction of the vector arrow represents the direction of sand particle movement, and the arrow size represents the movement speed. Additionally, deformation cloud maps for each component of the displacement vector can be obtained. The specific parameters of the grouting experiments are shown in Table 2. During the grouting process, if the soil sample exhibits overall uplift failure, the grouting is immediately stopped by closing the grouting valve. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{4}{c}{**Grouting Parameters**} & \multicolumn{4}{c}{**Sand Sample Parameters**} \\ \cline{2-9}  & **Grouting Pressure (MPa)** & **Grouting Volume (L)** & **Water-** & **Moisture Content Ratio** & **Void Ratio** & **Permeability Coefficient (10\({}^{-4}\) cm/s)** & **Internal Friction Angle (1\({}^{-4}\) cm/s)** & **Internal Friction Angle (\({}^{\circ}\))** \\ \hline Value & 0–0.5 & 2.66–3.12 & 0.8/1.0/1.2 & Saturation & 0.73–0.75 & 2.01–2.05 & 33.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Grouting test parameters. Figure 1: Transparent sand grouting testing system. ((a) a schematic diagram of transparent soil grouting visualization; (b) a test platform for realizing the 3D visualization of transparent soil). Figure 2: _Cont._  
Figure 2: The system of grouting model test.