## 2 Soil Physical Property Parameters
### Experimental Results
#### 2.4.2 Results of Direct Shear Tests of Soil with Different Moisture Content and Firmness  
A single-factor test of direct shear was conducted on soil with different water content and firmness. When soil firmness was used as the variable, the water content was controlled at a level of 6% and soil firmness was divided into five levels at equal intervals from 0.34 to 2.76 MPa; when soil water content was used as the variable, soil hardness was controlled at 1.55 MPa and soil water content was divided into four levels from 3 to 12%. The direct shear speed was set to 0.013 mm/s (0.8 mm/min) [26], the maximum distance of direct shear was 5 mm, and it took 6-7 min to directly shear a group. The force loop value was read once every 0.8 mm of direct shear, and after the direct shear the peak value was taken for calculation and fitting to obtain the values of cohesion and internal friction angle, and the results are shown in Table 2.  
4.3 Results of Lateral Limitless Compressive Test of Soil with Different Moisture Content and Firmness  
Similar to the direct shear test, a single-factor test of unconfined lateral limit resistance was conducted at the same factor level. The compression speed of the universal testing machine was set to 0.1 mm/s, and the sensor pressure data were recorded at a frequency of 5 Hz to calculate the unconfined compressive strength. The test results are shown in  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Water Content**} & \multirow{2}{*}{**Static Friction Coefficient (\(\mu_{1}\))**} & \multirow{2}{*}{**Rolling Friction Coefficient (\(\mu_{2}\))**} & \multirow{2}{*}{**Resting Angle(\({}^{\circ}\))**} \\ \cline{2-2} \cline{5-6}  & & **Min** & **Max** & **Min** & **Max** \\ \hline
3\% & 0.6400 & 0.7813 & 0.1663 & 0.2543 & 32.76 \\
6\% & 0.7265 & 0.8098 & 0.1877 & 0.2095 & 35.53 \\
9\% & 0.7813 & 0.8391 & 0.2543 & 0.3249 & 37.89 \\
12\% & 0.9014 & 0.9325 & 0.3265 & 0.3839 & 43.87 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Friction coefficient and rest angle of soil with different water content.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Water Content (\%)**} & \multirow{2}{*}{**Solidity (MPa)**} & \multirow{2}{*}{**Cross-Sectional Area (mm\({}^{2}\))**} & \multirow{2}{*}{**Direct Shear (mm)**} & \multirow{2}{*}{**Cohesion C (\(\alpha\) = 0)**} & \multirow{2}{*}{**Internal Friction (MPa)**} & \multirow{2}{*}{**Tangential Stiffness per Unit Area N**} \\  & & & & (MPa) & & **Angle \(\varphi\) (\({}^{\circ}\))** & **(m-m\({}^{2}\))** \\ \hline
6 & 0.34 & & & 0.0165 & 32.5 & \(3.3000\times 10^{6}\) \\  & 0.945 & & & 0.0282 & 38.4 & \(5.6480\times 10^{6}\) \\
6 & 1.55 & & & 0.0587 & 32.3 & \(1.1734\times 10^{7}\) \\  & 2.155 & & & 0.0563 & 40.3 & \(1.1262\times 10^{7}\) \\  & 2.76 & & & 0.0626 & 37.3 & \(1.2514\times 10^{7}\) \\ \hline
3 & & & & 0.0866 & 21.5 & \(1.7314\times 10^{7}\) \\
9 & 1.55 & & & 0.0575 & 35.4 & \(1.1490\times 10^{7}\) \\
12 & & & & 0.0818 & 19.2 & \(1.6360\times 10^{7}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of direct shear tests on soil with different moisture content and firmness.  
Table 3, indicating that soil samples with different moisture content and firmness had different physical properties of compressive resistance. With increased soil solidity and water content, the unconfined compressive strength tended to increase.