## 2 Experimental Soil Sample and Research Plan
### Experimental Methods  
(1) Indoor CBR Test Method. According to the relevant provisions of the \"Test Methods of Soils for Highway Engineering\" (JTG 3430-2020), the sample is prepared by the compaction molding method. The mass of the required specimen was calculated according to the compaction degree and water content. Among them, the compaction degree is calculated as \"the ratio of the dry density of the sample to the standard maximum dry density\". From this, the total sample mass can be determined from the compaction, sample volume, and maximum dry density. When the soil's moisture content exceeds the liquid limit, it becomes impossible to prepare high-ice-content permafrost samples by simply adding water. To address this, an ice crusher is used to crush ice to pass through a 2 mm \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Physical Indicators**} & \multicolumn{3}{c}{**Particle Size Mass Percentage/\%**} & **Plastic Limit/\%** & **Digital Moisture Content \(\omega_{0}\)/\%** & **Maximum Dry Density** \\ \cline{2-7}  & **\textless{}0.075 mm** & **0.075–0.25 mm** & **0.25–0.5 mm** & **0.5–2 mm** & **Limit/\%** & **Content \(\omega_{0}\)/\%** & \(\rho_{\rm dmas}\)/(g\(\cdot\)cm\({}^{-3}\)) \\ \hline Test Values & 16.75 & 61.54 & 12.47 & 9.24 & 13.3 & 21.9 & 14.1 & 1.61 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Basic physical indicators of test soil. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Test Number**} & **Temperature \(T\)/\({}^{\circ}\)C** & **Moisture Content \(\omega\)/\%** & **Compaction Degree K/\%** \\ \hline a & Room Temperature (\(\omega\)20\%), \(-0.6\), \(-1.2\), \(-2.1\), \(-3.1\), \(-4.5\), \(-5.3\) & 40 & 80, 85, 90 \\ b & \(-2.1\) & 10, 20, 30, 40, 60, 80, 100 & 80, 85, 90 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental scheme. sieve to produce ice sand, which is then mixed with ice water. The total mass of the sample (\(m\)), dry soil mass (\(m_{\rm s}\)), added water mass (\(m_{\omega}\)), and added ice sand mass (\(m_{\rm i}\)) are calculated according to Equations (1)-(4). During sample preparation, the mixture is poured into the mold in three layers, each compacted as per the prescribed number of impacts. After compacting the first layer, the surface of the specimen is \"roughened\" before adding more mixture and repeating the steps in layers. In highway engineering, CBR specimens are typically soaked for 4 days; however, for this experiment, considering the permafrost conditions, the formed specimens are immediately wrapped in cling film and placed in a low-temperature environmental chamber for temperature control, using sensors to monitor the internal temperature. After stabilizing the temperature for 1 day, a penetration test is conducted, measuring the unit pressure (\(p\)) and penetration depth (\(h\)). The bearing ratios at penetration depths of 2.5 mm and 5 mm are calculated using Equations (5) and (6), with the higher value taken as the CBR value. The CBR penetration test setup is shown in Figure 1.  
\[m=\rho_{\rm{dmax}}\cdot K\cdot(1+\omega)\cdot(V-\frac{m}{1+\omega}\cdot\omega_{ \rm i}\cdot n) \tag{1}\]  
\[m_{\rm s}=\frac{m}{1+\omega} \tag{2}\]  
\[m_{\omega}=m_{\rm s}\cdot\omega_{\omega} \tag{3}\]  
\[m_{\rm i}=m_{\rm s}\cdot\omega_{\rm i} \tag{4}\]  
\[CBR_{2.5}=\frac{p\cdot 100}{7000} \tag{5}\]  
\[CBR_{5}=\frac{p\cdot 100}{10500} \tag{6}\]  
where: \(m\) is the total mass of the sample \(\rm{e}\); \(\rho_{\rm{dmax}}\) denotes the maximum dry density; \(K\) is the degree of compaction; \(\omega=\omega_{\omega}+\omega_{\rm i}\) is the total moisture content, where \(\omega_{\omega}=m_{\omega}/m_{\rm s}\) is the moisture content by addition and \(\omega_{\rm i}=m_{\rm i}/m_{\rm s}\) is the ice sand content by addition; \(V\) is the volume of the specimen; \(n\) is the volume ratio of the same mass of water and ice sand, experimentally found to be 0.81; \(m_{\rm s}\) is the dry soil mass, \(m_{\omega}\) is the water mass added, and \(m_{\rm i}\) is the ice sand mass added.