# Experimental and Theoretical Study of the Influence of Saline Soils on Frozen Wall Formation
## 2 Experimental Study on the Effect of Salinity on Soil Thermophysical Properties
### Results and Processing of Experimental Measurements
This fact is clear from the point of view that there is more bound water in clays than in sands and chalk [6; 31]. In chalk and sand, a more pronounced reduction in the amount of unfrozen water can be observed with decreasing salt concentration. In a broader sense, it can be noted that freezing water in clay is considerably more challenging than in chalk and sand at any given salt concentration. 2. The impact of salt concentration on the thermal conductivity of all soils under consideration follows the same pattern--an increase in salt concentration leads to a decrease in thermal conductivity. Additionally, clay experiences a smoother decline in thermal conductivity as salt concentration rises, compared to chalk and sand. However, considering chalk, this observation holds true mainly for values close to zero, as the disparity in thermal conductivity between salt concentrations of 3.46 g/100 g and 6.9 g/100 g is noticeably smaller than the difference in thermal conductivity between salt concentrations of 0.01 g/100 g and 3.46 g/100 g.
3. The heat capacity of all soils increases with higher salt concentrations. Similar to the case of thermal conductivity, clay displays a more gradual change in heat capacity in response to changes in salt concentration compared to chalk and sand. Figure 7 shows the temperature dependencies of the unfrozen water content, the coefficient of thermal conductivity (dashed lines), and the effective heat transfer coefficient (solid lines) for different types of soils at a salinity of 6.9 g/100 g. The difference between the curves makes it possible to understand the soils in which it is easier to freeze water and in which the temperature field changes faster. The effective heat transfer coefficient refers to the ratio of thermal conductivity to the derivative of the specific enthalpy of temperature:  
\[a_{eff}=\lambda\left(\frac{\partial H}{\partial T}\right)^{-1}, \tag{12}\]  
where \(a_{eff}\) is the effective heat transfer coefficient (m\({}^{2}\)/c) and \(H\) is the specific heat of the soil (J/m\({}^{3}\)). The specific enthalpy consists of the perceived heat and the latent heat of the phase transition [32]:  
\[H=\int\limits_{T_{ref}}^{T}\rho c_{p}dT+\rho\frac{w_{0}}{1+w_{0}}L\gamma, \tag{13}\]  
where \(T_{ref}\) is the reference temperature (\({}^{\circ}\)C) and \(L\) is the specific heat of the phase transition of water (J/kg). In accordance with [27], the dependence of the specific heat of the phase transition of water can be defined as follows:  
\[L=L_{0}+L^{\prime}{}_{0}[T-(T_{norm}-273.15)], \tag{14}\]  
\[L_{0}=333427\Big{(}1-0.42c-15.47c^{4.145}+0.529c^{1.477}\Big{)}, \tag{15}\]  
\[L^{\prime}_{0}=2458.25\Big{(}1-0.4524c^{0.79}+145.824c^{3.56}+614412c^{10.17} \Big{)}, \tag{16}\]  
Figure 3:0where \(c\) is the concentration of NaCl solution in the porewater, which is associated with salinity by the following ratio:  
Figure 3:1  
where \(s\) is the salinity (g/100 g) and \(\rho_{NaCl}\) is the NaCl density (kg/m\({}^{3}\)). The NaCl density is multiplied by 100 to match the salinity unit. The analysis of the thermodynamic processes using the parameter of effective thermal conductivity allows us to consider the heat jump during the transition through the phase transition. Thus, it is possible to determine the zone where the temperature change due to the heat of the phase transition prevails or is comparable to the conductive heat transfer. Figure 7 shows that the temperature dependencies of the unfrozen water content for chalk and sand are almost the same. In clay, the curve is higher, and therefore, it is more difficult to freeze the porewater in it. It is noteworthy that the dependencies of the effective heat transfer coefficient on the temperatures for clay and chalk are almost the same, and for sand, the curve is higher. With a decrease in temperature, the difference between the dependencies increases, and at a temperature of \(-30\)\({}^{\circ}\)C, the effective heat transfer of sand is three times higher than that of clay or chalk.