# 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
### Methods of Measurement  
All experiments were implemented in the Laboratory of Physicochemical Mechanics of Natural Dispersed Systems of the Institute of Nature Management of the National Academy of Sciences of Belarus. The unfrozen water content, the freezing temperature of the porewater, the specific heat capacity, and the thermal conductivity of the soil were the studied thermophysical parameters during the freezing process. A calorimeter was used to determine the unfrozen water content, the freezing temperature of the porewater, and the specific heat capacity. The principle underlying these measurements is the creation of adiabatic conditions, or conditions of controlled heat exchange, around a calorimetric cup filled with the sample under study. This allows for the determination of the thermophysical parameters under study (water content and specific heat capacity) at positive and negative temperatures, as well as the investigation of the changes in unfrozen water content during freezing and thawing cycles. The accuracy of the device is \(\pm 0.01\)\({}^{\circ}\)C when measuring temperature, and the relative error in determining the heat of the phase transition is \(\pm 1\%\). Experimentally measured masses of water and ice in the sample were used to calculate the unfrozen water content according to the following equation:  
\[w=\frac{G_{w}-G_{i}}{G_{\rm S}}, \tag{1}\]where \(w\) is the unfrozen water content, \(G_{w}\) is the mass of water in the sample (kg), \(G_{i}\) is the mass of ice in the sample (kg), and \(G_{S}\) is the mass of the dry skeleton of the soil (kg). The specific heat capacity was calculated for the dry skeleton of the soil using the following equation:  
\[c_{s}=(1+w_{0})c_{meas}-wc_{w}-(w_{0}-w)c_{i}-L\frac{dw}{dT}, \tag{2}\]  
\[c_{meas}=\frac{\Delta Q_{meas}-C_{cal}\Delta T}{G_{\Sigma}\Delta T}, \tag{3}\]  
where \(c_{s}\) is the specific heat capacity of the dry skeleton (J/(kg.\({}^{\circ}\)C)); \(c_{meas}\) is the measured effective specific heat capacity of the soil sample (taking into account the phase transition of the moisture) (J/(kg.\({}^{\circ}\)C)); \(c_{w}\) and \(c_{i}\) are the specific heat capacities of water and ice (J/(kg.\({}^{\circ}\)C)), respectively; \(C_{cal}\) is the heat capacity of an empty calorimeter (J/\({}^{\circ}\)C); \(w_{0}\) is the initial soil moisture (kg/kg); \(L\) is the specific heat of the phase transition of the moisture (J/kg); \(\Delta Q_{meas}\) is the amount of heat required to supply the calorimeter so that its temperature changes by \(\Delta T\) (J); and \(G_{\sum}\) is the total mass of wet material (skeleton + water + ice) (kg). The thermal conductivity of the soils was determined using a unique device based on the method of the stationary thermal state of the soil samples. The device features the use of original heat flow sensors mounted in metal heat-exchanger housings. This makes it possible to average the temperature field in the measurement planes and to protect the heat flow and temperature sensors from mechanical, physical, and chemical damage. The relative error in determining the thermal conductivity is 6%. The calculation of the thermal conductivity coefficient was conducted in the stationary thermal state of the test sample according to the readings of the signals of the heat flow sensors with two heat exchangers. The first one is located on top of the sample, while the second one is located below it.