# Experimental and Theoretical Study of the Influence of Saline Soils on Frozen Wall Formation
## 1 Introduction  
The construction of mineshafts and subway tunnels under the condition of flooded soils is implemented using special methods. One of the most common of those methods is artificial ground freezing (AGF) [1, 2]. The purpose of AGF is to build a protective structure, consisting of frozen soils, around the future mineshaft. This structure is most commonly referred to as a \"frozen wall\" (FW) [3]. The functions of an FW are to prevent the flooding of the shaft with groundwater and to strengthen the loose walls of the shaft before the construction of a permanent concrete lining [3]. The freezing of the soil is implemented with the help of freeze pipes mounted along the perimeter of the designed mineshaft (see Figure 1a). The study and control of the formation of frozen walls are implemented using experimental and theoretical methods. Experimental methods involve monitoring the temperature distribution over the depth of several control boreholes drilled near the contour of the freeze pipes (see Figure 1b) [4]. The measured temperature distributions are used to adjust the parameters of the mathematical models of heat and mass transfer in the frozen media [5]. Further, the adjusted mathematical models are used to estimate the temperature distribution in the entire volume of the frozen soil to determine the actual thickness and continuity of the FW, with those being the main technical parameters of an FW. However, the mentioned methods for monitoring and predicting the state of an FW often do not consider the factor of soil salinity, which often occurs during the construction of mineshafts in potash salt deposits. The salinity of the soil leads to a change in its thermophysical and mechanical properties. In addition, an increase in the amount of dissolved salts in the porewater leads to a decrease in its freezing temperature [6,7], which can negatively affect the waterproofing and strength properties of an FW. There are many studies devoted to the effect of salinity on the freezing of porewater. [PERSON] [6] presents extensive theoretical and experimental information about the general patterns of freezing of saline soils, as well as practical aspects of taking into account salinity in the construction of surface structures. [PERSON] and [PERSON] [8] and [PERSON] et al. [9] obtained experimental dependences of the thermophysical properties of several frozen soils on the concentration of salts in them. [PERSON] et al. [10] focused on the mathematical modeling of heat and mass transfer in frozen saline soils and the comparison of the obtained results with the experimental base. In it, [PERSON] et al. obtained equations for simultaneous heat and mass flows at one of the interfaces for a wide range of temperatures and concentrations. [PERSON] et al. [11] investigated the electrical properties of frozen salted clay. [PERSON] and [PERSON] [12] evaluated the effects of soil salinity and organic matter content on the thermal properties of frozen and thawed soils. [PERSON] et al. [13] proposed a thermal conductivity model of saline soil considering the heat dissipation due to heat radiation. [PERSON] et al. [14] proposed a coupled hydro-thermal-salt-mechanical model with phase change to simulate the one-side freezing process of saturated sulfate saline soil. However, most studies are related to the natural freezing of the soil in permafrost regions, and they cannot be fully applied to the conditions involved with the artificial freezing of soils, because of the features of artificial freezing: higher temperature differences, faster changes in the amount of unfrozen groundwater over time, and higher values of rock and hydrostatic pressures due to greater depths. The effects of salinity on the artificial freezing of soils are described in [7,15-17]. [PERSON] et al. [15] investigated the change in the freezing point with the increase in concentration of NaCl in the pore brine. A new theoretical equation was developed that relates thermal conductivity to water content and temperature.