Abstract
The salinity of the pore solution is closely associated with the unfrozen water content and can be reflected by variation in electrical conductivity in frozen soils. However, the influence of salinity was not considered in the existing models for estimation of unfrozen water content based on electrical conductivity measurement, and a model considering the effect of salt content was therefore developed to estimate the change of unfrozen water content of saline sands with variation of salt content (0%, 0.2%, and 1%). The unfrozen water content and the electrical resistivity were measured by nuclear magnetic resonance (NRM) and using resistance test equipment under a temperature ranging from 25°C to −15°C, respectively. The results indicated that the model using a cementation exponent expressed by a piecewise function with respect to temperature can produce a reasonable estimation on the content of unfrozen water. There was an essential difference between nonsaline and saline frozen sands in the increase of electrical resistivity due to the different reduction rates of unfrozen water content. The variation of electrical resistivity in nonsaline sand was mainly caused by the decrease of free water when temperature was higher than the freezing point and adsorbed water when temperature was lower than the freezing point, whereas the reduction of free water in two stages was the main reason for the variation of electrical resistivity in saline sand. The results and data obtained provided a basis for further developing a novel approach to measure the unfrozen water content in the field.
Highlights
Academic Editor: Gang Zhou e salinity of the pore solution is closely associated with the unfrozen water content and can be reflected by variation in electrical conductivity in frozen soils
According to the descriptions by Konrad and Mccammon [29], the initial freezing temperatures of soil should be −0.5°C and −2.601°C corresponding to a salt content of 0.2% and 1%, respectively, which were consistent with temperatures occurring at inflection points. e soil electrical resistivity increased slightly with the decrease in the temperature under an unfrozen state
A model considering the effects of salt, temperature, and water content on soil resistivity was established to estimate the variation of unfrozen water and the pore concentration in the cooling process. e electrical resistivity and the unfrozen water content of the sand with different salinities were tested
Summary
Received 26 September 2020; Revised 13 January 2021; Accepted 19 January 2021; Published 4 February 2021. E salinity of the pore solution is closely associated with the unfrozen water content and can be reflected by variation in electrical conductivity in frozen soils. Where σT,sp,c0 and σT,w,c0 are the electrical conductivities of frozen soils and the pore solution with salt concentration c0 at the temperature T, respectively and θT is the volumetric water content at temperature equal to T. 3. Theoretical Model considering Salinity e electrical conductivity is primarily affected by temperature, water content, and pore solution concentration. Considering equations (4) and (7), the variation of soil electrical conductivity due to pore solution concentration and temperature can be obtained: σT,ss,c1 σT,ss,c1 σTr,ss,c0 σTr,ss,c1. The variation of soil electrical conductivity was influenced by temperature, unfrozen water content, and pore solution concentration. E unfrozen water content of frozen soils was measured by NMR, as shown in Figure 2. e test apparatus was divided into four parts, an industrial computer for data storage, processing, and sets of boundary temperatures ranging from −20°C to +30°C with an accuracy of ±0.01°C, a magnet unit that provided a uniform and stable main
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