A method for predicting soil salinity during freeze-thaw process

Abstract

The present invention belongs to the field of measurement technology, and specifically relates to a method for predicting soil salt content during a freeze-thaw process. The method comprises the following steps: measuring the dielectric constant, electrical conductivity, and temperature of the soil using a 5TE sensor, thereby calling a corresponding salt-free soil freezing characteristic curve in a database; calculating the dielectric constants of dry soil particles, water, air, ice, and crystallized salt in the soil under different temperature conditions using the relationship between temperature and dielectric constant; calculating the soluble salt content in unfrozen water at different temperatures using electrical conductivity; calculating the maximum saturated solubility of salt in water at different temperatures using a thermodynamic model; calculating the volume content of dry soil particles, water, air, ice, and crystallized salt; judging the presence of crystallized salt based on the relationship between the soluble salt content and the maximum saturated solubility, and predicting the total salt content. The present invention realizes a simple, accurate, and efficient inversion method for the total salt content of saline soil.

Description

Technical Field

[0001] The invention belongs to the field of measurement technology, and particularly relates to a method for predicting soil salt content during a freeze-thaw process. Background Art

[0002] Currently, the main technologies for measuring salinity in saline soil include mass methods, time domain reflectometry (TDR), frequency domain reflectometry (FDR), and remote sensing. Mass methods can be further divided into extract mass methods and extract conductivity methods based on their detection principles. Both methods involve preparing a soil extract (water-to-soil ratio of 5:1). The former measures the salinity by drying it in a water bath and weighing it, while the latter uses a sensor to measure the conductivity of the soil extract. The total salinity of the original soil is then calculated using an empirical relationship between conductivity and salinity. While this method provides the most accurate salt content measurement in saline soil, it is complex, time-sensitive, and incapable of on-site measurement. Currently, in-situ salinity measurement in saline soils, using time domain reflectometry and frequency domain reflectometry techniques, which measure the dielectric constant and conductivity of soil, has gained widespread international recognition. For example, the 5TE sensor offers advantages such as non-destructive soil analysis, short measurement times, and portability. In recent years, many researchers have sought to improve measurement accuracy by fitting measured dielectric constants and conductivity to salinity under various conditions, such as high-salinity environments and high water content, thereby calibrating the sensor model. However, existing models can only predict the soluble salt content in saline soils under positive temperatures. However, in heavily salinized areas such as the Yinbei Irrigation District in Yinchuan City, Ningxia, the soil contains crystalline salts and salt crusts form under negative winter temperatures. Therefore, a model is needed to predict the total salt content in soils at different temperatures based on dielectric constant, conductivity, and temperature. Although many researchers have explored the relationships between conductivity, dielectric constant, water content, salinity, and temperature, the quantitative nature of these relationships remains unclear, and they have yet to be combined with actual salt content measurements in saline soils. Therefore, a method is needed to predict the salt content of saline soils at different temperatures during freeze-thaw cycles based on the dielectric constant, conductivity, and temperature measured by sensors such as 5TE. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for predicting soil salinity during a freeze-thaw process.

[0004] In order to achieve the purpose of the present invention, we will adopt the following technical solutions to implement it:

[0005] A method for predicting soil salinity during a freeze-thaw process comprises the following steps:

[0006] S1. Measure the dielectric constant, electrical conductivity, and temperature of the soil using a 5TE sensor, and obtain the bulk density, specific gravity, and type of the soil by testing soil samples collected on-site. Enter the soil type into a model sample database, and obtain the freezing characteristic curve of the salt-free soil corresponding to the soil type from the model sample database; wherein the model sample database is obtained through a large number of experiments on different types of soil and their different bulk densities and proportions.

[0007] S2. Calculate the dielectric constants of dry soil particles, air, salt, water, and ice in the soil volume under different temperature conditions based on the relationship between temperature and dielectric constant;

[0008] S3. Calculate the ionic strength I in unfrozen water based on the conductivity measured by the 5TE sensor x , calculate the soluble salt content in unfrozen water based on the types and categories of salts in unfrozen water;

[0009] S4. Calculate the maximum saturated solubility of salt in water according to the thermodynamic model under different temperature conditions;

[0010] S5. Calculate the volume content of unfrozen water, ice, dry soil particles, and air;

[0011] S6. Determine whether there is crystallization in the soil based on the relationship between the soluble salt content calculated in step S3 and the maximum saturated solubility calculated in step S4, and predict the soil salinity during the freeze-thaw process, wherein:

[0012] If the soluble salt content calculated in step S3 is less than or equal to the maximum saturated solubility calculated in step S4, then there is no crystallization in the soil, and the soil salinity during the freeze-thaw process is the soluble salt content in the unfrozen water calculated in step S3;

[0013] If the soluble salt content calculated in step S3 is greater than the maximum saturated solubility calculated in step S4, crystallization precipitation occurs in the soil. The soil salt content during the freeze-thaw process is the sum of the volume content of the crystallized salt and the soluble salt content in the unfrozen water. The volume content of the crystallized salt is obtained by substituting the dielectric constants of the dry soil particles, air, water, and ice calculated in step S2, the volume content of unfrozen water, the volume content of ice, the volume content of dry soil particles, and the volume content of air calculated in step S5, and the soil dielectric constant measured by the 5TE sensor into the dielectric constant volume mixing model to obtain the volume content of the crystallized salt.

[0014] As a preferred embodiment of the present invention, the dielectric constant of the air is:

[0015] ε air =1+0i

[0016] The dielectric constant of the ice is:

[0017] ε ice =3.2

[0018] The dielectric constants of the dry soil particles and crystallized salt are:

[0019] ε soil =-0.026T+3.267

[0020] ε silt =-0.0139T+2.009

[0021] The dielectric constant of the water is:

[0022]

[0023] As a preferred embodiment of the present invention, the calculation process of the soluble salt content includes the following steps:

[0024] S31, calculating the ionic strength I of the salt in the unfrozen water according to the electrical conductivity x , ionic strength I x The expression is:

[0025]

[0026] Where A is expressed as:

[0027]

[0028] Where G is the electrical parameter; are the electrical conductivity of the soil at temperature T and the initial soil electrical conductivity; α is the slope of the change of electrical conductivity with temperature; T r is the reference temperature 25℃; I0 is the ionic strength; S is the saturation; n is the saturation index;

[0029] Simultaneous ionic strength I x The expression of and the expression of A are used to obtain the ionic strength of salt in unfrozen water;

[0030] S32. Based on the types and categories of salts in the unfrozen water, the concentration of soluble salts in the unfrozen water is obtained by the following formula:

[0031]

[0032] Among them, I x The concentration of the solution at any time is c i The ionic strength is expressed as:

[0033]

[0034] Where Z i is the charge number of each ion.

[0035] As a preferred embodiment of the present invention, the expression of the maximum saturation solubility is:

[0036]

[0037] Where K MX is the equilibrium constant at different temperatures; γ MX is the activity coefficient.

[0038] As a preferred embodiment of the present invention, the calculation process of the unfrozen water volume content includes the following steps:

[0039] S51. Determine the relationship between freezing temperature and salt content according to the soluble salt content in the unfrozen water:

[0040]

[0041] Where, T fo is the freezing temperature of saturated non-salinity soil; T f is the freezing temperature of soil, K fc is the freezing temperature reduction coefficient expressed in molar concentration; c ei The effective molar concentration in the soil solution; c0 is the molar concentration of the initial solution; k is the effective molar concentration correction factor, k = 0.7 mol / m 3 ; R is the universal gas constant, R = 8.31; η is the constant in the generalized Clapeyron equation, η ≈ 1.23 MPa / ℃;

[0042] S52. The differential equation for calculating the mass fraction of unfrozen water is:

[0043]

[0044] Where: n is the mass molar concentration of a salt; ρ is the mass density of water; b0 is the mass molar concentration of soluble salt calculated based on conductivity; ω0 is the initial water content; R is the ideal gas constant; η is the constant in the generalized Clapeyron equation; T f is the freezing temperature; ω r is the mass fraction of residual water; N is the test parameter related to soil properties;

[0045] The condition for the solution of the differential equation is that during the freezing process of the soil, the mass content of unfrozen water corresponding to the freezing temperature is the initial mass moisture content, so:

[0046]

[0047] Rewritten as:

[0048] w=a(T0-T) -N +w r

[0049] a=(w0-w r )(T0-T f ) N

[0050] Where ω is the mass water content of unfrozen water, ω0 is the mass water content of initial water, and ω r is the mass moisture content of residual water, N is the test parameter related to soil properties, a, N and ω r is obtained by fitting the freezing characteristic curve;

[0051] According to the differential equation and the boundary conditions of the differential equation, the differential equation is solved by using the Euler method to obtain the mass fraction of unfrozen water at any temperature;

[0052] S53. Based on the relationship between mass moisture content and volume moisture content, the volume content of unfrozen water is obtained as:

[0053]

[0054] Where: γ is the dry bulk density of soil.

[0055] As a preferred embodiment of the present invention, the ice volume content is based on the law of conservation of mass. The total moisture content of the soil remains unchanged during the freezing and thawing process. The ice volume content in the frozen soil is:

[0056]

[0057] Where: ρ l is the density of pure water, V total is the total volumetric water content in the soil, V w is the volumetric water content of unfrozen water after soil freezing, ρ i is the density of pure ice, V i is the volume content of ice after soil freezing;

[0058] Considering that the expansion coefficient of water ice is 1.1, the volume content of ice is:

[0059] V ice =1.1V i .

[0060] As a preferred embodiment of the present invention, the volume content of the dry soil particles is:

[0061]

[0062] Where: P is the porosity of the soil, ρb is the bulk density of soil, ρ s is the specific gravity of the soil.

[0063] As a preferred embodiment of the present invention, the volume content of the air is:

[0064] V air =PV ice -V water -V salt .

[0065] As a preferred embodiment of the present invention, the volume dielectric constant hybrid model is:

[0066] ε=ε air V air +ε soil V soil +ε salt V salt +ε water V water +ε ice V ice

[0067] As a preferred embodiment of the present invention, the mass content of the crystalline salt is:

[0068]

[0069] The mass content of soluble salt in the unfrozen water is:

[0070]

[0071] Beneficial effects

[0072] The present invention uses the dielectric constant and conductivity measured by the internationally widely used 5TE sensor to predict the total salt content (including the soluble salt content and crystallized salt content in unfrozen water) in saline soil at any temperature during the freeze-thaw process, realizing a simple, accurate and efficient inversion method for the total salt content of saline soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is a flow chart of the prediction method of the present invention;

[0074] Figure 2 This is a specific calculation flow chart of the model in the present invention;

[0075] Figure 3 is the freezing characteristic curve of the non-salinity soil in the present invention;

[0076] Figure 4 is a graph showing the relationship between the dielectric constant and temperature in the present invention;

[0077] Figure 5 is a graph showing the relationship between the concentration of soluble salts in pore water and temperature in the present invention;

[0078] Figure 6 are the parameters a, N and ω in the present invention r Fitting curve graph;

[0079] Figure 7 The graph is a relationship between the salt content in pore water and the crystallized salt content and temperature in the present invention;

[0080] Figure 8 The graph is a relationship between the salt content in pore water and the crystallized salt content and temperature in the present invention;

[0081] Figure 9 This is a graph showing the relationship between the salt content in pore water and the crystallized salt content as a function of temperature in the present invention. DETAILED DESCRIPTION

[0082] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0083] As an embodiment of the present invention, Figure 1-6 As shown, a method for predicting soil salinity during a freeze-thaw process includes the following steps:

[0084] S1 uses 5TE sensors to measure the parameters of saline soil, including dielectric constant, conductivity, temperature, and on-site sampling to obtain the bulk density, specific gravity, and soil type (clay, silt, etc.). The data obtained from on-site sampling is input into the model sample database, which contains the freezing characteristic curves of non-salty soil of different types of soil, such as Figure 3 The model sample database is obtained through a large number of experiments on different types of soils and their different bulk densities and proportions.

[0085] In step S2, the dielectric constant of each component (dry soil particles, air, salt, water, and ice) in the soil volume at different temperatures is calculated using the relationship between temperature and dielectric constant.

[0086] The dielectric constant of air is:

[0087] ε air =1+0i (17)

[0088] The dielectric constant of the ice is:

[0089] ε ice =3.2

[0090] The dielectric constants of soil and crystallized salt are Figure 4 As shown, the specific formula is:

[0091] ε soil=-0.026T+3.267 (18)

[0092] ε silt =-0.0139T+2.009 (19)

[0093] The dielectric constant of water is:

[0094]

[0095] In step S3, the soluble salt content in the unfrozen water is calculated using the conductivity measured by the 5TE sensor, wherein the ionic strength I in the unfrozen water calculated based on the conductivity is x for:

[0096]

[0097] The expression of A is:

[0098]

[0099] Where: G is the electrical parameter; are the electrical conductivity of the soil at temperature T and the initial soil electrical conductivity; α is the slope of the change of electrical conductivity with temperature; T r is the reference temperature 25℃; I0 is the ionic strength; S is the saturation; n is the saturation index.

[0100] The ionic strength of the salt in the unfrozen water, i.e., the pore water solution, can be obtained by combining formulas (21) and (22). Based on the type and type of salt in the pore water solution, the concentration of soluble salt in the pore water can be obtained by formula (23). The concentration of soluble salt in the pore water obtained by the experiment is as follows: Figure 5 shown.

[0101]

[0102] Among them, I x The concentration of the solution at any time is c i The ionic strength is expressed as:

[0103]

[0104] Where Z i is the charge number of each ion.

[0105] In step S4, the maximum saturated solubility of salt in water is calculated using a thermodynamic model.

[0106] Step S5: Calculate the volume content of each component. The volume content of unfrozen water needs to consider the relationship between freezing temperature and salt content. The soluble salt content in unfrozen water has been calculated in step S3, so the specific relationship between freezing temperature and salt content is:

[0107]

[0108] Where: T fo is the freezing temperature of saturated non-salinity soil (℃), T f is the freezing temperature of soil (℃), K fc is the freezing temperature reduction coefficient expressed in molar concentration, c ei Effective molar concentration (ion) in soil solution (mol / m 3 ), c0 is the molar concentration of the initial solution (ion) (mol / m 3 ). k is the effective molar concentration coefficient (mol / m 3 )(Calculate Na + and The effective molar concentration correction coefficient is k = 0.7 mol / m 3 ), R is the universal gas constant (R = 8.31 (J / (mol·K)), and η is the constant in the generalized Clapeyron equation (η ≈ 1.23 MPa / ℃).

[0109] The specific expression for calculating the mass fraction of unfrozen water is:

[0110]

[0111] Where: n is the mass molar concentration of a salt; ρ is the mass density of water; b0 is the mass molar concentration of soluble salt calculated based on conductivity; ω0 is the initial water content; R is the ideal gas constant; η is the constant in the generalized Clapeyron equation; T f is the freezing temperature; ω r is the mass fraction of residual water; N is the test parameter related to soil properties.

[0112] The definite solution of the differential equation is the mass content of unfrozen water corresponding to the freezing process of the soil (freezing temperature), that is, the initial mass moisture content, so:

[0113]

[0114] Rewrite formula (32) as:

[0115] w=a(T0-T) -N +w r (33)

[0116] a=(w0-w r )(T0-T f ) N (34)

[0117] Where: ω is the mass water content of unfrozen water (%), ω0 is the mass water content of initial water (%), ω r is the mass moisture content of residual water, and N is a test parameter related to soil properties.

[0118] According to the freezing characteristic curve of non-salinity soil, the parameters a, N and ω of the soil sample can be obtained by fitting r ,like Figure 6 shown.

[0119] According to formulas (30) to (34), the improved Euler method is used to solve differential equation (30) to obtain the mass fraction of unfrozen water at any temperature. According to the relationship between mass water content and volume water content, the volume content of unfrozen water is obtained as:

[0120]

[0121] Where: γ is the dry bulk density of soil (g / cm 3 ).

[0122] Calculate the volume content of ice. According to the law of conservation of mass, the total moisture content of the soil remains unchanged during the freezing and thawing process. The volume content of ice in the frozen soil is:

[0123]

[0124] Where: ρ l is the density of pure water, V total is the total volumetric water content in the soil (cm 3 / cm 3 ), V w is the volumetric water content of unfrozen water after soil freezing (cm 3 / cm 3 ), ρ i is the density of pure ice, V i is the volume content of ice after soil freezing (cm 3 / cm 3 ).

[0125] Considering that the expansion coefficient of water ice is 1.1, the volume content of ice is:

[0126] V ice =1.1V i (37)

[0127] The volume content of dry soil particles is:

[0128]

[0129] Where: P is the porosity of the soil (%), ρ b is the bulk density of the soil (g / cm 3), ρ s is the specific gravity of the soil (g / cm 3 ).

[0130] The volume content of air is:

[0131] V air =PV ice -V water -V salt (39)

[0132] S6, based on the dielectric constants of each component calculated by S2 and the volume content of each component calculated by S5, is brought into the volume dielectric constant mixing model, that is,

[0133] ε=ε air V air +ε soil V soil +ε salt V salt +ε water V water +ε ice V ice (40)

[0134] The volume content of the crystallized salt can be obtained. According to the volume content of the crystallized salt, the mass content of the crystallized salt can be converted into:

[0135]

[0136] The mass content of soluble salt in unfrozen water is:

[0137]

[0138] Where: V2 is the total volume of the soil, ρ silt is the density of salt.

[0139] The total salt content in the soil is the sum of the soluble salt content and the crystallized salt content in the unfrozen water, that is:

[0140] P=P1+P2 (43)

[0141] Among them, the relationship between the salt content and crystallized salt content in unfrozen water (i.e., pore water) and temperature is verified by indoor experiments as follows: Figures 7 to 9 As shown, it can be seen that the sum of the crystallized salt content and the salt content in the pore water is close to the initial salt content, so it is believed that this method has a higher accuracy.

[0142] The technical solution of the present invention is described in detail above in conjunction with the embodiments / drawings, but the present invention is not limited to the above technical solution. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent transformations and substitutions without departing from the principles of the present invention. These equivalent transformations and substitutions should also be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for predicting soil salinity during freeze-thaw process, characterized in that: The steps include: S1. Measure the dielectric constant, electrical conductivity, and temperature of the soil using a 5TE sensor, and obtain the bulk density, specific gravity, and type of soil by testing soil samples collected on-site. Enter the soil type into a model sample database, which is obtained through extensive testing of different types of soil and their different bulk densities and proportions. Obtain a freezing characteristic curve for the salt-free soil corresponding to the soil type from the database. S2. Calculate the dielectric constants of dry soil particles, air, salt, water, and ice in the soil volume under different temperature conditions based on the relationship between temperature and dielectric constant; S3. Calculate the ionic strength I in unfrozen water based on the conductivity measured by the 5TE sensor x , calculate the soluble salt content in unfrozen water based on the types and categories of salts in unfrozen water; S4. Calculate the maximum saturated solubility of salt in water according to the thermodynamic model under different temperature conditions; S5. Calculate the volume content of unfrozen water, ice, dry soil particles, and air; S6. Determine whether there is crystallization in the soil based on the relationship between the soluble salt content calculated in step S3 and the maximum saturated solubility calculated in step S4, and predict the soil salinity during the freeze-thaw process, wherein: If the soluble salt content calculated in step S3 is less than or equal to the maximum saturated solubility calculated in step S4, then there is no crystallization in the soil, and the soil salinity during the freeze-thaw process is the soluble salt content in the unfrozen water calculated in step S3; If the soluble salt content calculated in step S3 is greater than the maximum saturated solubility calculated in step S4, crystallization precipitation occurs in the soil. The soil salt content during the freeze-thaw process is the sum of the volume content of the crystallized salt and the soluble salt content in the unfrozen water. The volume content of the crystallized salt is obtained by substituting the dielectric constants of the dry soil particles, air, water, and ice calculated in step S2, the volume content of unfrozen water, the volume content of ice, the volume content of dry soil particles, and the volume content of air calculated in step S5, and the soil dielectric constant measured by the 5TE sensor into the dielectric constant volume mixing model to obtain the volume content of the crystallized salt.

2. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The dielectric constant of the air is: e air =1+0i The dielectric constant of the ice is: e ice =3.2 The dielectric constants of the dry soil particles and crystallized salt are: e soil =-0.026T+3.267 e silt =-0.0139T+2.009 The dielectric constant of the water is:

3. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The calculation process of the soluble salt content includes the following steps: S31, calculating the ionic strength I of the salt in the unfrozen water according to the electrical conductivity x , ionic strength I x The expression is: Where A is expressed as: Where G is the electrical parameter; are the electrical conductivity of the soil at temperature T and the initial soil electrical conductivity; α is the slope of the change of electrical conductivity with temperature; T r is the reference temperature 25℃; I0 is the ionic strength; S is the saturation; n is the saturation index; Simultaneous ionic strength I x The expression of and the expression of A are used to obtain the ionic strength of salt in unfrozen water; S32. Based on the types and categories of salts in the unfrozen water, the concentration of soluble salts in the unfrozen water is obtained by the following formula: Among them: I x The concentration of the solution at any time is c i The ionic strength is expressed as: Where Z i is the charge number of each ion.

4. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The expression of the maximum saturation solubility is: Where K MX is the equilibrium constant at different temperatures; γ MX is the activity coefficient.

5. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The calculation process of the unfrozen water volume content includes the following steps: S51. Determine the relationship between freezing temperature and salt content according to the soluble salt content in the unfrozen water: Where, T fo is the freezing temperature of saturated non-salinity soil; T f is the freezing temperature of soil, K fc is the freezing temperature reduction coefficient expressed in molar concentration; c ei The effective molar concentration in the soil solution; c0 is the molar concentration of the initial solution; k is the effective molar concentration correction factor, k = 0.7 mol / m 3 ; R is the universal gas constant, R = 8.31; η is the constant in the generalized Clapeyron equation, η ≈ 1.23 MPa / ℃; S52. The differential equation for calculating the mass fraction of unfrozen water is: Where: n is the mass molar concentration of a salt; ρ is the mass density of water; b0 is the mass molar concentration of soluble salt calculated based on conductivity; ω0 is the initial water content; R is the ideal gas constant; η is the constant in the generalized Clapeyron equation; T f is the freezing temperature; ω r is the mass fraction of residual water; N is the test parameter related to soil properties; The condition for the solution of the differential equation is that during the freezing process of the soil, the mass content of unfrozen water corresponding to the freezing temperature is the initial mass moisture content, so: In( T＝Tf )=w0 Rewritten as: w=a(T0-T) -N +w r a=(w0-w r )(T0-T f ) N Where ω is the mass water content of unfrozen water, ω0 is the mass water content of initial water, and ω r is the mass moisture content of residual water, N is the test parameter related to soil properties, a, N and ω r is obtained by fitting the freezing characteristic curve; According to the differential equation and the boundary conditions of the differential equation, the differential equation is solved by using the Euler method to obtain the mass fraction of unfrozen water at any temperature; S53. Based on the relationship between mass moisture content and volume moisture content, the volume content of unfrozen water is obtained as: Where: γ is the dry bulk density of soil.

6. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The ice volume content is based on the law of conservation of mass. The total moisture content of the soil remains unchanged during the freezing and thawing process. The ice volume content in the frozen soil is: Where: ρ l is the density of pure water, V total is the total volumetric water content in the soil, V w is the volumetric water content of unfrozen water after soil freezing, ρ i is the density of pure ice, V i is the volume content of ice after soil freezing; Considering that the expansion coefficient of water ice is 1.1, the volume content of ice is: V ice =1.1V i 。 7. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The volume content of the dry soil particles is: Where: P is the porosity of the soil, ρ b is the bulk density of soil, ρ s is the specific gravity of the soil.

8. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The volume content of the air is: V air =PV ice -V water -V salt 。 9. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The volume dielectric constant hybrid model is: e=e air V air +e soil V soil +e salt V salt +e water V water +e ice V ice 。 10. The method for predicting soil salinity during freeze-thaw process according to claim 1, wherein: The mass content of the crystalline salt is: The mass content of soluble salt in the unfrozen water is: Where V2 is the total volume of soil, ρ silt is the density of salt.

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