A method for characterizing the occurrence state of soil pore water

Abstract

The application provides a soil pore water occurrence state characterization method, and belongs to the field of geotechnical engineering and nuclear magnetic resonance detection. The method firstly performs low-field nuclear magnetic resonance transverse relaxation time measurement on the same type of soil sample under different water content conditions, extracts inherent strong bound water, weak bound water and capillary water surface relaxation intensity parameters of the soil by using multi-component surface relaxation physical model inversion; then performs nuclear magnetic resonance measurement on the to-be-measured soil sample and calculates the equivalent surface relaxation contribution value, compares with the theoretical model to judge the occurrence state of the pore water in the soil sample, and calculates the content of the strong bound water, the weak bound water and the capillary water. The method can avoid the deficiency of the traditional method which depends on the experience T2 threshold to divide the water type, realizes the universal and quantitative evaluation of the same type of soil different samples, has the advantages of clear physical mechanism, high detection efficiency and strong compatibility for various water content to-be-measured samples, and can be widely applied to the microstructure analysis and engineering property evaluation of cohesive soil.

Description

Technical Field

[0001] This application relates to the fields of geotechnical engineering and nuclear magnetic resonance testing, and in particular to a method for characterizing the state of pore water in soil. Background Technology

[0002] The state of pore water in soil (strongly bound water, weakly bound water, and capillary water) is the core microscopic factor determining its engineering properties such as shear strength, compressibility, and permeability. Accurate quantitative identification of the water content in different states is crucial for evaluating the engineering stability of soils and the transport patterns of pollutants in complex geological environments.

[0003] Currently, low-field nuclear magnetic resonance (LF-NMR) technology has become the mainstream method for investigating the distribution of water in the micropores of soil due to its non-destructive and efficient advantages. This technology uses the transverse relaxation time (T2) distribution spectrum to reflect the degree of freedom of water movement. Existing studies usually classify different types of water by setting empirical T2 threshold intervals, for example, classifying short T2 signals as bound water and long T2 signals as free water. However, this method has obvious limitations: (1) the different mineral compositions and differences in soil will significantly affect the NMR measurement results; (2) a single T 2. Thresholds cannot be applied to soils with different properties and working conditions; (3) Lack of physical model support.

[0004] Furthermore, nuclear magnetic resonance (NMR) theory indicates that the transverse relaxation of pore fluids in soil is primarily controlled by surface relaxation mechanisms, and its relaxation rate is related to the solid surface area in contact with the fluid and the surface relaxation intensity parameters. If the specific surface area characteristics of soil minerals can be combined with NMR relaxation parameters, a more reasonable method for identifying the pore water state can be established. Therefore, it is necessary to propose a new technical method that, by introducing surface relaxation intensity parameters and combining them with the specific surface area characteristics inside and outside the soil, can achieve quantitative identification of the pore water state in soil. Summary of the Invention

[0005] One of the objectives of this application is to provide a method for characterizing the pore water state of soil, in order to solve the problem that the identification accuracy is insufficient due to relying solely on the T2 threshold in the prior art. By introducing the surface relaxation strength parameter and combining it with the specific surface area characteristics inside and outside the soil, the quantitative identification of the pore water state of soil can be achieved.

[0006] The technical solution of this application is: A method for characterizing the state of pore water in soil includes the following steps: S1. Measure the specific surface area of ​​the soil sample, prepare soil samples with different water contents, and perform nuclear magnetic resonance (NMR) tests to obtain the transverse relaxation time of the soil samples with different water contents. T 2. Distribution spectrum data; S2, according to the T2. Distribution spectrum: The weighted geometric mean method was used to calculate the geometric mean of the transverse relaxation time of soil samples with different moisture contents. T 2g To characterize the overall relaxation properties of the soil; S3. Based on the nuclear magnetic resonance surface relaxation mechanism, a multi-component surface relaxation model considering the contribution of different pore water types was established. Soil pore water was divided into strongly bound water, weakly bound water and capillary water. Quantitative relationships were established between the relaxation contribution of each component, the specific surface area and the geometric mean of the transverse relaxation time. S4, using soil samples with different moisture contents T 2g The data is used to fit the multi-component surface relaxation model through parameter inversion method to obtain the surface relaxation intensity parameters corresponding to strongly bound water, weakly bound water and capillary water. S5, perform nuclear magnetic resonance (NMR) testing on the soil sample to be tested to obtain its... T 2. Calculate the distribution spectrum and its geometric mean transverse relaxation time. T 2g Moisture content w ; S6. Based on the surface relaxation strength parameters obtained in step S4, construct the theoretical relaxation limit under different pore water combination states, and calculate the equivalent surface relaxation contribution value of the soil sample to be tested. K obs ; S7, the equivalent surface relaxation contribution value K obs By comparing with various theoretical relaxation limits, the occurrence type of pore water in the soil sample to be tested is determined, and the content of each type of pore water is calculated to quantitatively identify the occurrence state of pore water.

[0007] As one technical solution of this application, in step S1, soil samples of the same type are selected, and basic physical property tests are performed on the soil samples, including total specific surface area. SSA all Internal specific surface area SSA in External specific surface area SSA out The internal specific surface area corresponds to the interlayer and microporous structure of clay minerals, while the external specific surface area corresponds to the external pore structure of particles. The soil sample is dried to constant weight at 105°C, and then deionized water is added to the soil sample according to a predetermined moisture content gradient and mixed thoroughly to prepare soil samples with different moisture contents. The preferred moisture content range of the soil samples is 5%–45%. The prepared soil samples are sealed and cured at a constant temperature for at least 48 hours to ensure uniform distribution of moisture in the soil's pore structure. Subsequently, the transverse relaxation time of each soil sample is measured using a low-field nuclear magnetic resonance spectrometer. T2. Measurement: The relaxation decay signal was obtained by using the CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence, and the T2 distribution spectrum was obtained by the inversion algorithm.

[0008] As a technical solution of this application, in step S2, based on the obtained T 2. Calculation of the geometric mean of transverse relaxation time using the distribution spectrum T 2g The calculation formula is shown in equation (1): (1); In the formula: T 2g For the soil sample T 2. Geometric mean of the transverse relaxation time of the distribution spectrum, which is used to characterize the overall relaxation behavior of the soil sample; T 2 is the first i One relaxation time component; f(T 2 ） This represents the signal amplitude corresponding to the relaxation time component.

[0009] As a technical solution of this application, in step S3, according to the nuclear magnetic resonance surface relaxation theory, the transverse relaxation of soil pore water is mainly controlled by the surface relaxation mechanism, and only the transverse relaxation time of surface relaxation is considered to satisfy the relationship shown in equation (2): (2); In the formula: T 2 represents the lateral relaxation time; ρ 2 represents the surface relaxation strength; S / V It is the ratio of pore surface area to pore volume; In soil systems, the interaction strength between different types of pore water and mineral surfaces varies, resulting in different surface relaxation strengths. ρ 2. There are also differences. Pore water in soil can be divided into strongly bound water, weakly bound water, and capillary water. Based on the above mechanism, a multi-component surface relaxation model is established, and its expression is shown in equation (3): (3); In the formula: T 2g For the soil sample T 2. Geometric mean of transverse relaxation time of the distribution spectrum; The density of water is generally taken as 1.0 g / cm³. 3 ; w For multiple groups of different moisture contents; fThe interlayer pore water weighting factor has a value range of 0 to 1. It reflects the distribution weight of weakly bound water in the interlayer pores due to surface binding. It can be determined based on mineral composition experiments or obtained through fitting. ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2 The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all ; ρ 2,3 The surface relaxation strength of capillary water; SSA eff,3 The effective specific surface area corresponds to capillary water, while for expansive soils containing montmorillonite and illite, it is the external specific surface area of ​​the soil sample. SSA out Other types of soil have a total specific surface area. SSA all .

[0010] As a technical solution of this application, in step S4, multiple sets of different moisture contents obtained in steps S1 to S3 are utilized. w Geometric mean of transverse relaxation time of soil samples T 2g The least squares regression method was used to perform parameter inversion on the multi-component surface relaxation model, and the surface relaxation intensity of strongly bound water was obtained by solving the problem. ρ 2,1 Surface relaxation strength of weakly bound water ρ 2,2 Surface relaxation strength of capillary water ρ 2,3 .

[0011] As a technical solution of this application, in step S5, low-field nuclear magnetic resonance measurement is performed on the soil sample to be tested. The core advantage of this method is that the relaxation strength parameters of the soil surface of this type are completed through steps S1 to S4. ρ 2,1 , ρ 2,2 , ρ2,3 Once calibrated, the model can be directly applied to multiple parallel samples of the same type of soil and can cover tests with any unknown moisture content. In practice, the soil sample to be tested is first subjected to low-field nuclear magnetic resonance measurement to obtain... T 2. Distribution spectrum, calculate its geometric mean of transverse relaxation time according to step S2. T 2g The water content w of the soil sample to be tested is calculated according to formula (4): (4); In the formula: w is the mass moisture content of the soil sample to be tested, % . m w Water quality obtained from nuclear magnetic resonance signal calibration; m 0 represents the total mass of the soil sample to be tested.

[0012] As one technical solution of this application, in step S6, the theoretical relaxation limit under different pore water combination states is constructed, and the equivalent surface relaxation contribution value of the soil sample to be tested is calculated. K obs include: Based on the surface relaxation strength parameters of the three types of pore water obtained in step S4, construct the theoretical limiting state of pore water: When only strongly bound water exists (no weakly bound water, no capillary water), then: (5); When strongly bound water and weakly bound water (no capillary water) are present, then: (6); When strongly bound water, weakly bound water, and capillary water are present, then: (7); In the formula: K A Parameters for distinguishing strongly bound water; ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; K B Parameters for distinguishing weakly bound water; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all ; K C Parameters for distinguishing capillary water; f This is the interlayer pore water weighting factor, with a value range of 0 to 1; ρ 2,3 The surface relaxation strength of capillary water; SSA eff,3 The effective specific surface area corresponds to capillary water, while for expansive soils containing montmorillonite and illite, it is the external specific surface area of ​​the soil sample. SSA out Other types of soil have a total specific surface area. SSA all ; Calculate the equivalent surface relaxation contribution value of the soil sample to be tested. K obs The calculation formula is as follows: (8); In the formula: K obs The contribution value is the equivalent surface relaxation value; w This represents the moisture content of the soil sample. ρ w The density of water; T 2g For the soil sample to be tested T 2. Geometric mean of transverse relaxation time of the distribution spectrum.

[0013] As a technical solution of this application, in step S7, the equivalent surface relaxation contribution value calculated in step S6 is used. K obs The pore water occurrence state in the soil sample is identified by comparing it with the theoretical limit state of pore water constructed. (1) If If only strongly bound water exists in the soil sample, then the water content of strongly bound water is... , ; (2) If The soil sample contains both strongly bound water and weakly bound water, with the strongly bound water having a water content of [missing information]. Weakly bound water content ; (3) If The soil sample contains strongly bound water, weakly bound water, and capillary water. Among these, the water content of strongly bound water is... The sum of the water content of strongly bound water and the water content of weakly bound water is The water content of weakly bound water is... Capillary water content ; In the formula: K obs The contribution value is the equivalent surface relaxation value; K A Parameters for distinguishing strongly bound water; w This represents the moisture content of the soil sample. K B Parameters for distinguishing weakly bound water; T 2g For the soil sample to be tested T 2. Geometric mean of transverse relaxation time of the distribution spectrum; ρ w The density of water; ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; w 1,2 for; f This is the interlayer pore water weighting factor, with a value range of 0 to 1; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2 The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all .

[0014] The beneficial effects of this application are: This invention first measures the transverse relaxation time of similar soil samples under different moisture contents using low-field nuclear magnetic resonance (NMR). Then, using a multi-component surface relaxation physics model, it extracts the inherent surface relaxation intensity parameters of strongly bound water, weakly bound water, and capillary water in this type of soil. Subsequently, NMR measurements are performed on the soil samples, and the equivalent surface relaxation contribution value is calculated. By comparing this value with the theoretical model, the state of pore water in the soil samples is determined, and the contents of strongly bound water, weakly bound water, and capillary water are calculated. This method breaks through the traditional... T 2. Limitations of the threshold classification method and the shortcomings of traditional methods that rely on empirical thresholds, which are difficult to adapt to different soil types. Physical characterization using surface relaxation strength parameters has better universality and can avoid the reliance on experience in traditional methods. TOvercoming the limitations of threshold-based water type classification, this method achieves universal quantitative evaluation of different samples of the same soil type and is applicable to characterizing the pore water occurrence state of different soil types. It boasts advantages such as a clear physical mechanism, high detection efficiency, and strong compatibility with samples in various water-bearing states, making it widely applicable to the microstructure analysis and engineering property evaluation of cohesive soils. Furthermore, by constructing a multi-component surface relaxation model, it can also achieve quantitative identification of pore water types, simultaneously obtaining the contents of strongly bound water, weakly bound water, and capillary water, thus improving the quantification of the results. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 A schematic diagram of the soil pore water occurrence state characterization method provided in the embodiments of this application; Figure 2 A schematic diagram of nuclear magnetic resonance measurement results of soil samples with different moisture contents prepared for embodiments of this application; Figure 3 A schematic diagram of the nuclear magnetic resonance measurement results of three clay samples to be tested, provided for an embodiment of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can typically be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0020] In the description of this application, it should be noted that the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only used to facilitate the description of this application and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] Furthermore, in this application, unless otherwise expressly specified and limited, "above or below" the first feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Moreover, "above," "over," and "on" the first feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature located at the lower outer periphery of the second feature and diagonally below it, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0022] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] Example 1: Please refer to Figure 1 (Refer to) Figure 2 to Figure 3 This embodiment calibrates the surface relaxation strength parameters. Taking a natural clay sample (mainly composed of montmorillonite and small amounts of illite and kaolinite) as an example, this embodiment obtains the true surface relaxation strength parameters of the three types of pore water—strongly bound water, weakly bound water, and capillary water—specific to this soil type through a series of gradient moisture content tests. The specific operating steps are as follows: Step 1: The specific surface area of ​​the selected natural clay sample was tested, and its total specific surface area was determined by ethylene glycol ethyl ether (EGME) adsorption method. SSA all =563m 2 / g, its external specific surface area was determined by the BET gas adsorption method. SSA out =28m 2 / g, the internal specific surface area is obtained from the difference between the total specific surface area and the external specific surface area. SSA in =535m 2 / g; After the soil sample is dried to constant weight at 105℃, it is taken out and placed in a desiccator to cool to room temperature; then, soil samples are prepared according to the preset mass moisture content gradient (in this embodiment, it is set to: 9%, 12%, 18%, 22%, 25%, 30%, 35%, 45%); the prepared soil samples are sealed and cured under constant temperature for no less than 48 hours to allow the moisture to be evenly distributed in the soil pore structure; Step 2: Use a nuclear magnetic resonance analyzer to measure the transverse relaxation time of soil samples at various moisture contents. T 2. Measurements were performed using a CPMG pulse sequence with the following parameters: echo interval TE = 0.08 ms, number of echoes NECH = 20000, and waiting time TW = 4 s. The T2 distribution spectrum under each water content gradient was obtained through an inversion algorithm, as shown in the attached figure. Figure 2 As shown; Step 3, based on the measured properties of the clay sample... Figure 2 The T2 distribution spectrum is shown. The weighted geometric mean of the transverse relaxation time of samples with different moisture contents is calculated using the weighted geometric mean method according to equation (1). T 2g The moisture content gradients of 9%, 12%, 18%, 22%, 25%, 30%, 35%, and 45% were obtained. T 2g The respective durations are 0.1ms, 0.13ms, 0.5ms, 0.8ms, 1.2ms, 1.8ms, 2.2ms, and 4.0ms; Step four: Based on the nuclear magnetic resonance surface relaxation mechanism, establish a multi-component surface relaxation model contributing to three types of pore water: strongly bound water, weakly bound water, and capillary water (see Equation 2); and apply the gradient water content obtained in step two... w With the corresponding T 2g Substituting the data into a multi-component surface relaxation model (see Equation 3), a global optimization fitting was performed using the nonlinear least squares method to obtain the surface relaxation intensity parameters of three types of pore water in the soil sample: strongly bound water, weakly bound water, and capillary water. Among these, the surface relaxation intensity of strongly bound water... ρ 2,1 =0.85μm / s, relaxation intensity of weakly bound water surface ρ 2,2 =0.28μm / s, capillary water surface relaxation strength ρ 2,3=0.08μm / s; the interlayer pore water weighting factor obtained by fitting. f =0.5, which reflects the unique water adsorption characteristics of this clay mineral.

[0025] Example 2: This embodiment is a quantitative identification and evaluation of the moisture content state of an unknown soil sample. This embodiment is based on the true surface relaxation strength of three types of pore water—strongly bound water, weakly bound water, and capillary water—calibrated in Example 1. ρ 2,1 , ρ 2,2 , ρ 2,3 This method enables rapid identification and quantitative evaluation of the moisture content of multiple similar clay samples. The specific implementation steps are as follows: Step 1: Nuclear Magnetic Resonance (NMR) Detection of the Samples: Three clay samples of the same type but with different water contents (Sample A, Sample B, and Sample C) were selected. NMR tests were performed on the three soil samples with unknown water contents to obtain the NMR values ​​for each sample. T 2. Distribution spectrum as attached Figure 3 The total moisture content of sample A was obtained through calculation. w A =5.2%, T 2g The time was 0.12 ms; the total moisture content of sample B was... w B =15%, T 2 is 0.32 ms; total moisture content of sample C w C =32%, T2g is 2.0ms; Step 2: Theoretical limit value of pore water and equivalent surface relaxation contribution value of the soil sample to be tested. K obs Calculation: Based on the actual surface relaxation intensities of the three types of pore water—strongly bound water, weakly bound water, and capillary water—obtained in Example 1, the theoretical limit values ​​of the three types of pore water were calculated: (1) Limit of strongly bound water K A This represents the maximum possible contribution value when only strongly bound water is present in the sample. K A =1.80; (2) Weakly bound water limit K B This represents the contribution value when both strongly bound water and weakly bound water in the sample reach their maximum values, and capillary water has not yet appeared. K B =2.95; (3) Fully saturated reference value K C It also involves contributions from strongly bound water, weakly bound water, and capillary water. K C=3.60; Based on equation (8), the measured equivalent surface relaxation contribution values ​​of the three test samples are calculated respectively. K obs :Sample A: K obs,A =1.40; Sample B: K obs,B =2.38; Sample C: K obs,C =3.45); Step 3: Determination and quantitative evaluation of the sample's state of existence: For sample A, since K obs,A < K A Therefore, it was determined that the pore water in the soil sample contained only strongly bound water, and the water content of strongly bound water was [missing information]. w 1,A =5.2%, with both weakly bound water and capillary water content being 0; For sample B, since K A < K obs,B < K B Therefore, it was determined that the pore water in the soil sample contained both strongly bound water and weakly bound water, and no capillary water was present; the water content of strongly bound water was... w 1,B =6.8%, weakly bound water content w 2,B = w B - w 1,B =8.2%; For sample C, since K B < K obs,C Therefore, the soil sample was determined to be in a state of coexistence of three phases: strongly bound water, weakly bound water, and capillary water. The water content of strongly bound water was... w 1,C =6.8%, weakly bound water content w 2,C =11.2%, capillary water content w 3,C =14.0%.

[0026] This embodiment demonstrates, through testing three samples with different water content states, that the surface relaxation strength parameters obtained in the first calibration step of this embodiment can accurately identify the occurrence state of any water content sample of this type of soil. This model can accurately capture the physical process of water evolution from single strongly bound water to multi-component water, exhibiting extremely high universality and engineering application value.

[0027] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for characterizing the state of pore water in soil, characterized in that, Includes the following steps: The specific surface area of ​​soil samples was measured, soil samples with different water contents were prepared and nuclear magnetic resonance tests were performed to obtain the transverse relaxation time T2 distribution spectrum data of soil samples with different water contents. According to the above T 2. Distribution spectrum: The weighted geometric mean method was used to calculate the geometric mean of the transverse relaxation time of soil samples with different moisture contents. T 2g To characterize the overall relaxation properties of the soil; Based on the nuclear magnetic resonance surface relaxation mechanism, a multi-component surface relaxation model considering the contributions of different pore water types was established. Soil pore water was divided into strongly bound water, weakly bound water and capillary water. Quantitative relationships were established between the relaxation contribution of each component, the specific surface area and the geometric mean of the transverse relaxation time. Using soil samples with different moisture contents T 2g The data is used to fit the multi-component surface relaxation model through parameter inversion method to obtain the surface relaxation intensity parameters corresponding to strongly bound water, weakly bound water and capillary water. Nuclear magnetic resonance (NMR) testing was performed on the soil sample to obtain its... T 2. Calculate the distribution spectrum and its geometric mean transverse relaxation time. T 2g Moisture content w ; Based on the obtained surface relaxation strength parameters, theoretical relaxation limits under different pore water combinations are constructed, and the equivalent surface relaxation contribution value of the soil sample is calculated. K obs ; The equivalent surface relaxation contribution value K obs By comparing with various theoretical relaxation limits, the occurrence type of pore water in the soil sample is determined, and the content of each type of pore water is calculated to quantitatively identify the occurrence state of pore water.

2. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, The specific surface area information of the measured soil sample includes: Select soil samples of the same type and perform basic physical property tests on the soil samples, including total specific surface area. SSA all Internal specific surface area SSA in External specific surface area SSA out Wherein, the internal specific surface area corresponds to the interlayer and microporous structure of clay minerals, and the external specific surface area corresponds to the external pore structure of particles; The soil sample is dried to constant weight, and deionized water is added to the soil sample according to a predetermined moisture content gradient and mixed thoroughly to prepare soil samples with different moisture contents, wherein the moisture content of the soil sample ranges from 5% to 45%; the prepared soil sample is sealed and cured under constant temperature conditions to ensure that the moisture is evenly distributed in the soil pore structure. The transverse relaxation time T2 of each soil sample was measured using a low-field nuclear magnetic resonance spectrometer, and the T2 distribution spectrum was obtained through an inversion algorithm.

3. The method for characterizing the state of pore water in soil according to claim 2, characterized in that, The transverse relaxation time is obtained by using a CPMG pulse sequence to acquire the relaxation decay signal. T 2. Measurement.

4. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, The geometric mean of the transverse relaxation time is calculated using the following formula. T 2g : ； In the formula: T 2g For the soil sample T 2. Geometric mean of transverse relaxation time of the distribution spectrum; T 2 represents the i-th relaxation time component; f(T) 2 ） This represents the signal amplitude corresponding to the relaxation time component.

5. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, Establishing a multi-component surface relaxation model that considers contributions from different pore water types includes: According to the nuclear magnetic resonance surface relaxation theory, the transverse relaxation time of surface relaxation satisfies the following relationship: ； In the formula: T 2 represents the lateral relaxation time; ρ 2 represents the surface relaxation strength; S / V It is the ratio of pore surface area to pore volume; Pore ​​water in soil is classified into strongly bound water, weakly bound water, and capillary water. A multi-component surface relaxation model is established using the following expression: ； In the formula: T 2g For the soil sample T 2. Geometric mean of transverse relaxation time of the distribution spectrum; Let the density of water be 1.0 g / cm³. 3 ; w For multiple groups of different moisture contents; f This is the interlayer pore water weighting factor, with a value range of 0 to 1; ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2 The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all ; ρ 2,3 The surface relaxation strength of capillary water; SSA eff,3 The effective specific surface area corresponds to capillary water, while for expansive soils containing montmorillonite and illite, it is the external specific surface area of ​​the soil sample. SSA out Other types of soil have a total specific surface area. SSA all .

6. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, Through obtaining multiple sets of different moisture contents w Geometric mean of transverse relaxation time of soil samples T 2g The least squares regression method was used to perform parameter inversion on the multi-component surface relaxation model, and the surface relaxation intensity of strongly bound water was obtained by solving the problem. ρ 2,1 Surface relaxation strength of weakly bound water ρ 2,2 Surface relaxation strength of capillary water ρ 2,3 .

7. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, Calculate the mass moisture content of the soil sample to be tested. w include: Low-field nuclear magnetic resonance (NMR) measurements were performed on the soil sample to be tested. T 2. Distribution spectrum: The weighted geometric mean of the transverse relaxation time of the soil sample was calculated. T 2g The mass moisture content of the soil sample to be tested is calculated according to the following formula. w : ； In the formula: w The water content of the soil sample to be tested is % (%). m w Water quality obtained from nuclear magnetic resonance signal calibration; m 0 represents the total mass of the soil sample to be tested.

8. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, The theoretical relaxation limits under different pore water combinations were constructed, and the equivalent surface relaxation contribution value of the soil sample was calculated. K obs include: The theoretical limiting state of pore water is constructed based on the surface relaxation strength parameters of the three types of pore water obtained: When only strongly bound water is present, then When both strongly bound water and weakly bound water are present, then When strongly bound water, weakly bound water, and capillary water are present, then ; In the formula: K A Parameters for distinguishing strongly bound water; ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; K B Parameters for distinguishing weakly bound water; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2 The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all ; K C Parameters for distinguishing capillary water; f This is the interlayer pore water weighting factor, with a value range of 0 to 1; ρ 2,3 The surface relaxation strength of capillary water; SSA eff,3 The effective specific surface area corresponds to capillary water, while for expansive soils containing montmorillonite and illite, it is the external specific surface area of ​​the soil sample. SSA out Other types of soil have a total specific surface area. SSA all ; The equivalent surface relaxation contribution value of the soil sample to be tested is calculated using the following formula. K obs : ； In the formula: K obs The contribution value is the equivalent surface relaxation value; w This represents the moisture content of the soil sample. ρ w The density of water; T 2g For the soil sample to be tested T 2. Geometric mean of transverse relaxation time of the distribution spectrum.

9. The method for characterizing the state of pore water in soil according to claim 1, characterized in that, Equivalent surface relaxation contribution value K obs The pore water occurrence state in the soil sample is identified by comparing it with the theoretical limit state of pore water constructed. like If only strongly bound water exists in the soil sample, then the water content of strongly bound water is... , ; like The soil sample contains both strongly bound water and weakly bound water. The water content of strongly bound water is... Weakly bound water content ; like The soil sample contains strongly bound water, weakly bound water, and capillary water. Among these, the water content of strongly bound water is... The sum of the water content of strongly bound water and the water content of weakly bound water is The water content of weakly bound water is Capillary water content ; In the formula: K obs The contribution value is the equivalent surface relaxation value; K A Parameters for distinguishing strongly bound water; w This represents the moisture content of the soil sample. K B Parameters for distinguishing weakly bound water; T 2g For the soil sample to be tested T 2. Geometric mean of transverse relaxation time of the distribution spectrum; ρ w The density of water; ρ 2,1 To enhance the relaxation strength of the bound water surface; SSA eff,1 The effective specific surface area corresponds to strongly bound water, while for expansive soils containing montmorillonite and illite, the internal specific surface area is used. SSA in Other types of soil have a total specific surface area. SSA all ; w 1,2 for; f This is the interlayer pore water weighting factor, with a value range of 0 to 1; ρ 2,2 The relaxation strength of weakly bound water surface; SSA eff,2 The effective specific surface area corresponds to weakly bound water, while for expansive soils containing montmorillonite and illite, it is the internal specific surface area of ​​the soil sample. SSA in Other types of soil have a total specific surface area. SSA all .

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