Nuclear magnetic resonance detection method for cohesive soil pore water state
Through the optimized CPMG sequence acquisition parameters and independent acquisition scheme, the problem of identifying and quantitative analysis of water in different states of water in geotechnical media is solved, and the accurate identification and quantitative measurement of water in clay soil is achieved, which improves the accuracy and practicality of detection.
Patent Information
- Application Number
- CN202510252644.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-05
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art is difficult to accurately identify and quantitatively analyze water in different expiration states in geotechnical media, especially when the relaxation time distributions of combined water, capillary water and gravity water overlap each other.
Using optimized CPMG sequence acquisition parameters, an independent acquisition scheme combining water, capillary and gravity water is designed. By setting different polarization waiting times, echo interval times and echo counts, signal distinction and accurate measurement of water in different states is achieved.
Accurate identification and quantitative measurement of water in different states in clay soil is realized, which improves the accuracy and practicality of detection and reduces the dependence on complex algorithms.
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Figure CN120177541A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of geotechnical testing, and particularly to a nuclear magnetic resonance detection method for the pore water state of cohesive soil. Background Art
[0002] Water in geotechnical media has a key impact on the basic mechanical properties of geotechnical materials. For example, the rheological and thixotropic properties of soft soil, frozen soil, and expansive soil are affected by the water stored in the pore media of geotechnical materials, which is influenced by pores and surfaces. The water in geotechnical materials mainly includes three storage states: gravitational water, capillary water, and bound water. How to accurately identify and quantitatively analyze these three different storage states of water is crucial for predicting the engineering behavior and hydrogeological response of soil masses.
[0003] Low-field nuclear magnetic resonance technology has been widely used in soil moisture detection and rock pore fluid analysis. However, due to the overlapping relaxation time distributions of bound water, capillary water, and gravitational water, it is difficult for traditional methods to accurately separate the target signals in the relaxation time T2 distribution and directly obtain the contents of water in different storage states. Summary of the Invention
[0004] To solve the problems of identifying and quantifying water in different storage states in geotechnical media, this application provides a nuclear magnetic resonance detection method for the pore water state of cohesive soil.
[0005] A nuclear magnetic resonance detection method for the pore water state of cohesive soil provided by this application adopts the following technical solutions: A nuclear magnetic resonance detection method for the pore water state of cohesive soil includes the following steps: Bound water detection: Collect nuclear magnetic resonance CPMG echo signals from a cohesive soil sample, set the polarization waiting time TW1, echo interval time TE1, and number of echoes NECH1 to obtain the echo signal of bound water in the cohesive soil sample; invert the echo signal of bound water to obtain the T2 distribution spectrum of bound water; calculate the content of bound water from the T2 distribution spectrum of bound water; Capillary water detection: Collect nuclear magnetic resonance CPMG echo signals from a cohesive soil sample, set the polarization waiting time TW2, echo interval time TE2, and number of echoes NECH2 to obtain the echo signals of bound water and capillary water in the cohesive soil sample; perform zonal inversion on the echo signals of bound water and capillary water to obtain the T2 distribution spectrum of capillary water; calculate the content of capillary water from the T2 distribution spectrum of capillary water; Gravitational water detection: Collect nuclear magnetic resonance CPMG echo signals from a cohesive soil sample, set the polarization waiting time TW3, echo interval time TE3, and number of echoes NECH3 to obtain the echo signal of gravitational water in the cohesive soil sample; invert the echo signal of gravitational water to obtain the T2 distribution spectrum of gravitational water; calculate the content of gravitational water from the T2 distribution spectrum of gravitational water; Among them, TW1 < TW2 < TW3, TE1 ≤ TE2 < TE3, and NECH1 < NECH3 < NECH2.
[0006] Furthermore, in the bound water detection step, when collecting the echo signal of bound water, only the bound water is polarized, and only the front-end echo signal with a short relaxation time is collected.
[0007] Furthermore, in the capillary water detection step, when collecting the echo signals of bound water and capillary water, both the bound water and the capillary water are polarized, and the collected echo signals include the echo signals of bound water and capillary water.
[0008] Furthermore, in the gravitational water detection step, when collecting the echo signal of gravitational water, the bound water, capillary water, and gravitational water are all polarized, and only the back-end echo signal with a long relaxation time is collected.
[0009] Furthermore, when collecting the echo signal of bound water, the acquisition parameters are set as follows: the polarization waiting time TW1 = 1 - 5 ms, the echo interval time TE1 ≤ 0.2 ms, and the number of echoes NECH1 ≤ 100.
[0010] Preferably, the denser the cohesive soil sample, the smaller the value of TW1 can be.
[0011] The transverse relaxation time T2 of the bound water in the cohesive soil sample is short, and the T2 range is 0.1 - 1 ms. In order to specifically measure the echo signal of bound water, by adjusting the echo interval time Time Wait (abbreviated as TW), polarization waiting time Time Echo (abbreviated as TE), and number of echoes Echo Number (abbreviated as NECH) in the CPMG sequence, only the echo signal of bound water with a short relaxation time is measured. Specifically, by setting a very short polarization waiting time, a short echo interval time, and a small number of echoes, the rapidly decaying echo signal is measured; by adjusting the acquisition parameters, only the bound water with a short relaxation time in the pores of the cohesive soil sample is polarized, and only the front-end echo signal needs to be collected.
[0012] Furthermore, when collecting the echo signals of bound water and capillary water, the acquisition parameters are set as follows: the polarization waiting time TW2 = 5 - 100 ms, the echo interval time TE2 ≤ 0.2 ms, and the number of echoes NECH2 = 100 - 1000.
[0013] Preferably, the denser the cohesive soil sample, the smaller the value of TW2 can be.
[0014] The transverse relaxation time T2 of capillary water in the cohesive soil sample is between that of bound water and gravitational water, and the T2 range is 1 - 50 ms. When adjusting the acquisition parameters of the CPMG sequence to collect the capillary water signal, it is inevitable to measure the signal of bound water at the same time, and then specifically extract the capillary water signal in the subsequent signal processing. Specifically, by setting a short polarization waiting time, a short echo spacing time, and a large number of echo numbers, the echo signal is measured. By adjusting the acquisition parameters, the bound water and capillary water in the pores of the cohesive soil sample are polarized, and the collected echo signal contains the echo signal of bound water with a short relaxation time and the echo signal of capillary water with a medium relaxation time.
[0015] Furthermore, when collecting the echo signal of gravitational water, the acquisition parameters are set as follows: the polarization waiting time TW3 ≥ 1000 ms, the echo spacing time TE3 ≥ 20 ms, and the number of echoes NECH3 = 100 - 1000.
[0016] The transverse relaxation time T2 of gravitational water in the cohesive soil sample is very long, greater than 100 ms. In order to specifically measure the echo signal of gravitational water, by adjusting the acquisition parameters in the CPMG sequence, only the echo signal of gravitational water with a long relaxation time is measured. Specifically, by increasing the polarization waiting time, setting a long echo spacing time and a large number of echo numbers, the echo signal with the slowest decay is measured; by adjusting the acquisition parameters, all the water in the pores of the cohesive soil sample is polarized, but only the echo signal with a long relaxation time at the back end is collected.
[0017] Furthermore, the data processing steps include: when inverting the echo signal of bound water, the number of echoes for inversion i = 1, 2, ……, NECH1, to obtain the relaxation time T2 distribution spectrum of bound water.
[0018] Furthermore, the data processing steps include: when performing zonal inversion on the echo signals of bound water and capillary water, the number of echoes for inversion i = , ……, NECH2, to obtain the relaxation time T2 distribution spectrum of capillary water.
[0019] In order to distinguish the echo signals of bound water and capillary water, zonal inversion is required, that is, the number of echoes for starting inversion i does not start from 1, but skips the front echo region with a short relaxation time (i.e., the echo signal of bound water), and starts the inversion from the middle section of the echo signal to obtain the T2 distribution spectrum of capillary water.
[0020] The relaxation time T2 range of bound water is 0.1 - 1 ms. When the acquisition time is greater than or equal to 3 times the relaxation time T2 of bound water (i.e., 3 ms), the bound water signal decays completely. Therefore, the number of echoes for starting inversion i ≥ 。
[0021] Further, the data processing step includes: when inverting the echo signal of gravitational water, the number of inverted echoes i = 1, 2, ……, NECH3, to obtain the relaxation time T2 distribution spectrum of gravitational water.
[0022] In summary, the present application includes the following beneficial technical effects: When identifying fluids with different properties through the T2 distribution spectrum, traditional methods usually use a fixed cut-off value to divide the T2 distribution spectrum. However, when the relaxation times of water in different states overlap in cohesive soil, it is impossible to accurately distinguish water in different states. Although subsequent spectral peak identification methods can improve the discrimination accuracy, they still require complex algorithms, increasing the computational cost. In contrast, the present application designs an independent acquisition scheme for bound water, capillary water, and gravitational water by optimizing the acquisition parameters of the CPMG sequence, realizing the signal discrimination of water in different states at the signal acquisition stage, thereby identifying and accurately measuring water in different states without relying on complex algorithms. This makes the present application have higher accuracy and practicality in the detection and characterization of pore water states in cohesive soil, providing a more reliable technical means for the moisture state analysis in geotechnical engineering. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 is a flowchart of a nuclear magnetic resonance detection method for the pore water state of cohesive soil in an embodiment of the present application; Figure 2 are the echo signal and inversion result of bound water in a cohesive soil sample in an embodiment of the present application, where (a) is the echo signal diagram and (b) is the inversion result diagram; Figure 3 are the echo signal and inversion result of capillary water in a cohesive soil sample in an embodiment of the present application, where (a) is the echo signal diagram and (b) is the inversion result diagram; Figure 4 are the echo signal and inversion result of gravitational water in a cohesive soil sample in an embodiment of the present application, where (a) is the echo signal diagram and (b) is the inversion result diagram. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0024] The following further elaborates on the present application in conjunction with the attached Figures 1-4 for a more detailed description.
[0025] The embodiment of the present application discloses a nuclear magnetic resonance detection method for the pore water state of cohesive soil. Referring to Figure 1 , the nuclear magnetic resonance detection method for the pore water state of cohesive soil includes the following steps: Step 1: Detection of bound water, and the specific method includes: Step 1-1: Collect the nuclear magnetic resonance CPMG echo signals of the cohesive soil sample, set a very short polarization waiting time, a short echo spacing time, and a small number of echo numbers, and obtain the echo signals of the bound water in the cohesive soil sample; the specific acquisition parameter settings are as follows: the polarization waiting time TW1 = 3 ms, the echo spacing time TE1 = 0.1 ms, and the number of echo numbers NECH1 = 50. During the acquisition process, only the bound water is polarized, and only the front echo signals with short relaxation times are collected, as shown in (a) of Figure 2 as shown.
[0026] Step 1-2: Invert the echo signals of the bound water obtained in Step 1-1 to obtain the T2 distribution spectrum of the bound water. The specific method is: The amplitude of the collected echo signals decays with time t in a single exponential decay as shown in Equation (1): Equation (1) In Equation (1), i is the number of echoes, is the i th echo amplitude; is the measurement acquisition time; is the j th transverse relaxation time in the T2 distribution of the transverse relaxation time, m is the total number of transverse relaxation times; is the amplitude corresponding to the j th transverse relaxation time, and by inversion, is obtained, that is, the T2 distribution spectrum is obtained.
[0027] Invert the echo signals of the bound water obtained in Step 1-1 according to Equation (1), and the number of inverted echoes i = 1, 2,..., 50, to obtain the T2 distribution spectrum of the bound water, as shown in (b) of Figure 2 as shown.
[0028] Step 1-3: Perform area integration on the T2 distribution spectrum of the bound water obtained in Step 1-2 according to Equation (2) to obtain the content of the bound water as 5.4 g.
[0029]
[0030] In Equation (2), is the water mass in the cohesive soil sample; and are the maximum and minimum values of the T2 distribution spectrum, respectively.
[0031] Step 2: Capillary water detection. The specific method includes: Step 2-1: Collect the nuclear magnetic resonance CPMG echo signals of the cohesive soil sample, set a short polarization waiting time, a short echo spacing time, and a large number of echo numbers to obtain the echo signals of the bound water and capillary water in the cohesive soil sample; the specific acquisition parameter settings are as follows: the polarization waiting time TW2 = 25 ms, the echo spacing time TE2 = 0.1 ms, and the number of echoes NECH2 = 500. During the acquisition process, both the bound water and capillary water are polarized, and the acquired echo signals contain the echo signals of the bound water and capillary water, as shown in Figure 3 as shown in (a) of
[0032] Step 2-2: Perform zonal inversion on the echo signals of the bound water and capillary water obtained in Step 2-1 according to formula (1), and the number of inverted echoes i = 30, 31, ……, 500, as shown in Figure 3 as shown in (a) of i That is, skip the front echo region with short relaxation time (i.e., the echo signal of the bound water), and start the inversion from the middle section of the echo signal i = 30 to obtain the T2 distribution spectrum of the capillary water, as shown in Figure 3 as shown in (b) of Step 2-3: Perform area integration on the T2 distribution spectrum of the capillary water obtained in Step 2-2 according to formula (2) to obtain the content of the bound water as 5.3 g.
[0033] Step 3: Detection of gravitational water, the specific method includes: Step 3-1: Collect the nuclear magnetic resonance CPMG echo signals of the cohesive soil sample, set a long polarization waiting time, a long echo spacing time, and a large number of echo numbers to obtain the echo signals of the gravitational water in the cohesive soil sample; the specific acquisition parameter settings are as follows: the polarization waiting time TW3 = 1000 ms, the echo spacing time TE3 = 20 ms, and the number of echoes NECH3 = 100. During the acquisition process, the bound water, capillary water, and gravitational water are all polarized, and only the back-end echo signals with long relaxation time are collected, as shown in Figure 4 as shown in (a) of
[0034] Step 3-2: Invert the echo signals of the gravitational water obtained in Step 3-1 according to formula (1), and the number of inverted echoes i = 1, 2, ……, 100 to obtain the T2 distribution spectrum of the gravitational water, as shown in Figure 4 as shown in (b) of
[0035] Step 3-3: Perform area integration on the T2 distribution spectrum of the gravitational water obtained in Step 3-2 according to formula (2) to obtain the content of the gravitational water as 5.4 g.
[0036] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims
1. A method for detecting the state of pore water in clay soil by nuclear magnetic resonance, characterized in that: The following steps are involved: Bound water detection: collect nuclear magnetic resonance CPMG echo signals of clay soil samples, set polarization waiting time TW1, echo interval time TE1, and echo number NECH1 to obtain the echo signals of bound water in clay soil samples; invert the echo signals of bound water to obtain the T2 distribution spectrum of bound water; calculate the content of bound water from the T2 distribution spectrum of bound water; Capillary water detection: collect nuclear magnetic resonance CPMG echo signals of clay soil samples, set the polarization waiting time TW2, echo interval time TE2, and echo number NECH2, and obtain the echo signals of bound water and capillary water in the clay soil samples; perform partition inversion on the echo signals of bound water and capillary water to obtain the T2 distribution spectrum of capillary water; calculate the content of capillary water from the T2 distribution spectrum of capillary water; Gravity water detection: collect nuclear magnetic resonance CPMG echo signals from clay soil samples, set the polarization waiting time TW3, echo interval time TE3, and echo number NECH3 to obtain the echo signals of gravity water in clay soil samples; invert the echo signals of gravity water to obtain the T2 distribution spectrum of gravity water; calculate the content of gravity water from the T2 distribution spectrum of gravity water; Among them, TW1 <TW2<TW3,TE1≤TE2<TE3,NECH1<NECH3<NECH2。 2. The method for detecting the pore water state of clay soil by nuclear magnetic resonance according to claim 1, characterized in that: In the bound water detection step, when the echo signal of bound water is collected, only the bound water is polarized, and only the front echo signal with a short relaxation time is collected.
3. The method for detecting the pore water state of clay soil by nuclear magnetic resonance according to claim 2, characterized in that: In the capillary water detection step, when the echo signals of bound water and capillary water are collected, both the bound water and the capillary water are polarized, and the collected echo signals include the echo signals of bound water and capillary water.
4. The method for detecting the pore water state of clay soil by nuclear magnetic resonance according to claim 3, characterized in that: In the gravity water detection step, when collecting the echo signal of gravity water, the bound water, capillary water and gravity water are all polarized, and only the back-end echo signal with a long relaxation time is collected.
5. The method for detecting the pore water state of clay soil by nuclear magnetic resonance according to claim 2, characterized in that: When collecting the echo signal of bound water, the acquisition parameters are set as follows: polarization waiting time TW1=1-5ms, echo interval time TE1≤0.2ms, and echo number NECH1≤100.
6. The method for detecting the state of pore water in clay soil by nuclear magnetic resonance according to claim 3, characterized in that: When collecting the echo signals of bound water and capillary water, the acquisition parameters are set as follows: polarization waiting time TW2=5-100ms, echo interval time TE2≤0.2ms, and echo number NECH2=100-1000.
7. The method for detecting the state of pore water in clay soil by nuclear magnetic resonance according to claim 4, characterized in that: When collecting the echo signal of gravity water, the acquisition parameters are set as follows: polarization waiting time TW3 ≥ 1000ms, echo interval time TE3 ≥ 20ms, and echo number NECH3 = 100-1000.
8. The method for detecting the state of pore water in clay soil by nuclear magnetic resonance according to claim 5, characterized in that: When inverting the echo signal of bound water, the number of inverted echoes i = 1, 2, …, NECH1, and obtain the relaxation time T2 distribution spectrum of bound water.
9. The method for detecting the state of pore water in clay soil by nuclear magnetic resonance according to claim 6, characterized in that: When performing partition inversion on the echo signals of bound water and capillary water, the number of inverted echoes i = ,…,NECH2, and obtain the relaxation time T2 distribution spectrum of capillary water.
10. The method for detecting the state of pore water in clay soil by nuclear magnetic resonance according to claim 7, characterized in that: When inverting the echo signal of gravity water, the number of inverted echoes i =1, 2, ..., NECH3, and obtain the relaxation time T2 distribution spectrum of gravitational water.