Method for testing change of clay permeability along with temperature
By using nuclear magnetic resonance technology and dry fine sand calibration experiments, the problem of measuring clay permeability at different temperatures was solved, enabling rapid and accurate permeability assessment and resolving the issue of large measurement errors in existing technologies.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-03-24
AI Technical Summary
Existing technologies are insufficient to accurately determine the permeability of cohesive soils at different temperatures, and conventional permeameters have large testing errors, making it difficult to change the temperature to affect the test results.
The permeability of clay was determined by nuclear magnetic resonance (NMR) technology. Soil samples were prepared by vacuum saturation method. Relaxation signals were collected at different temperatures using a constant temperature chamber and NMR instrument. The relationship between temperature and NMR signal intensity was established by combining dry fine sand calibration experiments, and the permeability of clay was calculated.
It enables non-destructive quantitative assessment of clay permeability, quickly and accurately measuring changes in clay permeability, avoiding the need for long-term permeability testing, and is highly efficient and accurate.
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Figure CN121721074A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soil testing technology, and in particular to a method for testing the change of clay permeability with temperature. Background Technology
[0002] Clayey soil, as a type of low-permeability soil, acts as a water barrier and is widely distributed in nature, such as at the bottom of riverbeds and on top of underground sand layers in the Yangtze River Delta plain. However, the permeability of clayey soil is not constant; it increases with rising temperature. Changes in permeability affect the interaction between clayey soil and groundwater. For example, during nuclear waste disposal, heat is continuously released, causing the permeability of backfilled clayey soil to change with temperature, thus affecting the migration of radionuclides.
[0003] Because of the low permeability of cohesive soil, conventional permeameters have low flow rates and large testing errors when measuring its permeability, and it is difficult to change the temperature of the testing environment. Therefore, it is a challenge to measure the permeability of cohesive soil at different temperatures. Summary of the Invention
[0004] The purpose of this invention is to provide a method for testing the change of clay permeability with temperature, aiming to solve or improve at least one of the above-mentioned technical problems.
[0005] To achieve the above objectives, the present invention provides the following solution: A method for testing the change of clay permeability with temperature, comprising: S1. Determine the initial permeability of the soil under test using a permeameter at room temperature. k 0, while recording the indoor temperature T 0; S2. Place the cohesive soil sample to be tested into a polytetrafluoroethylene soil sample tube and saturate the soil sample using the vacuum saturation method. S3. Seal the saturated soil sample from S2 and place it in a constant temperature chamber for more than 30 minutes. The temperature inside the constant temperature chamber is set to 30℃, 40℃, 50℃ and 60℃ successively. Before each temperature change, place the soil in a nuclear magnetic resonance spectrometer and use the CPMG sequence to collect the relaxation signal of the soil sample at different temperatures and draw the relaxation spectrum of the soil. S4. Prepare a dry fine sand sample, place it in a polytetrafluoroethylene soil sample tube, weigh the dry sand and the soil sample tube, and titrate with a predetermined amount of water. m w Repeat step S3 to measure the total sustained signal intensity of the fine sand at different temperatures. M T The nuclear magnetic resonance signal and temperature calibration line per unit mass of water were plotted to calibrate the relationship between nuclear magnetic resonance signal intensity and water mass at different temperatures. S5, using the calibration straight line drawn in step S4 to calibrate the relaxation spectrum in step S3, converting the vertical coordinate nuclear magnetic signal strength into water quality; S6, using the relaxation spectrum calibrated in S5 to T 2<10 ms statistically analyze the signals, calculate the logarithmic average of the relaxation time distribution at different temperatures, draw the relationship between the logarithmic average of the relaxation time distribution and the temperature, and fit the slope of the straight line a ; S7, using the slope of the straight line obtained in step S6 a to calculate the permeability of the clay at different temperatures.
[0006] Optionally, in S3, after each change in temperature, twist off the top and bottom of the soil sample tube to release some water and balance the internal pressure.
[0007] Optionally, in S4, the relationship between the nuclear magnetic signal strength and water quality at different temperatures is specifically calibrated as follows: Set the nuclear magnetic resonance signal strength of unit mass water at temperature T to , and sequentially calculate the nuclear magnetic signal strength , , and at different temperatures: ; According to the calculated nuclear magnetic signal strength, draw the nuclear magnetic resonance signal of unit mass water and the temperature calibration straight line, and based on the fitting straight line formula , calibrate the relationship between the nuclear magnetic signal strength and water quality at different temperatures; wherein, i is the slope of the fitting straight line, j is the intercept of the fitting straight line.
[0008] Optionally, in S5, the specific calculation process for converting the vertical coordinate nuclear magnetic signal strength into water quality includes: Using the nuclear magnetic signal strength at different temperatures in S4 to correct the nuclear magnetic signal strength in S3, to obtain the water quality T 2 S i ; According to the calculated water quality S i , draw the calibrated relaxation spectrum.
[0009] Optionally, in S6, the formula for calculating the logarithmic average of the relaxation time distribution at different temperatures is: ; wherein, represents the transverse relaxation time, S i represents the water quality, ln( T 2 LM ) represents T the logarithmic average of 2.
[0010] Optionally, in the S7, the permeability calculation formula of the clay at different temperatures is: ; wherein, is T the permeability at the temperature, is the initial permeability, is the initial density, is the initial water dynamic viscosity, is T the density at the temperature, is T the water dynamic viscosity at the temperature, is the initial temperature.
[0011] According to the specific embodiments provided by the present application, the following technical effects are disclosed: The application discloses a testing method for the change of clay permeability with temperature, which analyzes the change of clay permeability with temperature through nuclear magnetic resonance technology. Firstly, the initial permeability of a soil sample is determined and the soil sample is vacuum saturated, and then nuclear magnetic resonance relaxation signals are collected at different constant temperatures of 30 DEG C to 60 DEG C. A quantitative relationship between temperature and nuclear magnetic signal intensity is established through a dry fine sand calibration experiment, and the relaxation spectrum signal is converted into water quality. Finally, the permeability of clay at different temperatures is calculated based on the fitting slope of the logarithmic average of T2 spectrum and temperature. The method realizes the nondestructive quantitative evaluation of the clay permeability under the influence of temperature. The application can determine the flowability of water molecules in clay based on low-field nuclear magnetic resonance technology. The determination method only needs to determine the initial permeability, and does not need to perform a long-time permeability test after changing the temperature each time, and has the advantages of rapidness and high efficiency. BRIEF DESCRIPTION OF DRAWINGS
[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.
[0013] Figure 1 It is a flow chart of the testing method for the change of clay permeability with temperature of the present application; Figure 2 It is a relaxation spectrum graph at different temperatures in the present embodiment; Figure 3 The linear graph for calibrating the nuclear magnetic resonance signal to temperature in the embodiment; Figure 4 The relaxation spectrum graph after calibration at different temperatures in the embodiment; Figure 5 The linear relationship diagram of the logarithmic average value of T2 at different temperatures in the embodiment. DETAILED DESCRIPTION
[0014] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.
[0015] The purpose of the present application is to provide a testing method for the change of clay permeability with temperature, aiming to solve or improve at least one of the above technical problems.
[0016] In order to make the above purposes, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.
[0017] As shown in Figure 1 The present application provides a testing method for the change of clay permeability with temperature, comprising: S1, measuring the permeability of the soil to be tested at room temperature by using a permeameter k 0, record the indoor temperature at the same time T 0.
[0018] S2, the clay sample to be tested is placed in a polytetrafluoroethylene soil sample tube, and the soil sample is saturated by using a vacuum saturation method; a screw cap is arranged at the top and bottom of the soil sample tube, and the screw cap can balance the pressure after heating and eliminate the influence of the heating pressure.
[0019] S3, the saturated soil sample in S2 is sealed and placed in a thermostat for more than 30 minutes, and the temperature in the thermostat is set to 30℃, 40℃, 50℃ and 60℃ in sequence; before changing the temperature each time, the soil is placed in a nuclear magnetic resonance instrument, and the relaxation signal of the soil sample at different temperatures is collected by using a CPMG sequence, and a relaxation spectrum graph of the soil is drawn: (1) after changing the temperature each time, the top and bottom of the soil sample tube are unscrewed to release part of the water and balance the internal pressure.
[0020] (2) the CPMG sequence parameters are shown in Table 1: Table 1 CPMG sequence parameters
[0021] (3) such as Figure 2 As shown, the vertical axis of the relaxation spectrum represents the nuclear magnetic resonance signal intensity. M i The horizontal axis represents the horizontal relaxation. T 2.
[0022] S4. Prepare a dry fine sand sample, place it in a polytetrafluoroethylene soil sample tube, weigh the dry sand and the soil sample tube, and titrate a certain amount of water. m w Repeat step S3 to measure the total sustained signal intensity of the fine sand at different temperatures. M T Plot the nuclear magnetic resonance signal and temperature calibration line for a unit mass of water, and calibrate the relationship between nuclear magnetic resonance signal intensity and water mass at different temperatures.
[0023] (1) T The nuclear magnetic resonance signal intensity per unit mass of water at the temperature is Calculate in sequence , , , : ; (2) According to , , , Plot the nuclear magnetic resonance signal and temperature calibration line per unit mass of water (e.g.) Figure 3 As shown), based on the fitted straight line formula The relationship between NMR signal intensity and water quality at different temperatures was determined.
[0024] S5. The calibration line drawn in step S4 is used to calibrate the relaxation spectrum tested in step S3, and the NMR signal intensity on the vertical axis is converted into water mass: (1) According to S4 , , , The nuclear magnetic resonance signal intensity in S3 M i Corrections were made to obtain different soil samples. T2 Water quality S i .
[0025] ; (2) Draw the calibrated relaxation spectrum (e.g.) Figure 4 (As shown).
[0026] S6. Using the relaxation spectrum calibrated in S5,T 2<10 ms Statistical analysis of the signals ， Calculate the logarithmic mean of the relaxation time distribution at different temperatures, plot the relationship between the logarithmic mean of the relaxation time distribution and temperature, and perform a linear fit on this relationship to obtain the slope. a .
[0027] (1) The logarithmic mean of the relaxation time distribution at different temperatures is calculated as follows: ; In the formula: Indicates the lateral relaxation time. S i To represent the mass of water, ln( T 2 LM )express T The logarithmic mean of 2.
[0028] (2) Plot the relationship between the logarithmic mean of the relaxation time distribution and temperature as follows: Figure 5 As shown, a linear fit is performed, and the slope is... a .
[0029] S7. Using the slope obtained in step S6 a= 0.028, calculate the permeability of cohesive soil at different temperatures: ; in, for T Permeability at temperature Initial penetration rate, For the initial density, The initial hydrodynamic viscosity, for T Density at temperature for T Hydrodynamic viscosity at temperature This is the initial temperature.
[0030] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.
[0031] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.
Claims
1. A method for testing the change of clay permeability with temperature, characterized in that, include: S1. Determine the initial permeability of the soil under test using a permeameter at room temperature. k 0, while recording the indoor temperature T 0; S2. Place the cohesive soil sample to be tested into a polytetrafluoroethylene soil sample tube and saturate the soil sample using the vacuum saturation method. S3. Seal the saturated soil sample from S2 and place it in a constant temperature chamber for more than 30 minutes. The temperature inside the constant temperature chamber is set to 30℃, 40℃, 50℃ and 60℃ successively. Before each temperature change, place the soil in a nuclear magnetic resonance spectrometer and use the CPMG sequence to collect the relaxation signal of the soil sample at different temperatures and draw the relaxation spectrum of the soil. S4. Prepare a dry fine sand sample, place it in a polytetrafluoroethylene soil sample tube, weigh the dry sand and the soil sample tube, and titrate with a predetermined amount of water. m w Repeat step S3 to measure the total sustained signal intensity of the fine sand at different temperatures. M T The nuclear magnetic resonance signal and temperature calibration line per unit mass of water were plotted to calibrate the relationship between nuclear magnetic resonance signal intensity and water mass at different temperatures. S5. Use the calibration line drawn in step S4 to calibrate the relaxation spectrum tested in step S3, and convert the NMR signal intensity on the vertical axis into water mass. S6. Using the relaxation spectrum calibrated in S5, T 2<10 ms Statistical analysis was performed on the signal, and the logarithmic mean of the relaxation time distribution at different temperatures was calculated. The relationship between the logarithmic mean of the relaxation time distribution and temperature was plotted, and the slope of the fitted straight line was determined. a ; S7. Using the slope of the straight line obtained in step S6 a Calculate the permeability of cohesive soil at different temperatures.
2. The method for testing the change of clay permeability with temperature according to claim 1, characterized in that, In step S3, after each temperature change, the top and bottom of the soil sample tube are unscrewed to release some water and balance the internal pressure.
3. The method for testing the change of clay permeability with temperature according to claim 1, characterized in that, In step S4, the relationship between NMR signal intensity and water quality at different temperatures is specifically calibrated as follows: Set temperature T The nuclear magnetic resonance signal intensity per unit mass of water is The nuclear magnetic resonance signal intensity at different temperatures was calculated sequentially. , , and : ； Based on the calculated NMR signal intensities, a straight line was plotted between the NMR signal and temperature calibration per unit mass of water. This was then used to fit the straight line using the formula... The relationship between NMR signal intensity and water quality at different temperatures was calibrated; among them, i The slope of the fitted line, j This is the intercept of the fitted line.
4. The method for testing the change of clay permeability with temperature according to claim 1, characterized in that, In step S5, the specific calculation process for converting the vertical axis NMR signal intensity into water mass includes: By correcting the NMR signal intensity in S3 using the NMR signal intensity at different temperatures in S4, different transverse relaxations in the soil can be obtained. T Water quality under 2 S i ; Based on the calculated water quality S i Draw the calibrated relaxation spectrum.
5. The method for testing the change of clay permeability with temperature according to claim 1, characterized in that, In step S6, the formula for calculating the logarithmic mean of the relaxation time distribution at different temperatures is as follows: ； in, Indicates the lateral relaxation time. S i To represent the mass of water, ln( T 2 LM )express T The logarithmic mean of 2.
6. The method for testing the change of clay permeability with temperature according to claim 1, characterized in that, In S7, the formula for calculating the permeability of cohesive soil at different temperatures is as follows: ； in, for T Permeability at temperature Initial penetration rate, For the initial density, The initial hydrodynamic viscosity, for T Density at temperature for T Hydrodynamic viscosity at temperature This is the initial temperature.