Method and device for testing moisture migration in frost heaving and thaw collapse process of fiber cement soil based on low-field nuclear magnetic resonance

Abstract

The invention discloses a method and device for testing moisture migration in the frost heaving and thaw collapse process of fiber cement soil based on low-field nuclear magnetic resonance, and relates to the field of cement soil testing engineering.The method comprises the steps that T2 spectrums of the whole freezing process and the whole thawing process of a fiber cement soil sample are obtained; inverting a three-dimensional moisture distribution diagram of the whole freezing process and the whole melting process of the fiber cement soil sample according to the T2 spectrum; and determining moisture migration conditions of the whole freezing process and the whole melting process of the fiber cement soil sample according to the three-dimensional moisture distribution diagrams of the whole freezing process and the whole melting process of the fiber cement soil sample. According to the method, T2 spectrum data is mapped to a three-dimensional space position on the basis of a nuclear magnetic resonance (NMR) signal gradient positioning technology, and a pixel-level three-dimensional moisture distribution diagram of a fiber cement soil sample is obtained by performing data inversion on a T2 spectrum, so that pixel-level moisture migration conditions in the freezing process and the melting process of the fiber cement soil are visualized.

Description

Technical Field

[0001] This application relates to the field of cement soil testing engineering, and particularly to a method and device for testing water migration during the frost heaving and thaw settlement processes of fiber cement soil based on low-field nuclear magnetic resonance. Background Technique

[0002] The artificial ground freezing method is widely used in the construction process of underground engineering. However, soil often generates frost heaving and thaw settlement deformations during the freezing process, which is one of the main freezing responses of soil directly related to freezing method construction. It brings relatively high risks to the safety and stability of underground engineering construction, and at the same time generates pressure and deformation on structures above or below the ground, which may lead to structural damage or failure. In order to reduce frost heaving and thaw settlement deformations and enhance the strength of soil, on-site grouting is adopted. After using cement to improve and reinforce the soil to form cement soil, artificial freezing method construction is carried out; through the method of cement reinforcement, the effect of the freezing method can be further optimized from two aspects of inhibiting frost heaving and thaw settlement deformations and increasing strength, bringing greater guarantee to the construction safety, and having wide applications in underground engineering construction and complex working conditions.

[0003] With the progress of technology, the fiber incorporation technology also shows the potential in improving the mechanical properties of soil and reducing the problems of frost heaving and thaw settlement deformations. The incorporation of fibers can partially undertake the role of cement, reduce the cement dosage, thus significantly reducing the carbon footprint and environmental impact of the project, forming a green and environmentally friendly method; especially plant fibers, such as sisal fibers, have excellent tensile strength (mechanical properties) and water absorption. Therefore, exploring the thaw settlement deformation characteristics of fiber cement soil at different temperatures and different pressures and explaining its mechanism from the perspective of water migration can provide relevant references for the design and application of the freezing method in soft soil strata in coastal areas, so as to advocate more green, economical and safe underground engineering construction in coastal areas.

[0004] The existing water migration tests mainly adopt image recognition technology or X-ray tomography technology. X-ray scanning uses the absorption differences of rays by substances with different densities when X-rays penetrate the sample, and generates internal tomographic images through computer reconstruction, but the sample size is limited and the test takes a long time. Image recognition technology is a newly emerging technology in recent years that combines computer vision algorithms with cameras to identify and extract water, but the resolution is limited, and the requirements for shooting accuracy and noise interference are relatively high. Therefore, there are certain deficiencies in the accuracy of the analysis results of the existing water migration conditions. Summary of the Invention

[0005] The purpose of this application is to provide a method and device for testing water migration during the frost heaving and thaw settlement processes of fiber cement soil based on low-field nuclear magnetic resonance, which can analyze the water migration situation during the freezing process and melting process of fiber cement soil in real time and accurately.

[0006] To achieve the above object, the present application provides the following solutions: In a first aspect, the present application provides a method for testing water migration during the frost heaving and thaw settlement processes of fiber cement soil based on low-field nuclear magnetic resonance, including: Obtaining the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process; the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process are the T2 spectra obtained based on low-field nuclear magnetic resonance technology during the frost heaving and thaw settlement test of the fiber cement soil sample; Inverting the pixel-level three-dimensional water distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process based on the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process; Determining the pixel-level water migration conditions of the fiber cement soil sample during the entire freezing process and the entire melting process based on the pixel-level three-dimensional water distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process.

[0007] In a second aspect, the present application provides a device for testing water migration during the frost heaving and thaw settlement processes of fiber cement soil based on low-field nuclear magnetic resonance, including: A triaxial pressure component for simulating the true confining pressure and true axial pressure of the fiber cement soil sample in the target environment; A seepage component for simulating the true seepage situation of the fiber cement soil sample in the target environment; A temperature adjustment component for gradually freezing the fiber cement soil sample to the target temperature and gradually melting the frozen fiber cement soil sample; An imaging monitoring component for real-time collecting the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process based on low-field nuclear magnetic resonance technology; A data analysis component for executing the above method for testing water migration during the frost heaving and thaw settlement processes of fiber cement soil based on low-field nuclear magnetic resonance.

[0008] According to the specific embodiments provided by the present application, the following technical effects are disclosed: The present application provides a method and device for testing water migration during the freezing and thawing settlement of fiber cement soil based on low-field nuclear magnetic resonance, obtaining the T2 spectra of the entire freezing process and the entire thawing process of the fiber cement soil sample; inversely calculating the three-dimensional water distribution maps of the entire freezing process and the entire thawing process of the fiber cement soil sample from the T2 spectra of the entire freezing process and the entire thawing process of the fiber cement soil sample; and further determining the water migration situation of the entire freezing process and the entire thawing process of the fiber cement soil sample. The present application utilizes low-field nuclear magnetic resonance (LF-NMR) technology, through the inversion calculation of the T2 relaxation spectrum, constructs the water distribution image of the fiber cement soil sample at different freezing and thawing stages, and further determines the water migration situation. Different from the traditional image acquisition method, the present application is based on the nuclear magnetic resonance NMR signal gradient positioning technology, maps the T2 spectral data to three-dimensional spatial positions, and obtains the pixel-level three-dimensional water distribution map of the fiber cement soil sample through data inversion of the T2 spectrum, thereby realizing the visualization of the pixel-level water migration situation during the freezing process and the thawing process of the fiber cement soil and achieving high-precision analysis of water migration. Description of the Drawings

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0010] Figure 1 It is a flowchart of a method for testing water migration during the freezing and thawing settlement of fiber cement soil based on low-field nuclear magnetic resonance provided by an embodiment of the present application; Figure 2 It is a structural schematic diagram of a device for testing water migration during the freezing and thawing settlement of fiber cement soil based on low-field nuclear magnetic resonance provided by an embodiment of the present application; Figure 3 It is a structural schematic diagram of a triaxial compression assembly provided by an embodiment of the present application; Figure 4 It is a structural schematic diagram of a specimen unit provided by an embodiment of the present application; Figure 5 It is a schematic diagram of a testing process implemented by introducing specific components provided by an embodiment of the present application; Figure 6 It is a schematic diagram of water migration during the thawing process provided by an embodiment of the present application; Reference Numerals: 1. Imaging monitoring component, 2. Triaxial compression component, 3. Confining pressure chamber, 4. Specimen unit, 5. Upper ejector rod, 6. Lower ejector rod, 7. Upper plug, 8. Sealing ring, 9. Permeable stone, 10. Filter paper, 11. Latex film, 12. Lower plug, 13. Seepage outlet pipeline, 14. Seepage inlet pipeline, 15. Low-temperature circulation pump, 16. Circulation pipeline, 17. Three-way valve, 18. Confining pressure pipeline, 19. Axial pressure pipeline, 20. Peristaltic pump, 21. Compensation pipeline, 22. Triaxial pressure controller, 23. Seepage pipeline, 24. Connecting valve. Detailed implementation manner

[0011] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying 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 of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0012] Nuclear magnetic resonance is widely used in detecting the pore structure of cores, identifying the synthesis and decomposition of natural gas hydrates, and measuring the unfrozen water content in frozen soil. Compared with traditional testing methods for frost heaving and thaw settlement characteristics, nuclear magnetic resonance is the only method that can directly and non-destructively detect the water molecule content. Therefore, the present application proposes a method and device for testing water migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance, which can analyze the water migration situation during the freezing process and melting process of fiber cement soil in real time, dynamically, and accurately.

[0013] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0014] In an exemplary embodiment of the present application, a method for testing water migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance is proposed, as Figure 1 shown, including the following steps.

[0015] S1: Obtain the T2 spectra of the entire freezing process and the entire melting process of the fiber cement soil sample; the T2 spectra of the entire freezing process and the entire melting process of the fiber cement soil sample are the T2 spectra obtained based on low-field nuclear magnetic resonance technology during the frost heaving and thaw settlement test of the fiber cement soil sample.

[0016] S2: Invert the pixel-level three-dimensional water distribution maps of the entire freezing process and the entire melting process of the fiber cement soil sample according to the T2 spectra of the entire freezing process and the entire melting process of the fiber cement soil sample.

[0017] S3: Determine the pixel-level moisture migration conditions of the fiber cement soil sample during the entire freezing process and the entire melting process based on the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process.

[0018] In this application, combining the real-time and convenience of the frost heaving and thaw settlement tests and nuclear magnetic imaging, the T2 spectra are collected in real time at different freeze-thaw stages to reveal the moisture migration law of the fiber cement soil. Different from the traditional image acquisition methods, the test method of this application is based on the NMR signal gradient positioning technology. By mapping the T2 spectrum data to the three-dimensional spatial position, the visualization of the pixel-level moisture migration process is realized, and the moisture migration conditions during the freezing process and the melting process of the fiber cement soil can be analyzed in real time and dynamically, and the accuracy of the test results and the test efficiency are improved.

[0019] In another exemplary embodiment of this application, in step S2, according to the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process, the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process are inversely calculated, specifically including: (2-1) Determine the three-dimensional spatial distribution information of each pixel point of the fiber cement soil sample during the entire freezing process and the entire melting process according to the three-dimensional gradient magnetic field in the low-field nuclear magnetic resonance technology.

[0020] Three-dimensional space filling: The T2 spectral signals of each pixel point in the XYZ three-dimensional space are accurately positioned at the signal source position through the gradient magnetic field, so as to remap the collected initial T2 signal (the time-domain signal decaying with time) into a spatial distribution, and generate a T2 spectrum with three-dimensional spatial distribution information.

[0021] (2-2) Determine the moisture state of each pixel point according to the T2 spectrum with three-dimensional spatial distribution information by applying the Laplace inverse transform method or the BRD regularization inversion algorithm.

[0022] Through the Laplace inverse transform or the BRD regularization inversion algorithm for T2 spectrum inversion, the T2 relaxation time of each pixel point is obtained, and then different moisture states are obtained. For example: The T2 relaxation time < 1 ms indicates that the water at this position is bound water; 1 ms < T2 relaxation time < 10 ms indicates that the water at this position is capillary water; The T2 relaxation time > 10 ms indicates that the water at this position is free water; For example, the T2 relaxation time of the pixel point (x = 5, y = 7, z = 2) is 3 ms, and it can be located that the water at this position is mainly capillary water.

[0023] (2-3) Construct the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process according to the moisture state of each pixel point in the T2 spectrum.

[0024] In the pixel-level three-dimensional moisture distribution map of the fiber cement soil sample, the three-dimensional spatial position of each pixel point (or simply each point) of the fiber cement soil sample is determined, and the moisture state at each pixel point is also determined.

[0025] In another exemplary embodiment of the present application, in step S3, according to the pixel-level three-dimensional moisture distribution maps of the entire freezing process and the entire melting process of the fiber cement soil sample, the pixel-level moisture migration situation of the fiber cement soil sample during the entire freezing process and the entire melting process is determined, specifically including: (3-1) Analyze the evolution of moisture in the same position in the fiber cement soil sample based on the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the entire freezing process of the fiber cement soil sample, and obtain the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire freezing process.

[0026] Step (3-1) analyzes the evolution of moisture in the same position in the fiber cement soil sample based on the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the entire freezing process of the fiber cement soil sample, and obtains the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire freezing process, specifically including: 1) Use an interpolation algorithm to interpolate and fill the moisture state of each pixel point in the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample at each acquisition moment during the entire freezing process.

[0027] 2) Analyze the evolution of moisture in the same position in the fiber cement soil sample based on the interpolated and filled moisture state, and obtain the continuous pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire freezing process.

[0028] (3-2) Analyze the evolution of moisture in the same position in the fiber cement soil sample based on the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the entire melting process of the fiber cement soil sample, and obtain the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire melting process.

[0029] In order to obtain the continuous pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire melting process, an interpolation algorithm can be used to interpolate and fill the moisture state of each pixel point in the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample at each acquisition moment during the entire melting process, and analyze the evolution of moisture in the same position in the fiber cement soil sample based on the interpolated and filled moisture state, and obtain the continuous pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the entire melting process.

[0030] (3-3) Analyze the pixel-level three-dimensional moisture distribution maps corresponding to each acquisition moment during the entire freezing process and the entire melting process, and obtain the pixel-level moisture migration situation inside the fiber cement soil sample corresponding to each acquisition moment.

[0031] In order to analyze the pixel-level moisture migration inside the fiber cement soil sample at a certain time between the set acquisition times, an interpolation algorithm can be used to interpolate and fill the moisture state of each pixel point in the pixel-level three-dimensional moisture distribution map at each acquisition time during the entire freezing / thawing process of the fiber cement soil sample, and then analyze the pixel-level moisture migration situation at a certain time between the set acquisition times based on the interpolated and filled moisture state.

[0032] Perform LF-NMR tests at different freeze-thaw stages, combine the T2 spectrum data with the spatial position (XYZ coordinates) to construct a three-dimensional moisture distribution image, which is characterized by different grayscales. The grayscale image can be adjusted into a pseudo-color image. Record the evolution of the moisture state at the same position through periodic scanning to analyze the moisture migration path. The grayscale change of the same coordinate point at different freeze-thaw stages reflects the moisture change. Record the distribution of the moisture state at different positions at the same time to analyze the moisture distribution change at the same time.

[0033] In this application, the moisture migration situation is obtained by analyzing and processing the T2 spectrum data. The source position of the signal is located by the gradient magnetic field and converted into an image. Different moisture contents and moisture migration states will result in different signal intensities, thus presenting different brightness and contrast. By periodically obtaining the nuclear magnetic imaging of the specimen, the migration trajectory of moisture inside the soil body can be observed. In addition, this application can also analyze the influence of freezing and thawing and fiber incorporation on the moisture migration distribution according to the moisture migration path in the fiber cement soil sample.

[0034] In another exemplary embodiment of this application, after performing step S3 "determine the pixel-level moisture migration situation of the fiber cement soil sample during the entire freezing process and the entire melting process according to the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the entire freezing process and the entire melting process", the method for testing moisture migration during the frost heaving and thawing settlement process of fiber cement soil based on low-field nuclear magnetic resonance includes: (1) Compare the moisture migration situations of fiber cement soil samples with different fiber contents during the entire freezing process, and analyze the fiber reinforcement mechanism of the fiber cement soil sample during the entire freezing process.

[0035] (2) Compare the moisture migration situations of fiber cement soil samples with different fiber contents during the entire melting process, and analyze the fiber reinforcement mechanism of the fiber cement soil sample during the entire melting process.

[0036] In another exemplary embodiment of this application, in step S1, obtaining the T2 spectra of the fiber cement soil sample during the entire freezing process and the entire melting process specifically includes: (1-1) Simulate the true confining pressure, true axial pressure, and true seepage conditions of the fiber cement soil sample in the target environment.

[0037] Before performing step (1-1) "simulating the true confining pressure, true axial pressure, and true seepage conditions of the fiber cement soil sample in the target environment", the method for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance includes: Prepare a fiber cement soil sample according to the common construction plan of the artificial ground freezing method and the designed fiber incorporation ratio, and cure the fiber cement soil sample according to the standard curing period.

[0038] As an example, design a test plan according to the common construction plan of the artificial ground freezing method, configure cement with an incorporation ratio of 8% and fibers with an incorporation ratio of 0.3% to prepare a fiber cement sample. Stir the air-dried and sieved soil sample and cement evenly, dry mix after adding fibers, and then add water and mix until uniform; load the mixture into the mold in 3 layers, vibrate the mold once for each layer to exhaust air bubbles, then scrape off the excess fiber cement soil on the top of the sample, cover it with plastic wrap, and demold after standing for 24 hours, and complete the sample preparation after curing in the curing box for 14 days.

[0039] (1-2) Gradually freeze the fiber cement soil sample to the target temperature, and collect the T2 spectrum of the entire freezing process of the fiber cement soil sample in real time.

[0040] Gradually freezing the fiber cement soil sample to the target temperature specifically includes: Freeze the fiber cement soil sample according to the freezing temperature gradient, and during the freezing process, keep the confining pressure on the fiber cement soil sample at the preset confining pressure value and keep the axial pressure on the fiber cement soil sample at the preset axial pressure value.

[0041] (1-3) Gradually melt the frozen fiber cement soil sample, and collect the T2 spectrum of the entire melting process of the frozen fiber cement soil sample in real time. Scanning can be performed at each temperature node.

[0042] Gradually melting the frozen fiber cement soil sample specifically includes: Melt the fiber cement soil sample according to the melting temperature gradient, and during the melting process, keep the confining pressure on the fiber cement soil sample at the preset confining pressure value and keep the axial pressure on the fiber cement soil sample at the preset axial pressure value. During the entire freeze-thaw process, keep the axial pressure at 0.02 kN to ensure that the displacement sensor can measure the true value.

[0043] In another exemplary embodiment of the present application, before performing "collecting the T2 spectrum of the entire freezing process of the fiber cement soil sample in real time" in step (1-2), the method for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance includes: (1) Scanning settings: Select the basic imaging sequence The HSE (Hahn Spin Echo sequence) is used to excite the relaxation signal with radio frequency pulses to improve the signal-to-noise ratio and optimize the short relaxation time (the relaxation time of the moisture inside the cement soil is relatively short).

[0044] (2) Parameter settings To improve the signal quality and accurately locate the moisture distribution, the following parameter adjustments are required: a) Correct the frequency offset: Perform magnetic field uniformity correction to reduce the frequency shift caused by external interference and improve the data reliability.

[0045] b) Phase Encoding Duration: Select a phase encoding duration between 1 ms and 3 ms to optimize the balance between spatial resolution and signal-to-noise ratio.

[0046] c) Sweep Width: Since the relaxation time of the moisture inside the cement soil is relatively short, to obtain the best signal quality, the sweep width needs to be as small as possible to increase the acquisition sensitivity for short relaxation signals.

[0047] d) Echo Time (TE): Select an appropriate TE value (such as 100 µs - 1 ms) to capture the relaxation characteristics of different moisture states and ensure that bound water, capillary water, and free water can all be distinguished in the T2 spectrum.

[0048] (3) Image acquisition method settings: Prescan - Localization scan - Formal scan a) Prescan: Optimize the signal intensity and optimize the signal-to-noise ratio.

[0049] The prescan acquires a low-resolution reference signal and automatically adjusts the hardware parameters, such as the transmission power of the radio frequency, the sensitivity of the receiving coil, etc.

[0050] b) Localization scan: Accurately determine the water signal distribution at different positions inside the sample through the XYZ gradient magnetic field.

[0051] Apply gradient magnetic fields in the X, Y, and Z directions to make the resonance frequencies of H 1 differ at different spatial positions, thereby locating the position information in the XYZ directions.

[0052] c) Formal scan: Multilayer scan and collect signals pixel by pixel.

[0053] Multilayer scan means continuously collecting multiple parallel layers along a certain direction (such as the axial direction) of the sample and collecting signals pixel by pixel. After the formal scan, the T2 relaxation information of each pixel point will be obtained.

[0054] During formal scanning, the spatial position is encoded by the XYZ gradient magnetic field, and the T2 relaxation signals are collected pixel by pixel, finally forming the T2 relaxation signal data of each pixel in the three-dimensional space.

[0055] In this application, non-destructive and non-contact testing can be achieved, without relying on external cameras. Only by inverting the NMR data to construct the moisture distribution image, the moisture migration situation can be analyzed. Based on the positioning of the XYZ gradient magnetic field, the mapping of T2 data of a single pixel is realized, and high-precision analysis (pixel-level analysis) of moisture migration is achieved. This application can periodically scan to obtain the moisture change trend, track the moisture migration during the freeze-thaw process, and realize the dynamic monitoring of freeze-thaw.

[0056] In order to implement the above-mentioned method for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance, in another exemplary embodiment of this application, a device for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance is provided. Please refer to Figures 2 to 4 , including: a specimen unit 4, a triaxial pressure application assembly 2, a temperature regulation assembly, a seepage assembly, an imaging monitoring assembly 1, and a data analysis assembly.

[0057] The triaxial pressure application assembly 2 is used to simulate the true confining pressure and true axial pressure of the fiber cement soil sample in the target environment.

[0058] The seepage assembly is used to simulate the true seepage situation of the fiber cement soil sample in the target environment.

[0059] The temperature regulation assembly is used to gradually freeze the fiber cement soil sample to the target temperature and gradually melt the frozen fiber cement soil sample.

[0060] The imaging monitoring assembly 1 is used to collect the T2 spectra of the whole freezing process and the whole melting process of the fiber cement soil sample in real time.

[0061] The data analysis assembly is used to implement the above-mentioned method for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance. The data analysis assembly can be a host computer.

[0062] As an optional implementation manner, the device for testing moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance further includes: a pressure compensation assembly.

[0063] The pressure compensation assembly is used to maintain the pressure on the fiber cement soil sample at the preset confining pressure value during the whole freezing process and the whole melting process of the fiber cement soil sample.

[0064] As an alternative implementation, the moisture migration test device during the freeze-thaw cycle of fibrous cement soil based on low-field nuclear magnetic resonance further includes: a monitoring component for monitoring the pressure signal and temperature signal of the fibrous cement soil sample during the entire freezing process and the entire melting process of the fibrous cement soil sample.

[0065] The structures and functions of the above-mentioned components will be described in detail below: The triaxial compression component 2 has a confining pressure chamber 3 and can place the specimen unit 4. The triaxial compression component 2 can apply axial pressure to the specimen unit 4 in the confining pressure chamber 3 and can introduce circulating fluid into the confining pressure chamber 3 to apply confining pressure to the specimen unit 4; the temperature adjustment component is connected to the confining pressure chamber 3, and the temperature adjustment component can adjust the temperature of the circulating fluid and can circulate the circulating fluid with the confining pressure chamber 3 to achieve heat exchange; the pressure compensation component is connected to the confining pressure chamber 3 and can circulate the circulating fluid with the confining pressure chamber 3 to maintain the pressure stability in the confining pressure chamber 3; the seepage component is connected to the specimen unit 4, and the seepage component can introduce moisture into the specimen unit 4; the monitoring component is arranged in the confining pressure chamber 3 and can obtain the pressure signal and temperature signal; the imaging monitoring component 1 is used to monitor the specimen unit 4 and obtain the image information of the specimen unit 4.

[0066] Place the specimen unit 4 in the confining pressure chamber 3 of the triaxial compression component 2. The triaxial compression component 2 applies axial pressure while clamping the specimen unit 4, and the temperature adjustment component provides circulating fluid at different temperatures into the confining pressure chamber 3 to achieve heat exchange with the specimen unit 4 for freeze-thaw. At the same time, the circulating fluid can also apply confining pressure to the specimen unit 4 to simulate the stress state of the engineering soil mass. That is, both the application of confining pressure and temperature exchange are achieved through the circulating fluid in the confining pressure chamber 3, eliminating the need to arrange additional temperature control components on the confining pressure chamber 3, saving space; in addition, under the condition of constant pressure, in order to measure the freeze-thaw settlement rate of the specimen, it is necessary to carry out the cooling (freezing) condition and the heating (melting) condition. Considering that the circulating fluid causes pressure fluctuations in the confining pressure chamber 3 due to thermal expansion and contraction, affecting the accuracy of the test, by setting the pressure compensation component, under the indication of the pressure signal and temperature signal obtained by the monitoring component, the circulating fluid is supplemented or extracted through the circulation of the circulating fluid between the pressure compensation component and the confining pressure chamber 3 to achieve compensation for the floating pressure; the seepage component provides moisture into the specimen unit 4 to facilitate the moisture migration in the specimen unit 4. The imaging monitoring component 1 obtains the image information of the specimen unit 4 to facilitate the subsequent study of the settlement deformation characteristics and moisture migration evolution under the stress state of the engineering soil mass.

[0067] In an alternative embodiment of the present example, more preferably, the temperature adjustment component includes a low-temperature circulation pump 15 and a circulation pipeline 16. The low-temperature circulation pump 15 is connected to the confining pressure chamber 3 through the circulation pipeline 16. The low-temperature circulation pump 15 can adjust the temperature of the circulating liquid and can circulate the circulating liquid with the confining pressure chamber 3 through the circulation pipeline 16 to realize the heating or cooling of the circulating liquid in the confining pressure chamber 3; a three-way valve 17 capable of controlling on / off is provided on the circulation pipeline 16; the low-temperature circulation pump 15 can adjust the temperature of the circulating liquid, can meet the temperature of the circulating liquid required by the confining pressure chamber 3, and enable the circulating liquid to enter the confining pressure chamber 3 to adjust the temperature.

[0068] In an alternative embodiment of the present example, more preferably, the triaxial pressure application component 2 includes a confining pressure pipeline 18 connected to the confining pressure chamber 3, and the confining pressure pipeline 18 can introduce circulating liquid into the confining pressure chamber 3 to apply confining pressure to the specimen unit 4; specifically, the confining pressure chamber 3 can be connected to the confining pressure pipeline 18 and the circulation pipeline 16 through the three-way valve 17, that is, the circulation of the circulating liquid between the confining pressure pipeline 18 and the confining pressure chamber 3 and the circulation of the circulating liquid between the circulation pipeline 16 and the confining pressure chamber 3 can be in parallel. In this way, the temperature adjustment of the circulating liquid can be realized by the low-temperature circulation pump 15 on the premise of maintaining the confining pressure of the confining pressure chamber 3.

[0069] Furthermore, the triaxial pressure application component 2 further includes an axial pressure mechanism. The axial pressure mechanism can extend into the confining pressure chamber 3 to apply axial pressure to the specimen unit 4. Specifically, the axial pressure mechanism includes an upper ejector rod 5 and a lower ejector rod 6 respectively clamped on the upper and lower sides of the specimen unit 4; specifically, the triaxial pressure application component 2 can adopt a conventional triaxial soil stress loading system, and further includes a triaxial pressure controller 22. The axial pressure of the upper ejector rod 5 and the lower ejector rod 6 is controlled through the axial pressure pipeline 19, and the triaxial pressure controller 22 can also control the driving of the circulating liquid in the confining pressure pipeline 18, that is, control the water flow of the confining pressure and the seepage component.

[0070] In an alternative embodiment of the present example, more preferably, the pressure compensation component includes a peristaltic pump 20 and a compensation pipeline 21. The peristaltic pump 20 is connected to the confining pressure chamber 3 through the compensation pipeline 21, and the peristaltic pump 20 circulates the circulating liquid with the confining pressure chamber 3 through the compensation pipeline 21; specifically, the compensation pipeline 21 is connected to the confining pressure pipeline 18 through a connection valve 24. When the pressure in the confining pressure chamber 3 fluctuates and decreases, the peristaltic pump 20 replenishes the circulating liquid into the confining pressure pipeline 18 to compensate for the floating pressure. When the pressure in the confining pressure chamber 3 fluctuates and increases, the peristaltic pump extracts the extra circulating liquid on the confining pressure pipeline 18 to compensate for the floating pressure; among them, the peristaltic pump 20 is used for driving, which can realize high-precision pressure compensation and can cooperate with the triaxial pressure controller 22 to meet the confining pressure fluctuation caused by the temperature change of the circulating liquid; among them, the connection valve 24 can control the on / off of the compensation pipeline 21 and the confining pressure pipeline 18.

[0071] In an alternative embodiment of the present example, more preferably, please refer to Figure 4, the seepage assembly includes a seepage inlet pipeline 14 and a seepage outlet pipeline 13. The seepage inlet pipeline 14 and the seepage outlet pipeline 13 are respectively connected to the water inlet and outlet of the specimen unit 4. The seepage inlet pipeline 14 is connected to the seepage pump in the triaxial pressure application assembly 2 through a seepage pipeline 23 to be able to introduce water into the specimen unit 4.

[0072] Specifically, please refer to Figure 3 and Figure 4 , the specimen unit 4 adopts a conventional mechanism. The specimen is coated with a latex film 11, filter papers 10 and permeable stones 9 are sequentially arranged at both the upper and lower ends of the specimen, and upper and lower plugs 7 and 12 are hermetically arranged at both the upper and lower ends of the specimen through sealing rings 8. The seepage inlet pipeline 14 and the seepage outlet pipeline 13 are respectively connected to the inside of the specimen unit 4 through the upper plug 7 and the lower plug 12; specifically, the seepage inlet pipeline 14 can be connected to the fluid channel in the lower ejector rod 6, and the fluid channel penetrates through the lower plug 12 to be connected to the specimen unit 4.

[0073] In an alternative solution of this embodiment, preferably, the monitoring assembly includes a pressure sensor and a temperature sensor arranged in the confining pressure chamber 3; specifically, the pressure sensor may include sensors for respectively monitoring the confining pressure and the axial pressure.

[0074] In an alternative solution of this embodiment, preferably, the imaging monitoring assembly 1 is set as a low-field nuclear magnetic resonance device. The confining pressure chamber 3 and the specimen unit 4 are placed in the low-field nuclear magnetic resonance device, saving the overall space, so that the low-field nuclear magnetic resonance device can monitor the specimen unit 4; the low-field nuclear magnetic resonance device is a common conventional device. By collecting the signals released by the excitation in the specimen, the source position of the signals is determined through the gradient magnetic field and converted into an image. Different moisture contents and moisture migration states will result in different signal intensities, so different brightness and contrasts will be presented in the result. By periodically obtaining the nuclear magnetic resonance imaging of the specimen and comparing the images at different time points, the migration trajectory of moisture inside the soil body can be observed, providing support for analyzing the mechanical properties of fiber-reinforced cement soil.

[0075] Furthermore, the image signals of the low-field nuclear magnetic resonance device and the signals of the monitoring assembly can be transmitted to a data analysis device such as a computer terminal to process the relaxation signals generated by the nuclear magnetic resonance device, inversely analyze the obtained moisture information and deformation data, and generate visual images and signal quantity-relaxation time curves, thereby revealing the moisture migration law and the fiber reinforcement effect.

[0076] In an alternative solution of this embodiment, preferably, the circulating liquid adopts an electronic fluorinated liquid, which has good thermal conductivity, provides the confining pressure while transferring the low temperature of the low-temperature heat exchange system, ensures that the specimen can be accurately cooled, and at the same time ensures the stability of the confining pressure, and can meet the usage requirements of the low-field nuclear magnetic resonance device.

[0077] In an alternative embodiment of the present example, preferably, the triaxial pressure component 2 is made of a nuclear magnetic resonance compatible material, such as titanium alloy, nickel-aluminum alloy, and ceramics, etc., to avoid affecting the use of the low-field nuclear magnetic resonance equipment. At the same time, it has good thermal conductivity, can provide confining pressure through the internal fluorinated liquid while transferring low temperature, ensuring that the specimen can be accurately cooled and the confining pressure is stable.

[0078] Further preferably, in order to meet the cooling requirements of each heating element in the test device, such as pumps, a cooling bath is provided to cool each heating element, and the coolant can be water or other conventional coolants.

[0079] Based on the above-described test device for moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance, as Figure 5 shown, the complete process of performing the above-described test method for moisture migration during the freeze-thaw settlement of fiber cement soil based on low-field nuclear magnetic resonance is as follows: (1) Use the triaxial pressure component to simulate the true confining pressure and true axial pressure of the fiber cement soil sample in the target environment. Use the seepage component to simulate the true seepage situation of the fiber cement soil sample in the target environment.

[0080] Before performing this step, it is necessary to first connect the monitoring component and confirm normal response; exhaust the air in the triaxial pressure component 2 to avoid affecting the test accuracy, and complete the installation of the specimen unit 4; the confining pressure pump of the triaxial pressure component 2 replenishes the electronic fluorinated liquid in the confining pressure chamber 3 and discharges the gas in the chamber at the same time.

[0081] And before installing the fiber cement soil sample in front of the confining pressure chamber 3, the fiber cement soil sample needs to be placed in a saturator, placed in a vacuum saturation pump device to be evacuated and saturated with water, so as to more accurately measure the internal nuclear magnetic signal.

[0082] After each component is arranged, first, according to the set confining pressure, axial pressure, and seepage situation, simulate the underground stress environment in actual engineering. Specifically, through the triaxial pressure component 2, circulatory liquid is introduced into the confining pressure chamber 3 to apply confining pressure to the specimen unit 4, and the specimen unit 4 can be cooled and frozen. The triaxial pressure component 2 can also apply axial pressure to the specimen unit 4; through the seepage component, water is supplied to the specimen unit 4 to simulate the true seepage situation. Among them, during the loading process of the triaxial pressure component 2, the confining pressure is set and loaded first, and then the axial pressure is gradually applied to simulate the underground pressure environment in actual engineering.

[0083] (2) Use the temperature adjustment component to gradually freeze the fiber cement soil sample to the target temperature and gradually melt the frozen fiber cement soil sample.

[0084] The temperature adjustment component adjusts the temperature of the circulating liquid in the confining pressure chamber 3 so that the soil sample in the sample unit 4 begins to gradually freeze to the target temperature. Specifically, turn on the heater of the low-temperature circulating pump 15, and freeze the sample at a low temperature through the circulating liquid; cool the sample to a predetermined low-temperature condition, and perform heat exchange through the circulating fluorinated liquid to accurately control and maintain the target temperature of the sample.

[0085] When the sample reaches the set temperature and maintains this temperature stably, adjust the temperature setting of the low-temperature circulating pump 15 to adjust the temperature of the circulating liquid so that the soil sample begins to melt. During the freezing and melting processes, the loading state is maintained. The displacement sensor is in contact with the sample base (axial pressure is applied from bottom to top), and the displacement data can be measured in real time using the displacement sensor.

[0086] (3) Use the imaging monitoring component to collect the T2 spectra of the entire freezing process and the entire melting process of the fiber cement soil sample in real time.

[0087] (4) Use the data analysis component to analyze the moisture migration of the fiber cement soil sample based on the T2 spectra of the entire freezing process and the entire melting process of the fiber cement soil sample. As Figure 6 shown, Figure 6 the brighter the color, the higher the water content.

[0088] Use the upper computer to perform spatial positioning on the relaxation signals generated by the nuclear magnetic resonance equipment to generate a visualization image containing moisture distribution information, so as to reveal the moisture migration law and the fiber reinforcement effect.

[0089] The above test process has the following technical effects: (1) In this application, the sample unit is placed in the confining pressure chamber of the triaxial compression component. While the triaxial compression component clamps the sample unit, it applies axial pressure and introduces circulating liquid into the confining pressure chamber to apply confining pressure to the sample unit, simulating the stress state of the engineering soil mass. The temperature adjustment component provides circulating liquid at different temperatures to the confining pressure chamber to achieve heat exchange and freeze-thaw of the sample unit. That is, both the application of confining pressure and temperature exchange are realized through the circulating liquid in the confining pressure chamber, without arranging additional temperature control components on the confining pressure chamber, saving space.

[0090] (2) Under the condition of constant pressure, in order to measure the frost heave and thaw settlement rate of the sample, it is necessary to perform the cooling (freezing) condition and the heating (melting) condition. Considering that the pressure in the confining pressure chamber fluctuates due to the thermal expansion and contraction of the circulating liquid, affecting the accuracy of the test, by setting the pressure compensation component, under the indication of the pressure signal and temperature signal obtained by the monitoring component, the circulating liquid is circulated between the pressure compensation component and the confining pressure chamber to supplement or extract the circulating liquid, realizing the compensation of the floating pressure.

[0091] (3) This application utilizes an imaging monitoring component and a data analysis component to obtain the relaxation signal of the specimen unit and invert and locate it into image information. By periodically obtaining the nuclear magnetic imaging of the specimen, the evolution of moisture inside the soil body is observed, achieving the visualization effect of simultaneously testing the thaw settlement deformation characteristics and the moisture migration and evolution under the restored soil stress state.

[0092] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0093] Specific examples are used in this article to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, based on the idea of this application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A test method for moisture migration during the freeze-thaw settlement process of fiber-reinforced soil-cement based on low-field nuclear magnetic resonance, characterized in that, Including: Obtaining the T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process; The T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process are the T2 spectra obtained based on low-field nuclear magnetic resonance technology during the frost heaving and thaw settlement test of the fiber cement soil sample; Inverting the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the whole freezing process and the whole melting process from the T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process; Determining the pixel-level moisture migration situation of the fiber cement soil sample during the whole freezing process and the whole melting process according to the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the whole freezing process and the whole melting process.

2. The moisture migration test method during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 1, characterized in that Inverting the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the whole freezing process and the whole melting process from the T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process specifically includes: Determining the three-dimensional spatial distribution information of each pixel point of the fiber cement soil sample during the whole freezing process and the whole melting process according to the three-dimensional gradient magnetic field in low-field nuclear magnetic resonance technology, and obtaining the T2 spectrum with three-dimensional spatial distribution information; Determining the moisture state of each pixel point by applying the inverse Laplace transform method or the BRD regularization inversion algorithm according to the T2 spectrum with three-dimensional spatial distribution information; Constructing the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the whole freezing process and the whole melting process according to the moisture state of each pixel point in the T2 spectrum.

3. The moisture migration test method during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 2, characterized in that, Determining the pixel-level moisture migration situation of the fiber cement soil sample during the whole freezing process and the whole melting process according to the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample during the whole freezing process and the whole melting process specifically includes: Analyzing the evolution of the moisture in the fiber cement soil sample at the same position according to the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the whole freezing process of the fiber cement soil sample, and obtaining the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the whole freezing process; Analyzing the evolution of the moisture in the fiber cement soil sample at the same position according to the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the whole melting process of the fiber cement soil sample, and obtaining the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the whole melting process; Analyzing the pixel-level three-dimensional moisture distribution maps corresponding to each acquisition moment during the whole freezing process and the whole melting process, and obtaining the pixel-level moisture migration situation inside the fiber cement soil sample corresponding to each acquisition moment.

4. The moisture migration test method during the frost heaving and thaw settlement process of fiber-reinforced cement soil based on low-field nuclear magnetic resonance according to claim 3, wherein Analyzing the evolution of the moisture in the fiber cement soil sample at the same position according to the pixel-level three-dimensional moisture distribution maps at each acquisition moment during the whole freezing process of the fiber cement soil sample, and obtaining the pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the whole freezing process specifically includes: Using an interpolation algorithm to interpolate and fill the moisture state of each pixel point in the pixel-level three-dimensional moisture distribution maps of the fiber cement soil sample at each acquisition moment during the whole freezing process; Analyzing the evolution of the moisture in the fiber cement soil sample at the same position according to the interpolated and filled moisture state, and obtaining the continuous pixel-level moisture migration situation inside the fiber cement soil sample between each acquisition moment during the whole freezing process.

5. The moisture migration test method during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 1, wherein, After performing the step of "determining the pixel-level moisture migration during the whole freezing process and the whole melting process of the fiber cement soil sample according to the pixel-level three-dimensional moisture distribution map of the fiber cement soil sample during the whole freezing process and the whole melting process", the method for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance includes: Compare the moisture migration of fiber cement soil samples with different fiber contents during the whole freezing process, and analyze the fiber reinforcement mechanism of the fiber cement soil samples during the whole freezing process; Compare the moisture migration of fiber cement soil samples with different fiber contents during the whole melting process, and analyze the fiber reinforcement mechanism of the fiber cement soil samples during the whole melting process.

6. The method for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 1, wherein, Obtain the T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process, specifically including: Simulate the true confining pressure, true axial pressure and true seepage conditions of the fiber cement soil sample in the target environment; Gradually freeze the fiber cement soil sample to the target temperature, and based on low-field nuclear magnetic resonance technology, collect the T2 spectrum of the fiber cement soil sample during the whole freezing process in real time; Gradually melt the frozen fiber cement soil sample, and based on low-field nuclear magnetic resonance technology, collect the T2 spectrum of the frozen fiber cement soil sample during the whole melting process in real time.

7. The method for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 6, wherein, Gradually freeze the fiber cement soil sample to the target temperature, specifically including: Freeze the fiber cement soil sample according to the freezing temperature gradient, and during the freezing process, keep the confining pressure of the fiber cement soil sample at the preset confining pressure value and keep the axial pressure of the fiber cement soil sample at the preset axial pressure value; Gradually melt the frozen fiber cement soil sample, specifically including: Melt the fiber cement soil sample according to the melting temperature gradient, and during the melting process, keep the confining pressure of the fiber cement soil sample at the preset confining pressure value and keep the axial pressure of the fiber cement soil sample at the preset axial pressure value.

8. The moisture migration test method during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 1, characterized in that, Before performing the step of "collecting the T2 spectrum of the fiber cement soil sample during the whole freezing process in real time", the method for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance includes: Use the Hahn spin echo sequence to excite the relaxation signal with radio frequency pulses; Set the T2 spectrum acquisition parameters; the T2 spectrum acquisition parameters include the correction frequency offset, phase encoding duration, scan bandwidth and echo time; Set the T2 spectrum acquisition mode.

9. A moisture migration test device during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance, characterized in that, Include: A triaxial pressure application component for simulating the true confining pressure and true axial pressure of the fiber cement soil sample in the target environment; A seepage component for simulating the true seepage condition of the fiber cement soil sample in the target environment; A temperature regulation component for gradually freezing the fiber cement soil sample to the target temperature and gradually melting the frozen fiber cement soil sample; An imaging monitoring component for collecting the T2 spectra of the fiber cement soil sample during the whole freezing process and the whole melting process in real time based on low-field nuclear magnetic resonance technology; A data analysis component for performing the method for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to any one of claims 1 to 8.

10. The moisture migration testing device during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance according to claim 9, characterized in that, The device for testing moisture migration during the frost heaving and thaw settlement process of fiber cement soil based on low-field nuclear magnetic resonance further includes: a pressure compensation component; The pressure compensation component is used to maintain the confining pressure of the fiber cement soil sample at the preset confining pressure value during the whole freezing process and the whole melting process of the fiber cement soil sample.

Images