Method and device for testing moisture migration characteristics of frozen soil under low-temperature nuclear magnetic triaxial seepage

Abstract

The invention discloses a method and a device for testing moisture migration characteristics of frozen soil under low-temperature nuclear magnetic triaxial seepage, and relates to the technical field of frozen soil testing. In order to solve the problems that in the prior art, compatibility control of freezing and seepage cannot be achieved, and whole-process evolution of frozen soil moisture migration characteristics is difficult to dynamically capture, the scheme comprises the following steps that the real confining pressure, axial pressure and seepage speed of the environment where a soil sample is located are simulated; collecting a nuclear magnetic resonance image and an overall and layered T2 spectrum of the soil sample before freezing under the action of seepage; gradually freezing the soil sample based on different temperature gradients, and collecting a nuclear magnetic resonance image and an overall and layered T2 spectrum of the soil sample under the seepage and freezing coupling action in real time; data are collected according to the whole soil sample freezing process, and the evolution law of water migration characteristics in the soil body freezing process is analyzed. According to the invention, the whole-process, visual and nondestructive detection is realized, and the whole-process evolution rule of water migration characteristics such as unfrozen water content and pore cracks in the frozen soil under the seepage and freezing coupling action can be accurately captured.

Description

Technical Field

[0001] The present application relates to the technical field of frozen soil testing, and in particular to a method and device for testing the moisture migration characteristics of frozen soil under low-temperature nuclear magnetic triaxial seepage. Background Art

[0002] The water migration accompanying the freezing process of artificial frozen soil is the fundamental cause of frost heave or collapse of overlying buildings, which significantly affects the strength and deformation of the soil as well as the safety, stability and durability of the engineering structure. As the fundamental source of water migration, unfrozen water often uses pores and crack structures as migration channels, providing a continuous water supply for water migration, resulting in severe frost heave and deformation of the soil. In artificial freezing projects near cross-river and cross-sea tunnels and surface / groundwater drainage channels, large seepage may be encountered, which will seriously hinder the formation time and strength of the frozen wall, further leading to collapse of foundation pit projects and other accidents, seriously hindering the progress of the project. Therefore, it is very important to obtain the evolution characteristics of the whole process of water migration in the soil under the coupling of freezing and seepage.

[0003] Traditional methods for testing unfrozen water content, such as time domain reflectometry and differential scanning calorimetry, have significant errors, which may cause the results to become larger or interfere with the temperature field of frozen soil. In contrast, low-field nuclear magnetic resonance technology does not require sampling, which reduces the disturbance of soil samples, obtains the most realistic data of pore and crack structure during freezing, and more directly and accurately reflects the distribution and dynamic changes of water inside the soil, and then inverts and analyzes the evolution of pores and cracks. However, the existing testing technology usually takes out small-volume samples after freezing in a low-temperature box and then places them in a nuclear magnetic resonance device for testing. This not only has the problem of ice melting, but also ignores the limitation that the water migration characteristics of small-volume samples are not obvious, and cannot reflect the changes in water content at different heights of the soil, and does not consider the impact of the seepage process on the frozen soil. Therefore, there is an urgent need for a testing method and device that can realize the coupling of freezing and seepage, so as to realize the whole freezing process, visualize, and non-destructively monitor the evolution of water migration characteristics inside the soil, and provide reliable technical support for the safety and stability of frozen soil engineering. Summary of the invention

[0004] The purpose of this application is to provide a method and device for testing the moisture migration characteristics of frozen soil under low-temperature nuclear magnetic triaxial seepage, which can monitor the evolution law of the moisture migration characteristics inside the soil during the freezing process of the soil in a full, visual and non-destructive manner.

[0005] To achieve the above objectives, this application provides the following solutions: In the first aspect, the present application provides a method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage, comprising: S1, the real confining pressure, real axial pressure and real seepage velocity of the simulated soil sample environment; S2. Collect the nuclear magnetic resonance image, overall and layered T2 spectrum of the soil sample under the action of seepage before freezing; the overall and layered T2 spectrum refers to the overall T2 spectrum of the soil sample and the layered T2 spectrum at different heights of the soil sample; S3, gradually freezing soil samples based on different temperature gradients, and collecting real-time nuclear magnetic resonance images, overall and layered T2 spectra of soil samples under the coupling of seepage and freezing; S4. Based on the nuclear magnetic resonance images, overall and layered T2 spectra of soil samples before and during freezing, the evolution law of water migration characteristics during the whole freezing process of soil samples was analyzed; the water migration characteristics include the water distribution in the soil samples, the changes in water migration, the changes in unfrozen water content and the changes in pores and cracks.

[0006] In the second aspect, in order to realize the above-mentioned test method, the present application provides a test device for frozen soil water migration characteristics under low-temperature nuclear magnetic triaxial seepage, including: a soil triaxial test mechanism, a low-temperature freezing mechanism, a nuclear magnetic resonance test mechanism and a data acquisition and analysis mechanism; The soil triaxial testing mechanism is used to simulate the real confining pressure, real axial pressure and real seepage conditions of the environment in which the soil sample is located, and to collect the overall T2 spectrum of the soil sample under the seepage effect before freezing and under the seepage and freezing coupling effect during freezing; The low temperature freezing mechanism is used to gradually freeze the soil sample based on different temperature gradients; The nuclear magnetic resonance testing mechanism is used to provide a nuclear magnetic resonance magnetic field to the soil sample, and collect nuclear magnetic resonance images of the soil sample under the seepage effect before freezing and the seepage and freezing coupling effect during freezing, and layered T2 spectra at different heights of the soil sample; The data acquisition and analysis mechanism is used to obtain nuclear magnetic resonance images, overall T2 spectra and layered T2 spectra at different heights of the soil sample before and during freezing, and analyze the evolution law of water migration characteristics during the whole freezing process of the soil sample; the water migration characteristics include the water distribution in the soil sample, the change of water migration, the change of unfrozen water content and the change of pores and cracks.

[0007] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a method and device for testing the characteristics of frozen soil moisture migration under low-temperature nuclear magnetic triaxial seepage, which can simultaneously create a test environment for freezing and seepage, so as to facilitate further analysis of the evolution of the internal moisture content and pore and fissure structure of the soil under the simultaneous action of freezing and seepage. The present application can collect nuclear magnetic resonance images, overall and layered T2 spectra of the entire freezing process of soil samples under the coupling of seepage and freezing, and can analyze the moisture distribution, moisture migration changes, unfrozen water content changes and pore and fissure changes in soil samples based on a combination of qualitative and quantitative methods, and can monitor the evolution of the characteristics of internal moisture migration in the soil during the freezing process of the soil in a visual and non-destructive manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0009] Figure 1 This is a schematic diagram of a method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage in one embodiment of the present application; Figure 2 A schematic diagram of a nuclear magnetic resonance image of the clay water migration process under freezing and seepage provided in an embodiment of the present application; Figure 3 A schematic diagram of T2 spectra of clay under different freezing temperatures and seepage effects provided in one embodiment of the present application; Figure 4 A schematic diagram of clay pore changes under different freezing temperatures and seepage effects provided in one embodiment of the present application; Figure 5 This is a schematic diagram of the structure of a device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage in one embodiment of the present application; Figure 6 A schematic diagram of the structure of a soil triaxial testing mechanism provided in one embodiment of the present application; Figure 7 A detailed structural diagram of a soil triaxial testing mechanism provided in one embodiment of the present application; Figure 8 A schematic diagram of the structures of a confining pressure control pump, an axial pressure control pump and a seepage control pump provided in one embodiment of the present application; Fig. 9 A schematic diagram of the structure of a nuclear magnetic resonance testing mechanism provided in one embodiment of the present application.

[0010] Figure numerals: 1-soil triaxial test mechanism; 111-nuclear magnetic probe coil; 112-axial pressure loading cylinder; 113-lower push rod; 114-lower bottom plate; 115-soil sample lower base; 116-soil sample upper loading cap; 117-upper top plate; 118-upper push rod; 119-axial pressure reaction frame; 120-pressure sensor; 121-displacement sensor; 122-axial pressure inlet; 123-confining pressure chamber; 124-confining pressure inlet; 125-confining pressure outlet; 126-seepage inlet pipeline; 127-seepage outlet pipeline; 128-seepage inlet; 129-seepage outlet; 130-mobile test Frame; 131-displacement sensor base; 2-low-temperature freezing mechanism; 21-freezing circulation fluid inlet; 22-freezing circulation fluid outlet; 23 freezing circulation pipeline; 24-freezing circulation pump; 3-nuclear magnetic resonance testing mechanism; 31-low-field nuclear magnetic resonance instrument; 32-low-field nuclear magnetic resonance imaging module; 33-layered gradient module; 4-data acquisition and analysis mechanism; 5-axial pressure control pump; 6-confining pressure control pump; 7-seepage control pump; 8-liquid storage tank; 9-control switch; 10-confining pressure sensor; 11-axial pressure sensor; 12-seepage flow rate sensor; A-soil sample; B-nuclear magnetic resonance testing area. DETAILED DESCRIPTION

[0011] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0012] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0013] As an advanced nondestructive testing technology, low-field nuclear magnetic resonance (NMR) technology has been widely used in the fields of materials science, agricultural product quality testing, seed vitality assessment, etc. in recent years. This technology can indirectly reflect the moisture content, distribution state and dynamic change process inside the sample by measuring parameters such as the spin relaxation time of hydrogen protons in the sample. However, the application of low-field nuclear magnetic resonance technology to the test research under the coupling of soil freezing and seepage is still in its infancy, and a complete test method and device have not yet been formed. Especially in the environment of triaxial seepage coupling, how to ensure the simultaneous realization of freezing and seepage during the test, how to truly restore the true stress state of the soil, how to collect the evolution law of moisture migration during the freezing process, and how to achieve effective collection and analysis of nuclear magnetic resonance signals are all technical problems that need to be solved urgently.

[0014] Therefore, the present invention proposes a method and device for testing the moisture migration characteristics of frozen soil under low-temperature nuclear magnetic triaxial seepage, aiming to achieve comprehensive and accurate monitoring and analysis of the dynamic change process of soil under complex environmental conditions by integrating low-field nuclear magnetic resonance technology and triaxial test technology, so as to provide strong technical support for research and engineering practice in related fields.

[0015] In an exemplary embodiment of the present application, a method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage is provided. Figure 1 As shown, the following steps are included.

[0016] S1. Simulate the real confining pressure, real axial pressure and real seepage velocity of the environment in which the soil sample is located.

[0017] S2. Collect the nuclear magnetic resonance image, overall and layered T2 spectrum of the soil sample under seepage before freezing; the overall and layered T2 spectrum refers to the overall T2 spectrum of the soil sample and the layered T2 spectrum at different heights of the soil sample.

[0018] S3. Based on different temperature gradients, soil samples are gradually frozen, and nuclear magnetic resonance images, overall and layered T2 spectra of soil samples under the coupling of seepage and freezing are collected in real time.

[0019] S4. Based on the nuclear magnetic resonance images, overall and layered T2 spectra of soil samples before and during freezing, the evolution law of water migration characteristics during the whole freezing process of soil samples was analyzed; the water migration characteristics include the water distribution in the soil samples, the changes in water migration, the changes in unfrozen water content and the changes in pores and cracks.

[0020] More specifically, step S4 includes: (1) Based on the NMR images of soil samples before and during freezing, the moisture distribution and moisture migration changes during the freezing process of soil samples were qualitatively analyzed based on data post-processing. Figure 2 The figure shows a schematic diagram of the NMR image of the clay water migration process under freezing and seepage. Figure 2 Brighter locations indicate higher water content.

[0021] Nuclear magnetic resonance images are used to qualitatively analyze water migration. For example, the amount of water accumulated in different parts of a soil sample is different. The parts with more water accumulation will have a strong color in the image (the intensity of the color represents the amount of water), while the parts with less water accumulation will have basically no color. This can be used to determine the general pattern of water migration.

[0022] (2) Based on the overall and layered T2 spectra of soil samples before and during freezing, the changes in the unfrozen water content of the soil samples as a whole and at different height layers of the soil samples and the evolution of pores and cracks during the freezing process are quantitatively analyzed based on data post-processing; the evolution of pores and cracks is determined based on the changes in pore and crack radius. Figure 3Schematic diagram of the overall T2 spectrum of clay under different freezing temperatures and seepage effects. Figure 4 Schematic diagram of the changes in clay pores under different freezing temperatures and seepage effects.

[0023] The process of soil freezing water migration is mainly to observe the changes in the unfrozen water content in different height layers of the soil sample before and after freezing. The test process mainly uses the nuclear magnetic resonance test results to measure the nuclear magnetic resonance signals of the soil sample before and after freezing, and obtain the transverse relaxation time (T2) spectrum of the soil sample before and after freezing. Then, based on the nuclear magnetic resonance signal value of the soil sample at room temperature (before freezing), the corresponding unfrozen water content is calculated according to the nuclear magnetic resonance signals at different freezing temperatures and different heights of the soil sample, and the whole process of water migration can be quantitatively analyzed. Among them, the calculation formula of the unfrozen water content is: ; In the formula, w u is the unfrozen water content of the soil sample during freezing (%); w 0 is the total water content of the soil sample before freezing (%); is the total intensity value of the nuclear magnetic resonance signal before the soil sample is frozen. The total intensity value of the nuclear magnetic resonance signal is determined according to the T2 spectrum, which is the sum of the amplitude intensities of the nuclear magnetic resonance signals of each data point in the T2 spectrum before freezing. is the total intensity value of the NMR signal during the freezing process of the soil sample, and is the sum of the NMR signal amplitude intensities of each data point in the T2 spectrum at a certain low temperature during the freezing process.

[0024] T2 spectrum is a quantitative analysis of moisture information. For example, the moisture content at a specific location can be known through layered T2 spectrum. The moisture migration law can be determined through the moisture content at different locations at different times.

[0025] The observation of frozen pores and cracks in soil under triaxial seepage coupling based on low-field nuclear magnetic resonance is mainly based on the inversion analysis of the nuclear magnetic resonance transverse relaxation time (T2) spectrum to obtain the pore and crack structure characteristics of the soil sample. Pores and cracks are the storage places of water, the favorable channels for promoting water migration, and the important components of water migration characteristics. The transverse relaxation time T2 is related to the radius of pores or cracks. R The relationship can be expressed as the following formula.

[0026] .

[0027] Where, T2 is the transverse relaxation time of the collected T2 spectrum data, in ms; is the surface relaxation rate, in units of ; R is the crack or pore radius; the crack radius calculation formula is the same as the pore radius calculation formula. When calculating the crack radius, FExpressed as the crack characteristic factor, F =1; when calculating the pore radius, F Expressed as the pore characteristic factor, spherical pores, F =3; columnar pores, F =2. S is the pore (crack) surface area; V is the pore (crack) volume.

[0028] In another exemplary embodiment of the present application, in order to implement the above-mentioned low-temperature nuclear magnetic triaxial seepage frozen soil moisture migration characteristic test method, the present application provides a preferred test device for implementing the above-mentioned test method, that is, a low-temperature nuclear magnetic triaxial seepage frozen soil moisture migration characteristic test device, such as Figure 5 As shown, it includes: a soil triaxial testing mechanism 1, a low-temperature freezing mechanism 2, a nuclear magnetic resonance testing mechanism 3 and a data acquisition and analysis mechanism 4.

[0029] The soil triaxial testing mechanism 1 is used to simulate the real confining pressure, real axial pressure and real seepage conditions of the environment in which the soil sample is located, and to collect the overall T2 spectrum of the soil sample under the seepage effect before freezing and under the seepage and freezing coupling effect during freezing. The overall T2 spectrum is obtained by exciting the resonance of the soil sample and receiving the resonance signal of the soil sample; the resonance signal of the soil sample is used to obtain the overall T2 spectrum of the soil before and during freezing of the soil sample under the action of seepage. Figure 5 As shown, the soil triaxial test mechanism 1 is arranged in the nuclear magnetic resonance test area of ​​the nuclear magnetic resonance test mechanism 3. Fig. 9 In the figure, B refers to the NMR test area.

[0030] The low temperature freezing mechanism 2 is used to gradually freeze the soil sample based on different temperature gradients. The freezing temperature during the freezing process of the soil sample can be continuously changed by regulation.

[0031] The NMR testing mechanism 3 is used to provide a NMR magnetic field to the soil sample, and collect NMR images of the soil sample under the seepage effect before freezing and the seepage and freezing coupling effect during freezing, as well as layered T2 spectra at different heights of the soil sample.

[0032] The data acquisition and analysis mechanism 4 is used to obtain the nuclear magnetic resonance image of the soil sample before and during freezing, the overall T2 spectrum, and the layered T2 spectrum at different heights of the soil sample, and analyze the evolution law of the water migration characteristics of the soil sample during the whole freezing process; the water migration characteristics include the water distribution in the soil sample, the change of water migration, the change of unfrozen water content, and the change of pores and cracks. The data acquisition and analysis mechanism 4 can be a computer. The data acquisition and analysis mechanism 4 can be used to implement the data analysis process of step S4 in the above-mentioned test method.

[0033] The frozen cracks of soil under the action of triaxial seepage coupling based on low-field nuclear magnetic resonance are obtained based on nuclear magnetic resonance images. Because cracks are natural seepage channels filled with water, the principle of nuclear magnetic resonance images is mainly to image the signal information of water. Therefore, the information of water in the soil can be intuitively seen through nuclear magnetic resonance images, and the evolution image of cracks during freezing and seepage can be presented in real time. Since clay will produce cracks during the actual freezing process, this technology can effectively capture the changes in cracks.

[0034] In another exemplary embodiment of the present application, the soil triaxial testing mechanism 1 specifically includes: an axial pressure simulation module, a confining pressure simulation module, a seepage simulation module and a nuclear magnetic probe coil 111.

[0035] The axial pressure simulation module is used to simulate the real axial pressure of the environment in which the soil sample is located.

[0036] The confining pressure simulation module is used to simulate the actual confining pressure of the environment in which the soil sample is located.

[0037] The seepage simulation module is used to simulate the actual seepage conditions of the environment in which the soil sample is located.

[0038] The nuclear magnetic probe coil 111 adopts an integrated receiving design, which is used to excite the soil sample resonance and receive the soil sample resonance signal to obtain the overall T2 spectrum of the soil sample before and during freezing. The present application arranges the nuclear magnetic probe coil 111 in the soil triaxial testing mechanism 1 to collect the overall T2 spectrum of the soil body, and the soil sample resonance signal detected by the nuclear magnetic probe coil 111 is further inverted by the nuclear magnetic matching data processing software (such as the data acquisition and analysis mechanism 4) to obtain the overall T2 spectrum of the whole freezing process.

[0039] The axial pressure simulation module, the confining pressure simulation module, and the seepage simulation module in the soil triaxial testing mechanism 1 can be used to realize the simulation of the confining pressure, axial pressure, and seepage velocity in step S1 of the above test method, as well as the triaxial loading and seepage control. The collection of the overall T2 spectrum of the soil sample in step S2 and the overall T2 spectrum of the soil sample in step S3 of the above test method can be realized by using the nuclear magnetic probe coil 111 in the soil triaxial testing mechanism 1.

[0040] like Figure 6 and Figure 7 As shown, the axial pressure simulation module includes an axial pressure loading cylinder 112, a lower push rod 113, a lower base plate 114, a soil sample lower base 115, a soil sample upper loading cap 116, an upper top plate 117 (which can be called an axial loading upper top plate), an upper push rod 118 and an axial pressure reaction frame 119.

[0041] The upper end of the axial pressure loading cylinder 112 is connected to the lower end of the soil sample through the lower push rod 113, the lower bottom plate 114, and the soil sample lower base 115 in sequence; the lower push rod 113 penetrates the lower bottom plate 114 and contacts the lower end of the soil sample lower base 115. The lower bottom plate 114 (which can be called the axial loading lower bottom plate) uses water as a driving force to control the axial loading. Figure 7 The "A" in the table refers to the soil sample.

[0042] The lower push rod 113, the lower bottom plate 114 and the soil sample lower base 115 are fixedly connected and integrated.

[0043] The upper end of the soil sample is connected to the axial pressure reaction frame 119 through the soil sample upper loading cap 116, the upper top plate 117 and the upper push rod 118 in sequence; the lower end of the upper push rod 118 penetrates the upper top plate 117 and contacts the upper end of the soil sample upper loading cap 116. The soil sample upper loading cap 116, the upper top plate 117, the upper push rod 118 and the axial pressure reaction frame 119 are not fixedly connected, but are independent components. When axial pressure is applied, the components are in contact with each other. The material of the axial pressure reaction frame 119 can be selected from aluminum alloy, which has a certain strength.

[0044] A pressure sensor 120 is arranged between the upper push rod 118 and the axial pressure reaction frame 119; the pressure sensor 120 is connected to the data acquisition and analysis mechanism 4 in communication; the pressure sensor 120 is used to measure the magnitude of the axial pressure applied to the soil sample by the axial pressure loading cylinder 112. The pressure sensor 120 monitors the force applied to the upper push rod 118, measures the magnitude of the axial pressure applied to the soil sample by the axial pressure loading cylinder 112, records the changes in pressure during the triaxial freezing and seepage of the soil, and reflects the magnitude of the applied axial pressure in real time.

[0045] A displacement sensor base 131 is arranged at the upper end of the axial pressure loading cylinder 112, and the displacement sensor base 131 is fixedly connected to the axial pressure loading cylinder 112; the upper end of the displacement sensor base 131 contacts the lower end of the lower push rod 113, but is not fixedly connected. A displacement sensor 121 is arranged on the side of the displacement sensor base 131, and the displacement sensor 121 monitors the deformation caused by the axial pressure by monitoring the base deformation caused by the lower push rod 113 acting on the displacement sensor base 131; the displacement sensor 121 is connected to the data acquisition and analysis mechanism 4 in communication; the displacement change value during the triaxial freezing and seepage of the soil is monitored by monitoring the deformation of the displacement sensor base 131, and then the frost heave rate and thaw settlement coefficient can be obtained. The axial pressure inlet 122 of the axial pressure loading cylinder 112 is connected to the axial pressure control pump 5 through a pipeline to realize pressure loading.

[0046] In another exemplary embodiment of the present application, the lower base 115 of the soil sample is made of polytetrafluoroethylene material, which has no nuclear magnetic resonance signal; the upper loading cap 116 of the soil sample is made of ceramic or PEEK polyetheretherketone material, which has little effect on the nuclear magnetic resonance test.

[0047] In another exemplary embodiment of the present application, the confining pressure simulation module includes a confining pressure chamber 123; the soil sample, the lower base 115 of the soil sample and the upper loading cap 116 of the soil sample are placed in the confining pressure chamber 123; the upper end of the confining pressure chamber 123 is connected to the upper top plate 117, and the lower end of the confining pressure chamber 123 is connected to the lower bottom plate 114; the nuclear magnetic probe coil 111 is located outside the confining pressure chamber 123, for example, it is wound around the outside of the confining pressure chamber 123.

[0048] A confining pressure inlet 124 is provided at the lower end of the confining pressure chamber 123, and a confining pressure outlet 125 is provided at the upper end of the confining pressure chamber 123; control valves are provided at both the confining pressure inlet 124 and the confining pressure outlet 125. The confining pressure inlet 124 is connected to the confining pressure control pump 6 through a pipeline to realize pressure loading. The outer side of the confining pressure chamber 123 is made of non-metallic material containing less hydrogen elements, and the internal chamber is a hollow structure. During the test, fluorinated liquid is injected into the confining pressure chamber 123 and the pressure is controlled by the confining pressure control pump 6.

[0049] In another exemplary embodiment of the present application, the seepage simulation module includes a seepage inlet pipeline 126 and a seepage outlet pipeline 127 .

[0050] The seepage inlet pipeline 126 passes through the lower push rod 113 and the soil sample lower base 115 from bottom to top in sequence; the outlet of the seepage inlet pipeline 126 contacts the lower end of the soil sample; and the inlet of the seepage inlet pipeline 126 is arranged on the side wall of the lower push rod 113 .

[0051] The inlet of the seepage outlet pipeline 127 contacts the upper end of the soil sample, and the outlet of the seepage outlet pipeline 127 is located at the lower end of the confining pressure chamber 123; Figure 7 As shown, the inlet of the seepage inlet pipeline 126 is the seepage inlet 128 ; the outlet of the seepage outlet pipeline 127 is the seepage outlet 129 .

[0052] The seepage inlet 128 is connected to the seepage control pump 7 through a pipeline. The seepage control pump 7 can control the seepage speed, seepage inlet and outlet pressure and volume.

[0053] like Figure 8As shown, the inlets of the axial pressure control pump 5, the confining pressure control pump 6 and the seepage control pump 7 are respectively connected to the corresponding liquid storage tank 8. For axial pressure control, the liquid in the corresponding liquid storage tank 8 is distilled water, and for confining pressure control, the liquid in the corresponding liquid storage tank 8 can be fluorinated liquid. Control switches 9 are respectively provided on the pipelines at the outlets of the axial pressure control pump 5, the confining pressure control pump 6 and the seepage control pump 7. Confining pressure sensors 10, axial pressure sensors 11 and seepage flow rate sensors 12 are respectively provided in the axial pressure control pump 5, the confining pressure control pump 6 and the seepage control pump 7; the axial pressure control pump 5, the confining pressure control pump 6 and the seepage control pump 7 mainly control the confining pressure, axial pressure and seepage flow rate values, and can carry out unconsolidated undrained shear, consolidated undrained shear and consolidated drained shear tests. The confining pressure sensor 10, the axial pressure sensor 11 and the seepage flow rate sensor 12 mainly measure the values ​​of the actual loaded confining pressure, axial pressure and seepage flow rate.

[0054] In order to realize the support of soil triaxial testing mechanism 1, Figure 6 As shown, the soil triaxial test mechanism 1 is arranged on a mobile test frame 130, wherein the axial pressure reaction frame 119 is fixedly connected to the mobile test frame 130 through its support rod, and the axial pressure loading cylinder 112 is also arranged on the mobile test frame 130. In order to fix the nuclear magnetic probe coil 111, the nuclear magnetic probe coil 111 is fixed to the support rod of the axial pressure reaction frame 119 through a fixing device, so that the confining pressure chamber 123 is located at the center of the nuclear magnetic probe coil 111.

[0055] In another exemplary embodiment of the present application, Figure 7 As shown, the structure of the low-temperature freezing mechanism 2 is the same as that of the confining pressure simulation module; the freezing circulating liquid inlet 21 of the low-temperature freezing mechanism 2 is the confining pressure inlet 124; the freezing circulating liquid outlet 22 of the low-temperature freezing mechanism 2 is the confining pressure outlet 125, so that the confining pressure inlet and outlet are also used to apply liquid circulation to allow the sample to undergo a variable temperature freezing experiment.

[0056] The low temperature freezing mechanism 2 can be used to perform the operation of gradually freezing the soil sample using different temperature gradients in step S3.

[0057] The freezing circulation liquid inlet 21 and the freezing circulation liquid outlet 22 are connected to the low-temperature freezing circulation pump 24 through the freezing circulation pipeline 23; the inlet and outlet of the freezing circulation pipeline 23 are provided with a temperature sensor; the temperature sensor is connected to the data acquisition and analysis mechanism 4 in communication; the temperature sensor is used to measure the temperature of the freezing circulation liquid at the inlet and outlet of the freezing circulation pipeline 23 in real time. The actual response temperature of the soil sample can be determined by measuring the temperature of the inlet and outlet circulating liquid. Before the test, the freezing temperature of the soil sample is set, and three temperature sensors are used, two of which are at the inlet and outlet of the freezing circulation liquid, and the other is inserted into the soil body. By recording the soil body temperature and the average inlet and outlet temperature of the circulating liquid, a temperature difference can be obtained. In the actual test, the actual temperature value of the soil sample is obtained by adding and subtracting the temperature difference from the known inlet and outlet average temperature. In the actual test, the measurement of the actual temperature value of the soil sample is calibrated and calculated by using the reading of the temperature sensor inserted into the soil body before the test and the difference between the average inlet and outlet temperature of the circulating liquid, so as to minimize the influence of the temperature sensor on the soil body during the test. The actual temperature value of the soil body will be displayed in the data acquisition and analysis mechanism 4.

[0058] Among them, the operating temperature range of the low-temperature freezing mechanism 2 is 65℃~-95℃, the control accuracy is ±0.1℃, and the circulating liquid medium is fluorinated liquid. The freezing circulating liquid inlet 21 and the freezing circulating liquid outlet 22 are connected to the freezing circulating pump 24 through pipelines to achieve gradual freezing of water in the soil sample. The freezing circulating pump 24 includes a heat exchanger, and the temperature of the circulating liquid in the freezing circulating pump 24 can be heat exchanged through the heat exchanger. The stability of the circulating liquid temperature is controlled by the secondary temperature control to control the stability of the soil temperature and reduce temperature fluctuations. The freezing circulation pipeline 23 is an insulated pipeline with an operating temperature range of 65℃~-95℃. The circulating liquid is mainly injected into the hollow pressure chamber and shares a chamber with the confining pressure. The confining pressure simulation module simulates the real confining pressure of the environment in which the soil sample is located, and at the same time uses the same liquid medium as the low-temperature freezing mechanism 2 to provide pressure supplement, thereby compensating for the pressure loss caused by temperature changes during the low-temperature freezing test.

[0059] The freezing temperature can be set by the data acquisition and analysis unit 4 to achieve freezing simulation at different freezing temperatures.

[0060] In another exemplary embodiment of the present application, Fig. 9 As shown, the nuclear magnetic resonance testing mechanism 3 specifically includes: a low-field nuclear magnetic resonance instrument 31, a low-field nuclear magnetic resonance imaging module 32 and a layered gradient module 33; the low-field nuclear magnetic resonance instrument 31, the low-field nuclear magnetic resonance imaging module 32 and the layered gradient module 33 are all communicated with the data acquisition and analysis mechanism 4; during the test, the soil triaxial testing mechanism 1 is located in the nuclear magnetic resonance testing area (i.e., the soil sample testing area) of the nuclear magnetic resonance testing mechanism 3.

[0061] The low-field nuclear magnetic resonance instrument 31 is mainly responsible for providing a uniform and stable magnetic field; the principle of the nuclear magnetic resonance testing mechanism 3 to test unfrozen water is mainly based on the nuclear magnetic resonance phenomenon, that is, after the atomic nucleus is excited by the radio frequency pulse in the magnetic field, the energy level transition will occur and a resonance signal will be generated. For the water in the soil, due to the existence of hydrogen nuclei, the low-field nuclear magnetic resonance technology can be used to detect its distribution, migration and changes in pore and crack structures.

[0062] The low-field nuclear magnetic resonance imaging module 32 is mainly used to image the soil during the test to observe the moisture distribution phenomenon inside the soil. The principle is mainly based on low-field nuclear magnetic resonance technology. Through operations such as magnetization, excitation, relaxation and signal detection, the internal structure and composition of the soil sample are detected (based on the signal information of water). Then, through data post-processing and pseudo-color enhancement, the nuclear magnetic resonance image of the moisture migration change process inside the soil sample is drawn in real time.

[0063] The layered gradient module 33 can collect the T2 spectrum of each layer by non-destructively slicing and stratifying the soil sample according to a certain thickness, so as to analyze the water content of each layer and the distribution of pore and fracture structure by analyzing the nuclear magnetic resonance signal information at different positions along the height of the soil sample. Specifically, the layered gradient module 33 is used to slice the soil sample according to a certain thickness to obtain the nuclear magnetic resonance data within a certain thickness, so as to observe the moisture, pores, fractures, etc. within different thicknesses of the soil sample, so as to comprehensively analyze the distribution of the water content of each layer and the pore and fracture structure.

[0064] The nuclear magnetic resonance testing mechanism 3 can be used to collect the nuclear magnetic resonance images in step S2 and step S3 in the above-mentioned testing method and the layered T2 spectra of the soil sample at different heights.

[0065] Existing testing devices are unable to simulate low temperature and seepage environments under real working conditions, and it is difficult to simultaneously achieve the coupling of confining pressure, axial pressure, seepage simulation and low temperature control within the limited space of a triaxial device. The testing device designed in this application can solve the above-mentioned problems.

[0066] Based on the test device given above, a specific process of the test implemented by using the test device is given, and the specific steps are as follows.

[0067] Step 1: Use the soil triaxial test device 1 to perform a triaxial test on the soil sample to simulate the real confining pressure, real axial pressure and seepage velocity under actual working conditions in the environment where the soil sample is located.

[0068] First, the confining pressure simulation module of the soil triaxial test mechanism 1 is controlled to apply confining pressure to the soil sample according to the actual confining pressure of the environment in which the soil sample is located. Some preparation work needs to be done before the confining pressure loading is realized. The soil sample (for example, with a diameter of 3.91 cm and a height of 8 cm) is prepared. Before placing the soil sample in the soil triaxial test mechanism 1, the air in the pipeline of the seepage inlet 128 and the pipeline of the seepage outlet 129 of the soil triaxial test mechanism 1 is emptied. After the air is emptied, the soil sample is placed on the lower base 115 of the soil sample, the upper top and lower bottom of the soil sample, the upper loading cap 116 of the soil sample and the lower base 115 of the soil sample are fixed, and then the triaxial instrument housing is put on. The housing is a collection of the confining pressure chamber 123 and the nuclear magnetic probe coil 111. The axial pressure inlet 122, the confining pressure inlet 124, the confining pressure outlet 125, the seepage inlet 128, and the seepage outlet 129 are connected to the corresponding pipelines. After the connection is completed, the soil triaxial test mechanism 1 is pushed into the nuclear magnetic resonance test area of ​​the nuclear magnetic resonance test mechanism 3, and the confining pressure control pump 6 is operated to continuously inject fluorinated liquid into the confining pressure cavity 123. The reading of the confining pressure sensor is used to determine whether the loaded confining pressure reaches the target confining pressure value.

[0069] Then, according to the real axial pressure of the environment where the soil sample is located, the axial pressure simulation module of the soil triaxial test mechanism 1 is controlled to apply axial pressure to the soil sample. The reading of the axial pressure sensor is used to determine whether the loaded axial pressure reaches the target axial pressure value.

[0070] Finally, the seepage simulation module of the soil triaxial test mechanism 1 is controlled according to the actual working conditions to simulate the seepage velocity of the soil sample. The seepage velocity is set according to the actual working conditions, and whether the soil sample is completely seeping is determined according to the reading of the seepage velocity sensor 12. When the flow rate at the seepage outlet 129 is monitored to change and is close to the flow rate at the seepage inlet 128, it is considered that the soil sample has achieved complete seepage, that is, the seepage channel is unobstructed.

[0071] Step 2: Use the nuclear magnetic resonance testing device 3 to collect the nuclear magnetic resonance image of the soil sample under the seepage before freezing and the layered T2 spectrum of the soil sample at different heights, and use the soil triaxial testing device 1 to collect the overall T2 spectrum of the soil sample under the seepage before freezing.

[0072] Firstly, the nuclear magnetic resonance testing mechanism 3 is controlled to provide a nuclear magnetic resonance magnetic field to the soil sample, and the nuclear magnetic resonance imaging parameters (magnet type, radio frequency pulse frequency range, radio frequency frequency control accuracy, radio frequency pulse accuracy, radio frequency transmission power, maximum sampling bandwidth, etc.) are adjusted, and the nuclear magnetic resonance images of the soil sample under the action of normal temperature seepage and the layered T2 spectra of the soil sample at different heights are collected.

[0073] Secondly, the nuclear magnetic probe coil 111 loaded in the soil triaxial testing mechanism 1 is controlled to collect the overall T2 spectrum of the soil sample before the soil sample is frozen.

[0074] Step 3: Use a low-temperature freezing mechanism to gradually freeze the soil sample based on different temperature gradients, use a nuclear magnetic resonance testing mechanism 3 to collect in real time the nuclear magnetic resonance image of the soil sample under the coupling of seepage and freezing and the layered T2 spectrum at different heights, and use a soil triaxial testing mechanism 1 to collect in real time the overall T2 spectrum of the soil sample under the coupling of seepage and freezing.

[0075] First, the freezing circulation liquid inlet 21 and the freezing circulation liquid outlet 22 are connected to the freezing circulation pump 24 through pipelines to achieve gradual freezing of the water in the soil sample. During the freezing process, axial pressure and seepage always exist.

[0076] Secondly, record the readings of the displacement sensor 121, the pressure sensor 120, and the temperature sensor, set the freezing temperature of the pump body according to the research needs, turn on the freezing circulation pump 24, and at the same time turn on the control switch 9 of the seepage channel to achieve freezing and seepage at the same time.

[0077] Finally, data is collected in real time, including the nuclear magnetic resonance image of the soil sample under the coupling of seepage and freezing, the overall T2 spectrum, and the layered T2 spectrum at different heights. The test is terminated after all the test condition data are collected, and the data is analyzed later.

[0078] Step 4: Analyze the data to obtain the evolution law of the whole process of soil sample freezing water migration characteristics. Using the data acquisition and analysis mechanism, according to the nuclear magnetic resonance images of the soil samples before and during freezing, the water distribution and water migration changes during the freezing process of the soil samples are quantitatively analyzed based on data post-processing; according to the overall T2 spectrum of the soil samples before and during freezing and the layered T2 spectrum of the soil samples at different heights, the changes in the unfrozen water content of the soil samples as a whole and at different height layers of the soil samples and the evolution law of pores and cracks during the freezing process of the soil samples are quantitatively analyzed based on data post-processing. Figure 2 This is a schematic diagram of the NMR image of the water migration process in clay under freezing and seepage. Figure 2 Brighter locations indicate higher water content. Figure 3 Schematic diagram of the overall T2 spectrum of clay under different freezing temperatures and seepage effects. Figure 4 Schematic diagram of the changes in clay pores under different freezing temperatures and seepage effects.

[0079] Data analysis is performed through various images, T2 spectra or sensor readings collected during freezing and seepage, such as analyzing displacement sensor readings and frost heave deformation caused by freezing, thereby analyzing the frost heave deformation of the entire soil sample.

[0080] This application has the following technical effects.

[0081] 1) The test technology for the evolution characteristics of soil freezing water migration under the action of triaxial seepage coupling based on low-field nuclear magnetic resonance proposed in this application can simultaneously create a test environment for freezing and seepage, which is convenient for further analysis of the evolution law of soil internal water migration characteristics under the simultaneous action of freezing and seepage.

[0082] 2) This application can realize high-precision, non-destructive real-time monitoring of the water migration process when the soil is frozen. Compared with traditional methods such as time domain reflectometry and differential scanning calorimetry, low-field nuclear magnetic resonance technology can more directly and accurately reflect the distribution and dynamic changes of water inside the soil, improving the accuracy and reliability of test data.

[0083] 3) This application can realize non-invasive real-time acquisition of changes in pores and cracks during soil freezing. Compared with traditional methods, low-field nuclear magnetic resonance technology does not require sampling, reduces disturbance to soil samples, and obtains the most realistic data on pores and cracks during freezing.

[0084] 4) The test technology for the evolution characteristics of soil freezing water migration under triaxial seepage coupling based on low-field nuclear magnetic resonance proposed in this application significantly improves the test efficiency and reduces the test cost. Traditional test methods often require a large amount of sample collection and a long test cycle, while this application significantly improves the test efficiency through integrated test equipment and automated test processes, while reducing sample consumption and labor costs.

[0085] 5) The test technology for the evolution characteristics of soil freezing water migration under triaxial seepage coupling based on low-field nuclear magnetic resonance proposed in this application enhances the repeatability and comparability of data. The use of standardized test equipment and corresponding test methods makes the test results of different batches and under different conditions more repeatable and comparable, which is conducive to the in-depth scientific research and the wide application of the results.

[0086] In summary, this application can provide certain technical support for studying the evolution of water migration and pore cracks in soil under the coupling of freezing and seepage, and can effectively reveal the hydrothermal coupling mechanism of frozen soil. By constructing a test device under the coupling of triaxial seepage and combining corresponding test methods, the soil freezing process in the actual environment is simulated, which is helpful to promote the development and improvement of frozen soil theory, further optimize the parameter setting and construction process of artificial freezing technology, improve freezing effect and construction efficiency, and reduce engineering costs.

[0087] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0088] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage, characterized in that: include: S1, the real confining pressure, real axial pressure and real seepage velocity of the simulated soil sample environment; S2. Collect the nuclear magnetic resonance image, overall and layered T2 spectrum of the soil sample under the action of seepage before freezing; the overall and layered T2 spectrum refers to the overall T2 spectrum of the soil sample and the layered T2 spectrum at different heights of the soil sample; S3, gradually freezing soil samples based on different temperature gradients, and collecting real-time nuclear magnetic resonance images, overall and layered T2 spectra of soil samples under the coupling of seepage and freezing; S4. Based on the nuclear magnetic resonance images, overall and layered T2 spectra of soil samples before and during freezing, the evolution law of water migration characteristics during the whole freezing process of soil samples was analyzed; the water migration characteristics include the water distribution in the soil samples, the changes in water migration, the changes in unfrozen water content and the changes in pores and cracks.

2. The method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 1 is characterized in that: Based on the nuclear magnetic resonance images, overall and layered T2 spectra of soil samples before and during freezing, the evolution of water migration characteristics during the whole freezing process of soil samples was analyzed, including: Based on the NMR images of soil samples before and during freezing, the moisture distribution and moisture migration changes during the freezing process of soil samples were qualitatively analyzed based on data post-processing. According to the overall and layered T2 spectra of soil samples before and during freezing, the changes in unfrozen water content and the evolution of pores and cracks in the soil samples as a whole and at different height layers during freezing are quantitatively analyzed based on data post-processing; the evolution of pores and cracks is determined based on the changes in pore and crack radius.

3. The method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 2 is characterized in that: The calculation formula for unfrozen water content is: ； In the formula, w u It is the unfrozen water content of soil sample during freezing process; w 0 is the total water content of the soil sample before freezing; is the total intensity value of the nuclear magnetic resonance signal before the soil sample is frozen, and the total intensity value of the nuclear magnetic resonance signal is determined according to the T2 spectrum; is the total intensity value of the NMR signal during the freezing process of the soil sample.

4. The method for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 3 is characterized in that: The calculation formula for pore and crack radius is: ； Where T2 is the transverse relaxation time; F is the pore characteristic factor or the fracture characteristic factor; is the surface relaxation rate; R is the pore radius or crack radius.

5. A test device for frozen soil water migration characteristics under low-temperature nuclear magnetic triaxial seepage, characterized in that: The device for testing the characteristics of frozen soil moisture migration under low-temperature nuclear magnetic triaxial seepage is used to implement the method for testing the characteristics of frozen soil moisture migration under low-temperature nuclear magnetic triaxial seepage according to any one of claims 1 to 4, and the device for testing the characteristics of frozen soil moisture migration under low-temperature nuclear magnetic triaxial seepage comprises: a soil triaxial testing mechanism, a low-temperature freezing mechanism, a nuclear magnetic resonance testing mechanism, and a data acquisition and analysis mechanism; The soil triaxial testing mechanism is used to simulate the real confining pressure, real axial pressure and real seepage conditions of the environment in which the soil sample is located, and to collect the overall T2 spectrum of the soil sample under the seepage effect before freezing and under the seepage and freezing coupling effect during freezing; The low temperature freezing mechanism is used to gradually freeze the soil sample based on different temperature gradients; The nuclear magnetic resonance testing mechanism is used to provide a nuclear magnetic resonance magnetic field to the soil sample, and collect nuclear magnetic resonance images of the soil sample under the seepage effect before freezing and the seepage and freezing coupling effect during freezing, and layered T2 spectra at different heights of the soil sample; The data acquisition and analysis mechanism is used to obtain nuclear magnetic resonance images, overall T2 spectra and layered T2 spectra at different heights of the soil sample before and during freezing, and analyze the evolution law of water migration characteristics during the whole freezing process of the soil sample; the water migration characteristics include the water distribution in the soil sample, the change of water migration, the change of unfrozen water content and the change of pores and cracks.

6. The device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 5 is characterized in that: The soil triaxial testing mechanism specifically includes: an axial pressure simulation module, a confining pressure simulation module, a seepage simulation module and a nuclear magnetic probe coil; The axial pressure simulation module is used to simulate the real axial pressure of the environment in which the soil sample is located; The confining pressure simulation module is used to simulate the actual confining pressure of the environment in which the soil sample is located; The seepage simulation module is used to simulate the actual seepage conditions of the environment in which the soil sample is located; The nuclear magnetic probe coil is used to excite the soil sample to resonate and receive the soil sample resonance signal to obtain the overall T2 spectrum of the soil sample before and during freezing.

7. The device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 6 is characterized in that: The axial pressure simulation module includes an axial pressure loading cylinder, a lower push rod, a lower base plate, a soil sample lower base, a soil sample upper loading cap, an upper push plate, an upper push rod and an axial pressure reaction frame; The upper end of the axial pressure loading cylinder is connected to the lower end of the soil sample through the lower push rod, the lower bottom plate, and the lower base of the soil sample in sequence; the lower push rod penetrates the lower bottom plate and contacts the lower end of the lower base of the soil sample; The upper end of the soil sample is connected to the axial pressure reaction frame through the soil sample upper loading cap, the upper top plate and the upper push rod in sequence; the lower end of the upper push rod penetrates the upper top plate and contacts the upper end of the soil sample upper loading cap; A pressure sensor is arranged between the upper push rod and the axial pressure reaction frame; the pressure sensor is connected to the data acquisition and analysis mechanism for communication; the pressure sensor is used to measure the magnitude of the axial pressure exerted by the axial pressure loading cylinder on the soil sample; A displacement sensor base is arranged at the upper end of the axial pressure loading cylinder, the upper end of the displacement sensor base is in contact with the lower push rod, and a displacement sensor is arranged on the side of the displacement sensor base. The displacement sensor is used to monitor the axial pressure deformation by monitoring the deformation of the base caused by the lower push rod acting on the displacement sensor base; the displacement sensor is communicatively connected with the data acquisition and analysis mechanism.

8. The device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 7 is characterized in that: The confining pressure simulation module includes a confining pressure chamber; a soil sample, a lower base of the soil sample and an upper loading cap of the soil sample are placed in the confining pressure chamber; the upper end of the confining pressure chamber is connected to the upper top plate, and the lower end of the confining pressure chamber is connected to the lower bottom plate; the nuclear magnetic probe coil is located outside the confining pressure chamber; A confining pressure inlet is arranged at the lower end of the confining pressure chamber, and a confining pressure outlet is arranged at the upper end of the confining pressure chamber; control valves are arranged at both the confining pressure inlet and the confining pressure outlet.

9. The device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 8, characterized in that: The seepage simulation module includes a seepage inlet pipeline and a seepage outlet pipeline; The seepage inlet pipeline passes through the lower top rod and the lower base of the soil sample from bottom to top in sequence; the outlet of the seepage inlet pipeline contacts the lower end of the soil sample; the inlet of the seepage inlet pipeline is arranged on the side wall of the lower top rod; The inlet of the seepage outlet pipeline contacts the upper end of the soil sample, and the outlet of the seepage outlet pipeline is located at the lower end of the confining pressure cavity.

10. The device for testing the characteristics of frozen soil water migration under low-temperature nuclear magnetic triaxial seepage according to claim 8, characterized in that: The structure of the low-temperature freezing mechanism is the same as that of the confining pressure simulation module; the freezing circulating liquid inlet of the low-temperature freezing mechanism is the confining pressure inlet; the freezing circulating liquid outlet of the low-temperature freezing mechanism is the confining pressure outlet; The freezing circulation liquid inlet and the freezing circulation liquid outlet are connected to the freezing circulation pump through the freezing circulation pipeline; the inlet and outlet of the freezing circulation pipeline are provided with temperature sensors; the temperature sensors are connected to the data acquisition and analysis mechanism in communication; the temperature sensors are used to measure the temperature of the freezing circulation liquid at the inlet and outlet of the freezing circulation pipeline in real time; The freezing circulation pump includes a heat exchanger; the heat exchanger is used to perform heat exchange treatment on the freezing circulation fluid in the freezing circulation pump.

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