A Visualized Radial Permeability Test System and Method for Frozen Soil

Abstract

This invention relates to the field of permafrost permeability testing technology, and discloses a visualized radial permeability testing system for permafrost, comprising: a temperature control system, including a low-temperature control chamber; a sample permeation chamber, located inside the low-temperature control chamber, including a soil sample box and a microporous permeation tube, the soil sample box including a visual panel; a pressurized liquid replenishment system, including a pressure-volume controller and a storage tank, the storage tank containing a permeation medium, the permeation medium including dimethyl silicone oil mixed with a fluorescent agent, one end of the pressure-volume controller being immersed in the storage tank, and the other end being connected to the microporous permeation tube; a data acquisition system, including a data acquisition unit, at least one temperature sensor and at least one moisture sensor; and a visualization analysis system, including a computer, an industrial camera, and at least one ultraviolet lamp. This invention also discloses a visualized radial permeability testing method for permafrost. This invention closely follows actual seepage patterns, eliminates test deviations caused by the permeation medium at the source, provides visualized monitoring and data acquisition, and achieves high testing accuracy.

Description

Technical Field

[0001] This invention relates to the field of permafrost permeability testing technology, and in particular to a visual radial permeability testing system and method for permafrost. Background Technology

[0002] The permeability characteristics of frozen soil are core research parameters in engineering fields such as frost heave and thaw settlement of roadbeds in cold regions, slope seepage and instability, and seepage prevention design of hydraulic engineering projects. Essentially, it describes the volumetric flow rate of liquid water through a unit cross-sectional area of ​​soil per unit time under a unit head difference, and is a quantitative indicator reflecting the hydraulic conductivity of the soil. In frozen soil, larger voids are filled with ice, and an unfrozen water film coats the surface of ice and soil particles, forming a series of tortuous and continuous liquid channels through which unfrozen water infiltrates and migrates.

[0003] Traditional permeability testing technology for frozen soil has undergone three generations of iterations, but it still suffers from core problems such as disconnect from actual engineering conditions, insufficient testing accuracy, and limited monitoring methods. Currently, most commonly used permeability testing devices in the industry employ a unidirectional linear permeability mode. However, in natural permeable soil environments, groundwater and moisture migration often exhibit radial seepage patterns, spreading from a localized area to the surrounding soil. The testing scenarios of existing devices are severely disconnected from actual engineering conditions, and the measured test data cannot be directly used for seepage analysis in cold-region engineering. Secondly, it is impossible to visually observe the key processes such as the seepage path, diffusion morphology, and seepage range of the permeable medium within the frozen soil, resulting in insufficient intuitiveness and comprehensiveness of the test data. Furthermore, traditional constant head and variable head methods can only test the permeability coefficient of saturated soil at normal temperatures, failing to maintain sample structural stability under low-temperature freezing conditions. They also cannot cover full-condition testing of unsaturated frozen soil, soils with different dry densities, particle sizes, and soil types, making their applicability in the field of frozen soil engineering extremely low. In summary, existing permeability testing technology can no longer meet the precision requirements of current cold-region engineering construction and frozen soil mechanics research. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a visual radial permeability test system and method for frozen soil.

[0005] To achieve the above objectives, an embodiment of the present invention provides the following technical solution:

[0006] A visual radial permeability testing system for frozen soil includes:

[0007] A temperature control system, comprising a low-temperature control box;

[0008] The sample permeation chamber is located inside the low-temperature control box. The sample permeation chamber includes a soil sample box and a microporous permeation tube horizontally arranged in the center of the soil sample box. The soil sample box includes a visual panel.

[0009] A pressurized fluid replenishment system, comprising a pressure-volume controller and a storage tank, wherein the storage tank contains a permeation medium, the permeation medium comprising dimethyl silicone oil doped with a fluorescent agent, and one end of the pressure-volume controller is immersed in the storage tank, the other end of which is connected to the microporous permeation tube;

[0010] A data acquisition system, comprising a data acquisition unit and a sensor assembly connected to the data acquisition unit, the sensor assembly comprising at least one sensor group, the sensor group comprising at least one temperature sensor and at least one moisture sensor disposed in the soil sample box;

[0011] A visualization analysis system includes a computer, an industrial camera, and at least one ultraviolet light. The industrial camera, pressure and volume controller, and data acquisition device are all connected to the computer. The at least one ultraviolet light is located inside the low-temperature control chamber and faces the visual panel.

[0012] As a further improvement of the present invention, a scale is provided around the perimeter of the visible panel.

[0013] As a further improvement of the present invention, the sensor assembly includes two sensor groups symmetrically arranged relative to the microporous permeation tube, wherein the moisture sensor and the temperature sensor in each sensor group are alternately distributed along the horizontal direction.

[0014] As a further improvement of the present invention, the viscosity of the dimethyl silicone oil is 5 cst, and the fluorescent agent is LUYOR-6100 type fluorescent agent.

[0015] As a further improvement of the present invention, the soil sample box further includes an upper plate, a bottom plate, two side plates and a rear plate. The upper plate and the bottom plate are arranged opposite to each other, and the rear plate is arranged opposite to the visible panel. The visible panel, the upper plate, the bottom plate, the two side plates and the rear plate are connected as one unit.

[0016] As a further improvement of the present invention, the visible panel, the two side panels, and the rear panel are all snapped together with the bottom plate.

[0017] As a further improvement of the present invention, a first liquid injection valve is provided at the center of the rear plate, and the first liquid injection valve is connected to one end of the microporous permeation tube.

[0018] As a further improvement of the present invention, a second liquid injection valve is provided at the center of the visible panel, and the second liquid injection valve is connected to the other end of the microporous permeation tube.

[0019] A method for visualizing radial permeability testing of frozen soil, using the aforementioned visualizing radial permeability testing system, includes the following steps:

[0020] (1) Sample installation: When the sample is a saturated soil sample, proceed to step (2); when the sample is an unsaturated soil sample, proceed to step (3).

[0021] (2) For saturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeable tube, put the sample, temperature sensor and moisture sensor into the soil sample box, after putting the sample in, lay a filter cloth on the sample, then place a permeable stone on the filter cloth, and finally seal the soil sample box and put the soil sample box into the low temperature control box.

[0022] (3) For unsaturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeation tube, put the sample, temperature sensor and moisture sensor into the soil sample box, seal the soil sample box after putting the sample in, and put the soil sample box into the low temperature control box.

[0023] (4) Adjust the position of the industrial camera so that the view panel image is centered within the view of the industrial camera;

[0024] (5) Select dimethyl silicone oil as the permeation medium, add fluorescent agent into the dimethyl silicone oil and let it fully mix, immerse one end of the pressure volume controller in the storage tank containing the permeation medium, and connect the other end to the microporous permeation tube;

[0025] (6) Adjust the temperature of the low temperature control box to perform in-situ freezing. After the temperature inside the frozen soil sample reaches the freezing temperature and tends to stabilize, determine the data transmitted by the temperature sensor. Then adjust the temperature of the low temperature control box to the test temperature so that the temperature inside the sample reaches the test temperature and tends to stabilize.

[0026] (7) Turn on the pressure volume controller, adjust the permeation pressure to the pressure value required for the test, connect the microporous permeation tube, start the frozen soil permeation test, record the volume of the permeation medium injected at regular intervals and take photos with an industrial camera.

[0027] (8) During the test, the microporous permeation tube is always kept in one end with the permeation medium. After the test, the radial permeation velocity and permeability coefficient of the sample are calculated.

[0028] As a further improvement of the present invention, the formula for calculating the permeability coefficient is as follows:

[0029]

[0030] In the formula, Permeability coefficient, The density of the permeating medium, It is the acceleration due to gravity. For grouting volume, For grouting pressure, The length of the microporous permeation tube. The diffusion radius of the permeable medium in frozen soil. The radius of the microporous permeation tube is given.

[0031] The beneficial effects of this invention are:

[0032] (1) The permeation medium has the best compatibility and the test results are highly consistent with reality. Dimethyl silicone oil was selected as the core permeation medium. The addition of fluorescent agent does not change its physical properties. This mixed medium will neither freeze nor thaw the frozen soil sample, which meets the core temperature requirements for frozen soil permeation measurement. At the same time, its molecular size, wetting angle and viscosity are very close to those of water. The interaction law between it and frozen soil particles and unfrozen water film is consistent with the actual liquid water. This eliminates the test deviation caused by the permeation medium from the root and ensures that the test results can truly reflect the actual hydraulic conduction characteristics of frozen soil.

[0033] (2) Achieve visualized and precise monitoring of the permafrost seepage process. Through the visualization combination of dimethyl silicone oil, fluorescent agent, ultraviolet lamp, industrial camera, and visual panel, the seepage medium appears yellow-green inside the permafrost, allowing real-time observation of the seepage path and diffusion pattern. In addition, the scale of the visual panel can accurately measure key parameters such as seepage area and diffusion radius, which not only allows for intuitive analysis of the non-uniform seepage pattern inside the permafrost, but also provides accurate and intuitive parameters for calculating the permeability coefficient.

[0034] (3) Precise and stable pressure and temperature control significantly reduce test errors. The pressure and volume controller can achieve high-precision air pressure output and maintain stability for a long time. It monitors and displays the injection volume and discharge volume of the medium in real time, and the metering accuracy reaches micro-level, which greatly eliminates the error caused by air pressure fluctuations. The low temperature control box accurately controls the temperature throughout the process, avoiding the melting of frozen soil samples or changes in permeability caused by temperature fluctuations. It provides a stable and controllable pressure and temperature environment for the test, which greatly improves the reliability of the test results.

[0035] (4) Comprehensive and refined data acquisition enables synchronous monitoring of hydrothermal coupling. The symmetrical, multi-point arrangement of four moisture sensors and two temperature sensors covers the permeation center area and the area far from the permeation center of the frozen soil sample, realizing synchronous, multi-point, and refined monitoring of the temperature field and the unfrozen water content field. It can acquire hydrothermal coupling data in the frozen soil seepage process, providing comprehensive and reliable basic data for frozen soil seepage process analysis and hydrothermal coupling numerical calculation.

[0036] (5) The seepage simulation closely matches reality, enhancing the value of the test project. The use of columnar microporous permeable tubes to achieve radial diffusion of the permeable medium accurately simulates the actual seepage law of water migration from local areas to the surrounding radial direction in natural permafrost. Compared with the unidirectional linear permeability of existing technologies, the test results are more suitable for permafrost seepage analysis in actual engineering projects, enhancing the engineering application value of the test results.

[0037] (6) The system is modularly designed, making operation and maintenance convenient and efficient. Each system is independently modularly integrated, which simplifies the operation process of unsaturated sample preparation, sample installation and test debugging, and greatly improves test efficiency; each component can be quickly disassembled and replaced after damage, making it highly maintainable and versatile.

[0038] (7) The device has wide applicability and realizes integrated measurement of permeability coefficient of frozen and thawed soil. The comparative test under the previous thawed soil condition shows that the permeability coefficient measured by this system has good consistency with the results of traditional constant head and variable head tests. This proves that the system can not only accurately measure the permeability coefficient of frozen soil, but also be used to measure the permeability coefficient of thawed soil, realizing multiple uses of one system and greatly improving the practical value and application scenarios of the system.

[0039] (8) Automated data acquisition improves experimental efficiency and data reliability. The data acquisition system can automatically and periodically collect data such as temperature and unfrozen water content. The industrial camera automatically captures the seepage process, and the pressure-volume controller records the volume change of the permeating medium in real time. No manual intervention is required throughout the process, which not only improves the efficiency of experimental operation but also avoids errors caused by manual recording, ensuring the real-time, accuracy, and completeness of experimental data. A multi-dimensional permeability coefficient calculation model based on visualized permeable area and precise pressure values ​​has been established. Compared with the single indirect parameter calculation of existing technologies, the input parameters are more comprehensive and accurate. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of a preferred embodiment of the present invention;

[0042] Figure 2 This is a side view of the sample permeation chamber according to a preferred embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of the sample permeation chamber according to a preferred embodiment of the present invention;

[0044] Figure 4 This is a model diagram of the permeability coefficient of frozen soil according to a preferred embodiment of the present invention;

[0045] Figure 5 for Figure 4 BB-direction sectional view;

[0046] In the diagram: 1. Temperature control system; 11. Low temperature control box; 2. Sample permeation chamber; 21. Soil sample box; 211. Visual panel; 2111. Scale; 212. Top plate; 2121. Through hole; 213. Bottom plate; 214. Side plate; 2141. Screw hole; 215. Rear plate; 216. First injection valve; 217. Second injection valve; 22. Microporous permeation tube; 23. Silicone gasket; 3. Pressurized liquid replenishment system; 31. Pressure and volume controller; 32. Liquid storage tank; 33. Connecting pipe; 4. Data acquisition system; 41. Data acquisition device; 42. Temperature sensor; 43. Moisture sensor; 5. Visualization analysis system; 51. Computer; 52. Industrial camera; 53. Ultraviolet lamp. Detailed Implementation

[0047] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0048] Please see Figures 1-3This application discloses a visual radial permeability test system for frozen soil, including a temperature control system 1, a sample permeation chamber 2, a pressurized liquid replenishment system 3, a data acquisition system 4, and a visualization analysis system 5. The temperature control system 1 includes a low-temperature control box 11. The sample permeation chamber 2 is located inside the low-temperature control box 11 and includes a soil sample box 21 and a microporous permeation tube 22 horizontally positioned at the center of the soil sample box 21. The soil sample box 21 includes a visual panel 211. The pressurized liquid replenishment system 3 includes a pressure-volume controller 31 and a storage tank 32. The storage tank 32 contains a permeation medium, which includes dimethyl silicone oil mixed with a fluorescent agent. One end of the pressure-volume controller 31 is immersed in the storage tank 32, and the other end is connected to the microporous permeation tube 22. The data acquisition system 4 includes a data acquisition unit 41 and a sensor assembly connected to the data acquisition unit 41. The sensor assembly includes at least one sensor group, which includes at least one temperature sensor 42 and at least one moisture sensor 43 disposed in the soil sample box 21. The visualization analysis system 5 includes a computer 51, an industrial camera 52, and at least one ultraviolet lamp 53. The industrial camera 52, pressure volume controller 31, and data acquisition device 41 are all connected to the computer 51. At least one ultraviolet lamp 53 is located inside the low temperature control box 11 and faces the visual panel 211.

[0049] The cryogenic control chamber 11, as the core temperature control component, ensures constant temperature control of the frozen soil sample during the experiment, avoiding temperature fluctuations. During the experiment, the sample permeation chamber 2 is entirely placed inside the cryogenic control chamber 11, achieving constant temperature control of the frozen soil sample throughout the entire experiment. This prevents temperature fluctuations from interfering with the frozen soil's ice phase structure, unfrozen water content, and permeability characteristics, providing a stable low-temperature environment for the experiment. A centrally shaped microporous permeation tube 22 is used to achieve radial diffusion of the permeation medium, accurately simulating the actual permeation law of water migration radially from a local area to the surrounding area within natural frozen soil. The experimental results are more suitable for frozen soil permeation analysis in practical engineering, enhancing the engineering application value of the experimental results. The pressure-volume controller 31 enables precise air pressure adjustment and maintains stable pressure over long periods of operation. It monitors and displays the injection and discharge volumes of the permeation medium in real time, achieving micro-level measurement accuracy. Dimethyl silicone oil mixed with a fluorescent agent is used as the permeation medium. Low freezing point and thawing tests show that this mixed medium neither freezes nor thaws the frozen soil sample, and its physicochemical properties are highly similar to water, fundamentally solving the problem of poor compatibility of the permeation medium. The fluorescent agent is excited by a UV lamp 53, causing the dimethyl silicone oil to exhibit a yellow-green color, thus enabling visual tracking of the seepage process. Temperature sensor 42 and moisture sensor 43 can monitor the temperature field and unfrozen water content of the sample in real time, achieving simultaneous monitoring of temperature change characteristics and the moisture diffusion process.

[0050] Preferably, the soil sample box 21 further includes an upper plate 212, a bottom plate 213, two side plates 214, and a rear plate 215. The upper plate 212 and the bottom plate 213 are arranged opposite to each other, and the rear plate 215 is arranged opposite to the visible panel 211. The visible panel 211, the upper plate 212, the bottom plate 213, the two side plates 214, and the rear plate 215 are connected as a single unit. Specifically, the visible panel 211 is made of acrylic, while the upper plate 212, the bottom plate 213, the two side plates 214, and the rear plate 215 are all made of aluminum alloy. The two side plates 214 are respectively connected to the upper plate 212 and the rear plate 215 by screws. Preferably, multiple screw holes 2141 are provided on the side plates 214 to facilitate screws passing through the screw holes 2141 for tightening. Preferably, sealant is applied between each plate and inside the threads, and waterproof tape is applied to ensure airtightness. Preferably, the upper plate 212 is provided with multiple through holes 2121 to facilitate the passage of the wires of the temperature sensor 42 and the moisture sensor 43.

[0051] Preferably, silicone gaskets 23 are placed between the two ends of the microporous permeation tube 22 and the visible panel 211 and the back panel 215 of the soil sample box 21, respectively. Sealant is applied around the silicone gaskets 23 to increase the sealing of the soil sample box 21. Preferably, the microporous permeation tube is a PE microporous permeation tube, as PE material causes minimal damage to the interior of the soil sample, is environmentally friendly, and inexpensive.

[0052] To more accurately measure the final penetration area of ​​the test, it is preferable that the visible panel 211 is provided with scales 2111 around its perimeter.

[0053] Preferably, the visible panel 211, the two side panels 214, and the rear panel 215 are all snapped into the base plate 213. This design simplifies the operation process of sample preparation, sample installation, and test debugging, significantly improving test efficiency; damaged components can be quickly disassembled and replaced, offering strong maintainability and versatility. To improve sealing and stability, waterproof tape is preferably applied at the snap-fit ​​points between the visible panel 211, the two side panels 214, the rear panel 215, and the base plate 213.

[0054] Preferably, a first injection valve 216 is centrally located on the rear panel 215, and the first injection valve 216 is connected to one end of the microporous permeation tube 22. Preferably, the other end of the pressure-volume controller 31 is connected to the first injection valve 216 via a connecting pipe 33, facilitating the injection of the permeation medium from the storage tank 32 into the microporous permeation tube 22 along the connecting pipe 33 and the first injection valve 216. Preferably, a second injection valve 217 is centrally located on the visible panel 211, and the second injection valve 217 is connected to the other end of the microporous permeation tube 22. Before the permeation medium is introduced into the microporous permeation tube 22, the first injection valve 216 can be connected to an air pump for venting by opening the second injection valve 217. After the permeation medium is introduced into the microporous permeation tube 22, i.e., when the permeation test officially begins, the second injection valve 217 is closed and sealed with waterproof tape.

[0055] The preferred sensor assembly includes two sensor groups symmetrically arranged relative to the microporous permeation tube 22. In each sensor group, moisture sensors 43 and temperature sensors 42 are alternately distributed horizontally. Preferably, each sensor group includes one temperature sensor 42 and two moisture sensors 43, with the temperature sensor 42 located between the two moisture sensors 43. This symmetrical, multi-point arrangement of the two temperature sensors 42 and four moisture sensors 43 covers both the permeation center and the area far from permeation in the frozen soil sample, enabling synchronous, multi-point, and refined monitoring of the temperature field and the unfrozen moisture content field. This allows for the acquisition of hydrothermal coupling data during the frozen soil seepage process, providing more comprehensive and reliable basic data for frozen soil seepage process analysis and hydrothermal coupling numerical calculations. Of course, it is understood that more temperature sensors 42 and moisture sensors 43 can be set as needed. Preferably, the temperature sensor 42 is a thermistor temperature sensor.

[0056] The preferred dimethyl silicone oil has a viscosity of 5 cst, and the fluorescent agent is LUYOR-6100 type fluorescent agent, which further improves the compatibility with the permeation medium.

[0057] In use, the pressure volume controller 31 is connected to the first injection valve 216 of the sample permeation chamber 2 via the connecting pipe 33. Under air pressure, the permeation medium in the storage tank 32 is pressurized into the microporous permeation tube 22. Under air pressure, the permeation medium seeps into the frozen soil sample through the micropores, causing the permeation medium to diffuse radially from the center to the surrounding soil, simulating the seepage process inside natural frozen soil. During the test, the temperature control system 1 maintains a constant test temperature of the sample throughout the process through the low temperature control box 11. The data acquisition system 4 synchronously collects the temperature and unfrozen moisture content data inside the sample through the temperature sensor 42 and the moisture sensor 43, and transmits them to the computer 51 through the data acquisition device 41. The ultraviolet light of the visualization analysis system 5 excites the fluorescent agent to make the dimethyl silicone oil color. The industrial camera records the seepage process and diffusion morphology in real time. Finally, the accurate calculation of the permeability coefficient of frozen soil is completed through the matching theoretical model.

[0058] This invention introduces the columnar diffusion theory from the field of engineering grouting into the study of radial seepage in frozen soil. Combining Darcy's law, fractal theory and capillary bundle model, it establishes a theoretical system for calculating the permeability coefficient that is suitable for all working conditions of saturated and unsaturated frozen soil, providing complete theoretical support for the structural design, implementation of experimental methods and accurate quantification of permeability coefficient of this test system.

[0059] Grouting columnar diffusion theory is a physical model used to study the diffusion of liquids or gases in porous media. In permafrost research, water permeability is significantly affected by temperature, ice crystal formation, and the freezing process. Therefore, traditional soil permeability models often cannot accurately describe the water flow characteristics in permafrost. To address this issue, a permafrost permeability coefficient model is established by combining grouting columnar diffusion theory, which can more accurately simulate the water diffusion process in permafrost. Columnar diffusion theory is based on Darcy's law and the principle of mass conservation, and therefore rests on the following assumptions:

[0060] (1) Homogeneous porous medium, with porosity and permeability evenly distributed within the grouting area;

[0061] (2) The liquid is a Newtonian fluid with constant viscosity;

[0062] (3) The diffusion process is a steady-state flow (ignoring the time term), which conforms to Darcy's law;

[0063] (4) The effects of phase transition and temperature gradient are not considered.

[0064] Based on the above assumptions, when exploring the mechanism of columnar permeation, the following approach is adopted: Figure 4 , Figure 5 The permeability model of frozen soil is shown. Figure 4 , Figure 5 middle, This refers to the grouting pressure. It is the diffusion radius of the permeable medium in frozen soil (equivalent to the effective seepage length). This is the length of the microporous permeation tube. Because... Grouting volume meets the following requirements:

[0065]

[0066] In the formula, It can be read directly by a computer. It represents the surface area of ​​a power-law fluid undergoing annular diffusion in a porous medium, i.e., the flow area perpendicular to the direction of flow of the permeating medium. Radial seepage velocity, in m / s. It can be obtained from the following formula:

[0067]

[0068] Furthermore, assuming the flow is radially symmetric, under pressure-driven conditions, the radial seepage velocity formula is obtained by solving the flow problem using the Laplace equation:

[0069]

[0070] In the formula, The viscosity of the osmotic solution is expressed in Pa. s, Intrinsic permeability, in meters. 2 .

[0071] Substituting equations (2) and (3) into formula (1), we get:

[0072]

[0073] And for the radius from arrive Pressure from arrive integral( This refers to the pressure at the wall of the microporous permeable tube. diffusion radius The pressure value at the front edge is negligible due to the small pressure transmission loss within the permafrost; therefore, the values ​​selected later in this paper... The intrinsic permeability can be obtained by using the actual applied grouting pressure (not the grouting pressure difference). :

[0074]

[0075] In the formula, The radius of the microporous permeation tube is given.

[0076] Permeability coefficient With intrinsic permeability The relationship is:

[0077]

[0078] In the formula, Density of the permeating medium, in kg / m³ 3 , This is the acceleration due to gravity.

[0079] Substituting equation (5) into equation (6) yields the result based on grouting pressure. Permeability coefficient inversion formula:

[0080]

[0081] This application also discloses a method for visualizing radial permeability testing of frozen soil. Using the visualizing radial permeability testing system described above, the method includes the following steps:

[0082] (1) Sample installation: When the sample is a saturated soil sample, proceed to step (2); when the sample is an unsaturated soil sample, proceed to step (3).

[0083] (2) For saturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeable tube 22, put the sample, temperature sensor 42 and moisture sensor 43 into the soil sample box 21, after putting the sample in, lay a filter cloth on the sample, then place a permeable stone on the filter cloth, and finally seal the soil sample box 21 and put the soil sample box 21 into the low temperature control box 11.

[0084] Specifically, in step (2), the sample, after being left to stand for 24 hours, is layered from bottom to top into the soil sample box 21 and compacted. Temperature sensor 42 and moisture sensor 43 are installed at the sampling height. The sample is then loaded to a suitable height, and a filter cloth made of needle-punched felt is laid on the sample. A custom-made rectangular permeable stone is then placed on the filter cloth. The filter cloth and permeable stone are designed to prevent soil and mud from seeping out when the vacuum is saturated. Holes are pre-drilled in the filter cloth and permeable stone according to the distribution positions of temperature sensor 42 and moisture sensor 43 to facilitate the passage of wires from temperature sensor 42 and moisture sensor 43. Finally, the plate 212 is sealed. Temperature sensor 42 and moisture sensor 43 are both connected to data acquisition device 41 via wires. Data acquisition device 41 is connected to computer 51. Data acquisition device 41 collects data once at regular intervals. The sample permeation chamber 2, with the sample loaded, is placed inside the low-temperature control box 11 and positioned accordingly.

[0085] (3) For unsaturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeation tube 22, put the sample, temperature sensor 42 and moisture sensor 43 into the soil sample box 21, seal the soil sample box 21 after the sample is placed, and put the soil sample box 21 into the low temperature control box 11.

[0086] Specifically, in step (3), the sample, after being left to stand for 24 hours, is layered from bottom to top into the soil sample box 21 and compacted. Temperature sensor 42 and moisture sensor 43 are installed at the sampling height level. The sample is then filled to a suitable height, and finally the upper plate 212 is sealed. Temperature sensor 42 and moisture sensor 43 are both connected to data acquisition device 41 via wires. Data acquisition device 41 is connected to computer 51. Data acquisition device 41 collects data once at regular intervals. The sample permeation chamber 2, with the sample filled, is placed inside the low-temperature control box 11 and positioned correctly.

[0087] (4) Adjust the position of the industrial camera 52 so that the image of the visible panel 211 is centered within the image of the industrial camera 52.

[0088] (5) Select dimethyl silicone oil as the permeation medium, add fluorescent agent into the dimethyl silicone oil and let it fully mix, immerse one end of the pressure volume controller 31 in the storage tank 32 containing the permeation medium, and connect the other end to the microporous permeation tube 22.

[0089] Preferably, the dimethyl silicone oil has a viscosity of 5 cst and the fluorescent agent is LUYOR-6100 type fluorescent agent, which further improves the compatibility of the permeation medium.

[0090] (6) Adjust the temperature of the low temperature control box 11 to perform in-situ freezing. After the temperature inside the frozen soil sample reaches the freezing temperature and tends to stabilize, the temperature of the low temperature control box 11 is adjusted to the test temperature so that the temperature inside the sample reaches the test temperature and tends to stabilize.

[0091] The freezing temperature of the sample can be measured by a special freezing temperature test to ensure that the soil sample can freeze. After the temperature sensor 42 detects that the internal temperature of the sample has reached the freezing temperature, the next step is to adjust the temperature of the low temperature control box 11 to the test temperature.

[0092] (7) Turn on the pressure volume controller 31, adjust the permeation pressure to the pressure value required for the test, connect the microporous permeation tube 22, start the frozen soil permeation test, record the volume of the permeation medium injected at regular intervals and take pictures through the industrial camera 52.

[0093] (8) During the test, the microporous permeation tube 22 is always kept in one end with the permeation medium. After the test, the radial permeation velocity and permeability coefficient of the sample are calculated.

[0094] During the permeation test, different test temperatures and permeation pressures are set, and multiple sets of test data are collected through temperature sensor 42, moisture sensor 43 and pressure volume controller 31. The radial seepage velocity and permeability coefficient corresponding to each set of data are calculated, thereby obtaining the permeation characteristics of frozen soil under different test temperatures, unfrozen water content and permeation pressures.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0096] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A visual radial permeability testing system for frozen soil, characterized in that, include: A temperature control system, comprising a low-temperature control box; The sample permeation chamber is located inside the low-temperature control box. The sample permeation chamber includes a soil sample box and a microporous permeation tube horizontally arranged in the center of the soil sample box. The soil sample box includes a visual panel. A pressurized fluid replenishment system, comprising a pressure-volume controller and a storage tank, wherein the storage tank contains a permeation medium, the permeation medium comprising dimethyl silicone oil doped with a fluorescent agent, and one end of the pressure-volume controller is immersed in the storage tank, the other end of which is connected to the microporous permeation tube; A data acquisition system, comprising a data acquisition unit and a sensor assembly connected to the data acquisition unit, the sensor assembly comprising at least one sensor group, the sensor group comprising at least one temperature sensor and at least one moisture sensor disposed in the soil sample box; A visualization analysis system includes a computer, an industrial camera, and at least one ultraviolet light. The industrial camera, pressure and volume controller, and data acquisition device are all connected to the computer. The at least one ultraviolet light is located inside the low-temperature control chamber and faces the visual panel.

2. The visual radial permeability testing system for frozen soil according to claim 1, characterized in that, A ruler is provided around the perimeter of the visible panel.

3. The visual radial permeability testing system for frozen soil according to claim 1, characterized in that, The sensor assembly includes two sensor groups symmetrically arranged relative to the microporous permeation tube, with the moisture sensor and temperature sensor of each sensor group alternately distributed along the horizontal direction.

4. The visual radial permeability testing system for frozen soil according to claim 1, characterized in that, The viscosity of the dimethyl silicone oil is 5 cst, and the fluorescent agent is LUYOR-6100 type fluorescent agent.

5. The visual radial permeability testing system for frozen soil according to claim 1, characterized in that, The soil sample box also includes an upper plate, a bottom plate, two side plates, and a rear plate. The upper plate and the bottom plate are arranged opposite to each other, and the rear plate is arranged opposite to the visible panel. The visible panel, the upper plate, the bottom plate, the two side plates, and the rear plate are connected as one unit.

6. The visual radial permeability testing system for frozen soil according to claim 5, characterized in that, The visible panel, the two side panels, and the rear panel are all snapped together with the base plate.

7. The visual radial permeability testing system for frozen soil according to claim 5, characterized in that, A first liquid injection valve is provided at the center of the rear plate, and the first liquid injection valve is connected to one end of the microporous permeation tube.

8. The visual radial permeability testing system for frozen soil according to claim 7, characterized in that, A second liquid injection valve is provided at the center of the visible panel, and the second liquid injection valve is connected to the other end of the microporous permeation tube.

9. A method for visualizing radial permeability testing of frozen soil, characterized in that, Using the visualization radial permeability testing system for frozen soil as described in any one of claims 1-8, the following steps are included: (1) Sample installation: When the sample is a saturated soil sample, proceed to step (2); when the sample is an unsaturated soil sample, proceed to step (3). (2) For saturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeable tube, put the sample, temperature sensor and moisture sensor into the soil sample box, after putting the sample in, lay a filter cloth on the sample, then place a permeable stone on the filter cloth, and finally seal the soil sample box and put the soil sample box into the low temperature control box. (3) For unsaturated soil samples: Apply a layer of petroleum jelly evenly to the inner wall of the microporous permeation tube, put the sample, temperature sensor and moisture sensor into the soil sample box, seal the soil sample box after putting the sample in, and put the soil sample box into the low temperature control box. (4) Adjust the position of the industrial camera so that the view panel image is centered within the view of the industrial camera; (5) Select dimethyl silicone oil as the permeation medium, add fluorescent agent into the dimethyl silicone oil and let it fully mix, immerse one end of the pressure volume controller in the storage tank containing the permeation medium, and connect the other end to the microporous permeation tube; (6) Adjust the temperature of the low temperature control box to perform in-situ freezing. After the temperature inside the frozen soil sample reaches the freezing temperature and tends to stabilize, determine the data transmitted by the temperature sensor. Then adjust the temperature of the low temperature control box to the test temperature so that the temperature inside the sample reaches the test temperature and tends to stabilize. (7) Turn on the pressure volume controller, adjust the permeation pressure to the pressure value required for the test, connect the microporous permeation tube, start the frozen soil permeation test, record the volume of the permeation medium injected at regular intervals and take photos with an industrial camera. (8) During the test, the microporous permeation tube is always kept in one end with the permeation medium. After the test, the radial permeation velocity and permeability coefficient of the sample are calculated.

10. A method for visualizing radial permeability testing of frozen soil according to claim 9, characterized in that, The formula for calculating the permeability coefficient is: ， In the formula, Permeability coefficient, The density of the permeating medium, It is the acceleration due to gravity. For grouting volume, For grouting pressure, The length of the microporous permeation tube. The diffusion radius of the permeable medium in frozen soil. The radius of the microporous permeation tube is given.

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