Device for simulating water and salt migration in freezing and thawing process and measuring soil permeability

Abstract

The invention discloses a device for simulating water and salt migration in a freezing and thawing process and measuring soil permeability, which comprises a soil clamping cavity, the top of the soil clamping cavity is hermetically connected with a surface atmosphere simulation cavity, and the surface atmosphere simulation cavity is connected with a fluid supply unit and an atmosphere temperature and humidity control unit. The fluid supply unit provides a variable water head and variable gas pressure, and the atmosphere temperature and humidity control unit performs atmosphere temperature and humidity adjustment on a test soil sample to simulate a natural freezing and thawing process; an underground water supply end water inlet and an underground water discharge end water outlet are formed in the two sides of the soil clamping cavity, a plurality of temperature and humidity sensors are distributed in the surface atmosphere simulation cavity, and a plurality of hydrothermal salt sensors are uniformly distributed on the side wall of the soil clamping cavity in the vertical direction. The freezing and thawing time, the freezing depth, the ice layer burial depth at the last stage of thawing, the water head difference and the like can be provided as variables for permeability research under freezing and thawing of different soil samples, a freezing and thawing experiment device and a permeability experiment device are combined into a whole, and the experiment time is effectively shortened.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering testing equipment, specifically to a device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability. Background Technology

[0002] With global climate change and the development of cold-region engineering, the impact of freeze-thaw cycles on soil physical properties, water and salt transport characteristics, and permeability has received increasing attention. However, current experimental methods and devices for measuring soil water and salt migration and permeability during freeze-thaw processes face numerous technical bottlenecks, necessitating a more efficient, accurate, and integrated solution.

[0003] The freeze-thaw process of soil is accompanied by the migration of shallow groundwater to the freezing peak. The formation of ice and the precipitation of salt increase the proportion of solids per unit volume of soil, thereby reducing soil permeability. The impact of the freeze-thaw process on soil permeability can bring significant engineering safety risks and ecological environment changes, mainly manifested as the phenomenon of permeability first increasing and then decreasing, frost heave and thaw settlement, and aggravated soil erosion, which seriously affect the stability of infrastructure and the balance of ecosystems in cold regions.

[0004] Existing soil permeability measuring devices generally suffer from problems such as limited functionality, unrealistic environmental simulation, and incomplete data collection. They are unable to synchronously and accurately simulate the water and salt migration process during soil freeze-thaw cycles and measure key parameters such as permeability within the same system, thus hindering in-depth research on the evolution of soil properties under freeze-thaw conditions.

[0005] Therefore, it is of great necessity and innovative value to develop an integrated device that simulates the migration process of water and salt in soil under freeze-thaw cycles and measures its permeability evolution. Summary of the Invention

[0006] To address the existing technical problems, this invention provides a device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability, aiming to overcome the limitations of traditional experimental devices in measuring soil water and salt migration patterns and permeability under freeze-thaw conditions.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A device for simulating water and salt migration during freeze-thaw cycles and determining soil permeability includes a soil clamping cavity. The top of the soil clamping cavity is sealed and connected to a surface atmosphere simulation cavity. A test soil sample is clamped inside the soil clamping cavity. The surface atmosphere simulation cavity is connected to a fluid supply unit and an atmospheric temperature and humidity control unit. The fluid supply unit is used to provide variable water head and variable gas pressure to the test soil sample during permeability testing. The atmospheric temperature and humidity control unit is used to regulate the atmospheric temperature and humidity of the test soil sample to simulate a natural freeze-thaw process. The soil clamping cavity is provided with a groundwater recharge inlet and a groundwater discharge outlet on both sides. The groundwater recharge inlet is connected to the groundwater recharge storage tank, and the groundwater discharge outlet is connected to the groundwater discharge storage tank. A pressure sensor is installed on the pipeline connecting the groundwater discharge outlet and the groundwater discharge storage tank. The surface atmosphere simulation cavity contains multiple temperature and humidity sensors, and the sidewall of the soil clamping cavity is uniformly distributed with multiple hydrothermal and saline sensors along the vertical direction. The temperature and humidity sensors are electrically connected to the atmospheric temperature and humidity control unit, and both the temperature and humidity sensors and the hydrothermal and saline sensors are electrically connected to the data acquisition unit.

[0008] Preferably, the atmospheric temperature and humidity control unit includes an air inlet pipe and a gas circulation pipe. The air inlet pipe is connected to the air inlet of the surface atmospheric simulation cavity. One end of the gas circulation pipe is connected to the air outlet of the surface atmospheric simulation cavity, and the other end is connected to the air inlet pipe. A temperature and humidity control device is connected in series on the air inlet pipe, and the temperature and humidity sensor is electrically connected to the temperature and humidity control device.

[0009] Preferably, the intake pipe is provided with a first ball valve and a second ball valve, the temperature and humidity control device is located on the pipe section between the first ball valve and the second ball valve, the gas circulation pipe is provided with a third ball valve, and the connection between the gas circulation pipe and the intake pipe is located on the pipe section between the first ball valve and the temperature and humidity control device.

[0010] Preferably, an industrial fan is provided on the air intake pipe, and the industrial fan is located on the pipe section between the temperature and humidity control device and the second ball valve.

[0011] Preferably, the ambient temperature and humidity control unit further includes a freezer box, which is connected to the temperature and humidity control device. The freezer box contains snow samples, and temperature and humidity sensors are respectively installed at the upper and lower ends of the freezer box. The temperature and humidity sensors are electrically connected to the data acquisition unit.

[0012] Preferably, the fluid supply unit includes a first main pipe, one end of which is connected to the surface atmospheric simulation cavity, and the other end of which is connected to a first branch pipe and a second branch pipe. A fourth ball valve is provided on the first main pipe. The first branch pipe is connected to a water supply tank. A pressure regulating water pump and a fifth ball valve are connected in series on the first branch pipe. The second branch pipe is connected to an air compression station. A sixth ball valve is provided on the second branch pipe.

[0013] Preferably, the fluid supply unit further includes a gas supply pipe connected to the surface atmospheric simulation cavity, and a pressure relief valve and a seventh ball valve are connected in series on the gas supply pipe.

[0014] Preferably, the soil clamping cavity includes a middle clamping cavity and a bottom clamping cavity that is sealed and connected to the lower end of the middle clamping cavity. The inner diameter of the middle clamping cavity is the same as the inner diameter of the bottom clamping cavity, and the groundwater recharge outlet is located on the bottom clamping cavity.

[0015] Preferably, the central clamping cavity is formed by sequentially connecting multiple cavity segments through a connecting lock.

[0016] Preferably, the groundwater recharge end storage tank is connected to the groundwater recharge end inlet via a water supply pipe, and the groundwater discharge end storage tank is connected to the groundwater discharge end outlet via a drain pipe. An eighth ball valve is provided on the water supply pipe, and a ninth ball valve is provided on the drain pipe. The pressure sensor is provided on the drain pipe.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By providing variable water head and variable gas pressure through the fluid supply unit, the device of the present invention can provide precise water head difference changes, and the results of soil permeability measurement are more reliable; (2) The atmospheric temperature and humidity control unit can simulate the development of freezing peak under real freeze-thaw conditions to the greatest extent, and effectively shorten the freeze-thaw time and improve the accuracy of the results. The addition of snow samples can more realistically simulate the influence of snow depth on freezing depth under natural conditions, making the freeze-thaw experimental data more reliable. (3) By setting up groundwater supply end storage tank and groundwater discharge end storage tank on both sides of the soil clamping cavity, the water, heat and salt of the bottom soil in the freeze-thaw experiment can be simulated, realizing the continuous migration of water and salt to the frozen surface under real freezing conditions and the melting of the soil at both ends under thawing conditions, effectively increasing the reliability of freeze-thaw experiment data. (4) It can provide the freeze-thaw time, freezing depth, ice layer burial depth at the end of the thaw, water head difference and other variables to conduct permeability studies on different soil samples under freeze-thaw conditions. The overall volume of the experimental device is controllable and easy to assemble. The freeze-thaw experimental device and the permeability experimental device are combined into one, which can effectively shorten the experimental time and provide the permeability parameters required for engineering construction more quickly. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0020] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] As attached Figure 1 The device shown is for simulating water and salt migration during freeze-thaw cycles and determining soil permeability. It includes a soil clamping cavity, with a surface atmosphere simulation cavity 28 sealed to the top of the soil clamping cavity. The inner diameter of the surface atmosphere simulation cavity 28 is the same as that of the soil clamping cavity. A test soil sample 25 is clamped within the soil clamping cavity. The test soil sample 25 has a cylindrical structure within the soil clamping cavity. A fluid supply unit and an atmospheric temperature and humidity control unit are connected to the surface atmosphere simulation cavity 28. The fluid supply unit provides variable water head and variable gas pressure to the test soil sample 25 during permeability testing. The atmospheric temperature and humidity control unit regulates the temperature and humidity of the test soil sample 25 to simulate a natural freeze-thaw process while maintaining the low-temperature conditions of the freezer chamber 20.

[0022] The atmospheric temperature and humidity control unit includes an air inlet pipe 33 and a gas circulation pipe 11. The air inlet pipe 33 is connected to the air inlet of the surface atmosphere simulation cavity 28. One end of the gas circulation pipe 11 is connected to the air outlet of the surface atmosphere simulation cavity 28, and the other end is connected to the air inlet pipe 33. The gas circulation pipe 11 is connected to the surface atmosphere simulation cavity 28 to simulate the surface environment of the soil sample. A temperature and humidity control device 19 is connected in series on the air inlet pipe 33. The temperature and humidity sensor 24 in the surface atmosphere simulation cavity 28 is electrically connected to the temperature and humidity control device 19. Adjusting the temperature and humidity control device 19 can dynamically adjust the output power of the temperature and humidity control device 19 according to the measurement data fed back by the temperature and humidity sensor 24, thereby accurately simulating the atmospheric temperature and humidity environment of the natural freeze-thaw process.

[0023] Specifically, the air inlet pipe 33 is equipped with a first ball valve 1 and a second ball valve 2. The first ball valve 1 is used to connect to or isolate the external atmosphere. The temperature and humidity control device 19 is located on the pipe section between the first ball valve 1 and the second ball valve 2. The temperature and humidity control device 19 is responsible for regulating the temperature and humidity of the gas in the air inlet pipe 33 to simulate the ambient temperature and humidity environment of the soil sample 25 to be tested. The gas circulation pipe 11 is equipped with a third ball valve 6, and the connection between the gas circulation pipe 11 and the air inlet pipe 33 is located on the pipe section between the first ball valve 1 and the temperature and humidity control device 19. An industrial fan 23 is equipped on the air inlet pipe 33. The industrial fan 23 is located on the pipe section between the temperature and humidity control device 19 and the second ball valve 2 to drive gas circulation.

[0024] The ambient temperature and humidity control unit also includes a freezer 20, which is connected to the temperature and humidity control device 19 to maintain the low temperature conditions of the freezer 20. A snow sample 30 is placed inside the freezer 20. Temperature and humidity sensors 24 are respectively provided at the upper and lower ends of the freezer 20, and the temperature and humidity sensors 24 are electrically connected to the data acquisition unit 37.

[0025] The fluid supply unit includes a first main pipe 35, one end of which is connected to the surface atmospheric simulation cavity 28, and the other end is connected to a first branch pipe 34 and a second branch pipe 27. A fourth ball valve 9 is installed on the first main pipe 35. The first branch pipe 34 is connected to the water supply storage tank 14, and a pressure regulating water pump 13 and a fifth ball valve 4 are connected in series on the first branch pipe 34. The second branch pipe 27 is connected to the air compression station 12, and a sixth ball valve 5 and a compressed air pump are installed on the second branch pipe 27. The pressure regulating water pump 13 can pump the liquid in the water supply storage tank 14 into the soil clamping cavity at different head pressures. Then, by monitoring the water volume changes in the simulated groundwater discharge end water storage tank 15 and combining the test time, the permeability of the soil sample is determined.

[0026] The fluid supply unit also includes a gas supply pipe 26 connected to the surface atmospheric simulation cavity 28, and a pressure relief valve 16 and a seventh ball valve 3 are connected in series on the gas supply pipe 26.

[0027] The soil clamping cavity is provided with a groundwater recharge inlet and a groundwater discharge outlet on both sides. The groundwater recharge inlet is connected to the groundwater recharge storage tank 10, and the groundwater discharge outlet is connected to the groundwater discharge storage tank 15. A pressure sensor 38 is provided on the pipeline connecting the groundwater discharge outlet and the groundwater discharge storage tank 15.

[0028] Specifically, the groundwater recharge end storage tank 10 is connected to the groundwater recharge end inlet via a water supply pipe 32, and the groundwater discharge end storage tank 15 is connected to the groundwater discharge end outlet via a drainage pipe 36. An eighth ball valve 7 is provided on the water supply pipe 32, and a ninth ball valve 8 is provided on the drainage pipe 36. The pressure sensor 38 is provided on the drainage pipe 36, and the pressure sensor 38 and the pressure regulating pump 13 are electrically connected to the data acquisition unit 37.

[0029] In this embodiment, scale lines can be marked in the water supply tank 14, the groundwater recharge tank 10, and the groundwater discharge tank 15 respectively, so as to facilitate the measurement of the water volume changes in the water supply tank 14, the groundwater recharge tank 10, and the groundwater discharge tank 15.

[0030] By adjusting the temperature and salinity of the water in the simulated groundwater recharge tank 10, the effects of different groundwater conditions on the soil freeze-thaw process can be studied. Simultaneously, by controlling the water volume changes in the groundwater recharge tank 10 and the groundwater discharge tank 15, the dynamic conditions of the groundwater level during the freeze-thaw process under natural conditions can be realistically simulated.

[0031] The surface atmosphere simulation cavity 28 contains multiple temperature and humidity sensors 24. The sidewalls of the soil clamping cavity are uniformly distributed with multiple hydrothermal and saline sensors 22 along the vertical direction. These sensors are also arranged laterally along the sidewalls of the soil clamping cavity. By utilizing these sensors, the changes in the freeze-thaw depth of the soil and the migration of water and salt within it can be identified and recorded in real time. The temperature and humidity sensors 24 are electrically connected to a temperature and humidity control device 19. Adjusting the temperature and humidity control device 19 can be achieved through the temperature and humidity sensors 24. The measured data fed back dynamically adjusts the output power of the temperature and humidity control device 19 to accurately simulate the ambient temperature and humidity environment of the natural freeze-thaw process. Temperature and salinity sensors 31 are respectively installed at the groundwater inlet and the groundwater outlet on both sides of the soil clamping cavity. The temperature and humidity sensor 24, the hydrothermal and salinity sensor 22, and the temperature and salinity sensor 31 are all electrically connected to the data acquisition unit 37. The data acquisition unit 37 is electrically connected to the data processing workstation 21 and is controlled by the workstation 21, which is responsible for setting the data acquisition frequency and processing the acquired data.

[0032] In this embodiment, there are three temperature and humidity sensors 24 in the surface atmosphere simulation cavity 28, located at the positions between the air inlet and the air supply pipe 26 of the surface atmosphere simulation cavity 28, between the air supply pipe 26 and the first main pipe 35, and between the first main pipe 35 and the air outlet of the surface atmosphere simulation cavity 28.

[0033] In this embodiment, the soil clamping cavity includes a central clamping cavity 29 and a bottom clamping cavity 18 sealed and connected to the lower end of the central clamping cavity 29. The inner diameter of the central clamping cavity 29 is the same as the inner diameter of the bottom clamping cavity 18. The groundwater recharge outlet is located on the bottom clamping cavity 18. The central clamping cavity 29 is formed by multiple cavity segments sequentially and sealed together by connecting latches 17, making the overall volume of the experimental device controllable and easy to assemble.

[0034] In this embodiment, the surface atmosphere simulation cavity 28, the middle clamping cavity 29, the bottom clamping cavity 18, the fluid supply unit, the atmospheric temperature and humidity control unit, the groundwater recharge end storage tank 10, the groundwater discharge end storage tank 15, the water supply pipe 32, and the drainage pipe 36 are all heat-insulated or made of heat-insulating materials. This design ensures that in the freeze-thaw experiment, the temperature change of the sample only comes from its upper surface layer, thereby replicating the freezing front formation conditions under natural conditions to the greatest extent.

[0035] This invention accurately simulates the natural freeze-thaw cycle of soil through three aspects: simulating natural freeze-thaw conditions using an atmospheric temperature and humidity control unit at the top of the soil sample; simulating snow depth changes and adjusting freezing depth based on snow samples and the atmospheric temperature and humidity control unit; and simulating the effects of different groundwater levels, temperatures, and mineralization by controlling the hydrothermal and saline conditions of the bottom soil sample. Furthermore, by changing the head difference between the two ends of the sample using a pressure-regulating water pump and a compressed air pump, the invention simulates the gas-water displacement process and water-thermal-salt transport process in the vadose zone of the soil, and enables the determination of the constant-to-variable head permeability coefficient of the soil sample. Regarding engineering parameter requirements, to shorten the testing time, an industrial fan is used to accelerate atmospheric circulation at the soil surface, thus accelerating freeze-thaw cycles and effectively shortening the experimental time.

[0036] This invention is mainly carried out according to the following experimental steps: (1) Place the test soil sample 25 with a certain moisture content into the soil clamping cavity, and make the height of the test soil sample level with the height of the soil clamping cavity. Seal the surface atmosphere simulation cavity 28 and the top of the soil clamping cavity with the connecting lock 17. Inject the prepared constant temperature water-salt solution into the simulated groundwater recharge end storage tank 10, and then open the eighth ball valve 7 and the ninth ball valve 8. After the water flow stabilizes for a period of time, adjust the eighth ball valve 7 of the simulated groundwater recharge end until the water volume of the groundwater recharge end storage tank 10 and the groundwater discharge end storage tank 15 reaches a dynamic equilibrium state. (2) Confirm that all valves of the fluid supply unit and the atmospheric temperature and humidity control unit are closed. Open the first ball valve 1 to one-fifth of its opening. Open the second ball valve 2 and the third ball valve 6. Open the temperature and humidity control device 19 and set it to cooling -30℃ (or the required value). Turn on the industrial fan 23. After a period of time, observe the data of the data processing workstation 21. When the temperature at 5cm (or the required value) below the surface of the test soil drops below zero, open the connection lock 17 between the surface atmospheric simulation chamber 28 and the soil clamping chamber. Place the snow sample 30 in the freezing box 20 on the surface of the soil sample to the required thickness. Then seal the connection between the surface atmospheric simulation chamber 28 and the soil clamping chamber through the connection lock. Continue cooling to the required freezing depth (or a certain moment in the required freeze-thaw process). Then set the temperature and humidity control device 19 to heating 20℃ (or the required value). After a period of time, close all equipment and valves. (3) After taking out snow sample 30, seal the connection between the surface atmospheric simulation cavity 28 and the soil clamping cavity through the connecting lock, empty the groundwater discharge end storage tank 15, then open the ninth ball valve 8, place the experimental solution in the supply storage tank 14, open the pressure regulating water pump 13, the fifth ball valve 4, and the fourth ball valve 9, set the pressure regulating water pump 13 to 0.5m (or the required value) water head, and record the water volume change data of the supply storage tank 14 and the groundwater discharge end storage tank 15 during a certain period of time. (4) Close the pressure regulating water pump 13 and the fifth ball valve 4, open the air compressor station 12 and the sixth ball valve 5, and close the air compressor station 12 and all valves after almost no water flows out of the drain pipe 36. Open the pressure relief valve 16 and the seventh ball valve 3, and close the pressure relief valve 16 and the seventh ball valve 3 after the pressure stabilizes. (5) Copy all sensor monitoring data; (6) Close all equipment and valves, and empty all water tanks.

[0037] This method for testing the permeability of freeze-thawed soil involves the calculation formula for variable head permeability experiments based on changes in water head, which is briefly introduced below: The freeze-thaw process alters the content and depth of ice distribution in the vadose zone soil (salt precipitation is affected by various conditions and has little impact on permeability, so it is not considered here), thereby changing the soil pore structure. The change in soil pore structure affects the migration of hydrothermal salts during the freeze-thaw process, which in turn affects the content and depth of ice distribution. The evolution process can be characterized by soil permeability, and permeability testing satisfies Darcy's law.

[0038] Flow format: in: Q is the seepage flow rate (the volume of fluid passing through the porous medium per unit time, in meters). 3 / s) K is the permeability coefficient (m / s), reflecting the ability of porous media to allow fluids to permeate. A is the cross-sectional area perpendicular to the direction of water flow (m²). 2 ) h2 and h1 are the upstream and downstream water heads (or water levels, in meters), respectively. L is the seepage path length (m). J = h2 - h1 / L is the hydraulic gradient (head loss per unit length). Flow velocity form: Where v is the seepage velocity (m / s), also known as Darcy velocity or specific flow rate. Specifically, in this embodiment, Q corresponds to the change in solution volume in the groundwater discharge tank 15 during the test, A is the cross-sectional area of ​​the test soil sample 25, h2 is obtained from the data at the pressure regulating pump 13, h1 is obtained from the data at the pressure sensor 38, and L is the height of the soil clamping cavity or the height of the test soil sample 25. After obtaining the above-mentioned parameters through the test process, the permeability coefficient of the corresponding test soil can be calculated using the above formula.

[0039] The preferred embodiments of the present invention have been described above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A device for simulating water and salt migration during freeze-thaw cycles and measuring soil permeability, characterized in that: The system includes a soil clamping cavity, the top of which is sealed and connected to a surface atmosphere simulation cavity (28). The soil clamping cavity holds a test soil sample (25). The surface atmosphere simulation cavity (28) is connected to a fluid supply unit and an atmospheric temperature and humidity control unit. The fluid supply unit is used to provide the test soil sample (25) with variable water head and variable gas pressure during the permeability test. The atmospheric temperature and humidity control unit is used to adjust the atmospheric temperature and humidity of the test soil sample (25) to simulate the natural freeze-thaw process. The soil clamping cavity is provided with a groundwater recharge inlet and a groundwater discharge outlet on both sides. The groundwater recharge inlet is connected to the groundwater recharge storage tank (10), and the groundwater discharge outlet is connected to the groundwater discharge storage tank (15). A pressure sensor (38) is provided on the pipeline connecting the groundwater discharge outlet and the groundwater discharge storage tank (15). Multiple temperature and humidity sensors (24) are distributed inside the surface atmosphere simulation cavity (28). Multiple hydrothermal and salt sensors (22) are evenly distributed along the vertical direction on the side wall of the soil clamping cavity. The temperature and humidity sensors (24) are electrically connected to the atmospheric temperature and humidity control unit. Both the temperature and humidity sensors (24) and the hydrothermal and salt sensors (22) are electrically connected to the data acquisition unit (37).

2. The device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability according to claim 1, characterized in that: The atmospheric temperature and humidity control unit includes an air inlet pipe (33) and a gas circulation pipe (11). The air inlet pipe (33) is connected to the air inlet of the surface atmospheric simulation cavity (28). One end of the gas circulation pipe (11) is connected to the air outlet of the surface atmospheric simulation cavity (28), and the other end is connected to the air inlet pipe (33). A temperature and humidity control device (19) is connected in series on the air inlet pipe (33). The temperature and humidity sensor (24) is electrically connected to the temperature and humidity control device (19).

3. The device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability according to claim 2, characterized in that: The air inlet pipe (33) is provided with a first ball valve (1) and a second ball valve (2). The temperature and humidity control device (19) is located on the pipe section between the first ball valve (1) and the second ball valve (2). The gas circulation pipe (11) is provided with a third ball valve (6). The connection between the gas circulation pipe (11) and the air inlet pipe (33) is located on the pipe section between the first ball valve (1) and the temperature and humidity control device (19).

4. The device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability according to claim 3, characterized in that: An industrial fan (23) is installed on the air intake pipe (33), and the industrial fan (23) is located on the pipe section between the temperature and humidity control device (19) and the second ball valve (2).

5. The device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability according to claim 3, characterized in that: The ambient temperature and humidity control unit also includes a freezer (20), which is connected to the temperature and humidity control device (19). A snow sample (30) is placed inside the freezer (20). Temperature and humidity sensors (24) are respectively provided at the upper and lower ends of the freezer (20), and the temperature and humidity sensors (24) are electrically connected to the data acquisition unit (37).

6. The device for simulating water and salt migration during freeze-thaw processes and measuring soil permeability according to claim 2, characterized in that: The fluid supply unit includes a first main pipe (35), one end of which is connected to the surface atmospheric simulation cavity (28), and the other end of which is connected to the first branch pipe (34) and the second branch pipe (27). A fourth ball valve (9) is provided on the first main pipe (35). The first branch pipe (34) is connected to the water supply tank (14). A pressure regulating water pump (13) and a fifth ball valve (4) are connected in series on the first branch pipe (34). The second branch pipe (27) is connected to the air compression station (12). A sixth ball valve (5) is provided on the second branch pipe (27).

7. The device for simulating water and salt migration during freeze-thaw processes and determining soil permeability according to claim 6, characterized in that: The fluid supply unit also includes a gas supply pipe (26) connected to the surface atmospheric simulation cavity (28), and a pressure relief valve (16) and a seventh ball valve (3) are connected in series on the gas supply pipe (26).

8. The device for simulating water and salt migration during freeze-thaw processes and determining soil permeability according to claim 1, characterized in that: The soil clamping cavity includes a middle clamping cavity (29) and a bottom clamping cavity (18) that is sealed and connected to the lower end of the middle clamping cavity (29). The inner diameter of the middle clamping cavity (29) is the same as the inner diameter of the bottom clamping cavity (18). The groundwater recharge outlet is located on the bottom clamping cavity (18).

9. The device for simulating water and salt migration during freeze-thaw processes and determining soil permeability according to claim 8, characterized in that: The central clamping cavity (29) is formed by multiple cavity segments being sequentially and sealed together by connecting latches (17).

10. The device for simulating water and salt migration during freeze-thaw processes and determining soil permeability according to claim 1, characterized in that: The groundwater recharge end storage tank (10) is connected to the groundwater recharge end inlet through the water supply pipe (32), and the groundwater discharge end storage tank (15) is connected to the groundwater discharge end outlet through the drain pipe (36). The water supply pipe (32) is equipped with an eighth ball valve (7), and the drain pipe (36) is equipped with a ninth ball valve (8). The pressure sensor (38) is located on the drain pipe (36).

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