System and method for rapid testing of soil-water characteristic curves and soil freezing characteristic curves

Abstract

This invention discloses a system and method for rapidly testing soil-water characteristic curves and soil freezing characteristic curves. The system comprises a pressure chamber, a pneumatic loading system, a temperature control system, a water volume measurement system, and a data acquisition system. The pressure chamber consists of a metal mold, a base, a cover plate, and a high-air-intake clay plate. The pneumatic loading system consists of a barometer and an electronic pressure controller. The temperature control system consists of a low-temperature constant-temperature cold bath and silicone tubing. The data acquisition system consists of a temperature sensor, a pore water pressure gauge, a data acquisition instrument, and a computer. This invention solves the problems of low efficiency in current soil-water characteristic curve testing, the inability to directly obtain continuous soil-water characteristic curves and the cumbersome operation of obtaining soil-water characteristic curves after freeze-thaw cycles, and the inability to obtain continuous freezing characteristic curves. This invention can simultaneously test the soil-water characteristic curves and freezing characteristic curves of a sample.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology and relates to a system and method for rapidly testing soil-water characteristic curves and soil freezing characteristic curves. Background Technology

[0002] The roadbed is the foundation of the road structure, and its stability is crucial to the service life of the entire road and the safe operation of vehicles. The moisture state of the roadbed is a significant factor affecting its mechanical analysis and long-term performance. During actual service, the moisture state of the roadbed is constantly changing. Extensive engineering practice shows that roadbeds are often in an unsaturated state during operation. Therefore, it is essential to study the mechanical properties and long-term performance evolution of roadbeds under unsaturated conditions.

[0003] The soil-water characteristic curve (SMC) is the relationship between soil matrix suction (pore water potential energy) and soil moisture content or saturation. It can be used to characterize the water-holding capacity of soil and estimate the permeability of unsaturated soil. Currently, the most commonly used method for testing the SMC is the pressure plate apparatus based on the axis translation method. This method changes the pore air pressure to alter the matrix suction within the soil. After the matrix suction within the soil reaches equilibrium, the water displacement of the sample is measured. Then, by using the volumetric water content of the saturated sample measured before the test, the volumetric water content after different suction equilibration can be calculated. However, this method can only test discrete suction data of the sample under several different moisture content states and fit a continuous SMC using these discrete data. It cannot directly obtain a continuous SMC of the soil sample. Furthermore, equilibrating the matrix suction of the sample is time-consuming, typically taking several hours or even days for a single data point, resulting in low testing efficiency. Furthermore, in seasonally frozen soil regions, the roadbed is affected by freeze-thaw cycles. Temperature changes, the formation of ice lenses, and water migration significantly alter the soil structure, inevitably impacting its water-holding properties. Existing techniques involve freezing and thawing samples in a constant-temperature chamber before testing the soil-water characteristic curve, a process that is cumbersome and can affect test accuracy.

[0004] The soil freezing characteristic curve represents the relationship between sub-zero temperatures and the unfrozen water content in the soil, controlling the hydraulic and mechanical properties of frozen soil. Existing methods often employ a low-temperature isothermal cold bath combined with nuclear magnetic resonance (NMR) to obtain the soil freezing characteristic curve. This method calculates the unfrozen water content based on the ratio of signal intensity to liquid water by measuring the free induction decay of hydrogen nuclei in a magnetic field. While this method offers high accuracy and fast testing speed, the testing process is overly cumbersome and difficult to operate, requiring operators to have a strong foundation in electromagnetic theory. Furthermore, this method can only measure the unfrozen water content at a single temperature and cannot obtain continuous freezing characteristic curves. Summary of the Invention

[0005] This invention provides a system and method for rapidly testing soil-water characteristic curves and soil freezing characteristic curves, addressing the problems of low testing efficiency and the inability to directly obtain continuous soil-water characteristic curves from soil samples, as well as the cumbersome operation and inability to obtain continuous freezing characteristic curves after freeze-thaw cycles. Furthermore, this invention can simultaneously test both soil-water characteristic curves and freezing characteristic curves of a sample.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A system for rapidly testing soil-water characteristic curves and soil freezing characteristic curves includes a pressure chamber, an air pressure loading system, a temperature control system, a water volume measurement system, and a data acquisition system, wherein:

[0008] The pressure chamber consists of a metal mold, a base, a cover plate, and a high-intake-value clay plate;

[0009] The top of the metal mold and the cover plate, and the bottom of the metal mold and the base are detachably connected;

[0010] The pressure chamber is connected to the output end of the pneumatic loading system through the air inlet / exhaust port on the cover plate, which is used to control the air pressure inside the pressure chamber;

[0011] The base has a drainage hole in the center and a high-intake-value clay plate that is compatible with the inner diameter of the pressure chamber is embedded in the base.

[0012] The pneumatic loading system consists of a barometer and an electronic pressure controller. The barometer is connected to the electronic pressure controller, which is connected to a pressure regulator. The electronic pressure controller adjusts the air pressure value at a certain rate through the pressure regulator, thereby controlling the air pressure inside the metal mold. The barometer is used to measure the air pressure inside the metal mold.

[0013] The water volume measurement system is connected to the drain hole and is used to measure changes in water volume.

[0014] The temperature control system consists of a low-temperature constant-temperature cold bath and a silicone hose. The low-temperature constant-temperature cold bath is connected to the side wall of the metal mold through the silicone hose, so that the refrigerant circulates in the side wall of the metal mold to achieve the freezing and thawing of the sample.

[0015] The data acquisition system is used to acquire environmental information inside the sample. It consists of a temperature sensor, a pore water pressure gauge, a data acquisition instrument, and a computer. The data acquisition instrument is connected to the temperature sensor, the pore water pressure gauge, and the computer. The temperature sensor and the pore water pressure gauge are connected to the pressure chamber through through holes in the cover plate to test the temperature and pore water pressure of the sample in real time. The data acquisition instrument transmits the real-time temperature and pore water pressure of the test sample to the computer.

[0016] A method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves includes the following steps:

[0017] Step 1: Saturation of the sample and the high-air-entry-value clay plate:

[0018] Step 1: Obtain the optimum moisture content and maximum dry density of the soil through compaction tests; calculate the dry density at a certain degree of compaction and weigh the mass of dry soil required to compact to a specified volume at that dry density; then compact the soil in layers according to the optimum moisture content to a specified volume, so that the sample is in close contact with the clay plate of the base and the four walls of the metal mold.

[0019] Step 1 and Step 2: Place the base and metal mold into the vacuum saturation device for degassing. Extract the air from the device to create a low-pressure or vacuum environment. This removes air from the device and prevents air bubbles from forming when distilled water seeps into the pores of the sample. Then, open the knob on the bottom of the device to allow distilled water to cover the metal mold before closing the knob. During this process, to avoid negative pressure on one side of the clay plate, suction is required from that side to ensure pressure balance on both sides of the clay plate. This prevents the clay plate from being damaged or affecting the saturation process of the sample due to uneven pressure.

[0020] Step 13: After the distilled water has been fully degassed, stop the evacuation and apply an air pressure of about 100 kPa to the pressure chamber; after applying the air pressure, continue the suction operation from one side of the clay plate to extract the air from the sample so that the distilled water can fully penetrate into the pores of the sample to achieve a fully saturated state.

[0021] Step 1, Section 4: After saturation is complete, measure the total mass of the saturated sample.

[0022] Step 15: Connect the cover plate to the top of the metal mold and seal it with a sealing ring;

[0023] Step 16: Insert the temperature sensor and pore water pressure gauge into the center of the sample;

[0024] Step 2: Dehumidification and moisture absorption:

[0025] Step 21: Dehumidification: The electronic pressure controller increases the air pressure at a certain rate through the pressure regulator, thereby increasing the matrix suction in the sample. As the matrix suction increases, the water in the sample gradually seeps downward and is discharged out of the sample. After passing through the clay plate, it is discharged into the water volume measurement system through the drainage hole. The water volume measurement system obtains the amount of water discharged from the sample.

[0026] Step 22, Moisture Absorption: The electronic pressure controller reduces the air pressure at a certain rate through the pressure regulator, thereby reducing the matrix suction in the sample. As the matrix suction decreases, water is drawn into the sample through the water volume measurement system via the drainage hole and the clay plate. The water volume measurement system obtains the amount of water absorbed in the sample.

[0027] Steps 2 and 3: Use a data acquisition instrument to obtain the pore water pressure gauge readings in real time during the experiment. This allows for real-time measurement of the pore water pressure inside the sample, and thus real-time determination of the matrix suction within the sample. The matrix suction is calculated as the pore air pressure minus the pore water pressure, without waiting for the suction to reach equilibrium.

[0028] Step 24: Based on the mass of the saturated sample, the mass of the dry soil, and the amount of water drained during the test obtained in Step 1, the mass moisture content under different suction forces can be calculated. The conversion relationship is shown below:

[0029]

[0030] In the formula, m 湿 For the mass of wet soil, m 干 ω represents the dry soil mass, and ω represents the mass moisture content.

[0031] Step 25: The volumetric water content under different suction values ​​can be calculated using the following formula:

[0032] θ w =ρ d ×ω

[0033] In the formula, θ w ρ is the volumetric water content. d This refers to the dry density of the soil.

[0034] Step 26: Pressurize to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached dehydration equilibrium. Plot the dehydration soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model with matrix suction as the x-axis and log as the y-axis, and volume water content as the y-axis.

[0035] Step 27: Reduce the pressure to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached hygroscopic equilibrium. Plot the hygroscopic soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model with the matrix suction as the x-axis and the log axis as the y-axis.

[0036] Step 3: Soil freezing characteristic curve test:

[0037] Step 3: 1. Saturate the sample and clay slab according to Step 1. Then freeze the sample using a low-temperature constant temperature cold bath. Stop freezing after the pore water pressure count value no longer changes.

[0038] Step 2: Use a data acquisition instrument to acquire the values ​​of the temperature sensor and pore water pressure gauge in real time during the test. Calculate the unfrozen water content in the sample at the current temperature from the soil-water characteristic curve obtained in Step 2. Plot the freezing characteristic curve of the sample with temperature as the abscissa and the unfrozen water content of the sample as the ordinate.

[0039] Step 4: Test the soil-water characteristic curve after freeze-thaw cycle:

[0040] Step 41: Freeze the sample as in Step 31;

[0041] Step 4.2 After freezing, the sample is thawed, and the soil-water characteristic curve after the freeze-thaw cycle is measured according to Step 2.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] 1. Traditional methods for equilibrating the matrix suction of a soil sample are time-consuming and can only test discrete suction data under several different moisture contents, failing to directly obtain continuous soil-water characteristic curves. The continuous pressurization method based on axis translation proposed in this invention, by placing a pore water pressure gauge inside the sample, can measure the pore water pressure in real time, thereby obtaining the matrix suction within the sample in real time, without waiting for suction equilibrium. This significantly improves the testing efficiency of soil-water characteristic curves and allows for the direct acquisition of continuous soil-water characteristic curves. Furthermore, this invention uses a low-temperature constant-temperature cold bath to directly freeze and thaw the sample, enabling the testing of soil-water characteristic curves after freeze-thaw cycles, making the operation more convenient and significantly improving measurement accuracy.

[0044] 2. In the low-temperature constant-temperature cold bath freezing process, the current unfrozen water content can be calculated from the soil-water characteristic curve by measuring the matrix suction of the sample. The current temperature can be obtained through a temperature sensor inside the sample. Combining the temperature and unfrozen water content, a continuous freezing characteristic curve of the sample can be obtained. This invention is multifunctional, capable of simultaneously testing both the soil-water characteristic curve and the freezing characteristic curve of the sample. Attached Figure Description

[0045] Figure 1 A schematic diagram of the system for rapidly testing soil-water characteristic curves and soil freezing characteristic curves;

[0046] Figure 2 for Figure 1 A magnified view of a portion of the image;

[0047] In the diagram, 1-computer, 2-data acquisition instrument, 3-low temperature constant temperature cold bath, 4-temperature sensor, 5-pressure regulator, 6-electronic pressure controller, 7-double tube graduated cylinder, 8-differential pressure gauge, 9-soil sample, 10-pore water pressure gauge, 11-barometer, 12-multi-hole probe, 13-clay plate, 14-cover plate, 15-base, 16-switch knob. Detailed Implementation

[0048] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0049] This invention provides a system for rapidly testing soil-water characteristic curves and soil freezing characteristic curves, such as... Figure 1 and Figure 2 As shown, the system includes a pressure chamber, a pneumatic loading system, a temperature control system, a water volume measurement system, and a data acquisition system, wherein:

[0050] The pressure chamber consists of a metal mold, a base, a cover plate, a high-intake-value clay plate, and a sealing ring;

[0051] The top of the metal mold and the cover plate, and the bottom of the metal mold and the base are detachably connected and sealed with a sealing ring to prevent air leakage and pressure loss in the pressure chamber.

[0052] The pressure chamber is connected to the output end of the pneumatic loading system through the air inlet / exhaust port on the cover plate, which is used to control the air pressure inside the pressure chamber;

[0053] The base has a drainage hole at its center; a high-intake-value clay plate that matches the inner diameter of the pressure chamber is embedded in the base.

[0054] The pneumatic loading system consists of a barometer and an electronic pressure controller. The barometer is connected to the electronic pressure controller, which is connected to a pressure regulator. The electronic pressure controller adjusts the air pressure value at a certain rate through the pressure regulator, thereby controlling the air pressure inside the metal mold. The barometer is used to measure the air pressure inside the metal mold.

[0055] The water volume measurement system is connected to the drain hole and is used to measure changes in water volume. Various methods can be used; two schemes are listed below:

[0056] Option 1: It consists of a differential pressure gauge and a double-tube graduated cylinder. The differential pressure gauge is connected to the pressure regulator, and the double-tube graduated cylinder is connected to the drain hole through a conduit for drainage during the test. The differential pressure gauge is connected to the double-tube graduated cylinder to obtain the drainage volume.

[0057] Option 2: It consists of a laser displacement sensor, a double-tube graduated cylinder, and a float. The double-tube graduated cylinder is connected to a drain hole through a conduit for draining water during the test. A float is placed inside the double-tube graduated cylinder. The position change of the float is obtained by the laser displacement sensor to measure the change in water volume.

[0058] The temperature control system consists of a low-temperature constant-temperature cold bath and a silicone hose. The low-temperature constant-temperature cold bath is connected to the side wall of the metal mold through the silicone hose, so that the refrigerant circulates in the side wall of the metal mold to achieve the freezing and thawing of the sample.

[0059] The data acquisition system is used to acquire environmental information inside the sample. It consists of a temperature sensor, a pore water pressure gauge, a data acquisition instrument, and a computer. The data acquisition instrument is connected to the temperature sensor, the pore water pressure gauge, and the computer. The cover plate has a through hole, through which the temperature sensor and the pore water pressure gauge are connected to the pressure chamber to test the temperature and pore water pressure of the sample in real time. The data acquisition instrument transmits the real-time temperature and pore water pressure of the test sample to the computer.

[0060] A method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves includes the following steps:

[0061] Step 1: Saturation of the sample and the high-air-entry-value clay plate:

[0062] Step 1: Obtain the optimum moisture content and maximum dry density of the soil through compaction tests; calculate the dry density at a certain degree of compaction, and weigh the mass of dry soil required to compact to a specified volume at that dry density. Then, compact the soil in layers according to the optimum moisture content to the specified volume, ensuring the sample is in close contact with the clay plate of the base and the four walls of the metal mold.

[0063] Steps 1 and 2: Place the base and mold into the vacuum saturation apparatus for degassing. This removes air from the apparatus, creating a low-pressure or vacuum environment. This prevents air bubbles from forming when distilled water seeps into the pores of the sample. Then, open the knob on the lower side of the apparatus to allow distilled water to submerge the mold, then close the knob. During this process, to avoid negative pressure on one side of the clay plate, suction is applied from that side to ensure pressure balance on both sides of the clay plate. This prevents uneven pressure from damaging the clay plate or affecting the sample saturation process.

[0064] Step 13: After the distilled water has been fully degassed, stop the evacuation and apply an air pressure of approximately 100 kPa to the pressure chamber. After applying the air pressure, continue the suction operation from one side of the clay plate to extract the air from the sample, allowing the distilled water to fully penetrate into the pores of the sample, thereby achieving complete saturation.

[0065] Step 1, Section 4: After saturation is complete, measure the total mass of the saturated sample.

[0066] Step 15: Connect the cover plate to the top of the metal mold and seal it with a sealing ring.

[0067] Step 16: Insert the temperature sensor and pore water pressure gauge into the center of the sample.

[0068] Step 2: Dehumidification and moisture absorption:

[0069] Step Two: Dehumidification: The electronic pressure controller increases the air pressure at a certain rate through the pressure regulator, thereby increasing the matrix suction in the sample. As the matrix suction increases, the water in the sample gradually permeates downwards and is discharged out of the sample. After passing through the clay plate, it is discharged into the double-tube graduated cylinder through the conduit. The water volume measurement system can obtain the amount of water discharged from the sample.

[0070] Step 22, Moisture Absorption: The electronic pressure controller reduces the air pressure at a certain rate through the pressure regulator, thereby reducing the matrix suction in the sample. As the matrix suction decreases, water is drawn into the sample through the conduit from the double-tube graduated cylinder through the clay plate. The water volume measurement system can obtain the amount of water absorbed in the sample.

[0071] Steps 2 and 3: Use a data acquisition instrument to obtain the pore water pressure gauge value in real time during the test. This allows for real-time measurement of the pore water pressure in the sample, and thus real-time acquisition of the matrix suction in the sample (matrix suction is the pore air pressure minus the pore water pressure), without waiting for the suction to reach equilibrium.

[0072] Step 24: Based on the mass of the saturated sample, the mass of the dry soil, and the amount of water drained during the test obtained in Step 1, the mass moisture content under different suction forces can be calculated. The conversion relationship is shown below:

[0073]

[0074] In the formula, m 湿 For the mass of wet soil, m 干 ω represents the dry soil mass, and ω represents the mass moisture content.

[0075] Step 25: The volumetric water content under different suction values ​​can be calculated using the following formula:

[0076] θ w =ρ d ×ω

[0077] In the formula, θ w ρ is the volumetric water content. d This refers to the dry density of the soil.

[0078] Step 26, Dehydration: Pressurize to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached dehydration equilibrium. Plot the dehydration soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model, with matrix suction as the x-axis and logarithmic coordinates as the y-axis.

[0079] Step 27, Hygroscopic Absorption: Reduce the pressure to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached hygroscopic equilibrium. Plot the hygroscopic soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model, with the matrix suction as the x-axis and the log axis as the y-axis.

[0080] Step 3: Soil freezing characteristic curve test:

[0081] Step 3: 1. Saturate the sample and clay slab according to Step 1. Then freeze the sample using a low-temperature constant temperature cold bath. Stop freezing after the pore water pressure count value no longer changes.

[0082] Step 2: Use a data acquisition instrument to acquire the values ​​of the temperature sensor and pore water pressure gauge in real time during the test. The unfrozen water content in the sample at the current temperature can be calculated from the soil-water characteristic curve measured in Step 2. Plot the freezing characteristic curve of the sample with temperature as the abscissa and the unfrozen water content of the sample as the ordinate.

[0083] Step 4: Test the soil-water characteristic curve after freeze-thaw cycle:

[0084] Step 41: Freeze the sample as in Step 31.

[0085] Step 4.2 After freezing, the sample is thawed. Following Step 2, the soil-water characteristic curve after the freeze-thaw cycle of the sample can be measured.

Claims

1. A method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves, characterized in that... The method utilizes a system for rapidly testing soil-water characteristic curves and soil freezing characteristic curves to quickly predict these curves. The system includes a pressure chamber, a pneumatic loading system, a temperature control system, a water volume measurement system, and a data acquisition system, wherein: The pressure chamber consists of a metal mold, a base, a cover plate, and a high-intake-value clay plate; The top of the metal mold and the cover plate, and the bottom of the metal mold and the base are detachably connected; The pressure chamber is connected to the output end of the pneumatic loading system through the air inlet / exhaust port on the cover plate, which is used to control the air pressure inside the pressure chamber; The base has a drainage hole in the center and a high-intake-value clay plate that is compatible with the inner diameter of the pressure chamber is embedded in the base. The pneumatic loading system consists of a barometer and an electronic pressure controller. The barometer is connected to the electronic pressure controller, which is connected to a pressure regulator. The electronic pressure controller adjusts the air pressure value at a certain rate through the pressure regulator, thereby controlling the air pressure inside the metal mold. The barometer is used to measure the air pressure inside the metal mold. The water volume measurement system is connected to the drain hole and is used to measure changes in water volume; The temperature control system consists of a low-temperature constant-temperature cold bath and a silicone hose. The low-temperature constant-temperature cold bath is connected to the side wall of the metal mold through the silicone hose, so that the refrigerant circulates in the side wall of the metal mold to achieve the freezing and thawing of the sample. The data acquisition system is used to acquire environmental information inside the sample. It consists of a temperature sensor, a pore water pressure gauge, a data acquisition instrument, and a computer. The data acquisition instrument is connected to the temperature sensor, the pore water pressure gauge, and the computer. The temperature sensor and the pore water pressure gauge are connected to the pressure chamber through through holes on the cover plate to test the temperature and pore water pressure of the sample in real time. The data acquisition instrument transmits the real-time temperature and pore water pressure of the test sample to the computer. Includes the following steps: Step 1: Saturation of the sample and the high-air-entry-value clay plate: Step 1: Obtain the optimum moisture content and maximum dry density of the soil through compaction tests; calculate the dry density at a certain degree of compaction and weigh the mass of dry soil required to compact to a specified volume at that dry density; then compact the soil in layers according to the optimum moisture content to a specified volume, so that the sample is in close contact with the clay plate of the base and the four walls of the metal mold. Step 1 and Step 2: Place the base and metal mold into the vacuum saturation device for degassing. Extract the air from the device to create a low-pressure or vacuum environment. This removes air from the device and prevents air bubbles from forming when distilled water seeps into the pores of the sample. Then, open the knob on the bottom of the device to allow distilled water to cover the metal mold before closing the knob. During this process, to avoid negative pressure on one side of the clay plate, suction is required from that side to ensure pressure balance on both sides of the clay plate. This prevents the clay plate from being damaged or affecting the saturation process of the sample due to uneven pressure. Step 13: After the distilled water has been fully degassed, stop the evacuation and apply an air pressure of 100 kPa to the pressure chamber; after applying the air pressure, continue the suction operation from one side of the clay plate to extract the air from the sample so that the distilled water can fully penetrate into the pores of the sample to achieve a fully saturated state. Step 1, Section 4: After saturation is complete, measure the total mass of the saturated sample. Step 15: Connect the cover plate to the top of the metal mold and seal it with a sealing ring; Step 16: Insert the temperature sensor and pore water pressure gauge into the center of the sample; Step 2: Dehumidification and moisture absorption: Step 21: Dehumidification: The electronic pressure controller increases the air pressure at a certain rate through the pressure regulator, thereby increasing the matrix suction in the sample. As the matrix suction increases, the water in the sample gradually seeps downward and is discharged out of the sample. After passing through the clay plate, it is discharged into the water volume measurement system through the drainage hole. The water volume measurement system obtains the amount of water discharged from the sample. Step 22, Moisture Absorption: The electronic pressure controller reduces the air pressure at a certain rate through the pressure regulator, thereby reducing the matrix suction in the sample. As the matrix suction decreases, water is drawn into the sample through the water volume measurement system via the drainage hole and the clay plate. The water volume measurement system obtains the amount of water absorbed in the sample. Steps 2 and 3: Use a data acquisition instrument to obtain the pore water pressure gauge readings in real time during the experiment. This allows for real-time measurement of the pore water pressure inside the sample, and thus real-time determination of the matrix suction inside the sample. The matrix suction is the pore air pressure minus the pore water pressure, without waiting for the suction to reach equilibrium. Step 24: Based on the mass of the saturated sample, the mass of the dry soil, and the amount of water drained during the test obtained in Step 1, the mass moisture content under different suction forces can be calculated. The conversion relationship is shown below: In the formula, For the quality of wet soil, For dry soil quality, Moisture content (by weight); Step 25: The volumetric water content under different suction values ​​can be calculated using the following formula: In the formula, Water content by volume This refers to the dry density of the soil. Step 26: Pressurize to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached dehydration equilibrium. Plot the dehydration soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model with matrix suction as the x-axis and log as the y-axis, and volume water content as the y-axis. Step 27: Reduce the pressure to the target value at the set rate. When the water volume measurement system no longer changes, it indicates that the soil sample has reached hygroscopic equilibrium. Plot the hygroscopic soil-water characteristic curve of the sample using the Van Genuchten or Fredlund-Xing model with the matrix suction as the x-axis and the log axis as the y-axis. Step 3: Soil freezing characteristic curve test: Step 3:

1. Saturate the sample and clay slab according to Step 1. Then freeze the sample using a low-temperature constant temperature cold bath. Stop freezing after the pore water pressure count value no longer changes. Step 2: Use a data acquisition instrument to acquire the values ​​of the temperature sensor and pore water pressure gauge in real time during the test. Calculate the unfrozen water content in the sample at the current temperature from the soil-water characteristic curve obtained in Step 2. Plot the freezing characteristic curve of the sample with temperature as the abscissa and the unfrozen water content of the sample as the ordinate. Step 4: Test the soil-water characteristic curve after freeze-thaw cycle: Step 41: Freeze the sample as in Step 31; Step 4.2 After freezing, the sample is thawed, and the soil-water characteristic curve after the freeze-thaw cycle is measured according to Step 2.

2. The method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves according to claim 1, characterized in that... The top of the metal mold is sealed with a sealing ring, and the bottom of the metal mold is sealed with a sealing ring.

3. The method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves according to claim 1, characterized in that... The water volume measurement system consists of a differential pressure gauge and a double-tube graduated cylinder. The differential pressure gauge is connected to a pressure regulator, and the double-tube graduated cylinder is connected to a drain hole through a conduit for drainage during the test. The differential pressure gauge is connected to the double-tube graduated cylinder to obtain the drainage volume.

4. The method for rapidly predicting soil-water characteristic curves and soil freezing characteristic curves according to claim 1, characterized in that... The water volume measurement system consists of a laser displacement sensor, a double-tube graduated cylinder, and a float. The double-tube graduated cylinder is connected to a drain hole via a conduit for drainage during the test. A float is placed inside the double-tube graduated cylinder, and the position change of the float is obtained by the laser displacement sensor to measure the change in water volume.

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