Testing device and method capable of testing mechanical properties of hydrophilic and hydrophobic unsaturated soil

Abstract

The invention relates to a test device and method capable of testing mechanical properties of hydrophilic and hydrophobic unsaturated soil, the test device comprises a pressure chamber, the pressure chamber is located at the center position of the whole device, an axial loading system is located below the pressure chamber, and the axial loading system is connected with the pressure chamber through a loading frame; the axial loading system is connected with the information acquisition system; the pneumatic control system is positioned on the side of the pressure chamber and connected with the pressure chamber through a pipeline; the data acquisition system is positioned beside the console or the computer and is connected with the sensor at each unit; the data processing system is connected with the air pressure control system and the back pressure control system, and the data processing system is connected with the axial loading system; the sample is positioned in the center of the pressure chamber; the hydrophobic soil suction control unit and the hydrophilic suction control unit are located at the upper end and the lower end of the sample, make close contact with the sample, ensure uniform pressure transmission and are connected with the air pressure control system through pipelines. According to the invention, the accuracy and wide applicability of the mechanical property test of the unsaturated soil are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering test equipment, and in particular to a test device and method capable of testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil. Background Art

[0002] Most soils used in geotechnical engineering are unsaturated. Based on their water retention characteristics, they can be divided into hydrophilic and hydrophobic soils. The surface of hydrophilic soil particles is highly hydrophilic, with a contact angle less than 90°. During wetting and dewetting, the water film is concave, and the pore air pressure is generally greater than the pore water pressure, resulting in a significant capillary suction effect. In contrast, the surface of hydrophobic soil particles forms a hydrophobic coating due to chemical treatment or natural processes, resulting in a contact angle greater than 90° and significant drainage. In this case, the water film between particles is convex, resulting in the pore water pressure potentially being higher than the pore air pressure, which is fundamentally different from the characteristics of hydrophilic soil.

[0003] With the continuous advancement of infrastructure construction and environmental engineering practices such as slope engineering, landfill cover engineering, and anti-seepage engineering, hydrophobic soils have gradually become a common type of special soil in such projects. For example, artificial hydrophobic soils are often used to reduce rainwater infiltration, improve slope stability, or serve as landfill cover materials to reduce the risk of groundwater contamination. However, existing unsaturated soil mechanics testing equipment is mainly based on axial translation technology, that is, suction regulation is achieved by controlling the difference between pore air pressure and pore water pressure. However, this technology requires that the pore air pressure is greater than the pore water pressure, making it difficult to accurately test the suction and mechanical behavior of hydrophobic soils. This limitation has severely restricted the development of unsaturated hydrophobic soil mechanics theory and hindered the optimal design of related projects. Therefore, there is an urgent need for a unified suction control technology and mechanical property testing method that can be applied to both hydrophilic and hydrophobic soils to meet the needs of engineering practice. Summary of the Invention

[0004] To overcome the shortcomings of the aforementioned prior art, the present invention provides a test apparatus and method for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils. This approach addresses the problem that existing unsaturated soil mechanical property testing apparatuses are inapplicable to hydrophobic soils, thereby improving the accuracy and broad applicability of unsaturated soil mechanical property testing. This test apparatus can be quickly adapted from existing unsaturated triaxial equipment, offering high operability. The test method fully considers the differences in soil mechanical properties affected by hydrophilicity and hydrophobicity, selecting different suction control units for different soil types. This highly targeted approach allows for an accurate description of soil mechanical properties.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A test apparatus for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils comprises a pressure chamber located at the center of the apparatus, an axial loading system located below the pressure chamber for applying axial stress, and connected to the pressure chamber via a loading frame. The axial loading system is connected to an information acquisition system for controlling the loading rate and loading method. An air pressure control system is located on the side of the pressure chamber and connected to the pressure chamber via a pipeline. The air pressure control system functions as a gas pressure pump for providing confining pressure to the pressure chamber and pore air pressure to the top of the specimen. A data acquisition system is located next to a console or computer and is connected to sensors at each unit for measuring and acquiring parameters such as stress, strain, and pore pressure. A data processing system is connected to the air pressure control system and a back pressure control system for real-time monitoring and recording of test data. The data processing system is connected to the axial loading system for controlling the loading rate and loading method. The specimen is located at the center of the pressure chamber. A hydrophobic soil suction control unit and a hydrophilic soil suction control unit are located at the upper and lower ends of the specimen for transmitting pore air pressure and back pressure, maintaining close contact with the specimen to ensure uniform pressure transmission, and are connected to the air pressure control system via a pipeline.

[0007] The hydrophobic soil suction control unit is used to accurately control the pore gas pressure at the top of the hydrophobic soil sample;

[0008] The hydrophilic suction control unit is used to accurately control the pore water pressure at the bottom of the hydrophilic soil sample;

[0009] The axial loading system is used to precisely control the axial load of the specimen;

[0010] The air pressure control system is used to accurately control the confining pressure in the pressure chamber and the pore air pressure loaded on the top of the sample;

[0011] The back pressure control system is used to apply back pressure to the bottom of the sample;

[0012] The data acquisition system is used to collect data on pore gas pressure, confining pressure, back pressure, and volume change during the test;

[0013] The data processing system is used to record and process various data during the test process and present them in the computer in the form of graphics.

[0014] The hydrophobic soil suction control unit consists of a layer of expanded polytetrafluoroethylene (e-PTFE) film wrapped on the surface of a porous metal plate structure, which is installed together with the sample cap and located on the top of the sample. The contact angle of the expanded polytetrafluoroethylene (e-PTFE) surface is usually greater than 90°, and can even reach more than 120°. Such high hydrophobicity makes it impossible for water to wet the membrane surface, thereby preventing liquid water from passing through. The microporous structure of e-PTFE allows gas molecules to pass freely by diffusion or flow. The porous metal plate can ensure the passage of gas. Therefore, within a given pressure range, it can be achieved that the pore water pressure is greater than the pore air pressure.

[0015] The pressure chamber includes an outer pressure chamber and an inner pressure chamber. The outer pressure chamber is located between the vertical loading frame and the axial loading console, and the inner pressure chamber is installed inside the outer pressure chamber.

[0016] The hydrophilic suction control unit is mounted on a base, located at the bottom of the specimen, and is composed of a high air intake value clay plate;

[0017] The clay plate is made by mixing kaolin and quartz powder and other mineral raw materials and sintering them at high temperature. Uniform and continuous micron-scale capillary channels are formed inside the plate, with an average pore size between 0.1 and 1 micron, resulting in an air intake value of 200 to 500 kPa. It can prevent air infiltration under saturation while allowing water to flow freely within it. During the test, the clay plate is connected to the backpressure system to stably control the pore water pressure inside the soil. When the pore air pressure is loaded from above, a constant matrix suction boundary condition is established, ensuring reliable suction regulation and mechanical response testing of hydrophilic unsaturated soil under axial translation loading mode.

[0018] The high air intake value clay plate is a sintered ceramic material containing a large number of uniformly distributed tiny pores with a pore size of 0.5 microns, which is consistent with the size of the bottom of the sample, with a diameter of 40 mm and a thickness of 5 mm-10 mm.

[0019] When the internal pores of the high air permeability clay plate are completely saturated with water, the capillary force formed by the water film on the pore surface will prevent the gas from passing through. Therefore, within a given pressure range (0-5 bar), the pore gas pressure is greater than the pore water pressure.

[0020] The axial loading system includes a vertical loading frame and an axial loading console. The vertical loading frame is fixed with a crossbeam by screws and the end groove of the vertical loading rod is embedded in the protrusion on the specimen cap, thereby supporting and fixing the specimen to prevent the force line from deviating.

[0021] There is a vertically moving hydraulic rod on the axial loading console, which applies the corresponding axial stress by controlling the vertical displacement; the two work together to complete the axial loading and control of the specimen; the axial loading system is used to apply vertical loads and transfer the load to the upper part of the specimen through the loading head, thereby achieving compression, compression or shear deformation of the specimen.

[0022] The air pressure control system includes an air pressure control box and two gas pipelines, wherein the gas pipelines are a confining pressure pipeline and a pore air pressure pipeline. The confining pressure pipeline is connected to the external pressure chamber to provide the corresponding confining pressure, and the pore air pressure pipeline is connected to the sample top cap to provide the corresponding pore air pressure.

[0023] The outer pressure chamber is used to apply confining pressure, control pore pressure, provide a stable test environment, measure volume changes, and protect the sample. The inner pressure chamber is used to apply confining pressure and control pore pressure to ensure the accuracy and repeatability of the test results.

[0024] The outer pressure chamber is located between the vertical loading frame and the axial loading console, and the inner pressure chamber is installed inside the outer pressure chamber.

[0025] The outer pressure chamber is composed of a metal screw and a transparent organic glass cover, while the inner pressure chamber is a high-strength transparent organic glass cover. It is a key component for accommodating soil samples and applying confining pressure. It can provide a stable pressure environment for the sample, ensuring that the pressure around the sample is evenly distributed during the test, simulating the stress state of the soil in actual engineering. The bottom is equipped with a permeable plate to facilitate the drainage of pore water and the measurement of pore water pressure. The pressure chamber is well sealed to prevent pressure leakage and ensure the accuracy of test data. During the test, the confining pressure can be adjusted according to different test requirements to study its effect on the mechanical properties of unsaturated soil.

[0026] like Figure 13 As shown, the back pressure control system includes a pore water pressure sensor, a pressure regulator and a connecting pipeline, which are used to measure the pore water pressure and monitor the pore water pressure inside the soil sample in real time; the pressure regulator is used to adjust the pore water pressure to simulate different unsaturated states.

[0027] The porous metal plate is made of a highly permeable material to ensure efficient gas exchange. The gas valve is adjusted via an external control device to accommodate varying test conditions and requirements. The porous metal plate structure is connected to the pressure transfer cap of the triaxial apparatus's pressure chamber, and compression and shearing of the specimen are achieved by raising and lowering the base. The porous metal plate structure is also connected to a gas pressure controller to measure and control the pore pressure within the specimen.

[0028] The data acquisition system includes a static 8-channel data acquisition instrument and sensor data cables. These instruments are used to collect experimental data and convert sensor signals into digital signals. The data cables connect sensors to record experimental data in real time, such as stress, strain, volume change, pore water pressure, and pore gas pressure.

[0029] The data processing system includes a PLC control system, which is used to process experimental data, display the data in real time in the form of images, and calculate various experimental data, such as stress, strain, volume change, etc.

[0030] A method for using a test device capable of uniformly testing the mechanical properties of unsaturated hydrophobic soil and hydrophilic soil comprises the following steps: first, determining the hydrophilicity of the soil through a water drop test; for hydrophilic soil, preparing a sample with a diameter of 39.1 mm and a height of 80 mm according to geotechnical test specifications; saturating the sample and mounting it on a sample base; securing the upper and lower ends of the sample with rubber bands; then installing an external pressure chamber and an internal pressure chamber; connecting a water pump to inject airless water into the pressure chambers; and controlling the matrix suction of the hydrophilic sample through a hydrophilic suction control unit; the hydrophilic suction control unit only permits water to pass but not gas, thereby ensuring that the pore air pressure is greater than the pore water pressure.

[0031] For hydrophobic soils, specimens were prepared according to the same geotechnical test specifications, with the same dimensions of 39.1 mm in diameter and 80 mm in height. The testing process for hydrophobic soils is similar to that for hydrophilic soils, except that the hydrophilic suction control unit is removed and a hydrophobic suction control unit is installed on top of the specimen. The hydrophobic soil suction control unit ensures that only air enters the upper portion of the specimen, preventing water from passing through. This ensures that the pore water pressure is greater than the pore air pressure, thereby controlling the suction of the hydrophobic soil.

[0032] Beneficial effects of the present invention:

[0033] Traditional experimental methods often fail to consider the hydrophilicity and hydrophobicity of soils. When conducting unsaturated soil experiments, they often assume that the pore air pressure is greater than the pore water pressure. This can cause water in hydrophilic samples to flow back into the sample cap, affecting the volume change results. Furthermore, when conducting unsaturated soil experiments on hydrophobic samples, the experimental results can deviate significantly from the true values. Therefore, this device effectively improves the accuracy of experimental results in unsaturated soil experiments on hydrophilic and hydrophobic soil samples, such as volume change, pore air pressure, and pore water pressure, bringing the experimental results closer to the true values. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a non-saturated triaxial compression instrument and related system.

[0035] Figure 2 Detailed drawing of the loading frame of the present invention.

[0036] Figure 3 Detailed view of the external pressure chamber.

[0037] Figure 4 Detailed view of the internal pressure chamber.

[0038] Figure 5 Detailed drawing of the specimen and base.

[0039] Figure 6 Detail of the axial pressure control console.

[0040] Figure 7 This is a test device for testing the mechanical properties of unsaturated hydrophilic soil and hydrophilic soil.

[0041] Figure 8 This is a test device for testing the mechanical properties of unsaturated hydrophobic soil and hydrophobic soil.

[0042] Figure 9 Detailed drawing of the device.

[0043] Figure 10 Detailed diagram of the suction control unit for hydrophobic soil.

[0044] Figure 11 Detailed diagram of the suction control unit for hydrophilic soil.

[0045] Figure 12 Schematic diagram of the air pressure control box and gas pipeline.

[0046] Figure 13 This is a pressure sensor connection diagram.

[0047] Reference numerals:

[0048] 1: Data processing system, 2: Axial pressure control system, 3: External pressure chamber, 4: Internal pressure chamber, 5: Hydrophobic soil suction control unit, 6: Hydrophilic soil suction control unit, 7: Air pressure control system, 8: Back pressure control system, 9: Data acquisition system, 10: Screw, 11: Crossbeam, 12: Vertical loading rod, 13: End groove of vertical loading rod, 14: Hydraulic rod, 15: Air pressure control box, 16: Gas pipeline, 18: Sample top cap, 20: Metal screw, 21: Organic transparent glass cover, 22: High air intake value clay plate. DETAILED DESCRIPTION

[0049] The present invention will be described in further detail below with reference to the accompanying drawings.

[0050] like Figures 1-13As shown, the purpose of the present invention is to provide a test device and method that can uniformly test the mechanical properties of unsaturated hydrophobic soil and hydrophilic soil, so as to solve the problem that the existing unsaturated soil mechanical property test device cannot be applied to hydrophobic soil, and improve the accuracy and wide applicability of the unsaturated soil mechanical property test.

[0051] A test apparatus for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soils comprises a pressure chamber located at the center of the apparatus, an axial loading system 2 located below the pressure chamber for applying axial stress, and connected to the pressure chamber via a loading frame. The axial loading system 2 is connected to an information acquisition system 1 for controlling the loading rate and loading method. An air pressure control system 7 is located on the side of the pressure chamber and connected to the pressure chamber via a pipeline. The air pressure control system 7 functions as a gas pressure pump for providing confining pressure to the pressure chamber and pore pressure to the top of the specimen. A data acquisition system 9 is located next to a console or computer and is connected to sensors at each unit for measuring and acquiring parameters such as stress, strain, and pore pressure. A data processing system 1 is connected to the air pressure control system 7 and a back pressure control system 8 for real-time monitoring and recording of test data. The data processing system 1 is connected to the axial loading system 2 for controlling the loading rate and loading method. The specimen is located at the center of the pressure chamber. A hydrophobic soil suction control unit 5 and a hydrophilic soil suction control unit 6 are located at the upper and lower ends of the specimen for transmitting pore pressure and back pressure, maintaining close contact with the specimen to ensure uniform pressure transmission, and are connected to the air pressure control system 7 via a pipeline.

[0052] The hydrophobic soil suction control unit 5 is used to accurately control the pore gas pressure at the top of the hydrophobic soil sample;

[0053] The hydrophilic suction control unit 6 is used to accurately control the pore water pressure at the bottom of the hydrophilic soil sample;

[0054] The axial loading system 2 is used to precisely control the axial load of the specimen;

[0055] The air pressure control system 7 is used to accurately control the confining pressure in the pressure chamber and the pore air pressure loaded on the top of the sample;

[0056] The back pressure control system 8 is used to apply back pressure to the bottom of the sample;

[0057] The data acquisition system 9 is used to collect data on pore gas pressure, confining pressure, back pressure, and volume change during the test;

[0058] The data processing system 1 is used to record and process various data during the test process and present them in a graphical form on the computer.

[0059] This device mainly includes the following parts:

[0060] 1. Special film material: Expanded polytetrafluoroethylene (e-PTFE), a polymer film with a specific microstructure and physicochemical properties, is used. The pore size of this film allows gas molecules to pass freely, but has a significant barrier effect on water molecules. It is a polymer waterproof filter membrane material with high porosity and uniform micropore distribution, thus achieving the function of only allowing air to enter but not water. The micropore diameter ranges from 10 to 100 nanometers, which is very small compared to water droplets, making it impossible for water to pass through. However, the pore size is relatively large for air molecules, allowing air to pass smoothly. The film has good air-philic and hydrophobic properties, further enhancing its selective permeability to gas and water.

[0061] 2. Membrane Fixing Structure: A specialized fixing structure is designed to secure the membrane tightly and evenly to the upper surface of the unsaturated soil specimen. This fixing structure is constructed from a high-strength, corrosion-resistant material, namely a porous, thin stainless steel plate. The shape and dimensions of the structure are adapted to the specimen in the triaxial compression apparatus, measuring 50 mm in diameter and 5 mm thick, ensuring no impact on the specimen's stress and deformation during the test.

[0062] The relationship between the special film material, the film fixing structure and the unsaturated triaxial compression instrument and the related system is specifically composed of a layer of expanded polytetrafluoroethylene (e-PTFE) film wrapped on the surface of a porous metal plate structure ( Figure 10 ), often and sample cap ( Figure 9 ) are installed together and located on the top of the sample. When testing hydrophobic soil, it can ensure that the back pressure on the sample is greater than the pore air pressure and accurately control the suction force.

[0063] Test method:

[0064] Determine the hydrophilicity or hydrophobicity of the soil:

[0065] Water Drop Test: This test measures the contact angle of soil using an optical contact angle meter. The soil sample is pressed into a 1cm thick sheet or flat surface and a drop of water is placed on the surface. The shape of the drop is recorded, and the contact angle is determined using the Young-Laplace equation. A contact angle less than 90° indicates hydrophilic soil, while a contact angle greater than 90° indicates hydrophobic soil.

[0066] Sample preparation:

[0067] For remolded soil samples, calculate the required dry soil mass and water content based on the predetermined dry density and moisture content. Crush the air-dried soil sample and sieve it, typically using a 2mm sieve, to ensure uniformity of the soil particles. Weigh a calculated mass of dry soil into a mixing container and slowly add the appropriate amount of water, stirring thoroughly to evenly distribute the water between the soil particles. This remolded soil sample is sealed and allowed to stand for a period of time, typically 24 hours, to further evenly distribute the moisture within the sample and allow for interaction and adjustment between the soil particles.

[0068] Specimen installation:

[0069] (1) Select the appropriate rubber membrane: Select a rubber membrane of appropriate thickness and size based on the size of the specimen. The rubber membrane should have good elasticity and sealing properties, without damage or holes. Before use, carefully check the integrity of the rubber membrane and replace it promptly if any defects are found.

[0070] (2) Rubber film:

[0071] Place the rubber membrane over the membrane cylinder, folding the ends outward and securing them with rubber bands. Inject an appropriate amount of water or air into the membrane cylinder to slightly inflate the membrane, making it easier to insert the soil sample. Carefully place the prepared reshaped soil sample into the rubber membrane inside the membrane cylinder, minimizing the risk of creating gaps or wrinkles between the sample and the membrane. Specialized tools can be used to assist in placing the soil sample, ensuring it is centered and properly shaped within the rubber membrane. Remove the rubber membrane containing the soil sample from the membrane cylinder and secure it tightly to the top and bottom of the sample with rubber bands to ensure a good seal.

[0072] (3) Install the sample in the pressure chamber:

[0073] Place the specimen, with the rubber membrane attached, on the base of the triaxial pressure chamber. Adjust the specimen's position and place a layer of filter paper on the bottom and top of the specimen. For hydrophilic soils, place a permeable stone with a high air intake value on top of the specimen. For hydrophobic soils, place the device (a layer of expanded polytetrafluoroethylene (e-PTFE) film and porous metal sheet) on top of the specimen. Install the pressure chamber's top cover, ensuring a good seal between the cover and the base to prevent pressure leaks. During installation, be careful to avoid impacting or disturbing the specimen.

[0074] Instrument debugging and parameter setting:

[0075] (1) Check the triaxial compression instrument:

[0076] Check that all components of the triaxial compression instrument are functioning properly, including the pressure control system, displacement measurement system, pore water pressure measurement system, and pore air pressure measurement system. Ensure that the instrument's piping connections are tight and free of looseness and leaks. Calibrate the instrument's sensors to ensure accurate measurement data.

[0077] (2) Set the test parameters:

[0078] According to the test requirements, set the initial values of confining pressure, pore water pressure, pore gas pressure, and loading rate, among other parameters. The initial values of pore water pressure and pore gas pressure should be appropriately set based on the soil sample's saturation and the expected test conditions. The loading rate should be moderate, ensuring accurate capture of the soil sample's mechanical response while not causing the test to be too slow or too rapid.

[0079] Test process:

[0080] (1) Apply confining pressure:

[0081] Start the pressure control system and slowly apply confining pressure at a rate of 10kPa / min to 25kPa / min to the predetermined value. During the confining pressure application process, closely observe the pressure changes and the deformation of the specimen to ensure that the confining pressure is applied stably and evenly.

[0082] (2) Apply pore water pressure and pore gas pressure:

[0083] Apply a predetermined gas pressure to the sample. The predetermined gas pressure should be equal to the applied matrix suction in value and should be applied uniformly at a rate of 10kPa / min to 25kPa / min to the predetermined value. It is also advisable that the pressures of the inner and outer pressure chambers are increased simultaneously and equally so that the pressures of the inner and outer chambers are always 5kPa higher than the gas pressure.

[0084] If it is hydrophilic soil, it is generally required that the applied pore air pressure is greater than the pore water pressure, and the pore water pressure is greater than 0.

[0085] In case of hydrophobic soil, the applied pore water pressure is greater than the pore air pressure.

[0086] (3) Axial loading:

[0087] Once the pore water pressure, pore air pressure, and confining pressure have stabilized at their set values, the axial loading system is activated, and the specimen is axially loaded at the predetermined loading rate. During loading, data such as axial load, axial displacement, pore water pressure, and pore air pressure are recorded in real time. Loading continues until the specimen fails or the predetermined axial strain value is reached. During loading, the specimen's failure morphology and process are carefully observed, such as for visible cracks, bulging, or shear failure.

[0088] End of experiment and data processing:

[0089] (1) End of the experiment:

[0090] When the soil sample reaches the predetermined value, stop loading and record various data at the end of the experiment, including the failure stress and failure strain of the soil sample.

[0091] (2) Data processing:

[0092] Organize and analyze experimental data, plot stress-strain curves, pore water pressure-strain curves, etc. Evaluate the strength, deformation characteristics, and failure mechanism of hydrophilic or hydrophobic soils based on experimental results.

Claims

1. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil, characterized in that: The device comprises a pressure chamber, which is located at the center of the entire device; an axial loading system (2) is located below the pressure chamber and is used to apply axial stress; the axial loading system (2) is connected to the pressure chamber through a loading frame; the axial loading system (2) is connected to an information acquisition system (1) and is used to control the loading rate and loading mode; an air pressure control system (7) is located on the side of the pressure chamber and is connected to the pressure chamber through a pipeline, and acts as a gas pressure pump to provide confining pressure to the pressure chamber and pore air pressure to the top of the sample; The data acquisition system (9) is located next to the console or computer and is connected to sensors at each unit to measure and collect parameters of stress, strain, and pore pressure. The data processing system (1) is connected to the air pressure control system (7) and the back pressure control system (8) to monitor and record test data in real time. The data processing system (1) is connected to the axial loading system (2) to control the loading rate and loading method. The specimen is located at the center of the pressure chamber. The hydrophobic soil suction control unit (5) and the hydrophilic soil suction control unit (6) are located at the upper and lower ends of the sample, and are used to transmit pore air pressure and back pressure. They are in close contact with the sample to ensure uniform pressure transmission, and are connected to the air pressure control system (7) through a pipeline.

2. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The hydrophobic soil suction control unit (5) is used to accurately control the pore gas pressure at the top of the hydrophobic soil sample; The hydrophilic suction control unit (6) is used to accurately control the pore water pressure at the bottom of the hydrophilic soil sample; The axial loading system (2) is used to precisely control the magnitude of the axial load on the specimen; The air pressure control system (7) is used to accurately control the confining pressure in the pressure chamber and the pore air pressure loaded on the top of the sample; The back pressure control system (8) is used to apply back pressure to the bottom of the sample; The data acquisition system (9) is used to collect data on pore gas pressure, confining pressure, back pressure, and volume change during the test; The data processing system (1) is used to record and process various data during the test process and present them in a computer in a graphical form.

3. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The hydrophobic soil suction control unit (5) is composed of a layer of expanded polytetrafluoroethylene (e-PTFE) film wrapped on the surface of a porous metal plate structure, and is installed together with the sample cap and located on the top of the sample.

4. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The hydrophilic suction control unit (6) is usually installed on a base, located at the bottom of the sample, and is composed of a high-air intake value clay plate (22). The clay plate is made of a mixture of mineral raw materials such as kaolin and quartz powder, and is sintered at high temperature. Uniform and continuous micron-level capillary channels are formed inside the plate, with an average pore size between 0.1 and 1 micron, and an air intake value of 200 to 500 kPa. During the test, the clay plate is connected to the back pressure system to stably control the pore water pressure inside the soil body, and establish a constant matrix suction boundary condition when the pore air pressure is loaded from above, ensuring that the hydrophilic unsaturated soil can achieve reliable suction regulation and mechanical response testing under the axial translation loading mode; The high air intake value clay plate (22) is a sintered ceramic material containing a large number of uniformly distributed micropores, the pore size of which is 0.5 microns, which is consistent with the size of the bottom of the sample, with a diameter of 40 mm and a thickness of 5 mm to 10 mm; When the internal pores of the high air inlet value clay plate (22) are completely saturated with water, the capillary force formed by the water film on the pore surface will prevent the gas from passing through, so that within a given pressure range (0-5 bar), the pore gas pressure is greater than the pore water pressure.

5. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The axial loading system (2) includes a vertical loading frame and an axial loading console. The vertical loading frame is fixed by tightening a crossbeam (11) up and down with two pairs of screws (10) and embedding a vertical loading rod (12) and a groove (13) at the end of the vertical loading rod into a convex rod on the sample cap, thereby supporting and fixing the sample to prevent the force line from deviating. A hydraulic rod (14) that moves in a vertical direction is provided on the axial loading console and applies corresponding axial stress by controlling the vertical displacement.

6. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The air pressure control system (7) includes an air pressure control box (15) and two air pipes (16), wherein the air pipes 16 are a confining pressure pipe and a pore air pressure pipe, respectively. The confining pressure pipe is connected to the external pressure chamber (3) to provide a corresponding confining pressure, and the pore air pressure pipe is connected to the sample top cap (18) to provide a corresponding pore air pressure. The outer pressure chamber (3) is used to apply confining pressure, control pore pressure, provide a stable test environment, measure volume changes, and protect the sample, and the inner pressure chamber (4) is used to apply confining pressure and control pore pressure to ensure the accuracy and repeatability of the test results; The outer pressure chamber (3) is located between the vertical loading frame and the axial loading console, and the inner pressure chamber (4) is installed inside the outer pressure chamber.

7. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 6, characterized in that: The outer pressure chamber (3) is composed of a metal screw (20) and an organic transparent glass cover (21); the inner pressure chamber (4) provides a stable pressure environment for the sample, ensuring that the pressure around the sample is evenly distributed during the test, simulating the stress state of the soil in actual engineering; the bottom of the sample is equipped with a high air intake value clay plate (22) to facilitate the discharge of pore water and the measurement of pore water pressure.

8. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The back pressure control system (8) includes a pore water pressure sensor, a pressure regulator and a connecting pipeline, which are used to measure the pore water pressure and monitor the pore water pressure inside the soil sample in real time; the pressure regulator is used to adjust the pore water pressure to simulate different unsaturated states; The porous metal plate of the hydrophobic soil suction control unit (5) is made of a highly permeable material to ensure gas exchange efficiency; the gas valve is adjusted by an external control device to adapt to different test conditions and requirements; The porous metal plate structure is connected to the pressure transfer cap of the triaxial apparatus, and the sample is compressed and sheared by raising and lowering the base. The porous metal plate structure is connected to a gas pressure controller to measure and control the pore gas pressure in the sample.

9. A test device for testing the mechanical properties of hydrophilic and hydrophobic unsaturated soil according to claim 1, characterized in that: The data acquisition system (9) includes a static 8-channel data acquisition instrument and a sensor data line, which is used to collect experimental data and convert sensor signals into digital signals; the data line is connected to the sensor to record the experimental data in real time; The data processing system (1) includes a PLC control system, which is used to process experimental data, display the data in real time in the form of images, and calculate various experimental data.

10. A method for using a test device capable of uniformly testing the mechanical properties of unsaturated hydrophobic soil and hydrophilic soil, characterized in that: The method comprises the following steps: firstly, determining the hydrophilicity of the soil by a drip test; for hydrophilic soil, preparing a sample according to geotechnical test specifications; the sample size is 39.1 mm in diameter and 80 mm in height; saturating the sample and installing it on the sample base; fixing the upper and lower ends of the sample with rubber bands; then installing an outer pressure chamber (3) and an inner pressure chamber (4); connecting a water pump to inject airless water into the pressure chamber; and controlling the matrix suction of the hydrophilic sample by a hydrophilic suction control unit (6); the hydrophilic suction control unit (6) only allows water to pass through but does not allow gas to pass through. The test process of hydrophobic soil is similar to that of hydrophilic soil, except that the hydrophilic suction control unit (6) needs to be disassembled and the hydrophobic suction control unit (5) needs to be installed on the top of the sample. The hydrophobic soil suction control unit (5) ensures that only air enters the upper part of the sample and does not allow water to pass through, that is, the pore water pressure is greater than the pore air pressure, thereby achieving control of the hydrophobic soil suction.

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