Method for testing unsaturated soil body suction force

Abstract

The application discloses a kind of non-saturated soil body suction test methods, it is characterized in that, to be measured soil is placed in closed space and leaves out cavity for gas flow in closed space, the cavity is connected into a gas path system, and the cavity is realized by gas path system to the continuous gas supply and air extraction of the cavity, so that the cavity realizes a stable negative pressure variation process, the gas humidity of the cavity is detected in the process, when the gas humidity of the cavity and the gas humidity value of the cavity are consistent, it is judged that the suction of the soil to be measured and the negative pressure in the cavity are balanced at this time, and the size of the negative pressure in the cavity at this time can obtain the suction size of the soil to be measured.The application has the advantages of convenient operation, low cost, can reduce artificial interference to improve the measuring accuracy.

Description

Technical Field

[0001] This invention relates to the field of soil testing technology, and specifically to a method for testing the suction of unsaturated soil. Background Technology

[0002] Unsaturated soil is a type of soil in which water and air coexist in the pore space. In unsaturated soil, the interface between water and air generates capillary tension due to the meniscus effect. Simultaneously, water interacts with minerals in the soil, maintaining a state of equilibrium under the influence of air pressure, water pressure, and capillary tension. Its free energy is zero relative to pure water. Therefore, soil suction reflects the free energy state of water in the soil, vividly representing the soil's ability to retain water. Thus, the magnitude of soil suction is a crucial factor affecting the properties of unsaturated soil. Changes in suction directly influence the soil's permeability and mechanical properties. Accurately measuring the suction in unsaturated soil is an important part of its research. Currently, the main methods for measuring the suction of unsaturated soil include the filter paper method, the thermocouple hygrometer method, and the tensiometer method. The filter paper method is widely used due to its advantages such as low cost, wide suction measurement range, and ability to measure matrix suction and total suction. Its principle is that the filter paper can reach equilibrium with the soil with a certain suction through water vapor exchange. Based on the relationship curve between the suction of the calibrated filter paper and the moisture content, the soil suction can be calculated.

[0003] In the existing filter paper method for measuring soil suction, in order to protect the calibrated filter paper and ensure its surface cleanliness to improve measurement accuracy, protective filter paper is often placed on both sides of the calibrated filter paper. Then, two ring cutters containing soil samples are placed against the outside of the protective filter paper. Finally, after standing for a certain period of time, the calibrated filter paper is removed and its moisture content is measured.

[0004] While the filter paper method is inexpensive and easy to operate, it has several drawbacks. The soil sample in the ring sampler needs to be smoothed during operation to ensure good contact between the soil and the filter paper. Since the filter paper method measures the suction of pore water in the soil under the influence of air in the pores, the manual smoothing process disrupts the pore distribution on the soil sample surface and can easily clog many pores, leading to poor measurement accuracy. Furthermore, the uniformity of the filter paper during manufacturing is difficult to guarantee. Each measurement requires calibration of the suction-moisture content curve of the filter paper, and the relationship between the suction and moisture content is essentially fixed and uncontrollable, further increasing measurement error. Additionally, the measurement process using filter paper is slow, often requiring about a week for the suction to reach equilibrium with the soil suction, resulting in a long measurement cycle.

[0005] Therefore, how to design a method for testing the suction of unsaturated soil that is easy to operate, low in cost, causes little human interference to the soil surface, and has higher measurement accuracy and shorter measurement cycle has become a problem that needs to be considered and solved by those skilled in the art. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a method for testing the suction of unsaturated soil that is convenient to operate and measure, low in cost, and can reduce human interference to improve measurement accuracy.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for testing the suction of unsaturated soil is characterized by placing the soil to be measured in a closed space with a cavity for gas flow. This cavity is connected in series to a gas path system, which continuously supplies and extracts gas into the cavity, creating a stable negative pressure change process. During this process, the humidity of the gas supplied to and extracted from the cavity is detected. When the humidity values ​​of the extracted gas and the supplied gas are consistent, it is determined that the suction of the soil to be measured and the negative pressure in the cavity are balanced. The magnitude of the suction of the soil to be measured can be obtained based on the magnitude of the negative pressure in the cavity at this point.

[0009] In this method, the soil to be measured is placed in a closed space, and negative pressure is generated by supplying and extracting air through an air supply system. This changes the free energy state of the water in the soil, causing the water to migrate in the pores. The humidity of the gas extracted from the cavity changes through water vapor exchange, simulating the water vapor exchange process between the filter paper and the soil in the filter paper detection method. As the negative pressure in the cavity changes, when the negative pressure is balanced with the suction of the soil, the free energy of the water in the soil is zero, and the water in the soil no longer migrates. Therefore, no more water vapor exchange occurs, and the humidity of the gas extracted from the cavity is consistent with the humidity of the gas supplied to the cavity. Thus, the magnitude of the negative pressure in the cavity at the equilibrium point can be used to characterize the suction of the soil to be measured.

[0010] In addition, the detection is achieved by drawing suction into the cavity to create negative pressure. This cavity can be formed by a gap with natural cross-sections on both sides, which is formed by the fracture of the soil sample to be measured. The pore distribution of the natural cross-section without artificial interference is close to the pore distribution in the soil sample to be measured, making the measurement result closer to the suction of the soil under natural conditions, thereby improving the measurement accuracy.

[0011] Furthermore, the volume of the soil to be measured is more than 10 times the volume of the cavity.

[0012] In this way, the soil to be measured only needs to lose a very small proportion of water during the measurement process. Therefore, similar to the principle of filter paper detection, the suction of the soil before and after the test is considered to remain unchanged. When the suction of the soil to be measured and the negative pressure in the cavity are balanced, the magnitude of the negative pressure in the cavity is equal to the magnitude of the suction of the soil to be measured.

[0013] Furthermore, during the change of negative pressure provided to the cavity, the suction force of dry test filter paper is used as the initial suction force. Then, the test filter paper is used to conduct a suction test on the semi-saturated soil. The magnitude of the suction force of the filter paper is recorded after a fixed time interval, and the curve relationship between the change of filter paper suction force and time is obtained. Based on this curve relationship, the filter paper suction force is replaced by the magnitude of the negative pressure provided to the cavity, so as to realize the control of the change of negative pressure provided to the cavity over time.

[0014] This approach better simulates the filter paper testing method by providing a gradually decreasing negative pressure for the test, while avoiding the interference with the soil surface that can occur with the filter paper method, thus improving testing accuracy. Note that the entire control process does not use the minimum suction force of the filter paper in the suction test as the minimum control negative pressure. Instead, after the negative pressure reaches the minimum suction force of the filter paper in the suction test, if the humidity has not yet reached equilibrium, the negative pressure is continuously reduced according to the curve until it reaches zero. During this process, when the humidity reaches equilibrium (before the control negative pressure reaches zero), the negative pressure at this point is determined as the magnitude of the suction force of the soil to be measured.

[0015] During the experiment, conventional air can be used to supply gas to the cavity. Since the change in humidity of the extracted gas is caused by the negative pressure drawing moisture from the soil, the humidity change is only related to whether the negative pressure reaches equilibrium, and has little to do with the humidity of the supplied gas itself. However, if the humidity of the supplied gas differs significantly from the soil humidity, the accuracy of the test results may be affected by greater evaporation or natural water vapor exchange. Therefore, it is preferable that the humidity of the supplied gas is the same as or close to the moisture content of the soil to minimize the impact of excessive humidity difference on the test results.

[0016] Furthermore, this method employs an unsaturated soil suction test system, which includes two opposing ring cutters. A sealing sleeve is fitted over the open ends of each ring cutter. A clamp is installed at each end of the sealing sleeve to secure the ring cutter. After the two ring cutters are sealed, a detection gap with a width less than one-tenth of the ring cutter depth is left between the open ends. An air supply connector is connected outwards from one side of the sealing sleeve corresponding to the middle of the detection gap. The air supply connector is connected to an air supply device via an air supply pipe. An air extraction connector is connected outwards from the other side of the sealing sleeve, via an air extraction pipe to a negative pressure generating device. An inlet humidity sensor is also installed on the air supply pipe, and an outlet humidity sensor is also installed on the air extraction pipe. The system also includes a controller, which is connected to the air supply device, the negative pressure generating device, the inlet humidity sensor, and the outlet humidity sensor.

[0017] In this test, the sealing sleeve is removed, and the soil sample to be measured is cut into the ring cutter, ensuring the opening retains its natural cross-section. The sealing sleeve is then installed and secured with clamps to create a sealed space. The gap between the two ring cutters forms a cavity for gas flow. The test process is controlled by a controller, which calculates the results. Specifically, the controller regulates the air supply and negative pressure generating devices to adjust the negative pressure within the cavity, gradually decreasing it. Inlet and outlet humidity sensors monitor the humidity changes of the incoming and outgoing air. When the humidity is consistent, the suction of the soil sample and the negative pressure within the cavity are considered balanced. The suction of the soil sample can then be determined based on the magnitude of the negative pressure. This test process simulates the principle and process of the test paper method, but the surface of the soil sample is a natural cross-section, preventing damage from contact with the test paper and thus improving the accuracy of the test. In addition to being directly used for the suction test of unsaturated soil, this test system can also be used to conduct experimental research on the water gain and loss capacity and suction magnitude changes of unsaturated soil or other hygroscopic materials under different humidity and negative pressure conditions.

[0018] Furthermore, the gas supply device includes an air pump.

[0019] This allows the gas supply device to actively supply gas, thus better controlling the air pressure inside the cavity.

[0020] Furthermore, the air supply device also includes an air drying module.

[0021] In this way, when the humidity of the intake air is too high (reaching or approaching saturation), the air drying module can dry the intake air, preventing excessive humidity from affecting the test results. Because this equipment extracts moisture from the soil under negative pressure, in principle, whether moisture can be extracted depends only on whether the negative pressure is balanced, and is not related to the humidity of the intake air. However, if the humidity of the intake air has reached or approached saturation, it will obviously affect the effectiveness of extracting moisture from the soil into the air. Therefore, the intake air needs to maintain a certain degree of dryness to avoid excessive humidity affecting the test results.

[0022] Furthermore, the gas supply device also includes a temperature control component. This allows for convenient temperature adjustment as needed, preventing excessively high or low temperatures from affecting the experiment.

[0023] Furthermore, a pressure sensor is installed in the middle of the inner side of the sealing sleeve or on the extraction pipe. This allows for real-time monitoring of the air pressure inside the sealing sleeve. When the humidity of the incoming and outgoing air is consistent, the suction force of the soil being measured can be obtained based on the readings from the pressure sensor. This avoids pressure loss between the negative pressure generating device and the cavity, which could affect the accuracy of the test.

[0024] Furthermore, an arc-shaped air storage chamber is provided inside the air supply connector and the air extraction connector on the sealing sleeve. The back side of each of the two air storage chambers is connected to the corresponding air supply connector or air extraction connector. At least one air port is provided inside the air storage chamber and is connected to the inner cavity of the sealing sleeve. The air passage area of ​​the air port is larger than the air passage area of ​​the corresponding air supply connector or air extraction connector.

[0025] In this way, the transition between air intake and exhaust is achieved by relying on the air storage chamber, ensuring smoother and more stable adjustment and control of the internal air pressure, and avoiding excessive pressure concentration at the air intake and exhaust positions, which could affect the test results.

[0026] Furthermore, the air outlet is either a strip-shaped hole extending along the extension direction of the air storage tank or multiple spaced air outlets, with the axes of the multiple air outlets parallel to each other and the axes of the air outlets perpendicular to the axis of symmetry of the two air storage tanks. This better ensures the above-mentioned effect.

[0027] Furthermore, the sealing sleeve is made of rubber. This allows the clamp to achieve a tight seal more easily.

[0028] Furthermore, the surface of the ring cutter is also marked with the sealing sleeve installation position markings.

[0029] This allows for the creation of a small cavity between the ring cutters during the installation of the sealing sleeve, preventing the cavity from being too large and affecting the test accuracy.

[0030] Furthermore, each of the two ring cutters has a thrust drive device connected to its outward end at the end opposite to the circumferential cutter edge. The two thrust drive devices are relatively fixedly connected by a mounting bracket, and the stroke of the thrust drive device is greater than the depth of the ring cutter.

[0031] In this way, during the test, it is convenient to use the thrust drive device to control the insertion of the ring cutter into the soil sample, thereby achieving the cutting of the soil to be tested.

[0032] Furthermore, the thrust drive device is a pneumatic cylinder, an electric cylinder, or a hydraulic cylinder. It features a simple structure, real-time convenience, and low cost.

[0033] When the above-mentioned unsaturated soil suction test system is used in specific tests, it may include the following steps:

[0034] Obtain an unsaturated soil sample to be tested with a length exactly twice the depth of the ring cutter. Place the unsaturated soil sample between two ring cutters and use a driving device to make the two ring cutters cut into the soil sample simultaneously until the opposite end faces of the two ring cutters fit together and the ring cutters are filled with soil sample.

[0035] The driving device drives two ring cutters to move in opposite directions, causing the soil sample filled in the ring cutters to break and form a natural cross-section at the cutter edge.

[0036] Install the sealing sleeve so that both ends of the sealing sleeve are respectively fitted onto the outside of the two ring cutters, and are tightly connected to the side wall of the ring cutter by the clamp, so that the detection gap left between the two ring cutters forms a cavity for gas flow.

[0037] Keep the gas supply connector on the seal connected to the gas supply device, and the air extraction connector connected to the negative pressure generator; turn on the gas supply device and generate gas with preset humidity and / or temperature (usually room temperature air); start the negative pressure generator so that the gas supplied by the gas supply device enters the cavity through the gas supply connector and flows out through the air extraction connector. During this process, a stable negative pressure environment is formed in the cavity under the air extraction action of the negative pressure generator.

[0038] The negative pressure in the cavity is gradually reduced from large to small. At the same time, the humidity data of the gas entering and leaving the cavity are collected. When the humidity of the gas entering and leaving the cavity is the same, the suction of the soil sample is obtained according to the magnitude of the negative pressure in the air.

[0039] Therefore, this method has the following beneficial effects: This method uses two opposing ring cutters to cut soil samples, and stretches the soil samples to form natural cross-sections. There is no human interference at the cross-section. A non-contact suction testing system is created using negative pressure. An adjustable negative pressure environment is formed at the soil sample cross-section, and water vapor exchange occurs between the flowing gas and the soil sample. Humidity is detected to obtain the exchange status, and the suction of the soil sample is obtained by observing changes in humidity and negative pressure. This invention has minimal human interference, adjustable pressure, high measurement accuracy, and simple operation.

[0040] In summary, the present invention has the advantages of convenient operation, low cost, and the ability to reduce human interference to improve measurement accuracy. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the unsaturated soil suction test system used in this invention.

[0042] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of a central ring cutter. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to specific embodiments.

[0044] Implementation method: A method for testing the suction of unsaturated soil, characterized in that the soil to be measured is placed in a closed space with a cavity for gas flow. This cavity is connected in series to a gas path system, which continuously supplies and extracts gas into the cavity, resulting in a stable negative pressure change process. During this process, the humidity of the gas supplied to and extracted from the cavity is detected. When the humidity of the gas extracted from the cavity is the same as that of the gas supplied to the cavity, it is determined that the suction of the soil to be measured and the negative pressure in the cavity are in balance. The suction of the soil to be measured can be obtained based on the magnitude of the negative pressure in the cavity at this time.

[0045] In this method, the soil to be measured is placed in a closed space, and negative pressure is generated by supplying and extracting air through an air supply system. This changes the free energy state of the water in the soil, causing the water to migrate in the pores. The humidity of the gas extracted from the cavity changes through water vapor exchange, simulating the water vapor exchange process between the filter paper and the soil in the filter paper detection method. As the negative pressure in the cavity changes, when the negative pressure is balanced with the suction of the soil, the free energy of the water in the soil is zero, and the water in the soil no longer migrates. Therefore, no more water vapor exchange occurs, and the humidity of the gas extracted from the cavity is consistent with the humidity of the gas supplied to the cavity. Thus, the magnitude of the negative pressure in the cavity at the equilibrium point can be used to characterize the suction of the soil to be measured.

[0046] In addition, the detection is achieved by drawing suction into the cavity to create negative pressure. This cavity can be formed by a gap with natural cross-sections on both sides, which is formed by the fracture of the soil sample to be measured. The pore distribution of the natural cross-section without artificial interference is close to the pore distribution in the soil sample to be measured, making the measurement result closer to the suction of the soil under natural conditions, thereby improving the measurement accuracy.

[0047] During implementation, the volume of the soil to be measured should be more than 10 times the volume of the cavity.

[0048] In this way, the soil to be measured only needs to lose a very small proportion of water during the measurement process. Therefore, similar to the principle of filter paper detection, the suction of the soil before and after the test is considered to remain unchanged. When the suction of the soil to be measured and the negative pressure in the cavity are balanced, the magnitude of the negative pressure in the cavity is equal to the magnitude of the suction of the soil to be measured.

[0049] During implementation, the suction force of dry test filter paper is used as the initial suction force during the change of negative pressure provided to the cavity. Then, the suction force of the test filter paper is used to conduct a suction test on the semi-saturated soil. The magnitude of the suction force of the filter paper is recorded after a fixed time interval, and the curve relationship between the change of filter paper suction force and time is obtained. Based on this curve relationship, the filter paper suction force is replaced by the magnitude of the negative pressure provided to the cavity, so as to control the change of negative pressure provided to the cavity over time.

[0050] This approach better simulates the filter paper testing process by providing a gradually decreasing negative pressure for the experiment, while avoiding the interference with the soil surface that can occur with the filter paper method, thus improving testing accuracy. Note that the entire control process does not use the minimum suction force of the filter paper in the suction test as the minimum control negative pressure. Instead, after the negative pressure reaches the minimum suction force of the filter paper in the suction test, if the humidity has not yet reached equilibrium, the negative pressure is continuously reduced according to the curve until it reaches zero. During this process, when the humidity reaches equilibrium (before the control negative pressure reaches zero), the negative pressure at this point is determined to be the magnitude of the suction force of the soil being measured. In this embodiment, the change in negative pressure in the cavity simulates the linear relationship between the suction force of the filter paper and the decrease in moisture content. Of course, other methods can also be used, offering better controllability and real-time humidity detection, making the detection more convenient and faster. Furthermore, the water vapor exchange is achieved through air pressure changes, avoiding contact and damage to the soil surface, reducing the influence of human interference factors, and better characterizing the suction force of the in-situ soil sample, thus improving measurement accuracy.

[0051] During the experiment, conventional air can be used to supply gas to the cavity. Since the change in humidity of the extracted gas is caused by the negative pressure drawing moisture from the soil, the humidity change is only related to whether the negative pressure reaches equilibrium, and has little to do with the humidity of the supplied gas itself. However, if the humidity of the supplied gas differs significantly from the soil humidity, the accuracy of the test results may be affected by greater evaporation or natural water vapor exchange. Therefore, it is preferable that the humidity of the supplied gas is the same as or close to the moisture content of the soil to minimize the impact of excessive humidity difference on the test results.

[0052] Specifically, this method employs an unsaturated soil suction test system, as described in the following description: Figure 1-2 As shown, the device includes two opposing ring cutters 1. A sealing sleeve 2 is fitted over the open ends of the two ring cutters 1. A clamp 3 is installed at each end of the sealing sleeve 2 to seal and fix the ring cutter. After the two ring cutters are sealed and fixed, a detection gap 4 with a width less than one-tenth of the ring cutter depth is left between the open ends. An air supply connector 5 is connected outwards from one side of the sealing sleeve corresponding to the middle of the detection gap. The air supply connector 5 is connected to an air supply device 7 via an air supply pipe 6. An air extraction connector 8 is connected outwards from the other side of the middle of the sealing sleeve 2. The air extraction connector 8 is connected to a negative pressure generating device 10 via an air extraction pipe 9. An inlet humidity sensor 11 is also installed on the air supply pipe 5, and an outlet humidity sensor 12 is also installed on the air extraction pipe 8. The device also includes a controller (not shown in the figure), which is connected to the air supply device, the negative pressure generating device, the inlet humidity sensor, and the outlet humidity sensor.

[0053] In this test, the sealing sleeve is removed, and the soil sample to be measured is cut into the ring cutter, ensuring the opening retains its natural cross-section. The sealing sleeve is then installed and secured with clamps to create a sealed space. The gap between the two ring cutters forms a cavity for gas flow. The test process is controlled by a controller, which calculates the results. Specifically, the controller regulates the air supply and negative pressure generating devices to adjust the negative pressure within the cavity, gradually decreasing it. Inlet and outlet humidity sensors monitor the humidity changes of the incoming and outgoing air. When the humidity is consistent, the suction of the soil sample and the negative pressure within the cavity are considered balanced. The suction of the soil sample can then be determined based on the magnitude of the negative pressure. This test process simulates the principle and process of the test paper method, but the surface of the soil sample is a natural cross-section, preventing damage from contact with the test paper and thus improving the accuracy of the test. In addition to being directly used for the suction test of unsaturated soil, this test system can also be used to conduct experimental research on the water gain and loss capacity and suction magnitude changes of unsaturated soil or other hygroscopic materials under different humidity and negative pressure conditions.

[0054] The gas supply device 7 includes an air pump.

[0055] This allows the gas supply device to actively supply gas, thus better controlling the air pressure inside the cavity.

[0056] The gas supply device 7 also includes an air drying module.

[0057] In this way, when the humidity of the intake air is too high (reaching or approaching saturation), the air drying module can dry the intake air, preventing excessive humidity from affecting the test results. Because this equipment extracts moisture from the soil under negative pressure, in principle, whether moisture can be extracted depends only on whether the negative pressure is balanced, and is not related to the humidity of the intake air. However, if the humidity of the intake air has reached or approached saturation, it will obviously affect the effectiveness of extracting moisture from the soil into the air. Therefore, the intake air needs to maintain a certain degree of dryness to avoid excessive humidity affecting the test results.

[0058] The gas supply device 7 also includes a temperature control component. This allows for convenient temperature adjustment when needed, preventing excessively high or low temperatures from affecting the experiment.

[0059] A pressure sensor 13 is also installed on the inner center of the sealing sleeve 2 or on the air extraction pipe. This allows for real-time monitoring of the air pressure inside the sealing sleeve. When the humidity of the incoming and outgoing air is consistent, the suction force of the soil being measured can be obtained based on the readings from the pressure sensor. This avoids pressure loss between the negative pressure generating device and the cavity, which could affect the accuracy of the test.

[0060] Among them, see Figure 2 The sealing sleeve 2 is provided with an arc-shaped air storage chamber 14 inside the air supply connector 5 and the air extraction connector 6. The back side of each of the two air storage chambers is connected to the corresponding air supply connector or air extraction connector. At least one air port 15 is provided inside the air storage chamber 14 and is connected to the inner cavity of the sealing sleeve. The air passage area of ​​the air port is larger than the air passage area of ​​the corresponding air supply connector or air extraction connector.

[0061] In this way, the transition between air intake and exhaust is achieved by relying on the air storage chamber, ensuring smoother and more stable adjustment and control of the internal air pressure, and avoiding excessive pressure concentration at the air intake and exhaust positions, which could affect the test results.

[0062] The air outlet 15 is either a strip-shaped hole extending along the extension direction of the air storage tank or multiple spaced air outlets, with the axes of the multiple air outlets parallel to each other and the axes of the air outlets perpendicular to the axes of symmetry of the two air storage tanks. This better ensures the above-mentioned effect.

[0063] The sealing sleeve 2 is made of rubber. This allows the clamp to achieve a tight seal more easily.

[0064] The ring cutter surface is also marked with the sealing sleeve installation position markings.

[0065] This allows for the creation of a small cavity between the ring cutters during the installation of the sealing sleeve, preventing the cavity from being too large and affecting the test accuracy.

[0066] Among them, each of the two ring cutters 1 has a thrust drive device 16 connected to the outward end of the end opposite to the circumferential cutter edge. The two thrust drive devices 16 are relatively fixedly connected by a mounting bracket (not shown). The stroke of the thrust drive device is greater than the depth of the ring cutter.

[0067] In this way, during the test, it is convenient to use the thrust drive device to control the insertion of the ring cutter into the soil sample, thereby achieving the cutting of the soil to be tested.

[0068] The thrust drive device 16 is a pneumatic cylinder, an electric cylinder, or a hydraulic cylinder. It features a simple structure, real-time convenience, and low cost.

[0069] When the above-mentioned unsaturated soil suction test system is used in specific tests, it may include the following steps:

[0070] Obtain an unsaturated soil sample to be tested with a length exactly twice the depth of the ring cutter. Place the unsaturated soil sample between two ring cutters and use a driving device to make the two ring cutters cut into the soil sample simultaneously until the opposite end faces of the two ring cutters fit together and the ring cutters are filled with soil sample.

[0071] The driving device drives two ring cutters to move in opposite directions, causing the soil sample filled in the ring cutters to break and form a natural cross-section at the cutter edge.

[0072] Install the sealing sleeve so that both ends of the sealing sleeve are respectively fitted onto the outside of the two ring cutters, and are tightly connected to the side wall of the ring cutter by the clamp, so that the detection gap left between the two ring cutters forms a cavity for gas flow.

[0073] Keep the gas supply connector on the seal connected to the gas supply device, and the air extraction connector connected to the negative pressure generator; turn on the gas supply device and generate gas with preset humidity and / or temperature (usually room temperature air); start the negative pressure generator so that the gas supplied by the gas supply device enters the cavity through the gas supply connector and flows out through the air extraction connector. During this process, a stable negative pressure environment is formed in the cavity under the air extraction action of the negative pressure generator.

[0074] The negative pressure in the cavity is gradually reduced from large to small. At the same time, the humidity data of the gas entering and leaving the cavity are collected. When the humidity of the gas entering and leaving the cavity is the same, the suction of the soil sample is obtained according to the magnitude of the negative pressure in the air.

Claims

1. A method for testing the suction of unsaturated soil, characterized in that, The soil to be measured is placed in a closed space with a cavity for gas flow. This cavity is connected in series to a gas system. The gas system continuously supplies and extracts gas into the cavity, creating a stable negative pressure change process. During this process, the humidity of the gas supplied to and extracted from the cavity is detected. When the humidity of the gas extracted from the cavity is the same as that of the gas supplied to the cavity, it is determined that the suction of the soil to be measured and the negative pressure in the cavity are in balance. The suction of the soil to be measured can be obtained based on the magnitude of the negative pressure in the cavity at this time. During the process of changing the negative pressure provided to the cavity, the suction force of dry test filter paper is used as the initial suction force. Then, the test filter paper is used to conduct a suction test on the semi-saturated soil. The magnitude of the suction force of the filter paper is recorded after a fixed time interval, and the curve relationship between the change of filter paper suction force and time is obtained. Based on this curve relationship, the filter paper suction force is replaced by the magnitude of the negative pressure provided to the cavity, so as to control the process of changing the negative pressure provided to the cavity over time. The volume of the soil to be measured is more than 10 times the volume of the cavity. This method employs an unsaturated soil suction testing system, which includes two opposing ring cutters. A sealing sleeve is fitted over the open ends of each ring cutter. A clamp is installed at each end of the sealing sleeve to secure the ring cutter. After the two ring cutters are sealed, a detection gap with a width less than one-tenth of the ring cutter depth is left between the open ends. An air supply connector is connected outwards from one side of the sealing sleeve corresponding to the middle of the detection gap, and this connector is connected to an air supply device via an air supply pipe. An air extraction connector is connected outwards from the other side of the sealing sleeve, and this connector is connected to a negative pressure generating device via an air extraction pipe. An inlet humidity sensor is also installed on the air supply pipe, and an outlet humidity sensor is installed on the air extraction pipe. The system also includes a controller connected to the air supply device, the negative pressure generating device, the inlet humidity sensor, and the outlet humidity sensor. The detection gap between the two ring cutters forms a cavity for gas flow.

2. The method for testing the suction of unsaturated soil as described in claim 1, characterized in that, The gas supply device includes an air pump; The gas supply device also includes an air drying module; The gas supply device also includes a temperature control component.

3. The method for testing the suction of unsaturated soil as described in claim 2, characterized in that, A pressure sensor is also installed in the middle of the inner side of the sealing sleeve or on the air extraction pipe.

4. The method for testing the suction of unsaturated soil as described in claim 2, characterized in that, The sealing sleeve is also provided with an arc-shaped air storage chamber inside the air supply connector and the air extraction connector. The back side of each of the two air storage chambers is connected to the corresponding air supply connector or air extraction connector. At least one air port is provided inside the air storage chamber and is connected to the inner cavity of the sealing sleeve. The air passage area of ​​the air port is larger than the air passage area of ​​the corresponding air supply connector or air extraction connector.

5. The method for testing the suction of unsaturated soil as described in claim 4, characterized in that, The air outlet is a strip-shaped hole extending along the extension direction of the air storage tank or multiple air outlets spaced apart, with the axes of the multiple air outlets parallel to each other and the axes of the air outlets perpendicular to the axis of symmetry of the two air storage tanks.

6. The method for testing the suction of unsaturated soil as described in claim 4, characterized in that, The sealing sleeve is made of rubber material; The surface of the ring cutter also has markings indicating the installation position of the sealing sleeve.

7. The method for testing the suction of unsaturated soil as described in claim 4, characterized in that, Two ring cutters are each connected to a thrust drive device at the end opposite to the circumferential cutter edge. The two thrust drive devices are relatively fixedly connected by a mounting bracket, and the stroke of the thrust drive device is greater than the depth of the ring cutter. The thrust drive device is a pneumatic cylinder, an electric cylinder, or a hydraulic cylinder.

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