Test device for preparing unsaturated sand based on triaxial apparatus and test method thereof
By adopting water and gas replacement technology in the three-axis device, quantitative control of the gas inside the unsaturated sand sample is achieved, which solves the problem of insufficient gas control in traditional devices and improves the repeatability and accuracy of the test.
Patent Information
- Application Number
- CN202510052788.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-05-13
AI Technical Summary
When performing triaxial tests for unsaturated sand and soil, the traditional three-axis device lacks quantitative control of the gas inside the sample, resulting in poor repeatability of the test and is difficult to directly serve as the basis for subsequent mechanical characteristic tests.
Using water and gas replacement technology, gas with a smaller pressure is injected into the sample through the gas injection device to achieve quantitative control of the gas inside the sample and ensure gas content and uniformity.
Quantitative control of gas in the sample is achieved, gas content and uniformity are improved, test repeatability and accuracy are ensured, and non-saturated sandy soil samples with different saturation can be accurately prepared.
Smart Images
Figure CN119984981A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of geotechnical engineering geotechnical testing, and in particular to a triaxial apparatus-based unsaturated sand test device and a test method thereof. Background Art
[0002] Saturated sand liquefaction caused by dynamic loads such as earthquakes and traffic often causes disasters such as deformation of overlying structures, foundation instability, and embankment settlement. Therefore, in the field of geotechnical engineering, sand liquefaction prevention and control is generally considered an important and challenging problem. In the past decade, many scholars have conducted many studies on how to effectively alleviate sand liquefaction. Among these studies, induced partial saturation (IPS) as an economical and environmentally friendly technology has won the favor of many scholars in improving the ability of soil to resist liquefaction. This technology achieves desaturation by self-generated or externally injected gas, which can usually be divided into air injection method (Okamura et al., 2011), water electrolysis method (Yegian et al., 2007) and microbial induced desaturation method (Xiao et al., 2018). Among them, the air injection method is widely used due to its simple operation, high repeatability and reliable saturation control.
[0003] When conducting triaxial tests on unsaturated sand, traditional standard triaxial devices usually face the problem of unsaturated specimen preparation, lack of quantitative control of the gas inside the specimen, and poor test repeatability. Therefore, it is not easy to directly use it as a test device to carry out subsequent mechanical properties tests.
[0004] Based on the above problems, the traditional triaxial apparatus was modified and a test device for preparing unsaturated sand was proposed, which can quantitatively control the gas in the sample. Summary of the invention
[0005] In view of the shortcomings of the background technology, the technical problem to be solved by the present invention is to provide a non-saturated sand test device based on a triaxial apparatus, which adopts water-gas replacement to quantitatively control the gas in the sample, thereby achieving better gas content and uniformity control effects.
[0006] The present invention is completed by adopting the following technical scheme: a non-saturated sand test device based on a triaxial instrument, comprising a triaxial instrument, a confining pressure system and a loading device, the triaxial instrument comprising a triaxial instrument base and a pressure chamber, a sample seat installed on the triaxial instrument base and located in the pressure chamber, a sample placed on the sample seat, and a top cover is provided on the top of the sample, the loading device is located above the top cover, the confining pressure system is connected to the pressure chamber through a confining pressure channel, the triaxial instrument base and the sample seat are both provided with mutually conducting pore pressure pipelines and multi-purpose pipelines, the pore pressure pipeline is connected to an external pore pressure sensor, a gas injection device and a back pressure system are replaceably connected to the multi-purpose pipeline, the top cover is provided with a drainage channel and a pore pressure channel, the drainage channel is connected to an external drainage container through a drainage pipe, the pore pressure channel is connected to an external pore pressure sensor, the gas injection device, the back pressure system, the loading system and the confining pressure system are all connected to a data recorder and a computer.
[0007] Furthermore, a drainage monitoring device is provided in the top cover drainage channel, and the drainage monitoring device includes a water volume sensor and a flow reading meter. The water volume sensor monitors the drainage volume in real time and displays it through the flow reading meter. The flow reading meter is connected to the computer through a data recorder.
[0008] Furthermore, a one-way drainage valve is provided at the inlet end of the drainage channel of the top cover.
[0009] Furthermore, a gas flow sensor is provided at a position of the multi-purpose pipeline close to the sample, and the gas flow sensor is connected to an external gas flow display via a wire, and the gas flow display is connected to a computer via a data recorder.
[0010] Furthermore, a solenoid valve is provided below the gas flow sensor, and the solenoid valve is electrically connected to an external computer.
[0011] Furthermore, the gas injection device includes an air compressor and an air pressure control device, the air compressor is connected to the external port of the multi-purpose pipeline through a gas delivery pipeline, and the air pressure control device is arranged on the gas delivery pipeline.
[0012] Furthermore, the loading device includes a controller and a loading rod, and the lower end of the loading rod passes through the pressure chamber and is placed corresponding to the position of the sample top cover.
[0013] Furthermore, a test method for preparing an unsaturated sand test device based on a triaxial apparatus comprises the following steps:
[0014] 1) Prepare saturated sand samples,
[0015] The wet impact method was used to prepare sand samples of specified density in layers. The valves of the confining pressure system and the back pressure system were opened, and CO2 saturation and back pressure saturation were used in turn until the pore water pressure coefficient B value was greater than 0.96.
[0016] 2) The confining pressure system and the back pressure system are controlled by a computer, the back pressure and the confining pressure are linearly reduced, and the changes in the readings of the back pressure sensor in the back pressure system and the confining pressure sensor in the confining pressure system are observed until the confining pressure and the back pressure are both 0.
[0017] 3) Install the gas injection device,
[0018] Disconnect the back pressure system, install the gas injection device on the multi-purpose pipeline through the gas delivery pipeline, connect the drainage channel of the sample top cover to the external drainage container through the drainage pipe, the external port of the multi-purpose pipeline is equipped with a base valve, and the top cover valve is provided at the drainage channel of the top cover, and the base valve and the top cover valve are in a closed state;
[0019] 4) Water-gas replacement,
[0020] Turn on the air compressor of the gas injection device and set the target pressure value to 2kPa in the air pressure controller. After the controller reading reaches the target value, open the top cap valve and the base valve. The gas will enter the sample along the gas delivery pipeline, the triaxial instrument base and the sample seat. At the same time, the water inside the saturated sample is transmitted to the drainage container through the drainage pipe. The drainage container monitors the amount of water discharged to complete the water-gas replacement.
[0021] 5) After the specified amount of water is collected in the drainage container, close the base valve and the top hat valve in sequence, and the preparation of the unsaturated sand sample is completed;
[0022] 6) The gas injection device is removed and replaced with a back pressure system, followed by consolidation and shearing steps on the sample.
[0023] Furthermore, in step 4, the gas flow sensor monitors the gas flow in real time and transmits it to the computer through the data recorder. When the gas content reaches the design requirement, the computer sends a command to the solenoid valve to close the solenoid valve to stop supplying gas to the sample, and at the same time sends a command to the air compressor and the air pressure control device to stop working.
[0024] Furthermore, in step 4, the drainage monitoring device in the drainage channel at the top of the top cover monitors the amount of water discharged from the top cover in real time.
[0025] Beneficial effects of the present invention:
[0026] 1. The sample is desaturated by injecting gas at a low pressure into the sample through the gas injection device. Then the water inside the sample is discharged from the top cover into the drainage container. The drainage container collects the water discharged from the sample during the desaturation process, and calculates the replacement gas content and corresponding saturation in the soil in real time to achieve accurate control of the saturation. The quantitative control of the gas in the sample achieves a better gas content and uniformity control effect.
[0027] 2. The multi-purpose pipeline in the sample holder is equipped with a gas flow sensor to monitor the intake volume in real time. Since the gas flow value recorded by the air compressor and the air pressure controller includes the gas volume retained in the gas delivery pipeline and the multi-purpose pipeline, there is an error in the gas content input value. Therefore, the gas flow sensor is set near the entrance of the sample. The flow value recorded by the gas flow sensor does not include the gas volume retained in the pipeline, and can accurately monitor the gas content entering the sample.
[0028] 3. A solenoid valve is also provided on the multi-purpose pipeline, which is located below the volume flow sensor and is electrically connected to an external computer. When the gas flow sensor monitors the gas injection volume, the data recorder receives the gas injection volume data in real time and transmits it to the computer. When the gas injection volume reaches the design requirements, the computer sends a closing command to the solenoid valve, air compressor and air pressure control device. The solenoid valve is closed in time to stop supplying gas to the sample, preventing the gas trapped in the multi-purpose pipeline and the gas delivery pipeline from entering the sample, thereby ensuring the accuracy of the sample intake.
[0029] 4. A drainage monitoring device is provided at the drainage channel of the top cover to monitor the drainage volume in real time and display it through a flow reading meter, which is connected to a computer through a data recorder. Because part of the discharged water is retained in the drainage pipe, the drainage volume in the drainage container cannot be accurately monitored. Therefore, the drainage water volume is accurately monitored through the drainage monitoring device to provide data support for subsequent saturation calculations. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 It is a structural schematic diagram of a test device for preparing unsaturated sand based on a triaxial apparatus;
[0031] Figure 2 is a schematic diagram of the stress-strain curve in monotonic shear response;
[0032] Figure 3 Schematic diagram of the effective stress path in monotonic shear response. DETAILED DESCRIPTION
[0033] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.
[0034] Reference Figure 1As shown, the first embodiment of the present invention provides an unsaturated sand test device based on a triaxial instrument, including a confining pressure system 1, a loading device 2 and a triaxial instrument 3. The triaxial instrument 3 includes a triaxial instrument base 31 and a pressure chamber 32, a sample seat 4 is installed on the triaxial instrument base and located in the pressure chamber 32, a sample 5 is placed on the sample seat 4, and a top cover 6 is provided on the top of the sample 5. The confining pressure system 1 is connected to the pressure chamber 32 through a confining pressure channel 11, and a confining pressure sensor is configured in the confining pressure system 1. The confining pressure system 1 provides a confining pressure load for the sample in the pressure chamber, and the confining pressure sensor monitors the confining pressure indication. The loading device 2 includes a controller 21, a loading rod 22, a displacement sensor 23 and a loading sensor 24. The controller 21 is fixed by a reaction frame, and the loading rod 22 is installed on the controller. The lower end of the loading rod 22 passes through the top of the pressure chamber and is placed above the top cover 7. The loading device 2 provides a vertical displacement load for the sample 5 for subsequent shear or consolidation tests, and the displacement sensor 23 and the loading sensor 24 monitor the displacement data and loading data of the loading rod. The loading device 2 can customize dynamic loads with different waveforms and monitor the deformation of the sample in real time through displacement sensors and loading sensors. The loading system 2 and the confining pressure system 1 are both connected to the data recorder 12 and the computer 13, and the loading device and the confining pressure system are both connected to the data recorder and the computer.
[0035] The triaxial instrument base and the sample seat are both provided with a pore pressure pipeline 7 and a multi-purpose pipeline 8 (the triaxial instrument base pore pressure pipeline and the sample seat pore pressure pipeline are connected, and the triaxial instrument base multi-purpose pipeline and the sample seat multi-purpose pipeline are connected). The gas injection device 9 and the back pressure system 10 are replaceably connected to the multi-purpose pipeline 8, and the outer port of the multi-purpose pipeline 8 is equipped with a base valve 33. The top cover 6 is provided with a drainage channel and a pore pressure channel. The drainage channel is connected to the external drainage container 15 through a drainage pipe 14, and a top cover valve 61 is provided at the outlet of the top cover drainage channel. The pore pressure pipeline 7 of the triaxial instrument base and the sample seat is connected to an external pore pressure sensor 16, and the top cover pore pressure channel is connected to another external pore pressure sensor 16, and the pore pressure indication of the sample is monitored by the pore pressure sensor. The gas injection device 9, the back pressure system 10 and the pore pressure sensor 16 are all connected to the data recorder 12 and the computer 13, and each mechanical property index is collected by the data recorder 12 and transmitted to the computer 13. Wherein, the gas injection device 9 includes an air compressor 91 and an air pressure control device 92, the air compressor 91 is connected to the outer port of the multi-purpose pipeline 8 through a gas delivery pipeline 93, and the air pressure control device 92 is arranged on the gas delivery pipeline 93. The air compressor is a gas production device, and the air pressure control device is used to control the pressure of the delivered gas. During the desaturation process of the saturated soil sample, the gas is output by the air compressor, and the gas is injected at a lower pressure through the air pressure control device to reduce the disturbance to the sample. The low-pressure gas enters the bottom of the sample through the gas delivery pipeline 93 and the multi-purpose pipeline 8, and at the same time, the moisture inside the sample is transmitted to the drainage container 15 through the drainage channel of the top cover 6. The moisture discharged from the sample during the desaturation process is collected by the drainage container 15.
[0036] A gas flow sensor 17 is provided near the sample in the multi-purpose pipeline (the gas flow sensor is provided inside the sample holder), and the gas flow sensor 17 is connected to an external gas flow display 18 through a wire, and the gas flow display 18 is connected to a computer 13 through a data recorder 12, and the gas flow display displays the gas injection amount value, and transmits it to the computer 13 through the data recorder 12, and the computer updates the gas injection amount data in real time. Because the gas flow value recorded by the air compressor and the air pressure controller includes the amount of gas retained in the gas delivery pipeline and the multi-purpose pipeline, there is an error in the gas content input value. Therefore, the gas flow sensor 17 monitors the intake volume in real time, and the gas flow sensor 17 is provided at the entrance close to the sample, where the flow value recorded by the gas flow sensor 17 does not include the amount of gas retained in the pipeline, and can accurately monitor the gas content entering the sample, ensuring the accuracy of the gas injection amount counting.
[0037] There is a solenoid valve 19 below the gas flow sensor, and the solenoid valve 19 is electrically connected to an external computer. When the computer monitors that the gas injection volume reaches the design requirements, the computer 13 sends a closing command to the solenoid valve 19, the air compressor 91 and the air pressure control device 92. The air compressor 91, the air pressure control device 92 and the solenoid valve 19 are closed in time to stop supplying gas to the sample. If only the air compressor 91 and the air pressure control device 92 are closed, the gas trapped in the gas delivery pipeline 93 and the multi-purpose pipeline 8 will continue to enter the sample, and it is impossible to accurately prepare unsaturated sand with a saturation that meets the design requirements. Therefore, by closing the solenoid valve of the multi-purpose pipeline in the sample holder, it is possible to effectively prevent the gas trapped in the multi-purpose pipeline and the gas delivery pipeline from entering the sample, thereby ensuring the accuracy of the sample intake.
[0038] A drainage monitoring device 20 is provided in the drainage channel 62 of the top cover. A one-way drainage valve 63 is provided at the inlet end of the drainage channel 62 of the top cover (i.e., a one-way drainage valve is provided at the port of the drainage channel close to the sample). The drainage monitoring device 20 is provided at the water outlet end of the one-way drainage valve 63. The drainage monitoring device 20 includes a water volume sensor 201 and a flow reading meter 202. The water volume sensor is placed at the drainage channel. The flow reading meter is provided outside the top cover. The flow reading meter is electrically connected to the water volume sensor. The flow reading meter 202 is connected to the computer 13 through the data recorder 12. The water volume sensor 201 monitors the drainage volume in real time and displays it through the flow reading meter 202. At the same time, the drainage volume data is transmitted to the computer through the data recorder 12. Because part of the discharged water is retained in the drainage pipe and the drainage channel 62, the drainage in the drainage container cannot accurately monitor the drainage volume. Therefore, the drainage water volume is accurately monitored by the drainage monitoring device, and data support is provided for subsequent saturation calculation. At the same time, a one-way drain valve is provided in the drainage channel to prevent the water retained in the drainage pipe and the drainage channel from flowing back into the sample, thereby ensuring the accuracy of the sample's saturation.
[0039] The saturation calculation is carried out by injecting the numerical value of the gas content of the sample, and further verified by the amount of water discharged from the top of the sample. The replacement gas content and the corresponding saturation in the soil are calculated in real time to achieve precise control of the saturation. The quantitative control of the gas in the sample achieves a better control effect of gas content and uniformity, and realizes the preparation of unsaturated sand samples with different saturations (Sr>90%).
[0040] In order to prepare sand samples with different saturation, the air content in the sand needs to be calculated according to the saturation. a The reference calculation formula is as follows:
[0041]
[0042] Where V0 represents the total volume of the triaxial specimen; e represents the initial porosity of the specimen; S rRepresents the design saturation of the unsaturated sample. According to the saturation required by the design, the gas content of the sand sample with this saturation is calculated. Based on the equal relationship between the top cover drainage and the injected gas content during the gas injection process (i.e., the amount of water discharged from the top of the sample is equal to the gas content injected into the sample), the drainage container is monitored in real time according to the gas content result obtained by the calculation result until the drainage reaches the specified amount.
[0043] The above-mentioned test method for preparing an unsaturated sand test device based on a triaxial apparatus comprises the following steps:
[0044] 1) Prepare saturated sand samples,
[0045] Use the wet impact method to prepare sand samples of specified density in layers, install the back pressure system 10 and the confining pressure system 1, connect the back pressure system 11 to the multi-purpose pipeline 8, and connect the confining pressure system 1 to the confining pressure channel. Open the valves of the confining pressure system and the back pressure system, and use CO2 saturation and back pressure saturation (back pressure 200kPa, confining pressure 220kPa) in turn until the pore water pressure coefficient B value is greater than 0.96;
[0046] 2) The computer 13 controls the confining pressure system 1 and the back pressure system 10, linearly reduces the back pressure and the confining pressure, and observes the changes in the readings of the back pressure sensor in the back pressure system 10 and the confining pressure sensor in the confining pressure system 1 until the confining pressure and the back pressure are both 0.
[0047] 3) Install the gas injection device 9,
[0048] The back pressure system is removed from the multi-purpose pipeline, and the gas injection device 9 is installed on the outer port of the multi-purpose pipeline 8 through the gas delivery pipeline 93. The drainage channel of the sample top cover 6 is connected to the external drainage container 15 through the drainage pipe 14, and the base valve 33 and the top cover valve 61 are both in the closed state;
[0049] 4) Water-gas replacement,
[0050] Turn on the air compressor 91 of the gas injection device, and set the target pressure value to 2kPa in the air pressure controller 92. This pressure value can effectively inject gas into the sample, avoid gas accumulation at the end of the sample, and effectively reduce the disturbance of the injected gas to the sample. After the controller 92 reaches the target value, open the top hat valve 61 and the base valve 33, and the gas will enter the sample along the gas delivery pipeline 93, the triaxial instrument base 31 and the sample holder 4. At the same time, the water inside the saturated sample is transmitted from the drain pipe 14 to the drain container 15. The drain container 15 monitors the amount of water discharged to complete the water-gas replacement;
[0051] Among them, the gas flow sensor configured in the multi-purpose pipeline of the sample holder monitors the gas flow in real time and transmits it to the computer through the data recorder. When the gas content reaches the design requirement, the computer sends a command to the solenoid valve to close the solenoid valve to stop supplying gas to the sample, and sends a command to the air compressor and air pressure control device to stop working. The drainage monitoring device between the drainage channel on the top cover and the drainage pipe monitors the amount of water discharged from the top cover in real time.
[0052] 5) After a specified amount of water is collected in the drainage container 15, the base valve 33 and the top hat valve 61 are closed in sequence, and the preparation of the unsaturated sand sample is completed.
[0053] 6) The gas delivery pipeline 93 and the gas injection device 9 are removed and replaced with a back pressure system, and then the sample is subjected to consolidation and shearing steps.
[0054] Reference Figure 2-3 As shown in the figure, in order to further verify the effectiveness of the device for controlling the gas content in the soil, a series of undrained monotonic shear comparison tests of saturated sand and unsaturated sand were carried out. The stress-strain curves and effective stress paths of saturated sand and unsaturated sand under the initial effective confining pressure p0'=200, 400, 600 kPa are shown. Figure 2 As shown in Figure 2, all samples exhibit strain hardening behavior. When the axial strain εa is greater than 25%, the development of the deviatoric stress tends to be stable, and it can be considered that the sample reaches a critical state at this time. Figure 3 As shown in the figure, the saturated specimen initially exhibits shear contraction, and then develops dilatation behavior as loading progresses, especially under high confining pressure (p0' = 600 kPa). However, the decrease in saturation will cause the specimen to change from a shear contraction state to a dilatation state, and eventually tend to a critical state.
[0055] pass Figure 2 and Figure 3 It can be seen from the medium stress-strain curve and the effective stress path that the air content of the prepared soil sample is highly accurate. This device can accurately prepare unsaturated sand samples that meet the design requirements.
[0056] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.
Claims
1. A test device for preparing unsaturated sand based on a triaxial instrument, comprising a triaxial instrument, a confining pressure system and a loading device, wherein the triaxial instrument comprises a triaxial instrument base and a pressure chamber, a sample seat is mounted on the triaxial instrument base and is located in the pressure chamber, a sample is placed on the sample seat, and a top cover is provided on the top of the sample, the loading device is located above the top cover, and the confining pressure system is connected to the pressure chamber through a confining pressure channel, wherein the loading device is located above the top cover, and the confining pressure system is connected to the pressure chamber through a confining pressure channel, wherein the loading device is characterized in that: The triaxial instrument base and the sample seat are both provided with pore pressure pipelines and multi-purpose pipelines, the pore pressure pipelines are connected to the external pore pressure sensor, the gas injection device and the back pressure system are replaceably connected to the multi-purpose pipeline, the top cover is provided with a drainage channel and a pore pressure channel, the drainage channel is connected to the external drainage container through a drainage pipe, the pore pressure channel is connected to the external pore pressure sensor, the gas injection device, the back pressure system, the loading system and the confining pressure system are all connected to the data recorder and the computer.
2. According to claim 1, a triaxial test apparatus for preparing unsaturated sand soil is characterized by: A drainage monitoring device is provided in the drainage channel of the top cover, and the drainage monitoring device includes a water volume sensor and a flow reading meter. The water volume sensor monitors the drainage volume in real time and displays it through the flow reading meter. The flow reading meter is connected to a computer through a data recorder.
3. The unsaturated sand test device based on a triaxial apparatus according to claim 2 is characterized in that: A one-way drainage valve is provided at the inlet end of the drainage channel of the top cover.
4. A triaxial test apparatus for preparing unsaturated sand soil according to claim 1, 2 or 3, characterized in that: A gas flow sensor is arranged at a position of the multi-purpose pipeline close to the sample. The gas flow sensor is connected to an external gas flow display through a wire, and the gas flow display is connected to a computer through a data recorder.
5. The unsaturated sand test device based on a triaxial apparatus according to claim 4 is characterized in that: A solenoid valve is provided below the gas flow sensor, and the solenoid valve is electrically connected to an external computer.
6. A triaxial test apparatus for preparing unsaturated sand soil according to claim 1, 2, 3 or 5, characterized in that: The gas injection device comprises an air compressor and an air pressure control device. The air compressor is connected to the outer port of the multi-purpose pipeline through a gas delivery pipeline, and the air pressure control device is arranged on the gas delivery pipeline.
7. The unsaturated sand test device based on a triaxial apparatus according to claim 6 is characterized by: The loading device comprises a controller and a loading rod, the lower end of which passes through the pressure chamber and is placed corresponding to the position of the sample top cover.
8. A test method for preparing an unsaturated sand test device based on a triaxial apparatus according to claim 1, characterized in that: Includes the following step, 1) Prepare saturated sand samples, The wet impact method was used to prepare sand samples of specified density in layers. The valves of the confining pressure system and the back pressure system were opened, and CO2 saturation and back pressure saturation were used in turn until the pore water pressure coefficient B value was greater than 0.
96. 2) Computer controls the confining pressure system and the back pressure system, linearly reduces the back pressure and the confining pressure, and observes the changes in the readings of the back pressure sensor in the back pressure system and the confining pressure sensor in the confining pressure system until the confining pressure and the back pressure are both 0; 3) Install the gas injection device, Disconnect the back pressure system, install the gas injection device on the multi-purpose pipeline through the gas delivery pipeline, connect the drainage channel of the sample top cover to the external drainage container through the drainage pipe, the external port of the multi-purpose pipeline is equipped with a base valve, and the top cover valve is provided at the drainage channel of the top cover, and the base valve and the top cover valve are in a closed state; 4) Water-gas replacement, Turn on the air compressor of the gas injection device and set the target pressure value to 2kPa in the air pressure controller. After the controller reading reaches the target value, open the top cap valve and the base valve. The gas will enter the sample along the gas delivery pipeline, the triaxial instrument base and the sample seat. At the same time, the water inside the saturated sample is transmitted to the drainage container through the drainage pipe. The drainage container monitors the amount of water discharged to complete the water-gas replacement. 5) After the specified amount of water is collected in the drainage container, close the base valve and the top hat valve in sequence, and the preparation of the unsaturated sand sample is completed; 6) The gas injection device is removed and replaced with a back pressure system, followed by consolidation and shearing steps on the sample.
9. The test method for preparing an unsaturated sand test device based on a triaxial apparatus according to claim 8 is characterized by: In step 4, the gas flow sensor monitors the gas flow in real time and transmits it to the computer through the data recorder. When the gas content reaches the design requirement, the computer sends a command to the solenoid valve to close the solenoid valve to stop supplying gas to the sample, and at the same time sends a command to the air compressor and air pressure control device to stop working.
10. The test method for preparing an unsaturated sand test device based on a triaxial apparatus according to claim 9, characterized in that: In step 4, the drainage monitoring device in the drainage channel at the top of the top cover monitors the amount of water discharged from the top cover in real time.