Test and observation system and test method for deformation characteristics of soil in vacuum preloading with adjustable confining pressure

Abstract

The present invention discloses a test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure, including a soil vacuum consolidation system, a vacuum drive system, a confining pressure system and a monitoring system; the soil vacuum consolidation system includes: a model box for filling test soil; the confining pressure system is arranged in the model box, and slide plates are arranged on both sides of the model box, and the two slide plates respectively form expansion control cavities at both ends of the model box, wherein accordion airbags are arranged, and the accordion airbags are connected to an external air pump and an air pressure control device through a pipeline; the test soil in the model box is covered with a geotextile, and the geotextile is covered with a vacuum film; the vacuum drive system includes: a vacuum water vapor separation box for collecting water and gas discharged from the model box, a vacuum jet pump for providing negative pressure, and a vacuum pressure control device for adjusting the vacuum load in the test system. The above test and observation system can test and observe the deformation characteristics of the soil in vacuum preloading more accurately.

Description

Technical Field

[0001] The present invention relates to a test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure. The present invention also relates to a test method using the test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure. Background Art

[0002] The vacuum preloading drainage consolidation method is currently a commonly used method for soft soil foundation treatment. This method is widely used in soft soil foundation treatment in various projects such as sea reclamation, airports, and roads. However, there are still few cases of using vacuum preloading and prefabricated drainage boards to improve high-water-content blown-fill sludge (fluid soil), and its consolidation behavior mechanism is still unclear. In addition, during the vacuum preloading process of high-water-content blown-fill sludge, the soil around the drainage board will form a dense "soil column" with high strength and low permeability, which hinders the vacuum preloading. In order to solve the problem of soil column clogging, many scholars have conducted theoretical analysis on the causes of clogging based on specific assumptions, and some scholars have studied different types of drainage boards to solve the clogging problem. However, at this stage, there is still a lack of direct observation on the exact cause of soil column formation in vacuum preloading. In order to further study the formation mechanism of soil columns and the deformation law of soil, it is very necessary to conduct an intuitive visualization study on the formation of soil columns. In response to this problem, the applicant applied for an invention patent entitled "Test system and test method for observing soil particle movement during vacuum preloading" on March 17, 2020, with announcement number "CN111537415A".

[0003] The confining pressure and groundwater in the underground environment cause the test model to simulate the actual conditions inaccurately, which in turn leads to insufficient accuracy of the test data. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a test and observation system for the deformation characteristics of soil in vacuum preloading with adjustable confining pressure, which can more accurately simulate the real soil state to more accurately and visually display the reasons for the formation of soil columns in vacuum preloading.

[0005] To this end, the present invention provides a test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure, including a soil vacuum consolidation system, a vacuum drive system, a confining pressure system and a monitoring system;

[0006] The soil vacuum consolidation system comprises: a model box for filling the test soil, the model box is a rectangular box with an open top; an observation window is provided on the front side wall of the model box for observing the movement of clay; the observation window is covered with a glass plate of a size adapted to the observation window, and the glass plate is provided with marking points for calibrating the test results; a first sensor wire hole and a second sensor wire hole are provided on the rear side wall of the model box; a vacuum pipeline interface is provided on the left side wall of the model box; a bracket for fixing a plastic drain board is provided in the model box, and the plastic drain board is vertically fixed in the test soil by the bracket; the top end of the plastic drain board is connected to a hand-shaped joint, and the top end of the hand-shaped joint is connected to a horizontal connecting pipe, and the horizontal connecting pipe passes through the vacuum pipeline interface and is connected to the vacuum pipeline;

[0007] The confining pressure system is arranged in the model box, and slide plates are arranged on both sides of the model box, and pulleys are arranged at the matching places between the upper and lower ends of the slide plates and the model box frame, and slide rails are arranged at corresponding positions on the model box frame, and the slide plates and the inner side are covered and fixed with elastic sealing cloth, and the edges around the elastic sealing cloth are pressed against the side wall of the model box by pressure strips to form a liquid seal, and the slide plates on both sides respectively form expansion control chambers at the two side ends of the model box, and a foldable accordion airbag is arranged in the expansion control chamber, and the two side end faces of the accordion airbag are respectively attached and fixed to the inner side wall of the model box and the side wall of the slide plate, and the accordion airbag is connected to an external air pump and an airbag pressure control device through a pipeline;

[0008] Preferably, the test and observation system includes a groundwater simulation system, which includes a honeycomb water storage body arranged at the bottom, the honeycomb water storage body is connected to a vertically distributed transparent water storage barrel through a pipe, the transparent water storage barrel has a height scale, the upper end of the honeycomb water storage body is covered with wire mesh, and the soil body is arranged above the wire mesh.

[0009] Preferably, the model box has a bottom frame plate inside, the lower slide rail is arranged on the bottom frame plate, the placement groove is formed below the bottom frame plate, and the honeycomb water storage body is arranged in the placement groove.

[0010] Preferably, a rectangular first sealing frame is provided outwardly from the top edge of the model box, and a second sealing frame is connected to the upper surface of the first sealing frame by bolts; the test soil is covered with a geotextile, and the geotextile is covered with a vacuum membrane, the outer edge of the vacuum membrane is sandwiched between the first sealing frame and the second sealing frame, and a sealing gasket is provided between the vacuum membrane and the second sealing frame;

[0011] The vacuum drive system comprises: a vacuum water vapor separation box for collecting water and gas discharged from the model box, a vacuum jet pump for providing negative pressure, and a vacuum pressure control device for adjusting the vacuum load in the test system; a first connection port, a second connection port and a third connection port are provided on the top of the vacuum water vapor separation box, the first connection port is connected to the model box through a vacuum pipeline, the second connection port is connected to the vacuum pressure control device, and the third connection port is connected to the vacuum jet pump; a drain port is provided on the lower side wall of the vacuum water vapor separation box, the drain port is externally connected to a drain pipe, and a drain valve is provided on the drain pipe;

[0012] The monitoring system comprises: a pore water pressure sensor for monitoring the change of pore water pressure value in the soil during vacuum preloading, a vacuum gauge probe for measuring the vacuum degree of the soil at the bottom of the model box, an LVDT displacement sensor for collecting surface settlement data of the test soil, tracer particles for calculating the displacement field of the soil, and a high-definition camera for shooting and recording during the experiment; a sensor fixing bracket is provided at the top of the model box, and the LVDT displacement sensor is fixed on the sensor fixing bracket; a camera bracket is provided on the outer side of the observation window, and the high-definition camera is fixed on the camera bracket; a first sensor wire hole is inserted from the outside into the pore water pressure sensor, and the pore water pressure sensor is buried in the test soil; a second sensor wire hole is inserted from the outside into the vacuum gauge probe, and the vacuum gauge probe is buried in the test soil; the high-definition camera has a camera fixing aluminum rail for fixing the camera position, and LED lamps are installed around the model box to enhance the brightness of the photo, which is convenient for subsequent calculations.

[0013] Preferably, the glass plate of the observation window is made of organic aviation glass.

[0014] Preferably, the model box is made of aluminum plate, the guide rail is made of aluminum plate, the first sensor wire holes are staggered and closely spaced, and sealing plugs are provided in the first sensor wire holes and the second sensor wire holes.

[0015] The present invention also provides a test method for a test and observation system of soil deformation characteristics in vacuum preloading with the adjustable confining pressure, comprising the following steps:

[0016] Step 1: Model preparation:

[0017] First, determine the mass of soil sample required for the model box and configure the test soil sample; fix the plastic drainage board at the set position through the bracket, install the vacuum pipeline, pore water pressure sensor and vacuum gauge probe, spray the tracer particles on the inside of the observation window, add the configured test soil sample into the model box, cover the geotextile and vacuum membrane, and seal the model box; connect the model box in the soil vacuum consolidation system with the vacuum drive system through the vacuum pipeline to ensure the sealing of the entire test system;

[0018] Step 2: System debugging

[0019] Turn on the data monitoring system, set and adjust the data of the pore water pressure sensor and LVDT displacement sensor, turn on the vacuum pressure control device, observe the vacuum gauge and the readings of each sensor, and adjust the zero to ensure that the data correspond correctly. Install a high-definition camera on the camera fixing bracket, adjust the field of view, aperture and focal length, so that the tracer particles are clearly imaged in the field of view;

[0020] Step 3: Confining pressure setting:

[0021] Start the air pump and the air pressure control device to pressurize the accordion airbag until the set pressure value is reached, and the soil confining pressure is set by setting the pressure value;

[0022] Step 4: Vacuum pre-pressure extraction:

[0023] Starting the vacuum drive system to perform vacuum pre-pressure extraction;

[0024] Step 5: Test image analysis:

[0025] During the test, a high-definition camera was used to record photos of the soil and tracer particle particles within the field of view during the vacuum preloading process, and the photos were transmitted to a computer for processing through a data acquisition system. First, the control point center of the calibration point used to convert the image and spatial coordinates was calculated. Secondly, the analysis area was determined and divided into multiple grids. Then, the correlation coefficient was used to calculate the pixel coordinates of each grid in each frame of the image. The output data was filtered and analyzed using the correlation coefficient, and the erroneous output data was manually deleted. Finally, the pixel coordinates were converted into spatial coordinates to obtain the deformation information of the soil.

[0026] Preferably, in step 1, while preparing the model, the confining pressure of the soil at the sampling location is measured.

[0027] Technical effects of the present invention:

[0028] (1) The test image measurement method of the present invention has high accuracy and can measure soil movement information within a specified area. It also has high data resolution and can perform continuous measurement for a long time.

[0029] (2) The experimental arrangement of the model of the present invention is similar to the on-site construction conditions, which can better simulate the vacuum consolidation of the on-site soil and measure the soil movement during this process. The experimental data has practical research significance;

[0030] (3) The pore water pressure sensors of the model of the present invention are closely arranged and can be used in conjunction with PIV data to obtain real-time information of the soil column.

[0031] (4) The model of the present invention can fix the placement of the high-definition camera and reduce the subsequent calculation errors caused by the unstable camera.

[0032] (5) The model of the present invention can ensure good sealing during the test process. By cooperating with the pore water pressure sensor, displacement meter, vacuum meter, and PTV measurement system, it can record and measure the movement information of soil particles, the vertical displacement of the soil surface, the changes in pore water pressure and vacuum degree in the soil during the vacuum preloading process, monitor the test process in real time, and simulate the on-site construction of vacuum preloading to propose better engineering practice plans.

[0033] (6) The accordion airbag is punched by connecting the air pump and the air pressure control device until the set pressure value is reached. The soil confining pressure is set by setting the pressure value. In particular, the slide plate with elastic sealing cloth can ensure waterproof sealing and create a specific underground soil environment. It can also set the confining pressure by pressurizing the accordion airbag. The two ends of the accordion airbag are attached to the slide plate and the inner wall of the model box, which can more accurately and effectively apply pressure to the slide plate, thereby applying pressure to both sides of the soil. After the two sides of the soil are compressed, the confining pressure can be set under the conduction of force.

[0034] (7) By setting up a honeycomb water storage body under the soil, the environment of groundwater infiltration can be simulated. The honeycomb water storage body infiltrates water into the soil, and the transparent water storage bucket connected to the honeycomb water storage body adjusts the water head and then adjusts the water pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 An overall schematic diagram of the test and observation system for the deformation characteristics of soil in vacuum preloading with adjustable confining pressure provided in Example 1 of the invention.

[0036] Figure 2 for Figure 1 Schematic diagram of the top view of the model box in .

[0037] Figure 3 for Figure 1 Schematic diagram of the rear view of the model box in .

[0038] Figure 4 for Figure 1 Schematic side view of the model box in .

[0039] Figure 5 for Figure 1 Schematic diagram of the structure of the model box with the camera fixed on the single-side frame rod after the aluminum rail is installed.

[0040] Figure 6 Schematic diagram of the structure for installing the camera fixing aluminum rail on a single-side frame pole.

[0041] Figure 7This is a schematic diagram of the structure after the camera is fixed with aluminum rails on both sides of the frame rods.

[0042] Figure 8 for Figure 6 Schematic diagram of the structure of the frame rod of the model box, the frame rod has LED light tubes.

[0043] Fig. 9 for Figure 1 Schematic diagram of the structural cross-section of the model box.

[0044] Fig.10 This is a schematic cross-sectional view of the structure of the model box provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The same parts are represented by the same reference numerals. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "bottom surface" and "top surface", "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0046] Reference Figure 1-9 As shown, the test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure provided by the present invention includes a soil vacuum consolidation system, a vacuum drive system, a confining pressure system and a monitoring system;

[0047] The soil vacuum consolidation system comprises: a model box 1 for filling the test soil, the model box 1 is a rectangular box with an open top; an observation window 2 is provided on the front side wall of the model box 1 for observing the movement of clay; the observation window 2 is covered with a glass plate 3 of a size adapted to the observation window 2, and the glass plate 3 is provided with a marking point 4 for calibrating the test results; a first sensor wire hole 5 and a second sensor wire hole 6 are provided on the rear side wall of the model box 1; a vacuum pipeline interface 7 is provided on the left side wall of the model box 1; a bracket 9 for fixing a plastic drain board 8 is provided in the model box 1, and the plastic drain board 8 is vertically fixed in the test soil by the bracket 9; the top end of the plastic drain board 8 is connected to a hand-shaped joint 10, and the top end of the hand-shaped joint 10 is connected to a transverse connecting pipe 11, and the transverse connecting pipe 11 passes through the vacuum pipeline interface 7 and is connected to the vacuum pipeline 12;

[0048] The confining pressure system is arranged in the model box 1, and slide plates 13 are arranged on both sides of the model box 1. Pulleys 14 are arranged at the matching positions of the upper and lower ends of the slide plates 13 and the model box frame, and slide rails 15 are arranged at corresponding positions on the model box frame. The slide plates 13 and the inner side are covered and fixed with an elastic sealing cloth 16, and the edges around the elastic sealing cloth 16 are pressed against the side wall of the model box 1 by pressure strips to form a liquid seal. The slide plates 13 on both sides are respectively separated at the two side ends of the model box to form an expansion control chamber 17, and a foldable accordion airbag 18 is arranged in the expansion control chamber 17. The two side end surfaces of the accordion airbag 18 are respectively attached and fixed on the inner wall of the model box 1 and the side wall of the slide plate 13. The accordion airbag 18 is connected to an external air pump and an airbag air pressure control device through a pipeline. The air pressure control device usually includes an air pump and a control air pressure stabilization mechanism.

[0049] A rectangular first sealing frame 20 is provided outwardly from the top edge of the model box 1, and a second sealing frame 21 is connected to the upper surface of the first sealing frame 20 by bolts; the test soil is covered with a geotextile, and the geotextile is covered with a vacuum membrane 22, and the outer edge of the vacuum membrane 22 is sandwiched between the first sealing frame 20 and the second sealing frame 21, and a sealing gasket 23 is provided between the vacuum membrane 22 and the second sealing frame 21;

[0050] The vacuum drive system comprises: a vacuum water vapor separation box 24 for collecting water and gas discharged from the model box 1, a vacuum jet pump 25 for providing negative pressure, and a vacuum pressure control device 26 for adjusting the vacuum load in the test system; a first connection port 27, a second connection port 28 and a third connection port 29 are provided on the top of the vacuum water vapor separation box 24, the first connection port 27 is connected to the model box 1 through a vacuum pipeline, the second connection port 28 is connected to the vacuum pressure control device 26, and the third connection port 29 is connected to the vacuum jet pump 25; a drain port 30 is provided on the lower side wall of the vacuum water vapor separation box 24, the drain port 30 is externally connected to a drain pipe, and a drain valve 31 is provided on the drain pipe;

[0051] The monitoring system comprises: a pore water pressure sensor 32 for monitoring the change of pore water pressure value in the soil during vacuum preloading, a vacuum gauge probe for measuring the vacuum degree of the soil at the bottom of the model box 1, an LVDT displacement sensor 34 for collecting surface settlement data of the test soil, tracer particles for calculating the displacement field of the soil, and a high-definition camera 39 for shooting and recording during the experiment; a sensor fixing bracket 36 is provided at the top of the model box 1, and the LVDT displacement sensor 34 is fixed on the sensor fixing bracket 36; a camera bracket 38 is provided on the outside of the observation window 2, and the glass plate 3 of the observation window 2 is made of organic aviation glass, and the high-definition camera 39 is fixed on the camera bracket; the first sensor wire hole 5 is inserted from the outside into the pore water pressure sensor 32, and the pore water pressure sensor 32 is buried in the test soil; the second sensor wire hole 6 is inserted from the outside into the vacuum gauge probe, and the vacuum gauge probe is buried in the test soil; the high-definition camera 39 is equipped with a camera fixing aluminum rail 48 for fixing the camera position, and an LED lamp tube 42 is installed around the model box 1 to enhance the brightness of the photo, which is convenient for subsequent calculations. The model box 1 is made of aluminum plate, the guide rail is made of aluminum plate, the first sensor wire holes 5 are staggered and closely spaced, and sealing plugs are provided in the first sensor wire holes 5 and the second sensor wire holes 6.

[0052] Reference Figure 1-9 As shown, the present invention provides a test method for a test and observation system of soil deformation characteristics in vacuum preloading with the above-mentioned adjustable confining pressure, comprising the following steps:

[0053] Step 1: Model preparation:

[0054] First, determine the mass of soil sample required for the model box 1 and configure the test soil sample; fix the plastic drainage board 8 at the set position through the bracket, install the vacuum pipeline, pore water pressure sensor 32 and vacuum gauge probe, spray the tracer particles on the inside of the observation window 2, add the configured test soil sample into the model box 1, cover the geotextile and vacuum membrane 22, and seal the model box 1; connect the model box 1 in the soil vacuum consolidation system with the vacuum drive system through the vacuum pipeline to ensure the sealing of the entire test system;

[0055] While preparing the model in step 1, measure the confining pressure of the soil at the sampling location.

[0056] Step 2: System debugging

[0057] Start the data monitoring system, set and adjust the data of the pore water pressure sensor 32 and the LVDT displacement sensor 34, start the vacuum pressure control device 26, observe the vacuum gauge and the readings of each sensor, and perform zeroing to ensure that the data correspond correctly. Install a high-definition camera 39 on the camera fixing bracket, adjust the field of view of the shooting, adjust the aperture and focal length, so that the tracer particles are clearly imaged in the field of view;

[0058] Step 3: Confining pressure setting:

[0059] Start the air pump and the air pressure control device to pressurize the accordion airbag 18 until the set pressure value is reached, and the soil confining pressure is set by setting the pressure value;

[0060] Step 4: Vacuum pre-pressure extraction:

[0061] Starting the vacuum drive system to perform vacuum pre-pressure extraction;

[0062] Step 5: Test image analysis:

[0063] During the test, the high-definition camera 39 recorded the photos of the soil and tracer particles in the field of view during the vacuum preloading process, and transmitted them to the computer for processing through the data acquisition system; first, the control point center of the calibration point used to convert the image and the spatial coordinates was calculated, and then the analysis area was determined and divided into multiple grids. Then, the correlation coefficient was used to calculate the pixel coordinates of each grid in each frame of the image, and the output data was filtered and analyzed using the correlation coefficient. The erroneous output data was manually deleted, and finally the pixel coordinates were converted into spatial coordinates to obtain the deformation information of the soil.

[0064] Reference Fig.10 As shown, Embodiment 2 of the present invention is basically the same as Embodiment 1, and the only difference is that: the test and observation system includes a groundwater simulation system, and the groundwater simulation system includes a honeycomb water storage body 43 arranged at the bottom, and the honeycomb water storage body 43 is connected to a vertically distributed transparent water storage barrel 44 through a pipeline, and the transparent water storage barrel 44 has a height scale, and the upper end of the honeycomb water storage body 43 is covered with a wire mesh 45, and the soil body is arranged above the wire mesh 45. The model box 1 has a bottom frame plate 46 inside, and the lower slide rail 15 is arranged on the bottom frame plate 46. A placement groove 47 is formed below the bottom frame plate 46, and the honeycomb water storage body 43 is arranged in the placement groove 47. The honeycomb water storage body 47 can simulate groundwater, and the transparent water storage barrel 44 connected to the honeycomb water storage body 43 adjusts the water head, and then adjusts the water pressure, so as to improve the accuracy of the test.

[0065] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure, comprising a soil vacuum consolidation system, a vacuum drive system, a confining pressure system and a monitoring system; The soil vacuum consolidation system comprises: A model box used to fill the test soil, the model box is a rectangular box with an open top; An observation window is provided on the front side wall of the model box for observing the movement of the clay; the observation window is covered with a glass plate of a size suitable for the observation window, and the glass plate is provided with marking points for calibrating the test results; a first sensor wire hole and a second sensor wire hole are provided on the rear side wall of the model box; a vacuum pipeline interface is provided on the left side wall of the model box; a bracket for fixing a plastic drain board is provided in the model box, and the plastic drain board is vertically fixed in the test soil by the bracket; the top of the plastic drain board is connected to a hand-shaped joint, and the top of the hand-shaped joint is connected to a horizontal connecting pipe, and the horizontal connecting pipe passes through the vacuum pipeline interface and is connected to the vacuum pipeline; The confining pressure system is arranged in the model box, and slide plates are arranged on both sides of the model box, and pulleys are arranged at the matching positions of the upper and lower ends of the slide plates and the model box frame, and slide rails are arranged at corresponding positions on the model box frame, and the inner side of the slide plates is covered and fixed with an elastic sealing cloth, and the edges around the elastic sealing cloth are pressed against the side wall of the model box by pressure strips to form a liquid seal, and the slide plates on both sides respectively form expansion control cavities at the two side ends of the model box, and a foldable accordion airbag is arranged in the expansion control cavity, and the two side end surfaces of the accordion airbag are respectively attached and fixed to the inner side wall of the model box and the side wall of the slide plate, and the accordion airbag is connected to an external air pump and an airbag pressure control device through a pipeline; The test and observation system includes a groundwater simulation system, which includes a honeycomb water storage body arranged at the bottom, the honeycomb water storage body is connected to a vertically distributed transparent water storage barrel through a pipeline, the transparent water storage barrel has a height scale, the upper end of the honeycomb water storage body is covered with a wire mesh, and the soil body is arranged above the wire mesh; the model box has a bottom frame plate inside, the lower slide rail is arranged on the bottom frame plate, and an installation groove is formed below the bottom frame plate, and the honeycomb water storage body is arranged in the installation groove.

2. The test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure according to claim 1 is characterized in that: A rectangular first sealing frame is provided outwardly from the top edge of the model box, and a second sealing frame is connected to the upper surface of the first sealing frame by bolts; the test soil is covered with a geotextile, and the geotextile is covered with a vacuum membrane, the outer edge of the vacuum membrane is sandwiched between the first sealing frame and the second sealing frame, and a sealing gasket is provided between the vacuum membrane and the second sealing frame; The vacuum drive system comprises: a vacuum water vapor separation box for collecting water and gas discharged from the model box, a vacuum jet pump for providing negative pressure, and a vacuum pressure control device for adjusting the vacuum load in the test system; a first connection port, a second connection port and a third connection port are provided on the top of the vacuum water vapor separation box, the first connection port is connected to the model box through a vacuum pipeline, the second connection port is connected to the vacuum pressure control device, and the third connection port is connected to the vacuum jet pump; a drain port is provided on the lower side wall of the vacuum water vapor separation box, the drain port is externally connected to a drain pipe, and a drain valve is provided on the drain pipe; The monitoring system comprises: a pore water pressure sensor for monitoring the change of pore water pressure value in the soil during vacuum preloading, a vacuum gauge probe for measuring the vacuum degree of the soil at the bottom of the model box, an LVDT displacement sensor for collecting surface settlement data of the test soil, tracer particles for calculating the displacement field of the soil, and a high-definition camera for shooting and recording during the experiment; a sensor fixing bracket is provided at the top of the model box, and the LVDT displacement sensor is fixed on the sensor fixing bracket; a camera bracket is provided on the outer side of the observation window, and the high-definition camera is fixed on the camera bracket; a first sensor wire hole is inserted from the outside into the pore water pressure sensor, and the pore water pressure sensor is buried in the test soil; a second sensor wire hole is inserted from the outside into the vacuum gauge probe, and the vacuum gauge probe is buried in the test soil; the high-definition camera has a camera fixing aluminum rail for fixing the camera position, and LED lamps are installed around the model box to enhance the brightness of the photo, which is convenient for subsequent calculations.

3. The test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure according to claim 2 is characterized by: The glass plate of the observation window is made of organic aviation glass.

4. The test and observation system for soil deformation characteristics in vacuum preloading with adjustable confining pressure according to claim 1 is characterized by: The model box is made of aluminum plate, the slide rail is made of aluminum plate, the first sensor wire holes are staggered and closely spaced, and sealing plugs are provided in the first sensor wire holes and the second sensor wire holes.

5. A test method for testing and observing soil deformation characteristics in vacuum preloading with adjustable confining pressure according to claim 2, characterized in that: The steps include: Step 1: Model preparation: First, determine the mass of soil sample required for the model box and configure the test soil sample; fix the plastic drainage board at the set position through the bracket, install the vacuum pipeline, pore water pressure sensor and vacuum gauge probe, spray the tracer particles on the inside of the observation window, add the configured test soil sample into the model box, cover the geotextile and vacuum membrane, and seal the model box; connect the model box in the soil vacuum consolidation system with the vacuum drive system through the vacuum pipeline to ensure the sealing of the entire test system; Step 2: System debugging Turn on the data monitoring system, set and adjust the data of the pore water pressure sensor and LVDT displacement sensor, turn on the vacuum pressure control device, observe the vacuum gauge and the readings of each sensor, and adjust the zero to ensure that the data correspond correctly. Install a high-definition camera on the camera fixing bracket, adjust the field of view, aperture and focal length of the shooting, so that the tracer particles are clearly imaged in the field of view; Step 3: Confining pressure setting: Start the air pump and the air pressure control device to pressurize the accordion airbag until the set pressure value is reached, and the soil confining pressure is set by setting the pressure value; Step 4: Vacuum pre-pressure extraction: Starting the vacuum drive system to perform vacuum pre-pressure extraction; Step 5: Test picture analysis: During the test, a high-definition camera was used to record photos of the soil and tracer particle particles within the field of view during the vacuum preloading process, and the photos were transmitted to a computer for processing through a data acquisition system. First, the control point center of the calibration point used to convert the image and spatial coordinates was calculated. Secondly, the analysis area was determined and divided into multiple grids. Then, the correlation coefficient was used to calculate the pixel coordinates of each grid in each frame of the image. The output data was filtered and analyzed using the correlation coefficient, and the erroneous output data was manually deleted. Finally, the pixel coordinates were converted into spatial coordinates to obtain the deformation information of the soil.

6. The test method of the test and observation system of soil deformation characteristics in vacuum preloading with adjustable confining pressure according to claim 5 is characterized by: While preparing the model in step 1, measure the confining pressure of the soil at the sampling location.

Images