Observation system and method of fluid movement in soil under vacuum preloading based on optical flow digital image technology

Abstract

The present invention discloses a system and method for observing fluid movement in soil under vacuum preloading based on optical flow digital image technology. The system includes a vacuum preloading consolidation system and a data observation system. The vacuum preloading consolidation system includes a model box for filling soil, a vacuum suction device, and a vertical drainage board with a single-side sealing film. The present invention provides a method for accurately observing changes in the flow morphology of liquid in the vertical section of the soil during vacuum preloading, and performs scientific qualitative and quantitative analysis based on the optical flow PIV technology. The present invention can cooperate with various data monitoring systems to obtain changes in fluid movement under different moisture content gradations and boarding depths, and explore the mechanism of pulse drainage based on these data to optimize the consolidation efficiency in the later stage of vacuum preloading, and propose better engineering practice solutions.

Description

Technical Field

[0001] The present invention relates to the field of vacuum preloading, and in particular to a system and method for observing fluid movement in soil under vacuum preloading based on optical flow digital image technology. Background Art

[0002] The use of vertical drainage panels (PVDs) combined with vacuum preloading to accelerate soil drainage and consolidation is an economical and effective method for improving the strength of soft soils. Currently, vacuum preloading technology has been widely used in soft soil foundation treatment in my country's eastern coastal areas. However, in actual treatment of high-water content soils, it has been found that the drainage panels exhibit pulse-like drainage characteristics in the late consolidation stage of the soil. However, the mechanism of liquid flow within the drainage panels and the soil during pulse-like drainage remains unclear. Therefore, a method is needed to directly observe the flow pattern of liquid within the vertical profile of the soil during vacuum preloading, so as to quantitatively analyze the liquid flow state within the drainage panels and the soil in the late consolidation stage. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a test system and a test method which can completely and accurately observe the flow state of liquid-gas multiphase flow in a drainage board during vacuum preloading drainage consolidation.

[0004] In order to solve the above technical problems, the present invention proposes a test system for observing the liquid movement state of the vertical profile of soil under vacuum preloading based on optical flow digital image technology, which includes a vacuum preloading consolidation system and a data observation system.

[0005] The vacuum preloading consolidation system includes a model box for filling soil, a vacuum suction device, and a vertical drainage board with a single-side sealing film.

[0006] The model box used to fill the soil is a rectangular transparent box with an open top, h>2a, a=1.5b (where h is the height of the box, a is the length of the box, and b is the width of the box). The front wall of the box is the fluid motion state observation area, and the vertical rectangular area at the inner central axis of the front wall is the drainage board fitting and fixing area. Multiple image marking reference points are provided on the left and right sides of the drainage board; two vacuum pipe holes that are not opened at the same time are respectively provided on the upper part of the right wall of the box and the lower part of the box. The vacuum pipe connects the vacuum suction device to the hand-shaped joint of the drainage board through the hole, transmitting vacuum pressure for upward or downward suction; a rectangular lower sealing frame covered with bolt through holes extends outward from the top of the box. The upper sealing frame and the lower sealing frame have the same shape, and the bolt through holes coincide with each other. The lower sealing frame, sealing rubber ring, and upper sealing frame are connected by bolts; the top of the test soil is covered with a vacuum membrane, and the outer edge of the vacuum membrane is clamped between the lower sealing frame and the upper sealing frame.

[0007] In engineering applications, the vertical drainage board is an H-shaped double-layer translucent structure with geomembrane sealed on both sides. In order to observe the fluid movement more intuitively, the present invention simplifies the double-layer structure into a single-layer transparent C-shaped structure and seals the geomembrane on one side. The geomembrane side is in contact with the soil, and the other side of the board is tightly attached to the front wall of the model box; the drainage board is sealed with glass glue at the far end from the vacuum pressure, and a hand-shaped joint is provided at the proximal end for connecting to the vacuum suction device.

[0008] The vacuum extraction device consists of a water vapor separator bottle, which separates the phases of the multiphase water vapor flow, and a water ring vacuum pump that provides negative pressure. The water vapor separator bottle features a top and bottom nozzle suction flask. The top nozzle's steel hose is connected to a drain wrench connector to collect free water discharged during the vacuum preloading process. A plastic stop valve is installed at the top nozzle to control the on / off of the vacuum pressure, while a plastic stop valve is installed at the bottom nozzle to drain water from the filter bottle. The flask's mouth is sealed with a rubber stopper and equipped with a rubber hose and a vacuum gauge. The rubber hose is connected to the vacuum pump, and the vacuum gauge is used to measure changes in vacuum during the test.

[0009] The data observation system includes a vacuum gauge for measuring the vacuum level of the filtration bottle, an electronic balance for measuring the mass of the discharged water, a high-definition camera for recording image data from various areas of the model box's front wall, and a light source bracket for supplemental lighting on the model box's front wall. The vacuum gauge, mounted on the mouth of the filtration bottle, measures the vacuum level of the vacuum extraction system during the test; the electronic balance, placed below the water vapor separation bottle, records the change in the mass of the extracted free water; a high-definition industrial camera, mounted on a camera bracket and positioned directly in front of the model box's front wall, captures target image data during the test; and a non-stroboscopic light source, mounted on a light source bracket, is positioned in front of the model box.

[0010] Furthermore, the model box is made of highly transparent acrylic material.

[0011] Furthermore, the model box is a rectangular box with h>2a and a=1.5b, which simulates the installation depth and impact range of the drainage board on site.

[0012] Furthermore, a plurality of image marking reference points are arranged on the front wall of the model box, which are used to mark the reference points during data processing and to calibrate the unit length within the image.

[0013] Furthermore, both upper and lower vacuum pipe holes of the model box are provided with opening and closing means, and one of them can be opened at will for suction only downwards or only upwards.

[0014] Furthermore, the optical flow digital imaging technology captures fluorescent droplets or fluorescent particles. The experimental devices all use water mixed with water-based fluorescent tracers or fluorescent tracer particles, and the tracer will not stain the soil particles. The water in the soil will emit fluorescence under a constant light source and the fluorescence brightness per unit volume of liquid is consistent.

[0015] Furthermore, the drainage board used in the present invention is a C-shaped drainage board with a geomembrane sealed on only one side. The material is transparent and fits tightly to the area defined by the front wall of the model box, ensuring that when the fluid moves in the drainage board, there is no soil particles outside the board blocking the view.

[0016] Furthermore, a high-definition industrial camera is mounted on a camera bracket and fixed at a certain working distance in front of the front wall of the model box, ensuring that the focal plane is parallel to the front wall of the model box and the observation area is located in the center of the image field. The relevant layout data must meet the following requirements:

[0017] Target area height <= field of view size or imaging area height (FOV) = working distance (WD) * camera sensor model size (V or H) / focal length (f)

[0018] Furthermore, a non-stroboscopic light source is installed on the light source bracket and arranged in front of the model box to ensure that the experimental observation area is well-lit and uniform and the tracer emits consistent brightness.

[0019] To solve the above technical problems, according to another aspect of the present invention, the present invention provides a test method for observing fluid movement in a drainage board during vacuum preloading, comprising the following steps:

[0020] (1) Model preparation: Fit the drainage board to a specific area and connect it to a vacuum suction device. Prepare a soil sample with a water content twice the liquid limit and containing a fluorescent tracer. Place the soil sample in the model box and cover it with a vacuum film. Ensure that the overall sealing of the model box is intact and that the target vacuum degree can be achieved. Install and debug the relevant data observation device to ensure that the electronic balance can accurately and continuously record data. Ensure that the image of the observation area is complete and the camera image is clear.

[0021] (2) Test start: The vacuum pump starts working, applies a vacuum load, and begins vacuum preloading to dehydrate the soil. An electronic balance records the continuous change in water displacement during the consolidation process, and a high-definition camera begins recording the movement of the fluorescent liquid in the vertical section of the soil until consolidation is complete.

[0022] (3) Data processing: The flow of fluorescent liquid can be regarded as the velocity field generated by the movement of grayscale pixels on the image plane. Under a constant light environment, the fluorescence brightness of the liquid doped with fluorescent tracers per unit volume is consistent. The liquid moves only along a single vertical X-axis in the drainage board, and the seepage movement in the soil can be divided into two directions, X and Y. Consider the light intensity of a pixel I (x, y, t) in the first frame (where t represents the time dimension). It moves a distance of (dx, dy) to the next frame, and takes dt time. The data item is mainly based on the brightness conservation assumption, that is, the brightness (grayscale value) of the same pixel remains unchanged in two adjacent frames of the image, that is:

[0023] I(x+dx,y+dy,t+dt)=I(x,y,t)

[0024] Where I(x,y,t) represents the brightness (grayscale value) of the pixel with coordinates (x,y) at time t. Taylor expansion and arrangement of the above equation yields:

[0025]

[0026] Let u and v be the velocity vectors of the optical flow along the X-axis and Y-axis respectively, that is:

[0027]

[0028] make Respectively represent the partial derivatives of the grayscale of the pixel in the image along the X, Y, and T directions. In summary, we can get:

[0029] I x u+I y v+I t =0

[0030] Among them, I X ,I Y ,I T Both can be obtained from image data, and (u,v) is the required optical flow vector.

[0031] By performing background separation and particle calibration on the fluorescent liquid and analyzing the inter-frame displacement vectors of each pixel point, the displacement field of the unit volume of liquid is obtained by combining the vectors, and the law of liquid movement is obtained.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a method for accurately observing the changes in the flow pattern of liquid in the vertical section of the soil during vacuum preloading, and performs scientific qualitative and quantitative analysis based on the optical flow method PIV technology.

[0034] The experimental arrangement of the model of the present invention is relatively similar to the on-site construction conditions. It can better simulate the vacuum consolidation of on-site soil and measure the movement state of the fluid during the consolidation process. The experimental data has practical research significance.

[0035] The present invention can cooperate with various data monitoring systems to obtain the changes in fluid movement under different moisture content gradations and plate-building depths, and based on these data, explore the mechanism of pulse drainage to optimize the post-vacuum preloading consolidation efficiency and propose better engineering practice solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a device layout diagram of the present invention;

[0037] Figure 2 This is a cross-sectional structural diagram of a single-side sealed drainage board used in the present invention;

[0038] Figure 3 It is the three-view drawing of the model box in the present invention;

[0039] Figure 4 It is a schematic diagram of a vacuum suction device;

[0040] Figure 5 It is a three-view drawing of the light source bracket in the present invention.

[0041] Figure 6 This is an example diagram of the liquid streamline field effect obtained in the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] The present invention proposes a test system for observing the liquid movement state of the vertical section of soil under vacuum preloading based on the optical flow method digital image technology. Figure 1 As shown, it includes a vacuum preloading consolidation system and a data observation system.

[0044] The vacuum preloading consolidation system includes a vertical drainage board with a single-side sealing film, a model box for filling soil, and a vacuum suction device.

[0045] The vertical drainage board with single-side sealing membrane 1 is an H-shaped double-layer translucent structure with geomembrane sealing on both sides in engineering applications, which is used to observe the fluid movement more intuitively. Figure 2 As shown, the present invention simplifies the double-layer structure into a single-layer transparent C-shaped structure 11 and seals the geomembrane 12 on one side. The geomembrane 12 side is in contact with the soil, and the other side of the plate is tightly fitted to the drainage board fitting and fixing area 21 on the front wall of the model box; the drainage board is sealed with glass glue at the far end from the vacuum pressure, and a hand-shaped joint 13 is provided at the proximal end for connecting to the vacuum suction device.

[0046] like Figure 3 As shown, the model box 2 for filling soil is a rectangular transparent box with an open top, h>2a, a=1.5b, the front wall of the box is the fluid motion state observation area, the vertical rectangular area at the inner center axis of the front wall is the drainage board fitting and fixing area 21, and multiple image marking reference points 22 are provided on the left and right sides of the drainage board; two vacuum pipe holes 23 that are not opened at the same time are respectively provided on the upper part of the right wall of the box and the lower part of the box, and the vacuum pipe connects the vacuum suction device 3 to the hand-shaped joint 13 of the drainage board through the holes to transmit vacuum pressure for upward or downward suction; a rectangular lower sealing frame 24 covered with bolt through holes extends outward from the top of the box, and the upper sealing frame 25 has the same shape as the lower sealing frame 24, and the bolt through holes 26 are located in the same position, and the lower sealing frame 24, the sealing rubber ring 27, and the upper sealing frame 25 are connected by bolts; the top of the test soil is covered with a vacuum membrane 28, and the outer edge of the vacuum membrane 28 is clamped between the sealing rubber ring 27 and the upper sealing frame 25.

[0047] like Figure 4 As shown, the vacuum suction device consists of a water vapor separation bottle 3 for separating the phases in the water vapor multiphase flow and a water ring vacuum pump 4 that provides negative pressure. The water vapor separation bottle 3 adopts an upper and lower nozzle suction suction bottle. The steel wire hose 31 at the upper nozzle is connected to the drain wrench-shaped connector 13 to collect free water discharged during the vacuum preloading process. A plastic water stop valve 32 is installed at the upper nozzle to control the opening and closing of the vacuum pressure, and a plastic water stop valve 33 is installed at the lower nozzle to discharge water from the suction bottle. The mouth of the suction bottle is sealed with a rubber stopper 34 and is provided with a rubber hose 35 and a vacuum gauge 36. The rubber hose 35 is used to connect to the water ring vacuum pump 4, and the vacuum gauge 36 is used to measure the change in vacuum degree during the test.

[0048] The data observation system includes a vacuum gauge 36 for measuring the vacuum degree of the filtration bottle, an electronic balance 5 for measuring the mass of the discharged water, a high-definition camera 6 for recording image data of each area on the front wall of the model box, and a light source bracket 7 for supplementary light on the side of the front wall of the model box. Figure 4 As shown, the vacuum meter 36 is installed at the mouth of the water vapor separation bottle 3 to measure the vacuum degree of the vacuum suction system during the test; the electronic balance 5 is placed under the water vapor separation bottle 3 to record the change in the mass of the free water extracted; Figure 1 The high-definition industrial camera 6 shown is installed on a camera bracket and placed in front of the front wall of the model box to collect target image data during the test; a non-stroboscopic light source 71 is installed on the light source bracket 7 and arranged in front of the model box.

[0049] The conditions required to capture moving droplets are as follows. A water-based fluorescent tracer at a mass ratio of 1:500-1:1000 or a 4‰ mass ratio of 100μm PSP tracer particles is uniformly added to the liquid. Assume that the rectangular target observation area is 20cm wide, the lower edge of the area is 40cm from the ground, and the camera used is a 2 / 3-inch sensor with a length of 4.536mm and a width of 3.416mm. The lens has a focal length of 12mm. The camera is then mounted at a height of (40+20 / 2)=50cm, and the working distance is at least 70cm, satisfying the following requirements:

[0050] 20cm<=70cm*3.416mm / 12mm

[0051] The present invention also provides a test method for observing fluid movement in a drainage board during vacuum preloading, comprising the following steps:

[0052] (1) Model preparation: Fit the drainage board tightly to the fixed area and connect it to the vacuum suction device. Prepare a soil sample with a water content twice the liquid limit and containing fluorescent tracers or tracer particles. Place the soil sample in the model box and cover it with a vacuum film. Ensure that the overall sealing of the model box is intact and the target vacuum degree can be achieved. Install and debug the relevant data observation device to ensure that the electronic balance can accurately and continuously record data. Arrange the camera and ensure that the image of the observation area is complete and the camera image is clear.

[0053] (2) Test start: The water ring vacuum pump starts operating, applying a vacuum load and initiating vacuum preloading to dehydrate the soil. An electronic balance records the continuous change in water displacement during the consolidation process, and a high-definition camera begins recording the movement of the fluorescent liquid in the vertical section of the soil until consolidation is complete.

[0054] (3) Data processing: The flow of fluorescent liquid can be regarded as the velocity field generated by the movement of grayscale pixels on the image plane. Under constant light conditions, the unit volume of liquid has the same fluorescence brightness. The liquid moves only along a single vertical X-axis in the drainage board, and the seepage movement in the soil can be divided into two directions, X and Y. Consider the light intensity of a pixel I (x, y, t) in the first frame (where t represents the time dimension). It moves a distance of (dx, dy) to the next frame, and takes dt time. The data item is mainly based on the brightness conservation assumption, that is, the brightness (grayscale value) of the same pixel remains unchanged in two adjacent frames of the image, that is:

[0055] I(x+dx,y+dy,t+dt)=I(x,y,t)

[0056] Where I(x,y,t) represents the brightness (grayscale value) of the pixel with coordinates (x,y) at time t. Taylor expansion and arrangement of the above equation yields:

[0057]

[0058] Let u and v be the velocity vectors of the optical flow along the X-axis and Y-axis respectively, that is:

[0059]

[0060] make Respectively represent the partial derivatives of the grayscale of the pixel in the image along the X, Y, and T directions. In summary, we can get:

[0061] I x u+I y v+I t =0

[0062] Among them, I X ,I Y ,I T Both can be obtained from image data, and (u,v) is the required optical flow vector.

[0063] By performing background separation and particle calibration on the fluorescent liquid, and analyzing the inter-frame displacement vector of each pixel, such as Figure 6 As shown, the vectors are combined to obtain the unit volume liquid displacement field and mark the streamlines to derive the law of liquid motion.

Claims

1. A test system for observing the liquid movement state of a vertical section of soil under vacuum preloading based on optical flow digital image technology, characterized in that: include: Vacuum preloading consolidation system; Data observation system; The vacuum preloading consolidation system comprises: Model box for filling soil; Vertical drainage board with single-side sealing; The model box is a transparent rectangular box with an open top. The front wall of the box is the fluid motion state observation area. The vertical rectangular area at the center axis of the inner side of the front wall is the drainage board fitting and fixing area. Multiple image marking reference points are set on the left and right sides of the drainage board. The vertical drainage board is a single-layer transparent C-shaped structure and is sealed with a geomembrane on one side, with the geomembrane side in contact with the soil and the other side of the board tightly fitting the front wall of the model box; The vertical drainage plate is sealed at the far end from the vacuum pressure, and a hand-shaped joint is provided at the proximal end for connecting to a vacuum suction device; the data observation system includes: an industrial camera for recording image data of each area of ​​the front wall of the model box, the industrial camera is mounted on a camera bracket and placed in front of the front wall of the model box to collect target image data during the test; The optical flow digital imaging technology captures fluorescent droplets or fluorescent particles. The test system uses water mixed with a water-based fluorescent tracer or fluorescent tracer particles, and the tracer will not stain the soil particles.

2. The test system according to claim 1, characterized in that The top of the rectangular transparent box extends outward to form a rectangular lower sealing frame covered with bolt holes. The upper sealing frame has the same shape as the lower sealing frame, and the bolt holes are positioned at the same position. The lower sealing frame, the sealing rubber ring, and the upper sealing frame are connected by bolts. The test soil body is covered with a vacuum film, and the outer edge of the vacuum film is sandwiched between the lower sealing frame and the upper sealing frame.

3. The test system according to claim 1, characterized in that The vacuum suction device comprises: a water vapor separation bottle for separating the phases in the water vapor multiphase flow and a water ring vacuum pump for providing negative pressure.

4. The test system according to claim 3, characterized in that The water vapor separation bottle adopts an upper and lower nozzle suction bottle, and the upper nozzle of the suction bottle is connected to the hand-shaped joint of the vertical drainage board through a steel wire hose; The upper mouth of the suction filter bottle is equipped with an upper mouth plastic water stop valve, and the lower mouth is equipped with a lower mouth plastic water stop valve for draining water from the suction filter bottle; The mouth of the suction filtration bottle is sealed with a rubber stopper and is provided with a rubber hose, and the rubber hose is used to connect the vacuum pump.

5. The test system according to claim 1, characterized in that: The data observation system further includes: Vacuum gauge for measuring the vacuum degree of the filtration flask; electronic balance for measuring the mass of discharged water; Light source bracket for filling light on the front wall of the model box; The vacuum gauge is installed at the bottle mouth of the water vapor separation bottle; The electronic balance is placed below the water vapor separation bottle to record the change in the mass of the extracted free water; a non-stroboscopic light source is installed on the light source bracket and arranged on the front of the model box.

6. A method for observing the liquid movement state in a vertical section of soil, characterized in that: The test system according to any one of claims 1 to 5 comprises the following steps: (1) Model preparation: Attach the vertical drainage board with a single-side film seal to the area inside the model box and connect it to the vacuum suction device. Prepare a soil sample with a water content twice the liquid limit and a fluorescent tracer. Place the soil sample in the model box and cover it with a vacuum film. Ensure that the overall sealing of the model box is intact and that the target vacuum degree can be achieved. Install and debug the relevant data observation device to ensure that the electronic balance can accurately and continuously record data. Ensure that the image of the observation area is complete and the camera image is clear. (2) Test start: The vacuum pump starts working, the vacuum load is applied, and the vacuum preloading effect is started to dehydrate the soil. The electronic balance records the continuous change data of the drainage volume during the consolidation process. The industrial camera starts to record the movement image of the fluorescent liquid in the vertical section of the soil until the consolidation is completed. (3) Data processing: The flow of fluorescent liquid is considered as the velocity field generated by the movement of grayscale pixels on the image plane. Under a constant light environment, the fluorescence brightness of the liquid doped with fluorescent tracers or fluorescent tracer particles per unit volume is consistent. The liquid moves only along a single vertical X-axis in the drainage board. The seepage movement in the soil is divided into two directions, X and Y. Consider the light intensity of a pixel I (x, y, t) in the first frame, where t represents the time dimension. It moves a distance (dx, dy) to the next frame, which takes dt time. The brightness of the same pixel remains unchanged in two adjacent frames, that is: ； Where I(x,y,t) represents the brightness of the pixel with coordinates (x,y) at time t. Taylor expansion of the above equation yields: ； Let u and v be the velocity vectors of the optical flow along the X-axis and Y-axis respectively, that is: ， make , , Respectively represent the partial derivatives of the grayscale of the pixel in the image along the X, Y, and T directions. In summary, we can get: ； Among them, I X ,I Y ,I T Both can be obtained from image data, and (u, v) is the required optical flow vector; By performing background separation and particle calibration on the fluorescent liquid and analyzing the inter-frame displacement vectors of each pixel point, the displacement field of the unit volume of liquid is obtained by combining the vectors, and the law of liquid movement is obtained.

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