Full-automatic high-precision deformable red soil-water characteristic curve measuring system and method

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly discloses a full-automatic high-precision deformable red soil-water characteristic curve measuring system and method. The double-layer pressure chamber of the system is of a double-layer structure, water is filled between the double-layer pressure chamber and the inner layer which is not filled with water, the image recognition measuring device captures deformation characteristics in the sample dehumidification process, and the automatic bubble washing device controls opening and closing of an electromagnetic valve through a computer and efficiently washes bubbles in a pipeline through an air source. Reciprocating type accurate flushing and bubble collection of pipeline bubbles are achieved; the computer is connected with the evaporation compensation device and can accurately collect the evaporation capacity. The method comprises the steps of test preparation, data and image acquisition, bubble scouring, multi-stage suction force application, data processing and SWCC. The device has the advantages of being simple in structure, high in automation degree and accurate in result, especially can measure the volume change of the soil body in the dehumidification process in real time, and provides a highly valuable, efficient and reliable measurement means and technical scheme for the field of unsaturated soil research.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and specifically relates to a fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system and method with simple device structure, high degree of automation and accurate measurement results. Background Art

[0002] Yunnan is located in the southwest border area, with widespread water resources, but the mountains are high and the slopes are steep, and the economy is backward. Among the hydraulic structures in the province, more than 95% of the reservoirs are located in the red soil area. Red soil shrinks and deforms during water loss and expands and deforms during humidification. It is a deformable soil that is easily affected by water. During the long-term operation, more than half of the red soil reservoirs are "disease-bearing" and have shown varying degrees of damage and deterioration: such as dam cracks, deformation, leakage, bank collapse and other diseases. Not only can the basic functions of the red soil dam (flood control and drought relief, etc.) not be completed, and the economic growth cannot be driven, but with the further accumulation of dam diseases, the lives and property of the people downstream are seriously threatened. Focusing on the red soil core wall dam (such as Lubuge Hydropower Station, Yuanjiang Xiaobanbi Reservoir, Nuozhadu Hydropower Station, etc.), during the process of reservoir water level regulation, evaporation, and rainfall year after year, its core wall is in a repeated dry-wet cycle process, and the core wall is greatly affected by water, while the dam shell material is less affected by water than the core wall. This leads to significant differences in their deformation characteristics and permeability characteristics during the dry-wet cycle. The uncoordinated deformation leads to the occurrence and further aggravation of diseases. Therefore, it is a topic worth studying to correctly understand the water retention characteristics [characterizing the change process of soil water content, often expressed by the soil-water characteristic curve (SWCC)], deformation characteristics, and the mutual coupling relationship between the two during the water loss process of red soil. How to carry out experiments and form a set of effective methodologies is part of the work of the above topics, which is very important for disaster prevention and mitigation of red soil core wall dams during operation.

[0003] At present, the experimental research on soil-water characteristic curve mostly adopts soil-water characteristic curve pressure plate instrument, but the existing pressure plate instrument and soil-water characteristic curve measurement method have the following disadvantages: (1) Due to design defects, the automatic bubble flushing device of the existing pressure plate instrument has the problem of being unable to completely eliminate bubbles, and the degree of automation is low, which consumes a lot of manpower. (2) The measuring range and accuracy of the left and right measuring tubes of the existing pressure plate instrument cannot meet the needs of various soil types. (3) Since the volume of red soil generally shrinks during the water loss process, it has a great impact on the soil-water characteristic curve of the actual soil. However, most of the existing measurement methods do not consider the volume change of the sample or do not directly consider the volume change. Therefore, it is difficult to accurately restore the characteristics of the change in the water holding capacity of red soil. Summary of the invention

[0004] In order to overcome the above-mentioned defects of the pressure plate instrument in the prior art, the present invention provides a fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system with simple device structure, high degree of automation and accurate measurement results, and also provides a fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method.

[0005] The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system of the present invention is realized as follows: it comprises a double-layer pressure chamber, an automatic bubble flushing device, and an image recognition measurement device; The double-layer pressure chamber comprises an outer plexiglass wall, a clay plate, a base I, an inner plexiglass wall, and an plexiglass cover. The outer plexiglass wall and the inner plexiglass wall are nested and fixed on the top surface of the base I. The space between the outer plexiglass wall and the inner plexiglass wall is filled with water. The plexiglass cover is detachably sealed and fixed on the top of the outer plexiglass wall and / or the inner plexiglass wall. The interior of the inner plexiglass wall forms a closed pressure-bearing space through the base I and the plexiglass cover. The clay plate is detachably fixed in the groove of the base I inside the inner plexiglass wall. The plexiglass cover is connected to the air source through an air pressure control implementation device. The side wall of the base I is symmetrically provided with a liquid inlet I and a liquid inlet II connected to the bottom end of the pressure-bearing space. The automatic bubble flushing device includes a main flushing unit and an auxiliary flushing unit. The main flushing unit includes a gas collecting bottle II connected to the liquid inlet II of the base I, and a port of the gas collecting bottle II away from the liquid inlet II is sequentially connected to a small water storage tank II, a measuring tube II, a non-contact pipeline liquid level sensor II and a gas pressure control implementation device; the auxiliary flushing unit includes a gas collecting bottle I connected to the liquid inlet I of the base I, and a port of the gas collecting bottle I away from the liquid inlet I is sequentially connected to a small water storage tank I, a measuring tube I, a non-contact pipeline liquid level sensor I and a gas pressure control implementation device; the gas pressure control implementation device is respectively connected to a gas source and a computer; A drainage detection device is also connected to the connecting pipeline between the gas collecting bottle II of the main flushing unit and the liquid inlet II of the base I. The signal output end of the drainage detection device is electrically connected to the computer. The inlet end of the small water storage tank II and the drainage detection device are respectively connected in series with the control valve I and the control valve II; the signal output end of the non-contact pipeline liquid level sensor II is electrically connected to the computer; A control valve III is connected in series on the pipeline between the small water storage tank I and the gas collecting bottle I of the auxiliary flushing unit, and the signal output end of the non-contact pipeline liquid level sensor I is electrically connected to the computer; The computer is also electrically connected to an evaporation compensation device; The image recognition and measurement device includes a top shooting device arranged on the top surface of the organic glass cover and a side shooting device arranged on the outside of the outer organic glass wall. The top shooting device and the side shooting device are electrically connected to a computer respectively, and can take a top view and a side view of the deformable red clay sample in real time.

[0006] Furthermore, the top end of the gas collecting bottle II is connected to a high-precision measuring tube I, and a water level regulating valve I is arranged on the upper part of the high-precision measuring tube I; the top end of the gas collecting bottle II is connected to a high-precision measuring tube II, and a water level regulating valve II is arranged on the upper part of the high-precision measuring tube II.

[0007] Furthermore, the displacement detection device includes a data acquisition balance II, a sealing cover, and a measuring bottle. The measuring bottle is fixedly arranged on the data acquisition balance II, the sealing cover is sealingly fixedly arranged on the opening at the top of the measuring bottle, the pipeline connected to the control valve II passes through the sealing cover and extends into the measuring bottle, and the data acquisition balance II is electrically connected to the computer.

[0008] Furthermore, the evaporation compensation device includes a measuring tube III and a base II. The measuring tube III is vertically arranged and the bottom end is embedded in a groove on the top surface of the base II. The base II is arranged on a data acquisition balance I, and the data acquisition balance I is electrically connected to a computer.

[0009] Furthermore, the high-precision measuring tube I, high-precision measuring tube II, measuring tube II and measuring tube I are all transparent glass tubes, and the measuring tube II and measuring tube I are respectively vertically fixed on a plastic panel with scales by U-shaped nails.

[0010] Furthermore, the scale length and measuring range of the high-precision measuring tube I and the high-precision measuring tube II are 10 cm and 0-100×0.0126 g, respectively, and the scale length and measuring range of the plastic panel are 100 cm and 0-1000×0.0196 g, respectively.

[0011] The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method of the present invention is implemented as follows: based on the aforementioned fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system, including test preparation, data and image acquisition, bubble flushing, SWCC measurement without considering volume change correction, data processing, and SWCC measurement without considering volume change correction. The specific steps are as follows: A. Test preparation: Saturate the clay plate and install it on the top surface of base I inside the inner plexiglass wall, place the sample of deformable red clay on the clay plate, and then fill the space between the outer plexiglass wall and the inner plexiglass wall with water; B. Data and image acquisition: After the sample is placed, the computer controls the gas pressure control implementation device to apply the first level of matrix suction to the pressure space, and the data acquisition system on the computer measures and records the changes in suction value, discharged water volume and evaporated water volume in real time; when the discharged water volume v<0.1g / 24h is detected, the suction value, discharged water volume and evaporated water volume readings at this time are recorded, and the top view and side view of the sample at the last time under this level of suction are collected at the same time; C. Bubble flushing: After step B is completed, close the control valve II, use the main flushing unit and the auxiliary flushing unit to reciprocately flush the pipeline and the clay plate with bubbles, and record the volume of the discharged bubbles through the high-precision measuring tube II and the high-precision measuring tube I. When the non-contact pipeline liquid level sensor II and the non-contact pipeline liquid level sensor I detect that the measuring tube II and the measuring tube I have reached the highest water level, the main flushing unit and the auxiliary flushing unit stop the bubble flushing; D. SWCC measurement without considering volume change correction: Suction was applied according to the suction path set in step B and step C. At the same time, the computer collected the data of the change of the discharged water volume over time, and the evaporation compensation device recorded the evaporated water volume and the top view and side view of the sample after the suction balance of different matrices; E. Data processing: the recorded bubble volume is distributed and compensated to each level of suction to correct the evaporation, and then the saturation of the sample at each moment is calculated based on the data of the initial water content, drainage, evaporation and bubble volume of the sample; F. SWCC without volume change correction: the matrix suction collected by the computer and the sample saturation obtained in step E are matched one by one, that is, the soil-water characteristic curve of the sample without volume change correction is obtained; at the same time, the top shooting device and the side shooting device respectively collect the top view and side view of the sample at preset intervals, and then the area of ​​the sample in the horizontal direction and the height in the vertical direction are obtained based on image recognition technology.

[0012] Furthermore, the sample in step A is also subjected to the following pretreatment steps: A1. Refer to GB / T50123 "Standard for Geotechnical Test Methods" to determine the air-dried moisture content of red soil: soak the soil at the initial moisture content and soak for 24 hours so that the moisture is evenly distributed in space; A2. Saturate the filter paper and permeable stone of the same size as the ring knife in the vacuum saturator for 1 hour, and saturate the permeable stone of the pressure plate instrument; A3, weigh the mass of the empty ring cutter, then apply vaseline on the inner wall of the ring cutter, weigh the total mass of the ring cutter and vaseline, weigh the red clay obtained in A1 and put it into the ring cutter for compaction to obtain a sample, and ensure that the loss of the sample is less than 0.1% during compaction; A4. Place a saturated filter paper and a saturated permeable stone on the upper and lower surfaces of the sample, then place it in the airless water in the vacuum saturator and apply a vacuum value of more than 85kPa for at least 48 hours. When no obvious bubbles are observed, the saturation process is considered complete; A5. At this time, the initial saturation and initial volume water content of the sample can be calculated according to formula 1; Where: sat 、m w 、m s are the moisture content of the sample after saturation, the mass of water in the sample, and the mass of soil particles in the sample; ω0, ρ do are the initial moisture content and initial dry density of the sample when the soil is soaked in step A3; m w1 is the mass of water entering the sample during the saturation stage of the vacuum pumping in step A4; V is the volume of the sample.

[0013] Furthermore, the method of obtaining the area in the horizontal direction and the height in the vertical direction of the sample based on the image recognition technology includes the steps of image preprocessing, image processing, and geometric parameter measurement, and each step is specifically as follows: F1. Image preprocessing: The top camera and the side camera take pictures of the top view and the side view of the sample respectively, and then the views are imported into MATLAB to be converted into digital images, and then the images are cropped into circles and rectangles based on morphological operations; F2, image processing: First, perform gamma correction on the cropped image of F1 to obtain a gamma-corrected grayscale image; then perform Fourier transform and filtering on the grayscale image, and finally fill in the holes and process the non-connected small areas; F3. Geometric parameter measurement: Use MATLAB's measurement function to measure the top area and height of the sample; Furthermore, the sample is a cylinder, and the soil-water characteristic curve corrected by volume change is not considered in the F step. If the volume change during the dehumidification process of the red soil is to be corrected, the specific size of the sample during the dehumidification process is obtained in combination with the image recognition measurement device. The specific steps are as follows: F4. Calculation of sample volume strain: Based on the diameter and height of the sample at each level of suction measured above, the volume change of the sample under the current equilibrium suction can be obtained. Assuming that the initial diameter of the sample is r0' and the height is Z0', the volume change at a certain moisture content state during the shrinkage process of the sample is ΔV, and the volume strain Δ V / V0 is: Where: Δz is the height of the sample reduced due to water loss at a certain moment, Z0 is the initial height of the sample, Δr is the diameter of the sample reduced due to water loss at a certain moment, r0 is the initial diameter of the sample, and V0 is the volume of the sample before water loss and shrinkage; F5. Calculation of void ratio and saturation: Based on equations 3 and 4, the void ratio e and saturation S under different equilibrium suction states during the shrinkage of the sample are obtained. r : e=e0-ΔV(1+e0) / V0 Formula 3, S r =G s w / e formula 4, Where: e0 is the initial porosity of the sample, Gs is the specific gravity of the sample; F6. Considering volume change correction SWCC: Based on the soil-water characteristic curve without considering volume change correction and Equations 2 to 4, the soil-water characteristic curve considering volume change correction under various levels of matrix suction of the sample can be obtained.

[0014] Beneficial effects of the present invention: 1. The measuring system of the present invention realizes the automation of the soil-water characteristic curve measurement process and the bubble flushing process, and is equipped with a high-precision measuring device, and takes into account the evaporation of water and the water loss shrinkage effect of red soil. By designing an automatic bubble flushing device, and covering components such as evaporation compensation device, gas collecting bottles I and II, small water storage tanks I and II, measuring tubes I and II, and non-contact pipeline liquid level sensors I and II, in the entire suction path, the application of pore gas pressure and the flushing and collection of bubbles after each level of suction balance are all instructed by the computer, and then specifically executed by the gas pressure control implementation device; by collecting and processing the discharged water volume, evaporated water volume and bubbles, the soil-water characteristic curve of red soil without considering volume change correction after each level of suction balance can be obtained. The measuring system of the present invention significantly improves the measurement accuracy of the soil-water characteristic curve, greatly enhances the degree of automation of the measurement, reduces human interference factors, and thus ensures the accuracy and reliability of the measurement results.

[0015] 2. The measurement method of the present invention fully relies on the unique advantages of the measurement system. With the help of the top shooting device and the side shooting device, the side view and the top view are respectively taken for the sample after each level of suction balance. Then, with the help of the image recognition technology in the computer, the volume change of the sample can be accurately obtained, so as to effectively correct the influence of the volume change of the deformable red soil on the soil-water characteristic curve, and finally effectively improve the accuracy and scientificity of the measurement results, providing more accurate data support and technical guarantee for related research and practice.

[0016] In summary, the present invention has the remarkable characteristics of simple structure, excellent degree of automation, and accurate measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system of the present invention; Figure 2 It is a schematic diagram of the connection between the measuring tube and the plastic panel of the present invention; Figure 3It is a schematic diagram of the pipe connection of the automatic bubble flushing device of the present invention; Figure 4 Detailed steps for measuring sample size using image recognition technology; Figure 5 It is a top-view morphological cropping diagram of the present invention; Figure 6 It is an area measurement diagram after the top-view image processing of the present invention; Figure 7 is a gamma-corrected grayscale image of the side-view direction of the present invention; Figure 8 is a high-frequency enhanced grayscale image in the side-view direction of the present invention; Fig. 9 is a lateral sample binary image of the present invention; Fig.10 It is a diagram of the area measurement after the non-connected area is processed by filling the cavities of the lateral specimen of the present invention; In the figure: 1-external organic glass wall, 2-sample, 3-ceramic plate, 4-base I, 5-gas pressure control implementation device, 6-gas source, 7-computer, 8-evaporation compensation device, 9-data acquisition balance I, 10-data acquisition balance II, 11-sealing cover, 12-volume bottle, 13-high-precision volume tube II, 14-water level regulating valve II, 15-gas collecting bottle I, 16-high-precision volume tube I, 17-water level regulating valve I, 18- Gas collecting bottle II, 19- non-contact pipeline liquid level sensor II, 20- small water storage tank II, 21- small water storage tank I, 22- measuring tube II, 23- measuring tube I, 24- control valve II, 25- control valve III, 26- non-contact pipeline liquid level sensor I, 27- control valve I, 28- inner organic glass wall, 29- organic glass cover, 30- top shooting device, 31- side shooting device, 32- U-shaped nail, 33- plastic panel. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited in any way. Any changes or improvements made based on the teachings of the present invention belong to the protection scope of the present invention.

[0019] like Figure 1 , 2 As shown in 3, the fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system of the present invention includes a double-layer pressure chamber, an automatic bubble flushing device, and an image recognition measurement device; The double-layer pressure chamber comprises an outer organic glass wall 1, a clay plate 3, a base Ⅰ4, an inner organic glass wall 28, and an organic glass cover 29. The outer organic glass wall 1 and the inner organic glass wall 28 are nested and fixed on the top surface of the base Ⅰ4. The space between the outer organic glass wall 1 and the inner organic glass wall 28 is filled with water. The organic glass cover 29 is detachably sealed and fixed on the top of the outer organic glass wall 1 and / or the inner organic glass wall 28. The interior of the inner organic glass wall 28 forms a closed pressure-bearing space through the base Ⅰ4 and the organic glass cover 29. The clay plate 3 is detachably fixed in the groove of the base Ⅰ4 inside the inner organic glass wall 28. The organic glass cover 29 is connected to the gas source 6 through a gas pressure control implementation device 5 for adjusting the pore gas pressure in the pressure-bearing space. The side wall of the base Ⅰ4 is symmetrically provided with a liquid inlet Ⅰ and a liquid inlet Ⅱ connected to the bottom end of the pressure-bearing space. The automatic bubble flushing device includes a main flushing unit and an auxiliary flushing unit. The main flushing unit includes a gas collecting bottle Ⅱ18 connected to the liquid inlet Ⅱ of the base Ⅰ4, and a port of the gas collecting bottle Ⅱ18 away from the liquid inlet Ⅱ is sequentially connected to a small water storage tank Ⅱ20, a measuring tube Ⅱ22, a non-contact pipeline liquid level sensor Ⅱ19 and a gas pressure control implementation device 5; the auxiliary flushing unit includes a gas collecting bottle Ⅰ15 connected to the liquid inlet Ⅰ of the base Ⅰ4, and a port of the gas collecting bottle Ⅰ15 away from the liquid inlet Ⅰ is sequentially connected to a small water storage tank Ⅰ21, a measuring tube Ⅰ23, a non-contact pipeline liquid level sensor Ⅰ26 and a gas pressure control implementation device 5; the gas pressure control implementation device 5 is respectively connected to a gas source 6 and a computer 7; A drainage detection device is also connected to the connecting pipeline between the gas collecting bottle II 18 of the main flushing unit and the liquid inlet II of the base I 4, and the signal output end of the drainage detection device is electrically connected to the computer 7. The small water storage tank II 20 and the inlet end of the drainage detection device are respectively connected in series with a control valve I 27 and a control valve II 24; the signal output end of the non-contact pipeline liquid level sensor II 19 is electrically connected to the computer 7; A control valve III 25 is connected in series on the pipeline between the small water storage tank I 21 of the auxiliary flushing unit and the gas collecting bottle I 15, and the signal output end of the non-contact pipeline liquid level sensor I 26 is electrically connected to the computer 7; The computer 7 is also electrically connected to an evaporation compensation device 8; The image recognition and measurement device includes a top shooting device 30 arranged on the top surface of the organic glass cover 29 and a side shooting device 31 arranged on the outside of the outer organic glass wall 1. The top shooting device 30 and the side shooting device 31 are electrically connected to the computer 7 respectively, and can take a top view and a side view of the deformable red clay sample 2 in real time.

[0020] The top of the gas collecting bottle II 18 is connected to a high-precision measuring tube I 16, and a water level regulating valve I 17 is arranged on the top of the high-precision measuring tube I 16; the top of the gas collecting bottle I 15 is connected to a high-precision measuring tube II 13, and a water level regulating valve II 14 is arranged on the top of the high-precision measuring tube II 13.

[0021] The displacement detection device includes a data acquisition balance II 10, a sealing cover 11, and a measuring bottle 12. The measuring bottle 12 is fixedly arranged on the data acquisition balance II 10. The sealing cover 11 is sealingly fixedly arranged on the opening at the top of the measuring bottle 12. The pipeline connected to the control valve II 24 passes through the sealing cover 11 and extends into the measuring bottle 12. The data acquisition balance II 10 is electrically connected to the computer 7.

[0022] The evaporation compensation device 8 includes a measuring tube III and a base II. The measuring tube III is vertically arranged and the bottom end is embedded in a groove on the top surface of the base II. The base II is arranged on a data acquisition balance I9, and the data acquisition balance I9 is ​​electrically connected to the computer 7.

[0023] It should be noted that the accuracy of the data acquisition balance I9 is ​​0.01g. The computer 7 collects the mass change of water in the evaporation compensation device 8 within the same time interval through the data acquisition system to provide test data for calculating the soil-water characteristic curve.

[0024] The high-precision measuring tube I 16 , high-precision measuring tube II 13 , measuring tube II 22 and measuring tube I 23 are all transparent glass tubes, and the measuring tube II 22 and measuring tube I 23 are respectively vertically fixed on a plastic panel 33 with scales by U-shaped nails 32 .

[0025] The scale length and measuring range of the high-precision measuring tube I16 and the high-precision measuring tube II13 are 10 cm and 0-100×0.0126 g respectively, and the scale length and measuring range of the plastic panel 33 are 100 cm and 0-1000×0.0196 g respectively.

[0026] The high-precision measuring tube I16, high-precision measuring tube II13, measuring tube II22 and measuring tube I23 are all transparent glass tubes; the measuring tube II22 and measuring tube I23 are vertically fixed on a plastic panel 33 with scales by U-shaped nails 32, respectively. The length of the measuring tube II22 and the measuring tube I23 is 120 cm, the outer diameter is 7 mm, the inner diameter is 5 mm, and the thickness is 2 mm. The measuring tube is divided into 100 large grids and 1000 small grids along the height, each large grid is 1 cm, each small grid is 1 mm, and the mass of water contained in each small grid is 0.0196 g.

[0027] It should be noted that the high-precision measuring tube I16 and the high-precision measuring tube II13 are both double-layer transparent glass tubes with inner and outer layers, and are 10 cm in length, 6 mm in outer diameter, and 4 mm in inner diameter. The high-precision measuring tubes are divided into 10 large grids and 100 small grids along the height. Each large grid is 1 cm, each small grid is 1 mm, and the mass of water contained in each small grid is 0.0126 g.

[0028] It should be noted that the small water storage tank I21 and the small water storage tank II20 are cylindrical tanks made of plastic with a capacity of 30 ml, and both ends of the cylindrical tanks are respectively connected to pipes with an outer diameter of 8 mm.

[0029] The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method of the present invention is based on the aforementioned fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system, including test preparation, data and image acquisition, bubble flushing, SWCC measurement without considering volume change correction, data processing, and SWCC measurement without considering volume change correction. The specific steps are as follows: A. Test preparation: saturate the clay plate 3 and install it on the top surface of the base Ⅰ4 inside the inner organic glass wall 28, place the sample 2 of deformable red clay on the clay plate 3, and then fill the space between the outer organic glass wall 1 and the inner organic glass wall 28 with water; B. Data and image acquisition: After the sample 2 is placed, the computer 7 controls the air pressure control implementation device 5 to apply the first level of matrix suction to the pressure space, and the data acquisition system on the computer 7 measures and records the changes in the suction value, the amount of water discharged, and the amount of evaporated water in real time; when the amount of water discharged v<0.1g / 24h is detected, the suction value, the amount of water discharged, and the amount of evaporated water readings at this time are recorded, and the top view and side view of the sample 2 at this level of suction are collected for the last time; C. Bubble flushing: After step B is completed, close the control valve II24, use the main flushing unit and the auxiliary flushing unit to reciprocately flush the pipeline and the clay plate 3 with bubbles, and record the volume of the discharged bubbles through the high-precision measuring tube II13 and the high-precision measuring tube I16. When the non-contact pipeline liquid level sensor II19 and the non-contact pipeline liquid level sensor I26 detect that the measuring tube II22 and the measuring tube I23 have reached the highest water level, the main flushing unit and the auxiliary flushing unit stop bubble flushing; D. SWCC measurement without considering volume change correction: Suction is applied according to the suction path set in step B and step C, while the computer 7 collects the variation data of the discharged water volume over time, and the evaporation compensation device 8 records the evaporated water volume and the top view and side view of the sample 2 after the suction balance of different matrices; E. Data processing: The recorded bubble volume is distributed and compensated to each level of suction to correct the evaporation amount, and then the saturation corresponding to each moment of sample 2 is calculated based on the data of initial water content, drainage, evaporation and bubble volume of sample 2; F. SWCC without considering volume change correction: The matrix suction collected by computer 7 and the saturation of sample 2 obtained in step E are matched one by one, that is, the soil-water characteristic curve of sample 2 without considering volume change correction is obtained; at the same time, the top shooting device and the side shooting device respectively collect the top view and the side view of the sample at a preset interval time, and then the area of ​​the sample in the horizontal direction and the height in the vertical direction are obtained based on image recognition technology.

[0030] Sample 2 in step A also undergoes the following pretreatment steps: A1. Refer to GB / T50123 "Standard for Geotechnical Test Methods" to determine the air-dried moisture content of red soil: soak the soil at the initial moisture content and soak for 24 hours so that the moisture is evenly distributed in space; A2. Saturate the filter paper and permeable stone of the same size as the ring knife in the vacuum saturator for 1 hour, and saturate the permeable stone of the pressure plate instrument; A3, weigh the mass of the empty ring cutter, then apply vaseline on the inner wall of the ring cutter, weigh the total mass of the ring cutter and vaseline, weigh the red clay obtained in A1, put it into the ring cutter for compaction to obtain sample 2, and ensure that the loss of sample 2 is less than 0.1% during compaction; A4. Place a saturated filter paper and a saturated permeable stone on the upper and lower surfaces of sample 2, and then place it in the airless water in the vacuum saturator. Apply a vacuum value of more than 85kPa for at least 48 hours. When no obvious bubbles are observed, the saturation process is considered complete; A5. At this time, the initial saturation and initial volumetric water content of sample 2 can be calculated according to formula 1; Where: sat 、m w 、m s are the moisture content of sample 2 after saturation, the mass of water in sample 2, and the mass of soil particles in sample 2; ω0, ρ do are the initial moisture content and initial dry density of sample 2 when the soil is soaked in step A3; m w1 is the mass of water entering the sample 2 during the saturation stage of the vacuum pumping in step A4; V is the volume of the sample 2.

[0031] The method of obtaining the horizontal area and vertical height of the sample 2 based on the image recognition technology includes the steps of image preprocessing, image processing, and geometric parameter measurement. The specific steps are as follows: F1. Image preprocessing: The top camera 30 and the side camera 31 respectively take the top view and the side view of the sample 2, and then import the view into MATLAB to convert it into a digital image, and then perform circular and rectangular cropping of the image based on morphological operations; It should be noted that, Figure 4 , Figure 5 , Figure 6As shown, since the top view is less affected by the environment, morphological circular cropping is performed. In step F2, it only needs to be converted into a binary image and the holes are filled before area measurement. After the side view is morphologically cropped with a rectangle, it enters steps F2 and F3.

[0032] F2, image processing: First, perform gamma correction on the cropped image of F1 to obtain a gamma-corrected grayscale image; then perform Fourier transform and filtering on the grayscale image, and finally fill in the holes and process the non-connected small areas; It should be noted that if Figure 7 As shown in the figure, after gamma correction, the contrast between the black tape area and the side view image is enhanced, which is conducive to the subsequent image recognition. Gamma correction uses the fact that the human eye is more sensitive to dark areas than bright areas, increases the storage value range of dark areas, adjusts the nonlinear illumination intensity, and enriches the expression of image details. Its mathematical expression is as follows: Where: Vin is a non-negative real value, such as an image pixel, A is a constant, usually 1, the input and output range is [0, 1], γ<1, the light intensity becomes stronger, γ>1, the light intensity becomes weaker.

[0033] It should be noted that if Figure 8 As shown in the figure, the image after gamma correction, Fourier transform and filtering denoising is superimposed with the grayscale image to obtain a high-frequency enhanced grayscale image in the side view direction of the image; since most of the image content is concentrated in the low-frequency part, the noise represents the sudden change of the grayscale value on the image, corresponding to the high-frequency part of the image, so the Fourier transform is used to process the image after gamma correction, and the image is converted from the spatial domain to the frequency domain. The amplitude value of each pixel in the image can be obtained. The amplitude represents the size of the energy at each frequency. The energy value of the high-frequency part is set to 0, and the inverse Fourier transform is performed to remove the noise on the image. The mathematical expression of Fourier transform is as follows: Where: p = 0, 1, ..., M-1, q = 0, 1, ..., N-1; and are the forward transform kernel and inverse transform kernel respectively, m and n are the spatial domain sampling values, and F(p,q) is the frequency spectrum of the discrete signal f(x,y).

[0034] It should be noted that if Fig. 9 As shown, for the side view, due to the uneven soil surface, holes, tiny cracks, etc., there are many small-area objects in its binary image, and its threshold coincides with the threshold represented by the black tape. It is necessary to fill the image area and remove the small-area objects outside the image area.

[0035] F3, geometric parameter measurement: MATLAB measurement function is used to measure the top area and height of sample 2. Sample 2 is a cylinder. The soil-water characteristic curve corrected by volume change is not considered in step F. If the volume change during the dehumidification of red soil is to be corrected, the specific dimensions of sample 2 during the dehumidification process are obtained in combination with the image recognition measurement device. The specific steps are as follows: F4. Calculation of sample volume strain: Based on the diameter and height of sample 2 at each level of suction measured above, the volume change of sample 2 at the current equilibrium suction can be obtained. Assuming that the initial diameter of sample 2 is r0' and the height is Z0', the volume change at a certain moisture content state during the shrinkage process of sample 2 is ΔV, and the volume strain Δ V / V0 is: Where: Δz is the height of sample 2 reduced due to water loss at a certain moment, Z0 is the initial height of sample 2, Δr is the diameter of sample 2 reduced due to water loss at a certain moment, r0 is the initial diameter of sample 2, and V0 is the volume of sample 2 before water loss shrinkage; F5. Calculation of void ratio and saturation: Based on equations 3 and 4, the void ratio e and saturation S of sample 2 under different equilibrium suction states during contraction are obtained. r : e=e0-ΔV(1+e0) / V0 Formula 3, S r =G s w / e formula 4, Where: e0 is the initial porosity of sample 2, Gs is the specific gravity of sample 2; F6. Considering volume change correction SWCC: Based on the soil-water characteristic curve without considering volume change correction and Equations 2 to 4, the soil-water characteristic curve considering volume change correction under various levels of matrix suction of sample 2 can be obtained.

[0036] Example 1 like Figures 1 to 10 As shown, based on the fully automatic high-precision deformable laterite soil-water characteristic curve measurement system of the present invention, a laterite SWCC measurement method is performed, and the specific steps are as follows: S100: The clay plate 3 is saturated and mounted on the top surface of the base Ⅰ4 inside the inner organic glass wall 28, and the deformable red clay sample 2 is placed on the clay plate 3, and then the space between the outer organic glass wall 1 and the inner organic glass wall 28 is filled with water. The sample 2 also undergoes the following pretreatment steps: S110. Refer to GB / T50123-2019 "Standard for Geotechnical Test Methods" to determine the air-dried moisture content of red soil: soak the soil at the initial moisture content and infiltrate it for 24 hours so that the moisture is evenly distributed in space.

[0037] S120. Saturate the filter paper and permeable stone of the same size as the ring knife in the vacuum saturator for 1 hour, and saturate the permeable stone of the pressure plate instrument.

[0038] S130, weigh the mass of the empty ring cutter, then apply vaseline on the inner wall of the ring cutter, weigh the total mass of the ring cutter and the vaseline, weigh the red clay obtained in A1, put it into the ring cutter for compaction to obtain sample 2, and ensure that the loss of sample 2 is less than 0.1% during compaction.

[0039] S140. Place a saturated filter paper and a saturated permeable stone on the upper and lower surfaces of sample 2, and then put it into the airless water in the vacuum saturator. Apply a vacuum value of more than 85 kPa for at least 48 hours. When no obvious bubbles are observed, the saturation process is considered to be completed.

[0040] S150, at this time, the initial saturation and initial volume water content of sample 2 can be calculated according to formula 1; Where: sat 、m w 、m s are the moisture content of sample 2 after saturation, the mass of water in sample 2, and the mass of soil particles in sample 2; ω0, ρ do are the initial moisture content and initial dry density of sample 2 when soaking soil; m w1 is the mass of water entering into sample 2 during the saturation stage; V is the volume of sample 2.

[0041] S200: After the sample 2 is placed, the computer 7 controls the air pressure control implementation device 5 to apply the first level of matrix suction to the pressure space, and the data acquisition system on the computer 7 measures and records the changes in the suction value, the amount of discharged water, and the amount of evaporated water in real time; when the amount of discharged water v<0.1g / 24h is detected, the suction value, the amount of discharged water, and the amount of evaporated water readings at this time are recorded, and at the same time, the top view and the side view of the sample 2 for the last time under this level of suction are collected.

[0042] S300: After S200 is completed, close the control valve II24, use the main flushing unit and the auxiliary flushing unit to reciprocately flush the pipeline and the clay plate 3 with bubbles, and record the volume of the discharged bubbles through the high-precision measuring tube II13 and the high-precision measuring tube I16. When the non-contact pipeline liquid level sensor II19 and the non-contact pipeline liquid level sensor I26 detect that the measuring tubes II22 and I23 have reached the highest water level, the main flushing unit and the auxiliary flushing unit stop the bubble flushing.

[0043] S400: Implement the suction path set in S200 and S300 to obtain a complete soil-water characteristic curve and the change data of the drainage volume and the size of the sample 2 over time, measure the change data of the water discharge volume of the sample 2 over time under different matrix suction conditions, and at the same time, the evaporation compensation device 8 records the evaporated water volume in real time.

[0044] S500: The recorded bubble volume is distributed and compensated to each level of suction to correct the evaporation amount, and then the saturation corresponding to the sample 2 at each moment is calculated based on the data of the initial water content, drainage, evaporation and bubble volume of the sample 2.

[0045] S600: According to the matrix suction collected by the computer 7 and the saturation of the sample 2 obtained in S500, the soil-water characteristic curve of the sample 2 without considering the volume change correction is obtained; at the same time, the top shooting device 30 and the side shooting device 31 respectively collect the top view and the side view of the sample 2 at a preset interval time, and then the area in the horizontal direction and the height in the vertical direction of the sample 2 are obtained based on the image recognition technology.

[0046] Assuming that sample 2 is a cylinder, if the SWCC of deformable red soil is to be considered, it also includes volume change correction based on the dehumidification shrinkage of sample 2. The specific idea is to take side view and top view of sample 2 after balance under each level of suction, calculate the top area and side area based on image recognition technology, and then obtain the SWCC of red soil corrected by volume change based on the basic mass-volume relationship of sample 2 and the aforementioned SWCC. In order to illustrate the reliability of the image recognition measurement device, a layer of tape is deliberately attached to the side wall of the cylindrical sample 2 to increase the difficulty of recognition. The specific steps are as follows: S610: The top camera 30 and the side camera 31 shoot the side view and the top view of the sample 2, and then import the view into MATLAB to convert it into a digital image, and then perform circular and rectangular cropping of the image based on morphological operations; It should be noted that if Figure 4 , Figure 5 , Figure 6 As shown, since the top view is less affected by the environment, morphological circular cropping is performed, and in step S610, it only needs to be converted into a binary image and the holes are filled before area measurement. The side view is cropped with morphological rectangles before area calculation.

[0047] S620: First, perform gamma correction on the side view after morphological cropping to obtain a gamma-corrected grayscale image (such as Figure 7 ); then perform Fourier transform and filtering on the grayscale image, and finally fill in the holes and process the non-connected small areas.

[0048] It should be noted that if Figure 7As shown in the figure, after gamma correction, the contrast between the black tape area and the side view image is enhanced, which is conducive to the subsequent image recognition. Gamma correction uses the fact that the human eye is more sensitive to dark areas than bright areas, increases the storage value range of dark areas, adjusts the nonlinear illumination intensity, and enriches the expression of image details. Its mathematical expression is as follows: Where: Vin is a non-negative real value, such as an image pixel, A is a constant, usually 1, the input and output range is [0, 1], γ<1, the light intensity becomes stronger, γ>1, the light intensity becomes weaker.

[0049] It should be noted that if Figure 8 As shown in the figure, the image after gamma correction, Fourier transform and filtering denoising is superimposed with the grayscale image to obtain a high-frequency enhanced grayscale image in the side view direction of the image; since most of the image content is concentrated in the low-frequency part, the noise represents the sudden change of the grayscale value on the image, corresponding to the high-frequency part of the image, so the Fourier transform is used to process the image after gamma correction, and the image is converted from the spatial domain to the frequency domain. The amplitude value of each pixel in the image can be obtained. The amplitude represents the size of the energy at each frequency. The energy value of the high-frequency part is set to 0, and the inverse Fourier transform is performed to remove the noise on the image. The mathematical expression of Fourier transform is as follows: Where: p = 0, 1, ..., M-1, q = 0, 1, ..., N-1; and are the forward transform kernel and inverse transform kernel respectively, m and n are the spatial domain sampling values, and F(p,q) is the frequency spectrum of the discrete signal f(x,y).

[0050] It should be noted that if Fig. 9 As shown, for the side view, due to the uneven soil surface, holes, tiny cracks, etc., there are many small-area objects in its binary image, and its threshold coincides with the threshold represented by the black tape. It is necessary to fill the image area and remove the small-area objects outside the image area.

[0051] S630: Use MATLAB measurement function to measure the top area and height of sample 2.

[0052] S640: Based on the diameter and height of the sample 2 at each level of suction measured above, the volume change of the sample 2 at the current equilibrium suction can be obtained. Assuming that the initial diameter of the sample 2 is r0' and the height is Z0', the volume change at a certain moisture content state during the water loss shrinkage process of the sample 2 is ΔV, and the volume strain Δ V / V0 is: Wherein: Δz is the height of sample 2 reduced due to water loss at a certain moment, Z0 is the initial height of sample 2, Δr is the diameter of sample 2 reduced due to water loss at a certain moment, r0 is the initial diameter of sample 2, and V0 is the volume of sample 2 before water loss and shrinkage.

[0053] S650: Based on the basic mass-volume relationship of soil, as shown in the following equations 3 and 4, the void ratio e and saturation S of sample 2 under different equilibrium suction states during shrinkage are obtained: r : e=e0-ΔV(1+e0) / V0 Formula 3, S r =G s w / e formula 4, Where: e0 is the initial porosity of sample 2, Gs is the specific gravity of sample 2.

[0054] S660: Based on the soil-water characteristic curve without considering the volume change correction and equations 2 to 4, the soil-water characteristic curve of sample 2 with considering the volume change correction under various levels of matrix suction can be obtained.

[0055] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system, characterized by: It includes a double-layer pressure chamber, an automatic bubble flushing device, and an image recognition and measuring device; The double-layer pressure chamber comprises an outer organic glass wall (1), a clay plate (3), a base I (4), an inner organic glass wall (28), and an organic glass cover (29); the outer organic glass wall (1) and the inner organic glass wall (28) are nested and fixed on the top surface of the base I (4); the space between the outer organic glass wall (1) and the inner organic glass wall (28) is filled with water; the organic glass cover (29) is detachably sealed and fixed on the top of the outer organic glass wall (1) and / or the inner organic glass wall (28); the interior of the inner organic glass wall (28) forms a closed pressure-bearing space by means of the base I (4) and the organic glass cover (29); the clay plate (3) is detachably fixed in a groove of the base I (4) inside the inner organic glass wall (28); and the organic glass cover (29) is connected to an air source (6) via an air pressure control implementation device (5); The side wall of the base I (4) is symmetrically provided with a liquid inlet I and a liquid inlet II connected to the bottom end of the pressure-bearing space. The automatic bubble flushing device comprises a main flushing unit and a secondary flushing unit. The main flushing unit comprises a gas collecting bottle II (18) connected to the liquid inlet II of the base I (4). A port of the gas collecting bottle II (18) away from the liquid inlet II is sequentially connected to a small water storage tank II (20), a measuring tube II (22), a non-contact pipeline liquid level sensor II (19) and a gas pressure control implementation device (5); the secondary flushing unit comprises a gas collecting bottle I (15) connected to the liquid inlet I of the base I (4). A port of the gas collecting bottle I (15) away from the liquid inlet I is sequentially connected to a small water storage tank I (21), a measuring tube I (23), a non-contact pipeline liquid level sensor I (26) and a gas pressure control implementation device (5); the gas pressure control implementation device (5) is respectively connected to a gas source (6) and a computer (7); A drainage detection device is also connected to the connecting pipeline between the gas collecting bottle II (18) of the main flushing unit and the liquid inlet II of the base I (4); the signal output end of the drainage detection device is electrically connected to the computer (7); the small water storage tank II (20) and the inlet end of the drainage detection device are respectively connected in series with a control valve I (27) and a control valve II (24); the signal output end of the non-contact pipeline liquid level sensor II (19) is electrically connected to the computer (7); A control valve III (25) is connected in series on the pipeline between the small water storage tank I (21) of the auxiliary flushing unit and the gas collecting bottle I (15), and the signal output end of the non-contact pipeline liquid level sensor I (26) is electrically connected to the computer (7); The computer (7) is also electrically connected to an evaporation compensation device (8); The image recognition and measurement device comprises a top shooting device (30) arranged on the top surface of the organic glass cover (29) and a side shooting device (31) arranged on the outside of the outer organic glass wall (1); the top shooting device (30) and the side shooting device (31) are respectively electrically connected to a computer (7) and can shoot a top view and a side view of the deformable red clay sample (2) in real time.

2. The fully automatic high-precision deformable laterite soil-water characteristic curve measurement system according to claim 1 is characterized in that: The top end of the gas collecting bottle II (18) is connected to a high-precision measuring tube I (16), and a water level regulating valve I (17) is arranged on the top of the high-precision measuring tube I (16); the top end of the gas collecting bottle I (15) is connected to a high-precision measuring tube II (13), and a water level regulating valve II (14) is arranged on the top of the high-precision measuring tube II (13).

3. The fully automatic high-precision deformable laterite soil-water characteristic curve measurement system according to claim 2 is characterized in that: The displacement detection device comprises a data acquisition balance II (10), a sealing cover (11), and a measuring bottle (12); the measuring bottle (12) is fixedly arranged on the data acquisition balance II (10); the sealing cover (11) is sealingly fixedly arranged on the opening at the top of the measuring bottle (12); the pipeline connected to the control valve II (24) passes through the sealing cover (11) and extends into the measuring bottle (12); the data acquisition balance II (10) is electrically connected to the computer (7).

4. The fully automatic high-precision deformable laterite soil-water characteristic curve measurement system according to claim 2 is characterized in that: The evaporation compensation device (8) comprises a measuring tube III and a base II. The measuring tube III is arranged vertically and the bottom end is embedded in a groove on the top surface of the base II. The base II is arranged on a data acquisition balance I (9). The data acquisition balance I (9) is electrically connected to a computer (7).

5. The fully automatic high-precision deformable laterite soil-water characteristic curve measurement system according to any one of claims 2 to 4, characterized in that: The high-precision measuring tube I (16), high-precision measuring tube II (13), measuring tube II (22) and measuring tube I (23) are all transparent glass tubes. The measuring tube II (22) and measuring tube I (23) are respectively vertically fixed on a plastic panel (33) with scales by U-shaped nails (32).

6. The fully automatic high-precision deformable laterite soil-water characteristic curve measurement system according to claim 6 is characterized in that: The scale length and measuring range of the high-precision measuring tube I (16) and the high-precision measuring tube II (13) are 10 cm and 0-100×0.0126 g respectively, and the scale length and measuring range of the plastic panel (33) are 100 cm and 0-1000×0.0196 g respectively.

7. A fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method, based on the fully automatic and high-precision deformable laterite soil-water characteristic curve measurement system according to any one of claims 3 to 6, characterized in that: It includes test preparation, data and image acquisition, bubble flushing, SWCC measurement without considering volume change correction, data processing, and SWCC measurement considering volume change correction. The specific steps are as follows: A. Test preparation: Saturate the clay plate (3) and install it on the top surface of the base I (4) inside the inner plexiglass wall (28), place the sample (2) of deformable red clay on the clay plate (3), and then fill the space between the outer plexiglass wall (1) and the inner plexiglass wall (28) with water; B. Data and image acquisition: After the sample (2) is placed, the computer (7) controls the air pressure control implementation device (5) to apply the first level of matrix suction to the pressure-bearing space, and the data acquisition system on the computer (7) measures and records the changes in the suction value, the amount of water discharged, and the amount of evaporated water in real time; when the amount of water discharged v<0.1g / 24h is detected, the suction value, the amount of water discharged, and the amount of evaporated water readings at this time are recorded, and at the same time, the top view and the side view of the sample (2) at the last time under this level of suction are collected; C. Bubble flushing: After step B is completed, the control valve II (24) is closed, and the main flushing unit and the auxiliary flushing unit are used to reciprocately flush the pipeline and the clay plate (3) with bubbles, and the volume of the discharged bubbles is recorded by the high-precision measuring tube II (13) and the high-precision measuring tube I (16). When the non-contact pipeline liquid level sensor II (19) and the non-contact pipeline liquid level sensor I (26) detect that the measuring tube II (22) and the measuring tube I (23) have reached the highest water level, the main flushing unit and the auxiliary flushing unit stop the bubble flushing; D. SWCC measurement without considering volume change correction: Suction is applied according to the suction path set in step B and step C, while the computer (7) collects the data of the change of the discharged water volume over time, and the evaporation compensation device (8) records the evaporation water volume and the top view and side view of the sample (2) after the suction balance of different matrices; E. Data processing: The recorded bubble volume is distributed and compensated to each level of suction to correct the evaporation amount, and then the saturation corresponding to each moment of the sample (2) is calculated based on the data of the initial water content, drainage, evaporation, and bubble volume of the sample (2); F. SWCC without considering volume change correction: The matrix suction collected by the computer (7) and the saturation of the sample (2) obtained in step E are matched one by one, that is, the soil-water characteristic curve of the sample (2) without considering volume change correction is obtained; at the same time, the top shooting device (30) and the side shooting device (31) respectively collect the top view and the side view of the sample (2) at a preset interval time, and then the area in the horizontal direction and the height in the vertical direction of the sample (2) are obtained based on image recognition technology.

8. The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method according to claim 7 is characterized in that: The sample (2) in step A is also subjected to the following pretreatment steps: A1. Refer to GB / T50123 "Standard for Geotechnical Test Methods" to determine the air-dried moisture content of red soil: soak the soil at the initial moisture content and soak for 24 hours so that the moisture is evenly distributed in space; A2. Saturate the filter paper and permeable stone of the same size as the ring knife in the vacuum saturator for 1 hour, and saturate the permeable stone of the pressure plate instrument; A3, weigh the mass of the empty ring cutter, then apply vaseline on the inner wall of the ring cutter, weigh the total mass of the ring cutter and the vaseline, weigh the red clay obtained in A1, put it into the ring cutter and compact it to obtain sample (2), and ensure that the loss of sample (2) is less than 0.1% during compaction; A4. Place a saturated filter paper and a saturated permeable stone on the upper and lower surfaces of the sample (2), and then place it in the airless water in the vacuum saturator. Apply a vacuum value of more than 85 kPa for at least 48 hours. When no obvious bubbles are observed, the saturation process is considered to be complete. A5. At this time, the initial saturation and initial volumetric water content of sample (2) can be calculated according to formula 1; Where: sat 、m w 、m s are the moisture content of sample (2) after saturation, the mass of water in sample (2), and the mass of soil particles in sample (2); ω0, ρ do are respectively the initial moisture content and initial dry density of the sample (2) when the soil is soaked in step A3; m w1 is the mass of water entering the sample (2) during the saturation stage of the vacuum pumping in step A4; V is the volume of the sample (2).

9. The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method according to claim 7, characterized in that: The method of obtaining the area in the horizontal direction and the height in the vertical direction of the sample (2) based on the image recognition technology includes the steps of image preprocessing, image processing, and geometric parameter measurement, and each step is specifically as follows: F1. Image preprocessing: The top camera (30) and the side camera (31) respectively capture the top view and the side view of the sample (2), and then import the views into MATLAB to convert them into digital images, and then perform circular and rectangular cropping of the images based on morphological operations; F2, image processing: First, perform gamma correction on the cropped image of F1 to obtain a gamma-corrected grayscale image; then perform Fourier transform and filtering on the grayscale image, and finally fill in the holes and process the non-connected small areas; F3. Geometric parameter measurement: Use the measurement function of MATLAB to measure the top area and height of the sample (2).

10. The fully automatic and high-precision deformable laterite soil-water characteristic curve measurement method according to claim 9, characterized in that: The sample (2) is a cylinder. The soil-water characteristic curve corrected by volume change is not considered in step F. If the volume change during the dehumidification process of red soil is to be corrected, the specific size of the sample (2) during the dehumidification process is obtained in combination with an image recognition measurement device. The specific steps are as follows: F4. Calculation of sample volume strain: Based on the diameter and height of the sample (2) at each level of suction measured above, the volume change of the sample (2) at the current equilibrium suction can be obtained. Assume that the initial diameter of the sample (2) is r0 ’ And the height is Z0 ’ The volume change of sample (2) at a certain moisture content during the shrinkage process is ΔV, and the volume strain Δ V / V0 is: Wherein: Δz is the height of the sample (2) reduced due to water loss at a certain moment, Z0 is the initial height of the sample (2), Δr is the diameter of the sample (2) reduced due to water loss at a certain moment, r0 is the initial diameter of the sample (2), and V0 is the volume of the sample (2) before water loss shrinkage; F5. Calculation of void ratio and saturation: Based on equations 3 and 4, the void ratio e and saturation S of sample (2) under different equilibrium suction states during shrinkage are obtained: r : e=e0-ΔV(1+e0) / V0 Formula 3, S r =G s w / e formula 4, Where: e0 is the initial porosity of sample (2), Gs is the specific gravity of sample (2); F6. SWCC with volume change correction: Based on the soil-water characteristic curve without volume change correction and equations 2 to 4, the soil-water characteristic curve with volume change correction for sample (2) at various levels of matrix suction can be obtained.

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