CN115524256A - Cohesive soil drying shrinkage and water-soil characteristic curve combined determination device and method - Google Patents
Cohesive soil drying shrinkage and water-soil characteristic curve combined determination device and method Download PDFInfo
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- 239000002689 soil Substances 0.000 title claims abstract description 178
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Abstract
The invention relates to a cohesive soil drying shrinkage and water-soil characteristic curve combined determination device and a method, which comprises the following steps: camera, fixed bolster, high range tensiometer, upper and lower base, sealed lid, revolving stage, electronic scale, data acquisition equipment and the examination spare that awaits measuring. When measuring this curve, the examination test piece that awaits measuring is placed on the base, and the pedestal mounting has high range tensiometer, and test piece, base and revolving stage are located the electronic scale. The discontinuous dry shrinkage process of the test piece is controlled through the sealing cover, after the suction force of the test piece reaches a stable state, the suction force of the matrix is measured through the high-range tensiometer, the mass of the test piece is measured through the electronic scale, the water content of the test piece is inversely calculated, the volume of the test piece is measured through a 360-degree photo of the test piece shot by the camera through the rotating table, and the porosity and the saturation are calculated. Drawing a drying shrinkage curve by taking the water content as a horizontal axis and the porosity as a vertical axis; the water-soil characteristic curve is drawn by taking the substrate suction as a horizontal axis and taking the saturation as a vertical axis. The invention solves the difficult problem of joint measurement of cohesive soil drying shrinkage and water-soil characteristic curve.
Description
Technical Field
The invention relates to the technical field of soil engineering property testing, in particular to a cohesive soil drying shrinkage and water-soil characteristic curve combined determination device and method, which are suitable for simultaneous determination of cohesive soil drying shrinkage and water-soil characteristic curve.
Background
The desiccation and water-soil characteristic curve is an important reference for describing the hydraulic characteristics of soil. The cohesive soil shrinks after being dried and dehydrated and causes obvious surface settlement or uneven deformation, and even generates soil body cracking phenomenon in serious conditions. The overall settlement, uneven deformation, drying shrinkage cracks and the like of the actual building can obviously reduce the safety and the service life of the actual building. The volume change characteristic of cohesive soil during drying and water loss is generally described by a drying shrinkage curve. The water-soil characteristic curve is widely used for researching water distribution and migration in soil, predicting soil permeability coefficient, strength characteristics and the like. The water-soil characteristic curve should be used in combination with the drying shrinkage curve. The traditional dry shrinkage curve measuring methods (including a vernier caliper method, a displacement sensor method, an air sphere method based on the Archimedes principle, a paraffin method and the like) have the problems of low volume measuring precision, poor applicability and the like. The traditional method for measuring the water-soil characteristic curve comprises the following steps: the axis translation method, the filter paper method, the hygrometer method, and the like. However, these methods are time consuming and labor intensive and have low accuracy. In addition, CN208588651U, a full-automatic measurement system of a complete soil-water characteristic curve, CN108508044B, a measurement apparatus and method of a soil characteristic curve under dry-wet cycle, can only realize the measurement of a water-soil characteristic curve, and lacks the dry shrinkage curve measurement capability. The above drying shrinkage and water-soil characteristic curve measurements must be made individually (i.e., only one curve at a time) using multiple test pieces having the same stress history. It is difficult to prepare a plurality of test pieces having exactly the same stress history. Therefore, the use of test pieces with different stress histories directly affects the measurement accuracy and efficiency of the dry shrinkage and water-soil characteristic curve. The volume change and the matrix suction development rule of the viscous soil body in the drying and shrinking process are mastered, and the method has important significance and engineering value for the reasonable application of the soil body in the actual engineering.
Disclosure of Invention
The invention aims to provide a testing device and a testing method which are simple in structure, accurate and efficient and solve the problems that the measurement accuracy of a drying shrinkage curve of cohesive soil and a water-soil characteristic curve is low and the time is long.
In order to solve the technical problems, the invention provides the following technical scheme: based on single test piece, through interrupting evaporation test come simultaneous measurement stickness soil's dry shrinkage and water-soil characteristic curve, specifically do: placing a saturated cohesive soil test piece to be tested on a base, covering the test piece with a sealing cover, and realizing discontinuous dry shrinkage of the test piece by controlling different lengths of time that the test piece is exposed in the air in the test process; the base is divided into an upper part and a lower part, wherein 3 holes are formed in the upper base and the lower base, 3 saturated and checked high-range tensiometers are respectively distributed in the holes, and the bottom surface of the cohesive soil test piece is contacted with the top surfaces of the 3 high-range tensiometers; the spring is arranged at the bottom of the tensiometer, the test piece is always in contact with the high-range tensiometer through the spring, and the suction force of the cohesive soil test piece matrix in the test process is directly measured through the tensiometer; a rotating platform capable of rotating 360 degrees is arranged below the base; the rotating platform, the upper base, the lower base, the high-range tensiometer, the cohesive soil test piece and the sealing cover are placed on the electronic scale, the mass change of the test piece in the test process is recorded in real time through the electronic scale, and the water content of the test piece at different moments is further calculated back according to the final water content after the test is finished; the upper base is provided with 12 measurement control points, the side surface and the top surface of the test piece are provided with two fixed cameras, and the reconstruction and the volume measurement of a three-dimensional model of the test piece are realized by taking pictures at different moments in the test process; and calculating the porosity and saturation of the soil body according to the volume measurement result and by combining the water content and the relative density of the soil body, and drawing a dry shrinkage and water-soil characteristic curve.
As an optimal technical scheme of the cohesive soil drying shrinkage and water-soil characteristic curve combined measuring device, the high-range tensiometer is used for measuring the suction force of a soil matrix in real time, the measuring range is 1.5MPa, and the soil matrix is saturated and checked before the test is started.
As a preferred technical scheme of the device for jointly measuring the drying shrinkage of the cohesive soil and the water-soil characteristic curve, the sealing cover is a black plastic cover, and the inner side of the sealing cover is sprayed with an antifogging agent.
As an optimal technical scheme of the cohesive soil dry shrinkage and water-soil characteristic curve combined measuring device, the base is divided into an upper part and a lower part, a 45-degree slope is arranged at the edge of the upper base, 12 measuring control points are distributed on the slope, the base is provided with 3 mounting holes of a high-range tensiometer, and a spring is arranged at the bottom of each hole.
As a preferred technical scheme of the device for jointly measuring the drying shrinkage of the cohesive soil and the water-soil characteristic curve, the to-be-tested piece is cylindrical, and the surface of the to-be-tested piece is covered with a layer of paint speckles.
As a preferred technical scheme of the cohesive soil dry shrinkage and water-soil characteristic curve combined determination device, the method comprises the following steps of system setting, test piece preparation, system assembly, stable-free evaporation circulation and final water content determination so as to realize the dry shrinkage and water-soil characteristic curve measurement of cohesive soil; A. the system is set, the cameras check system parameters of 2 cameras, specifically including physical size of an image sensor, central point position, pixel number, lens focal length, related lens distortion parameters and saturation and checking high-range tensiometer, 12 control points are set and measured on the slope surface of an upper base, and a three-dimensional Cartesian coordinate system is established by combining photogrammetry technology; B. preparing a test piece, namely preparing a saturated cylindrical cohesive soil test piece (with the height of 25mm and the diameter of 70 mm), and spraying mist paint on the top surface and the 360-degree side surface of the saturated cylindrical cohesive soil test piece to prepare speckles; C. the system assembly comprises the steps that saturated clay is coated on a sensing surface of a high-range tensiometer to enable the sensing surface to be in a saturated state, a cable penetrates through a spring, penetrates out of a hole of a lower base and is connected with a data acquisition instrument, an upper base is placed on the lower base, a cylindrical cohesive soil test piece is installed on the base, the base and the test piece are placed on a rotating table, then the base and the test piece are placed on an electronic scale together with the rotating table and are integrally moved to a table top of a camera fixing support, and finally a sealing cover is covered on the cohesive soil test piece; D. stable-free evaporation circulation, after the substrate suction of the test piece reaches a stable state, reading the substrate suction value through a data acquisition instrument, and measuring and recording the system mass m through an electronic scale i Then, the sealing cover is removed and the rotating table is opened, pictures of the top surface and the side surface of the test piece at different rotation angles are shot through two cameras, volume measurement is carried out based on the pictures, specifically, all the pictures are processed and analyzed through photogrammetry software to obtain all the camera positions and azimuth angles, photogrammetry analysis is carried out, the camera positions at different rotation angles are calculated in a reverse mode by combining an established coordinate system, the pictures shot at positions close to the cameras are paired, each camera is analyzed on the shot pictures based on a 3D-DIC technology to generate a two-dimensional pixel point cloud covering the side surface of the test piece, and the point cloud of the surface of the cohesive soil test piece is calculated by combining the two-dimensional pixel point cloud, camera checking results, corresponding camera positions and a front intersection technologyCombining point clouds on the top surface and the side surface of the test piece, then carrying out triangular meshing and calculating the volume V of the cohesive soil test piece i ；
In the formula: v i Is the volume of the test piece, V ij J mesh in the triangular mesh established for the point cloud of the test piece and the volume of a tetrahedron formed by combining the center point of the bottom surface of the test piece, wherein n is the total number of the triangular meshes, and P is the total number of the triangular meshes o Center point position of specimen bottom surface, P 1j ，P 2j ，P 3j The positions of the three vertices in the jth mesh,
is the vector formed by the center point of the bottom surface and the three vertexes of the jth grid. After the cohesive soil test piece is freely evaporated for a section, covering a sealing cover on the cohesive soil test piece, and repeating the step until the volume of the cohesive soil test piece is kept constant; and (3) final water content determination: taking down the cohesive soil test piece from the base, and weighing the total mass m if Then measuring the dry soil mass m by a drying method d And final water content w f (ii) a Data analysis and curve plotting: the water content of the cohesive soil test piece at different moments is inversely calculated through the final mass and the water content of the cohesive soil test piece and the mass change recorded in the test process,
in the formula: w is a i Is the water content of a cohesive soil test piece, w f Is the final water content m of the cohesive soil test piece at the end of the test i Total mass, m, of test piece and volume and suction measuring device if Is the total mass of the test piece and the volume and suction measuring device at the end of the test, is the mass of the test piece at the end of the test, m d The mass of the test piece after drying. According to the relative density d of the soil sample s Calculating and obtaining the porosity e of the cohesive soil test piece at different moments by combining the results of the water content, the mass and the volume i And saturation S i ，
e i Porosity of the test piece, V i Is the specimen volume, d s Is the relative density of the soil, p w Is the density of water, S i Is the saturation of the test piece. Drawing a soil body dry shrinkage curve by taking the water content of the cohesive soil test piece as a transverse axis and the porosity as a vertical axis; and drawing a water-soil characteristic curve of the soil body by taking the substrate suction as a horizontal axis and taking the saturation as a vertical axis. Drawing a soil body dry shrinkage curve by taking the water content of the test piece as a transverse axis and the porosity as a vertical axis; and drawing a water-soil characteristic curve of the soil body by taking the suction of the matrix as a horizontal axis and the saturation as a vertical axis.
The invention provides a device and a method for measuring cohesive soil drying shrinkage and water-soil characteristic curve through an intermittent evaporation test, which are used for simultaneously measuring the drying shrinkage and water-soil characteristic curve of the cohesive soil under different initial dry density conditions, and compared with the prior art, the device can achieve the following beneficial effects: the drying shrinkage and water-soil characteristic curve of the cohesive soil can be simultaneously measured through one test piece in one test, the influence of different test pieces on the measurement result due to different stress histories can be effectively removed by using the same test piece, and the measurement precision of the drying shrinkage and water-soil characteristic curve is improved; meanwhile, the measurement efficiency of the water-soil characteristic curve is obviously improved by using the intermittent evaporation test to measure the water-soil characteristic curve, and the time required by one intermittent evaporation test is generally less than 24 hours; in addition, the adoption of discontinuous dry shrinkage can improve the uniformity of internal and external deformation of the test piece in the dry shrinkage process and obviously reduce the probability of crack generation; finally, the speckle is used, and the photogrammetry and the 3D-DIC technology are combined, so that the top surface and the side surface of the test piece can be finely reconstructed, and the volume measurement precision is improved.
Drawings
FIG. 1 is a schematic structural view of the cohesive soil drying shrinkage and water-soil characteristic curve testing device;
FIG. 2 is a schematic view of a sealing cover of the cohesive soil drying shrinkage and water-soil characteristic curve testing device;
FIG. 3 is a schematic view of an upper base of the testing device for drying shrinkage and water-soil characteristic curve of cohesive soil;
FIG. 4 is a schematic view of a lower base of the testing device for drying shrinkage and water-soil characteristic curve of cohesive soil;
1, preparing a cohesive soil test piece; 2. an upper base; 3. a lower base; 4. a high range tensiometer; 5. a camera; 6. a camera; 7. measuring a control point; 8. a sealing cover; 9. an electronic scale; 10. a spring; 11. a camera fixing bracket; 12. a rotating table; 13. and (3) data acquisition equipment.
Detailed Description
The technical solution of the test device for drying shrinkage and water-soil characteristic curve of cohesive soil is described below by referring to the accompanying drawings and specific examples, and it should be understood that the technical solution described herein is only used for illustrating and explaining the test device for drying shrinkage and water-soil characteristic curve of cohesive soil, and is not used for limiting the test device for drying shrinkage and water-soil characteristic curve of cohesive soil.
Referring to fig. 1, the invention provides a test device and a test method for cohesive soil drying shrinkage and water-soil characteristic curve. The test device comprises: the tension measuring device comprises a high-range tensiometer 4, an upper base 2, a measuring control point 7 positioned at the edge of the upper base 2, a lower base 3, a sealing cover 8, an electronic scale 9, a camera 5 and a fixing bracket 11 thereof.
The stickness soil test piece 1 is placed on the top surface of the upper base 2, and is contacted with the upper surface of the high-range tensiometer 4, and the dry shrinkage of the stickness soil test piece 1 or the suction balance process is controlled and realized by removing or covering the sealing cover 8 respectively.
High-range tensiometer 4 places in the three hole of last base 2 and lower base 3, three hole is the article font and distributes, measure the matrix suction of stickness soil test piece different positions respectively, in the hole of lower base 3, the bottom of high-range tensiometer 4 is furnished with spring 10, spring 10 can guarantee that the test piece bottom surface keeps the elastic contact state with the perception face (being the top surface) of high-range tensiometer 4 all the time, the matrix suction that high-range tensiometer 4 measured is read in real time by data acquisition equipment 13, under the stable condition of matrix suction reading of three high-range tensiometer 4, regard its average value as the matrix suction representative value of stickness soil test piece 1.
The water content of the cohesive soil test piece 1 at different moments is obtained by back calculation of the mass read by the electronic scale 9 and the water content measurement result at the end of the test.
The volume of stickness soil test piece 1 is shot the photo analysis by camera 5 that is located the test piece top and camera 6 of side respectively and is obtained, when shooting the photo, start revolving stage 12, shoot the photo of complete stickness soil test piece 1 top under different rotation angles through camera 5, camera 6 shoots the side photo of stickness soil test piece 1, then combine to measure control point 7 and photogrammetry technique can calculate the position of camera 5 and camera 6 when the photo is shot, speckle based on test piece surface and side, combine 3D-DIC technique and camera position and generate the point cloud that represents 1 top surface of stickness soil test piece and bottom surface, then generate the triangular mesh and further calculate the volume of stickness soil test piece 1 at different moments according to the point cloud.
According to the volume of the cohesive soil test piece 1 at different moments, the relative density of soil and the dried mass, the porosity of the cohesive soil test piece 1 at different moments can be calculated, and then the dry shrinkage curve of the cohesive soil test piece 1 can be drawn by combining the water content; according to the mass of the cohesive soil test piece 1 at different moments, the relative density, the volume and the final water content of soil and the dried mass, the saturation of the cohesive soil test piece 1 at different moments can be calculated, and then the water-soil characteristic curve of the cohesive soil test piece 1 can be drawn by combining the suction force of a matrix.
Specifically, as shown in fig. 1, the device and the method for simultaneously determining the drying shrinkage and the water-soil characteristic curve of the cohesive soil through the intermittent evaporation test provided by the invention take remolding of saturated cohesive soil as an example, and when the device is used, the measurement of the drying shrinkage and the water-soil characteristic curve comprises the following specific steps:
A. the two cameras used for volume measurement are respectively checked to obtain basic camera parameters (including pixel number, physical size, focal length, principal point position, radial distortion parameter, and eccentric distortion parameter).
B. The measurement control points are adhered to the slope (36, which can be made of waterproof plastic paper and evenly distributed on the slope) and the top surface (12 and evenly distributed on the top surface) of the upper base 2, a three-dimensional Cartesian coordinate system is established through photogrammetry technology and real physical dimensions, the top surface of the upper base 2 is set as an x-y plane of the coordinate system, the origin of the coordinate system is set as the central point of the upper base, the z axis is vertical upward, and the three-dimensional positions of all the control points on the slope of the upper base 2 are obtained based on the coordinate system and photogrammetry analysis results.
C. The three high-range tensiometers 4 are respectively saturated and checked, cables of the high-range tensiometers 4 penetrate through the springs 10 and then penetrate through the lower base 3, then the upper base 2 is installed, the upper parts of the three high-range tensiometers 4 are located in holes of the upper base 2, then saturated cohesive soil is smeared on the sensing surface (namely the top surface) of the high-range tensiometers 4 to maintain the saturation state of the tensiometers, the cables of the tensiometers are connected with the data acquisition instrument, the bases (comprising the upper base 2, the lower base 3 and the high-range tensiometers 4) are placed on the rotating platform 12, and then the rotating platform 12 is connected with the rotating platform 12 and placed on the electronic scale and integrally moved to the table top of the camera fixing support 11.
D. Saturated stickness soil test piece 1 is prepared, then the initial dry density of stickness soil test piece 1 is changed through the one-dimensional consolidation apparatus, oil spray paint mist is formed on the top surface and the side surface of stickness soil test piece 1, speckles required for volume measurement are formed, a layer of vaseline is smeared on the top surface of the upper base 2, and the stickness soil test piece 1 is placed on the top surface of the upper base 2 and the bottom surface of the stickness soil test piece 1 is contacted with the sensing surface of the high-range tensiometer 4.
E. Spraying antifogging agent on the inner surface of the sealing cover 8 to cover the sealing cover 8 on the cohesive soil test piece 1, and recording the substrate suction readings of the three high-range tensiometers 4 and the whole mass m displayed by the electronic scale 9 after the substrate suction readings of the three high-range tensiometers 4 are stable i Then, the sealing cover 8 is removed, the rotating table 12 is opened, and the top and side surfaces of the specimen are photographed at different rotation angles by the camera 5 and the camera 6 (4 top surfaces and 20 side surfaces)Covering 360 deg. of the full side).
F. Removing the sealing cover 8 to enable the cohesive soil test piece 1 to be in a free evaporation state, monitoring the substrate suction readings of three Gao Liangcheng tensiometers 4, covering the sealing cover 8 to enable the substrate suction of the cohesive soil test piece 1 to tend to be stable after the substrate suction rises to a certain extent (for example, 20kPa is increased), reading the substrate suction through the data acquisition equipment 13 after the suction is stable, taking the average value of the three substrate suction readings as the substrate suction of the test piece under the stable condition, reading the mass through the electronic scale 9, then removing the sealing cover 8, carrying out photo shooting required by volume measurement, repeating the steps until the volume of the cohesive soil test piece 1 reaches the stable state, weighing the mass of the cohesive soil test piece 1, and measuring the water content of the cohesive soil test piece 1 at the end of the test.
G. For the photo obtained by each photo shooting, performing photogrammetric analysis, performing inverse calculation on the camera positions at different rotation angles by combining a coordinate system established by a measurement control point 7, matching the photos shot at the positions close to the cameras (taking 20 photos of the side surface of the test piece as an example, matching is performed by using the photos 1, 2,2, 3,3, 4, … …,19, 20 and 1), performing 3D-DIC analysis on the corresponding photo by each camera to generate a two-dimensional pixel point cloud covering the side surface of the test piece, obtaining the three-dimensional position of the point cloud on the surface of the test piece by combining the two-dimensional pixel point cloud, a camera check result and the corresponding camera position through a front intersection technology, obtaining the three-dimensional point cloud on the top surface of the test piece by adopting a similar method, combining the point clouds on the top surface and the side surface of the test piece, performing triangular grid division, and calculating the volume V (V) of the test piece at the moment through a formula 1 i 。
In the formula: v i Is the volume of the test piece, V ij The volume of a tetrahedron formed by the jth grid in the triangular grids established for the point cloud of the test piece and the central point of the bottom surface of the test piece is combined, n is the total number of the triangular grids, P is the total number of the triangular grids o Center point position of specimen bottom surface, P 1j ，P 2j ，P 3j Is as followsThe positions of three vertices in the j meshes,
a vector formed by a bottom surface center point and three vertexes of the jth grid;
H. and (4) inversely calculating the water content of the test piece at different moments by combining the measurement result of the electronic scale 9 and the final water content through a formula 2.
In the formula: w is a i Is the water content of the test piece, w f The final water content of the test piece at the end of the test, m i Total mass, m, of test piece and volume and suction measuring device if Is the total mass of the test piece and the volume and suction measuring device at the end of the test, is the mass of the test piece at the end of the test, m d The mass of the test piece after drying.
I. And (3) respectively calculating the porosity and the saturation of the test piece through formulas 3 and 4 by combining the relative density, the water content, the mass and the volume of the test piece.
e i Porosity of the test piece, V i Is volume, d s Is the relative density of the soil, p w Is the density of water.
S i Is the saturation of the test piece.
J. Drawing a soil body drying shrinkage curve by taking the water content of the test piece as a transverse axis and the porosity as a vertical axis; and drawing a water-soil characteristic curve of the soil body by taking the substrate suction as a horizontal axis and taking the saturation as a vertical axis.
The above description is illustrative, and the embodiments of the present invention are not limited thereto, and any person skilled in the art should be able to cover the technical scope of the present invention, the technical solutions according to the present invention and the inventive concept with equivalent substitutions or changes. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the illustrated embodiments. On the premise of not departing from the basic technical idea of the cohesive soil drying shrinkage and water-soil characteristic curve testing device, the above preferred embodiment can also make other various modifications, substitutions or combinations, and the obtained other embodiments all fall within the protection scope of the cohesive soil drying shrinkage and water-soil characteristic curve testing device.
Claims (6)
1. A cohesive soil drying shrinkage and water-soil characteristic curve combined measuring device and a method are characterized in that the device mainly comprises: 2 cameras that are used for the photo to shoot and fixed bolster, 3 high-range tensiometer, upper and lower base, sealed lid, revolving stage, electronic scale, data acquisition equipment and the examination spare that awaits measuring.
2. The cohesive soil drying shrinkage and water-soil characteristic curve combined measuring device as claimed in claim 1, wherein 3 high-range tensiometers with the measuring range of 1.5MPa are used for measuring the substrate suction force.
3. The cohesive soil drying shrinkage and water-soil characteristic curve joint measurement device as claimed in claim 1, wherein the sealing cover for controlling the intermittent evaporation process of the test piece is black, and internally sprays the anti-fogging spray.
4. The apparatus as claimed in claim 1, wherein the base is divided into an upper portion and a lower portion, the upper portion has a 45 ° slope at the edge, 12 measurement control points are disposed on the slope, the base has 3 mounting holes for high-range tensiometer, and the bottom of the hole has a spring.
5. The apparatus for combined determination of drying shrinkage and water-soil characteristic curve of cohesive soil as claimed in claim 1, wherein the test piece is cylindrical and characterized by a layer of paint speckles covering the surface.
6. A cohesive soil drying shrinkage and water-soil characteristic curve combined determination device and a method are characterized in that the method for realizing the combined determination of the drying shrinkage and the water-soil characteristic curve mainly comprises the following steps: A. the method comprises the following steps of setting a system, checking system parameters of 2 cameras by the cameras, specifically comprising physical size of an image sensor, a central point position, pixel number, lens focal length and related lens distortion parameters, setting 12 measurement control points on a slope surface of an upper base and establishing a three-dimensional Cartesian coordinate system by combining a photogrammetry technology, and setting a saturation and checking high-range tensiometer; B. preparing a test piece, namely preparing a saturated cylindrical cohesive soil test piece, and spraying mist paint on the top surface and the 360-degree side surface of the saturated cylindrical cohesive soil test piece to prepare speckles; C. the system assembly comprises the steps that saturated clay is coated on a sensing surface of a high-range tensiometer to enable the sensing surface to be in a saturated state, a cable penetrates through a spring, penetrates out of a hole of a lower base and is connected with a data acquisition instrument, an upper base is placed on the lower base, a cylindrical cohesive soil test piece is installed on the base, the base and the test piece are placed on a rotating table, then the base and the test piece are placed on an electronic scale together with the rotating table and are integrally moved to a table top of a camera fixing support, and finally a sealing cover is covered on the cohesive soil test piece; D. the method comprises the steps of performing stable-free evaporation circulation, reading a substrate suction value through a data acquisition instrument after the substrate suction of a test piece reaches a stable state, measuring and recording the system mass through an electronic scale, then removing a sealing cover and opening a rotating table, shooting pictures of the top surface and the side surface of the test piece at different rotating angles through two cameras and performing volume measurement based on the pictures, specifically, processing and analyzing all the pictures through photogrammetry software to obtain all the camera positions and azimuth angles, performing photogrammetry analysis, calculating the camera positions when shooting at different rotating angles in a reverse mode by combining an established coordinate system, pairing the pictures shot at the positions close to the cameras, analyzing the shot pictures by each camera based on a 3D-DIC (three-dimensional digital computer) technology, generating a two-dimensional pixel point cloud covering the side surface of the test piece, calculating the three-dimensional position of the point cloud on the surface of the cohesive soil test piece by combining the two-dimensional pixel point cloud and camera checking results and corresponding camera positions and a forward intersection technology, combining the top surface point cloud of the test piece and the side surface of the test piece together, performing triangular grid division and calculating the volume of the cohesive soil test piece, covering the sealing cover after the cohesive soil test piece is freely evaporated for a section, and repeating the step until the cohesive soil volume is kept constant; E. measuring the final water content, taking down the cohesive soil test piece from the base, weighing the total mass, and measuring the dry soil mass and the final water content by using a drying method; F. data analysis and curve drawing, inversely calculating the water contents of the cohesive soil test piece at different moments through the final mass and the water content of the cohesive soil test piece and the mass change recorded in the test process, calculating and obtaining the porosity and the saturation of the cohesive soil test piece at different moments according to the relative density of a soil sample and combining the water content, the mass and the volume result, and drawing a dry shrinkage curve of a soil body by taking the water content of the cohesive soil test piece as a transverse axis and the porosity as a vertical axis; and drawing a water-soil characteristic curve of the soil body by taking the substrate suction as a horizontal axis and taking the saturation as a vertical axis.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117686686A (en) * | 2023-12-13 | 2024-03-12 | 水利部交通运输部国家能源局南京水利科学研究院 | System and method for monitoring clay shrinkage crack development in drought environment |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117686686A (en) * | 2023-12-13 | 2024-03-12 | 水利部交通运输部国家能源局南京水利科学研究院 | System and method for monitoring clay shrinkage crack development in drought environment |
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