Frozen soil column test device and method based on thermoelectric cooling and DIC monitoring

Abstract

The present invention discloses a frozen soil column test device and method based on thermoelectric cooling and DIC monitoring. The device includes a transparent soil column container, a temperature control system, and a digital image acquisition system. The transparent soil column container is used to fill the soil column sample, and the transparent soil column tube is composed of two double-walled acrylic semi-cylinders. This allows the frozen soil freezing process and frost heave behavior to be visualized, facilitating real-time monitoring and analysis. During the experiment, the temperature control system accurately adjusts the internal and external temperatures to simulate the frozen soil freezing process. The digital image acquisition system uses a high-resolution camera to capture real-time images of the soil column surface. Combined with digital speckle, digital image correlation technology is used to monitor and analyze the amount of soil frost heave and the position of the freezing front in real time, capable of highly accurately measuring the soil frost heave characteristics and the dynamic changes of the freezing front.

Description

Technical Field

[0001] The present invention relates to the technical field of soil frost heave and freezing front testing, in particular to a frozen soil column testing device and method based on thermoelectric cooling and DIC monitoring. Background Art

[0002] In the study of frozen soil mechanics, the frost heave deformation characteristics of frozen soil, the freezing process, and the evolution of the freeze front are core research issues. However, existing frozen soil experimental equipment typically uses traditional cooling methods such as liquid nitrogen and compressors, which have many limitations. First, the temperature control of traditional cooling systems is imprecise, making it difficult to finely adjust the cooling rate and temperature gradient. This leads to uneven temperatures during the freezing process, affecting the frost heave deformation and the evolution of the freeze front, and thus the accuracy of experimental results. Furthermore, these traditional devices are generally unable to dynamically adjust the cooling rate, making it difficult to simulate the actual cooling process under different frozen soil environments. Second, existing experimental equipment typically relies solely on point-based data acquisition devices such as temperature sensors and pressure sensors, making it difficult to dynamically monitor frozen soil samples throughout the freezing process. In particular, there is a lack of comprehensive real-time monitoring of soil deformation, frost heave, and the evolution of the freeze front during the freezing process. These technical limitations hinder in-depth research on frozen soil behavior, especially in the precise monitoring of the freeze front and frost heave deformation, making it difficult to meet the needs of in-depth research on the mechanical properties of frozen soil, frost heave behavior, and the evolution of the freeze front. Summary of the Invention

[0003] The purpose of the present invention is to provide a frozen soil column test device and method based on thermoelectric cooling and DIC monitoring, which can accurately control the cooling rate and temperature gradient and monitor the deformation, frost heave and freezing front evolution of frozen soil samples in real time and comprehensively.

[0004] The technical solution of the present invention is:

[0005] A frozen soil column test device based on thermoelectric cooling and DIC monitoring comprises: a transparent soil column container, comprising: a water replenishing bin base, the top surface of which is provided with a plurality of circular holes; a permeable stone, arranged on the top of the water replenishing bin base; a transparent soil column tube, one end of which is sleeved on the water replenishing bin base, and is used to accommodate a soil column sample, the soil column sample is located above the permeable stone, the transparent soil column tube comprises two double-layered acrylic semi-cylinders connected by fastening parts, the hollow space of the double-layer wall of each double-layered acrylic semi-cylinder is filled with a transparent heat-insulating material, such as colorless silicone oil, and each double-layered acrylic semi-cylinder is reserved with a plurality of first mounting holes; a transparent rubber film, used to wrap the soil column sample, and the transparent rubber film is reserved with a plurality of second mounting holes, the positions of the second mounting holes are aligned with the first mounting holes; an air pump is connected to a plastic sleeve with a suction nozzle, and is used to install the transparent rubber film on the outside of the soil column sample. The transparent rubber membrane acts as a thermal insulator and a flexible wall, and its outer surface is covered with digital speckle patterns to monitor soil deformation. A double layer of transparent insulation material and transparent rubber membrane is used to achieve thermal insulation and visualization of the side walls of the soil column during freezing. The temperature control system includes: a cold storage material disposed in a transparent soil column container and located directly above the soil column sample; a thermoelectric cooling module composed of multiple thermoelectric semiconductors, located above the cold storage material. Controlled by a control center, the thermoelectric cooling module composed of multiple thermoelectric semiconductors absorbs heat and cools down at one end in contact with the cold storage material, and dissipates heat and heats up at the other end away from the cold storage material. This can effectively neutralize the external temperature changes of the side wall of the soil column sample caused by the low temperature environment and achieve a one-way freezing environment; multiple temperature and humidity sensors, each of which can be installed inside the soil column sample through a first mounting hole and a second mounting hole; a digital image acquisition system, including: a digital speckle pattern disposed on the surface of the soil column sample; a binocular camera connected to the control center and located outside the transparent soil column tube for collecting digital speckle patterns on the soil column sample; an illumination lamp, irradiated in a direction toward the transparent soil column tube, for ensuring that the binocular camera can clearly capture the digital speckle patterns on the surface of the soil column sample; and a calibration plate covering the outer surface of the transparent rubber film for acquiring digital speckle patterns.

[0006] Furthermore, the water replenishment tank base is a cylindrical boss structure. The diameter of the cylindrical portion of the raised portion is equal to the diameter of the soil column sample, and an annular groove is provided on the circumference. The annular groove is equipped with an annular rubber ring, which is used to fix the transparent rubber membrane at the bottom of the soil column sample. The water replenishment tank base is internally provided with a control component for adjusting different water replenishment environments. Specifically, the control component is a slide plate. The slide plate is parallel to the top surface of the cylindrical portion of the raised portion of the water replenishment tank base and slides on the top surface of the cylindrical portion of the raised portion. The sliding of the slide plate controls the size of the circular hole on the top surface of the cylindrical portion of the raised portion.

[0007] Furthermore, the two double-walled acrylic semi-cylinders are secured together with screws and nuts, and a sealing gasket is installed at the connection between the two double-walled acrylic semi-cylinders. The function of the sealing gasket is to adjust the tightness between the transparent soil column and the soil column sample, as well as to provide thermal insulation at the connection between the two double-walled acrylic semi-cylinders.

[0008] Furthermore, the control center includes: a control system, a data collector, a data line and a power supply. The temperature and humidity sensor, the data collector and the control system are connected via a data line, and the power supply is connected to the thermoelectric cooling module.

[0009] Furthermore, a binocular camera is connected to a display screen to collect and record speckle patterns on the sample surface during the freezing process to reflect the deformation of the soil sample.

[0010] Furthermore, the two binocular cameras are placed on the same side of the transparent soil column, at different heights of the transparent soil column, and are both focused on the same collection point on the transparent soil column. An illuminating light is positioned between the two binocular cameras, and the line connecting the two binocular cameras and the lines connecting the two binocular cameras and the collection points form an isosceles triangle, wherein the isosceles triangle is a 30° isosceles triangle. That is, the distances between the two binocular cameras and the collection points of the soil column sample are identical, and the angle between the line connecting the binocular cameras and the soil column sample and the line connecting the two binocular cameras is 30°, ensuring that the two binocular cameras can simultaneously capture the same area on the sample surface.

[0011] Furthermore, the sizes of the first mounting hole and the second mounting hole are both larger than the sizes of the temperature and humidity sensor, and a reinforcement ring is arranged around the second mounting hole, and a sealing film is provided between the reinforcement ring and the second mounting hole to prevent leakage and avoid rupture of the rubber film during the insertion of the temperature and humidity sensor.

[0012] A frozen soil column test method based on thermoelectric cooling and DIC monitoring includes the following steps:

[0013] The first step is to fasten the two double-walled acrylic semi-cylinders together through fixings without placing sealing gaskets at the connection between the two double-walled acrylic semi-cylinders, place permeable stones on the base of the water replenishment tank, and fix the combined transparent soil column tube on the base of the water replenishment tank.

[0014] In the second step, the prepared soil column samples are placed in two double-walled acrylic semi-cylinders; the soil column samples can be original soil columns or reshaped soil columns.

[0015] In the third step, the digital speckle pattern is covered on the outer surface of the transparent rubber film, and the second mounting hole is sealed with a sealing film. The sealed transparent rubber film is inserted into the inner side of the transparent soil column, and an air pump is connected to the plastic sleeve to extract air so that the transparent rubber film is tightly attached to the inner side of the transparent soil column.

[0016] The fourth step is to remove the two double-walled acrylic semi-cylinders, slowly put the transparent rubber film attached to the inner side of the transparent soil column tube on the outer surface of the soil column sample, turn off the vacuum pump, remove the sealing film on the two double-walled acrylic semi-cylinders and the transparent rubber film, and use a ring-shaped rubber ring to fix the excess transparent rubber film at the bottom of the soil column sample to the raised part of the water replenishment tank base to prevent water from leaking from the contact between the rubber film and the base.

[0017] In the fifth step, the two double-walled acrylic semi-cylinders are installed again through the fixings, and a sealing gasket is placed at the connection between the two double-walled acrylic semi-cylinders. The outer diameter of the transparent soil column is adjusted through the fixings to fit the soil column sample wrapped with a transparent rubber film; the transparent soil column is used for heat insulation and to provide a certain degree of rigid support.

[0018] Step 6: Place the binocular camera on the side of the transparent soil column. Set the two binocular cameras at different heights and symmetrically to form a 30° isosceles triangle with the line connecting the transparent soil column. Set the lighting in the middle of the two binocular cameras, connect the binocular cameras, data collector, and display screen, and calibrate the binocular cameras using a calibration plate.

[0019] In the seventh step, cold storage materials and a thermoelectric cooling module composed of multiple thermoelectric semiconductors are placed on the top of the soil column sample in sequence. The cold storage material is wrapped in the excess transparent rubber film on the upper part of the soil column sample. The temperature and humidity sensor is inserted into the soil column sample through the first mounting hole and the second mounting hole, and the second mounting hole is sealed with a sealing film, and the power supply and control system are connected.

[0020] In the eighth step, the control system is used to adjust different freezing temperatures. After the data collector determines that the experimental setting temperature has been reached, the binocular camera is used to collect the digital speckle pattern of the transparent rubber film.

[0021] The ninth step is to capture the displacement and deformation fields during the freezing process using digital image correlation (DIC). The displacement field cloud map and strain field cloud map are analyzed to identify the frost heave, thaw, and deformation as well as the freezing front position. The displacement field is described by the motion of digital speckle patterns using the formula:

[0022] ;

[0023] in, are the coordinates of the scattered speckles in the undeformed image; are the coordinates of the corresponding points in the deformed image; is a function of the displacement components.

[0024] The strain field identification uses the Green-Lagrange strain formula:

[0025] ;

[0026] is the Green-Lagrange strain tensor component, which indicates the degree of deformation of the material in different directions and is used to reflect the deformation of the material in different directions. and Tension and compression in the direction; Indicates that the material is deformed along the Directional displacement; Indicates that the material is deformed along the Directional displacement; For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When the value is 1, When , the value is 0, which is used to distinguish normal strain from shear strain; and Respectively represent the deformation trailing edge and The displacement gradient in the direction, that is, the rate of change of deformation.

[0027] The freezing front is identified by the strain gradient field, and the formula is:

[0028] ;

[0029] is the strain gradient, which reflects the local strain change rate of the soil during the freezing deformation process. The strain gradient mutation point is the freezing front identification point.

[0030] The moving speed of the freezing front is determined by the time relationship of the freezing front displacement. The formula is:

[0031] ;

[0032] s To freeze the front's movement path, t is the moving time, v The speed at which the freezing front moves.

[0033] The tenth step is that during the one-way freezing process, due to the change in soil temperature, moisture will continuously migrate to the low temperature area. Different water replenishment environments can be achieved by adjusting the size of the circular hole at the base of the water replenishment bin.

[0034] Step 11. When the test is completed, turn off the power and remove the soil column samples one by one.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention incorporates thermoelectric cooling technology and digital image correlation (DIC) monitoring. This technology precisely controls the cooling rate and temperature gradient, achieving temperature uniformity and precise control of the cooling process during soil freezing, overcoming the limitations of traditional cooling methods. DIC technology also enables real-time and comprehensive monitoring of the deformation, frost heave, and freezing front evolution of frozen soil samples. High-precision deformation data is obtained through image processing, overcoming the limitations of traditional sensors that only provide point-level data. Furthermore, the invention utilizes a transparent soil column composed of two double-walled acrylic semi-cylinders, which, in conjunction with DIC monitoring technology, visualizes the freezing process and frost heave behavior of frozen soil, facilitating real-time monitoring and analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the main structure of the present invention.

[0038] Figure 2 Schematic diagram of the transparent rubber film structure of the present invention.

[0039] Figure 3 It is a schematic diagram of the calibration plate structure of the present invention.

[0040] Figure 4 This is a schematic structural diagram of the thermoelectric cooling module of the present invention.

[0041] Figure 5 It is a schematic diagram of the transparent soil column structure of the present invention.

[0042] Figure 6 It is a schematic structural diagram of the water replenishment tank base of the present invention.

[0043] Among them, 1. Water filling tank base, 2. Permeable stone, 3. Double-walled acrylic semi-cylinder, 4. Screws, 5. Nuts, 6. Transparent soil column, 7. Transparent rubber membrane, 8. Soil column sample, 9. Sealing gasket, 10. Transparent thermal insulation material, 11. Cold storage material, 12. Thermoelectric cooling module, 13. Control system, 14. Data collector, 15. Power supply, 16. Temperature and humidity sensor, 17. Calibration plate, 18. Digital speckle, 19. Lighting, 20. Binocular camera, 21. Display screen, 22. Second mounting hole, 23. Data cable. DETAILED DESCRIPTION

[0044] The following combination Figures 1 to 6, a detailed description of the specific embodiments of the present invention is provided. In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction. Therefore, they should not be construed as limiting the present invention.

[0045] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features; and in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0046] It should be noted that the circuit connections involved in the present invention all adopt conventional circuit connection methods and do not involve any innovation.

[0047] Example

[0048] like Figure 1 As shown, a frozen soil column test device based on thermoelectric cooling and DIC monitoring includes: a transparent soil column container, a temperature control system and a digital image acquisition system. The transparent soil column container includes: a water replenishment tank base 1, a permeable stone 2 and a transparent soil column tube 6. The top surface of the water replenishment tank base 1 is provided with multiple circular holes; the permeable stone 2 is arranged on the top of the water replenishment tank base 1; one end of the transparent soil column tube 6 is sleeved on the water replenishment tank base 1 to accommodate a soil column sample 8. The soil column sample 8 is located above the permeable stone 2. Figure 5 As shown, the transparent soil column 6 includes two double-walled acrylic semi-cylinders 3 connected by fasteners, the hollow space of the double-walled acrylic semi-cylinder 3 is filled with a transparent heat-insulating material 10, and each double-walled acrylic semi-cylinder 3 is reserved with a plurality of first mounting holes; Figure 2 As shown, the transparent rubber film 7 reserves a plurality of second mounting holes 22; the reserved positions of the second mounting holes 22 on the transparent rubber film 7 are consistent with the reserved positions of the first mounting holes on the transparent soil column tube 6, ensuring that the first mounting holes and the second mounting holes 22 are aligned; the transparent rubber film 7 plays the role of heat insulation and flexible wall, and the outer surface of the transparent rubber film 7 is covered with digital speckle 18 to monitor soil deformation. A double layer of heat insulation material 10 and a transparent rubber film 7 is used to achieve heat insulation and visualization of the side walls during the freezing process of the soil column sample 8. The temperature control system includes: a cold storage material 11, a thermoelectric cooling module 12 and a temperature and humidity sensor 16. The cold storage material 11 is arranged in the transparent soil column container, directly above the soil column sample 8; as shown Figure 1 and Figure 4 As shown, the thermoelectric cooling module 12 is composed of multiple thermoelectric semiconductors and is located above the cold storage material 11. Under the control of the control center, the end of the thermoelectric cooling module 12 composed of multiple thermoelectric semiconductors in contact with the cold storage material 11 absorbs heat and cools down, and the end away from the cold storage material 11 dissipates heat and heats up, which can effectively neutralize the temperature change of the side wall of the soil column sample 8 caused by the low temperature environment and realize a one-way freezing environment; multiple temperature and humidity sensors 16 can be installed inside the soil column sample 8 through the first mounting hole and the second mounting hole 22; Figure 1 As shown, the digital image acquisition system includes: a binocular camera 20, a digital speckle pattern 18, an illuminator 19, and a calibration plate 17. The digital speckle pattern 18 is set on the surface of the soil column sample 8. The binocular camera 20 is connected to the control center and is located outside the transparent soil column tube 6. It is used to collect the digital speckle pattern 18 on the soil column sample 8. The illuminator 19 is irradiated toward the transparent soil column tube 6 to ensure that the binocular camera 20 can clearly capture the digital speckle pattern 18 on the surface of the soil column sample 8. Figure 3 As shown, the calibration plate 17 covers the outer surface of the transparent rubber film 7 and is used to calibrate the binocular camera 20.

[0049] In some embodiments, as Figure 1 and Figure 6 As shown, the water replenishment tank base 1 is a cylindrical boss structure. The diameter of the cylindrical portion of the raised portion is equal to the diameter of the soil column sample 8. An annular groove is provided on the circumference. An annular rubber ring is provided in the annular groove. The annular rubber ring is used to fix the transparent rubber membrane 7 at the bottom of the soil column sample 8. A control component is provided inside the water replenishment tank base 1 to adjust different water replenishment environments. Specifically, the control component is a slide plate. The slide plate is parallel to the top surface of the cylindrical portion of the raised portion of the water replenishment tank base 1 and slides on the top surface of the cylindrical portion of the raised portion. When the slide plate slides, it can cover and close the circular hole. By controlling the sliding of the slide plate, the size of the circular hole can be controlled.

[0050] In some embodiments, as Figure 5 As shown, the two double-walled acrylic semi-cylinders 3 are fixed together by screws 4 and nuts 5, and a sealing gasket 9 is provided at the connection between the two double-walled acrylic semi-cylinders 3. The function of the sealing gasket 9 is to adjust the tightness between the transparent soil column 6 and the soil column sample 8, and to provide thermal insulation at the connection between the two double-walled acrylic semi-cylinders 3.

[0051] In some embodiments, as Figure 1 and Figure 4 As shown, the control center includes: a control system 13, a data collector 14, a data line 23 and a power supply 15. The temperature and humidity sensor 16, the data collector 14 and the control system 13 are connected via the data line 23, and the power supply 15 is connected to the thermoelectric cooling module 12.

[0052] In some embodiments, a binocular camera 20 is connected to a display screen 21. The binocular camera 20 is used to collect and record digital speckle patterns 18 on the surface of the soil column sample 8 during the freezing process to reflect the deformation of the soil column sample 8. The binocular camera 20 captures information about the digital speckle patterns 18 on the surface of the soil column sample 8 during the freezing process, and processes the displacement of the digital speckle patterns 18 using relevant software and code based on the principles of continuum mechanics and digital imaging technology to reflect the deformation of the sample.

[0053] In some embodiments, as Figure 1 As shown, two binocular cameras 20 are placed on the same side of the transparent soil column 6, and the two binocular cameras 20 are respectively located at different heights of the transparent soil column 6, and the two binocular cameras 20 are focused on the same collection point on the transparent soil column 6; the lighting lamp 19 is set in the middle position of the two binocular cameras 20 to illuminate the collection point. For example, the line between the two binocular cameras 20 and the lines between the two binocular cameras 20 and the collection points respectively form an isosceles triangle, and the isosceles triangle is a 30° isosceles triangle, ensuring that the two binocular cameras 20 can simultaneously capture the same area on the surface of the soil column sample 8.

[0054] In some embodiments, the size of the first mounting hole and the second mounting hole 22 are both larger than the size of the temperature and humidity sensor 16, and a reinforcement ring is provided around each second mounting hole 22 to prevent leakage, and a sealing film is provided between the reinforcement ring and the second mounting hole 22 to prevent the rubber film from rupturing during the insertion of the temperature and humidity sensor 16.

[0055] A frozen soil column test method based on thermoelectric cooling and DIC monitoring is conducted using the above-mentioned device, comprising the following steps:

[0056] In the first step, two double-layered acrylic semi-cylinders 3 are fastened together by screws 4 and nuts 5. No sealing gasket 9 is placed at the connection between the two double-layered acrylic semi-cylinders 3. Permeable stone 2 is placed on the water replenishment tank base 1, and the combined transparent soil column 6 is fixed to the water replenishment tank base 1.

[0057] In the second step, the prepared soil column sample 8 is placed in two double-walled acrylic semi-cylinders 3; the soil column sample 8 can be an original soil column or a reshaped soil column.

[0058] In the third step, the digital speckle pattern 18 is covered on the outer surface of the transparent rubber film 7, and the second mounting hole 22 on the transparent rubber film 7 is sealed with a sealing film. The sealed transparent rubber film 7 is inserted into the inner side of the transparent soil column 6, and an air pump is connected to the plastic sleeve to evacuate air so that the transparent rubber film 7 is tightly attached to the inner side of the transparent soil column 6. It is worth noting that the plastic sleeve is a common membrane-bearing tube in indoor geotechnical tests.

[0059] The fourth step is to remove the two double-walled acrylic semi-cylinders 3, slowly put the transparent rubber film 7 attached to the inner side of the transparent soil column tube 6 on the outer surface of the soil column sample 8, turn off the air pump, remove the sealing film on the two double-walled acrylic semi-cylinders 3 and the transparent rubber film 7, and use a ring-shaped rubber ring to fix the excess transparent rubber film 7 at the bottom of the soil column sample 8 to the raised part of the water replenishment tank base 1.

[0060] In the fifth step, the two double-walled acrylic semi-cylinders 3 are installed again through the fixing parts, and a sealing gasket 9 is placed at the connection between the two double-walled acrylic semi-cylinders 3. The outer diameter of the transparent soil column tube 6 is adjusted by the screw 4 and the nut 5 to fit the soil column sample 8 wrapped with a transparent rubber film 7; the transparent soil column tube 6 is used for heat insulation and to provide a certain degree of rigid support.

[0061] In the sixth step, the binocular camera 20 is placed on the side of the transparent soil column 6. The two binocular cameras 20 are set at different heights and symmetrically, forming a 30° isosceles triangle with the line connecting the transparent soil column 6. The lighting lamp 19 is set in the middle position of the two binocular cameras 20, the binocular camera 20, the data collector 14 and the display screen 21 are connected, and the binocular camera 20 is calibrated using the calibration plate 17.

[0062] In the seventh step, a cold storage material 11 and a thermoelectric cooling module 12 composed of multiple thermoelectric semiconductors are placed on the top of the soil column sample 8 in sequence. The cold storage material 11 is wrapped in the excess transparent rubber film 7 on the upper part of the soil column sample 8. The temperature and humidity sensor 16 is inserted into the soil column sample 8 through the first mounting hole and the second mounting hole 22, and the second mounting hole 22 is sealed with a sealing film. The power supply 15 and the control system 13 are connected.

[0063] In the eighth step, the control system 13 is used to adjust different freezing temperatures, and after the data collector 14 determines that the test setting temperature has been reached, the binocular camera 20 is used to collect the digital speckle pattern 18 of the transparent rubber film 7 .

[0064] The ninth step is to capture the displacement and deformation fields during the freezing process using the digital image correlation method (DIC). The displacement field cloud map and the strain field cloud map are analyzed to identify the frost heave, thaw, and deformation and the freezing front position. The displacement field is described by the movement of the digital speckle pattern 18, and the formula is:

[0065] ;

[0066] in, are the coordinates of the scattered speckles in the undeformed image; are the coordinates of the corresponding points in the deformed image; is a function of the displacement components.

[0067] The strain field identification uses the Green-Lagrange strain formula:

[0068] ;

[0069] is the Green-Lagrange strain tensor component, which indicates the degree of deformation of the material in different directions and is used to reflect the deformation of the material in different directions. and Tension and compression in the direction; Indicates that the material is deformed along the Directional displacement (position after deformation); Indicates that the material is deformed along the Directional displacement (position after deformation); For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When the value is 1, When , the value is 0, which is used to distinguish normal strain from shear strain; and Respectively represent the deformation trailing edge and The displacement gradient in the direction, that is, the rate of change of deformation.

[0070] The freezing front is identified by the strain gradient field, and the formula is:

[0071] ;

[0072] is the strain gradient, which reflects the local strain change rate of the soil during the freezing deformation process. The strain gradient mutation point is the freezing front identification point.

[0073] The moving speed of the freezing front is determined by the time relationship of the freezing front displacement. The formula is:

[0074] ;

[0075] s To freeze the front's movement path, t is the moving time, v The speed at which the freezing front moves.

[0076] The tenth step is to achieve different water replenishment environments by adjusting the size of the circular hole in the water replenishment tank base 1.

[0077] Step 11: After the test is completed, turn off the power supply 15 and remove the soil column samples 8 in sequence.

[0078] The above disclosures are only several preferred specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A frozen soil column test method based on thermoelectric cooling and DIC monitoring, characterized in that: The test was conducted using a frozen soil column test device based on thermoelectric cooling and DIC monitoring. The test device includes: A transparent soil column container comprises: a water replenishment bin base (1), the top surface of which is provided with a plurality of circular holes; a permeable stone (2), which is arranged on the top of the water replenishment bin base (1); a transparent soil column tube (6), one end of which is sleeved on the water replenishment bin base (1) and is used to accommodate a soil column sample (8), wherein the soil column sample (8) is located above the permeable stone (2); the transparent soil column tube (6) comprises two double-layered acrylic semi-cylinders (3) connected by fastening members, the hollow portion of the double-layered wall of each double-layered acrylic semi-cylinder (3) is filled with a transparent heat-insulating material (10), and each double-layered acrylic semi-cylinder (3) is reserved with a plurality of first mounting holes; a transparent rubber film (7), which is used to wrap the soil column sample (8), and the transparent rubber film (7) is reserved with a plurality of second mounting holes (22); The temperature control system comprises: a cold storage material (11) arranged in a transparent soil column container and located directly above the soil column sample (8); a thermoelectric cooling module (12) located above the cold storage material (11) and controlled by a control center; and a plurality of temperature and humidity sensors (16), each of which can pass through a first mounting hole and a second mounting hole (22) and be arranged inside the soil column sample (8). The digital image acquisition system comprises: a digital speckle pattern (18) arranged on the surface of a soil column sample (8); a binocular camera (20) connected to a control center and located outside a transparent soil column tube (6) for collecting the digital speckle pattern (18) on the soil column sample (8); an illumination lamp (19) irradiating toward the transparent soil column tube (6); and a calibration plate (17) covering the outer surface of a transparent rubber film (7); The water replenishment tank base (1) is a cylindrical boss structure, the diameter of the cylinder of the raised portion is equal to the diameter of the soil column sample (8), and an annular groove is provided on the circumference, and an annular rubber ring is provided in the annular groove, and the annular rubber ring is used to fix the transparent rubber membrane (7) at the bottom of the soil column sample (8). A control component is provided inside the water replenishment tank base (1) for adjusting different water replenishment environments; The two double-walled acrylic semi-cylinders (3) are fixed by screws (4) and nuts (5), and a sealing gasket (9) is provided at the connection between the two double-walled acrylic semi-cylinders (3); The two binocular cameras (20) are placed on the same side of the transparent soil column (6), the two binocular cameras (20) are respectively located at different heights of the transparent soil column (6), and the two binocular cameras (20) are focused on the same acquisition point on the transparent soil column (6); the lighting lamp (19) is set in the middle position of the two binocular cameras (20); The frozen soil column test method comprises the following steps: The first step is to install the test device; In the second step, different freezing temperatures are controlled by a temperature control system. After reaching the experimental setting temperature, a binocular camera (20) is used to collect digital speckles (18) on the transparent rubber film (7); The third step is to capture the displacement and deformation fields during the freezing process through digital image correlation (DIC) and analyze the displacement and strain field cloud maps to identify the frost heave, thaw, and deformation as well as the freezing front position. Step 4: Adjust the size of the circular hole in the water filling tank base (1) to achieve different water filling environments; Step 5: After the test, remove the soil column samples (8) in sequence; The first step of the test device installation includes the following steps: Two double-walled acrylic semi-cylinders (3) are fastened together by fixing members, a permeable stone (2) is placed on the water replenishment tank base (1), and a combined transparent soil column (6) is fixed to the water replenishment tank base (1); Place the prepared soil column sample (8) in two double-walled acrylic semi-cylinders (3); Covering the digital speckle (18) on the outer surface of the transparent rubber film (7), and inserting the transparent rubber film (7) into the inner side of the transparent soil column (6); Remove the two double-walled acrylic semi-cylinders (3) and slowly put the transparent rubber film (7) on the outer surface of the soil column sample (8); The two double-walled acrylic semi-cylinders (3) are reinstalled through the fixing parts, the binocular camera (20) is placed on one side of the transparent soil column (6), and the binocular camera (20) is calibrated using a calibration plate (17); A cold storage material (11) and a thermoelectric cooling module (12) are sequentially placed on the top of the soil column sample (8), the cold storage material (11) is wrapped in an excess transparent rubber film (7) on the upper part of the soil column sample (8), and a temperature and humidity sensor (16) is inserted into the soil column sample (8) through the first mounting hole and the second mounting hole (22).

2. A frozen soil column test method based on thermoelectric cooling and DIC monitoring according to claim 1, characterized in that: The control center includes: a control system (13), a data collector (14), a data line (23) and a power supply (15); the temperature and humidity sensor (16), the data collector (14) and the control system (13) are connected via the data line (23); and the power supply (15) is connected to the thermoelectric cooling module (12).

3. The frozen soil column test method based on thermoelectric cooling and DIC monitoring according to claim 1 is characterized in that: The sizes of the first mounting hole and the second mounting hole (22) are larger than the size of the temperature and humidity sensor (16), a reinforcement ring is provided around the second mounting hole (22), and a sealing film is provided between the reinforcement ring and the second mounting hole (22).

4. The frozen soil column test method based on thermoelectric cooling and DIC monitoring according to claim 1 is characterized in that: The displacement field is described by the motion of the digital speckle (18), formula (1) is: ； in, are the coordinates of the scattered speckles in the undeformed image; are the coordinates of the corresponding points in the deformed image; is the displacement component function; The strain field is identified using the Green-Lagrange strain formula (2): ； is the Green-Lagrange strain tensor component, which indicates the degree of deformation of the material in different directions and is used to reflect the deformation of the material in different directions. and Tension and compression in the direction; Indicates that the material is deformed along the Directional displacement; Indicates that the material is deformed along the Directional displacement; For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When the value is 1, When , the value is 0, which is used to distinguish normal strain from shear strain; and Respectively represent the deformation trailing edge and The displacement gradient in the direction, that is, the rate of change of deformation; The freezing front is identified by the strain gradient field, and formula (3) is: ； is the strain gradient, which reflects the local strain change rate of the soil during the freezing deformation process. The mutation point of the strain gradient is the freezing front identification point; The moving speed of the freezing front is determined by the time relationship of the freezing front displacement; ； s To freeze the front's movement path, t is the moving time, v The speed at which the freezing front moves.

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