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

Abstract

The invention discloses a frozen soil column test device and method based on thermoelectric refrigeration and DIC monitoring, the device comprises a transparent soil column container, a temperature control system and a digital image acquisition system, the transparent soil column container is used for containing a soil column sample, and the transparent soil column container is formed by combining two double-layer cylinder wall acrylic semicircular cylinders; the frozen soil freezing process and the frost heaving behavior are visualized, and real-time monitoring and analysis are facilitated. During an experiment, internal and external temperatures are accurately adjusted through a temperature control system to simulate a frozen soil freezing process; the digital image acquisition system shoots a soil column surface image in real time through a high-resolution camera, digital speckles are combined, real-time monitoring and analysis of the soil body frost heaving amount and the freezing frontal surface position are carried out through a digital image related technology, and the soil body frost heaving characteristic and the freezing frontal surface dynamic change can be measured with high precision.

Description

Technical Field

[0001] The 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 freezing front are the core issues of the study. However, the existing frozen soil experimental equipment usually uses traditional cooling methods such as liquid nitrogen and compressors, which have many limitations. First, the temperature control of the traditional cooling system is not accurate, and the cooling rate and temperature gradient are difficult to finely adjust, resulting in uneven temperature during the freezing process, affecting the frost heave deformation and the evolution of the freezing front, and thus affecting the accuracy of the experimental results. Moreover, these traditional equipment usually cannot achieve dynamic adjustment of the cooling rate, and it is difficult to simulate the actual cooling process under different frozen soil environments. Secondly, the existing experimental equipment usually relies only on point data acquisition devices such as temperature sensors and pressure sensors, which is difficult to achieve dynamic monitoring of the entire process of frozen soil samples, especially the deformation of the soil body during the freezing process, the amount of frost heave, and the evolution of the freezing front lack comprehensive real-time monitoring. The limitations of these technologies make it impossible to deepen the study of frozen soil behavior, especially in the accurate monitoring of the freezing front and frost heave deformation. It is difficult to meet the needs of in-depth research on the mechanical properties of frozen soil, frost heave behavior, and the evolution of the freezing 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: A frozen soil column test device based on thermoelectric cooling and DIC monitoring comprises: a transparent soil column container, comprising: a water replenishment bin base, with a plurality of circular holes on the top surface; a permeable stone arranged on the top of the water replenishment bin base; a transparent soil column tube, one end of which is sleeved on the water replenishment bin base and 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 through fixing parts, the hollow part of the double-layered acrylic semi-cylinder wall of each double-layered acrylic semi-cylinder is filled with 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; and 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 film plays the role of heat insulation and flexible wall, and the digital speckle is covered on the outer surface of the transparent rubber film to monitor soil deformation. The double-layer heat insulation material of transparent heat insulation material and transparent rubber film is used to achieve heat insulation and visualization of the side wall during the freezing process of the soil column sample. The temperature control system comprises: a cold storage material, which is arranged in a transparent soil column container and is located directly above the soil column sample; a thermoelectric cooling module composed of multiple thermoelectric semiconductors, which is located above the cold storage material and is 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 one end away from the cold storage material, which can effectively neutralize the temperature change on the side wall of the soil column sample caused by the low temperature environment and realize a one-way freezing environment; multiple temperature and humidity sensors, each of which can be arranged inside the soil column sample through a first mounting hole and a second mounting hole; a digital image acquisition system, which comprises: a digital speckle, which is arranged on the surface of the soil column sample; a binocular camera, which is connected to the control center and is located outside the transparent soil column tube and is used to collect the digital speckle on the soil column sample; an illuminating lamp, whose irradiation direction is toward the transparent soil column tube, which is used to ensure that the binocular camera can clearly capture the digital speckle on the surface of the soil column sample; and a calibration plate, which covers the outer surface of the transparent rubber film and is used to obtain a digital speckle image.

[0005] Furthermore, the water replenishment tank base is a cylindrical boss structure, the diameter of the cylinder of the raised part is equal to the diameter of the soil column sample, and an annular groove is arranged on the circumference, and an annular rubber ring is arranged in the annular groove, and the annular rubber ring is used to fix the transparent rubber film at the bottom of the soil column sample, and a control component is arranged inside the water replenishment tank base to adjust different water replenishment environments. Specifically, the control component is a slide plate, which is parallel to the top surface of the cylinder of the raised part of the water replenishment tank base and slides on the top surface of the cylinder of the raised part, and the size of the circular hole on the top surface of the cylinder of the raised part is controlled by sliding the slide plate.

[0006] Furthermore, the two double-walled acrylic semi-cylinders are fixed by screws and nuts, and a sealing gasket is provided at the connection of 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 and the heat insulation of the connection position of the two double-walled acrylic semi-cylinders.

[0007] 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 the data line, and the power supply is connected to the thermoelectric cooling module.

[0008] 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.

[0009] Furthermore, the two binocular cameras are placed on the same side of the transparent soil column, the two binocular cameras are respectively located at different heights of the transparent soil column, and the two binocular cameras are both focused on the same collection point on the transparent soil column; the lighting lamp is set in the middle of the two binocular cameras, and the line between the two binocular cameras and the lines between the two binocular cameras and the collection points respectively form an isosceles triangle, and the isosceles triangle is a 30° isosceles triangle. That is, the distances from the two binocular cameras to the collection points of the soil column sample are consistent, and the angle between the line between the binocular camera and the soil column sample and the line between the two binocular cameras is 30°, which is used to ensure that the two binocular cameras can simultaneously capture the same area on the sample surface.

[0010] 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 arranged between the reinforcement ring and the second mounting hole to prevent leakage and avoid rupture of the rubber film during insertion of the temperature and humidity sensor.

[0011] A frozen soil column test method based on thermoelectric cooling and DIC monitoring includes the following steps: 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 bin, and fix the combined transparent soil column tube on the base of the water replenishment bin.

[0012] The second step is to place the prepared soil column samples in two double-walled acrylic semi-cylinders; the soil column samples can be original soil columns or reshaped soil columns.

[0013] The third step is to cover the outer surface of the transparent rubber film with digital speckle, seal the second mounting hole with a sealing film, insert the sealed transparent rubber film into the inner side of the transparent soil column, and use an air pump connected to the plastic sleeve to evacuate air, so that the transparent rubber film is tightly attached to the inner side of the transparent soil column.

[0014] 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 an annular 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 leakage from the contact between the rubber film and the base.

[0015] The fifth step is to install the two double-walled acrylic semi-cylinders again through the fixings, and place sealing gaskets 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.

[0016] The sixth step is to place the binocular camera on the side of the transparent soil column. The two binocular cameras are set at different heights and symmetrically to form an isosceles triangle of 30° with the line between the transparent soil column. The lighting is set in the middle of the two binocular cameras, the binocular cameras, data collector and display screen are connected, and the binocular cameras are calibrated using a calibration board.

[0017] 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 turn. 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.

[0018] In the eighth step, the control system is used to adjust different freezing temperatures, and after the data collector determines that the experimental setting temperature has been reached, the binocular camera is used to collect the digital speckle of the transparent rubber film.

[0019] The ninth step is to capture the displacement field and deformation field during the freezing process through the digital image correlation method DIC, analyze the displacement field cloud map and the strain field cloud map to identify the frost heave, thaw and sink deformation and the freezing front position. The displacement field is described by the motion of the digital speckle, and the formula is: ; in, are the coordinates of the scattered spots in the undeformed image; are the coordinates of the corresponding points in the deformed image; is a function of the displacement components.

[0020] The strain field identification adopts the Green-Lagrange strain formula: ; 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 Directional displacement; Indicates that the material is deformed along Directional displacement; For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When 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.

[0021] The freezing front is identified by the strain gradient field, and the formula is: ; It 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.

[0022] The moving speed of the freezing front is determined by the time relationship of the freezing front displacement. The formula is: ; s To freeze the front's moving path, t For the moving time, v Freeze front movement speed.

[0023] The tenth step, 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.

[0024] Step 11. When the test is completed, turn off the power supply and remove the soil column samples one by one.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces thermoelectric cooling technology and digital image correlation technology (DIC) monitoring. The present invention can accurately control the cooling rate and temperature gradient through thermoelectric cooling technology, realize the uniformity of temperature during soil freezing and accurate control of the cooling process, and overcome the problem that traditional cooling methods cannot be regulated. At the same time, the deformation, frost heave and freezing front evolution of frozen soil samples are monitored in real time and comprehensively through DIC technology, and high-precision deformation data is obtained through image processing, overcoming the limitation that traditional sensors can only provide point data. In addition, the present invention adopts a transparent soil column composed of two double-wall acrylic semi-cylinders to cooperate with DIC monitoring technology, so that the freezing process and frost heave behavior of frozen soil can be visualized, which is convenient for real-time monitoring and analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the main structure of the present invention.

[0027] Figure 2 It is a schematic diagram of the transparent rubber film structure of the present invention.

[0028] Figure 3 It is a schematic diagram of the calibration plate structure of the present invention.

[0029] Figure 4 It is a schematic diagram of the structure of the thermoelectric cooling module of the present invention.

[0030] Figure 5 It is a schematic diagram of the transparent soil column structure of the present invention.

[0031] Figure 6 It is a schematic diagram of the structure of the water replenishment tank base of the present invention.

[0032] Among them, 1. Water replenishment tank base, 2. Permeable stone, 3. Double-layer acrylic semi-cylinder with double wall, 4. Screws, 5. Nuts, 6. Transparent soil column, 7. Transparent rubber film, 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 acquisition device, 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

[0033] Combine the following Figures 1 to 6, the specific embodiments of the present invention are described in detail. 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", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0034] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0035] 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.

[0036] Example 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 bin base 1, a permeable stone 2 and a transparent soil column tube 6. The top surface of the water replenishment bin base 1 is provided with a plurality of circular holes; the permeable stone 2 is arranged on the top of the water replenishment bin base 1; one end of the transparent soil column tube 6 is sleeved on the water replenishment bin base 1 to accommodate a soil column sample 8. The soil column sample 8 is located above the permeable stone 2, as shown in FIG. Figure 5 As shown, the transparent soil column 6 includes two double-walled acrylic semi-cylinders 3 connected by fastening parts, the hollow of the double-walled acrylic semi-cylinder 3 is filled with 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 heat insulation material of transparent heat insulation material 10 and 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 a transparent soil column container, directly above the soil column sample 8; as shown Figure 1 and Figure 4As shown, the thermoelectric cooling module 12 is composed of a plurality of thermoelectric semiconductors and is located above the cold storage material 11. Through the control of the control center, the thermoelectric cooling module 12 composed of the plurality of thermoelectric semiconductors absorbs heat and cools down at one end in contact with the cold storage material 11, and dissipates heat and heats up at the other end away from the cold storage material 11, which can effectively neutralize the temperature change on the side wall of the soil column sample 8 caused by the low temperature environment, and realize a one-way freezing environment; the plurality of temperature and humidity sensors 16 can be arranged 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 18, an illuminator 19 and a calibration plate 17. The digital speckle 18 is arranged 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, and is used to collect the digital speckle 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 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 .

[0037] In some embodiments, Figure 1 and Figure 6 As shown, the water replenishment tank base 1 is a cylindrical boss structure, the diameter of the cylinder of the raised part is equal to the diameter of the soil column sample 8, and an annular groove is set on the circumferential side, and an annular rubber ring is matched in the annular groove. The annular rubber ring is used to fix the transparent rubber film 7 at the bottom of the soil column sample 8. A control component is set inside the water replenishment tank base 1 to adjust different water replenishment environments. Specifically, the control component is a slide plate, which is parallel to the top surface of the cylinder of the raised part of the water replenishment tank base 1 and slides on the top surface of the cylinder of the raised part, and the slide plate can cover and close the circular hole when sliding, and the size of the circular hole can be controlled by controlling the sliding of the slide plate.

[0038] In some embodiments, Figure 5 As shown, 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 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 play a heat insulation role at the connection position of the two double-walled acrylic semi-cylinders 3.

[0039] In some embodiments, 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.

[0040] In some embodiments, the binocular camera 20 is connected to the display screen 21. It is used to collect and record the digital speckle 18 on the surface of the soil column sample 8 during the freezing process to reflect the deformation of the soil column sample 8, capture the information of the digital speckle 18 on the surface of the soil column sample 8 during the freezing process, and process the displacement of the digital speckle 18 through relevant software and code based on the principle of continuous medium mechanics and digital image technology to reflect the deformation of the sample.

[0041] In some embodiments, Figure 1 As shown, 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 collection point on the transparent soil column 6; the lighting lamp 19 is set in the middle position of the two binocular cameras 20, for illuminating 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, which ensures that the two binocular cameras 20 can simultaneously capture the same area on the surface of the soil column sample 8.

[0042] 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 arranged around each second mounting hole 22 to prevent leakage, and a sealing film is arranged between the reinforcement ring and the second mounting hole 22 to prevent the rubber film from breaking during the insertion of the temperature and humidity sensor 16.

[0043] A frozen soil column test method based on thermoelectric cooling and DIC monitoring, using the above device to conduct an experiment, includes the following steps: In the first step, two double-layer 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-layer acrylic semi-cylinders 3. Permeable stones 2 are placed on the water replenishment tank base 1, and the combined transparent soil column 6 is fixed to the water replenishment tank base 1.

[0044] 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.

[0045] The third step is to cover the digital speckle 18 on the outer surface of the transparent rubber film 7, and seal the second mounting hole 22 on the transparent rubber film 7 with a sealing film, insert the sealed transparent rubber film 7 into the inner side of the transparent soil column 6, and use a vacuum pump connected to a 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 mentioning that the plastic sleeve is a common membrane-bearing tube in indoor geotechnical tests.

[0046] The fourth step is to remove the two double-layer 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 vacuum pump, remove the sealing film on the two double-layer 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.

[0047] The fifth step is to install the two double-walled acrylic semi-cylinders 3 again through the fixing parts, and place a sealing gasket 9 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 screws 4 and nuts 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.

[0048] The sixth step is to place the binocular camera 20 on the side of the transparent soil column 6. The two binocular cameras 20 are set at high and low positions, and the two binocular cameras 20 are set symmetrically to form an isosceles triangle of 30° with the connecting line between 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.

[0049] 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, and the power supply 15 and the control system 13 are connected.

[0050] 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 18 of the transparent rubber film 7 .

[0051] The ninth step is to capture the displacement field and deformation field during the freezing process by using the digital image correlation method DIC, and analyze the displacement field cloud map and the strain field cloud map to identify the frost heave, thaw and sink deformation and the freezing front position. The displacement field is described by the movement of the digital speckle 18, and the formula is: ; in, are the coordinates of the scattered spots in the undeformed image; are the coordinates of the corresponding points in the deformed image; is a function of the displacement components.

[0052] The strain field identification adopts the Green-Lagrange strain formula: ; 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 Directional displacement (position after deformation); Indicates that the material is deformed along Directional displacement (position after deformation); For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When 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.

[0053] The freezing front is identified by the strain gradient field, and the formula is: ; It 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.

[0054] The moving speed of the freezing front is determined by the time relationship of the freezing front displacement. The formula is: ; s To freeze the front's moving path, t For the moving time, v Freeze front movement speed.

[0055] 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.

[0056] Step 11. After the test is finished, turn off the power supply 15 and remove the soil column samples 8 one by one.

[0057] 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 protection scope of the present invention.

Claims

1. A frozen soil column test device based on thermoelectric cooling and DIC monitoring, characterized in that: include: A transparent soil column container, comprising: 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), and the transparent soil column tube (6) comprises two double-layered acrylic semi-cylinders (3) which are fastened together by fixing parts, the hollow part of the 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 a soil column sample (8); a thermoelectric cooling module (12) located above the cold storage material (11) and controlled by a control center; 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 (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 (18) on the soil column sample (8); an illumination lamp (19) irradiating in a direction toward the transparent soil column tube (6); and a calibration plate (17) covering the outer surface of a transparent rubber film (7).

2. A frozen soil column test device based on thermoelectric cooling and DIC monitoring according to claim 1, characterized in that: The water replenishment bin base (1) is a cylindrical boss structure, the diameter of the cylindrical body of the raised portion is equal to the diameter of the soil column sample (8), and an annular groove is arranged on the circumference, and an annular rubber ring is arranged 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 arranged inside the water replenishment bin base (1) for adjusting different water replenishment environments.

3. The frozen soil column test device based on thermoelectric cooling and DIC monitoring according to claim 1 is characterized in that: The two double-walled acrylic semi-cylinders (3) are fixed by means of screws (4) and nuts (5), and a sealing gasket (9) is provided at the connection between the two double-walled acrylic semi-cylinders (3).

4. The frozen soil column test device based on thermoelectric cooling and DIC monitoring according to claim 1 is characterized in that: The control center comprises: 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).

5. The frozen soil column test device based on thermoelectric cooling and DIC monitoring according to claim 1 is characterized in that: 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 both focused on the same acquisition point on the transparent soil column (6); and the lighting lamp (19) is arranged in the middle of the two binocular cameras (20).

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

7. A frozen soil column test method based on thermoelectric cooling and DIC monitoring, characterized in that: The experiment is carried out using the frozen soil column test device described in any one of claims 1 to 6. The following steps are involved: The first step is to install the test device; In the second step, different freezing temperatures are adjusted by a temperature control system. After reaching the test 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 field and deformation field during the freezing process through the digital image correlation method DIC, and analyze the displacement field cloud map and strain field cloud map to identify the frost heave, thaw and sink deformation and the freezing front position; Step 4: different water replenishment environments are achieved by adjusting the size of the circular hole in the water replenishment tank base (1); Step 5: After the test, remove the soil column samples (8) one by one.

8. A frozen soil column test method based on thermoelectric cooling and DIC monitoring according to claim 7, characterized in that: The first step of the test device installation includes the following steps: Two double-wall acrylic semi-cylinders (3) are fastened together by means of fixing parts, 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 a 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 the 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 a first mounting hole and a second mounting hole (22).

9. A frozen soil column test method based on thermoelectric cooling and DIC monitoring according to claim 7, characterized in that: The displacement field is described by the motion of the digital speckle (18) as follows: ； in, are the coordinates of the scattered spots in the undeformed image; are the coordinates of the corresponding points in the deformed image; is the displacement component function; The strain field identification adopts the Green-Lagrange strain formula: ； 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 Directional displacement; Indicates that the material is deformed along Directional displacement; For materials at the deformation front The original position of the direction; is the Kronecker symbol, when When 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 the formula 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 moving path, t For the moving time, v Freeze front movement speed.

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