CN114487012B - Soil body surface crack development pre-judging method - Google Patents

Abstract

The invention discloses a soil body surface crack development pre-judging method, and belongs to the field of infrared remote sensing-geological engineering. It comprises the following steps: s1, shooting the surface of a soil body to be monitored by adopting an infrared thermal imaging camera to obtain a soil body surface temperature field; s2, drawing a soil isothermal map according to a soil surface temperature field; and S3, determining a main crack development area on the soil surface according to the soil isothermal line graph. According to the invention, the surface temperature field change in the soil body cracking process is analyzed through the real-time acquired soil surface temperature field information, so that the crack development of the soil body surface is predicted, the crack development of the soil body surface can be effectively and rapidly monitored, and the soil body crack development prediction method is a simple and efficient soil body crack development prediction method.

Description

A method for predicting the development of cracks on the soil surface

Technical field

The invention belongs to the field of infrared remote sensing-geological engineering, and more specifically, relates to a method for predicting the development of cracks on the soil surface.

Background technique

All objects with a surface temperature above absolute zero (-273.15°C) will continuously radiate electromagnetic waves to the outside world. When the surface temperature of an object changes, the radiation intensity and wavelength distribution characteristics of electromagnetic waves will also change accordingly. Electromagnetic waves with wavelengths between 2.0μm and 1000μm are called thermal infrared rays. Thermal infrared rays have extremely poor penetrating ability to most solid and liquid substances, so the thermal infrared radiation of objects to the outside world only appears as surface radiation. When thermal infrared rays are transmitted in the atmosphere, they will be absorbed by atmospheric components, and their intensity will drop significantly. They only have good penetration in the two wave bands of 3μ~5μm and 8~12μm. Infrared imaging equipment captures the thermal infrared rays of these two bands and performs real-time calculations to achieve the inversion of the surface temperature field of the target object. Taking advantage of this characteristic, the infrared thermal imaging camera captures the thermal infrared rays of these two characteristic bands radiated by the soil sample, and calculates and inverts the temperature field distribution on the surface of the soil sample based on its radiation intensity. This technology is effective and convenient. It is a non-destructive monitoring method. It was first used in forest fire prevention and electrical fault inspection. It was later promoted and applied to the stress field and crack monitoring of rocks and concrete. Its application research in soil is mostly limited to measurement. Moisture content, thermal conductivity, and monitoring of soil surface cracks started late.

Under the influence of arid climate, natural soil will crack due to water loss and shrinkage, and a network of crisscrossing fissures will develop on the surface. The occurrence of cracks destroys the integrity of the soil and provides a convenient channel for water migration in the soil, thus causing various problems. Finding solutions to this type of problem must start with rapid monitoring of soil fissure networks. Currently, there are two main methods for monitoring soil fissures: contact and non-contact. Contact crack monitoring methods include optical fiber sensing technology (BOTDR), high-density resistivity imaging technology (ERT) and other methods. Before use, these methods need to bury optical fibers, probes or sensors inside the soil, which destroys the soil to a certain extent. The body structure thus affects the cracking process of the soil, and the drying and shrinkage process of the soil will cause the deformation of the embedded objects, resulting in inaccurate monitoring results. Existing non-contact methods such as digital image correlation (DIC) observe the changes in surface strain/displacement field during the dry shrinkage and cracking process of soil. The non-destructive monitoring method ensures the accuracy of in-situ monitoring of soil and can only be used in advance. The development direction of cracks can be inferred, but this method has a short prediction time in advance and is difficult to be promoted in engineering applications.

The prior art of Chinese patent document publication number CN108398368A discloses a device and method for extracting fissures and pores on the soil surface. This method limits the size and placement position of the soil sample, and sets up an opaque photography studio outside the soil sample placement stage. The camera device shoots and records through the opening on the top of the studio. The application of this technology is limited to indoor testing and does not involve monitoring cracks in the in-situ state of the soil. In addition, this technology only monitors and records the development of cracks in the soil, but the development of soil cracks is closely related to factors such as ambient temperature and internal moisture field of the soil. This technology does not examine the factors that affect the development of cracks on the soil surface. Monitoring records.

The prior art of Chinese patent document publication number CN109470595A discloses a soil testing method that synchronizes automatic weighing and crack photography. This method automatically takes pictures and weighs by controlling the time of taking pictures and weighing, and can accurately record the evolution of cracks and moisture content changes in the soil. It has little disturbance to the pattern and is easy to use. However, this method is only suitable for monitoring small-scale soil surface cracks in the laboratory, and the monitoring of the moisture field of the soil during the evaporation process only focuses on monitoring the overall moisture content of the soil.

The prior art of Chinese patent document publication number CN103983514A discloses an infrared radiation monitoring test method for the development of coal and rock cracks. This method is suitable for studying the development and monitoring of cracks generated during the deformation of coal and rock in mines, and the cracking object involved is coal and rock. The prior art of Chinese patent document publication number CN109696354A discloses an infrared radiation monitoring device and method during the destruction and evolution of fractured rock mass. The difference in infrared heat radiation during the monitoring process of the above technology comes from the heat energy generated by deformation and movement. However, the difference in infrared heat radiation during the development of soil cracks comes from the evaporation of water inside the soil. The engineering properties of rock and soil are significantly different, and the causes of cracking are also different, so this technology is not suitable for monitoring the crack network of soil.

In summary, in view of the problem of dry shrinkage and cracking of soil in nature, how to find a more effective, more convenient and more accurate non-destructive technical means to predict the development of cracks on the soil surface, so as to better understand the dry shrinkage and cracking of soil. Mechanism and knowing in advance the area and direction of crack development on the soil surface have become urgent problems to be solved, which will bring positive significance to mechanism analysis in scientific research and disaster prevention and reduction in engineering.

Contents of the invention

1. Problem to be solved

Although existing technologies can quickly monitor the fissure network on the soil surface, most of these methods require destroying the original structure of the soil, which is time-consuming and labor-intensive and affects monitoring accuracy. In view of the problem that it is difficult to non-destructively predict the development of cracks on the soil surface with the existing technology, the present invention provides a method for predicting the development of cracks on the soil surface, which can more effectively, conveniently and accurately predict the development of cracks on the soil surface without disturbing the soil. Cracks can be predicted to predict the initiation and evolution of soil cracks.

2. Technical solutions

In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

A method for predicting the development of cracks on the soil surface, including the following steps:

S1 uses an infrared thermal imaging camera to photograph the surface of the soil to be monitored and obtain the soil surface temperature field;

S2 draws the soil isotherm map based on the soil surface temperature field;

S3 Determine the main crack development area on the soil surface based on the soil isotherm map.

Preferably, the method for determining the main crack development area on the soil surface in step S3 includes:

S3-1 Determine the low-temperature core area based on the soil isotherm map; the junction of adjacent low-temperature core areas is the main crack development area on the soil surface; and/or

S3-2 The main crack development area on the soil surface along the isotherm direction.

Preferably, the low-temperature core area refers to the area where the temperature of the isotherm decreases from outside to inside. The temperature in this low-temperature core area is significantly lower than the average temperature in other areas of the soil surface.

Preferably, the temperature difference between the average temperature of the low-temperature core area and the highest temperature of the soil should be greater than 1.5°C (the specific difference should depend on the ambient temperature).

Preferably, the junction of adjacent low-temperature core areas in step S3-1 refers to the junction surrounding the isotherms of two adjacent low-temperature core areas in the soil isotherm diagram. For example, two adjacent low-temperature core areas form an "8"-shaped area, and the junction of adjacent low-temperature core areas is the connection line between the "8"-shaped depressions.

It should be noted that a main fissure is defined as a fissure whose development point within the soil mass does not originate from other fissures.

Preferably, the main cracks on the soil surface in step S3-1 develop along the direction of the boundary line at the junction of the adjacent low-temperature core areas.

At the junction between adjacent low-temperature core areas, main cracks will develop and extend along the boundary line of adjacent low-temperature core areas. The reason for the above phenomenon is that the temperature at the junction of the low-temperature core area is relatively high, and the temperature on both sides of the junction is low. The soil at the junction continues to move toward the low-temperature core areas on both sides. Due to the opposite movement of soil particles in different areas, local soil The body is in a state of tension, and the tensile stress continues to accumulate. When this tensile stress exceeds the tensile strength of the soil at the corresponding location, cracks will occur, so cracks will occur at the junction.

Preferably, after step S3, it also includes:

S4 Determine the secondary crack: a secondary crack is generated in a direction perpendicular to the main crack. The secondary crack refers to a crack generated from a certain position of the main crack.

Preferably, the cracks tend to develop along the isotherm direction after being generated in step S4.

Preferably, the main crack development area on the soil surface along the isotherm direction in step S3-2 includes the edge of the low-temperature core area, and the edge of the low-temperature core area refers to the outermost isotherm of the low-temperature core area. area.

At the edge of the low-temperature core area is the main crack development area on the soil surface along the isotherm direction. This is due to the large evaporation/shrinkage rate gradient at the edge of the low-temperature core area. It can be seen from the soil surface temperature field that the temperature at the edge of the low-temperature core area is not completely consistent. The temperature gradually decreases from the edge to the core, and there is a temperature gradient. The temperature gradient indicates that there may be an evaporation/shrinkage rate gradient in the direction perpendicular to the isotherm, that is, some soil shrinks quickly (near the low-temperature core area because evaporation is fast), and another part of the soil shrinks slowly (near the temperature boundary area because evaporation is slow). . The fast-shrinking soil is restricted by the slow-shrinking soil during the deformation process, causing concentration of tensile stress, and the direction of the main tensile stress is also orthogonal to the direction of the isotherm, so soil along the direction of the isotherm is produced here. Main surface cracks.

A method for predicting the development of cracks on the soil surface of the present invention includes the following steps:

(1) Determine the scope of soil to be monitored, paste black 3M tape around the soil, set up infrared thermal imaging cameras and SLR cameras (to verify the accuracy of the prediction method) and connect them to the computer;

(2) Calibrate the ambient temperature;

(3) Enter the soil emissivity parameters, calibrated ambient temperature, and relative humidity in the software ResearchIR, set the shooting interval of the infrared thermal imaging camera and SLR camera, and start automatic shooting;

(4) Real-time monitoring of the development of cracks on the soil surface:

S1 uses an infrared thermal imaging camera to photograph the surface of the soil to be monitored and obtain the soil surface temperature field;

S2 draws the soil isotherm map based on the soil surface temperature field;

S3 Determine the main crack development area on the soil surface based on the soil isotherm map:

S3-1 Determine the low-temperature core area based on the soil isotherm map; the junction of adjacent low-temperature core areas is the main crack development area on the soil surface; the low-temperature core area refers to the area where the temperature of the isotherm decreases from outside to inside; so The junction of adjacent low-temperature core areas refers to the junction surrounding the isotherms of two adjacent low-temperature core areas in the soil isotherm diagram; the main cracks on the soil surface are along the junction of the adjacent low-temperature core areas. develop in the direction of the junction line; and/or

S3-2 The main crack development area on the soil surface along the isotherm direction;

S4 Determine secondary cracks: secondary cracks are generated in the direction perpendicular to the main crack. After the secondary cracks are generated, they tend to develop along the isotherm direction.

Among them, it should be noted that the situations of steps S3-1 and S3-2 may exist at the same time, or only one of them may exist. When there is an adjacent low-temperature core area on the soil surface, it must exist predetermined by S3-1. The main crack obtained by the S3-1 prediction method; when there is no adjacent low-temperature core area on the soil surface, such as when there is only an isolated low-temperature core area, there is no main crack obtained by the S3-1 prediction method, but there is a main crack obtained by the S3-1 prediction method. -2 The main crack obtained by the pre-judgment method; no matter which one or both of the above two main cracks occur, the secondary crack develops from a certain position on the main crack as a starting point.

The main crack development area on the soil surface along the isotherm direction of S3-2 includes the edge of the low-temperature core area, and the edge of the low-temperature core area refers to the outermost isotherm area of the low-temperature core area, where The area is more likely to produce main cracks on the soil surface along the isotherm direction as described in S3-2.

While using infrared thermal imaging camera monitoring results to predict the development of cracks on the soil surface, SLR cameras are used to capture images to verify the crack development process.

3. Beneficial effects

Compared with the existing technology, the beneficial effects of the present invention are:

(1) The present invention aims at the problem of predicting the development of cracks on the soil surface by destroying the original structure of the soil in the existing in-situ soil cracking process monitoring methods, and uses infrared thermal imaging to obtain the surface temperature of the soil in the early evaporation stage. field, non-destructively predicting the starting position and extension direction of crack development on the soil surface based on the temperature field distribution. This method can successfully predict the generation area and development direction of cracks up to 48 hours before crack formation, avoiding the layout of existing technologies. Monitoring facilities cause damage to soil structures, and the prediction time is much earlier than other crack monitoring methods (such as ERT (Resistivity Tomography), DIC (Digital Image Related Technology), etc.), and surface cracks can be obtained earlier Developmental trends.

(2) Existing non-contact crack monitoring methods such as digital image correlation (DIC) assume that the soil is a homogeneous body with uniform moisture content at each point, and can only simply record the surface strain/displacement field of the soil. , although the starting position of the crack can be predicted in advance, the advance prediction time is short, and the influence of evaporation differences across the soil surface cannot be considered, nor can the differences in moisture content of individual points be analyzed; the present invention uses infrared thermal imaging The technology can record the temperature changes at various points on the soil surface, obtain the temperature field differences at each point, and further predict the development of cracks on the soil surface based on the temperature field differences. It can predict the development of soil surface cracks up to 48 hours in advance.

(3) The device of the present invention is simple, easy to operate, and the monitoring results are accurate. The scope of application is not limited by environmental conditions. It is suitable for indoor tests and in-situ undisturbed soil crack development monitoring. The present invention is conducive to predicting the development of soil cracks in advance. status, real-time monitoring of the development of soil cracks, and providing early warning data basis for disasters caused by cracks.

Description of drawings

Figure 1 is a schematic diagram of the device structure of the present invention;

Figure 2(a)-Figure 2(f) are isotherm diagrams of the soil in the monitoring area in Embodiment 1;

Figures 3(a) to 3(f) are diagrams of the development of cracks on the soil surface at different times taken by the SLR camera in Example 1;

Figure 4(a) and Figure 4(b) are the infrared imaging images and SLR camera images of the sample in Example 2;

Figure 5(a)-Figure 5(d) are isotherm diagrams and single crack predictions 48 hours before the first crack occurs in Example 3;

Figures 6(a) to 6(c) show isotherm diagrams and crack predictions 48 hours before the first crack occurs in Example 3.

In the picture: 1. Computer; 2. Infrared thermal imaging camera; 3. Temperature/humidity meter; 4. SLR camera; 5. Black 3M tape; 6. Soil in the monitoring area; 7~11. Cracks.

Detailed ways

Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the technical field of the invention; the term "and/or" used herein includes one or more of the relevant listed Any and all combinations of items.

If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

The black 3M tape used in the present invention is produced by 3M Company of the United States. The model is 1500 black and the emissivity parameter is 0.95; the infrared imager model is FLIR-T620, the camera resolution is 640×480pix, and the temperature measurement sensitivity is ±0.04°C. Accuracy ±0.1℃.

As shown in Figure 1, the infrared thermal imaging camera should be located directly above the monitoring area and adjusted to a suitable height to ensure that the soil in the monitoring area and the black 3M tape fill the viewfinder frame to the maximum extent. The SLR camera should be installed above the monitoring area and adjusted to a suitable height to ensure that the soil in the monitoring area fills the viewfinder frame.

(1) The method of calibrating the ambient temperature is:

a) Use a thermometer to measure the ambient temperature;

b) Enter the black 3M tape emissivity parameters and ambient temperature into the software ResearchIR;

c) Use an infrared thermal imaging camera to measure the temperature of the area covered by the black 3M tape;

d) Compare the tape temperature in step c) with the ambient temperature entered in step b). If the two are consistent, the calibration is over; if they are inconsistent, change the ambient temperature entered in step b) and repeat step c) until the black 3M tape temperature is reached. consistent with the ambient temperature.

For most types of soil, the thermal infrared emissivity of its surface is between 0.90 and 0.95. When the specific thermal infrared emissivity of the soil is unknown, its average value of 0.925 is generally taken as the soil sample emissivity parameter.

The automatic photo-taking function of the infrared thermal imaging camera is implemented by the software ResearchIR. The set shooting interval is based on the cracking speed of the soil. Generally, 10 minutes is taken as the shooting interval. The soil thermal infrared radiation temperature field image is directly obtained by the software ResearchIR. The thermal infrared radiation temperature data of the soil at each time are directly exported by the software ResearchIR, and the isotherm map of the soil in the monitoring area at each time is drawn by the software Surfer 16.

The automatic shooting interval of the SLR camera is consistent with the automatic shooting time of the infrared thermal imaging camera.

(2) The present invention’s method for predicting the development of cracks on the soil surface is:

S1 uses an infrared thermal imaging camera to photograph the surface of the soil to be monitored and obtain the soil surface temperature field;

S2 draws the soil isotherm map based on the soil surface temperature field;

S3 Determine the main crack development area on the soil surface based on the soil isotherm map:

S3-1 Determine the low-temperature core area based on the soil isotherm map; the junction of adjacent low-temperature core areas is the main crack development area on the soil surface;

The low-temperature core area refers to the area where the temperature of the isotherm decreases from outside to inside; the junction of adjacent low-temperature core areas refers to the junction of the isotherms surrounding two adjacent low-temperature core areas in the soil isotherm diagram; the soil surface The main crack develops along the direction of the junction line at the junction of adjacent low-temperature core areas; and/or

S3-2 The main crack development area on the soil surface along the isotherm direction;

S4 Determine the secondary cracks: secondary cracks are generated in the direction perpendicular to the main crack. After the secondary cracks are generated, they tend to develop along the direction of the isotherm.

Soil cracks generally first occur along the isotherm line at the junction of adjacent low-temperature core areas or at the edge of the low-temperature core area. The corresponding soil cracks along the isotherm line at the junction of adjacent low-temperature core areas or at the edge of the low-temperature core area extend quickly and the cracks The degree of development is high; in the soil in the high temperature zone, the crack extension speed is slow and the degree of crack development is low, but the width of the crack expands quickly and the overall shrinkage of the soil is high. The high temperature area here refers to the area where the temperature decreases from the inside to the outside of the isotherm.

Various parameters for monitoring cracks with an SLR camera are obtained by analyzing and processing photos using CIAS software independently developed by Nanjing University.

The present invention will be further described below with reference to specific embodiments.

Example 1

The soil in this example is an initially saturated Xiashu soil mud sample. The sieved dried Xiashu soil sample is mixed with distilled water, stirred thoroughly to prepare a saturated mud sample with a moisture content of 170%, and vibrated on a vibrating table. 5 minutes to eliminate air bubbles generated inside the mud during the mixing process. Then, seal the slurry sample in the container and let it stand for 48 hours. After the mud sedimentation is stable, the surface clear liquid is pumped away, and the moisture content is measured to be about 70% at this time. Pour the prepared mud sample evenly into a 20×20cm, 4cm high plexiglass box. The inner walls of the container, including the side plates and bottom plates, are lubricated with Vaseline to minimize the impact of friction between the side walls and the bottom plate of the container on soil shrinkage and cracking. The prepared samples were placed in a room with a constant temperature of 31°C to dry. Two fans are placed on the left and right sides of the plexiglass box to blow air to the soil surface, causing differences in the temperature field distribution on the soil surface.

(1) The shrinkage zone at the edge of the container boundary may be mistaken for soil cracks in the analysis, resulting in inaccurate monitoring results. In order to reduce the impact of the edge shrinkage area on crack prediction, only the 18 × 18 cm part in the center of the sample was selected for monitoring, and black 3M tape was pasted around the soil. Set up an infrared thermal imaging camera, and fill the camera viewfinder with soil in the monitoring area and black 3M tape.

(2) According to the method of calibrating the ambient temperature in (1), the calibrated ambient temperature is 31.0°C.

(3) Remove the Shu soil, the emissivity parameter is 0.925, the calibrated ambient temperature is 31.0°C, and the relative humidity is 70% measured by a hygrometer. Enter the software ResearchIR, set the photo interval to 10 minutes, and start monitoring the soil. Development of surface cracks.

(4) Real-time monitoring of the development of cracks on the soil surface:

S1 uses an infrared thermal imaging camera to capture the surface of the soil to be monitored. Through the software ResearchIR, the changes in the current soil surface temperature field can be monitored in real time to obtain the soil surface temperature field;

S2 Draw the soil isotherm map based on the soil surface temperature field: obtain the soil isotherm map of the monitoring area at each time in Figure 2(a)~Figure 2(f) (take t=15, 55, 115, 185, 265, 305min analyze);

S3 Determine the main crack development area on the soil surface based on the soil isotherm map:

Predict the development of cracks based on (2) Soil surface crack development prediction method.

S3-1 is shown in Figure 2(d) and 12 in Figure 3(d). At the junction between the two low-temperature core areas, a main crack will develop and extend toward the junction line. The reason for the above phenomenon is that the temperature at the junction of the low-temperature core area is relatively high, and the temperature on both sides of the junction is low. The soil at the junction continues to move toward the low-temperature core areas on both sides. Due to the opposite movement of soil particles in different areas, local soil The body is in a state of tension, and the tensile stress continues to accumulate. When this tensile stress exceeds the tensile strength of the soil at the corresponding location, cracks will occur, so cracks will occur at the junction.

S3-2 is shown in Figures 2(b) to 2(d) and 7 to 11 in Figures 3(b) to 3(d). As evaporation continues, the main cracks on the soil surface along the isotherm direction It will first be generated at the edge of the low-temperature core area and extend along the temperature field isotherm. The reason for the above phenomenon is that there is a large evaporation/shrinkage rate gradient at the edge. It can be seen from the soil surface temperature field that the temperature at the edge of the low-temperature core area is not completely consistent. The temperature gradually decreases from the edge to the core, and there is a temperature gradient. The temperature gradient indicates that there may be an evaporation/shrinkage rate gradient in the direction perpendicular to the isotherm, that is, some soil shrinks quickly (near the core of the low-temperature core zone because evaporation is fast), and another part of the soil shrinks slowly (near the edge of the low-temperature core zone) , because evaporation is slow). The fast-shrinking soil is restricted by the slow-shrinking soil during the deformation process, causing concentration of tensile stress, and the direction of the main tensile stress is also orthogonal to the direction of the isotherm, so soil along the direction of the isotherm is produced here. Main surface cracks.

In this embodiment, the main cracks S3-1 and S3-2 exist at the same time.

Experimental results: In this embodiment, this method can be used to accurately obtain the temperature field distribution on the soil surface, so that the development shape of the cracks on the soil surface can be predicted. The cracks predicted by the soil isotherm map in the monitoring area can correspond well to the actual soil cracking conditions (shown in Figure 3(a)-Figure 3(f)).

Through the verification of the SLR camera, the method for predicting the development of cracks on the soil surface of the present invention can reasonably predict the development direction of cracks on the soil surface based on the soil surface temperature field data 170 minutes before the occurrence of cracks, and the prediction accuracy is high.

Example 2

The soil conditions and related parameters in this embodiment are the same as those in Embodiment 1, and the implementation steps are basically the same as those in Embodiment 1. The differences are:

The bottom of the plexiglass box is not coated with Vaseline to limit soil shrinkage (to influence the number and width of cracks).

Experimental results: As shown in Figure 4, Figure 4(a) is the infrared thermal imaging image, and Figure 4(b) is the SLR camera image after 2h. As shown in Figure 4(a), according to the soil surface crack development prediction method S3-1, there will be cracks in the soil at the junction of the two low-temperature core areas. This crack is the main crack, and the cracks continue to develop along the junction line. . Its formation mechanism is mainly attributed to moisture migration and soil particle movement. According to soil surface crack development prediction method S4, secondary cracks are generated on the original main cracks. The crack development path starts perpendicular to the original main cracks and tends to develop along the isotherm direction after generation. It is a series of friction-induced Surface subcracks.

This embodiment is a case where there are only S3-1 main cracks and S4 secondary cracks.

The prediction results of infrared thermal imaging images can correspond well to the SLR camera images.

Example 3

The types and characteristics of the soil in this example are the same as those in Example 1, and the implementation steps are basically the same as those in Example 1. The differences are:

The moisture content of the saturated mud sample of Xiashu soil was 60% when initially evaporated. The dimensions of the plexiglass box container are 40×60cm and 4cm high. Considering the large size of the specimen, the specimen was manually shaken for 15 minutes to remove internal air bubbles. The fans at both ends of the plexiglass box were removed and the specimen evaporated naturally.

In this embodiment, in order to reduce the impact of the edge shrinkage area on crack prediction, only the 28×28cm portion of the center of the sample is selected for monitoring.

Experimental results: Figure 5(a) shows the predicted path for the development of the main crack at the junction of the low-temperature core zone based on S3-1 through the isotherm map 48 hours before the first crack is generated during the evaporation process. Figure 5(b) ) is the real main crack (left in Figure 5(b)) and development extension (right in Figure 5(b)) taken through the SLR camera image after 48 hours; Figure 5(c) shows the first crack during the evaporation process. 48 hours before the crack occurs, based on the predicted path of the main crack development at the edge of the low-temperature core area through the isotherm map of S3-2, Figure 5(d) shows the real main crack captured by the SLR camera image 48 hours later (Figure 5(d) left) and developmental extension (right in Figure 5(d)). It can be seen that the isotherm map obtained through infrared thermal imaging image data processing can better predict the direction of crack development and extension during the evaporation process, and the prediction time is much earlier than other prediction methods.

Figure 6(a) shows the isotherm diagram 48 hours before the first crack occurs. According to the crack determination methods S3-1, S3-2 and S4 of the present invention, the crack prediction map shown in Figure 6(b) is obtained , it can be seen by comparison that it corresponds well to the actual fracture network shown in Figure 6(c).

The above content is a schematic description of the present invention and its embodiments. This description is not limiting. What is shown in the drawings is only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person of ordinary skill in the art is inspired by the invention and without departing from the spirit of the invention, can devise structural methods and embodiments similar to the technical solution without inventiveness, they shall all fall within the protection scope of the invention. .

Claims (7)

1. A method for predicting the development of cracks on the soil surface, which is characterized by including the following steps: S1 uses an infrared thermal imaging camera to photograph the surface of the soil to be monitored and obtain the soil surface temperature field; S2 draws the soil isotherm map based on the soil surface temperature field; S3 Determine the main crack development area on the soil surface based on the soil isotherm map; The method for determining the main crack development area on the soil surface in step S3 includes: S3-1 Determine the low-temperature core area based on the soil isotherm map; the junction of adjacent low-temperature core areas is the main crack development area on the soil surface; and/or S3-2 The main crack development area on the soil surface along the isotherm direction; the main crack development area on the soil surface along the isotherm direction includes the edge of the low-temperature core area, and the edge of the low-temperature core area refers to the The outermost isotherm area of the low-temperature core area; The low-temperature core area refers to the area where the temperature of the isotherm decreases from outside to inside. 2. The method for predicting the development of cracks on the soil surface according to claim 1, characterized in that the temperature difference between the average temperature of the low-temperature core area and the highest temperature of the soil should be greater than 1.5°C. 3. The method for predicting the development of cracks on the soil surface according to claim 1, characterized in that the junction of adjacent low-temperature core areas in step S3-1 refers to the area surrounding the adjacent low-temperature core areas in the soil isotherm diagram. The junction of the two low-temperature core zone isotherms. 4. The method for predicting the development of cracks on the soil surface according to claim 3, characterized in that the main cracks on the soil surface in step S3-1 develop along the direction of the junction line at the junction of the adjacent low-temperature core areas. . 5. The method for predicting the development of cracks on the soil surface according to claim 1, characterized in that, after step S3, it also includes: S4 Determine secondary cracks: secondary cracks are generated in the direction perpendicular to the main crack. 6. The method for predicting the development of cracks on the soil surface according to claim 5, characterized in that, after the cracks are generated in step S4, they tend to develop along the isotherm direction. 7. A method for predicting the development of cracks on the soil surface, which is characterized by including the following steps: (1) Determine the scope of the soil to be monitored, paste black 3M tape around the soil, set up an infrared thermal imaging camera and connect it to the computer; (2) Calibrate the ambient temperature; (3) Enter the soil emissivity parameters, calibrated ambient temperature, and relative humidity in the software ResearchIR, set the shooting interval of the infrared thermal imaging camera, and turn on automatic shooting; (4) Real-time monitoring of the development of cracks on the soil surface: S1 uses an infrared thermal imaging camera to photograph the surface of the soil to be monitored and obtain the soil surface temperature field; S2 draws the soil isotherm map based on the soil surface temperature field; S3 Determine the main crack development area on the soil surface based on the soil isotherm map: S3-1 Determine the low-temperature core area based on the soil isotherm map; the junction of adjacent low-temperature core areas is the main crack development area on the soil surface; the low-temperature core area refers to the area where the temperature of the isotherm decreases from outside to inside; so The junction of adjacent low-temperature core areas refers to the junction surrounding the isotherms of two adjacent low-temperature core areas in the soil isotherm diagram; the main cracks on the soil surface are along the junction of the adjacent low-temperature core areas. develop in the direction of the junction line; and/or S3-2 The main crack development area on the soil surface along the isotherm direction. The main crack development area on the soil surface along the isotherm direction includes the edge of the low-temperature core area. The edge of the low-temperature core area refers to the The outermost isotherm area of the low-temperature core area.