CN110579585A - A Determination Method of Sample Thickness Based on Soil Cracking Research - Google Patents

Abstract

The invention discloses a method for determining sample thickness based on soil cracking research in the technical field of soil cracking, comprising step 1, taking samples with the same soil diameter, and designing cracking experiments based on soil samples with different thicknesses of soil; step 2, targeting each group of soil For the thickness cracking experiment, calculate the average value and standard deviation of the soil crack surface characteristics of each repeated sample, and compare the reproducibility of the crack surface characteristics under different soil thicknesses; step 3, for each group of soil thickness cracking experiments, use the image method to calculate The cracking area of the sample is compared with the difference of the two methods under different thicknesses to determine the measurability of the crack volume of the same thickness sample. The present invention has better repeatability of the final cracking index parameter value of the soil between different repetitions under the same thickness. The method of combining images and fine needles realizes the replacement of the soil cracking volume value measured by the iron powder method; and can more accurately measure and calculate the optimum thickness for soil cracking research.

Description

A Determination Method of Sample Thickness Based on Soil Cracking Research

technical field

The invention relates to the technical field of soil cracking, in particular to a method for determining sample thickness based on soil cracking research.

Background technique

In the case of soil cracking, the final cracking state of the soil quantifies the degree of soil shrinkage, and the determination of the soil shrinkage characteristic curve can dynamically describe the volume change in the process of soil dehydration. The difficulty in determining the shrinkage curve lies in the quantification of soil volume. In the field, Abou et al. (2010) filled soil cracks with latex and measured the cracked volume of the soil. Dasog et al. (1993) estimated the volume of soil cracks by measuring the length of cracks with a string and inserting a ruler to measure the depth of cracks. No studies have considered the presence of soil cracking when determining soil shrinkage curves in the laboratory. Generally, the volume change of the whole soil is measured. For example, Kim et al. used the displacement method to measure the soil volume; Stewart et al. (2010) mainly used the image reconstruction technology to construct the photos in different directions to obtain the three-dimensional image of the soil, and then obtained the soil re-loss by coordinate analysis. Moisture change in water process. Shao Mingan et al. (2003) obtained the soil volume change by measuring with a ruler. However, studies have shown that there are large differences in the degree of cracking of samples under different environments and sample sizes, so choosing an appropriate soil sample size is a problem that needs to be solved.

Based on this, the present invention designs a sample thickness determination method based on soil cracking research to solve the above problems.

Contents of the invention

The purpose of the present invention is to provide a method for determining sample thickness based on soil cracking research, so as to solve the existing problem of how to select a suitable soil sample size raised in the background art above.

To achieve the above object, the present invention provides the following technical solutions: a method for determining sample thickness based on soil cracking research, comprising the following steps:

Step 1. Take samples with the same soil diameter, and design cracking experiments based on soil samples with different soil thicknesses;

Step 2, for each group of soil thickness cracking experiments, calculate the average value and standard deviation of the soil crack surface characteristics of each repeated sample, and compare the reproducibility of the crack surface characteristics under different soil thicknesses;

Step 3. For each group of soil thickness cracking experiments, use the image method to calculate the cracking area of the sample, compare the difference between the two methods under different thicknesses, and determine the measurability of the crack volume of the same thickness sample;

Step 4. For each group of soil thickness cracking experiments, calculate the relationship between the cracking area and water content of each repeated sample under the same thickness during the cracking process, and compare the coincidence of the two relationships between the repeated samples of different soil thicknesses ;

Step 5. According to the reproducibility of fracture surface characteristics, the measurability of fracture volume, and the coincidence of the relationship between fracture area and water loss, select the optimal thickness among the design thicknesses to conduct fracture research.

Preferably, the thickness range of the soil sample in the step 1 is 4-15mm, and the steps of the soil cracking experiment include:

A. Sieve and process according to the thickness range of the soil sample, and divide the thickness gradient;

B. Place soil samples with different thickness gradients in organic plastic boxes, add deionized water and stir evenly, and the mass ratio of soil samples to deionized water in each group of organic plastic boxes is 5:2;

C. Dry the mixture treated in step B naturally in a constant temperature and humidity chamber with a temperature of 19-21° C. and a humidity of 40%.

Preferably, when performing natural drying in step C, the soil drop height during the drying process is measured by a direct measurement method.

Preferably, the soil drop height determination process comprises the steps:

a) mark at least eight fixed positions on the edge of the organic plastic box;

b) measure the distance between the soil surface and each of the fixed positions when natural drying starts and after drying, and get the average distance L ₀ and L _x ;

c) Subtracting the average distance L ₀ and L _x from the height of the organic plastic box is the soil thickness h ₀ and h _x at the beginning of natural drying and after drying;

d) The difference between the soil thickness h ₀ and h _x degree at the beginning of natural drying and after drying is the soil drop height h _d .

Preferably, the specific steps of measuring the depth of soil cracks by image method in the step 3 are: inserting a fine needle into the cracks of the soil to measure the depth, during the insertion process, stop when resistance occurs at the front end of the needle, and then use the accuracy of 0.01mm The vernier caliper is used to measure the length of the needle inserted into the crack; each time the soil crack depth is measured, several points in the crack are measured, and then the average value is calculated as the crack depth value h _c .

Preferably, during the process of natural air-drying, the water content of soil samples at different water content stages is measured, and the specific steps include: taking out a soil sample, dividing the soil sample into upper and lower layers evenly with a blade, and then drying method to determine the mass water content of different layers of soil.

Preferably, the measurement positions of the surface characteristics of cracks with different soil thicknesses in the step 2 are from the initial point of soil cracking to the point of differentiation and from the point of generation to the end of each differentiation.

Compared with the prior art, the beneficial effect of the present invention is: the present invention has better repeatability of the final cracking index parameter value of the soil between different repetitions under the same thickness, and the method of combining images and fine needles realizes the iron powder The replacement of the soil cracking volume value determined by the method; and the optimum thickness for soil cracking research can be calculated more accurately.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that are required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. Those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.

Fig. 1 is different sample thicknesses of the present invention to soil cracking process figure;

Fig. 2 is the schematic diagram of soil cracking form under different sample thicknesses of the present invention;

Fig. 3 is soil cracking area of the present invention with water content change figure;

Fig. 4 is the variation figure of soil cracking volume with water content of the present invention;

Fig. 5 is the variation figure of soil shrinkage volume with water content of the present invention;

Fig. 6 is the table figure of soil cracking volume difference measured by image method and iron powder method of the present invention;

Fig. 7 is the figure of moisture content difference between the upper layer of the soil and the lower layer of the present invention;

Fig. 8 is a statistical diagram of soil cracking characteristic parameters under different sample thicknesses of the present invention;

Fig. 9 is an overall flowchart of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Please refer to Fig. 1-8, the present invention provides a kind of technical scheme: a kind of sample thickness determination method based on soil cracking research, comprises the following steps:

Step 1. Take samples with the same soil diameter, and design cracking experiments based on soil samples with different soil thicknesses;

Step 2, for each group of soil thickness cracking experiments, calculate the average value and standard deviation of the soil crack surface characteristics of each repeated sample, and compare the reproducibility of the crack surface characteristics under different soil thicknesses;

Step 3. For each group of soil thickness cracking experiments, use the image method to calculate the cracking area of the sample, compare the difference between the two methods under different thicknesses, and determine the measurability of the crack volume of the same thickness sample;

Step 4. For each group of soil thickness cracking experiments, calculate the relationship between the cracking area and water content of each repeated sample under the same thickness during the cracking process, and compare the coincidence of the two relationships between the repeated samples of different soil thicknesses ;

Step 5. According to the reproducibility of fracture surface characteristics, the measurability of fracture volume, and the coincidence of the relationship between fracture area and water loss, select the optimal thickness among the design thicknesses to conduct fracture research.

It should be noted that the optimal selection of crack thickness was not considered in the previous crack research, so the proposal of this method is beneficial to improve the accuracy and comparability of crack research.

A further embodiment is that the thickness range of the soil sample in the step 1 is 4-15mm, and the steps of the soil cracking experiment include:

A. Sieve and process according to the thickness range of the soil sample, and divide the thickness gradient;

B. Place soil samples with different thickness gradients in organic plastic boxes, add deionized water and stir evenly, and the mass ratio of soil samples to deionized water in each group of organic plastic boxes is 5:2;

C. Dry the mixture treated in step B naturally in a constant temperature and humidity chamber with a temperature of 19-21°C and a humidity of 40%;

It needs to be explained that in order to measure the cracking process of the soil in the process of dehydration, three thickness treatments can be preferably set, which are 4-5mm, 9-10mm and 14-15mm respectively. The sieved soil sample is placed in an organic plastic box with a height of 25mm and a diameter of 110mm, and then deionized water is added to make the mass water content about 0.60g/g. Dry naturally in a humid box (20±1°C, 40%), do 8 sets of repetitions for each thickness of soil sample, and calculate the final soil cracking index. Under each treatment, three soil samples have completely measured the soil cracking from the beginning to complete the cracking process.

A further embodiment is that when the natural drying is carried out in step C, the height of the soil drop in the drying process is measured by a direct measurement method; since the soil is in a supersaturated state at the beginning of the experiment, the soil has a certain degree of expansion. The soil height drops during the drying process, and its falling volume is measured by direct measurement method. Experimental tool: vernier caliper with an accuracy of 0.01mm. .

A further embodiment is that the soil drop height determination process includes the following steps:

a) mark at least eight fixed positions on the edge of the organic plastic box;

b) measure the distance between the soil surface and each of the fixed positions when natural drying starts and after drying, and get the average distance L ₀ and L _x ;

c) Subtracting the average distance L ₀ and L _x from the height of the organic plastic box is the soil thickness h ₀ and h _x at the beginning of natural drying and after drying;

d) The difference between the soil thickness h ₀ and h _x degree at the beginning of natural drying and after drying is the soil drop height h _d ;

The main process of this step is to mark eight fixed positions on the edge of the organic plastic box, and measure the distance between the soil surface and these eight points while measuring the soil water content each time, and then obtain the average distance. Since the height of the cultivation box is fixed, the thickness of the soil can be obtained by subtracting the average distance from the height of the cultivation box, and the soil drop height can be calculated according to the difference between the two soil thicknesses before and after: v ₀ =A ₀ *hd;

Where v ₀ (mm ³ ) is the descending volume of the soil, A ₀ (mm ² ) is the soil surface area, and hd (mm) is the soil descending.

A further embodiment is that the specific steps of measuring the depth of soil cracks by the image method in the step three are: insert a fine needle into the crack of the soil to measure the depth. During the insertion process, stop when there is resistance at the front end of the needle, and then use The vernier caliper with an accuracy of 0.01mm measures the length of the fine needle inserted into the crack; each time the soil crack depth is measured, multiple points in the crack are measured, and then the average value is calculated as the crack depth value h _c ;

During the test, a fine needle was inserted into the crack of the soil for depth measurement (the fine needle was selected in this experiment because the fine needle is relatively hard and not easy to deform, and on the other hand, the fine needle is easy to buy and has a variety of sizes) . Due to the different soil cracking conditions under different water content conditions, the number of points to measure the soil cracking depth increases with the increase of the cracking area. At each measurement of the crack depth, the cracked area of the soil was measured using the image method. The soil crack volume is then calculated as follows:

v _c =A*h _c ;

Among them, v _c (mm ³ ) is the soil cracking volume, and A (mm ² ) is the soil cracking area.

And compared with the image method, there is the iron powder method to measure the soil volume. The iron powder (passed through 200 mesh) sieved by 0.075mm is filled into the soil cracks to estimate the soil crack volume. Experimental process: First, iron powder is filled into a measuring cylinder with a known volume, and the relationship coefficient D between the two is calculated by filling the mass and volume of iron powder. Then fill the crack with a certain mass (m ₁ ) of iron powder until the crack is filled, and then weigh the remaining iron powder mass m2 to calculate the volume of the soil crack:

mi=m1-m2;

Among them, m _i is the mass of iron powder loaded into the soil cracks.

Although this method is simple to operate compared with the image and fine needle methods, the process of taking out the iron powder will cause damage to the soil, so continuous measurement cannot be performed;

Linear fitting is carried out through the relationship between the mass and volume of the iron powder, and the coefficient of the linear relationship is 0.3118g/mm3, and R ² =0.99. Table 1 compares the difference between the iron powder method and the image method to measure the soil crack volume. It can be seen that the soil crack volume measured by the image method is larger than that measured by the iron powder method. However, for soil samples with a soil sample thickness of 4-5mm, the difference in cracking volume measured by the two methods is within 9%. are 7.89% and 8.98%, and the maximum difference reaches 13.12% and 14.26% respectively. Part of the reason for this imagination is that when the thickness of the soil sample is 4-5mm, the soil cracks evenly and the soil cracks to the bottom very quickly. From the observation during the experiment, the width of the soil crack is basically rectangular from top to bottom. When the thickness of the soil sample is 9-10mm and 15-16mm, the width of the soil cracks presents an inverted triangle from top to bottom, the upper part is wider and the lower part is narrower. At the same time, the soil cracks extend downward for a long time. During this process, Soil cracks continuously produce branches, and the crack depths of successive branches have great differences. In our calculation process, the average crack depth is used to calculate the soil crack volume, so the difference between the image method and the iron powder method in the measurement process is relatively large. The reason why the width of soil cracks are different from top to bottom may also be related to soil evaporation. Some studies believe that when the soil clay content is high, the upward migration speed of water in the soil will slow down. In this experiment, Although the soil properties are the same, there may be differences in the moisture between the upper and lower layers of the thicker soil. In order to verify this idea, we compared the differences between the upper and lower layers of soil samples with different thicknesses.

A further embodiment is to measure the water content of soil samples at different water content stages during the natural air-drying process. The specific steps include: taking out a soil sample, dividing the soil sample into upper and lower layers evenly with a blade, Then use the drying method to measure the mass water content of different layers of soil; in the experiment, 5 soil samples were refilled for each thickness, and at different water content stages, a soil sample was taken out, and the thickness of the soil sample was 9-10mm and 15-16mm soil samples are evenly divided into upper and lower layers with a blade, that is, the thickness of 9-10mm soil samples after layering is about 4-5mm, and the thickness of 15-16mm soil samples after layering is about 7 -8mm, and then use the drying method to measure the mass water content of different layers of soil (take five small soil samples for each layer for average processing), and the soil samples with a thickness of 4-5mm are not layered, and directly measure different positions of the same soil sample The water content, and then take the average value, the results are shown in Table 6-3. It can be seen from the table that when the thickness of the soil sample is 4-5 mm, the difference in water content in each position of the soil sample is very small. When the soil sample thickness is 9-10mm and 1516mm, the water content of the lower soil layer is higher than that of the upper soil layer, and the difference in water content caused by evaporation may be the main reason for the inconsistent width of the upper and lower soil cracks. When the thickness of the soil sample is 9-10mm and 15-16mm, the moisture difference in different positions of the soil is also higher than 4-5mm, mainly because the soil samples with a thickness of 9-10mm and 15-16mm have large cracks. The position of the wall is easy to evaporate moisture.

It can be concluded from Figure 8 that the final cracking area of different samples with the same thickness does not change much. However, it can be seen from Figure 3 that for soils of the same thickness, the cracking area of different samples varies with soil moisture content. When the soil sample thickness was 4-5mm and 15-16mm, the reproducibility among soil samples was better, and when the soil sample thickness was 9-10mm, the difference among the repetitions was large. When the soil sample thickness is 4-5mm, the water content range when cracking occurs is 38.82-40.80g/g, and the water content range is 13.58-14.79g/g when the cracking area is stable; when the soil sample thickness is 9-10mm , the water content range when cracking occurs is 33.06-46.85g/g, and the water content range when the cracking area is stable is 11.40-13.12g/g; when the thickness of the soil sample is 15-16mm, the water content range when cracking occurs The water content range is 38.41-41.32g/g, and the water content range is 8.33-12.58g/g when the cracking area is stable; when the thickness of the soil sample is 4-5mm, the range of water content change when the soil cracks and the cracking is stable is the smallest. When the thickness of the soil sample is 9-10mm, the water content is the most unstable when cracking occurs, and when the thickness of the soil sample is 15-16mm, the water content is the most unstable when the cracking stops. According to the observations during the experiment, the reason for this phenomenon may be: when the thickness of the soil sample is 15-16mm, the cracking of the soil often starts from a point (defect point or weak point) in the soil, indicating that it mainly Affected by the soil itself, at this thickness, the later cracking process of the soil may not occur on the soil surface. Because the soil cracks are wider (Table 1), and the water content of the lower layer of the soil is higher than that of the upper layer, the inner wall of the soil cracks evaporates. Part of the evaporation process brings about an increase in the volume of soil cracking, so the stabilization of the cracked area on the soil surface does not mean that the cracking has stopped. It can be seen from Figure 1 that when the thickness of the soil sample is 4-5mm, the cracking of the soil often does not start from one point, but multiple cracks occur at the same time, which shows that when the soil is at this thickness, the cracking is not caused by the soil itself alone. It is caused by some defect points, and environmental factors also have a greater impact on it. During the cracking process, when the thickness of the soil sample is 9-10mm, the soil cracking is more random, and the cracking may start at one point or at multiple points.

A further embodiment is that, in the step 2, the measurement positions of the surface characteristics of cracks with different soil thicknesses are from the initial point of soil cracking to the point of differentiation and from the point of differentiation to the end of each differentiation;

Figure 1 shows the cracking of samples with different thicknesses during the dehydration process. It can be seen from the figure that when the thickness of the soil sample is 9-10mm and 15-16mm, the soil cracking starts from a point, along which the soil cracks lengthen and widen, and when the soil crack width reaches a certain value, nodes will be generated, Other cracking branches will be generated at the nodes, and the depth of soil cracks will continue to deepen with the evaporation process. When the thickness of the soil sample is 4-5mm, there will be cracks at multiple points at the same time, and multiple cracks will be generated at the same time, and finally multiple cracks will be connected together as the length increases.

It should be noted that, as can be seen from Figure 2, according to the statistics of characteristic parameters of different thicknesses, although the size of the soil culture box becomes larger, the cracking of the soil under different thicknesses increases with the thickness of the soil sample. The crack pattern becomes simpler. It can be seen from Table 2 that after the soil has completely shrunk, the difference between the crack index parameters is not very large, and the standard deviations of Dc, CI, P and EW crack parameters are the smallest when the thickness of the soil sample is 4-5 mm, which are 0.38%, 0.38%, and 0.02, 0.07%, and 0.54 pixels. The standard deviation of the Lc value is the smallest when the thickness is 9-10mm, which is 0.05%. The FD value is the smallest when the soil sample thickness is 4-5mm and 15-16mm, both are 0.02. It can be seen that for soil, under the same thickness, the reproducibility of soil cracking characteristics is good, but the standard deviation of 4-5mm soil cracking index is the smallest;

And Fig. 4 is a graph showing the variation of soil cracking volume (image method) with soil water content. It can be seen from the figure that the change law of soil crack volume is basically consistent with the change law of soil area. When the thickness of the soil sample is 4-5mm, the repeatability of the fracture volume of different samples is better. When the soil sample thickness is 15-16mm, the crack volume gap between different soil samples is greater than the soil area. In addition, it can be seen from the figure that under different thicknesses, the water content of the soil when the cracking volume occurs is consistent with the cracking of the soil. When the soil cracking volume is stable, except for the water content of 4-5mm, the other two thicknesses are different from that of the cracking area. The water content range of 9-10mm soil cracking volume is 3.12-14.51g/g, 15- 16mm of soil is 4.47-8.33g/g. These phenomena are related to the occurrence and measurement of soil depth. When the thickness of the soil sample is 4-5mm, the soil will soon crack to the bottom, and the difference between different crack depths is small. The soil crack area determines the soil crack volume. When the thickness of the soil sample is 9-10cm and 15-16mm, the degree of crack cracking of successive time cracks is quite different, and there is a big error between the depth obtained by taking the average value and the real depth, and due to the difference in the moisture content of the upper and lower layers of the soil, Soil depth can continue to occur while surface cracking area is stable;

Then, the total soil shrinkage volume is the sum of the soil cracking volume and the soil falling volume. Figure 5 shows the variation of total soil shrinkage volume with water content. It can be seen from the figure that under different thickness treatments, the water content when the soil shrinks is about 0.50g/g. The soil shrinkage volume has better repeatability when the soil sample thickness is 4-5mm and 15-16mm, and the soil shrinkage volume further increases when the soil thickness is 9-10mm. It shows that when the thickness of the soil sample is 4-5mm and 15-16mm, the descending volume changes little.

In the description of this specification, descriptions with reference to the terms "one embodiment", "example", "specific example" and the like mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. In an embodiment or example. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The preferred embodiments of the invention disclosed above are only to help illustrate the invention. The preferred embodiments are not exhaustive in all detail, nor are the inventions limited to specific embodiments described. Obviously, many modifications and variations can be made based on the contents of this specification. This description selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The invention is to be limited only by the claims, along with their full scope and equivalents.

Claims (7)

1. a sample thickness determination method based on soil cracking research is characterized in that: the method comprises the following steps:

taking samples with the same soil diameter, and designing different soil thickness cracking experiments based on the soil samples;

Step two, calculating the average value and the standard deviation of the surface characteristics of the soil cracks of each repeated sample aiming at each group of soil thickness cracking experiments, and comparing the reproducibility of the surface characteristics of the cracks under different soil thicknesses;

Step three, aiming at each group of soil thickness cracking experiments, calculating the cracking area of the sample by using an image method, comparing the differences of the two methods under different thicknesses, and determining the testability of the crack volume of the sample with the same thickness;

step four, respectively calculating the relationship between the cracking area and the water content of each repeated sample under the same thickness in the cracking process aiming at each group of soil thickness cracking experiments, and comparing the coincidence between the two relationships of the repeated samples of different soil thickness;

And fifthly, selecting the optimal thickness in the design thickness according to the reproducibility of the surface characteristics of the crack, the measurable property of the crack volume and the coincidence of the crack area and the water loss relation to carry out crack research.

2. The method for determining the thickness of the sample based on the soil cracking research according to claim 1, wherein the method comprises the following steps: the thickness range value of the soil sample in the first step is 4-15mm, and the soil cracking experiment comprises the following steps:

A. Sieving according to the thickness range of the soil sample, and dividing the thickness gradient;

B. placing the soil samples with different thickness gradients in organic plastic boxes, adding deionized water, and uniformly stirring, wherein the mass ratio of the soil samples in each group of organic plastic boxes to the deionized water is 5: 2;

C. and C, placing the mixture treated in the step B into a constant temperature and humidity cabinet with the temperature of 19-21 ℃ and the humidity of 40% for natural drying.

3. The method for determining the thickness of the sample based on the soil cracking research according to claim 2, wherein the method comprises the following steps: in the case of the natural drying in step C, the soil reduction height during the drying process was measured by a direct measurement method.

4. The method for determining the thickness of the sample based on the soil cracking research according to claim 3, wherein the method comprises the following steps: the soil descending height measuring process comprises the following steps:

a) marking the edges of the organic plastic box with at least eight fixed positions;

b) Measuring the distances from the surface of the soil to the fixed positions at the beginning of natural drying and after drying, and taking the average distance L₀and L_x；

c) Subtracting the average distance L from the height of the organic plastic case₀And L_xI.e. the thickness h of the soil at the beginning of natural drying and after drying₀And h_x；

d) Soil thickness h at the beginning of natural drying and after drying₀and h_xthe thickness difference of the soil is the soil descending height h_d。

5. The method for determining the thickness of the sample based on the soil cracking research according to claim 1, wherein the method comprises the following steps: the image method in the third step is used for measuring the depth of the soil crack, and the specific steps are as follows: inserting the fine needle into the crack of the soil for depth measurement, stopping when resistance occurs at the front end of the needle in the inserting process, and measuring the length of the fine needle inserted into the crack by using a vernier caliper with the precision of 0.01 mm; measuring a plurality of points in the crack each time when the crack depth of the soil is determined, and then calculating the average value as the crack depth value h_c。

6. The method for determining the thickness of the sample based on the soil cracking research according to claim 2, wherein the method comprises the following steps: in the process of natural air drying, the soil samples at different water content stages are subjected to water content determination, and the method comprises the following specific steps: taking out a soil sample, uniformly dividing the soil sample into an upper layer and a lower layer by using a blade, and then measuring the mass water content of different layers of the soil by using a drying method.

7. The method for determining the thickness of the sample based on the soil cracking research according to claim 1, wherein the method comprises the following steps: and in the second step, the measuring positions of the surface characteristics of the cracks with different soil thicknesses are from the initial point of the soil cracking to the differentiation point and from the differentiation point to each differentiation end point.