CN110579585A - Sample thickness determination method based on soil cracking research - Google Patents

Sample thickness determination method based on soil cracking research Download PDF

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Publication number
CN110579585A
CN110579585A CN201910885336.3A CN201910885336A CN110579585A CN 110579585 A CN110579585 A CN 110579585A CN 201910885336 A CN201910885336 A CN 201910885336A CN 110579585 A CN110579585 A CN 110579585A
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soil
thickness
cracking
sample
crack
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魏翠兰
曹秉帅
邹长新
干方群
彭双
秦品珠
王燕
张琨
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Nanjing Institute of Environmental Sciences MEE
Jiangsu Open University of Jiangsu City Vocational College
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Nanjing Institute of Environmental Sciences MEE
Jiangsu Open University of Jiangsu City Vocational College
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/18—Measuring arrangements characterised by the use of mechanical techniques for measuring depth
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/24—Earth materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
    • G01N5/04—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by removing a component, e.g. by evaporation, and weighing the remainder
    • G01N5/045—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by removing a component, e.g. by evaporation, and weighing the remainder for determining moisture content

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Abstract

the invention discloses a sample thickness determination method based on soil cracking research in the technical field of soil cracking, which comprises the following steps of taking samples with the same soil diameter, and designing cracking experiments of different soil thicknesses based on 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, respectively utilizing an image method to calculate the cracking area of a sample, 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; and the optimal thickness of the soil cracking research can be accurately measured.

Description

sample thickness determination method based on soil cracking research
Technical Field
The invention relates to the technical field of soil cracking, in particular to a sample thickness determination method based on soil cracking research.
background
Under the condition that the soil is cracked, the final cracking state of the soil quantifies the shrinkage degree of the soil, and the measurement of the soil shrinkage characteristic curve can dynamically describe the volume change of the soil in the water loss process. The difficulty in shrinkage curve determination is the quantification of soil volume. In the field, Abou et al (2010) filled the cracks in the soil with latex and the crack volume of the soil was measured. Dasog et al (1993) estimate the volume of the soil fracture by measuring the length of the fracture with a string and inserting a ruler to measure the depth of the fracture. In the laboratory determination of soil shrinkage curves, the presence of soil cracks has not been considered. Generally, the volume change of the whole soil is measured, for example, Kim and the like measure the volume of the soil by using a displacement method; stewart et al (2010) mainly uses image reconstruction technology to construct photos in different directions to obtain a three-dimensional image of soil, and then obtains moisture change in the soil dehydration process through coordinate analysis. Shore Mingan et al (2003) and others obtain the volume change of the soil by means of ruler measurement. However, there are studies that show that the cracking degree of the sample is greatly different under different environments and sample sizes, and therefore, selecting the proper soil sample size is a problem to be solved.
based on the above, the invention designs a sample thickness determination method based on soil cracking research, so as to solve the problems.
disclosure of Invention
the invention aims to provide a sample thickness determining method based on soil cracking research, which aims to solve the problem of how to select a proper soil sample size in the prior art.
In order to achieve the purpose, the invention provides the following technical scheme: a sample thickness determination method based on soil cracking research 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.
preferably, the soil sample in the first step has a thickness ranging from 4 mm to 15mm, and the soil cracking test 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.
Preferably, when the natural drying is performed in the step C, the soil reduction height during the drying process is measured by a direct measurement method.
Preferably, the soil descent height determination 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 Lx；
c) Subtracting the average distance L from the height of the organic plastic case0and LxI.e. the thickness h of the soil at the beginning of natural drying and after drying0And hx；
d) Soil thickness h at the beginning of natural drying and after drying0And hxThe thickness difference of the soil is the soil descending height hd。
Preferably, the image method in the third step for determining the depth of the soil crack comprises the following specific steps: 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 hc。
Preferably, in the process of natural air drying, the water content of the soil samples at different water content stages is measured, and the specific steps comprise: 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.
preferably, the measuring positions of the surface characteristics of the cracks with different soil thicknesses in the second step are from the initial point of the soil cracking to the differentiation point and from the differentiation point to each differentiation end point.
Compared with the prior art, the invention has the beneficial effects that: the method has the advantages that the repeatability of the final cracking index parameter value of the soil between different repetitions is good under the same thickness, and the replacement of the cracking volume value of the soil measured by the iron powder method is realized by the method of combining the image and the fine needle; and the optimal thickness of the soil cracking research can be accurately measured.
drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a graph of the process of soil cracking versus thickness for different samples according to the invention;
FIG. 2 is a schematic view of the form of soil cracking at different sample thicknesses according to the present invention;
FIG. 3 is a graph of the change in area of soil cracking with water content in accordance with the present invention;
FIG. 4 is a graph of the volume of soil cracking as a function of water content in accordance with the present invention;
FIG. 5 is a graph of soil shrinkage volume as a function of water content in accordance with the present invention;
FIG. 6 is a table diagram of the difference of the cracking volumes of the soil measured by the image method and the iron powder method according to the present invention;
FIG. 7 is a graph showing the difference in moisture content between the upper and lower soil layers according to the present invention;
FIG. 8 is a statistical chart of soil cracking characteristic parameters for different sample thicknesses according to the present invention;
Fig. 9 is an overall flow chart of the present invention.
Detailed Description
the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
referring to fig. 1-8, the present invention provides a technical solution: a sample thickness determination method based on soil cracking research 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.
It should be noted that in the previous crack studies, the optimal choice of crack thickness was not taken into account, so the proposed method is advantageous to improve the accuracy and comparability of the crack studies.
In a further embodiment, the soil sample in the first step has a thickness ranging from 4 mm to 15mm, and the soil cracking test comprises the steps of:
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. 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;
it should be explained that for measuring the cracking process of the soil during water loss, three thickness treatments, 4-5mm, 9-10mm and 14-15mm, respectively, can be preferably set. Placing the screened soil sample into an organic plastic box with the height of 25mm and the diameter of 110mm, adding deionized water to ensure that the mass water content of the soil sample is approximately 0.60g/g, after sufficient balance, placing the mixture into a constant temperature and humidity box (20 +/-1 ℃, 40%) for natural drying, repeating 8 groups of soil samples with each thickness, counting the final soil cracking index, and completely measuring the process from the beginning to the completion of the cracking of the soil by three soil samples under each treatment.
In a further embodiment, when the natural drying is performed in the step C, the soil reduction height during the drying process is measured by a direct measurement method; because the experiment begins soil all to be the oversaturation state, soil has certain degree expansion, and soil height descends in dry process, and its decline volume adopts direct assay method survey, the experimental tool: vernier calipers with an accuracy of 0.01 mm. .
In a further embodiment, the soil descent height determination process comprises the steps of:
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 Lx；
c) subtracting the average distance L from the height of the organic plastic case0And Lxi.e. the thickness h of the soil at the beginning of natural drying and after drying0And hx；
d) Soil thickness h at the beginning of natural drying and after drying0And hxThe thickness difference of the soil is the soil descending height hd；
The main process of the step is that eight fixed positions are marked on the edge of the organic plastic box, the distance from the surface of the soil to the eight points is measured while the water content of the soil is measured each time, and then the average distance is obtained. Because the height of the culture box is fixed, the thickness of the soil is obtained by subtracting the average distance from the height of the culture box, and the soil descending height can be calculated according to the difference of the thicknesses of the soil twice before and after: v. of0＝A0*hd；
Wherein v is0(mm3) Is the reduced volume of the soil, A0(mm2) Is the soil surface area, hd (mm) is the soil reduction.
in a further embodiment, the image method in the third step is specifically to determine the depth of the soil crack by the following steps: 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 hc；
in the test process, the fine needle is inserted into a crack of soil for depth measurement (the fine needle is selected in the test because the fine needle has higher hardness and is not easy to deform, and the fine needle is easy to buy and has various sizes on the other hand). Because the soil cracking conditions are different under the conditions of different water contents, the number of points of the measured soil cracking depth is increased along with the increase of the cracking area. The area of the soil where cracks occurred was measured by an image method every time the crack depth was measured. The soil crack volume is then calculated as follows:
vc＝A*hc；
Wherein v isc(mm3) Volume of soil cracking, A (mm)2) The area of the soil crack.
And the volume of the soil was measured by the iron powder method as compared with the image method, and the volume of the soil fracture was estimated by filling the iron powder (200 mesh) passing through a 0.075mm sieve into the soil fracture. The experimental process comprises the following steps: the iron powder is first filled into a measuring cylinder of known volume by filling the iron powder mass and volumeAnd calculating a relation coefficient D between the two. Then a certain mass (m)1) The iron powder is filled into the cracks until the cracks are filled, then the mass m2 of the rest iron powder is weighed, and the volume of the soil cracks can be calculated:
mi＝m1-m2；
wherein m isiThe weight of the iron powder filled in the soil cracks.
although this method is simple to operate compared with the image and fine needle method, the process of taking out iron powder damages the soil, and thus continuous measurement cannot be performed;
Linear fitting is carried out through the relation between the mass and the volume of the iron powder to obtain the coefficient of the linear relation of 0.3118g/mm3, R20.99. Table 1 compares the difference between the volume of the soil cracks measured by the iron powder method and the image method, and it can be seen that the volume of the soil cracks measured by the image method is larger than that measured by the iron powder method. However, for the soil sample with the soil sample thickness of 4-5mm, the crack volume difference measured by the two methods is within 9%, when the soil sample thickness is 9-10mm and 15-16mm, the minimum difference of the two methods is 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 is cracked uniformly, and the soil is cracked to the bottom quickly. It was observed during the experiment that the width of the soil crack appeared substantially rectangular from top to bottom. When the thickness of the soil sample is 9-10mm and 15-16mm, the width of the soil crack is in an inverted triangle from top to bottom, the upper part is wide, the lower part is narrow, meanwhile, the downward extension time of the soil crack is long, in the process, the soil crack continuously generates branches, and the crack depths of the successively generated branches are greatly different. In the calculation process, the average cracking depth is taken to calculate the cracking volume of the soil, so that the difference formed in the measurement process by an image method and an iron powder method is large. For the reason that the width of the soil crack is different from top to bottom and is possibly related to soil evaporation, researches suggest that the upward migration speed of water in the soil is reduced under the condition of higher soil clay content, and in the test, the soil with larger thickness is higher than the soil with the same soil propertyThere may be differences between the moisture of the lower layers, and to verify this idea, we compared the differences between the moisture of the upper and lower layers of soil samples of different thicknesses.
in a further embodiment, in the process of natural air drying, the water content of the soil samples at different water content stages is measured, and the specific steps include: 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; in the experiment, 5 soil samples are reloaded in each thickness, one soil sample is taken out at different water content stages, the soil samples with the soil sample thicknesses of 9-10mm and 15-16mm are uniformly divided into an upper layer and a lower layer by a blade, namely, the thickness of the soil sample with the soil sample thickness of 9-10mm after layering is about 4-5mm, the thickness of the soil sample with the soil sample thickness of 15-16mm after layering is about 7-8mm, then the mass water content of different layers of the soil is measured by a drying method (five small soil samples are taken for each layer for average treatment), the soil sample with the soil sample thickness of 4-5mm is not layered, the water content of different positions of the same soil sample is directly measured, and then the average value is taken, and the result is shown in tables 6-3. As can be seen from the table, when the thickness of the soil sample is 4 to 5mm, the difference in water content at each position of the soil sample is small. When the thickness of the soil sample is 9-10mm and 1516mm, the water content of the lower layer of the soil is higher than that of the upper layer of the soil, and the difference of the water content caused by evaporation can be a main reason for causing the upper and lower widths of the soil crack to be inconsistent. When the soil samples are 9-10mm and 15-16mm thick, the water difference of different positions of the soil is also higher than 4-5mm, mainly because the soil samples with the thickness of 9-10mm and 15-16mm are cracked greatly, and water is easy to evaporate at the positions along the crack wall in the drying process.
as can be seen from FIG. 8, the final crack area of the soil of the same thickness and different samples does not change greatly. As can be seen from fig. 3, for the same thickness of soil, the cracking area of different samples is different according to the change of the water content of the soil. When the thickness of the soil sample is 4-5mm and 15-16mm, the reproducibility among soil samples is good, and when the thickness of the soil sample is 9-10mm, the difference among the repetitions is large. When the thickness of the soil sample is 4-5mm, the water content range of the soil sample is 38.82-40.80g/g when cracking occurs, and the water content range is 13.58-14.79g/g when the cracking area is stable; when the thickness of the soil sample is 9-10mm, the water content range of the soil sample is 33.06-46.85g/g when cracking occurs, and the water content range is 11.40-13.12g/g when the cracking area is stable; when the thickness of the soil sample is 15-16mm, the water content range of the soil sample is 38.41-41.32g/g when cracking occurs, 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 water content change range is the minimum when the soil cracks and the cracks are stable. The water content is most unstable when the soil sample cracks when the thickness is 9-10mm, and the water content is most unstable when the cracking stops when the thickness is 15-16 mm. According to observations during the experiment, the reason for this phenomenon may be: when the soil sample thickness is 15-16mm, the cracking of the soil is usually started from a point (a defect point or a weak point) in the soil, which indicates that the cracking is mainly influenced by the soil, and at the thickness, the later cracking process of the soil may not occur on the soil surface, and because the soil cracks are wider (table 1), and the water content of the lower soil layer is higher than that of the upper soil layer, the inner wall of the soil cracks is evaporated, and the evaporation process of the part brings about the increase of the cracking volume of the soil, so that the stable cracking area on the soil surface cannot indicate the stopping of the cracking. As can be seen from FIG. 1, when the thickness of the soil sample is 4-5mm, the cracking of the soil often occurs at a plurality of positions instead of one point, which indicates that the cracking of the soil at the thickness is not caused by a plurality of defect points existing in the soil itself and is greatly influenced by environmental factors. In the cracking process, when the thickness of the soil sample is 9-10mm, the soil cracking is more random, and the cracking may begin to be one point or multiple points.
in a further embodiment, the measuring positions of the surface characteristics of the cracks with different soil thicknesses in the second step are from the initial point of the soil cracking to the differentiation point and from the differentiation point to each differentiation end point;
FIG. 1 is a graph of cracking of samples of different thicknesses during water loss. As can be seen from the figure, when the thickness of the soil sample is 9-10mm and 15-16mm, the soil cracking starts from a point, the soil crack lengthens and widens along the point, when the width of the soil crack reaches a certain value, a node is generated, other cracking branches are generated at the node, and the depth of the soil crack is continuously deepened along with the evaporation process. When the thickness of the soil sample is 4-5mm, a plurality of points can crack simultaneously in the same time, a plurality of cracks can be generated simultaneously, and finally the plurality of cracks can be connected together along with the increase of the length.
it can be seen from fig. 2 that, although the size of the soil culture box is increased for statistics of characteristic parameters of different thicknesses, the soil cracking state is simpler as the thickness of the soil sample is increased for different thicknesses. As can be seen from Table 2, after the soil is completely contracted, the difference between the crack indicator parameter values is not very large, and the standard deviation of the crack parameters Dc, CI, P and EW is the smallest when the soil sample thickness is 4-5mm, and is respectively 0.38%, 0.02%, 0.07% and 0.54 pixel. The Lc value is 0.05% with the smallest difference between the standards at a thickness of 9-10 mm. The FD values were the smallest at 4-5mm and 15-16mm soil sample thickness, both 0.02. Therefore, for the soil, the reproducibility of the soil cracking characteristics is better under the same thickness, but the standard deviation of the 4-5mm soil crack cracking index is the smallest;
And figure 4 is a graph of soil crack volume (image method) as a function of soil moisture content. As can be seen from the figure, the change rule of the cracking volume of the soil is basically consistent with the change rule of the soil area. When the thickness of the soil sample is 4-5mm, the repeatability of the crack volume of different samples is good. When the thickness of the soil sample is 15-16mm, the difference of the cracking volume between different soil samples is larger than the soil area. In addition, it can be seen that the water content at which the soil develops a crack volume is consistent with the soil developing cracks at different thicknesses. The water content of the soil with stable cracking volume is 4-5mm, the other two thicknesses are different from the thickness of the soil with stable cracking area, the water content range of the soil with stable cracking volume of 9-10mm is 3.12-14.51g/g, and the water content of the soil with stable cracking volume of 15-16mm is 4.47-8.33 g/g. The phenomena are related to the occurrence and the measurement of the soil depth, when the soil sample thickness is 4-5mm, the soil is cracked to the end quickly, the difference of different crack depths is small, and the cracking area of the soil determines the cracking volume of the soil. When the thickness of the soil sample is 9-10cm and 15-16mm, the crack cracking degree of the cracks cracked in time is greatly different, the depth obtained by averaging has a large error with the real depth, and the soil depth can continue to occur when the surface cracking area is stable due to the difference of the moisture of the upper layer and the lower layer of the soil;
The total soil shrinkage volume is then the sum of the soil cracking volume and the soil reduction volume. Figure 5 is the total shrinkage volume of soil as a function of water content. As can be seen from the figure, under the treatment of different thicknesses, the water content of the soil is about 0.50g/g when the soil shrinks. The soil shrinkage volume has better repeatability when the thickness of the soil sample is 4-5mm and the thickness of the soil sample is 15-16mm, and the soil shrinkage volume is further increased when the soil sample is 9-10 mm. It is shown that the volume reduction of the soil is not changed much in the case of soil sample thicknesses of 4 to 5mm and 15 to 16 mm.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular 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 intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and 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 Lx；
c) Subtracting the average distance L from the height of the organic plastic case0And LxI.e. the thickness h of the soil at the beginning of natural drying and after drying0And hx；
d) Soil thickness h at the beginning of natural drying and after drying0and hxthe thickness difference of the soil is the soil descending height hd。
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 hc。
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.
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Citations (2)

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CN107300521A (en) * 2017-07-12 2017-10-27 广西大学 The assay method and measure device of swelled ground cracking water content
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