CN114280103A - Method for measuring moisture content or suction distribution of soil surface layer by using infrared thermal imaging technology - Google Patents
Method for measuring moisture content or suction distribution of soil surface layer by using infrared thermal imaging technology Download PDFInfo
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Abstract
The invention discloses a method for measuring the moisture content or suction distribution of a soil surface layer by using an infrared thermal imaging technology, and belongs to the cross field of geotechnical engineering and environmental engineering. Measuring soil body surface suction includes: firstly, obtaining a relation calibration formula between surface water content and interface temperature difference in a soil evaporation process, acquiring an in-situ soil surface temperature field by using an infrared thermal imager, and inverting the soil surface water content field; calibrating a soil-water characteristic curve of a test soil body, determining the relation between the soil body suction and the water content, further obtaining the suction of a specific position of the soil body surface layer at any moment, and inverting the soil body surface layer suction field. The method can quickly, accurately and real-timely acquire the change characteristics of the surface temperature field under the soil body drying condition, further invert and quantize the water content and suction distribution of the soil body, evaluate the dry-wet state and strength characteristics of the soil body, guide the development of subsequent geotechnical or environmental engineering work, and has the advantages of no damage to the in-situ soil body, convenient data acquisition, rich data points, high accuracy and the like.
Description
Technical Field
The invention belongs to the cross field of geotechnical engineering and environmental engineering, and particularly relates to a method for measuring the moisture content or suction distribution of a soil surface layer by using an infrared thermal imaging technology.
Background
Under extreme drought conditions, the vapor pressure gradient on the atmosphere-soil body interface is higher, so that the evaporation intensity of the water in the soil body is higher. The evaporation of water can directly change the spatial distribution of a water field on the surface layer of the soil body, and the engineering property of the soil body is very sensitive to the change of the water content, so that the geological problems of geotechnical engineering and environmental engineering, such as cracking, salinization, soil degradation, ground settlement and the like, are induced. In recent years, a wide range of hydrological changes has increased the drought in many areas of the world, subject to global climate change. The frequent occurrence of extreme drought climate makes regional geotechnical/geological engineering problems or disasters with water content inducement more obvious, such as large-area damage of ground infrastructure caused by differential settlement caused by shrinkage deformation of foundation soil, mechanical property weakening caused by soil body cracking and reduction of engineering structure stability caused by permeability increase. Therefore, how to accurately evaluate the water content distribution of the surface soil body has attracted great attention in recent years.
According to a traditional soil body surface water field parameter evaluation method, measuring instruments are buried in a surface soil body, and the instrument is used for monitoring the reduction of the soil body mass or the temperature change, so that the change of water field parameters (water content and suction) is inverted. However, most of the methods are point-line type data acquisition, the acquired data are discrete, and the economic cost and the time cost are high. Meanwhile, the embedding of the moisture measuring equipment can damage the local soil body structure, disturb the moisture migration path and influence the accuracy of the final research result to a certain extent.
In conclusion, parameters of a water field of a soil body, such as the surface water content of the soil body and the suction distribution, are acquired without damage, and the method is applied to different practical engineering conditions, and an effective solution is not available at present.
Disclosure of Invention
1. Problems to be solved
The invention aims to overcome the defects that the accuracy of a research final result is influenced to a certain extent by disturbing a water migration path through equipment embedded and damaged local soil body structure in the conventional in-situ soil body surface water field parameter distribution such as water content or suction distribution measurement, and provides a method for measuring the soil body surface water field parameters such as water content or suction distribution by using an infrared thermal imaging technology.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a method for measuring the distribution of the surface water content of a soil body by utilizing an infrared thermal imaging technology comprises the following steps: an infrared thermal imager is utilized to collect an in-situ soil body surface temperature field, and the water content of a soil body surface specific position at any moment is obtained through a formula (1):
wherein, ω istIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0The initial water content of the specific position of the soil surface layer is shown, delta T is an interface temperature difference, namely the difference value of the soil surface layer temperature and the environment temperature, the unit is DEG C, alpha and beta are constant parameters, T is the drying time of the specific position of the soil surface layer, and the unit is h.
Preferably, the values of α and β of said formula (1) are determined by: and (3) measuring the average water content and the average interface temperature difference of the soil body at different drying times by using a measuring area in-situ small-scale soil sample calibration test, combining the average water content and the average interface temperature difference, and fitting to obtain a relation curve of the surface water content and the interface temperature difference of the soil body, thereby obtaining alpha and beta values.
Preferably, the average water content ω of the soil sample at a specific time is obtained by the following methodt：
Placing the soil sample in the center of a high-precision electronic balance, recording the mass change of the soil sample in the water evaporation process in real time, and calculating the average water content according to the following formula:
in the formula, ωtThe average water content of the soil sample at a specific moment, omega0Is the initial water content of the soil sample, and is the change of the soil sample mass (g) in Delta msThe dry soil mass (g).
The invention also provides a method for measuring the suction distribution of the soil surface layer by using the infrared thermal imaging technology, which comprises the following steps: the method comprises the following steps of collecting an in-situ soil body surface temperature field by using an infrared thermal imager, obtaining the water content of a specific position of a soil body surface at any moment through a formula (1), and obtaining the soil body surface suction at the position at the moment through a formula (2):
wherein, ω istIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0Is the initial water content, omega, of a specific position on the surface layer of the soil bodysIs the saturated water content of soil body, omegarIs the residual water content of the soil body, delta T is the interface temperature difference, namely the difference between the surface temperature of the soil body and the environmental temperature, alpha and beta are constant parameters, T is the drying time of a specific position of the surface layer of the soil body,
suction for specific position of soil surface layerAnd (3) a force value, wherein a is a suction value corresponding to the air inlet value of the target soil body, and m and n are parameters reflecting the pore size distribution of the soil body respectively and are used for controlling the drying rate of the unsaturated section on the surface layer of the soil body and the symmetry of the soil-water characteristic curve.
The soil body suction is free energy of water in soil and consists of matrix suction and osmotic suction.
Preferably, the method comprises in particular the steps of:
s1, establishing a relational expression between the surface water content and the interface temperature difference in the soil evaporation process:
i.e. the calibration formula, where ωtIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0The initial water content of a specific position of the soil surface layer is obtained, delta T is an interface temperature difference, namely the difference value of the soil surface layer temperature and the environment temperature, alpha and beta are constant parameters, and T is the drying time of the specific position of the soil surface layer;
the α and β values of said formula (1) are determined by the following method: method for measuring average water content omega of soil body under different drying times by using in-situ small-scale soil sample calibration test of measuring areatAnd fitting the mean interface temperature difference delta T and the mean interface temperature difference delta T after the mean interface temperature difference delta T and the mean interface temperature difference delta T are combined to obtain the surface water content omega of the soil bodytObtaining values of alpha and beta according to a relation curve of the interface temperature difference delta T; wherein the average water content omega of the soil sample at a specific moment is obtained by the following methodt：
Placing the soil sample in the center of a high-precision electronic balance, recording the mass change of the soil sample in the water evaporation process in real time, and calculating the average water content according to the following formula:
in the formula, ωtThe average water content of the soil sample at a specific moment, omega0Is the initial water content of the soil sample, and is the change of the soil sample mass (g) in Delta msDry soil mass (g);
s2, carrying out in-situ monitoring, and acquiring a surface temperature field in the soil sample drying process by using an infrared thermal imager to obtain an interface temperature difference;
s3 inverting the soil surface water content field according to the standard formula (1) in the step S1;
s4, combining the expression of the soil-water characteristic curve formula (3) of the target soil body with the calibration formula (1) to obtain the relational expression (2) of the interface temperature difference and the soil body surface layer suction force, thereby obtaining the soil body suction force at the specific position of the soil body surface layer:
wherein ω is the water content of the soil sample (which may also be referred to as the average water content ω of the soil sample at a specific time)t)，ω0Is the initial water content, omega, of a specific position on the surface layer of the soil bodysIs the saturated water content of soil body, omegarIs the residual water content of the soil body, delta T is the interface temperature difference, namely the difference between the surface temperature of the soil body and the environmental temperature, alpha and beta are constant parameters, T is the drying time of a specific position of the surface layer of the soil body,
and controlling the drying rate of the unsaturated section and the symmetry of the soil-water characteristic curve.
Preferably, the values of the parameters a, m and n in the target soil and water characteristic curve formula (3) in step S4 are determined by the following method: collecting a plurality of (for example, 9 groups of) in-situ small-scale soil samples of the measuring area, drying the soil samples to different water contents, measuring the suction force value of the soil sample by using a dew point water potential instrument to obtain a water content-suction force curve of the soil body of the measuring area, and fitting the curve by using a vG model to obtain a target soil body soil-water characteristic curve formula (3) and corresponding parameters a, m and n.
Preferably, an infrared thermal imager is used to obtain the average interface temperature of the surface layer of the soil body, and a difference is made between the average interface temperature and the ambient temperature to obtain the average interface temperature difference Δ T in the step S1.
Preferably, the model of the infrared thermal imager is FLIR-T620, the working waveband of the infrared thermal imager is 7.8-14 μm, the resolution of a camera is 640 multiplied by 480pix, the temperature measurement sensitivity can reach +/-0.04 ℃, and the precision can reach +/-0.1 ℃.
Preferably, the preset parameters of the infrared thermal imager during initialization are shown in table 2:
table 2 infrared thermal imager preset parameters
Preferably, when the interface temperature difference is measured in step S1 or S2, the infrared thermal imaging instrument is erected over the soil sample, the surface average temperature and the ambient temperature during the evaporation process of the water in the soil sample are measured in real time, and the interface temperature difference is calculated.
Preferably, the dew point water potential instrument is WP4C, the measuring range is 0-300 MPa, the precision is +/-0.05 MPa within the range of 0-5 MPa, and the precision is +/-1% within the range of-5-300 MPa.
Preferably, in the calibration test of the in-situ small-scale soil sample of the measuring area, the in-situ soil sample is collected by using a cutting ring, and the inner diameter of the cutting ring is 64mm, and the height of the cutting ring is 20 mm.
Preferably, in the calibration test of the in-situ small-scale soil sample of the measuring area, the in-situ soil sample is collected on site by using a cutting ring, the diameter of the soil sample is 61.8mm, and the height of the soil sample is 20 mm; taking out the cutting ring sample, placing the cutting ring sample in a prefabricated mould, and wrapping the inner wall of the mould with a heat-insulating preservative film to ensure that the soil sample does not generate lateral heat loss in the test process to influence the test result; vaseline is coated on the front surface of the preservative film, so that cracking of the soil sample in the water loss shrinkage process is prevented.
Preferably, the reading precision of the high-precision electronic balance is +/-0.005 g.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:
(1) the invention adopts the infrared thermal imaging technology to measure the moisture content or the suction distribution of the surface layer of the soil body, is a non-contact measuring method, does not need to embed an instrument in the in-situ soil body, greatly reduces the disturbance to the in-situ soil body in the measuring process and improves the accuracy of the measuring result; the water content omega of the specific position of the surface layer of the soil body at any moment is calculated and determined by adopting a calibration formula and a soil-water characteristic curvetAnd soil mass suction
Experiments verify that the consistency of the water field parameter value calculated by the method and the actual value is high;
(2) the method adopts an infrared thermal imaging technology to evaluate the moisture content or suction distribution of the surface layer of the soil body, and compared with the traditional moisture field parameter measuring instruments such as a lysimeter, an FBG (fiber Bragg Grating) optical fiber and the like, the infrared thermal imager has the advantages of lower instrument cost, higher economy and wider application field;
(3) the method adopts an infrared thermal imaging technology to measure the moisture content or suction distribution of the surface layer of the soil body, the resolution ratio of a camera of an infrared thermal imaging instrument is 640 multiplied by 480pix, the temperature measurement sensitivity can reach +/-0.04 ℃, the precision can reach +/-0.1 ℃, and compared with a point-line type data acquisition mode of a traditional measuring instrument, the spatial resolution ratio is higher, and the distribution condition of the moisture field parameter of the surface layer of the soil body can be obtained more finely;
(4) the invention adopts the infrared thermal imaging technology to measure the parameters of the moisture field of the surface layer of the soil body, such as the moisture content or the suction distribution, and the infrared thermal imaging technology is taken as a new frontier technical means and is widely applied to the fields of various engineering; the invention is combined with the remote sensing infrared technology, and the temperature field distribution of the surface layer of the soil body in a large-scale area is obtained through the satellite technology, so that the measurement of the water field parameters of the surface layer of the soil body in a larger-scale range can be realized.
Drawings
FIG. 1 is a schematic diagram showing the construction of a calibration test apparatus in example 1;
FIG. 2 is a graph showing the temperature difference at the interface of the standard sample in example 1 as a function of the drying time;
FIG. 3 is a plot of water cut versus drying time fit for the standard samples of example 1.
FIG. 4 is a graph of the temperature difference field of the surface of the slope soil in example 1 (the right-side color bars indicate the temperature difference).
FIG. 5 is a graph showing the distribution of water content in the surface layer of the slope soil in example 1 (the water content is shown by the color bars on the right).
FIG. 6 is a graph showing the change in the temperature difference and the suction force at the surface interface of the slope soil body in example 1.
FIG. 7 is a graph showing the distribution of the residual water content of the surface layer of the slope soil in example 1.
FIG. 8 is a graph showing the suction distribution in the soil surface layer of the slope in example 1.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Temperature, amount, and other numerical data may be presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limit values of 1 to about 4.5, but also include individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be construed to include all of the aforementioned values and ranges. Moreover, such an interpretation should apply regardless of the breadth of the range or feature being described.
The type of the infrared thermal imaging instrument adopted in the invention is FLIR-T620, the working waveband of the instrument is 7.8-14 μm, the camera resolution is 640 multiplied by 480pix, the temperature measurement sensitivity can reach +/-0.04 ℃, and the precision can reach +/-0.1 ℃.
The preset parameters of the infrared thermal imager during initialization are shown in table 1.
When the interface temperature difference is measured in the following step S1 or S2, the infrared thermal imaging instrument is erected right above the soil sample, and the surface average temperature and the ambient temperature in the water evaporation process of the soil sample are measured in real time.
The dew point water potential instrument adopted in the invention has the model of WP4C, the measurement range is 0-300 MPa, wherein the precision is +/-0.05 MPa within the range of 0-5 MPa and +/-1% within the range of-5-300 MPa.
In the calibration test of the in-situ small-scale soil sample in the measuring area, the in-situ soil sample is collected by the cutting ring, and the inner diameter of the cutting ring is 64mm, and the height of the cutting ring is 20 mm. In a calibration test of the in-situ small-scale soil sample of the survey area, the ring cutter is used for collecting the in-situ soil sample on site, and the soil sample has the diameter of 61.8mm and the height of 20 mm; taking out the cutting ring sample, placing the cutting ring sample in a prefabricated mould, and wrapping the inner wall of the mould with a heat-insulating preservative film to ensure that the soil sample does not generate lateral heat loss in the test process to influence the test result; vaseline is coated on the front surface of the preservative film to prevent the soil sample from cracking in the process of dehydration and shrinkage.
The reading precision of the high-precision electronic balance adopted by the invention is +/-0.005 g.
The invention is further described with reference to specific examples.
Example 1
The soil body of the embodiment is a 10-degree slope surface soil body, the length of the slope body is 40cm, the width of the slope body is 40cm, the soil property is silty clay, the engineering environment temperature is 26.7 ℃, the environment humidity is 50 +/-2%, the engineering requirement is that the soil surface layer is monitored in real time, and the distribution of the water content of the surface layer of the slope is evaluated.
S1, establishing a relational expression between the water content and the interface temperature difference in the soil evaporation process:
i.e. the calibration formula, where ωtIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0The initial water content of a specific position of the soil surface layer is obtained, delta T is an interface temperature difference, namely the difference value of the soil surface layer temperature and the environment temperature, alpha and beta are constant parameters, and T is the drying time of the specific position of the soil surface layer;
wherein the average water content omega of the soil sample at a specific moment is obtained by the following methodt：
Placing the soil sample in the center of a high-precision electronic balance, recording the mass change of the soil sample in the water evaporation process in real time, and calculating the average water content according to the following formula:
in the formula, ωtThe average water content of the soil sample at a specific moment, omega0Is the initial water content of the soil sample, and is the change of the soil sample mass (g) in Delta msDry soil mass (g);
s1-1, collecting an in-situ soil sample of a measuring area by using a cutting ring with the inner diameter of 64mm and the height of 20mm, and performing a small-scale calibration test: placing the soil sample in the middle of a high-precision electronic balance, and recording the mass change of the soil sample in the water evaporation process in real time; meanwhile, an infrared thermal imager (the model of the infrared thermal imager is FLIR-T620, the working waveband of the infrared thermal imager is 7.8-14 mu m, and the resolution is 640 multiplied by 480pix) is erected at a position 1m above the soil sample, and the surface average temperature and the ambient temperature in the water evaporation process of the soil sample are measured in real time; the parameters of the infrared thermal imager are preset in a table 3, and the test device is erected as shown in figure 1;
TABLE 3
S1-2, making difference between the average interface temperature of the soil surface layer obtained at different drying time and the environment temperature to obtain an average interface temperature difference change curve at different drying time, as shown in figure 2; meanwhile, the mass changes of the soil body at different drying times are obtained by using a high-precision electronic balance, and moisture content curves at different drying times are obtained, as shown in fig. 3;
after the test is finished, drying and weighing the soil sample to obtain the initial water content of the soil body to be 15%;
s1-3, the interface temperature difference and the water content of the calibrated soil body are combined and fitted, and the fitting obtains a linear relation as follows:
comparing with the calibration formula (1), obtaining a calibration parameter alpha which is 0.891 and a calibration parameter beta which is 0.105;
s2, carrying out in-situ monitoring, erecting an infrared thermal imager 2m above the slope body, and acquiring a surface temperature field image of the soil sample in the drying process by using the infrared thermal imager, as shown in figure 4; making a difference value between the surface interface temperature of the soil body and the environment temperature to obtain an actually measured interface temperature difference;
s3, inverting the soil surface water content field according to the calibration formula obtained by measuring and calculating in the step S1-3, as shown in the figure 5;
s4 the characteristic curve of the soil and water of the target soil body is determined by the following method: collecting 9 groups of in-situ small-scale soil samples of the measuring area, drying the soil samples to different water contents, and measuring the suction value of the soil samples by using a dew point water potential meter
Obtaining a water content-suction curve of a soil body of a measuring area, and fitting the curve by adopting a vG model:
wherein omega is the water content of the soil sample and omegasIs the saturated water content of soil body, omegarThe water content of the residual soil body is the water content,
the suction value of the soil sample is used, a is the suction value corresponding to the air inlet value of the target soil body, and m and n reflect the pore size distribution of the soil body and are used for controlling the drying rate of the unsaturated section and the symmetry of the soil-water characteristic curve;
combining the soil-water characteristic curve expression (3) of the target soil body with the calibration formula (1) to obtain an interface temperature difference and soil body surface layer suction relational expression (2), thereby obtaining the soil body suction at a specific position of the soil body surface layer:
the method specifically comprises the following steps: collecting 9 groups of in-situ small-scale soil samples of the measuring area by using a cutting ring, drying the soil samples to different water contents, measuring the suction value of the soil samples by using a dew point water potential instrument to obtain a water content-suction curve of the soil body of the measuring area, and fitting the curve by using a vG model to obtain the values of parameters a, m and n in a soil-water characteristic curve formula (3) of the soil body of the measuring area:
a is 58.16, m is 0.23, n is 1.3;
s5, a calibration formula (1) and a soil-water characteristic curve (3) are established in a simultaneous mode to obtain a suction value of a specific position of the soil surface, and the suction of the soil surface is inverted, as shown in figure 6;
and (3) verification: after the test is finished, dividing the slope body into 4 multiplied by 4 equal-area areas, respectively excavating in-situ surface layer soil samples and weighing, then measuring the suction distribution of the surface layer of the soil body by using a WP4C dew point water potential instrument, drying the soil samples and measuring the water content, and referring to figure 7; and obtaining an actual map of the suction distribution of the soil surface layer, as shown in figure 8. Comparing the actual mapping 7 with the water content distribution graph 5 inverted by the method of the invention, the method for obtaining the water content distribution by inversion according to the interface temperature difference has higher accuracy.
The above embodiments are only preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, and combinations that do not depart from the spirit and principle of the present invention should be regarded as equivalent alternatives, which are within the scope of the present invention.
Claims (10)
1. A method for measuring the distribution of the surface water content of a soil body by utilizing an infrared thermal imaging technology is characterized by comprising the following steps: an infrared thermal imager is utilized to collect an in-situ soil body surface temperature field, and the water content of a soil body surface specific position at any moment is obtained through a formula (1):
wherein, ω istIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0The initial water content of the specific position of the soil surface layer is shown, delta T is an interface temperature difference, namely the difference value of the soil surface layer temperature and the environment temperature, the unit is DEG C, alpha and beta are constant parameters, T is the drying time of the specific position of the soil surface layer, and the unit is h.
2. The method for measuring the moisture content distribution on the surface layer of the soil body by using the infrared thermal imaging technology as claimed in claim 1, wherein the values of α and β of the formula (1) are determined by the following method: and (3) measuring the average water content and the average interface temperature difference of the soil body at different drying times by using a measuring area in-situ small-scale soil sample calibration test, combining the average water content and the average interface temperature difference, and fitting to obtain a relation curve of the surface water content and the interface temperature difference of the soil body, thereby obtaining alpha and beta values.
3. The method for measuring the distribution of the water content of the surface layer of the soil body by using the infrared thermal imaging technology as claimed in claim 2, wherein the average water content ω of the soil sample at a specific moment is obtained by the following methodt：
Placing the soil sample in the center of a high-precision electronic balance, recording the mass change of the soil sample in the water evaporation process in real time, and calculating the average water content according to the following formula:
in the formula, ωtThe average water content of the soil sample at a specific moment, omega0Is the initial water content of the soil sample, and is the change of the soil sample mass (g) in Delta msThe dry soil mass (g).
4. A method for measuring the suction distribution of the surface layer of a soil body by using an infrared thermal imaging technology is characterized by comprising the following steps: the method comprises the following steps of collecting an in-situ soil body surface temperature field by using an infrared thermal imager, obtaining the water content of a specific position of a soil body surface at any moment through a formula (1), and obtaining the soil body surface suction at the position at the moment through a formula (2):
wherein, ω istIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0Is the initial water content, omega, of a specific position on the surface layer of the soil bodysIs the saturated water content of soil body, omegarIs the residual water content of the soil body, delta T is the interface temperature difference, namely the difference between the surface temperature of the soil body and the environmental temperature, alpha and beta are constant parameters, T is the drying time of a specific position of the surface layer of the soil body,
the suction value of the specific position of the soil surface layer is defined as a, the suction value corresponding to the air inlet value of the target soil body is defined as a, and m and n are parameters reflecting the pore size distribution of the soil body respectively.
5. The method for measuring the suction distribution on the surface layer of a soil body by using the infrared thermal imaging technology as claimed in claim 4, which is characterized by comprising the following steps:
s1, establishing a relational expression between the surface water content and the interface temperature difference in the soil evaporation process:
i.e. the calibration formula, where ωtIs the water content, omega, of a specific position on the surface layer of the soil body at any moment0The initial water content of a specific position of the soil surface layer is obtained, delta T is an interface temperature difference, namely the difference value of the soil surface layer temperature and the environment temperature, alpha and beta are constant parameters, and T is the drying time of the specific position of the soil surface layer;
the α and β values of said formula (1) are determined by the following method: method for measuring average water content omega of soil body under different drying times by using in-situ small-scale soil sample calibration test of measuring areatAnd fitting the mean interface temperature difference delta T and the mean interface temperature difference delta T after the mean interface temperature difference delta T and the mean interface temperature difference delta T are combined to obtain the surface water content omega of the soil bodytObtaining values of alpha and beta according to a relation curve of the interface temperature difference delta T; wherein the average water content omega of the soil sample at a specific moment is obtained by the following methodt：
Placing the soil sample in the center of a high-precision electronic balance, recording the mass change of the soil sample in the water evaporation process in real time, and calculating the average water content according to the following formula:
in the formula, ωtThe average water content of the soil sample at a specific moment, omega0Is the initial water content of the soil sample, and is the change of the soil sample mass (g) in Delta msDry soil mass (g);
s2, carrying out in-situ monitoring, and acquiring a surface temperature field in the soil sample drying process by using an infrared thermal imager to obtain an interface temperature difference;
s3 inverting the soil surface water content field according to the standard formula (1) in the step S1;
s4, combining the expression of the soil-water characteristic curve formula (3) of the target soil body with the calibration formula (1) to obtain the relational expression (2) of the interface temperature difference and the soil body surface layer suction force, thereby obtaining the soil body suction force at the specific position of the soil body surface layer:
wherein omega is the water content of the soil sample and omega0Is the initial water content, omega, of a specific position on the surface layer of the soil bodysIs the saturated water content of soil body, omegarIs the residual water content of the soil body, delta T is the interface temperature difference, namely the difference between the surface temperature of the soil body and the environmental temperature, alpha and beta are constant parameters, T is the drying time of a specific position of the surface layer of the soil body,
the suction value of the specific position of the soil surface layer is defined as a, the suction value corresponding to the air inlet value of the target soil body is defined as a, and m and n are parameters reflecting the pore size distribution of the soil body respectively.
6. The method for measuring the suction distribution on the soil surface layer by using the infrared thermal imaging technology as claimed in claim 5, wherein the values of the parameters a, m and n in the target soil and water characteristic curve formula (3) in the step S4 are determined by the following method: collecting in-situ small-scale soil samples of a plurality of measuring areas, drying the soil samples to different water contents, measuring the suction values of the soil samples by using a dew point water potential instrument to obtain water content-suction curves of soil bodies of the measuring areas, and fitting the curves by using a vG model to obtain a target soil body soil-water characteristic curve formula (3) and corresponding parameters a, m and n.
7. The method of claim 6, wherein the difference between the average interface temperature of the soil surface and the ambient temperature is obtained by an infrared thermal imaging instrument to obtain the interface temperature difference Δ T.
8. The method for measuring the suction distribution on the surface layer of the soil body by using the infrared thermal imaging technology as claimed in claim 7, wherein the model of the infrared thermal imaging instrument is FLIR-T620, the operating waveband of the instrument is 7.8-14 μm, and the resolution of the camera is 640 x 480 pix.
9. The method for measuring the suction distribution on the surface layer of a soil body by using the infrared thermal imaging technology as claimed in claim 8, wherein the preset parameters of the infrared thermal imaging instrument during initialization are shown in table 1:
TABLE 1 Infrared thermal imaging Meter Preset parameters
10. The method for measuring the suction distribution on the surface layer of the soil body by using the infrared thermal imaging technology as claimed in any one of claims 6 to 9, wherein the dew point water potential instrument is WP4C, and the measuring range is 0 to-300 MPa.
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