CN108344740B - Expansive soil field judgment method based on PIV technology - Google Patents

Abstract

The invention discloses a field discrimination method for the free expansion rate of expansive soil based on a PIV technology. The method comprises the steps of manufacturing an undisturbed sample test piece of the expansive soil, determining the stabilization time of the surface crack displacement of the test piece by utilizing the PIV technology, obtaining the accumulated displacement scalar average value of each point on the surface at the moment, establishing the corresponding relation between the displacement scalar average value and the free expansion rate of the soil sample of the test piece to obtain a linear correlation model, correcting the linear correlation model according to the experimental results of the undisturbed soil sample under different initial water contents, and finally obtaining the field discrimination method of the free expansion rate of the expansive soil based on the PIV technology. When the method is applied on site, the real-time accumulated displacement scalar average value of the soil sample on site and the initial water content of the soil sample are tested, and the expansibility of the soil layer can be rapidly judged on site by applying the method.

Description

A Field Discrimination Method of Expansive Soil Based on PIV Technology

technical field

The invention relates to the field of soil expansiveness grade discrimination, in particular to an on-site discrimination method for expansive soil based on PIV technology.

Background technique

Particle image veloci-metry (PIV) is a particle displacement measurement technology based on image processing and identification technology. It has the advantages of continuous displacement measurement, high efficiency and no intervention measurement, etc. Mechanics and other related disciplines.

On-site identification of soil expansiveness grades is an essential part of civil engineering construction in expansive soil distribution areas. In general, weak expansive soil can be used and the base surface is weakly protected, and the medium or above expansive soil is discarded and the base surface is strongly protected.

SUMMARY OF THE INVENTION

The invention provides an on-site judging method for the free expansion rate of expansive soil based on the PIV technology. The method is used to indirectly and quickly determine the free expansion rate of the soil body, so as to achieve the purpose of quickly judging the expansiveness of the soil layer on site.

The present invention solves its technical problem and realizes through the following technical solutions:

A method for on-site identification of expansive soil based on PIV technology, comprising the following steps:

(1) Make the original saturated expansive soil sample;

(2) Using particle image velocimetry to determine the time when the displacement of the specimen surface is stable;

(3) Calculate the average value of the cumulative displacement scalar on the surface of the specimen;

(4) Test the free expansion rate of the specimen;

(5) Establish the relationship between the average value of the cumulative displacement scalar on the surface of the specimen and the free expansion rate;

(6) Calculate the correction factor for the influence of soil moisture content on the average value of the cumulative displacement scalar on the undisturbed surface of the expansive soil sample;

(7) On-site determination of expansive soil expansiveness.

Further, the specific method of the step (1) is: take undisturbed soil samples of different expansion grades, and use the undisturbed soil samples of different expansion grades as test pieces after saturation, and the upper surface of the test piece is covered with a single-layer particle size. Standard sand of 0.075-0.25mm is used to identify the surface of the specimen as a combination of aggregates with different characteristics.

Further, the test piece was sampled from the original soil sample by a steel mold, the steel mold was cylindrical, and the diameter of the steel mold was 61.8 mm and the height was 10 mm, and one end of the steel mold was open and closed. As a cutting edge, the other end of the steel mold is closed.

Further, the method of the step (2) is: placing the test pieces obtained in the step (1) in a constant temperature environment of 100° C. respectively, and using the particle image velocimetry technology to process the test pieces obtained respectively at two adjacent time nodes. The surface image can be used to obtain the displacement scalar of different particles on the surface of the specimen during this time period: the gradient color between black and white corresponds to the displacement scalar value, so that the displacement scalar of each pixel is displayed in the form of a grayscale image. When there is no displacement of each pixel in the image captured at two adjacent time points, that is, the displacement of each particle on the surface of the specimen in the two adjacent time points is zero, and the grayscale image is displayed in black at this time. The displacement of each point on the surface of the piece reaches a stable state, and the latter time node of the two adjacent time nodes is determined as the displacement stabilization time.

Further, the specific method of the step (3) is: count the displacement scalars of all the pixel points in the grayscale image, calculate the scalar mean value and define the scalar mean value as the incremental displacement scalar mean value, and obtain according to the standard step (2). Calculate the time when the displacement is stable, and add the scalar mean value of the incremental displacement in the grayscale image obtained before the stable time to obtain the mean value of the cumulative displacement scalar.

Further, the specific method of the step (4) is as follows: according to the free expansion rate test procedure in Appendix D of the "Technical Specification for Building in Expansive Soil Areas", the free expansion rate test is performed on the soil samples of different expansion grades.

Further, the specific method of step (5) is: linearly fitting the correlation state between the average cumulative displacement scalar on the surface of the test piece and the free expansion rate of the soil sample of the test piece to obtain a linear correlation empirical model.

Further, the specific method of the step (6) is: the undisturbed soil samples of the same free expansion rate result are saturated and then air-dried to different moisture contents, and then made into samples respectively, and the upper surfaces of the samples are also covered with a single-layer particle size. It is standard sand of 0.075-0.25mm, used to identify the surface of the sample as a combination composed of different characteristic aggregates, and perform steps (2) and (3) of the foregoing test on the sample to obtain the surface cumulative displacement scalar average value , establish the corresponding relationship between the initial water content and the scalar mean value of cumulative surface displacement, and obtain the initial water content correction coefficient based on the linear correlation empirical model of the saturated undisturbed sample.

Further, the specific method of the step (7) is as follows: according to the steps (1) to (3), the undisturbed soil sample test piece is made on site, and the average value of the cumulative displacement scalar on the surface of the test piece is obtained; the soil sample is measured according to the alcohol combustion method Initial moisture content: According to steps (5) and (6), the free expansion rate of the soil sample is obtained through the linear correlation empirical model and the initial moisture content correction, thereby judging the expansion of the soil sample.

Further, in the described step (2), the specific steps of using the PIV method to determine the stability time of the upper surface displacement of the test piece are:

step1: From the moment the specimen is placed in a constant temperature environment, use an industrial camera to acquire the surface image of the specimen at equal intervals, and the interval can be 5-10 minutes;

以及照片中该直径长度包含的像素点个数，定义图片单像素点的长度；step2: According to the diameter of the ring knife

And the number of pixels contained in the diameter length in the photo, which defines the length of a single pixel in the picture;

step3: Determine a scalar maximum value according to the maximum incremental displacement scalar of the expansive land area, which is defined as the scalar maximum value of the area; the size of the displacement scalar is divided by the color change of the grayscale image. In the grayscale image, the scalar extreme value The large value is displayed as white, the zero value of the scalar is displayed as black, and the intermediate value of the scalar is displayed as the gradient color, which defines the corresponding relationship between the displacement scalar and the gray color;

Step4: Use the particle image velocimetry technology to process the surface images of the specimen taken at adjacent moments to obtain the incremental displacement grayscale image;

Step5: When there is no displacement of each pixel point of the image captured at two adjacent time points, that is, the displacement of each particle on the surface within this period is zero, and the grayscale image is displayed in black at this time, so that each point on the surface of the specimen is determined. The displacement reaches a stable state, and the back node of the period is determined as the displacement stabilization time.

The beneficial effects of the present invention are:

Compared with the prior art, the PIV image processing technology is simple to operate, can obtain the surface displacement field of the specimen without contact, and obtain its dynamic displacement process, and the measurement result has high accuracy, which can meet the requirements of experimental analysis.

Description of drawings

Figure 1 is a grayscale image of incremental displacement from 0 to 10 min;

Figure 2 is a grayscale image of incremental displacement for 40 to 50 minutes;

Figure 3 is a grayscale image of incremental displacement for 50 to 60 minutes;

Figure 4 is a grayscale standard ruler;

Fig. 5 is a standard fitting curve for swellability discrimination.

Detailed ways

The present invention will be further described in detail below through specific examples. The following examples are only descriptive, not restrictive, and cannot limit the protection scope of the present invention.

A method for on-site identification of expansive soil based on PIV technology, comprising the following steps:

(1) Make the original sample of expansive soil after saturation. The specific method is as follows: take undisturbed soil samples of different expansion grades, and the specimens are sampled by a steel mold. The steel mold is cylindrical, and the diameter of the steel mold is 61.8mm and the height is 10mm. For the cutting edge, the other end of the steel mold is closed. After the undisturbed soil samples of different expansion grades are saturated, the specimens are made according to the sample preparation method in 3.1 Specimen Preparation in the "Standards for Geotechnical Test Methods". , used to identify the features at different positions on the surface of the specimen, and identify the surface of the specimen as a combination of aggregates with different characteristics.

(2) Use PIV technology to determine the time when the surface displacement of the specimen is stable. The specimens obtained in step (1) were placed in a constant temperature environment of 100 °C, and the surface images of the specimens obtained at two adjacent time nodes were processed by PIV technology, so as to obtain different aggregates on the surface of the specimen during this time period. Displacement scalar: the gradient color between black and white corresponds to the displacement scalar value, so that the displacement scalar of each pixel point is displayed in the form of a grayscale image, and each pixel point of the image captured at two adjacent time points has no displacement. , that is, the displacement of each particle on the surface of the specimen in the two adjacent time nodes is zero, and the grayscale image is displayed in black at this time, so it is determined that the displacement of each point on the surface of the specimen has reached a stable state, and the adjacent two points are in a stable state. The next time node of each time node is determined as the displacement stabilization time.

In step (2), the specific steps of using the PIV method to determine the stability time of the upper surface displacement of the specimen are:

step1: The time of starting the experiment is recorded as time 0. Since the time when the test piece is placed in a constant temperature environment, use an industrial camera to take a photo every 10 minutes to obtain the surface image of the test piece;

以及照片中该直径长度包含的像素点个数，定义图片单像素点的长度；step2: Before using the PIV software to process the picture, according to the diameter of the ring knife

And the number of pixels contained in the diameter length in the photo, which defines the length of a single pixel in the picture;

step3: Determine a scalar maximum value according to the maximum incremental displacement scalar of the expansive land area, which is defined as the scalar maximum value of the area; the size of the displacement scalar is divided by the color change of the grayscale image. In the grayscale image, the scalar extreme value The large value is displayed as white, the zero value of the scalar is displayed as black, and the intermediate value of the scalar is displayed as the gradient color, which defines the corresponding relationship between the displacement scalar and the gray color;

图像处理软件进行处理；同理，实验进行到20min时，可对10min和20min拍摄的两组照片利用软件进行处理；将0min和10min，10min和20min(20min和30min、30min和40min…)处理的结果称为增量位移灰度图；step4: When the experiment reaches 10min, the two photos taken at 0min and 10min can be passed through

Image processing software for processing; Similarly, when the experiment reaches 20min, the two groups of photos taken at 10min and 20min can be processed by software; The result is called the incremental displacement grayscale map;

Step5: Count the gray value of each pixel in the incremental displacement grayscale image. When each pixel of the image captured by two adjacent time nodes has no displacement, that is, the displacement of each granule on the surface within this period is zero. At this time, the grayscale image is displayed in black, thus it is determined that the displacement of each point on the surface of the specimen reaches a stable state, and the rear node of the period is determined as the displacement stabilization time.

(3) Calculate the average value of the cumulative displacement scalars on the surface of the specimen; count the displacement scalars of all pixel points in the grayscale image, calculate the scalar average value and define the scalar average value as the incremental displacement scalar average value, according to the standard step (2) to obtain Calculate the time when the displacement is stable, and add the scalar mean value of the incremental displacement in the grayscale image obtained before the stable time to obtain the mean value of the cumulative displacement scalar.

(4) Test the free expansion rate of the specimen; according to the free expansion rate test procedure in Appendix D of "Technical Specifications for Building in Expansive Soil Areas", test the free expansion rate of the soil samples of different expansion grades.

(5) Establish the relationship between the average value of the cumulative displacement scalar on the surface of the specimen and the free expansion rate; linearly fit the correlation state between the average value of the cumulative displacement scalar on the surface of the specimen and the free expansion rate of the soil sample of the specimen, and obtain a linear relevant empirical models.

(6) Calculate the correction factor for the influence of soil moisture content on the average value of the cumulative displacement scalar on the undisturbed surface of expansive soil samples; the undisturbed soil samples with the same free expansion rate result are saturated and air-dried to different moisture contents, and then made into samples respectively. The upper surface of the sample is also covered with a single layer of standard sand with a particle size of 0.075 to 0.25 mm, which is used to identify the surface of the sample as a combination composed of different characteristic aggregates, and the sample is subjected to steps (2) and steps of the previous test. (3) Obtain the scalar average value of cumulative surface displacement, establish the corresponding relationship between the initial water content and the scalar average value of cumulative surface displacement, and obtain the initial water content correction coefficient based on the linear correlation empirical model of saturated undisturbed samples.

(7) On-site determination of expansive soil expansiveness; according to steps (1) to (3), undisturbed soil sample specimens are made on site, and the scalar average value of cumulative displacement on the surface of the specimens is obtained; the initial moisture content of soil samples is determined according to the alcohol combustion method ; According to steps (5) and (6), the free expansion rate of the soil sample is obtained through the linear correlation empirical model and the initial moisture content correction, thereby determining the expansion of the soil sample.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. A expansive soil field distinguishing method based on a PIV technology is characterized in that: the method comprises the following steps:

(1) manufacturing a saturated test piece of an undisturbed sample of expansive soil, wherein the test piece is sampled from the undisturbed soil sample by a steel mould, the steel mould is cylindrical, the diameter of the steel mould is 61.8mm, the height of the steel mould is 10mm, one end of the steel mould is open and is set as a cutting edge, and the other end of the steel mould is closed;

(2) respectively placing the test piece obtained in the step (1) in a constant temperature environment of 100 ℃, and processing the surface images of the test piece respectively obtained by two adjacent time nodes by using a particle image velocimetry technology, so as to obtain displacement scalars of different aggregates on the surface of the test piece in the time period: the gradual change color between black and white corresponds to the displacement scalar value, so that the displacement scalar of each pixel point is displayed in the form of a gray scale graph, when each pixel point of images shot at two adjacent time points does not have displacement, namely the displacement of each aggregate on the surface of the test piece at the two adjacent time points is zero, the gray scale graph is displayed to be black, the displacement of each point on the surface of the test piece is determined to reach a stable state, and the next time node of the two adjacent time nodes is determined as the displacement stable time;

(3) calculating the average value of the accumulated displacement scalars on the surface of the test piece;

(4) testing the free expansion rate of the test piece;

(5) establishing a relation between the average value of the accumulated displacement scalar quantity of the surface of the test piece and the free expansion rate;

(6) calculating a correction coefficient of the influence of the water content of the soil sample on the average value of the accumulated displacement scalar on the surface of the undisturbed sample of the expansive soil;

(7) and (4) field judgment of the expansibility of the expansive soil.

2. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 1, wherein: the specific method of the step (1) comprises the following steps: the method comprises the following steps of taking undisturbed soil samples with different expansion grades, taking the undisturbed soil samples with different expansion grades as test pieces after the undisturbed soil samples are saturated, and covering a single layer of standard sand with the grain diameter of 0.075-0.25 mm on the upper surface of each test piece for marking the surface of each test piece as a combination consisting of granules with different characteristics.

3. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 1, wherein: the specific method of the step (3) is as follows: and (3) counting the displacement scalars of all pixel points in the gray scale image, calculating a scalar mean value of the displacement scalars, defining the scalar mean value as an increment displacement scalar mean value, and accumulating the increment displacement scalar mean value in the gray scale image obtained before the stabilization time according to the displacement stabilization time obtained in the step (2) to obtain an accumulated displacement scalar mean value.

4. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 3, wherein: the specific method of the step (4) comprises the following steps: and (3) testing the free expansion rate of the test piece soil samples with different expansion grades according to the free expansion rate test steps in appendix D in the expansive soil area building technical Specification.

5. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 4, wherein: the specific method of the step (5) is as follows: and linearly fitting the correlation state between the average value of the accumulated displacement scalar on the surface of the test piece and the free expansion rate of the soil sample of the test piece to obtain a linear correlation empirical model.

6. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 3, wherein: the specific method of the step (6) is as follows: and (3) saturating the undisturbed soil sample with the same free expansion rate result, air-drying the undisturbed soil sample to different water contents, respectively manufacturing samples, covering the upper surface of each sample with standard sand with a single-layer grain size of 0.075-0.25 mm, identifying the surface of each sample as a combination consisting of granules with different characteristics, performing the step (2) and the step (3) of the test on the sample, obtaining a surface accumulative displacement scalar average value, and establishing a corresponding relation between the initial water content and the surface accumulative displacement scalar average value to obtain an initial water content correction coefficient based on a linear correlation empirical model of the saturated undisturbed sample.

7. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 6, wherein: the specific method of the step (7) is as follows: according to the steps (1) to (3), manufacturing an undisturbed soil sample test piece on site, and obtaining an average value of accumulated displacement scalars on the surface of the test piece; measuring the initial water content of the soil sample according to an alcohol combustion method; and (5) according to the step (5) and the step (6), obtaining the free expansion rate of the soil sample through the linear correlation empirical model and the initial water content correction, and judging the expansibility of the soil sample.

8. The expansive soil site distinguishing method based on the PIV technology as claimed in claim 1, wherein: the specific steps of determining the time for stabilizing the displacement of the upper surface of the test piece by using the PIV method in the step (2) are as follows:

step 1: acquiring surface images of the test piece by using an industrial camera within equal time intervals from the moment when the test piece is placed in a constant temperature environment, wherein the time intervals can be 5-10 min;

step 2: defining the length of a single pixel point of a picture according to the diameter of the cutting ring and the number of pixel points contained in the diameter length in the picture;

step 3: determining a scalar maximum value according to the maximum increment displacement scalar of the expansive soil area, and defining the scalar maximum value as the scalar maximum value of the area; the size of the displacement scalar is divided by the color change of the gray map, in the gray map, the scalar maximum value is displayed as white, the scalar zero value is displayed as black, and the scalar intermediate value is displayed as gradient color, thereby defining the corresponding relation between the displacement scalar and the gray color;

step 4: processing the surface image of the test piece shot at the adjacent moment by utilizing a particle image velocimetry technology to obtain an incremental displacement gray scale map;

step 5: when the pixel points of the images shot at two adjacent time points do not displace, namely the displacement of each aggregate on the inner surface in the time period is zero, the gray level image is displayed to be black, the displacement of each point on the surface of the test piece is determined to reach a stable state, and the node after the time period is determined as the displacement stabilization time.

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