A method for measuring fracture characteristic values

Abstract

The present invention discloses a method for measuring fracture characteristic values, belonging to the technical field of geotechnical engineering, including: obtaining a true-color fracture image; converting the true-color fracture image into a grayscale fracture image and performing thinning preprocessing on the grayscale fracture image; vectorizing the preprocessed grayscale fracture image to obtain a fracture vector map; drawing a closed-curve positioning line on the fracture vector map so that the positioning line intersects with the fracture contour line; measuring and marking the fracture width at each intersection of the positioning line and the fracture contour line to obtain a fracture width measurement value, and performing characteristic processing on it to obtain a fracture characteristic value; significantly improving the fracture measurement accuracy and being able to help better reveal the fracture development process and trend.

Description

Technical Field

[0001] The present invention relates to a method for measuring fracture characteristic values, belonging to the technical field of geotechnical engineering. Background Art

[0002] Expansive soil is a special cohesive soil with multi-fracture property, strong swelling and shrinkage property, and strength attenuation property generated during the natural geological formation process; Highways constructed in typical expansive soil areas have the characteristics of "sliding inevitably in cuts and collapsing inevitably in embankments", indicating the complexity and long-term harmfulness of expansive soil slopes; The fracture property of expansive soil is closely related to slope stability, mainly manifested in that after long-term environmental action, due to fracture development, the strength decays, and then slope instability is caused; In recent years, in the construction of transportation and water resources projects such as roads and railways, the problem of expansive soil slope stability has become increasingly prominent; Therefore, studying the development law of expansive soil fractures has become an important topic concerned by the geotechnical engineering community.

[0003] Methods for recording the degree of fracture development usually include surface digital photography, CT machine depth scanning, and laser scanners. The fracture ratio is the ratio of the fracture area to the specimen area, which can reflect the degree of fracture development. Although the fracture ratio generally describes the fracture development situation, due to the shrinkage of the core sample, fractures will also be generated at the boundary between the specimen and the core cutter, and this fracture has a significant impact on the fracture ratio value. Considering all the boundary fractures generated by the shrinkage of the core sample in the obtained fracture ratio is called the total fracture ratio; During the process of water loss and shrinkage of the specimen, the total fracture ratio shows a monotonic increase with the decrease of the water content; The fracture ratio obtained without considering the boundary fractures generated by the shrinkage of the core sample is the corrected fracture ratio; Then the corrected fracture ratio decreases in the later stage with the decrease of the water content; Therefore, how to reasonably reflect the influence of the specimen boundary is still controversial; In addition, the fracture width is also a description index, but when the fracture width increases from small to large, the length increases accordingly, and other fractures may be generated, forming a bifurcated structure, so it is difficult to determine the specific position of the maximum fracture width along the length direction, and thus the fracture width is difficult to measure. To sum up, to reveal the fracture development mechanism, the lack of a measurement method with high precision is an urgent problem to be solved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring fracture characteristic values, which solves the problem of low measurement accuracy in the prior art.

[0005] To achieve the above purpose, the present invention is implemented by adopting the following technical solution:

[0006] The present invention provides a method for measuring fracture characteristic values, including:

[0007] Obtaining a true-color fracture image;

[0008] Converting the true-color fracture image into a grayscale fracture image, and performing thinning preprocessing on the grayscale fracture image;

[0009] Vectorize the preprocessed crack grayscale image to obtain a crack vector map;

[0010] Draw a closed curve type positioning line on the crack vector map so that the positioning line intersects the crack contour line;

[0011] Measure and label the crack width at each intersection of the positioning line and the crack contour line to obtain the crack width measurement value, and perform feature processing on it to obtain the crack feature value.

[0012] Further, the refinement preprocessing is as follows:

[0013] Perform despeckling on the crack surface in the crack grayscale image.

[0014] Further, the crack feature values include:

[0015] The maximum line value of the crack width, obtained by taking the maximum value of the crack width measurement values at each intersection on the positioning line;

[0016] The minimum line value of the crack width, obtained by taking the minimum value of the crack width measurement values at each intersection on the positioning line;

[0017] The average line value of the crack width, obtained by taking the average value of the crack width measurement values at each intersection on the positioning line;

[0018] The crack line crack rate, obtained by dividing the sum of the crack width measurement values at each intersection on the positioning line by the length of the positioning line;

[0019] The crack spacing, obtained by dividing the length of the positioning line by the number of intersections.

[0020] Further, it also includes the step of determining the crack development trend:

[0021] Each intersection on the positioning line represents a crack. Measure and label the crack width at each intersection to obtain the measurement value, and then divide the measurement value into grades to obtain the crack development trend.

[0022] Further, the crack width measurement value is obtained by directly labeling the crack width at each intersection of the positioning line and the crack contour line in CAD software.

[0023] Further, it also includes the step of measuring the true value of the crack width:

[0024] Specify the width and height of the crack vector map;

[0025] Enlarge the crack vector map until the pixel grid can be observed, determine the boundary of the crack according to the color difference, and mark the boundary line between the crack and the soil body;

[0026] Obtain the true value of the fracture width at the measuring point according to the mark.

[0027] Further, it also includes the step of calculating the measurement accuracy of the fracture width, and the measurement accuracy is calculated by the following method:

[0028]

[0029] where Δ is the measurement accuracy, B T is the true value of the fracture width, B i is the measured value of the fracture width.

[0030] Further, it also includes the step of determining the optimal threshold of the fracture vector map:

[0031] Draw a closed curve type positioning line on the fracture grayscale map so that it intersects with the fracture contour line. Take m measuring points from the positioning lines on the fracture grayscale map, and the taken measuring points correspond to m measuring points on the positioning lines of the fracture vector map with different thresholds;

[0032] Measure the true value of the fracture width at m measuring points on the positioning line of the fracture grayscale map, and take its average value as B Tav ;

[0033] Measure the measured value of the fracture width at m measuring points on the positioning line of the fracture vector map with different thresholds, and take its average value as B iav ;

[0034] Draw a relationship curve between the difference in the average fracture width |B Tav -B iav | and the threshold, and take the threshold corresponding to the minimum value of the difference in the average fracture width as the optimal threshold.

[0035] Further, the index expression of the fracture rate included in the fracture characteristic values also includes:

[0036] Total fracture rate, obtained by dividing the fracture area by the total area of the soil mass when including the fixed boundary fracture effect;

[0037] Corrected fracture rate, obtained by dividing the fracture area by the total area of the soil mass when not including the fixed boundary fracture effect;

[0038] The expression of the total fracture rate, corrected fracture rate and the linear fracture rate enriches the characterization of the fracture variation law.

[0039] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0040] A method for measuring fracture characteristic values provided by the present invention proposes a closed curve type positioning line for auxiliary measurement, which significantly improves the fracture measurement accuracy;

[0041] The fracture line fracture rate is obtained by dividing the sum of the fracture width measurement values at each intersection on the positioning line by the length of the positioning line, which solves the problem of the total fracture rate and the corrected fracture rate calculated by the area ratio regarding how to consider the boundary contraction effect. The line fracture rate can reflect the development process of the fracture first increasing and then decreasing, so as to better understand the fracture change law. Brief Description of the Drawings

[0042] Figure 1 is a flowchart of a method for measuring fracture characteristic values provided by an embodiment of the present invention;

[0043] Figure 2 is a fracture vector diagram provided by an embodiment of the present invention;

[0044] Figure 3 is a fracture midline vector diagram provided by an embodiment of the present invention;

[0045] Figure 4 is a schematic diagram of measuring points of a fracture vector diagram provided by an embodiment of the present invention;

[0046] Figure 5 is a relationship curve diagram of the average fracture width difference and the threshold value provided by an embodiment of the present invention;

[0047] Figure 6 is a relationship diagram of the fracture rate changing with the moisture content provided by an embodiment of the present invention. Detailed Embodiment

[0048] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0049] As Figure 1 shown, a method for measuring fracture characteristic values provided by an embodiment of the present invention includes:

[0050] S1. Obtain a true-color fracture image.

[0051] In this embodiment, a digital camera is used to take pictures of the fracture development pictures of the ring knife specimen to obtain a true-color fracture image.

[0052] S2. Convert the true-color fracture image into a grayscale fracture image and perform thinning preprocessing on the grayscale fracture image.

[0053] In this embodiment, the true-color fracture image is converted into a grayscale fracture image through R2V software, and then thinning preprocessing (i.e., speckle removal processing) is performed on the fracture surface in the grayscale fracture image.

[0054] S3. Vectorize the preprocessed grayscale fracture image to obtain a fracture vector diagram.

[0055] In this embodiment, the preprocessed crack grayscale image is vectorized by R2V software. When outputting the crack vector map, it is set to the DXF format, which can be used as a drawing exchange file for CAD software.

[0056] S4. Draw a closed curve type positioning line on the crack vector map so that the positioning line intersects with the crack contour line.

[0057] In this embodiment, import the crack vector map into CAD software, and then draw a closed curve type positioning line on the crack vector map so that the positioning line intersects with the crack contour line, as Figure 2 and Figure 3 shown.

[0058] S5. Mark and measure the crack width at each intersection of the positioning line and the crack contour line to obtain the crack width measurement value, and perform feature processing on it to obtain the crack feature value.

[0059] In this embodiment, mark and measure the crack width at each intersection of the positioning line and the crack contour line in CAD software to obtain the crack width measurement value.

[0060] Then calculate the crack feature value. The crack feature value includes the maximum crack width line value, the minimum crack width line value, the average crack width line value, the crack line crack rate, and the crack spacing. The calculation method is as follows:

[0061] The maximum crack width line value is obtained by taking the maximum value of the crack width measurement values at each intersection on the positioning line. The minimum crack width line value is obtained by taking the minimum value of the crack width measurement values at each intersection on the positioning line. The average crack width line value is obtained by taking the average value of the crack width measurement values at each intersection on the positioning line. The crack line crack rate is obtained by dividing the sum of the crack width measurement values at each intersection on the positioning line by the length of the positioning line. The crack spacing is obtained by dividing the length of the positioning line by the number of intersections.

[0062] A method for measuring crack feature values provided by an embodiment of the present invention further includes the step of determining the crack development trend:

[0063] Each intersection on the positioning line represents a crack. The crack width at each intersection is marked and measured respectively to obtain the measurement value, and then the measurement value is graded to obtain the crack development trend.

[0064] A method for measuring crack feature values provided by an embodiment of the present invention further includes the step of calculating the measurement accuracy of the crack width. The measurement accuracy is calculated by the following method:

[0065]

[0066] where Δ is the measurement accuracy, B Tis the true value of the crack width, B i is the measured value of the crack width.

[0067] The true value of the crack width is calculated by the following method:

[0068] Input IMAGEATTCH in the CAD software command bar to import the crack vector image, and specify that both the width and height of the crack vector image are 61.8 mm;

[0069] Enlarge the crack vector image until the pixel grid can be observed, determine the boundary of the crack according to the color difference, and mark the dividing line between the crack and the soil mass;

[0070] Obtain the true value B of the crack width at the measuring point according to the marking T .

[0071] A method for measuring crack characteristic values provided by an embodiment of the present invention further includes the step of determining the optimal threshold of the crack vector image:

[0072] Import the crack grayscale image into the CAD software;

[0073] Draw a closed curve type positioning line on the crack grayscale image so that it intersects with the crack contour line, take 8 measuring points from the positioning lines on the crack grayscale image, and the taken measuring points correspond to 8 measuring points (a, b, c, d, e, f, g, h) on the positioning lines of the crack vector image with different thresholds (i.e., Figure 4 );

[0074] Measure the true value of the crack width at 8 measuring points on the positioning line of the crack grayscale image, and take its average value as B Tav ;

[0075] Measure the measured values of the crack width at 8 measuring points on the positioning line of the crack vector image with different thresholds, and take its average value as B iav ;

[0076] Draw the relationship curve of the average crack width difference |B Tav -B iav | and the threshold K (as shown in Figure 5 ), and take the threshold K corresponding to the minimum average crack width difference as the optimal threshold. As can be seen from Figure 5 , the optimal threshold in this embodiment is 108.

[0077] For Figure 4 , analyze the measurement accuracy of the 8 measuring points on the two rings at the threshold of 108. The measurement accuracy is calculated according to the following formula:

[0078] ΔB = |B Ti -B i |

[0079]

[0080] Among them, ΔB is the absolute difference, with the unit of mm, and B Ti is the true value of the fracture width at the i-th intersection point, with the unit of mm, and B i is the measured value of the fracture width at the i-th intersection point, with the unit of mm, and Δ is the relative error (i.e., the measurement accuracy).

[0081] The accuracy analysis results of each measuring point are shown in Table 1 below.

[0082] Table 1 Determination of the relative error of the fracture width measurement

[0083]

[0084] Table 1 shows the relative errors of the fracture widths measured at each measuring point by the vector method when the vectorization threshold of the fracture vector diagram is selected as 108. It can be seen that the relative error of the fracture width measured by this method is less than 0.7%, and the average value is 0.5%.

[0085] This embodiment also explains the application of the linear fracture rate:

[0086] The dry density of the remolded expansive soil sample is 1.58 g / cm 3 , the initial soil sample is in a saturated state, with a water content of 31.4%. The temperature of the constant temperature and humidity test chamber is adjusted to 35 °C and the relative humidity is adjusted to 25% to simulate the natural environment, and the soil sample is dehumidified; the soil samples dehumidified for 0, 1, 2, 3, 4, 6, 8, 10, 12, 18, 24, 26 h are respectively photographed and weighed for recording.

[0087] Figure 6 are the variation relationships of the linear fracture rate, the total fracture rate, and the corrected fracture rate with the water content respectively. By comparing the three curves, it can be found that in the first stage before the surface fractures of the soil mass develop, the relationships between the linear fracture rate, the total fracture rate, the corrected fracture and the water content are very close in terms of the variation trend and numerical value; when the surface fractures of the soil mass develop to the maximum extent in the latter stage, the total fracture rate gradually stabilizes, while the corrected fracture rate decreases significantly, and the linear fracture rate is between the two.

[0088] The total fracture rate considers the surface range as the area of the inner diameter of the cutting ring, that is, a circle with a diameter of 61.8 mm. Since the inner surface area of the cutting ring is a constant value; the calculation formula for the total fracture rate is:

[0089]

[0090] Among them, R1 is the total fracture rate; A i is the area of the i-th fracture, with the unit of mm 2 ; A is the inner surface area of the cutting ring inner diameter, with the unit of mm 2; n1 is the number of crack pixels, with the unit of piece; n2 is the number of soil block pixels, with the unit of piece.

[0091] Since the inner surface area of the core cutter is constant, so (n1 + n2) is a constant value; as the water content of the specimen decreases, cracks formed after the shrinkage of the specimen make n1 increase and n2 decrease; as the shrinkage stabilizes, the corresponding total crack rate also gradually stabilizes; the total crack rate shows a monotonically increasing development trend and can reflect the shrinkage situation of the specimen.

[0092] Adopt a concentric circle with the core cutter (such as 0.8R, where R is the inner diameter of the core cutter) to intercept the crack grayscale image, then respectively count the number of crack and soil block pixels in the concentric circular ring, and calculate the corrected crack rate according to the following formula:

[0093]

[0094] Among them, R2 is the corrected crack rate; A′ i is the area of the i-th crack in the concentric circular ring, with the unit of mm 2 ; A′ is the surface area of the 0.8R circular ring, with the unit of mm 2 ; n 1’ is the number of crack pixels in the 0.8R circular ring, with the unit of piece; n 2’ is the number of soil block pixels in the 0.8R circular ring, with the unit of piece.

[0095] When calculating the corrected crack rate, a fixed circle concentric with the core cutter artificially cuts off the boundary. When the boundary shrinkage is large, due to the shrinkage of the specimen, the mass of the soil block in the fixed circle increases significantly, and the crack pixels in the circular ring are on the small side because the boundary crack area is not included, resulting in a small corrected crack rate; when the boundary shrinkage is small, mainly local shrinkage occurs, then the mass of the specimen in the fixed circle increases insignificantly or decreases, resulting in a decrease in the soil block pixels in the fixed circle and a large modified crack rate.

[0096] The variable of the linear crack rate is not the overall area. Correspondingly, there is no problem of how to calculate the boundary change. The boundary change only has a slight offset effect on the position of the measurement line, and the position offset of the measurement line will not have an obvious impact on the measurement value. Therefore, this measurement value can truly reflect the development of cracks; therefore, as Figure 6 shown, the linear crack rate is between the total crack rate and the corrected crack.

[0097] Neither the linear crack rate nor the corrected crack rate includes the boundary change situation between the specimen and the core cutter.

[0098] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A method for measuring crack characteristic values, characterized in that, Including: Obtain the true - color crack image; Convert the true - color crack image into a grayscale crack image, and perform thinning pre - processing on the grayscale crack image; Vectorize the pre - processed grayscale crack image to obtain a crack vector image; Draw a closed - curve positioning line on the crack vector image so that the positioning line intersects the crack contour line; Measure and label the crack widths at the intersection points of the positioning line and the crack contour line to obtain crack width measurement values, and perform feature processing on them to obtain crack feature values. The crack feature values include the crack line crack rate, which is obtained by dividing the sum of the crack width measurement values at each intersection point on the positioning line by the length of the positioning line; It also includes the step of determining the optimal threshold of the crack vector image: Draw a closed curve type positioning line on the fracture grayscale image, making it intersect with the fracture contour line, and select m measuring points from the positioning line on the fracture grayscale image. The selected measuring points correspond to m measuring points in the positioning line on the fracture vector images with different thresholds; Measure the true values of the fracture widths at the measuring points on the positioning line in the grayscale fracture map, and take their average value as m ; ; Measure the crack width measurement values of the measuring points on the positioning line of different threshold crack vector diagrams, and take their average value as m ; ; Draw the relationship curve between the average width difference of fractures and the threshold value, and take the threshold value corresponding to the minimum average width difference of fractures as the optimal threshold value.

2. The crack characteristic value measurement method according to claim 1, characterized in that The thinning pre - processing is: Perform despeckling on the crack surface in the grayscale crack image.

3. A method for measuring crack characteristic values according to claim 1, characterized in that, The crack feature values include: The maximum crack width line value, which is obtained by taking the maximum value of the crack width measurement values at each intersection point on the positioning line; The minimum crack width line value, which is obtained by taking the minimum value of the crack width measurement values at each intersection point on the positioning line; The average crack width line value, which is obtained by taking the average value of the crack width measurement values at each intersection point on the positioning line; The crack spacing, which is obtained by dividing the length of the positioning line by the number of intersection points.

4. A method for measuring crack characteristic values according to claim 1, characterized in that, It also includes the step of determining the crack development trend: Each intersection point on the positioning line represents a crack. Measure and label the crack widths at each intersection point to obtain measurement values, and then classify the measurement values to obtain the crack development trend.

5. A method for measuring crack characteristic values according to claim 1, characterized in that The crack width measurement value is obtained by directly labeling the crack widths at the intersection points of the positioning line and the crack contour line in CAD software.

6. The method for measuring crack characteristic values according to claim 1, wherein It also includes the step of measuring the true value of the crack width: Specify the width and height of the crack vector image; Enlarge the crack vector image until pixel grids can be observed, determine the boundary of the crack according to the color difference, and mark the boundary between the crack and the soil body; Obtain the true value of the crack width at this measurement point according to the marking.

7. A method for measuring crack characteristic values according to claim 6, characterized in that, It also includes the step of calculating the measurement accuracy of the crack width. The measurement accuracy is calculated by the following method: ； Among them, is the measurement accuracy, is the true value of the fracture width, is the measured value of the fracture width.

8. A method for measuring crack characteristic values according to claim 2, characterized in that, The index expression of the crack rate included in the crack feature values also includes: The total crack rate, which is obtained by dividing the crack area including the fixed - boundary crack effect by the total area of the soil body; The corrected crack rate, which is obtained by dividing the crack area without including the fixed - boundary crack effect by the total area of the soil body.

Images