CN113063810B - Method for obtaining macroscopic and microscopic damage evolution law under sandstone freeze thawing action - Google Patents
Method for obtaining macroscopic and microscopic damage evolution law under sandstone freeze thawing action Download PDFInfo
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Abstract
The invention discloses a method for obtaining a macroscopic and microscopic damage evolution rule under the freezing and thawing action of sandstone, which comprises the steps of carrying out two-dimensional longitudinal fault CT scanning and a uniaxial compression test on a sandstone test piece to obtain a plurality of groups of CT scanning images and macroscopic physical parameters of the sandstone test piece; obtaining a binaryzation processed CT image; performing phenomenological theory analysis and three-dimensional reconstruction on each group of binaryzation processed CT images to obtain a two-dimensional pore structure evolution diagram and a three-dimensional digital core of the sandstone test piece; obtaining the microscopic structure parameters of the sandstone test piece; obtaining a macroscopic and microscopic damage evolution rule of the sandstone test piece according to the two-dimensional pore structure evolution diagram and the three-dimensional digital core of the sandstone test piece; obtaining a freeze-thaw damage evolution curve; and determining the life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area according to the macroscopic and microscopic damage evolution rule and the freeze-thaw damage evolution curve of the sandstone test piece.
Description
Technical Field
The invention belongs to the technical field of freeze-thaw rocks, and particularly relates to a method for obtaining a macroscopic and microscopic damage evolution rule under the freeze-thaw action of sandstone.
Background
In recent years, in China, cold area engineering construction is seriously affected by secondary disasters induced by rock freezing and thawing, and for example, surrounding rocks of finished roadways are cracked under the action of frost heaving to further induce instability of a supporting structure. Compared with long-term freezing and seasonal freezing, the influence of day and night freezing and thawing cycle effects on the strength of the rock is more obvious, and the research of the law of physical and mechanical property deterioration under the freezing and thawing effect of the rock is the core work for guiding the control of engineering disasters in cold regions.
Under the action of a freezing and thawing environment, the pore water in the rock is repeatedly frozen and thawed to generate huge frost heaving force which can act on the inner surface of the internal pore structure, so that primary pores are further expanded and communicated, secondary independent pores appear, the original bearing effect of the rock structure is finally failed, and engineering freezing damage is caused. The evolution of the mesoscopic pore structure is the key for inducing the damage of the rock structure on the macroscopic representation, so that the connection between the deterioration of the physical and mechanical properties of the sandstone and the evolution of the pore structure is researched, the deterioration degree of the physical and mechanical properties of the rock in the cold region is predicted from the mesoscopic level, and the mesoscopic pore structure has important significance and application value for the prevention and control of engineering disasters in the cold region.
At present, students and researchers have conducted more systematic research aiming at engineering problems in cold regions, such as Zhang Junyue [1] And (3) performing a freeze-thaw cycle test and a uniaxial compression test under different freeze-thaw times on the saturated red sandstone sample, and analyzing the influence rule of the freeze-thaw process on the physical force property of the rock. Zhang Hui Mei, etc [2] The freeze-thaw damage is macroscopically defined by the elastic modulus, and the coupled calculation of the freeze-thaw damage and the load damage is realized. Song Yong army [3] Carrying out uniaxial loading real-time CT scanning on the sandstone at different temperatures, and quantitatively researching the damage and destruction evolution rule of the frozen rock based on the proportional relation between the CT number H value and the density;
however, the following problems still exist in the existing research:
1. research is mostly focused on qualitatively and quantitatively describing the occurring deterioration behaviors on a test level, the evolution disaster-causing mechanism of a rock pore structure is lacked, and the evolution rule of a microscopic structure under the action of freeze-thaw cycle is not clear. In fact, the evolution behavior of the rock pore structure in a freeze-thaw environment is key to the deterioration of its properties;
2. the study on a microscopic level is that a corresponding acquisition and characterization method is lacked for the growth and development of a pore structure of a freeze-thaw rock, and when a CT image is processed and parameters are extracted, the efficiency and the accuracy of the processing method need to be improved;
3. the damage variable obtained according to the microscopic parameters is difficult to establish connection with the macro, and the mechanical properties of the rock cannot be predicted from the microscopic scale without a method for realizing macro-microscopic combination.
The evolution of the rock microscopic structure cannot be accurately known, the dependency relationship between the microscopic damage and the rock physical and mechanical properties is not clear, the research progress of predicting the failure of the bearing capacity of rock materials such as sandstone is greatly limited, and the prevention and control of engineering disasters in cold regions are difficult to perform.
Disclosure of Invention
In view of the above, the main purpose of the present invention is to provide a method for obtaining the macroscopic and microscopic damage evolution law under the action of sandstone freeze thawing.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the embodiment of the invention provides a method for obtaining a macro-micro damage evolution rule under the freezing and thawing action of sandstone, which comprises the following steps:
carrying out two-dimensional longitudinal tomography CT scanning and a uniaxial compression test on the sandstone test piece to obtain a plurality of groups of CT scanning images and macroscopic physical parameters of the sandstone test piece;
preprocessing each group of CT scanning images to obtain binaryzation processed CT images;
performing phenomenological theory analysis and three-dimensional reconstruction on each group of binaryzation processed CT images to obtain a two-dimensional pore structure evolution diagram and a three-dimensional digital core of the sandstone test piece;
performing statistical analysis on each group of binaryzation-processed CT images to obtain the mesoscopic structure parameters of the sandstone test piece;
obtaining a macroscopic and microscopic damage evolution rule of the sandstone test piece according to the two-dimensional pore structure evolution diagram and the three-dimensional digital core of the sandstone test piece;
establishing damage variables according to the microscopic structure parameters and the macroscopic physical parameters of the sandstone test piece, and obtaining a freeze-thaw damage evolution curve according to the macroscopic damage variables;
and determining the life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area according to the macroscopic and microscopic damage evolution rule and the freeze-thaw damage evolution curve of the sandstone test piece.
In the above scheme, the macroscopic physical parameters of the sandstone test piece at least include: the elastic modulus of the sandstone test piece after different freezing and thawing cycle times; the mesoscopic structure parameters of the sandstone test piece at least comprise: and (3) the porosity and the pore fractal dimension of the sandstone test piece after different freeze-thaw cycle times.
In the above scheme, the preprocessing is performed on each group of CT scan images to obtain a binarized CT image, and specifically:
carrying out 3-to-3 median filtering denoising processing on each group of CT scanning images to obtain denoised CT images;
carrying out Laplace operator sharpening processing on the denoised CT scanning image to obtain a sharpened and enhanced CT image;
and carrying out binarization processing on the CT scanning image subjected to sharpening enhancement processing to obtain the CT image subjected to binarization processing.
In the foregoing scheme, the binarizing processing is performed on the CT scan image after the sharpening enhancement processing to obtain the binarized CT image, and specifically includes:
dividing the CT image subjected to sharpening enhancement processing into a pore area and a rock area according to a threshold t, and respectively determining the accumulated probability P of the gray scale of the pore area T (t) and cumulative probability of rock zone grayness P B (t)：
according to the accumulated probability P of the gray scale of the pore area T (t) and cumulative probability of rock zone grayness P B (t) determining the total image entropy H (t) of the CT after sharpening enhancement processing under all threshold values t:
and searching the maximum value of the total entropy in the image total entropy H (t), and performing binarization processing on the CT image after sharpening enhancement processing by using a corresponding threshold value.
In the above scheme, the two-dimensional pore structure evolution diagram of the sandstone test piece at least comprises: and performing phenomenological theory analysis according to the binarized CT image to draw a pore evolution rose diagram of the sandstone test piece, and performing phenomenological theory analysis according to the binarized CT image to draw a pore structure growth diagram of the sandstone test piece.
In the above scheme, the analyzing and drawing the porosity evolution rose diagram of the sandstone test piece according to the binarized CT image by the phenomenological theory specifically includes:
expressing the binarized image by a digital matrix M multiplied by N to obtain the center of the matrix
Establishing a rectangular coordinate system by taking the center of the matrix as a reference, starting to divide the matrix into 24 parts in a clockwise direction along the positive direction of the y axis of the rectangular coordinate system, taking the trend of every 15 degrees as a part, and counting the number of pores in the part;
and drawing the pore evolution rose diagram according to the trend part and the number of pores in the part.
In the scheme, a phenomenological theory analysis is carried out according to the CT image after the binarization processing to draw a pore structure growth diagram of the sandstone test piece; the pore structure growth diagram at least comprises: arrows representing pore growth trends, closed solid line shapes representing pore morphology, closed dashed line shapes representing new morphology that pores will develop under freeze-thaw action.
In the above scheme, the establishing of the damage variable according to the microscopic structure parameter and the macroscopic physical parameter of the sandstone test piece, and the obtaining of the freeze-thaw damage evolution curve according to the macroscopic damage variable specifically include:
selecting the porosity of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece, and defining the damage degree D n ：
D n ＝λ n (n＝0,5,10,20,40)
In the formula of n The porosity of the sandstone test piece after different freezing and thawing cycle times;
selecting the elastic modulus of the sandstone test piece after different freezing-thawing cycle times in the macroscopic physical parameters of the sandstone test piece, and defining a macroscopic damage variable D En ；
Wherein E is the elastic modulus of the hypothetical ideal undamaged sandstone n The elastic modulus of the sandstone test piece after different freezing and thawing cycle times;
selecting the damage degree D of the pore fractal dimension of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece n Correcting to obtain microscopic damage variable D Bn ：
D Bn ＝B n D n (n＝0,5,10,20,40)
In the formula B n The fractal dimension of the pores of the test piece after different freezing and thawing times;
selecting the mesoscopic structure parameters and the macroscopic physical parameters of the sandstone test piece to determine the elastic modulus E of the ideal nondestructive sandstone test piece:
in the formula of 0 ，B 0 And E 0 Respectively the porosity, the pore fractal dimension and the elastic modulus of the sandstone test piece after 0 freeze-thaw cycle;
and (4) combining the macro and micro damage variables to obtain a freeze-thaw damage evolution curve.
In the above scheme, the determining of the life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area according to the macroscopic and microscopic damage evolution law and the freeze-thaw damage evolution curve of the sandstone test piece specifically includes: obtaining a macroscopic damage variable according to the microscopic damage variable of the sandstone test piece and the quantitative part of the sandstone macroscopic damage evolution rule, obtaining a macroscopic damage variable according to the microscopic damage variable of the sandstone test piece and the sandstone macroscopic damage evolution rule, and determining a freeze-thaw cycle period required when the macroscopic damage variable reaches the rock damage so as to predict the damage life under the rock freeze-thaw environment; and determining a rock macroscopic crack pore evolution mode and a region with high damage density inside the material according to the macroscopic and microscopic damage evolution rule of the sandstone test piece, and providing guidance for the prevention and treatment of engineering disasters in cold regions by taking measures such as adhesion, reinforcement and the like at regular time and fixed points.
In the above scheme, the step of obtaining the macroscopic damage variable according to the mesoscopic damage variable of the sandstone test piece in combination with the macroscopic damage evolution law of the sandstone, and determining the freeze-thaw cycle period required when the macroscopic damage variable reaches the rock damage so as to predict the damage life of the rock in the freeze-thaw environment specifically comprises the steps of: if the test piece is a test piece made of materials such as rock, concrete and the like, and the macroscopic damage variable loses 40% of the reference value, the test piece is determined to lose bearing effect or damage, the time length of each freeze-thaw period is determined according to the number of freeze-thaw cycle periods required by rock damage and local actual measurement low-temperature data of the sample, and the time required by rock failure is obtained so as to predict the damage life of the rock in the freeze-thaw environment.
Compared with the prior art, the method provided by the invention is simple and feasible to operate, can clearly and intuitively reflect the change of the sandstone pore structure in the freeze-thaw cycle, accurately quantizes the characteristics of the internal pore structure of the sandstone material, researches the evolution rule of the primary pores and the secondary pores of the sandstone in the freeze-thaw environment, and has important significance for accurately describing the evolution disaster-causing mechanism of the rock pore structure and guiding the control of cold region engineering disasters.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a schematic flow chart of the method for obtaining the evolution law of the pore structure of sandstone under the action of freeze thawing;
FIG. 2 is a binarized image of a section of a sandstone test piece under different freezing and thawing cycle times in the test of the invention;
FIG. 3 is a pore evolution rosegram of a sandstone test piece in the test of the invention;
FIG. 4 is a pore structure growth diagram of a sandstone test piece in the test of the invention;
FIG. 5 is a three-dimensional digital core of a sandstone test piece under different freezing and thawing cycle times in the test of the invention;
FIG. 6 is a histogram of the contribution rate of the pore structure of a sandstone test piece under different freeze-thaw cycle times in the test of the invention;
FIG. 7 is a box diagram of the change rule of the porosity of the section of a sandstone test piece under different freezing and thawing cycle times in the test of the invention;
FIG. 8 is a line graph of the change rule of the mean value of the fractal dimension of the cross section pore of the sandstone test piece under different freezing and thawing cycle times in the test of the invention;
FIG. 9 is a macro-microscopic damage evolution law diagram under different freeze-thaw cycle times in the experiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a method for obtaining a macro-micro damage evolution rule under the freezing and thawing action of sandstone, which is realized by the following steps as shown in figures 1-9:
step 1: carrying out two-dimensional longitudinal tomography CT scanning and a uniaxial compression test on the sandstone test piece to obtain a plurality of groups of CT scanning images and macroscopic physical parameters of the sandstone test piece;
specifically, the macroscopic physical parameters of the sandstone test piece at least comprise: the elastic modulus of the sandstone test piece after different freezing and thawing cycle times;
step 2: preprocessing each group of CT scanning images to obtain binaryzation processed CT images;
specifically, 3-by-3 median filtering denoising processing is carried out on each group of CT scanning images to obtain denoised CT images;
carrying out Laplace operator sharpening processing on the denoised CT scanning image to obtain the CT image subjected to sharpening enhancement processing, thus removing noise signals contained in the CT image under the condition of not changing the original information of the sandstone CT image and simultaneously improving the contrast of the CT image;
and carrying out binarization processing on the CT scanning image subjected to sharpening enhancement processing to obtain the CT image subjected to binarization processing.
The binarization processing is performed on the CT scanned image after the sharpening enhancement processing to obtain the CT image after the binarization processing, which specifically includes:
dividing the CT image subjected to sharpening enhancement processing into a pore area and a rock area according to a threshold t, and respectively determining the accumulated probability P of the gray scale of the pore area T (t) and cumulative probability of rock zone grayness P B (t)：
according to the accumulated probability P of the gray scale of the pore area T (t) and cumulative probability of rock zone grayness P B (t) determining the total image entropy H (t) of the CT after sharpening enhancement processing under all threshold values t:
and searching the maximum value of the total entropy in the image total entropy H (t), and performing binarization processing on the CT image after sharpening enhancement processing by using a corresponding threshold value.
And calculating a total entropy selection threshold value of the image by combining a genetic algorithm to carry out binarization processing on the CT image, so that a binarization image which truly represents the pore structure of the longitudinal section of the sandstone can be quickly and accurately obtained.
And step 3: performing phenomenological theory analysis and three-dimensional reconstruction on each group of binaryzation processed CT images to obtain a two-dimensional pore structure evolution diagram and a three-dimensional digital core of the sandstone test piece;
and 4, step 4: performing statistical analysis on each group of binarized CT images to obtain the mesoscopic structure parameters of the sandstone test piece;
specifically, the macroscopic physical parameters of the sandstone test piece at least comprise: the elastic modulus of the sandstone test piece after different freezing and thawing cycle times; the mesoscopic structure parameters of the sandstone test piece at least comprise: and (3) the porosity and the pore fractal dimension of the sandstone test piece after different freeze-thaw cycle times.
And statistically analyzing the binarized image to obtain the fractal dimension of the section pore of the sandstone test piece under different freeze-thaw times, wherein the fractal dimension can reflect the change condition of the overall pore structure of the sandstone under the action of freeze-thaw cycles.
And 5: obtaining a macroscopic and microscopic damage evolution rule of the sandstone test piece according to the two-dimensional pore structure evolution diagram and the three-dimensional digital core of the sandstone test piece;
specifically, the sandstone test piece pore evolution rose diagram is drawn by performing phenomenological theory analysis according to the binarized CT image, and the sandstone test piece pore structure growth diagram is drawn by performing phenomenological theory analysis according to the binarized CT image.
The porosity evolution rose diagram of the sandstone test piece is drawn by the phenomenological theory analysis according to the binarized CT image, and specifically comprises the following steps:
expressing the binarized image by a digital matrix M multiplied by N to obtain the center of the matrix
Establishing a rectangular coordinate system by taking the center of the matrix as a reference, dividing the matrix into 24 parts in the clockwise direction along the positive direction of the y axis of the rectangular coordinate system, taking the trend of every 15 degrees as one part, and counting the number of pores in the parts;
and drawing the pore evolution rose diagram according to the trend part and the number of pores in the trend part.
And (4) according to the pore junction evolution rose diagram of the sandstone test piece drawn by the CT image after binarization processing, the evolution trend under the two-dimensional view of the pore structure under different freeze-thaw cycle times can be quantitatively analyzed.
And analyzing and drawing a pore structure growth diagram of the sandstone test piece according to the binaryzation-processed CT image by using a phenomenological theory.
The pore structure growth diagram at least comprises: arrows representing pore growth tendency, closed solid line shape representing pore morphology, and closed dotted line shape representing new morphology into which pores will grow and develop under freeze-thaw action.
According to a pore structure growth diagram of the sandstone test piece drawn according to the image after binarization processing, the growth evolution law of primary pores and secondary pores under the action of freeze-thaw cycles can be intuitively understood.
The three-dimensional digital core of the sandstone test piece under different freezing and thawing times obtained by stacking the CT image after binarization processing can be used for directly observing the spatial distribution of the pore structure, including the structural characteristics of the connected pores and the structural characteristics of the independent pores, and can also quantify the expansion and connection conditions of the primary pores and the growth and development conditions of the secondary pores in the freezing and thawing cycle process, and the evolution rule of the pore structure of the sandstone under the freezing and thawing action can be obtained from the obtained data.
Step 6: establishing damage variables according to the microscopic structure parameters and the macroscopic physical parameters of the sandstone test piece, and obtaining a freeze-thaw damage evolution curve according to the macroscopic damage variables;
specifically, the porosity of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece is selected, and the damage degree D is defined n ：
D n ＝λ n (n＝0,5,10,20,40)
In the formula of lambda n The porosity of the sandstone test piece after different freezing and thawing cycle times;
selecting the elastic modulus of the sandstone test piece after different freezing-thawing cycle times in the macroscopic physical parameters of the sandstone test piece, and defining a macroscopic damage variable D En ；
Wherein E is the elastic modulus of the hypothetical ideal undamaged sandstone n The elastic modulus of the sandstone test piece after different freezing and thawing cycle times;
selecting the damage degree D of the pore fractal dimension of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece n Correcting to obtain microscopic damage variable D Bn ：
D Bn ＝B n D n (n＝0,5,10,20,40)
In the formula B n The fractal dimension of the pores of the test piece after different freeze thawing times is adopted;
selecting the mesoscopic structure parameters and the macroscopic physical parameters of the sandstone test piece to determine the elastic modulus E of the ideal nondestructive sandstone test piece:
in the formula of 0 ，B 0 And E 0 Respectively the porosity, the pore fractal dimension and the elastic modulus of the sandstone test piece after the medium 0 times of freeze-thaw cycle;
and (4) combining the macro and micro damage variables to obtain a freeze-thaw damage evolution curve.
And 7: and determining the life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area according to the macroscopic and microscopic damage evolution rule and the freeze-thaw damage evolution curve of the sandstone test piece.
Specifically, the service life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area are determined according to the macroscopic and microscopic damage evolution rule and the freeze-thaw damage evolution curve of the sandstone test piece, and specifically the method comprises the following steps: obtaining a macroscopic damage variable according to the microscopic damage variable of the sandstone test piece and by combining the macroscopic damage evolution rule of the sandstone test piece, and determining a freeze-thaw cycle period required when the macroscopic damage variable reaches rock damage so as to predict the damage life of the rock in the freeze-thaw environment; and determining a rock macroscopic crack pore evolution mode and a region with high damage density inside the material according to the macroscopic and microscopic damage evolution rule of the sandstone test piece, and providing guidance for the prevention and treatment of engineering disasters in cold regions by taking measures such as adhesion, reinforcement and the like at regular time and fixed points.
And if the sandstone test piece is rock, concrete and other materials, the macroscopic damage variable loses 40% of the reference value, the sandstone test piece is determined to lose the bearing effect or damage, the duration of each freeze-thaw period is determined according to the number of freeze-thaw cycle periods required during rock damage and local actual measurement low-temperature data of the sample, and the time required by rock failure is obtained so as to predict the damage life of the rock in the freeze-thaw environment.
According to the macroscopic and microscopic damage evolution rule visualization part of the sandstone test piece, the evolution mode of the macroscopic crack pores of the rock and the area with high damage density inside the material can be artificially determined, and measures such as adhesion, reinforcement and the like are taken at regular time and fixed points to provide guidance for prevention and control of engineering disasters in cold regions.
The theoretical range of the damage variable is 0-1, but the damage variable of the actual rock is 0.2-1, and since no natural and undamaged rock exists in nature, the condition judgment is generally 0.6 to determine that the rock fails; the freeze-thaw cycle period needs to be combined with local practical conditions, for example, the material in the test of the invention has a period of about 6-8 months.
The macro-micro damage variable established based on the macro-physical parameters and the micro-structure parameters of the sandstone test piece can truly reflect the damage degree evolution rule of the sandstone on the macro scale and the micro scale, explore the relation between the deterioration of the sandstone physical mechanical properties and the pore structure evolution in the freeze-thaw environment, and realize the macro-micro combined multi-scale analysis of the sandstone freeze-thaw damage.
The method provided by the invention is simple and feasible to operate, can clearly and intuitively reflect the change of the sandstone pore structure in the freeze-thaw cycle, accurately quantizes the characteristics of the internal pore structure of the sandstone material, researches the evolution rules of the primary pore and the secondary pore of the sandstone in the freeze-thaw environment, and has important significance for accurately describing the evolution disaster-causing mechanism of the rock pore structure and guiding the control of engineering disasters in cold regions.
The technical solution of the present invention can be further illustrated by the following experiments.
(1) Selecting a chalk series lohe group sandstone sample with wide cold region distribution, preparing an international standard rock sample with the specification of phi 50mm multiplied by 100mm through the working procedures of trepanning coring, cutting, polishing and the like, and screening a batch of test pieces which have no obvious defects and have similar wave velocity average values through manual work and a sound wave velocimeter.
(2) Performing a freeze-thaw cycle test: and grouping and numbering the sandstone test pieces. And respectively carrying out rapid freeze-thaw cycle tests on the numbered test pieces by adopting an XMT605 American rapid freeze-thaw testing machine, wherein the cycle times are 0 time, 5 times, 10 times, 20 times and 40 times, taking out and wiping off surface overflowing water after each group of test pieces reach the preset freeze-thaw cycle times, carrying out a uniaxial compression test, and counting the macroscopic physical parameters of the sandstone test pieces under different freeze-thaw cycle times.
And performing CT nondestructive scanning on the test piece under the specific freezing and thawing cycle times by using a Compact-225 type industrial CT machine to obtain a certain amount of two-dimensional tomographic scanning images.
The industrial CT machine scans the same test piece with the height of 100mm and the diameter of 50mm along the longitudinal direction under different freezing and thawing cycle times, the number of the scanning layers of the test piece is about 850, each layer of image is numbered, the pixel of a single-layer scanning image is 500 multiplied by 500, and the corresponding actual scale of a single pixel point is 0.1 mm.
(3) And (3) carrying out preprocessing such as denoising, sharpening enhancement, binaryzation and the like on the image in batches by adopting software according to the following sequence to obtain the CT image after the binaryzation processing of the sandstone test piece under different freezing-thawing cycle times.
Because the top and bottom images of the CT scanning original image are incomplete and the data is invalid, images with the numbers of 50-750 are selected and preprocessed in MATLAB software. The denoising processing adopts 3-by-3 median filtering to denoise, the sharpening enhancement adopts a Laplace operator to sharpen, and finally, a genetic algorithm is adopted to search a threshold value corresponding to the maximum entropy value of the image to carry out binarization processing on the image.
By adopting the method, the binary image which retains the effective information of the image and has obvious contrast is obtained while the noise interference is effectively removed, and the segmentation speed is high and the precision is accurate. As shown in fig. 2, black in the binarized image represents pores and low-density rock particles which are damaged and lose original bearing capacity, white represents the rock particles, and clearly represents the distribution change of the sandstone pore structure under different freeze-thaw cycle times.
(4) And drawing a pore evolution rose diagram and a pore structure growth diagram according to the binary images under different freeze-thaw cycle times.
The drawing software is Origin software, a pore evolution rosette is provided according to the evolution situation of the cross-section pore structure under different freezing and thawing cycle times, as shown in figure 3, wherein each 15 degrees is a trend, the image respectively counts the pore structure size situation in each trend part, and the method can be used for quantitatively analyzing the trend of the pore evolution along the trend; the pore structure growth diagram is provided aiming at the evolution situation of the cross-section pore structure under different freezing and thawing cycle times, as shown in fig. 4, wherein arrows represent the pore growth trend, the shape of closed solid lines represents the pore morphology, and the shape of closed dotted lines represents the new morphology which is developed and grown under the freezing and thawing action of the pores, and the image can intuitively understand the growth evolution law of primary pores and secondary pores under the freezing and thawing cycle action.
And importing the image after binarization processing into software for stacking processing to obtain three-dimensional digital cores of the sandstone test piece under different freezing and thawing times, counting the connected porosity contribution rate and the independent porosity contribution rate of the sandstone test piece under different freezing and thawing cycle times, and drawing a line graph of the change rule of the sandstone test piece.
The processing and statistical software is Avizo software, the spatial distribution of the pore structure can be directly observed from the three-dimensional digital core of the sandstone test piece under different freezing and thawing times, the spatial distribution comprises the structural characteristics of connected pores and the structural characteristics of independent pores, and the processing and statistical software is shown in figure 5; and (3) accumulating a histogram of the contribution rate of the sandstone test piece pore structure under different freezing and thawing times obtained by statistical analysis of the three-dimensional digital core, as shown in fig. 6, so that the expansion and communication conditions of primary pores and the growth and development conditions of secondary pores in the freezing and thawing cycle process can be quantified.
(5) And importing the image after binarization processing into software, counting the section porosity and section pore fractal dimension of the sandstone test piece under different freezing and thawing cycle times, and drawing a box diagram of the section porosity change rule of the sandstone test piece and a line diagram of the average change rule of the section pore fractal dimension of the sandstone test piece.
The statistical software is MATLAB software, according to the digital image matrix theory, the binary image is formed by a group of matrixes consisting of 0 and 1 of 500 x 500, the element 0 is black to represent pores and low-density rock particles which are damaged and lose original bearing capacity, the element 1 is white to represent the rock particles, and the ratio of the element number (pores) with the statistical value of 0 to the sum of the matrix element number is the section porosity; and calculating the fractal dimension of the cross-section pore by using a box method.
The drawing software is Origin software, and the box diagram of the section porosity change rule of the sandstone test piece drawn by the drawing software not only can reflect the discrete degree of the number of the sandstone two-dimensional longitudinal section pores, but also can show the change condition of the whole porosity of the sandstone under the action of freeze-thaw cycle, as shown in figure 7; the drawn line graph of the change rule of the mean value of the section pore fractal dimension of the sandstone test piece can reflect the change condition of the complexity of the whole pore structure of the sandstone under the action of freeze-thaw cycles, such as the graph of fig. 8.
(6) And (3) comparing and analyzing a two-dimensional pore structure evolution diagram and a three-dimensional digital core of the sandstone test piece under different freezing and thawing cycle times with macroscopic damage characteristics (such as particle stripping, cracking, fracture and the like) of the sandstone test piece under corresponding freezing and thawing cycle times, and realizing visualization of the sandstone macroscopic and microscopic damage evolution rule.
(7) Selecting the porosity of the sandstone test piece after the different freezing-thawing cycle times in the microscopic structure parameters of the sandstone test piece, and defining the damage degree D n ；
D n ＝λ n (n＝0,5,10,20,40)
In the formula of n The porosity of the sandstone test piece after different freezing-thawing cycle times.
Selecting the elastic modulus of the sandstone test piece after different freezing-thawing cycle times in the macroscopic physical parameters of the sandstone test piece, and defining a macroscopic damage variable D En ；
Where E is the modulus of elasticity of the hypothetical ideal undamaged sandstone, E n The elastic modulus of the sandstone test piece after different times of freeze-thaw cycles.
Selecting the damage degree D of the pore fractal dimension of the sandstone test piece after the different freezing-thawing cycle times in the microscopic structure parameters of the sandstone test piece n Correcting to obtain microscopic damage variable D Bn 。
D Bn ＝B n D n (n＝0,5,10,20,40)
In the formula B n The fractal dimension of the pores of the test piece after different freeze thawing times.
And selecting the microscopic structure parameters and the macroscopic physical parameters of the sandstone test piece to calculate the elastic modulus E of the ideal nondestructive sandstone test piece.
In the formula of 0 ，B 0 And E 0 Respectively is the porosity, the pore fractal dimension and the elastic modulus of the sandstone test piece after the freezing and thawing cycle of the middle 0 times.
And (3) combining the macro-micro damage variables to obtain a freeze-thaw damage evolution curve, as shown in fig. 9, the freeze-thaw damage variables and the freeze-thaw times are in a nonlinear increasing relationship and increase along with the increase of the freeze-thaw times, the damage evolution rates are different in different freeze-thaw cycle stages, the macro-micro rock freeze-thaw damage variables are better integrally matched and have consistency, macro-micro combination is realized, and the sandstone macro-micro damage evolution rule is quantized.
(8) And (4) combining the macro and micro damage evolution law of the sandstone. According to the quantitative result obtained by the test, the initial damage variable of the rock in the area is about 0.2, the macroscopic damage variable reaches 0.6-0.8 between 18-20 freeze-thaw cycle periods, the freeze-thaw cycle period is about 6-8 months by combining the test with the actual engineering environment at-20 ℃, so that measures should be taken for reinforcement after the support is used for 9-10 years in the freeze-thaw environment; according to the visual result obtained by the test, the rock structure is compact, no obvious macroscopic cracks exist, the freeze-thaw damage forms mainly include the peeling and flaking of the particles on the surface of the rock, and the measures such as wire netting and the like are recommended to be adopted for reinforcement treatment.
The same or similar reference numerals in the drawings of the present embodiment correspond to the same or similar components; in the description of the present invention, it is to be understood that the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, the terms describing the positional relationships in the drawings are only for illustrative purposes and are not to be construed as limitations of the present patent, and specific meanings of the terms may be understood by those skilled in the art according to specific situations.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, article, or apparatus that comprises the element.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.
Claims (9)
1. A method for obtaining a macroscopic and microscopic damage evolution rule under the freezing and thawing action of sandstone is characterized by comprising the following steps:
carrying out two-dimensional longitudinal tomography CT scanning and a uniaxial compression test on the sandstone test piece to obtain a plurality of groups of CT scanning images and macroscopic physical parameters of the sandstone test piece;
preprocessing each group of CT scanning images to obtain binaryzation processed CT images;
performing phenomenological theory analysis and three-dimensional reconstruction on each group of binaryzation processed CT images to obtain a two-dimensional pore structure evolution diagram and a three-dimensional digital core of the sandstone test piece;
performing statistical analysis on each group of binarized CT images to obtain the mesoscopic structure parameters of the sandstone test piece;
obtaining a macroscopic and microscopic damage evolution rule of the sandstone test piece according to the two-dimensional pore structure evolution diagram and the three-dimensional digital core of the sandstone test piece;
establishing damage variables according to the microscopic structure parameters and the macroscopic physical parameters of the sandstone test piece, and obtaining a freeze-thaw damage evolution curve according to the damage variables;
the method specifically comprises the following steps: selecting the porosity of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece, and defining the damage degree D n ：
D n ＝λ n ，n＝0,5,10,20,40；
In the formula of n The porosity of the sandstone test piece after different freezing and thawing cycle times;
selecting the elastic modulus of the sandstone test piece after different freezing-thawing cycle times in the macroscopic physical parameters of the sandstone test pieceAmount, definition of macroscopic Damage variables D En ；
Wherein E is the elastic modulus of the hypothetical ideal undamaged sandstone n The elastic modulus of the sandstone test piece after different freezing and thawing cycle times;
selecting the damage degree D of the pore fractal dimension of the sandstone test piece after different freezing-thawing cycle times in the mesoscopic structure parameters of the sandstone test piece n Correcting to obtain microscopic damage variable D Bn ：
D Bn ＝B n D n ，n＝0,5,10,20,40；
In the formula B n The fractal dimension of the pores of the test piece after different freezing and thawing times;
selecting the mesoscopic structure parameters and the macroscopic physical parameters of the sandstone test piece to determine the elastic modulus E of the ideal nondestructive sandstone test piece:
in the formula of 0 ，B 0 And E 0 Respectively the porosity, the pore fractal dimension and the elastic modulus of the sandstone test piece after 0 freeze-thaw cycle;
obtaining a freeze-thaw damage evolution curve by combining the macro and micro damage variables;
and determining the life prediction and the material stability of the rock bearing or supporting structure in the freeze-thaw environment in the sample collection area according to the macroscopic and microscopic damage evolution rule and the freeze-thaw damage evolution curve of the sandstone test piece.
2. The method for obtaining the evolution law of macroscopic and microscopic damage under the freezing and thawing action of sandstone according to claim 1, wherein the macroscopic physical parameters of the sandstone test piece at least comprise: the elastic modulus of the sandstone test piece after different freezing and thawing cycle times; the mesoscopic structure parameters of the sandstone test piece at least comprise: and (3) the porosity and the pore fractal dimension of the sandstone test piece after different freeze-thaw cycle times.
3. The method for obtaining the evolution law of macroscopic and microscopic damage under the freeze-thaw action of sandstone according to claim 1 or 2, wherein the step of preprocessing each group of CT scan images to obtain the binaryzation processed CT images comprises the following steps:
carrying out 3-to-3 median filtering denoising processing on each group of CT scanning images to obtain denoised CT images;
carrying out sharpening enhancement processing on the denoised CT scanning image to obtain a sharpened and enhanced CT image;
and carrying out binarization processing on the CT scanning image subjected to sharpening enhancement processing to obtain the CT image subjected to binarization processing.
4. The method for obtaining the evolution law of macroscopic and microscopic damage under the action of sandstone freezing and thawing according to claim 3, wherein the CT scanned image subjected to sharpening enhancement processing is subjected to binarization processing to obtain the CT image subjected to binarization processing, and the method specifically comprises the following steps:
dividing the CT image after sharpening enhancement treatment into a pore area and a rock area according to a threshold t, and respectively determining the cumulative probability P of the gray level of the pore area T (t) and cumulative probability of rock zone grayness P B (t)：
according to the accumulated probability P of the gray scale of the pore area T (t) and cumulative probability of rock zone grayness P B (t) determining the total image entropy H (t) of the CT after sharpening enhancement processing under all threshold values t:
and searching the maximum value of the total entropy in the image total entropy H (t), and performing binarization processing on the CT image after sharpening enhancement processing by using a corresponding threshold value.
5. The method for obtaining the evolution law of macroscopic and microscopic damage under the freezing and thawing action of sandstone according to claim 4, wherein the two-dimensional pore structure evolution diagram of the sandstone test piece at least comprises: and performing phenomenological theory analysis according to the binarized CT image to obtain a pore evolution rose diagram of the sandstone test piece, and performing phenomenological theory analysis according to the binarized CT image to obtain a pore structure growth diagram of the sandstone test piece.
6. The method for obtaining the macroreticular damage evolution law under the sandstone freezing and thawing action according to claim 5, wherein the pore evolution rosette of the sandstone test piece, which is drawn by the phenomenological theory analysis according to the binarized CT image, specifically comprises:
expressing the binarized image by a digital matrix M multiplied by N to obtain the center of the matrix
Establishing a rectangular coordinate system by taking the center of the matrix as a reference, starting to divide the matrix into 24 parts in a clockwise direction along the positive direction of the y axis of the rectangular coordinate system, taking the trend of every 15 degrees as a part, and counting the number of pores in the part;
and drawing the pore evolution rose diagram according to the trend part and the number of pores in the part.
7. The method for obtaining the macroscopic and microscopic damage evolution law under the sandstone freezing and thawing action according to claim 6, wherein a growth diagram of a pore structure of a sandstone test piece is drawn by performing phenomenological analysis according to the CT image subjected to binarization processing; the pore structure growth diagram at least comprises: arrows representing pore growth tendency, closed solid line shape representing pore morphology, and closed dotted line shape representing new morphology into which pores will grow and develop under freeze-thaw action.
8. The method for obtaining the macroreticular damage evolution law under the sandstone freezing and thawing effect according to claim 7, wherein the life prediction and the material stability of the rock bearing or supporting structure in the freezing and thawing environment in the sample collection area are determined according to the macroreticular damage evolution law and the freezing and thawing damage evolution curve of the sandstone test piece, and specifically comprise the following steps: obtaining a macroscopic damage variable according to the microscopic damage variable of the sandstone test piece and the quantitative part of the sandstone macroscopic damage evolution rule, obtaining a macroscopic damage variable according to the microscopic damage variable of the sandstone test piece and the sandstone macroscopic damage evolution rule, and determining a freeze-thaw cycle period required when the macroscopic damage variable reaches the rock damage so as to predict the damage life under the rock freeze-thaw environment; and determining a rock macroscopic crack pore evolution mode and a region with high damage density inside the material according to the macroscopic and microscopic damage evolution rule of the sandstone test piece, and providing guidance for the prevention and treatment of engineering disasters in cold regions by taking bonding and reinforcing measures at regular time and fixed points.
9. The method for obtaining the macroscopic and microscopic damage evolution law under the sandstone freezing and thawing effect according to claim 8, wherein the macroscopic damage variable is obtained according to the microscopic damage variable of the sandstone test piece and the sandstone macroscopic and microscopic damage evolution law, and the freezing and thawing cycle period required when the macroscopic damage variable reaches the rock damage is determined so as to predict the damage life under the rock freezing and thawing environment, specifically: if the test piece is that the macroscopic damage variable of the rock or concrete material loses 40% of the reference value, the test piece is determined to lose the bearing effect or damage, the time length of each freeze-thaw period is determined according to the number of the freeze-thaw cycle periods required by the rock damage and the local measured low-temperature data of the sample, and the time required by the rock failure is obtained so as to predict the damage life of the rock in the freeze-thaw environment.
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