CN116046773A - Method for determining rock initial microcrack density based on quantitative statistics - Google Patents
Method for determining rock initial microcrack density based on quantitative statistics Download PDFInfo
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- CN116046773A CN116046773A CN202211677112.1A CN202211677112A CN116046773A CN 116046773 A CN116046773 A CN 116046773A CN 202211677112 A CN202211677112 A CN 202211677112A CN 116046773 A CN116046773 A CN 116046773A
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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Abstract
The invention discloses a method for determining initial microcrack density of rock based on quantitative statistics, which comprises the following steps of S1: carrying out slice extraction on the rock specimen, and preparing specimen slices with a specified size; s2: directly observing the condition of the rock specimen slice by using a polarizing microscope, and uniformly amplifying the image structure in the specimen slice by a designated multiple; s3: quantitatively measuring the image obtained in the step S2 through image processing software to obtain the total length of microcracks in the observation area; s4: the total length obtained in S3 is compared with the area of the observation area in S2, and the ratio is defined as the initial microcrack density value independent of the direction. And a parameter for evaluating the microcrack density is redefined, the physical meaning of the parameter is clear, and the rock initial microcrack density is evaluated by using the parameter to be more visual and reasonable.
Description
Technical Field
The invention belongs to the technical field of rock mechanics and geotechnical engineering, and particularly relates to a method for determining initial microcrack density of rock based on quantitative statistics.
Background
The rock mass in the crust is a complex geologic body which is formed by the joint, the fissure, the fault and the like of the rock mass and the geologic structure surface together and is subjected to long-term geologic structure action. The engineering rock mass is under the geological environment of ground stress, groundwater, chemical reaction and the like, and is influenced by complex geological structure activities and artificial activities, and a certain number of discontinuous microcracks or pores with different sizes are contained in the engineering rock mass. These microcracks affect the physical and mechanical properties of the rock mass and only a careful study of the discontinuous microcracks inside the rock mass will allow further accurate assessment of the damage of the engineered rock mass.
The macroscopic mechanical properties of rock are closely related to the closure, development, expansion, penetration and other conditions of microcracks in the rock. The number and the length of the microcracks are important parameters for quantitatively representing the microcrack behaviors of the rock test piece, and the microcrack damage of the rock is caused by the growth of the microcracks, namely, the larger the density of the microcracks contained in the rock is, the stronger the microcrack damage is, and the lower the strength and the effective elastic modulus of the rock are. And an increase in the density of microcracks within the rock also increases the likelihood of penetration of the penetration channels within the rock, resulting in enhanced permeability of the rock. Therefore, the research on the density of the initial microcracks of the rock is of great significance for quantitatively evaluating the damage of the microcracks in the rock and grasping the macroscopic damage mechanism of the rock.
The indoor test method is often used for evaluating the damage degree of the engineering rock mass, wherein the fine observation test method is widely used for directly observing the microcrack occurrence condition in the rock, and common means comprise microscopic observation of a fine section, electron microscope scanning, CT scanning, nuclear magnetic resonance and the like, so that the accuracy is high. In the aspect of representing the density of the microcracks, the method of the total number of the microcrack intersection points on a unit length reference line is commonly used for defining the density of the microcracks, namely a reference line is manually drawn in a certain microscopic observation area of the rock, and the formula is ρ based on the number of the intersection points of the microcracks and the reference line L ＝N m L m In ρ L For the density of microcracks, nm is the number of intersections of microcracks with the reference line, lm is the reference line length. However, the method has larger error, and the representativeness of the intersection number of the microcracks on the reference line cannot be ensured because the initial microcracks of the rock have no obvious dominant direction. If the authenticity of the crack density is ensured, the method needs to be operated repeatedly, and the method has the characteristics of simplicity and easiness.
Disclosure of Invention
The invention aims to provide a method for determining the initial microcrack density of rock based on quantitative statistics, which can simply, intuitively and objectively determine the microcrack density.
The technical scheme adopted by the invention is as follows: a method for determining rock initiation microcrack density based on quantitative statistics, comprising the steps of:
s1: carrying out slice extraction on the rock specimen, and preparing specimen slices with a specified size;
s2: directly observing the condition of the rock specimen slice by using a polarizing microscope, and uniformly amplifying the image structure in the specimen slice by a designated multiple;
s3: quantitatively measuring the image obtained in the step S2 through image processing software to obtain the total length of microcracks in the observation area;
s4: the total length obtained in S3 is compared with the area of the observation area in S2, and the ratio is defined as the initial microcrack density value independent of the direction.
In S1, preferably, not less than 3 sample pieces are extracted from the same rock sample, i.e., from the top, middle and bottom.
Further preferably, in S2, the same sample sheet is observed and imaged by a nine-image method.
Further preferably, in S2, the polarizer is placed under the sample sheet for observation, and the analyzer is placed over the sample sheet for observation.
Further preferably, in S2, the central region of the specimen sheet is observed.
The invention has the beneficial effects that: the method has the advantages that the parameter for evaluating the density of the microcracks is redefined, the physical meaning of the parameter is clear, the density of the rock initial microcracks is more visual and reasonable, the direction of the rock initial microcracks is mostly irrelevant and disordered because the rock initial microcracks do not have the dominant direction, if the method of the intersection point of the reference lines is adopted, the error is easily caused to be larger, and the method of the ratio of the length of the microcracks to the observation area is adopted, the whole microcracks are included from the whole observation area, and the whole situation is planned.
Drawings
Fig. 1 is an image observed in the present invention.
FIG. 2 is a schematic diagram of the observation by nine-image method in the present invention.
FIG. 3 is a graph showing the relationship between initial microcrack density and temperature of rock based on quantitative statistical determination in an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
as shown in fig. 1-3, a method for determining initial microcrack density of rock based on quantitative statistics specifically comprises the following steps:
the first step: the rock specimen was subjected to sheet extraction and a specimen sheet of a prescribed size was produced, wherein the specimen sheet was a square specimen sheet having a side length of 25mm and a thickness of 0.03 mm. To increase the coverage during sampling and eliminate errors, 6 sheets were extracted from the upper, middle and lower layers of a rock specimen, respectively.
And a second step of: and directly observing the condition of the rock specimen slice by using a polarizing microscope, and uniformly magnifying the image structure in the specimen slice by a designated multiple. In order to facilitate the observation of subsequent microcracks, the microstructure of the image in the sample sheet is uniformly magnified 100 times, namely 5 times of the lens of the eye is multiplied by 20 times of the objective lens, the size of each image obtained in the state is 2.6mm multiplied by 2.0mm, and the corresponding image resolution is 1938 multiplied by 2591 pixels.
In order to facilitate the identification of microcracks, a polarizer is firstly placed below a specimen sheet for observation, plane polarized light is generated at the moment, then an analyzer is placed above the specimen sheet, cross polarized light is generated at the moment, and microcracks can be easily identified through image comparison of the plane polarized light and the cross polarized light.
In order to ensure that the observation area with proper size and high resolution are provided, a nine-image method is adopted for imaging the same specimen slice, namely, the specimen slice is placed on a rotating device, images are continuously shot one by one, the shot 9 adjacent observation images are combined together, and the size of the observation area assembled on the rock specimen slice is 8.0mm multiplied by 6.0mm. In order to avoid the influence of the rock specimen slice on the microcrack observation in the grinding manufacturing process, the center of the specimen slice is set as an aggregate observation area.
And a third step of: and (3) quantitatively measuring the rock microcracks on the image obtained in the second step through image processing software, and obtaining the total length of the microcracks in the observed area.
Fourth step: and (3) comparing the total length obtained in the step (S3) with the area of the observation area in the second step, and defining the ratio as an initial microcrack density value irrelevant to the direction.
Examples
Since temperature has a large influence on the development of micro-cracks inside the rock, this example is illustrated by experimental data of rock samples under different heat cycle times (i.e. under different damages). The rock used in the experiment is dolomitic marble, and the experiment temperature is set to 600 ℃.
The method comprises the following specific steps:
the first step: the experimental rock sample is placed in a heating furnace, the rock sample is gradually heated to 600 ℃ at a heating rate of 10 ℃/min, and a heating device can be automatically controlled. After reaching the predetermined temperature, the sample is kept in the furnace at the same temperature for 4 hours, and then taken out from the heating device, and naturally cooled to room temperature, generally for about 12 hours. The above process acts as a heating and cooling cycle.
And a second step of: the number of heating and cooling cycles of this embodiment is set to 7 groups of 0 (i.e., no heating and cooling treatment is performed), 1, 2, 4, 6, 8, and 16, respectively.
And a third step of: and processing 7 groups of rock samples subjected to heat cycle treatment into sample slices conforming to observation, and placing the sample slices under a polarization microscope for microcrack observation.
Fourth step: recording the length of the microcracks in the observation area by means of image processing software, comparing the length with the area of the observation area, and quantitatively counting to obtain the microcrack density of the rock.
As can be seen from fig. 3, the microcrack density of the rock is the smallest at 0 thermal cycles, and increases with the increase of the number of thermal cycles; the more the rock thermal cycle times, the larger the damage is, the better the result is matched with the actual, and the reliability of the method is also verified.
Claims (5)
1. A method for determining rock initiation microcrack density based on quantitative statistics, comprising the steps of:
s1: carrying out slice extraction on the rock specimen, and preparing specimen slices with a specified size;
s2: directly observing the condition of the rock specimen slice by using a polarizing microscope, and uniformly amplifying the image structure in the specimen slice by a designated multiple;
s3: quantitatively measuring the image obtained in the step S2 through image processing software to obtain the total length of microcracks in the observation area;
s4: the total length obtained in S3 is compared with the area of the observation area in S2, and the ratio is defined as the initial microcrack density value independent of the direction.
2. The method for determining rock initiation microcrack density based on quantitative statistics of claim 1 wherein: in S1, not less than 3 sample slices are extracted from the upper, middle and lower sides of the same rock sample.
3. The method for determining rock initiation microcrack density based on quantitative statistics of claim 1 wherein: in S2, the same sample sheet is observed and imaged by a nine-image method.
4. The method for determining rock initiation microcrack density based on quantitative statistics of claim 1 wherein: in S2, in the observation, a polarizer is placed under the sample sheet, and then the analyzer is placed over the sample sheet, and then the observation is performed.
5. The method for determining rock initiation microcrack density based on quantitative statistics of claim 1 wherein: in S2, the central region of the specimen sheet is observed.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202211677112.1A CN116046773A (en) | 2022-12-26 | 2022-12-26 | Method for determining rock initial microcrack density based on quantitative statistics |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202211677112.1A CN116046773A (en) | 2022-12-26 | 2022-12-26 | Method for determining rock initial microcrack density based on quantitative statistics |
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| CN116046773A true CN116046773A (en) | 2023-05-02 |
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