A method for preparing rock samples with different damage degrees

Abstract

The present application discloses a method for preparing rock samples with different damage degrees, which relates to the field of rock mechanics and geotechnical engineering. The method includes processing rocks to obtain N standard rock samples; performing micro-CT scanning on the N standard rock samples to determine the micro-defect volume and spatial distribution characteristics of each standard rock sample, and selecting M spare rock samples; performing uniaxial compression test and acoustic emission test on the m spare rock samples to determine the reference value of crack initiation stress and the reference value of peak stress; performing variable amplitude uniaxial cyclic loading and unloading test and micro-CT scanning test on the remaining spare rock samples respectively to obtain the first internal defect volume and the second internal defect volume; using the functional relationship between the damage degree and the internal defect volume, determining the damage degree of the remaining spare rock samples, thereby obtaining rock samples with different damage degrees. The present application can accurately determine the damage degree of rock samples under external loads, and can prepare rock samples with different damage degrees.

Description

Technical Field

[0001] This application relates to the field of rock mechanics and geotechnical engineering, and particularly to a method for preparing rock specimens with different degrees of damage. Background Technique

[0002] In the processes of engineering construction and construction such as open-pit mining, road slope construction, tunnel excavation, and underground resource mining, blasting and mechanical excavation are the main rock-breaking methods. Part of the energy generated by explosive explosion and mechanical disturbance is used to break and peel the rock mass to achieve the purpose of engineering excavation, and part is transmitted to the surrounding rock mass in the form of stress waves, which will inevitably cause a certain degree of damage and destruction to the surrounding rock, thus threatening the stability of the rock mass. Therefore, it is very necessary to determine the degree of damage caused by excavation disturbance to the rock mass to provide basic parameters for engineering stability analysis and evaluation and reinforcement.

[0003] At present, the indoor test method is the most commonly used method to determine the degree of rock damage. According to different test methods, it can be further divided into macroscopic detection methods and microscopic detection methods. The macroscopic detection method mainly evaluates the degree of rock damage by detecting the macroscopic mechanical parameters of the rock, such as through indicators such as the strength parameters, deformation parameters, and energy parameters of the rock, and then estimates the damage degree of the rock under a certain stress state; the microscopic damage degree detection method is mainly realized through non-destructive testing equipment such as CT scanning, nuclear magnetic resonance, electron microscope scanning, electron microscope observation, and casting press slicing. Although the above two methods basically realize the evaluation of the damage degree of rocks with initial damage or rocks after experiencing a certain load, through the above methods, it is impossible to prepare rock specimens with different degrees of damage. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing rock specimens with different degrees of damage to achieve the preparation of rock specimens with different degrees of damage.

[0005] To achieve the above purpose, this application provides the following solutions:

[0006] In the first aspect, this application provides a method for preparing rock specimens with different degrees of damage, including:

[0007] Processing the rock to obtain N standard rock specimens;

[0008] Performing micro-CT scanning on the N standard rock specimens to determine the micro-defect volume and spatial distribution characteristics of each standard rock specimen;

[0009] Based on the micro-defect volume and spatial distribution characteristics of each standard rock specimen, determining M spare rock specimens; M < N; the spare rock specimens are standard rock specimens with micro-defect volume and spatial distribution characteristics within the corresponding set range;

[0010] Performing uniaxial compression test and acoustic emission test on m of the spare rock samples to determine the reference values ​​of the crack initiation stress and the peak stress of the spare rock samples; <M;

[0011] Based on the crack initiation stress reference value and the peak stress reference value, the remaining Mm spare rock specimens are respectively subjected to variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests to obtain Mm first internal defect volumes and Mm second internal defect volumes; the first internal defect volume is the internal defect volume of the spare rock specimen corresponding to when the load reaches the crack initiation stress reference value; the second internal defect volume is the internal defect volume of the spare rock specimen corresponding to when the load reaches the peak stress reference value;

[0012] According to each of the first internal defect volumes and each of the second internal defect volumes, the damage degrees of the remaining Mm spare rock samples are determined using the functional relationship between the damage degree and the internal defect volume, thereby obtaining rock samples with different damage degrees; the functional relationship between the damage degree and the internal defect volume is determined using a nonlinear fitting method.

[0013] Optionally, micro-CT scanning is performed on N standard rock samples to determine the volume and spatial distribution characteristics of micro defects of each standard rock sample, specifically including:

[0014] Performing micro-CT scanning on the N standard rock samples to determine a CT image of each standard rock sample;

[0015] The automatic image acquisition and processing software in the micro-CT scanning system is used to perform three-dimensional reconstruction, filtering and binarization processing on each of the CT images to obtain the micro-defect volume and spatial distribution characteristics of each of the standard rock samples.

[0016] Optionally, performing a uniaxial compression test and an acoustic emission test on the m spare rock samples to determine a reference value of a crack initiation stress and a reference value of a peak stress of the spare rock samples specifically includes:

[0017] Performing uniaxial compression tests and acoustic emission tests on the m spare rock samples respectively to determine the crack initiation stress and peak stress of each spare rock sample;

[0018] The average value of the m crack initiation stresses and the average value of the m peak stresses are determined to obtain a reference value of the crack initiation stress and a reference value of the peak stress of the spare rock sample.

[0019] Optionally, a uniaxial compression test and an acoustic emission test are performed on the m spare rock samples to determine a reference value of a crack initiation stress and a reference value of a peak stress of the spare rock samples, and then the method further includes:

[0020] Determine the difference between the reference value of the crack initiation stress and the reference value of the peak stress;

[0021] The difference is segmented to determine the segmented stress.

[0022] Optionally, segmenting the difference to determine the segmented stress specifically includes:

[0023] Using the formula Determine the segmental stress; where F d is the segment stress; F z is the peak stress reference value; F q is the reference value of the crack initiation stress; L is the number of segments of the difference between the reference value of the crack initiation stress and the reference value of the peak stress.

[0024] Optionally, based on the crack initiation stress reference value and the peak stress reference value, variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests are respectively performed on the remaining Mm spare rock samples to obtain Mm first internal defect volumes and Mm second internal defect volumes, specifically including:

[0025] A variable amplitude uniaxial cyclic loading and unloading test is performed on each of the spare rock samples. After reaching the maximum initial load value, a micro-CT scanning test is performed on the corresponding spare rock sample to obtain a corresponding CT image; the maximum initial load value is the reference value of the crack initiation stress;

[0026] Using the image automatic acquisition and processing software in the micro-CT scanning system, the CT image is subjected to three-dimensional reconstruction, filtering and binarization processing to obtain the first internal defect volume of the spare rock sample;

[0027] Taking the segmented stress as the increment, the variable amplitude uniaxial cyclic loading and unloading test is performed on the spare rock sample until the peak stress reference value is reached and the spare rock sample is destroyed, and a micro-CT scanning test is performed on the destroyed rock sample to obtain a corresponding CT image;

[0028] The automatic image acquisition and processing software in the micro-CT scanning system is used to perform three-dimensional reconstruction, filtering and binarization processing on the CT image to obtain the second internal defect volume of the spare rock sample.

[0029] Optionally, the functional relationship between the damage degree and the internal defect volume is:

[0030] ;

[0031] Where D(n) is the damage degree of the spare rock sample after n cycles of loading and unloading tests; V(n) is the internal micro-defect volume of the spare rock sample after n cycles of loading and unloading tests; V qis the first internal defect volume; V z is the second internal defect volume.

[0032] According to the specific embodiments provided in this application, this application has the following technical effects:

[0033] The present application provides a method for preparing rock samples with different damage degrees, wherein the rock is processed to obtain N standard rock samples; the N standard rock samples are subjected to micro-CT scanning to determine the micro-defect volume and spatial distribution characteristics of each standard rock sample, and M spare rock samples are selected; the m spare rock samples are subjected to uniaxial compression test and acoustic emission test to determine the reference value of the crack initiation stress and the reference value of the peak stress; based on the reference value of the crack initiation stress and the reference value of the peak stress, the remaining Mm spare rock samples are subjected to variable amplitude uniaxial cyclic loading and unloading test and micro-CT scanning test to obtain Mm first internal defect volumes and second internal defect volumes; according to each first internal defect volume and each second internal defect volume, the damage degree of the remaining Mm spare rock samples is determined by using the functional relationship between the damage degree and the internal defect volume, thereby obtaining rock samples with different damage degrees; the functional relationship between the damage degree and the internal defect volume is determined by using a nonlinear fitting method. Based on the determination of rock cracking stress, this application conducts micro-CT scanning on rock samples after variable amplitude cyclic loading and unloading, fully utilizing the advantages of high precision and non-destructive testing of micro-CT, and quantitatively extracts the microscopic damage characteristics inside the rock sample after variable amplitude cyclic loading and unloading through digital processing techniques such as three-dimensional reconstruction and binarization, and establishes a functional relationship between the damage variable and the load increment, thereby being able to accurately determine the damage degree of the rock sample under the action of external loads, and being able to prepare rock samples with different damage degrees. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A schematic diagram of a process for preparing rock samples with different degrees of damage provided in one embodiment of the present application;

[0036] Figure 2 It is a schematic diagram of cyclic loading and unloading;

[0037] Figure 3 Schematic diagram of the loading cycle-damage degree relationship curve. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0040] In an exemplary embodiment, Figure 1 As shown, a method for preparing rock samples with different damage degrees is provided, comprising the following steps:

[0041] S1: Process the rock to obtain N standard rock samples.

[0042] In practical applications, according to the purpose of the test, in accordance with the requirements of relevant specifications such as "Rock Test Procedures for Water Conservancy and Hydropower Engineering" (DL / T5368-2020), the rock is processed into a standard rock sample that meets the test requirements; the standard rock sample is a cylindrical rock sample with a height-to-diameter ratio of 2 to 2.5:1 or a rectangular rock sample with a long side to short side ratio of 2 to 2.5:1. In this embodiment, the size of the rock sample is 50mm×100mm, and the appearance is basically consistent and flawless.

[0043] In order to reduce the impact of the discreteness of the rock samples themselves on the test results, the rock samples used are taken from the same large piece of rock as much as possible. Each group of rock samples shall not be less than 14, including no less than 5 rock samples for uniaxial compression and no less than 9 rock samples for uniaxial variable amplitude cyclic loading and unloading tests, so as to further ensure the test precision and accuracy of the results.

[0044] S2: Perform micro-CT scanning on the N standard rock samples to determine the micro-defect volume and spatial distribution characteristics of each standard rock sample.

[0045] In practical applications, the thickness of CT slices is no more than 1 mm, and the accuracy of micro-CT is no more than 5 μm. After the CT scan is completed, the CT image is reconstructed, filtered and binarized using the image automatic acquisition and processing software provided by the CT scanning system to extract the volume of micro-defects inside the rock sample. Based on the micro-defect volume and its spatial distribution characteristics, rock samples with similar micro-defect volumes and spatial distribution characteristics are selected as spare rock samples.

[0046] As an optional implementation, S2 specifically includes:

[0047] S21: Perform micro-CT scanning on N of the standard rock specimens to determine the CT images of each standard rock specimen.

[0048] S22: Use the image automatic acquisition and processing software inside the micro-CT scanning system to perform three-dimensional reconstruction, filtering, and binarization processing on each CT image to obtain the micro-defect volume and spatial distribution characteristics of each standard rock specimen.

[0049] S3: Based on the micro-defect volume and spatial distribution characteristics of each standard rock specimen, determine M spare rock specimens; M < N; the spare rock specimens are standard rock specimens with micro-defect volume and spatial distribution characteristics within the corresponding set ranges.

[0050] In practical applications, perform micro-CT scanning on standard rock specimens that meet the test requirements. The CT slice thickness is not greater than 1 mm, the accuracy of the micro-CT is not greater than 5 μm. After the CT scanning is completed, use the image automatic acquisition and processing software自带 by the CT scanning system to perform three-dimensional reconstruction, filtering, and binarization processing on the CT images, extract the volume and spatial distribution characteristics of the original micro-defects inside the rock specimens, and select rock specimens with similar micro-defect volume and spatial partial characteristics as spare rock specimens.

[0051] S4: Perform uniaxial compression tests and acoustic emission tests on m of the spare rock specimens to determine the crack initiation stress reference value and peak stress reference value of the spare rock specimens; m < M.

[0052] As an optional implementation method, S4 specifically includes:

[0053] S41: Perform uniaxial compression tests and acoustic emission tests on m of the spare rock specimens respectively to determine the crack initiation stress and peak stress of each spare rock specimen.

[0054] S42: Determine the mean value of the m crack initiation stresses and the mean value of the m peak stresses to obtain the crack initiation stress reference value and peak stress reference value of the spare rock specimens.

[0055] As an optional implementation method, after S42, it further includes:

[0056] Determine the difference between the crack initiation stress reference value and the peak stress reference value.

[0057] Segment the difference to determine the segmented stress. Specifically, it includes:

[0058] Use the formula to determine the segmented stress; where F d is the segmented stress; F z is the peak stress reference value; F qis the reference value of the crack initiation stress; L is the number of segments of the difference between the reference value of the crack initiation stress and the reference value of the peak stress.

[0059] In practical applications, mechanical tests and acoustic emission tests were carried out on some spare rock samples under uniaxial compression conditions. The mechanical experiment was loaded by displacement, with a loading rate of 0.12 mm / min. The test was terminated when the rock sample was damaged. The acoustic emission monitoring system was started at the same time as the mechanical loading. The specific parameters of the acoustic emission monitoring system are: pre-gain, 40 dB; frequency range, 100 kHz~1 MHz; sampling frequency, 1 MSPS; pre-trigger, 256; threshold value, 45 dB; PDT, 300; HDT, 600; HLT, 1000. According to the characteristics of the acoustic emission signal change, the kaiser point of the rock is determined. The stress value corresponding to the kaiser point is the cracking stress of the rock sample. The final cracking stress reference value and peak stress reference value are determined according to the average of the cracking stress and peak stress of each rock sample. The number of segmented stress segments is not less than 10.

[0060] S5: Based on the crack initiation stress reference value and the peak stress reference value, the remaining Mm spare rock specimens are subjected to variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests, respectively, to obtain Mm first internal defect volumes and Mm second internal defect volumes; the first internal defect volume is the internal defect volume of the spare rock specimen corresponding to when the load reaches the crack initiation stress reference value; the second internal defect volume is the internal defect volume of the spare rock specimen corresponding to when the load reaches the peak stress reference value.

[0061] The remaining spare rock samples were subjected to variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests. Figure 2 As shown in the figure, the reference value of the cracking stress is taken as the maximum value of the first cycle of loading and unloading. After reaching this value, the sample is unloaded. The maximum value of each subsequent loading is increased by one segmented stress compared with the previous one until the rock sample is destroyed. After each loading and unloading, the rock sample is scanned by micro-CT. The CT image is reconstructed, filtered and binarized using the image automatic acquisition and processing software provided by the CT scanning system. The increment of micro defects in the rock sample after each cycle of loading and unloading is extracted and the total amount of internal micro defects when the rock sample is destroyed is calculated. The above test is repeated for no less than 9 times. By calculation, the internal defect volume V of the rock sample when the load reaches the reference value of the cracking stress can be obtained. q When the load reaches the peak stress reference value, the internal defect volume of the rock sample is V z .

[0062] The loading and unloading rates are the same during the loading and unloading test. When the load reaches the cracking stress, the internal defect volume of the rock sample is V q, when the load reaches the peak stress, the internal defect volume of the rock sample is V z All are calculated according to the arithmetic mean of the measured rock samples.

[0063] As an optional implementation, S5 specifically includes:

[0064] S51: Perform a variable amplitude uniaxial cyclic loading and unloading test on each of the spare rock samples, and after reaching the maximum initial load, perform a micro-CT scanning test on the corresponding spare rock sample to obtain a corresponding CT image; the maximum initial load is the reference value of the crack initiation stress.

[0065] S52: Using the automatic image acquisition and processing software in the micro-CT scanning system, the CT image is subjected to three-dimensional reconstruction, filtering and binarization processing to obtain the first internal defect volume of the spare rock sample.

[0066] S53: taking the segmented stress as the increment, performing a variable amplitude uniaxial cyclic loading and unloading test on the spare rock sample until the peak stress reference value is reached and the spare rock sample is destroyed, and performing a micro-CT scanning test on the destroyed rock sample to obtain a corresponding CT image.

[0067] S54: Using the automatic image acquisition and processing software in the micro-CT scanning system, the CT image is subjected to three-dimensional reconstruction, filtering and binarization processing to obtain a second internal defect volume of the spare rock sample.

[0068] S6: According to each of the first internal defect volumes and each of the second internal defect volumes, the damage degrees of the remaining Mm spare rock samples are determined by using the functional relationship between the damage degree and the internal defect volume, so as to obtain rock samples with different damage degrees; the functional relationship between the damage degree and the internal defect volume is determined by using a nonlinear fitting method. The nonlinear fitting method is used to fit the test data, and the fitting software is Matlab, Origin, etc.

[0069] As an optional implementation method, the functional relationship between the damage degree and the internal defect volume is:

[0070] .

[0071] Where D(n) is the damage degree of the spare rock sample after n cycles of loading and unloading tests; V(n) is the internal micro-defect volume of the spare rock sample after n cycles of loading and unloading tests; V q is the first internal defect volume; V z is the second internal defect volume.

[0072] In practical applications, take a large piece of rock and use the above steps S1-S5 to obtain test data, such as Figure 3 As shown in the figure, with the number of cyclic loading as the horizontal axis and the damage degree of the rock sample after each cyclic loading and unloading as the vertical axis, a nonlinear fitting method is used to establish the functional relationship between the damage degree of the rock sample and its internal crack volume (internal defect volume), and then rock samples with different damage degrees can be obtained according to the cyclic loading and unloading test.

[0073] Based on the determination of rock cracking stress, this application conducts micro-CT scanning on rock samples after variable amplitude cyclic loading and unloading, fully utilizing the advantages of high precision and non-destructive testing of micro-CT, and quantitatively extracts the microscopic damage characteristics inside the rock sample after variable amplitude cyclic loading and unloading through digital processing techniques such as three-dimensional reconstruction and binarization, and establishes a functional relationship between the damage variable and the load increment, thereby being able to accurately determine the damage degree of the rock sample under the action of external load, providing a new way to prepare rock samples with different damage degrees.

[0074] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for preparing rock samples with different degrees of damage, characterized in that: Including: Processing the rock to obtain N standard rock specimens; Performing micro-CT scanning on the N standard rock specimens to determine the micro-defect volume and spatial distribution characteristics of each standard rock specimen; Based on the micro-defect volume and spatial distribution characteristics of each standard rock specimen, determining M spare rock specimens; M < N; the spare rock specimens are standard rock specimens with micro-defect volume and spatial distribution characteristics within the corresponding set ranges; Performing uniaxial compression tests and acoustic emission tests on m of the spare rock specimens to determine the crack initiation stress reference value and peak stress reference value of the spare rock specimens; m < M; Based on the crack initiation stress reference value and the peak stress reference value, respectively performing variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests on the remaining M - m spare rock specimens to obtain M - m first internal defect volumes and M - m second internal defect volumes; the first internal defect volume is the internal defect volume of the corresponding spare rock specimen when the load reaches the crack initiation stress reference value; the second internal defect volume is the internal defect volume of the corresponding spare rock specimen when the load reaches the peak stress reference value; According to each of the first internal defect volumes and each of the second internal defect volumes, using the functional relationship between the damage degree and the internal defect volume, determining the damage degree of the remaining M - m spare rock specimens, thereby obtaining rock specimens with different damage degrees; the functional relationship between the damage degree and the internal defect volume is determined using the non-linear fitting method; The functional relationship between the damage degree and the internal defect volume is: ； Where D(n) is the damage degree of the spare rock sample after n cycles of loading and unloading tests; V(n) is the internal micro-defect volume of the spare rock sample after n cycles of loading and unloading tests; V q is the first internal defect volume; V z is the second internal defect volume.

2. The method for preparing rock samples with different degrees of damage according to claim 1, characterized in that: Performing micro-CT scanning on the N standard rock specimens to determine the micro-defect volume and spatial distribution characteristics of each standard rock specimen, specifically including: Performing micro-CT scanning on the N standard rock specimens to determine the CT image of each standard rock specimen; Using the image automatic acquisition and processing software inside the micro-CT scanning system to perform three-dimensional reconstruction, filtering, and binarization processing on each CT image to obtain the micro-defect volume and spatial distribution characteristics of each standard rock specimen.

3. The method for preparing rock samples with different damage degrees according to claim 1, characterized in that: Performing uniaxial compression tests and acoustic emission tests on m of the spare rock specimens to determine the crack initiation stress reference value and peak stress reference value of the spare rock specimens, specifically including: Respectively performing uniaxial compression tests and acoustic emission tests on m of the spare rock specimens to determine the crack initiation stress and peak stress of each spare rock specimen; Determining the mean value of the m crack initiation stresses and the mean value of the m peak stresses to obtain the crack initiation stress reference value and peak stress reference value of the spare rock specimens.

4. The method for preparing rock samples with different degrees of damage according to claim 1, characterized in that: After performing uniaxial compression tests and acoustic emission tests on m of the spare rock specimens to determine the crack initiation stress reference value and peak stress reference value of the spare rock specimens, it further includes: Determining the difference between the crack initiation stress reference value and the peak stress reference value; Segmenting the difference to determine the segmented stress.

5. The method for preparing rock samples with different degrees of damage according to claim 4, characterized in that: Segmenting the difference to determine the segmented stress, specifically including: Using the formula Determine the segmental stress; where F d is the segment stress; F z is the peak stress reference value; F q is the reference value of the crack initiation stress; L is the number of segments of the difference between the reference value of the crack initiation stress and the reference value of the peak stress.

6. The method for preparing rock samples with different damage degrees according to claim 4, characterized in that: Based on the crack initiation stress reference value and the peak stress reference value, variable amplitude uniaxial cyclic loading and unloading tests and micro-CT scanning tests are respectively performed on the remaining Mm spare rock samples to obtain Mm first internal defect volumes and Mm second internal defect volumes, specifically including: A variable amplitude uniaxial cyclic loading and unloading test is performed on each of the spare rock samples. After reaching the maximum initial load value, a micro-CT scanning test is performed on the corresponding spare rock sample to obtain a corresponding CT image; the maximum initial load value is the reference value of the crack initiation stress; Using the image automatic acquisition and processing software in the micro-CT scanning system, the CT image is subjected to three-dimensional reconstruction, filtering and binarization processing to obtain the first internal defect volume of the spare rock sample; Taking the segmented stress as the increment, the variable amplitude uniaxial cyclic loading and unloading test is performed on the spare rock sample until the peak stress reference value is reached and the spare rock sample is destroyed, and a micro-CT scanning test is performed on the destroyed rock sample to obtain a corresponding CT image; The automatic image acquisition and processing software in the micro-CT scanning system is used to perform three-dimensional reconstruction, filtering and binarization processing on the CT image to obtain the second internal defect volume of the spare rock sample.

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