CN110618032B - Method for identifying rock crack damage stress by using acoustic emission technology - Google Patents
Method for identifying rock crack damage stress by using acoustic emission technology Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/0202—Control of the test
- G01N2203/0212—Theories, calculations
- G01N2203/0218—Calculations based on experimental data
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/025—Geometry of the test
- G01N2203/0252—Monoaxial, i.e. the forces being applied along a single axis of the specimen
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0658—Indicating or recording means; Sensing means using acoustic or ultrasonic detectors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
Abstract
The invention discloses a method for identifying damage stress of a rock crack by using an acoustic emission technology, which comprises the following steps: (1) the core taken from the engineering site is arranged according toProcessing the rock sample to be tested according to the international rock mechanics society standard; (2) performing uniaxial compression test on the rock sample to be tested, measuring and recording the axial stress value in the test process to obtain the uniaxial compressive strength sigma of the rock samplec(ii) a (3) Carrying out acoustic emission test under multistage cyclic loading of a rock sample to be tested, and measuring and recording axial stress and acoustic emission signals in the loading process; (4) and identifying the Felicity effect in the acoustic emission test, calculating the Felicity ratio FR in each stage of cyclic loading, and obtaining the crack damage stress range of the rock sample to be detected according to the established rock crack damage stress identification method. According to the method, the crack damage stress is identified by utilizing the Felicity effect from the physical essence of the rock acoustic emission phenomenon, and the quantitative identification result range is obtained by combining the setting of the stress increment among the multi-stage cyclic loading.
Description
Technical Field
The invention relates to a rock engineering technology, in particular to a method for identifying damage stress of a rock crack by using an acoustic emission technology.
Background
With the large-scale development of underground engineering in China, such as petroleum and natural gas exploitation, underground tunnel engineering, deep burying and disposal of high-level wastes and the like, rocks are used as important engineering media, and the research on the mechanical properties of the rocks is more and more focused. The rock characteristic stress is threshold stress for dividing different stages of rock stress deformation damage, wherein the fracture damage stress marks that a fracture expands into an unstable stage, and damage accumulation begins to develop rapidly and is also regarded as the long-term strength of the rock. Therefore, the accurate recognition of the damage stress of the rock cracks has important theoretical and practical significance for accurately dividing rock deformation stages and developing damage evolution research.
When the stress level borne by the rock exceeds the damage stress of the crack, the deformation characteristic of the rock is changed certainly, the internal crack of the rock starts to interact and is connected and communicated to enter an unstable development stage, the volume strain curve bends, and the damage accumulation starts to be intensified. In the research on characterization of damage under uniaxial compression of rock and comparison of evolution rules, macro-microscopic characterization corresponding to rock characteristic stress is analyzed, and the evolution process of rock damage is quantified through crack volume strain, acoustic emission, acoustic wave characteristics and the like (see the 6 th year in 2019, the author: Zhangnational Kai, and the like), the reverse point of a rock volume strain curve is indicated to correspond to crack damage stress, but the volume strain calculation depends on accurate measurement of strain, particularly transverse strain. Meanwhile, the acoustic emission energy is used for representing the damage with better reliability, and the essential characteristic of rock damage fracture is reflected.
The ' brocade screen deep-buried marble cracking characteristic and damage evolution law ' determines the characteristic strength of brittle rocks under different confining pressure conditions, and further analyzes the stress state of a damaged area to deeply disclose the damage characteristics of the surrounding rocks (see ' report on rock mechanics and engineering, 2012, 8, author: Liuning, etc.). It is noted that in the region of the volume strain curve inversion, the stress corresponding to the point where the relative volume strain stiffness is 0 is the crack damage stress. But is greatly affected by the interval of the sampling points when calculating the volume strain stiffness.
The acoustic emission is a phenomenon that energy accumulated inside a material in a loading process is released in a stress wave form, and the rock acoustic emission technology can monitor the activity condition of cracks inside rocks in real time and reflect deformation damage information. Therefore, the crack damage stress can be identified according to the change of the acoustic emission signal parameters of the rock at different stages in the compression process. In the research on the thermal damage acoustic emission mechanical property of the marble, the stress of the 2 nd sudden jump of an acoustic emission signal in the loading process of the marble is utilized to determine the crack damage stress (see the 12 th year in the report of rock mechanics and engineering, the author: Guo Qing Lu, and the like), and a volume strain curve method is used for verification, so that the results obtained by the two methods are basically consistent, but the judgment subjectivity of the mutation point of the acoustic emission signal is strong, and the acoustic emission signal is easily influenced by noise and other interference signals. A method for identifying crack damage stress by using acoustic emission signal parameters is introduced in hard rock crack initiation strength and damage strength evaluation method discussion (see rock and soil mechanics, 4 th 2014, authors: Zhou Hui, and the like), the stress level obtained by using an acoustic emission impact rate curve cannot completely correspond to the crack damage strength of a rock, and the acoustic emission signal parameters can be used as an auxiliary means for qualitatively or semi-quantitatively identifying the crack stress, but accurate quantitative values are difficult to obtain.
A rock crack dynamic evolution process research based on acoustic emission positioning introduces a three-dimensional space evolution mode of internal microcrack inoculation, initiation, expansion, nucleation and communication in a granite rock sample fracture instability process containing different prefabricated cracks by applying acoustic emission and a positioning technology thereof and adopting a test method under the action of uniaxial compression load (see the report on rock mechanics and engineering in 2007, 5 th year, the author: Zhaohongdong, and the like). The acoustic emission event is verified to be closely related to the generation of cracks in the rock, but the technology is not repeated with the technology of the invention, and the technology of the invention is better supported.
In conclusion, the existing rock crack damage stress identification method has some defects, such as high dependence on accurate measurement of strain data, strong identification subjectivity of identification points, and difficulty in obtaining quantitative identification results. The acoustic emission technology can acquire deformation damage information of the rock, but only utilizes a simple acoustic emission signal change rule to identify rock crack damage stress, and has certain limitation.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for identifying the damage stress of the rock cracks by using an acoustic emission technology, which is used for identifying the damage stress of the cracks by using the Felicity (Ferrisidit) effect from the physical essence of the acoustic emission phenomenon of the rock and obtaining a quantitative identification result range by combining the setting of the stress increment among the multi-stage cyclic loading.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for identifying damage stress of rock cracks by using an acoustic emission technology comprises the following steps:
(1) processing the rock core taken from the engineering site into a rock sample to be tested according to the international rock mechanics society standard;
(2) carrying out uniaxial compression test on the rock sample to be tested, measuring and recording the axial stress value in the test process to obtain the uniaxial compressive strength sigma of the rock samplec；
(3) Carrying out acoustic emission test under multistage cyclic loading of a rock sample to be tested, and measuring and recording axial stress and acoustic emission signals in the loading process;
(4) and identifying the Felicity effect in the acoustic emission test, calculating the Felicity ratio FR in each stage of cyclic loading, and obtaining the crack damage stress range of the rock sample to be detected according to the established rock crack damage stress identification method.
And (2) the rock sample to be detected in the step (1) is a small rock core with the height of 50mm and the diameter of 25mm, and the parallelism tolerance of two end faces of the small rock core is not more than 0.1 mm.
In the step (2), the uniaxial compression test equipment adopts an electro-hydraulic servo control rock loading system, and stress and strain data in the test process can be collected by the system and automatically recorded.
In the step (3), the peak stress of the first-stage loading in the multi-stage cyclic loading is 0.55 sigmac。
In the step (3), the stress increment between cyclic loading in the multistage cyclic loading is 0.05 sigmac。
In the step (3), after the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered, the signal exceeding a preset threshold value is collected and recorded by the system, and the contact between the acoustic emission probe and the core sample is coupled by Vaseline.
In the step (4), the established rock fracture damage stress identification method comprises the following steps: along with the cyclic loading, the internal damage of the rock is gradually accumulated, the Felicity ratio FR is gradually reduced, if i is more than or equal to 4 in the ith loading process, the reduction amplitude of the FR value is suddenly increased, which shows that the peak stress P of the ith-1 loadingmax(i-1)The fracture damage stress is exceeded, the fracture propagation enters an unstable stage, the rock damage starts to be accumulated in an aggravating way, and the range of the recognition result of the rock fracture damage stress is Pmax(i-2)To Pmax(i-1)。
The single-axis compression test and the acoustic emission test under the multi-stage cyclic loading in the invention are both the prior art, and are not described herein again.
The Felicity effect in the acoustic emission test is essentially caused by the occurrence of rock damage, and the FR value is gradually reduced along with the accumulation of damage, so that the irreversibility of the accumulation of the rock damage is reflected. Therefore, crack damage stress identification is carried out by utilizing the Felicity effect in the rock multistage cyclic loading acoustic emission test, and a good physical significance basis is achieved.
The invention has the following beneficial effects:
(1) the rock crack damage stress identification method provided by the invention does not need strain measurement, reduces the requirement on test equipment, and simultaneously avoids identification result errors caused by inaccurate measurement of variable data;
(2) the required crack damage stress identification precision range can be obtained by adjusting the magnitude of the stress increment among the multistage cyclic loading;
(3) the subjective interpretation of the identification points is avoided, the objectivity of the solution result is ensured, and the method can be widely applied to the research on the mechanical properties of rocks in the engineering fields of energy, water and electricity, traffic and the like.
Drawings
FIG. 1 is a schematic flow diagram of the present invention;
FIG. 2 is a schematic diagram of a multi-stage cyclic loading path of the present invention;
FIG. 3 is a diagram of an acoustic emission testing system;
FIG. 4 shows the acoustic emission signal and FR values in the cyclic loading of the rock sample in the example.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
The structures, proportions, sizes, and other dimensions shown in the drawings and described in the specification are for understanding and reading the present disclosure, and are not intended to limit the scope of the present disclosure, which is defined in the claims, and are not essential to the art, and any structural modifications, changes in proportions, or adjustments in size, which do not affect the efficacy or achievement of the intended purposes of the present disclosure, are intended to be included within the scope of the present disclosure. In addition, the terms "upper", "lower", "left", "right", "middle" and "one" used in the present specification are for clarity of description, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the terms is not to be construed as a scope of the present invention.
The method for identifying the damage stress of the rock cracks by using the acoustic emission technology is further described in the following with reference to fig. 1 to 4:
(1) and (3) processing the rock core taken from the engineering site into a small rock core with the height of 50mm and the diameter of 25mm by using equipment such as rock core drilling, cutting and grinding according to the International Society for Rock Mechanics (ISRM) standard, wherein the parallelism tolerance of two end surfaces of the small rock core after being ground to be flat is not more than 0.1 mm. Because the random difference of the internal structure of the natural rock is large, in order to avoid influencing the test result, the selected rock core should avoid the appearance of cracks, cavities, inclusions and the like which are visible to the naked eye.
(2) The uniaxial compression test is carried out on the rock sample to be tested, the test equipment adopts an electro-hydraulic servo control rock loading system, and data such as stress, strain and the like in the test process can be collected by the system and automatically recorded. Here, a uniaxial compression test of 3 small cores was carried out to obtain an average uniaxial compression strength σc196.4MPa, the recorded strain data can be used for verification by using a volume strain curve identification method.
(3) Alternatively, the rock sample to be tested is taken to perform acoustic emission test under multistage cyclic loading, the path of the multistage cyclic loading is shown in figure 2, the peak stress of the first-stage loading is 0.55 sigmac(108MPa) stress increase between cyclic loadings of 0.05. sigmac(9.8 MPa). Description of the case of setting the stress delta between the peak stress and cyclic loading of the first stage loading: if the peak stress of the first-stage loading is set to be too small, the number of cyclic loading is increased, and the research results show that the fracture damage stress level of the rock is generally more than 65% of the uniaxial compressive strength, so that the peak stress of the first-stage loading is set to be 0.55 sigmac(ii) a According to the crack damage stress identification method provided by the invention, the magnitude of the stress increment between cyclic loading is directly related to the range of the crack damage stress identification result, the identification precision is higher when the stress increment is smaller, but the stress increment between cyclic loading is set to be 0.05 sigma when the complexity of test operation and the requirement of engineering application are considered at the same timec. As shown in figure 3, when the acoustic emission signal of the rock is detected by the transducer, the signal passes throughAnd after the amplification and filtering treatment, signals exceeding a preset threshold value are collected and recorded by the system, and in order to reduce the influence of acoustic impedance and the like as much as possible, Vaseline is used for coupling treatment when the acoustic emission probe is in contact with the core sample.
(4) During the rock acoustic emission test, sometimes a significant acoustic emission signal occurs without reaching the maximum stress previously experienced, a phenomenon known as the Felicity effect, where the Felicity ratio is defined as follows:
in the formula: FR is the Felicity ratio, PAEIs the value of the stress, P, at the beginning of the occurrence of the acoustic emission signalmaxIs the maximum stress value of the superior loading. When FR is<And when the acoustic emission intensity is 1.0, the effective Felicity effect is generated in the rock acoustic emission test.
The acoustic emission signals monitored in the multistage cyclic loading process of the rock sample to be measured and the calculated FR values are shown in figure 4. As can be seen from the graph, the stress is 0.8 σ at the peak loadcIn the cycle of (157.1MPa), the decrease amplitude of the FR value is suddenly increased, and is reduced from 0.83 of the previous cycle to 0.66 and reaches 0.17, while in the previous loading cycle, the decrease amplitude of the FR value is 0.02 or 0.03, which shows that the damage degree of the rock sample is suddenly increased, so that the peak stress of the previous stage cyclic loading is inferred to be 0.75 sigmac(147.3MPa) exceeds the fracture damage stress, and the fracture expansion enters an unstable stage, so that the identification result range of the fracture damage stress of the rock sample to be detected is 0.7-0.75 sigmac(137.5-147.3 MPa). In order to verify the reliability of the crack damage stress identification method provided by the invention, the crack damage stress identification is carried out on 3 small cores by utilizing a widely-applied volume strain curve identification method, and the stress value at the reversal point of the volume strain curve is read to obtain the average value of the crack damage stress of 144.2MPa (0.73 sigma)c) Within the scope of the recognition results of the present invention.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (5)
1. A method for identifying the damage stress of a rock crack by using an acoustic emission technology is characterized by comprising the following steps:
(1) processing the rock core taken from the engineering site into a rock sample to be tested according to the international rock mechanics society standard;
(2) performing uniaxial compression test on the rock sample to be tested, measuring and recording the axial stress value in the test process to obtain the uniaxial compressive strength sigma of the rock samplec；
(3) Carrying out acoustic emission test under multistage cyclic loading of a rock sample to be tested, and measuring and recording axial stress and acoustic emission signals in the loading process;
(4) identifying the Felicity effect in the acoustic emission test, calculating the Felicity ratio FR in each stage of cyclic loading, and obtaining the crack damage stress range of the rock sample to be detected according to the established rock crack damage stress identification method;
in the step (4), the established rock fracture damage stress identification method comprises the following steps: along with the cyclic loading, the internal damage of the rock is gradually accumulated, the Felicity ratio FR is gradually reduced, if i is more than or equal to 4 in the ith loading process, the reduction amplitude of the FR value is suddenly increased, which shows that the peak stress P of the ith-1 loadingmax(i-1)The fracture damage stress is exceeded, the fracture propagation enters an unstable stage, the rock damage starts to be accumulated in an aggravating way, and the range of the recognition result of the rock fracture damage stress is Pmax(i-2)To Pmax(i-1)(ii) a In the step (3), the peak stress of the first-stage loading in the multi-stage cyclic loading is 0.55 sigmac。
2. The method for identifying the damage stress of the rock cracks by using the acoustic emission technology as claimed in claim 1, wherein the rock sample to be detected in the step (1) is a small rock core with the height of 50mm and the diameter of 25mm, and the parallelism tolerance of two end faces of the small rock core is not more than 0.1 mm.
3. The method for identifying the damage stress of the rock cracks by using the acoustic emission technology as claimed in claim 1, wherein in the step (2), the uniaxial compression test equipment adopts an electro-hydraulic servo-controlled rock loading system, and the stress and strain data in the test process can be collected and automatically recorded by the system.
4. The method for identifying a fracture damage stress in a rock using acoustic emission techniques as claimed in claim 1, wherein in said step (3), the stress increment between cyclic loading in the multistage cyclic loading is 0.05 σc。
5. The method for identifying the damage stress of the rock cracks by using the acoustic emission technology as claimed in claim 1, wherein in the step (3), after the acoustic emission signals of the rock are detected by the transducer, the signals are amplified and filtered, the signals exceeding a preset threshold value are collected and recorded by the system, and the contact between the acoustic emission probe and the rock core sample is coupled by using vaseline.
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| CN111122710A (en) * | 2019-12-30 | 2020-05-08 | 重庆大学 | Method for analyzing rock micro-damage and crack forms by using acoustic emission power spectrum |
| CN112557203B (en) * | 2020-11-11 | 2022-08-16 | 核工业北京地质研究院 | Hot hydraulic coupling triaxial test method for fractured rock |
| CN112697617B (en) * | 2020-12-03 | 2022-02-01 | 中国科学院地质与地球物理研究所 | Method for quantitatively depicting progressive rock failure mechanical parameters |
| CN113218766B (en) * | 2021-05-27 | 2022-12-06 | 江西理工大学 | Rock crack initiation stress and damage stress identification method based on moment tensor analysis |
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