WO2020228386A1 - Method for identifying crack initiation stress of rock using acoustic emission technology - Google Patents

Method for identifying crack initiation stress of rock using acoustic emission technology Download PDF

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WO2020228386A1
WO2020228386A1 PCT/CN2020/075310 CN2020075310W WO2020228386A1 WO 2020228386 A1 WO2020228386 A1 WO 2020228386A1 CN 2020075310 W CN2020075310 W CN 2020075310W WO 2020228386 A1 WO2020228386 A1 WO 2020228386A1
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rock
stress
acoustic emission
identifying
crack initiation
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田勇
俞然刚
张尹
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青岛理工大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/14—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/36—Detecting the response signal, e.g. electronic circuits specially adapted therefor
    • 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
    • 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
    • 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
    • G01N2203/0001—Type of application of the stress
    • G01N2203/0005—Repeated or cyclic
    • 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
    • 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
    • G01N2203/0064—Initiation of crack
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/023—Solids
    • G01N2291/0232—Glass, ceramics, concrete or stone
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/0289—Internal structure, e.g. defects, grain size, texture

Definitions

  • the invention relates to a rock engineering technology, in particular to a method for identifying rock crack initiation stress by using acoustic emission technology.
  • rock is an important engineering medium, and the study of its mechanical properties has attracted more and more attention.
  • the characteristic rock stress is the threshold stress that divides the different stages of rock deformation and failure.
  • the crack initiation stress is considered as the end of the elastic deformation stage and also represents the beginning of the accumulation of rock damage. Therefore, the accurate identification of rock crack initiation stress has important theoretical and practical significance for accurately dividing rock deformation stages and conducting damage evolution research.
  • the rock deformation characteristics must change.
  • the predecessors experienced a process from volume strain curve to transverse strain curve, and then to a relatively mature crack volume strain curve.
  • the volumetric strain of the crack is obtained by subtracting the elastic strain from the total volumetric strain during rock compression.
  • the volumetric strain of the crack tends to zero (the original crack is closed) and deviates from the stress value at the zero point , Is the crack initiation stress.
  • Acoustic emission is a phenomenon in which the energy accumulated inside the material is released in the form of stress waves during the process of loading.
  • Rock acoustic emission technology can monitor the activity of internal cracks in the rock in real time and reflect the deformation and failure information. Therefore, according to the changes in the acoustic emission signal parameters of the rock at different stages during the compression process, the crack initiation stress can be identified.
  • "Hard Rock Discussion damage and crack initiation strength intensity value method” paper describes a method using acoustic emission signal parameter identification stress fracture initiation (see “Soil Mechanics", 2014 No. 4, of: circumferential Hui, etc.) For granite, the intensity value obtained by the acoustic emission impact rate curve is very close to the crack initiation intensity.
  • acoustic emission signal parameters can be used as an auxiliary means to identify crack stress qualitatively or semi-quantitatively, and it is difficult to obtain accurate quantitative values.
  • ultrasonic Wave speed of rock can characterize its internal structure and mechanical properties. Therefore, in engineering rock mass testing, ultrasonic Testing is an important non-destructive testing method.
  • the existing methods for identifying the initiation stress of rock cracks have some shortcomings, such as highly dependent on accurate measurement of strain data, the interpretation of identification points is subjective, and it is difficult to obtain quantitative identification results.
  • Acoustic emission technology can obtain information about the deformation and damage of rocks, but only using simple acoustic emission signal changes to identify the initiation stress of rock cracks has certain limitations.
  • the purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for identifying the initiation stress of rock cracks by using acoustic emission technology.
  • the Felicity effect is used to identify Crack initiation stress, combined with the setting of stress increment between multi-level cyclic loading, obtains the range of quantitative identification results.
  • a method for identifying the initiation stress of a rock crack by using acoustic emission technology includes the following steps:
  • the rock sample to be tested is a small core with a height of 50 mm and a diameter of 25 mm, and the tolerance of parallelism between the two ends of the small core is not greater than 0.1 mm.
  • the uniaxial compression test equipment adopts an electro-hydraulic servo-controlled rock loading system, and the stress and strain data during the test can be collected by the system and automatically recorded.
  • the peak stress of the first stage loading in the multi-stage cyclic loading is 0.3 ⁇ c .
  • the stress increment between cyclic loading in the multi-stage cyclic loading is 0.05 ⁇ c .
  • step (3) when the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered, and the signal exceeding a predetermined threshold will be collected and recorded by the system.
  • the contact between the acoustic emission probe and the core sample Use petroleum jelly for coupling treatment.
  • the established method for identifying the crack initiation stress of rock fractures is: in the multi-stage cyclic loading acoustic emission test, if the first Felicity effect occurs in the i-th loading process, i ⁇ 2, then obvious sound stress value of the transmission signal at P AE (i) must be less than the first i-1 peak stress subloading of P max (i-1), if P AE (i) larger than i-2 times the peak stress load P max (i -2) , then the range of the identification result of the rock crack initiation stress is P AE(i) to P max(i-1) , otherwise, the range of the identification result is P max(i-2) to P max(i-1) .
  • the uniaxial compression test and the acoustic emission test under multi-stage cyclic loading in the present invention are both the prior art, and will not be repeated here.
  • the Felicity effect in the acoustic emission test is closely related to the propagation of cracks inside the rock, which reflects the irreversibility of the accumulation of rock damage. Therefore, the use of the Felicity effect in the rock multi-stage cyclic loading acoustic emission test to identify the crack initiation stress has a good physical basis.
  • the method for identifying the initiation stress of rock cracks provided by the present invention does not require strain measurement, which reduces the requirements for test equipment, and at the same time avoids the identification result error caused by inaccurate strain data measurement;
  • Figure 1 is a schematic flow diagram of the present invention
  • Figure 2 is a schematic diagram of the multi-stage cyclic loading path of the present invention.
  • Figure 3 is a diagram of the acoustic emission test system
  • Figure 4 is a diagram of acoustic emission signals during multi-stage cyclic loading of a rock sample in the embodiment.
  • the cores retrieved from the project site are processed into small cores with a height of 50mm and a diameter of 25mm using core drilling, cutting, grinding and other equipment according to the International Society of Rock Mechanics (ISRM) standards.
  • the tolerance of end face parallelism is not more than 0.1mm. Due to the large random variation in the internal structure of natural rocks, in order to avoid affecting the test results, the selected core should avoid the appearance of visible cracks, cavities and inclusions.
  • the rock sample to be tested is subjected to a uniaxial compression test.
  • the test equipment adopts an electro-hydraulic servo-controlled rock loading system.
  • the stress and strain data during the test can be collected and automatically recorded by the system.
  • the uniaxial compression test of 3 small cores is performed here, and the average uniaxial compressive strength ⁇ c is 80.6 MPa, and the recorded strain data can be used for verification using the crack volume strain identification method.
  • the rock sample to be tested is selected for the acoustic emission test under multi-stage cyclic loading.
  • the path of the multi-stage cyclic loading is shown in Figure 2.
  • the peak stress of the first stage loading is 0.3 ⁇ c (24.2MPa), and the cyclic loading interval
  • the stress increment of is 0.05 ⁇ c (4MPa).
  • the rock acoustic emission signal When the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered, and the signal exceeding a predetermined threshold will be collected and recorded by the system, in order to minimize the acoustic impedance, etc.
  • the contact between the acoustic emission probe and the core sample is coupled with petroleum jelly.
  • FR is the Felicity ratio
  • P AE is the stress value when the acoustic emission signal begins to appear
  • P max is the maximum stress value loaded by the superior.
  • the acoustic emission signal monitored during the multi-stage cyclic loading of the rock sample to be tested is shown in Figure 4. It can be seen from the figure that the Felicity effect first appeared in the fourth loading process, that is, when the loading stress has not exceeded the upper limit. When the maximum stress is applied for the first time (the third time), an obvious acoustic emission signal appears. In the fourth loading, the stress value P AE(4) where the obvious acoustic emission signal appears is 29.6MPa, which is less than the peak stress P max(3) (32.2MPa) of the third loading.

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Abstract

A method for identifying a crack initiation stress of a rock using acoustic emission technology, comprising the following steps: (1) processing a rock core obtained from a construction site into a rock sample to be tested according to the standard of International Society for Rock Mechanics; (2) performing a uniaxial compression test on the rock sample to be tested, and measuring and recording an axial stress value during the test process to obtain a uniaxial compressive strength σc of the rock sample; (3) performing an acoustic emission test under multistage cyclic loading on the rock sample to be tested, and measuring and recoding an axial stress and an acoustic emission signal during the loading process; and (4) identifying a first Felicity effect during the acoustic emission test, and obtaining a range of crack initiation stress of the rock sample to be tested according to an established method for identifying a crack initiation stress of a rock. A quantitative identification result range is obtained by identifying a crack initiation stress using the Felicity effect and setting a stress increment during multistage cyclic loading.

Description

利用声发射技术识别岩石裂缝起裂应力的方法Method for identifying the initiation stress of rock cracks using acoustic emission technology 技术领域Technical field
本发明涉及一种岩石工程技术，尤其是一种利用声发射技术识别岩石裂缝起裂应力的方法。The invention relates to a rock engineering technology, in particular to a method for identifying rock crack initiation stress by using acoustic emission technology.
背景技术Background technique
随着我国地下工程的大规模发展，如石油天然气开采、地下隧洞工程、高放废物深埋处置等，岩石作为重要的工程介质，其力学性能的研究越来越受到重视。岩石特征应力是划分岩石受力变形破坏不同阶段的阈值应力，其中裂缝起裂应力被认为是弹性变形阶段的终点，也代表了岩石损伤累积的开始。因此，岩石裂缝起裂应力的精确识别，对于准确划分岩石变形阶段和开展损伤演化研究具有重要理论和实际意义。With the large-scale development of underground engineering in my country, such as oil and natural gas exploitation, underground tunnel engineering, and deep burial disposal of high-level radioactive waste, rock is an important engineering medium, and the study of its mechanical properties has attracted more and more attention. The characteristic rock stress is the threshold stress that divides the different stages of rock deformation and failure. The crack initiation stress is considered as the end of the elastic deformation stage and also represents the beginning of the accumulation of rock damage. Therefore, the accurate identification of rock crack initiation stress has important theoretical and practical significance for accurately dividing rock deformation stages and conducting damage evolution research.
从岩石的变形特性分析，当加载应力超过裂缝起裂应力时，岩石的变形特征必定发生变化。前人在利用应变方法识别裂缝起裂应力的过程中，经历了从体积应变曲线到横向应变曲线，再发展到相对成熟的裂纹体积应变曲线的过程。利用岩石压缩过程中的总体积应变减去弹性应变得到裂纹体积应变，在轴向应力—裂纹体积应变曲线中，裂纹体积应变趋于0后(原有裂纹闭合)再次偏离0点处的应力值，即为裂缝起裂应力。《大理岩损伤强度的识别及基于损伤控制的参数演化规律》一文介绍了裂纹体积应变的计算方法和利用轴向应力—裂纹体积应变曲线识别裂缝起裂应力的方法(参见《岩石力学与工程学报》2012年增2期，作者：汪斌，等)，对大理岩的识别结果为裂缝起裂应力与单轴抗压强度的比值均值范围为0.38-0.52。该识别方法物理意义明确，但高度依赖于应变的精确测量，尤其是横向应变。From the analysis of rock deformation characteristics, when the loading stress exceeds the crack initiation stress, the rock deformation characteristics must change. In the process of identifying the crack initiation stress by the strain method, the predecessors experienced a process from volume strain curve to transverse strain curve, and then to a relatively mature crack volume strain curve. The volumetric strain of the crack is obtained by subtracting the elastic strain from the total volumetric strain during rock compression. In the axial stress-crack volume-strain curve, the volumetric strain of the crack tends to zero (the original crack is closed) and deviates from the stress value at the zero point , Is the crack initiation stress. The article "Identification of Marble Damage Strength and the Law of Parameter Evolution Based on Damage Control" introduces the calculation method of crack volume strain and the method of identifying crack initiation stress using the axial stress-crack volume strain curve (see Chinese Journal of Rock Mechanics and Engineering "2012 by two authors: Wang Bin, etc.), the recognition result of the marble is the ratio of the mean range of fracturing and stress crack uniaxial compressive strength of 0.38-0.52. The physical meaning of this identification method is clear, but it highly depends on the accurate measurement of strain, especially the transverse strain.
声发射是材料受载荷过程中内部积聚的能量以应力波形式释放的一种现象，岩石声发射技术能够实时监测岩石内部裂纹的活动情况，反应变形破坏信息。因此，根据岩石在受压过程中不同阶段声发射信号参数的变化，可以进行裂缝起裂应力的识别。《硬岩裂纹起裂强度和损伤强度取值方法探讨》一文介绍了利用声发射信号参数识别裂缝起裂应力的方法(参见《岩土力学》2014年第4期，作者：周辉，等)，对于花岗岩，利用声发射撞击率曲线获得的强度值与裂缝起裂强度非常接近。但文中同时指出，声发射信号参数可以作为定性或者半定量识别裂缝应力的一种辅助手段，很难获得准确的定量数值。Acoustic emission is a phenomenon in which the energy accumulated inside the material is released in the form of stress waves during the process of loading. Rock acoustic emission technology can monitor the activity of internal cracks in the rock in real time and reflect the deformation and failure information. Therefore, according to the changes in the acoustic emission signal parameters of the rock at different stages during the compression process, the crack initiation stress can be identified. "Hard Rock Discussion damage and crack initiation strength intensity value method" paper describes a method using acoustic emission signal parameter identification stress fracture initiation (see "Soil Mechanics", 2014 No. 4, of: circumferential Hui, etc.) For granite, the intensity value obtained by the acoustic emission impact rate curve is very close to the crack initiation intensity. However, the article also pointed out that acoustic emission signal parameters can be used as an auxiliary means to identify crack stress qualitatively or semi-quantitatively, and it is difficult to obtain accurate quantitative values.
《基于声发射定位的岩石裂纹动态演化过程研究》一文介绍了应用声发射及其定位技术，在单轴压缩载荷作用下，应用盖格尔定位算法，采用试验方法研究包含不同预制裂纹 的花岗岩岩样破裂失稳过程中其内部微裂纹孕育、萌生、扩展、成核和贯通的三维空间演化模式(参见《岩石力学与工程学报》2007年第5期，作者：赵兴东，等)。验证了声发射事件与岩石内部裂纹的扩展产生有密切关系，但是该技术和本发明的技术并不重复，对发明的技术有较好的支撑。The article "Research on the Dynamic Evolution Process of Rock Cracks Based on Acoustic Emission Positioning" introduces the application of acoustic emission and its positioning technology. Under uniaxial compression loads, the Geiger positioning algorithm is applied and experimental methods are used to study granite rocks containing different prefabricated cracks. samples Steady Failure during its internal microcracks gave birth, initiation, propagation, into a three-dimensional space evolution of nuclear and penetrating (see "rock Mechanics and Engineering" 2007, No. 5, author: Zhaoxing Dong, etc.). It is verified that the acoustic emission event is closely related to the propagation of the internal cracks in the rock, but this technology and the technology of the present invention are not duplicated, and it has a good support for the technology of the invention.
弹性波在传播过程中遇到某些障碍时，如夹杂、孔洞、裂缝等，波速将会发生改变，岩石的超声波波速可以表征其内部结构与力学性质，因此，在工程岩体测试中，超声测试是一种重要的无损检测手段。《岩石单轴压缩下损伤表征及演化规律对比研究》一文介绍了利用岩石声波波速各项异性系数的变化规律识别裂缝起裂应力的方法(参见《岩土工程学报》2018年第6期，作者：张国凯，等)，识别结果与裂纹体积应变曲线的识别结果吻合较好，但该方法体现的识别信息太过单一，且仅能辅助识别裂缝起裂应力。When the elastic wave encounters certain obstacles in the propagation process, such as inclusions, holes, cracks, etc., the wave speed will change. The ultrasonic wave speed of rock can characterize its internal structure and mechanical properties. Therefore, in engineering rock mass testing, ultrasonic Testing is an important non-destructive testing method. The article "Comparative Study on the Characterization and Evolution Law of Rock Damage under Uniaxial Compression" introduces the method of identifying the initiation stress of cracks by using the variation law of the anisotropy coefficient of rock acoustic wave velocity (see Chinese Journal of Geotechnical Engineering, Issue 6, 2018, author (Zhang Guokai, et al.), the identification results are in good agreement with the identification results of the crack volume strain curve, but the identification information embodied by this method is too single and can only assist in identifying the crack initiation stress.
综上所述，现有的岩石裂缝起裂应力识别方法存在一些不足，如高度依赖于应变数据的精确测量、识别点的判读主观性较强、很难获得定量的识别结果。声发射技术能够获取岩石的变形损伤信息，但仅利用简单的声发射信号变化规律来识别岩石裂缝起裂应力，有一定的局限性。In summary, the existing methods for identifying the initiation stress of rock cracks have some shortcomings, such as highly dependent on accurate measurement of strain data, the interpretation of identification points is subjective, and it is difficult to obtain quantitative identification results. Acoustic emission technology can obtain information about the deformation and damage of rocks, but only using simple acoustic emission signal changes to identify the initiation stress of rock cracks has certain limitations.
发明内容Summary of the invention
本发明的目的是为克服上述现有技术的不足，提供一种利用声发射技术识别岩石裂缝起裂应力的方法，从岩石声发射现象的物理本质出发，利用Felicity(费利西蒂)效应识别裂缝起裂应力，结合多级循环加载间应力增量的设置，获得定量识别结果范围。The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for identifying the initiation stress of rock cracks by using acoustic emission technology. Starting from the physical nature of the rock acoustic emission phenomenon, the Felicity effect is used to identify Crack initiation stress, combined with the setting of stress increment between multi-level cyclic loading, obtains the range of quantitative identification results.
为实现上述目的，本发明采用下述技术方案：In order to achieve the above objectives, the present invention adopts the following technical solutions:
一种利用声发射技术识别岩石裂缝起裂应力的方法，包括以下步骤：A method for identifying the initiation stress of a rock crack by using acoustic emission technology includes the following steps:
(1)将工程现场取回来的岩芯按照国际岩石力学学会标准加工成待测岩样；(1) Process the cores retrieved from the project site into rock samples to be tested according to the standards of the International Society of Rock Mechanics;
(2)进行待测岩样的单轴压缩试验，测量并记录试验过程中的轴向应力值，获得岩样的单轴抗压强度σ c； (2) Conduct a uniaxial compression test of the rock sample to be tested, measure and record the axial stress value during the test, and obtain the uniaxial compressive strength σ c of the rock sample;
(3)进行待测岩样多级循环加载下的声发射试验，测量并记录加载过程中的轴向应力和声发射信号；(3) Conduct acoustic emission test under multi-stage cyclic loading of the rock sample to be tested, measure and record the axial stress and acoustic emission signal during the loading process;
(4)进行声发射试验中首次Felicity效应的识别，并根据建立的岩石裂缝起裂应力识别方法获得待测岩样的裂缝起裂应力范围。(4) Perform the first Felicity effect identification in the acoustic emission test, and obtain the crack initiation stress range of the rock sample to be tested according to the established rock crack initiation stress identification method.
所述步骤(1)中待测岩样为高50mm、直径25mm的小岩芯，小岩芯两端面平行度公差不大于0.1mm。In the step (1), the rock sample to be tested is a small core with a height of 50 mm and a diameter of 25 mm, and the tolerance of parallelism between the two ends of the small core is not greater than 0.1 mm.
所述步骤(2)中，单轴压缩试验设备采用电液伺服控制的岩石加载***，试验过程中 的应力、应变数据能被***采集并自动记录。In the step (2), the uniaxial compression test equipment adopts an electro-hydraulic servo-controlled rock loading system, and the stress and strain data during the test can be collected by the system and automatically recorded.
所述步骤(3)中，多级循环加载中第一级加载的峰值应力为0.3σ c。 In the step (3), the peak stress of the first stage loading in the multi-stage cyclic loading is 0.3σ c .
所述步骤(3)中，多级循环加载中循环加载间的应力增量为0.05σ c。 In the step (3), the stress increment between cyclic loading in the multi-stage cyclic loading is 0.05σ c .
所述步骤(3)中，当岩石声发射信号被换能器检测到后，信号经过放大、过滤处理，超过预定阈值的信号就会被***采集记录，声发射探头和岩芯样品间的接触采用凡士林进行耦合处理。In the step (3), when the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered, and the signal exceeding a predetermined threshold will be collected and recorded by the system. The contact between the acoustic emission probe and the core sample Use petroleum jelly for coupling treatment.
所述步骤(4)中，建立的岩石裂缝起裂应力识别方法为：在多级循环加载声发射试验中，若首次Felicity效应发生在第i次加载过程中，i≥2，那么出现明显声发射信号处的应力值P AE(i)必定小于第i-1次加载的峰值应力P max(i-1)，如果P AE(i)大于第i-2次加载的峰值应力P max(i-2)，那么岩石裂缝起裂应力的识别结果范围为P AE(i)到P max(i-1)，否则，识别结果范围为P max(i-2)到P max(i-1)。 In the step (4), the established method for identifying the crack initiation stress of rock fractures is: in the multi-stage cyclic loading acoustic emission test, if the first Felicity effect occurs in the i-th loading process, i≥2, then obvious sound stress value of the transmission signal at P AE (i) must be less than the first i-1 peak stress subloading of P max (i-1), if P AE (i) larger than i-2 times the peak stress load P max (i -2) , then the range of the identification result of the rock crack initiation stress is P AE(i) to P max(i-1) , otherwise, the range of the identification result is P max(i-2) to P max(i-1) .
本发明中的单轴压缩试验和多级循环加载下的声发射试验均为现有技术，在此不再赘述。The uniaxial compression test and the acoustic emission test under multi-stage cyclic loading in the present invention are both the prior art, and will not be repeated here.
声发射试验中的Felicity效应与岩石内部裂纹的扩展有密切关系，体现了岩石损伤累积的不可逆性。因此，利用岩石多级循环加载声发射试验中的Felicity效应进行裂缝起裂应力识别，具有良好的物理意义基础。The Felicity effect in the acoustic emission test is closely related to the propagation of cracks inside the rock, which reflects the irreversibility of the accumulation of rock damage. Therefore, the use of the Felicity effect in the rock multi-stage cyclic loading acoustic emission test to identify the crack initiation stress has a good physical basis.
本发明具有如下有益效果：The present invention has the following beneficial effects:
(1)本发明提供的岩石裂缝起裂应力识别方法无需应变测量，降低了对试验设备的要求，同时避免了因应变数据测量不准确带来的识别结果误差；(1) The method for identifying the initiation stress of rock cracks provided by the present invention does not require strain measurement, which reduces the requirements for test equipment, and at the same time avoids the identification result error caused by inaccurate strain data measurement;
(2)通过调整多级循环加载间应力增量的大小，可获得所需的裂缝起裂应力识别精度范围；(2) By adjusting the size of the stress increment between multi-stage cyclic loading, the required crack initiation stress identification accuracy range can be obtained;
(3)避免了识别点的主观判读，保证了求解结果的客观性，可广泛应用于能源、水电、交通等工程领域的岩石力学性能研究。(3) The subjective interpretation of the identification points is avoided, and the objectivity of the solution results is ensured. It can be widely used in the study of rock mechanics performance in energy, hydropower, transportation and other engineering fields.
附图说明Description of the drawings
图1为本发明的流程示意图；Figure 1 is a schematic flow diagram of the present invention;
图2为本发明的多级循环加载路径示意图；Figure 2 is a schematic diagram of the multi-stage cyclic loading path of the present invention;
图3为声发射试验***图；Figure 3 is a diagram of the acoustic emission test system;
图4为实施例中岩样多级循环加载中的声发射信号图。Figure 4 is a diagram of acoustic emission signals during multi-stage cyclic loading of a rock sample in the embodiment.
具体实施方式Detailed ways
下面结合附图和实施例对本发明进一步说明。The present invention will be further described below in conjunction with the drawings and embodiments.
本说明书所附图式所绘示的结构、比例、大小等，均仅用以配合说明书所揭示的内容， 以供熟悉此技术的人士了解与阅读，并非用以限定本发明可实施的限定条件，故不具技术上的实质意义，任何结构的修饰、比例关系的改变或大小的调整，在不影响本发明所能产生的功效及所能达成的目的下，均应仍落在本发明所揭示的技术内容得能涵盖的范围内。同时，本说明书中所引用的如“上”、“下”、“左”、“右”、“中间”及“一”等的用语，亦仅为便于叙述的明了，而非用以限定本发明可实施的范围，其相对关系的改变或调整，在无实质变更技术内容下，当亦视为本发明可实施的范畴。The structure, ratio, size, etc. shown in the drawings in this specification are only used to match the content disclosed in the specification for the understanding and reading of those who are familiar with this technology, and are not used to limit the implementation of the present invention. Therefore, it does not have any technical significance. Any structural modification, proportional relationship change or size adjustment should still fall within the disclosure of the present invention without affecting the effects and objectives that the present invention can produce. The technical content must be covered. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the text. The scope of implementation of the invention, the change or adjustment of its relative relationship, without substantial changes to the technical content, shall also be regarded as the scope of implementation of the invention.
下面结合图1-图4对利用声发射技术识别岩石裂缝起裂应力的方法作进一步说明：The method of identifying the initiation stress of rock cracks using acoustic emission technology will be further explained below in conjunction with Figures 1 to 4:
(1)将从工程现场取回来的岩芯，利用岩芯钻、切、磨等设备按国际岩石力学学会(ISRM)标准加工成高50mm、直径25mm的小岩芯，磨平后的小岩芯两端面平行度公差不大于0.1mm。因天然岩石内部构造的随机差异性较大，为避免对试验结果造成影响，所选岩芯应避免肉眼可见的裂缝、空洞及夹杂物等的出现。(1) The cores retrieved from the project site are processed into small cores with a height of 50mm and a diameter of 25mm using core drilling, cutting, grinding and other equipment according to the International Society of Rock Mechanics (ISRM) standards. The tolerance of end face parallelism is not more than 0.1mm. Due to the large random variation in the internal structure of natural rocks, in order to avoid affecting the test results, the selected core should avoid the appearance of visible cracks, cavities and inclusions.
(2)将待测岩样进行单轴压缩试验，试验设备采用电液伺服控制的岩石加载***，试验过程中的应力、应变等数据能被***采集并自动记录。此处进行3块小岩芯的单轴压缩试验，得到平均单轴抗压强度σ c为80.6MPa，记录的应变数据可为利用裂纹体积应变识别法进行验证使用。 (2) The rock sample to be tested is subjected to a uniaxial compression test. The test equipment adopts an electro-hydraulic servo-controlled rock loading system. The stress and strain data during the test can be collected and automatically recorded by the system. The uniaxial compression test of 3 small cores is performed here, and the average uniaxial compressive strength σ c is 80.6 MPa, and the recorded strain data can be used for verification using the crack volume strain identification method.
(3)另选取待测岩样进行多级循环加载下的声发射试验，多级循环加载的路径如图2所示，第一级加载峰值应力为0.3σ c(24.2MPa)，循环加载间的应力增量为0.05σ c(4MPa)。关于第一级加载的峰值应力和循环加载间的应力增量设置情况的说明：若第一级加载的峰值应力设置过小，会增加循环加载的次数，且岩石加载初始阶段的压密过程会产生干扰的声发射信号，已有的研究成果表明岩石裂缝的起裂发生在应力水平超过单轴抗压强度的30％之后，故第一级加载的峰值应力设置为0.3σ c；根据本发明提供的裂缝起裂应力识别方法，循环加载间应力增量的大小直接关系到裂缝起裂应力识别结果的范围，应力增量越小，识别精度越高，但同时考虑到试验操作的繁琐程度和满足工程应用的需要，循环加载间的应力增量设置为0.05σ c。声发射测试试验***如图3所示，当岩石声发射信号被换能器检测到后，信号经过放大、过滤处理，超过预定阈值的信号就会被***采集记录，为了尽量减小声学阻抗等的影响，声发射探头和岩芯样品间的接触采用凡士林进行耦合处理。 (3) In addition, the rock sample to be tested is selected for the acoustic emission test under multi-stage cyclic loading. The path of the multi-stage cyclic loading is shown in Figure 2. The peak stress of the first stage loading is 0.3σ c (24.2MPa), and the cyclic loading interval The stress increment of is 0.05σ c (4MPa). Explanation about the setting of the peak stress of the first stage loading and the stress increment between cyclic loading: If the peak stress of the first stage loading is set too small, the number of cyclic loading will increase, and the compaction process of the initial stage of rock loading will be affected. Produce disturbing acoustic emission signals. Existing research results indicate that the initiation of rock cracks occurs after the stress level exceeds 30% of the uniaxial compressive strength, so the peak stress of the first-stage loading is set to 0.3σ c ; according to the present invention The provided crack initiation stress identification method, the size of the stress increment between cyclic loading is directly related to the range of the crack initiation stress identification result, the smaller the stress increment, the higher the identification accuracy, but at the same time, the cumbersomeness of the test operation and the To meet the needs of engineering applications, the stress increment between cyclic loading is set to 0.05σ c . The acoustic emission test system is shown in Figure 3. When the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered, and the signal exceeding a predetermined threshold will be collected and recorded by the system, in order to minimize the acoustic impedance, etc. The contact between the acoustic emission probe and the core sample is coupled with petroleum jelly.
(4)在岩石声发射试验过程中，有时在未达到之前所受的最大应力时也会有明显的声发射信号出现，这种现象被称为Felicity效应，Felicity比定义如下：(4) In the process of rock acoustic emission test, sometimes obvious acoustic emission signal appears before the maximum stress experienced before. This phenomenon is called the Felicity effect. The Felicity ratio is defined as follows:
Figure PCTCN2020075310-appb-000001
Figure PCTCN2020075310-appb-000001
式中：FR是Felicity比值，P AE是当声发射信号开始出现时的应力值，P max是上级加载 的最大应力值。当FR<1.0时，说明岩石声发射试验中产生了有效的Felicity效应。 Where: FR is the Felicity ratio, P AE is the stress value when the acoustic emission signal begins to appear, and P max is the maximum stress value loaded by the superior. When FR<1.0, it means that the effective Felicity effect is produced in the rock acoustic emission test.
待测岩样多级循环加载过程中监测到的声发射信号如图4所示，从图中可看出，在第四次加载过程中首先出现了Felicity效应，即当加载应力还未超过上一次(第三次)加载的最大应力时，就有明显的声发射信号出现。在第四次加载中，出现明显声发射信号处的应力值P AE(4)为29.6MPa，小于第三次加载的峰值应力P max(3)(32.2MPa)，如果P AE(4)大于第二次加载的峰值应力P max(2)，那么岩石裂缝起裂应力的识别结果范围为P AE(4)到P max(3)，否则，识别结果范围为P max(2)到P max(3)。此处，P max(2)为28.2MPa，小于P AE(4)，故待测岩样裂缝起裂应力的识别结果范围为29.6-32.2MPa(0.37-0.4σ c)。为了验证本发明提出的裂缝起裂应力识别方法的可靠性，利用广泛应用的裂纹体积应变曲线法对3块小岩芯进行裂缝起裂应力识别，读取在轴向应力—裂纹体积应变曲线中裂纹体积应变趋于0后(原有裂纹闭合)再次偏离0点处的应力值，得出裂缝起裂应力平均值为30.8MPa(0.38σ c)，在本发明的识别结果范围内。 The acoustic emission signal monitored during the multi-stage cyclic loading of the rock sample to be tested is shown in Figure 4. It can be seen from the figure that the Felicity effect first appeared in the fourth loading process, that is, when the loading stress has not exceeded the upper limit. When the maximum stress is applied for the first time (the third time), an obvious acoustic emission signal appears. In the fourth loading, the stress value P AE(4) where the obvious acoustic emission signal appears is 29.6MPa, which is less than the peak stress P max(3) (32.2MPa) of the third loading. If P AE(4) is greater than The peak stress of the second load is P max(2) , then the identification result of rock crack initiation stress ranges from P AE(4) to P max(3) , otherwise, the identification result ranges from P max(2) to P max (3) . Here, P max(2) is 28.2MPa, which is less than P AE(4) , so the range of the identification result of the crack initiation stress of the rock sample to be tested is 29.6-32.2MPa (0.37-0.4σ c ). In order to verify the reliability of the crack initiation stress identification method proposed by the present invention, the widely used crack volume strain curve method was used to identify the crack initiation stress of three small cores, and read the crack in the axial stress-crack volume strain curve. After the volumetric strain tends to 0 (the original crack is closed), it deviates again from the stress value at the 0 point, and the average value of the crack initiation stress is 30.8MPa (0.38σ c ), which is within the range of the identification result of the present invention.
上述虽然结合附图对本发明的具体实施方式进行了描述，但并非对本发明保护范围的限制，所属领域技术人员应该明白，在本发明的技术方案的基础上，本领域技术人员不需要付出创造性劳动即可做出的各种修改或变形仍在本发明的保护范围以内。Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to make creative efforts. Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (7)

  1. 一种利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，包括以下步骤：A method for identifying the initiation stress of a rock crack by using acoustic emission technology, which is characterized by including the following steps:
    (1)将工程现场取回来的岩芯按照国际岩石力学学会标准加工成待测岩样；(1) Process the cores retrieved from the project site into rock samples to be tested according to the standards of the International Society of Rock Mechanics;
    (2)对待测岩样做单轴压缩试验，测量并记录试验过程中的轴向应力值，获得岩样的单轴抗压强度σ c； (2) Perform a uniaxial compression test on the rock sample to be tested, measure and record the axial stress value during the test, and obtain the uniaxial compressive strength σ c of the rock sample;
    (3)进行待测岩样多级循环加载下的声发射试验，测量并记录加载过程中的轴向应力和声发射信号；(3) Conduct acoustic emission test under multi-stage cyclic loading of the rock sample to be tested, measure and record the axial stress and acoustic emission signal during the loading process;
    (4)进行声发射试验中首次Felicity效应的识别，并根据建立的岩石裂缝起裂应力识别方法获得待测岩样的裂缝起裂应力范围。(4) Perform the first Felicity effect identification in the acoustic emission test, and obtain the crack initiation stress range of the rock sample to be tested according to the established rock crack initiation stress identification method.
  2. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(1)中待测岩样为高50mm、直径25mm的小岩芯，小岩芯两端面平行度公差不大于0.1mm。The method for identifying rock fracture initiation stress using acoustic emission technology according to claim 1, wherein the rock sample to be tested in the step (1) is a small core with a height of 50 mm and a diameter of 25 mm, and the two ends of the small core are parallel The degree tolerance is not more than 0.1mm.
  3. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(2)中，单轴压缩试验设备采用电液伺服控制的岩石加载***，试验过程中的应力、应变数据能被***采集并自动记录。The method for identifying rock crack initiation stress by using acoustic emission technology according to claim 1, characterized in that, in the step (2), the uniaxial compression test equipment adopts an electro-hydraulic servo-controlled rock loading system, and during the test The stress and strain data can be collected by the system and recorded automatically.
  4. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(3)中，多级循环加载中第一级加载的峰值应力为0.3σ c。 The method for identifying the initiation stress of a rock fracture by using acoustic emission technology according to claim 1, characterized in that, in the step (3), the peak stress of the first-stage loading in the multi-stage cyclic loading is 0.3σ c .
  5. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(3)中，多级循环加载中循环加载间的应力增量为0.05σ c。 The method for identifying the initiation stress of a rock fracture by using acoustic emission technology according to claim 1, characterized in that, in the step (3), the stress increment between cyclic loading in the multi-stage cyclic loading is 0.05σ c .
  6. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(3)中，当岩石声发射信号被换能器检测到后，信号经过放大、过滤处理，超过预定阈值的信号就会被***采集记录，声发射探头和岩芯样品间的接触采用凡士林进行耦合处理。The method for identifying rock fracture initiation stress by using acoustic emission technology according to claim 1, characterized in that, in the step (3), after the rock acoustic emission signal is detected by the transducer, the signal is amplified and filtered Processing, signals exceeding a predetermined threshold will be collected and recorded by the system, and the contact between the acoustic emission probe and the core sample is coupled with petroleum jelly.
  7. 如权利要求1所述的利用声发射技术识别岩石裂缝起裂应力的方法，其特征是，所述步骤(4)中，建立的岩石裂缝起裂应力识别方法为：在多级循环加载声发射试验中，若首次Felicity效应发生在第i次加载过程中，i≥2，那么出现明显声发射信号处的应力值P AE(i)必定小于第i-1次加载的峰值应力P max(i-1)，如果P AE(i)大于第i-2次加载的峰值应力P max(i-2)，那么岩石裂缝起裂应力的识别结果范围为P AE(i)到P max(i-1)，否则，识别结果范围为P max(i-2)到P max(i-1)。 The method for identifying rock crack initiation stress using acoustic emission technology according to claim 1, characterized in that, in said step (4), the established method for identifying rock crack initiation stress is: loading acoustic emission in a multi-stage cycle In the test, if the first Felicity effect occurs during the i-th loading process, i≥2, then the stress value P AE(i) where the obvious acoustic emission signal appears must be less than the peak stress P max(i -1) , if P AE(i) is greater than the peak stress P max(i-2) of the i- 2th load, the identification result of the rock crack initiation stress ranges from P AE(i) to P max(i- 1) Otherwise, the range of the recognition result is P max(i-2) to P max(i-1) .
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