阅读说明：本技术 基于优势声发射震源能量特征的岩石长期强度确定方法 (Rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics ) 是由 龚囱 王文杰 许永斌 赵奎 曾鹏 于 2021-09-26 设计创作，主要内容包括：本发明涉及岩石物理力学性质测试技术领域,公开了一种基于优势声发射震源能量特征的岩石长期强度确定方法,包括以下步骤：对标准岩石试件进行纵波波速测试,在标准岩石试件上布置声发射传感器,对标准岩石试件进行分级蠕变破坏声发射震源定位试验,计算得到各个声发射声发射震源对应的P波到时与初动振幅,对各个声发射震源对应的矩张量进行求解,根据矩张量特征值对声发射震源进行分类,确定优势声发射震源,对各级优势声发射震源的绝对能量进行拾取,计算各级蠕变优势声发射震源的绝对能量平均值,绘制绝对能量平均值-蠕变应力曲线,将绝对能量-蠕变应力曲线上最低点与最低点之后第一个数据点对应的蠕变应力平均值作为岩石平均值为长期强度σ-(∞)。(The invention relates to the technical field of rock physical and mechanical property testing, and discloses a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics, which comprises the following steps: the method comprises the steps of testing the longitudinal wave velocity of a standard rock test piece, arranging acoustic emission sensors on the standard rock test piece, conducting a graded creep rupture acoustic emission source positioning test on the standard rock test piece, calculating the arrival time and the initial motion amplitude of a P wave corresponding to each acoustic emission source, solving a moment tensor corresponding to each acoustic emission source, classifying the acoustic emission sources according to the characteristic values of the moment tensor, determining dominant acoustic emission sources, picking up the absolute energy of each dominant acoustic emission source, calculating the average absolute energy of each grade of creep dominant acoustic emission sources, drawing an average absolute energy-creep stress curve, and corresponding to the lowest point on the absolute energy-creep stress curve and the first data point behind the lowest pointThe average value of the variable stress is the long-term strength sigma as the average value of the rock ∞ 。)

1. A rock long-term strength determination method based on dominant acoustic emission seismic source energy features is characterized by comprising the following steps:

carrying out longitudinal wave velocity test on the standard rock test piece for not less than 6 times to obtain the average value of the longitudinal wave velocity of the rock;

arranging at least 6 acoustic emission sensors on the standard rock test piece, and recording the position coordinates of each acoustic emission sensor;

taking the position coordinates of the acoustic emission sensor and the average value of the longitudinal wave velocity as experiment input parameters, and carrying out a graded creep rupture acoustic emission seismic source positioning experiment on the standard rock test piece to obtain the coordinates of an acoustic emission seismic source;

respectively extracting waveform files corresponding to the acoustic emission sources, calculating to obtain P wave arrival time and initial motion amplitude corresponding to each acoustic emission source, and on the basis, solving the moment tensors corresponding to each acoustic emission source to obtain characteristic values corresponding to each moment tensor;

classifying the acoustic emission seismic sources according to the characteristic values;

determining a dominant acoustic emission source through the type of the acoustic emission source;

picking up absolute energy of each stage of the dominant acoustic emission seismic source in the stage creep rupture acoustic emission seismic source positioning test;

calculating the average value of the absolute energy of the dominant acoustic emission seismic source in each stage of creep process according to the absolute energy;

drawing an absolute energy average value-creep stress curve according to the absolute energy average value of the dominant acoustic emission seismic source in each stage of creep process;

taking the creep stress average value corresponding to the lowest point and the first data point after the lowest point on the absolute energy average value-creep stress curve as the long-term strength sigma of the rock_∞。

2. The method for determining the long-term strength of the rock based on the energy characteristics of the dominant acoustic emission seismic source of claim 1, wherein the step-by-step loading mode of the step-by-step creep rupture acoustic emission source positioning test adopts step-by-step loading, the loading rate is controlled to be between 0.1MPa/s and 0.5MPa/s, and the creep stress of each step is beta sigma_ciWherein σ is_ciBeta is a coefficient whose magnitude is 1.0/1.1/1.2/1.3 … n, n is an arithmetic series with a tolerance of 0.1, and the maximum creep stress n is_maxσ_ciLess than uniaxial compressive strength sigma of rock_cI.e. n_maxσ_ci＜σ_c。

3. The method of determining long-term strength of rock based on dominant acoustic emission source energy signatures of claim 1, wherein the moment tensor is solved by extracting the incipient motion amplitude a of six significant signals_iAnd the distance R and direction cosine R of the seismic source and the sensor, solving six independent components of the moment tensor M according to the formula (1):

in the formula: a (x) -is the initial motion amplitude;

r, R is the distance between the sound source and the sensor and the direction cosine thereof, and is obtained by calculating the coordinates of the sensor and the coordinates of the seismic source;

C_Scalibrating the sensitivity correlation coefficient of the sensor in a lead breaking mode;

ref (t, r) -reaction coefficient, calibrated by a lead-breaking test, taking the value of 2,

due to moment tensorEach element being symmetrical about a diagonal, i.e. mi_j＝m_jiTherefore, the initial motion amplitude A (x), the distance R between the sound source and the sensor, the direction cosine R, and the sensitivity correlation coefficient C of the sensor corresponding to 6 sensors are known_SThe elements m of the moment tensor are in the condition of reaction coefficient Ref (t, r)_ijAnd (6) completing the solution.

4. The method for determining long-term rock strength based on dominant acoustic emission source energy signatures of claim 3, wherein the acoustic emission sources are classified as:

(1) tensor of momentCorresponding 3 characteristic values are obtained, wherein the maximum, middle and minimum characteristic value definitions are defined as lambda_max、λ_int、λ_min；

(2) Normalizing the 3 characteristic values to obtain X, Y and Z, wherein X is lambda_max/λ_max，Y＝λ_int/λ_max，Z＝λ_min/λ_max；

(3) Solving a system of equations

(4) According to the X value, identifying the seismic source type according to the formula (3)

5. The method for determining long-term strength of rock based on dominant acoustic emission source energy signature of claim 1, wherein the method for identifying a type of dominant acoustic emission source during creep rupture comprises:

(1) counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in each stage of creep process, and recording S_iZFor tensioning the seismic source number, S, in the i-th stage creep process_iJShearing the number of seismic sources during i-stage creep, S_iHThe number of mixed seismic sources in the ith-level creep process;

(2) counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in the whole creep process, and recording S_ZFor tensioning the number of seismic sources, S, during the entire creep_JShearing the number of seismic sources, S, for the entire creep process_HAnd correspondingly calculating the number of mixed seismic sources in the whole creep process, namely formula (4):

in the formula: m is the grading frequency;

(3) comparison S_Z、S_J、S_HThe value is the maximum value max (S)_Z,S_J,S_H) The corresponding acoustic emission source of some type is the dominant source.

6. The method of determining long-term strength of rock based on energy characteristics of a dominant acoustic emission source of claim 1, wherein picking up the absolute energy of the dominant acoustic emission source comprises:

for picking up absolute energy of certain determined dominant acoustic emission seismic source, the time-to-time minimum min (T) of P wave of acoustic emission signal is received_i) The corresponding absolute energy value serves as a scale for the magnitude of the absolute energy of the dominant source.

7. The method of determining long-term strength of rock based on dominant acoustic emission source energy signature of claim 1, wherein in the step creep rupture acoustic emission source localization test, note N_YiFor dominant acoustic emission source number, E, during i-stage creep_YiThe sum of the energy of the dominant acoustic emission source in the ith stage creep process is the average absolute energy of the dominant acoustic emission source in each stage creep processCalculated from equation (5):

8. the method of determining long-term intensity of rock based on dominant acoustic emission source energy signatures of claim 1, wherein the long-term intensity of rock σ is determined_∞The determination of (1) comprises:

(1) taking the minimum value of the average absolute energy curve of the creep stress-dominant acoustic emission source as an A point, and expressing the coordinate of the minimum value as a

(2) Taking the first data point after the average absolute energy curve A of the creep stress-dominant acoustic emission source as B, and expressing the coordinates of the first data point as

(3) Taking the coordinate value sigma of the X axis of the point A_iAnd the X-axis coordinate value sigma of point B_i+1Mean value as rock long-term strength σ_∞Value, i.e.

Technical Field

The invention relates to the technical field of rock physical and mechanical property testing, in particular to a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics.

Background

Rock creep is characterized by the phenomenon of rock deformation increasing with time under a certain constant load. Engineering practice shows that: the damage of rock mass in the underground mining process of metal mine is closely related to the rock creep property, and the rock creep property is one of the main factors inducing typical disasters such as roof fall, goaf collapse and the like of metal mine stopes. The strength of the rock decreases with increasing load application time. The long-term strength of the rock is defined as the minimum strength value corresponding to the time when the load action is close to infinity. Therefore, when the creep stress is smaller than the long-term strength σ_∞The rock does not creep and damage. When the creep stress is greater than the long-term strength σ_∞The rock will eventually creep rupture.

Determination of long-term rock strength σ_∞The method mainly comprises a direct method and an indirect method. The direct method is to perform creep tests under different creep stress conditions on a certain number of rock test pieces. On the basis of the above, the maximum creep stress corresponding to the case where the creep rupture does not occur in the rock is defined as the long-term strength σ_∞. As the method needs to creep a plurality of rock test pieces, when the creep stress is slightly larger than the long-term strength sigma_∞The total duration of rock failure can be months or even years. Therefore, this method has a limitation of a long test duration. Meanwhile, the rock is a heterogeneous material, and even the rock with the same lithology in the same production place has different microscopical structures and structures, so that the long-term strength sigma obtained by different test pieces_∞There is also some variability. The indirect method is carried out by carrying out a graded or multistage loading creep test on a single test piece. On the basis, the long-term strength sigma is solved mainly through an isochronous stress-strain curve or an equivalent stress relaxation curve converted from an isochronous stress-strain curve family_∞And the test efficiency is improved to a certain extent. However, rocks are not only heterogeneous materials, but also anisotropic materials. Thus, the axial and transverse creep characteristics of the rock are relatively significantly different, unidirectional creepThe variation characteristics do not represent the overall creep characteristics of the rock. Meanwhile, certain subjectivity and randomness also exist when the inflection point of the relevant curve is selected.

Rock creep failure is essentially the result of the continued evolution of microcracks. When the creep stress is less than the long-term strength σ of the rock_∞And when the creep stress is not enough to enable the rock to generate new microcracks, the rock microcrack evolution mainly shows that the primary microcracks in the rock are gradually compacted along with the increase of creep time, and the rock is not subjected to creep damage. When the creep stress is greater than the long-term strength σ of the rock_∞At the moment, the creep stress already has the capability of promoting the rock to generate new cracks, namely, the new cracks are continuously inoculated, initiated, expanded and communicated along with the increase of creep time, and finally the rock is subjected to creep failure. Theories and practices show that: the evolution process of the rock microcracks is accompanied by an acoustic emission phenomenon, and the spatial-temporal evolution rule of an acoustic emission seismic source is close to the evolution activity of the microcracks. Therefore, the rock creep mesoscopic mechanism is interpreted to a certain extent by researching the evolution rule of the acoustic emission seismic source.

The problems of the prior art are as follows:

(1) the direct method has the limitations of long creep duration and poor timeliness.

(2) The indirect method does not fully consider that the axial and transverse creep characteristics of the rock have relatively obvious difference, and the unidirectional creep characteristics cannot represent the overall creep characteristics of the rock. Meanwhile, certain subjectivity and randomness also exist when the inflection point of the relevant curve is selected.

Disclosure of Invention

The invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics_∞The contact of (2). On the basis, the long-term strength sigma of the rock with clear physical meaning and easy operation is provided_∞And determining a method.

The invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics, which comprises the following steps:

carrying out longitudinal wave velocity test on the standard rock test piece for not less than 6 times to obtain the average value of the longitudinal wave velocity of the rock;

arranging at least 6 acoustic emission sensors on the standard rock test piece, and recording the position coordinates of each acoustic emission sensor;

taking the position coordinates of the acoustic emission sensor and the average value of the longitudinal wave velocity as experiment input parameters, and carrying out a graded creep rupture acoustic emission seismic source positioning experiment on the standard rock test piece to obtain the coordinates of the acoustic emission seismic source;

respectively extracting waveform files corresponding to the acoustic emission sources, calculating to obtain P wave arrival time and initial motion amplitude corresponding to each acoustic emission source, and on the basis, solving moment tensors corresponding to each acoustic emission source to obtain characteristic values corresponding to each moment tensor;

classifying the acoustic emission sources according to the characteristic values;

determining a dominant acoustic emission source according to the type of the acoustic emission source;

picking up absolute energy of each stage of dominant acoustic emission sources in a stage creep rupture acoustic emission source positioning test;

calculating the average value of the absolute energy of the dominant acoustic emission seismic source in each stage of creep process according to the absolute energy;

drawing an absolute energy average value-creep stress curve according to the absolute energy average value of the dominant acoustic emission seismic source in each stage of creep process;

taking the creep stress average value corresponding to the lowest point and the first data point after the lowest point on the absolute energy average value-creep stress curve as the long-term strength sigma of the rock_∞。

Optionally, the step-by-step creep rupture acoustic emission seismic source positioning test loading mode adopts step-by-step loading, the loading rate is controlled to be between 0.1MPa/s and 0.5MPa/s, and the creep stress at each step is beta sigma_ciWherein σ is_ciBeta is a coefficient whose magnitude is 1.0/1.1/1.2/1.3 … n, n is an arithmetic series with a tolerance of 0.1, and the maximum creep stress n is_maxσ_ciLess than uniaxial compressive strength sigma of rock_cI.e. n_maxσ_ci＜σ_c。

Optionally, the solution of the moment tensor is specifically to extract the initial motion amplitude a of the six effective signals_iAnd the distance R and direction cosine R of the seismic source and the sensor, solving six independent components of the moment tensor M according to the formula (1):

in the formula: a (x) -is the initial motion amplitude;

r, R is the distance between the sound source and the sensor and the direction cosine thereof, and is obtained by calculating the coordinates of the sensor and the coordinates of the seismic source;

C_Scalibrating the sensitivity correlation coefficient of the sensor in a lead breaking mode;

ref (t, r) -reaction coefficient, which can be calibrated by a lead-breaking test and takes the value of 2,

due to moment tensorEach element being symmetrical about a diagonal, i.e. mi_j＝m_jiTherefore, the initial motion amplitude A (x), the distance R between the sound source and the sensor, the direction cosine R, and the sensitivity correlation coefficient C of the sensor corresponding to 6 sensors are known_SThe elements m of the moment tensor are in the condition of reaction coefficient Ref (t, r)_ijAnd (6) completing the solution.

Optionally, the acoustic emission seismic source is classified specifically as:

(1) tensor of momentCorresponding 3 characteristic values are obtained, wherein the maximum, middle and minimum characteristic value definitions are defined as lambda_max、λ_int、λ_min；

(2) Normalizing the 3 characteristic values to obtain X, Y and Z, wherein X is lambda_max/λ_max，Y＝λ_int/λ_max，Z＝λ_min/λ_max；

(3) Solving a system of equations

(4) According to the X value, identifying the seismic source type according to the formula (3)

Optionally, the method for identifying the type of the dominant acoustic emission source in the creep rupture process includes:

(1) counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in each stage of creep process, and recording S_iZFor tensioning the seismic source number, S, in the i-th stage creep process_iJShearing the number of seismic sources during i-stage creep, S_iHThe number of mixed seismic sources in the ith-level creep process;

(2) counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in the whole creep process, and recording S_ZFor tensioning the number of seismic sources, S, during the entire creep_JShearing the number of seismic sources, S, for the entire creep process_HAnd correspondingly calculating the number of mixed seismic sources in the whole creep process, namely formula (4):

in the formula: m is the grading frequency;

(3) comparison S_Z、S_J、S_HThe value is the maximum value max(S_Z,S_J,S_H) The corresponding acoustic emission source of some type is the dominant source.

Optionally, picking up the absolute energy of the dominant acoustic emission source includes:

for picking up absolute energy of certain determined dominant acoustic emission seismic source, the time-to-time minimum min (T) of P wave of acoustic emission signal is received_i) The corresponding absolute energy value serves as a scale for the magnitude of the absolute energy of the dominant source.

Optionally, in the positioning test of the graded creep rupture acoustic emission seismic source, recording N_YiFor dominant acoustic emission source number, E, during i-stage creep_YiThe sum of the energy of the dominant acoustic emission source in the ith stage creep process is the average absolute energy of the dominant acoustic emission source in each stage creep processCalculated from equation (5):

optionally, long term rock strength σ_∞The determination of (1) comprises:

(1) taking the minimum value of the average absolute energy curve of the creep stress-dominant acoustic emission source as an A point, and expressing the coordinate of the minimum value as a

(2) Taking the first data point after the average absolute energy curve A of the creep stress-dominant acoustic emission source as B, the coordinate of the first data point can be expressed as

(3) Taking the coordinate value sigma of the X axis of the point A_iAnd the X-axis coordinate value sigma of point B_i+1Mean value as rock long-term strength σ_∞Value, i.e.

Compared with the prior art, the invention has the beneficial effects that: the invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics. On the basis, the long-term rock strength is determined according to the absolute energy change characteristics corresponding to the dominant acoustic emission seismic source type. The method fully considers the relationship between the type of the acoustic emission seismic source and the macroscopic failure mode of the rock in the creep process of different types of rocks, builds the relation between the long-term strength of the rock and microcracks in the rock failure process, has the characteristics of clear physical significance and easiness in operation, and is an effective supplement of the method for determining the long-term strength of the rock.

Drawings

FIG. 1 is a standard cylindrical test piece provided in example 1 of the present invention;

FIG. 2 is a drawing of relative coordinates of a standard cylindrical test piece provided in embodiment 1 of the present invention;

FIG. 3 is a diagram showing a sensor arrangement provided in embodiment 1 of the present invention;

fig. 4 is a schematic diagram of a loading manner and a loading rate according to embodiment 1 of the present invention;

FIG. 5 is a result of the calculation of the spatial coordinates of the seismic source provided in embodiment 1 of the present invention;

FIG. 6 shows the arrival time t of P-wave provided in embodiment 1 of the present invention_iAnd initial amplitude A_iPicking up;

FIG. 7 is a schematic diagram of absolute energy picking up of a dominant acoustic emission seismic source provided in embodiment 1 of the present invention;

FIG. 8 is a graph of the average absolute energy of a creep stress-dominant acoustic emission source provided in example 1 of the present invention;

FIG. 9 shows the long-term intensity σ provided in example 1 of the present invention_∞Determining a schematic diagram;

FIG. 10 is a standard cylindrical rock specimen provided in example 2 of the present invention;

FIG. 11 is a schematic diagram of the main equipment provided in example 2 of the present invention, in which FIG. (a) is a three-axis rheometer and FIG. (b) is an acoustic emission sensor;

fig. 12 is a drawing of relative coordinates of a standard cylindrical test piece provided in embodiment 2 of the present invention;

FIG. 13 is a layout diagram of a Nano30 type acoustic emission sensor provided in embodiment 2 of the present invention;

FIG. 14 is a schematic structural diagram of a rock longitudinal wave velocity test provided in embodiment 2 of the present invention;

FIG. 15 is a result of the calculation of the spatial coordinates of the seismic source provided in embodiment 2 of the present invention;

fig. 16 shows the recognition result of the shearing source provided in embodiment 2 of the present invention;

fig. 17 shows the identification result of the tension seismic source according to embodiment 2 of the present invention;

FIG. 18 is a mixed source identification provided in embodiment 2 of the present invention;

FIG. 19 is a graph of the average absolute energy of the creep stress-dominant acoustic emission source provided in example 2 of the present invention;

FIG. 20 shows the long-term intensity σ provided in example 2 of the present invention_∞Determination of (1);

FIG. 21 shows the steady-state creep rate method for long-term strength σ in example 2 of the present invention_∞And (4) determining.

Detailed Description

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the embodiment.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing technical solutions of the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

Determination of long-term rock strength σ_∞The method mainly comprises a direct method and an indirect method. The direct method is to perform creep tests under different creep stress conditions on a certain number of rock test pieces. On the basis of the above, the maximum creep stress corresponding to the case where the creep rupture does not occur in the rock is defined as the long-term strength σ_∞. As the method needs to creep a plurality of rock test pieces, when the creep stress is slightly larger than the long-term strength sigma_∞The total duration of rock failure can be months or even years. Therefore, this method has a limitation of a long test duration. Meanwhile, the rock is a heterogeneous material, and even the rock with the same lithology in the same production place has different microscopical structures and structures, so that the long-term strength sigma obtained by different test pieces_∞There is also some variability. The indirect method is carried out by carrying out a graded or multistage loading creep test on a single test piece. On the basis, the long-term strength sigma is solved mainly through an isochronous stress-strain curve or an equivalent stress relaxation curve converted from an isochronous stress-strain curve family_∞And the test efficiency is improved to a certain extent. However, rocks are not only heterogeneous materials, but also anisotropic materials. Therefore, the axial and transverse creep characteristics of the rock are relatively obvious, and the unidirectional creep characteristics cannot represent the overall creep characteristics of the rock. Meanwhile, certain subjectivity and randomness also exist when the inflection point of the relevant curve is selected.

Rock creep failure is essentially the result of the continued evolution of microcracks. When the creep stress is less than the long-term strength σ of the rock_∞And when the creep stress is not enough to enable the rock to generate new microcracks, the rock microcrack evolution mainly shows that the primary microcracks in the rock are gradually compacted along with the increase of creep time, and the rock is not subjected to creep damage. When the creep stress is greater than the long-term strength σ of the rock_∞At the moment, the creep stress already has the capability of promoting the rock to generate new cracks, namely, the new cracks are continuously inoculated, initiated, expanded and communicated along with the increase of creep time, and finally the rock is subjected to creep failure. Theories and practices show that: evolution of rock microcracksThe spatial-temporal evolution rule of the acoustic emission source is close to the micro-crack evolution activity along with the acoustic emission phenomenon in the process. Therefore, the rock creep mesoscopic mechanism is interpreted to a certain extent by researching the evolution rule of the acoustic emission seismic source.

The problems of the prior art are as follows:

(1) the direct method has the limitations of long creep duration and poor timeliness.

(2) The indirect method does not fully consider that the axial and transverse creep characteristics of the rock have relatively obvious difference, and the unidirectional creep characteristics cannot represent the overall creep characteristics of the rock. Meanwhile, certain subjectivity and randomness also exist when the inflection point of the relevant curve is selected.

Based on the problems, the invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics, which tries to establish microcrack (acoustic emission seismic source) evolution characteristics and long-term strength sigma in the rock creep rupture process_∞The contact of (2). On the basis, the long-term strength sigma of the rock with clear physical meaning and easy operation is provided_∞And determining a method.

The invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics, which comprises the following steps:

carrying out longitudinal wave velocity test on the standard rock test piece for not less than 6 times to obtain the average value of the longitudinal wave velocity of the rock;

arranging at least 6 acoustic emission sensors on the standard rock test piece, and recording the position coordinates of each acoustic emission sensor;

taking the position coordinates of the acoustic emission sensor and the average value of the longitudinal wave velocity as experiment input parameters, and carrying out a graded creep rupture acoustic emission seismic source positioning experiment on the standard rock test piece to obtain the coordinates of the acoustic emission seismic source;

respectively extracting waveform files corresponding to the acoustic emission sources, calculating to obtain P wave arrival time and initial motion amplitude corresponding to each acoustic emission source, and on the basis, solving moment tensors corresponding to each acoustic emission source to obtain characteristic values corresponding to each moment tensor;

classifying the acoustic emission sources according to the characteristic values;

determining a dominant acoustic emission source according to the type of the acoustic emission source;

picking up absolute energy of each stage of dominant acoustic emission sources in a stage creep rupture acoustic emission source positioning test;

calculating the average value of the absolute energy of the dominant acoustic emission seismic source in each stage of creep process according to the absolute energy;

drawing an absolute energy average value-creep stress curve according to the absolute energy average value of the dominant acoustic emission seismic source in each stage of creep process;

taking the creep stress average value corresponding to the lowest point and the first data point after the lowest point on the absolute energy average value-creep stress curve as the long-term strength sigma of the rock_∞。

The invention provides a rock long-term strength determination method based on dominant acoustic emission seismic source energy characteristics. On the basis, the long-term rock strength is determined according to the absolute energy change characteristics corresponding to the dominant acoustic emission seismic source type. The method fully considers the relationship between the type of the acoustic emission seismic source and the macroscopic failure mode of the rock in the creep process of different types of rocks, builds the relation between the long-term strength of the rock and microcracks in the rock failure process, has the characteristics of clear physical significance and easiness in operation, and is an effective supplement of the method for determining the long-term strength of the rock.

The invention is suitable for the long-term strength sigma of the rock under the condition of uniaxial compression_∞The method of (1). The complete technical scheme comprises the following steps: preparing a standard rock test piece, performing a rock creep rupture acoustic emission source positioning test, solving a moment tensor, identifying the type of an acoustic emission source and identifying the long-term strength sigma_∞And determining the composition of the five parts.

Example 1:

1.1 preparation of Standard rock test pieces

And preparing a test piece according to the Standard of engineering rock testing methods (GB/T50266-2013). The test piece may be prepared from a drilled core or piece of rock. Take a cylinder with a standard diameter of 50mm and a height of 100mm as an example. The instrumentation required for specimen preparation included: core drilling machine, cutting machine, stone grinding machine, etc. The core drilling machine is used for drilling a core with the diameter of 50mm and the height of more than 100 mm. The cutting machine is used for cutting the drilled core to obtain a cylindrical core with the diameter of 50mm and the height of slightly more than 100 mm. The grinding machine is used for polishing the end face of the cut cylindrical rock core, and finally a cylinder with the diameter of 50mm and the height of 100mm is obtained. In order to ensure the test accuracy, the non-parallelism of the two end faces of the test piece is less than 0.05mm, the diameter error is less than 0.3mm along the height direction of the test piece, the end face of the test piece is perpendicular to the axis of the test piece, and the deviation is less than 0.25 degrees. The standard cylindrical test piece is shown in figure 1.

1.2 Acoustic emission seismic source positioning test in rock creep process

1.2.1 instruments and devices

The required instruments and equipment include: the device comprises a rigid press with a creep function, an acoustic emission instrument, an acoustic emission sensor, a related fixing device, an acoustic emission instrument, a strain gauge and the like. The rigid press machine has the function of automatically acquiring axial stress (force) and axial strain (displacement). If the axial strain (displacement) cannot be acquired, a strain gauge can be pasted on the test piece instead. The acoustic emission instrument has a three-dimensional positioning function, and a PCI-2 system is suggested to be prepared by the PAC acoustic emission instrument. The acoustic emission sensor suggests a Nano30 sensor. The sound wave instrument is used for testing the longitudinal wave velocity of the rock test piece, and an RSM-RCT (B) sound wave instrument is suggested.

1.2.2 Standard Cylinder relative coordinate compilation

In order to facilitate the installation and positioning of the acoustic emission sensor and the calculation of the space coordinates of the seismic source, the relative coordinates of the standard cylinder are compiled. The method comprises the following steps:

(1) and establishing a space coordinate system by taking the center of the bottom surface of the test piece as a coordinate origin, the lower end surface of the test piece as an X-Y plane and the axial direction of the test piece as a Z axis.

(2) And taking the X axis as a starting point, marking the X axis as a 0-degree scale mark, and drawing parallel lines of the Z axis at intervals of 30 degrees along the surface of the test piece anticlockwise.

(3) Taking the X-Y plane as a starting point, and making circumference lines every 10mm along the Z-axis direction. The relative coordinates of the test piece are compiled and are shown in figure 2.

1.2.3 Acoustic emission sensor arrangement

The method comprises the following steps of symmetrically arranging 8 acoustic emission sensors in total:

(1) the pencil is used to make a straight line L1 along the axial direction of the surface of the test piece. And precisely measuring points which are 10mm away from the upper end surface and the lower end surface along the linear direction by using a vernier caliper, and taking the two points (the point No. 2 and the point No. 6) as the central points of the arrangement positions of the acoustic emission sensors.

(2) And taking the axis of the test piece as a symmetrical line L2 of L1, and taking symmetrical points of No. 2 point and No. 6 point as the arrangement center points of No. 4 and No. 8 sensors.

(3) Similarly, straight lines L3 and L4 are drawn along the surface of the test piece respectively, the plane formed by L3 and L4 is perpendicular to the plane formed by L1 and L2, and the arrangement center points of the remaining sensors No. 1 and No. 5, and No. 3 and No. 7 are determined.

(4) And finally, respectively calculating and recording the coordinates of the arrangement center points of the 8 sensors by taking the center of the bottom surface of the test piece as a coordinate origin. The arrangement of the seismic source positioning sensors is shown schematically in FIG. 3.

1.2.4 rock longitudinal wave velocity test

And (3) testing the longitudinal wave velocity of the rock by using an RSM-RCT (B) sound wave instrument for not less than 5 times, and taking an average value as a calculation parameter for seismic source positioning.

1.2.5 implementation of rock creep rupture acoustic emission seismic source positioning test

(1) Loading mode and loading rate

The loading mode of the positioning test of the creeping acoustic emission seismic source adopts graded loading, and the loading rate is recommended to be controlled between 0.1MPa/s and 0.5 MPa/s. The creep stress at each stage is suggested to be beta sigma_ci. Wherein σ_ciBeta is a coefficient whose magnitude is 1.0/1.1/1.2/1.3 … n (n is an arithmetic series with a tolerance of 0.1) for the rock initiation strength under uniaxial compression, and the maximum creep stress n_maxσ_ciShould be less than uniaxial compressive strength sigma of rock_cI.e. n_maxσ_ci＜σ_c. For crack initiation strength σ_ciThe determination of the crack is suggested to be carried out by adopting a crack strain model calculation methodAnd (5) solving. The loading mode and the loading rate are shown schematically in FIG. 4.

(2) Acoustic emission acquisition parameter settings

The setting of acoustic emission parameters is related to the rock type and the test environment. Different rocks have different acoustic emission parameters under different test environments. Taking the red sandstone acoustic emission test as an example, the acoustic emission parameters are set, and see table 1.

TABLE 1 Acoustic emission parameter settings

(3) And (3) completing the test of the longitudinal wave velocity of the test piece, placing the test piece in a rigid press with a creep function, completing the setting of loading rate, acoustic emission acquisition parameters and the like, and performing a rock destruction acoustic emission seismic source positioning test. Wherein, the rigid press and the acoustic emission acquisition time are required to be ensured to be synchronously carried out, namely the acquisition starting time of the rigid press and the acquisition starting time of the acoustic emission acquisition time are the same.

(4) Seismic source spatial coordinate calculation

The acoustic emission source coordinates may be calculated by a second-most multiplication, a simplex algorithm, or the like. Meanwhile, the acoustic emission instrument can also directly obtain the acoustic emission signal.

As an example, the PAC acoustic emission instrument is used for positioning results, and the seismic source positioning results are shown in FIG. 5.

1.3 moment tensor solution

The acoustic emission source type identification comprises the following steps: selection of waveform file, P wave arrival time t_iAnd initial amplitude A_iThe method comprises the following four parts of picking, moment tensor solving and type identification.

1.3.1 selection of waveform files

In acoustic emission source positioning, for calculation of the generation time and corresponding spatial coordinates of an acoustic emission source, a minimum of 4 waveform files collected by acoustic emission sensors are required. However, the acoustic emission seismic source type identification based on the moment tensor analysis can be realized only by the waveform file acquired by the 6 acoustic emission sensors at least. Thus, the number of sources corresponding to a type of acoustic emission source is theoretically less than the number of sources corresponding to an acoustic emission source location.

According to the actual number of acoustic emission source localizations, a waveform file corresponding to a single acoustic emission source type identification is generally extracted by two methods. First, the number of seismic source locations is small, and the seismic source locations can be directly extracted manually. Secondly, the seismic sources can be extracted in batch by programming related programs according to the storage rule of the acoustic emission instrument waveform file when the number of seismic source positioning is large.

1.3.2P wave arrival time t_iAnd initial amplitude A_iIs picked up

Taking 6 acoustic emission sensors as an example, the information about the seismic source is acquired by 6 acoustic emission sensors "at the same time".

(1) According to the physical criteria of Chichi information (AIC), using F_C3And simultaneously selecting a point from the signal starting point to the point with the maximum energy change as a detection interval as a characteristic function of the arrival time of the picked P wave. The AIC function value was calculated as in equation (1-1):

AIC(k_w)＝k_w·log(var(R_w(1,k_w)))+(n_w-k_w-1)·log(var(R_w(1+k_w,n_w))) (1-1)

in the formula: r_w、k_w-time series for the selected window and all time series, respectively.

var、n_w-is the variance function and the sample length.

(2) Taking the minimum point of the AIC function as the arrival time t of the P wave_i。

(3) With t_iThen the first maximum point in the amplitude is used as the initial motion amplitude A_iThe value of (c).

Therefore, 6 sets of P-wave arrival times t can be obtained for 6 acoustic emission sensors_iAnd initial amplitude A_i。

Taking a certain sensor as an example: p wave arrival time t_iAnd initial amplitude A_iAnd solving, such as fig. 6.

1.3.3 moment tensor solution

By extracting the initial amplitude A of six effective signals_iAnd distance of the seismic source from the sensorR and the direction cosine R. The moment tensor M six independent components are solved according to equation (1):

in the formula: a (x) -is the initial motion amplitude;

r, R is the distance between the sound source and the sensor and the direction cosine thereof, which can be calculated by the sensor coordinate and the seismic source coordinate;

C_Sthe sensor sensitivity correlation coefficient can be calibrated in a lead breaking mode;

ref (t, r) -reaction coefficient, which can be calibrated by the lead-breaking test, usually taken as 2.

Due to moment tensorEach element being symmetrical about a diagonal, i.e. m_ij＝m_ji. Therefore, the initial motion amplitude A (x), the distance R between the sound source and the sensor, the direction cosine R, and the sensitivity correlation coefficient C of the sensor corresponding to 6 sensors are known_SThe elements m of the moment tensor are in the condition of reaction coefficient Ref (t, r)_ijThe solution may be completed.

1.4 Source type identification

(1) Tensor of momentCorresponding 3 characteristic values are obtained, wherein the maximum, middle and minimum characteristic value definitions are defined as lambda_max、λ_int、λ_min。

(2) And carrying out normalization processing on the 3 characteristic values to obtain X, Y and Z. Wherein X ═ λ_max/λ_max,Y＝λ_int/λ_max，Z＝λ_min/λ_max。

(3) Solving equation set (2)

(4) According to the X value, identifying the seismic source type according to the formula (3)

1.5 Long-term Strength σ_∞Determining

1.5.1 identification of dominant acoustic emission seismic source type in creep rupture process

The existing tests show that: given the same shape, size and loading, an acoustic emission source of a certain type will "run through" the entire rock destruction process, and be the largest in number. The invention defines the seismic source as a dominant seismic source, and the identification method comprises the following steps:

(1) and counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in the creep process of each stage. Note S_iZFor tensioning the seismic source number, S, in the i-th stage creep process_iJShearing the number of seismic sources during i-stage creep, S_iHThe number of mixed sources in the i-th stage creep process.

(2) And counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in the whole creep process. Note S_ZFor tensioning the number of seismic sources, S, during the entire creep_JShearing the number of seismic sources, S, for the entire creep process_HThe number of sources is blended throughout the creep process. Corresponding calculation, see formula (4):

in the formula: m is the grading times.

(3) Comparison S_Z、S_J、S_HThe value is the maximum value max (S)_Z,S_J,S_H) The corresponding acoustic emission source of some type is the dominant source.

1.5.2 dominant acoustic emission seismic source absolute energy pickup

The method for identifying the type of the seismic source comprises the following steps: for a certain determined dominant acoustic emission source, it corresponds to a minimum of 6 acoustic emission waveform files. I.e. for a certain determined dominant acoustic emission source, there are a minimum of 6 absolute energy values. Space coordinates often have some "randomness" due to the individual acoustic emission sources. Thus, in the usual case, the distance L of a single source to each sensor receiving a signal_iNot equal, resulting in the time T for each sensor to receive the acoustic emission signal even under certain rock wave velocity conditions_iAnd not the same. Meanwhile, the attenuation characteristic of the absolute energy of the acoustic emission seismic source in the propagation process is considered. The invention proposes to pick up the absolute energy of a certain determined dominant acoustic emission source so as to receive the arrival-time minimum min (T) of the P wave of the acoustic emission signal_i) The corresponding absolute energy value serves as a scale for the magnitude of the absolute energy of the dominant source. Taking FIG. 7 as an example, assume time T corresponding to the 2# sensor receiving the acoustic emission signal₂If the numerical value is minimum, the 2# sensor is adopted to acquire the absolute energy E of the acoustic emission₂As the dominant source absolute energy magnitude.

1.5.3 calculation of mean absolute energy of dominant acoustic emission seismic source in creep process of each stage

And counting the number and absolute energy of dominant acoustic emission sources in each stage of creep process. Note N_YiFor dominant acoustic emission source number, E, during i-stage creep_YiThe sum of the energy of the dominant acoustic emission source in the ith stage creep process is the average absolute energy of the dominant acoustic emission source in each stage creep processCan be calculated from equation (5):

1.5.4 drawing dominant acoustic emission seismic source average absolute energy curve under creep stress conditions of all levels

At each stage creep stress σ_iIs an X axis, and the average absolute energy E of a dominant acoustic emission seismic source in each stage of creep process_YiThe average absolute energy curve of the creep stress-dominant acoustic emission source is plotted for the Y-axis, as shown in fig. 8.

1.5.4 Long term intensity σ_∞Determining

(1) Taking the minimum value of the average absolute energy curve of the creep stress-dominant acoustic emission source as an A point, and the coordinate of the minimum value can be expressed as

(2) Taking the first data point after the average absolute energy curve A of the creep stress-dominant acoustic emission source as B, the coordinate of the first data point can be expressed as

(3) Taking the coordinate value sigma of the X axis of the point A_iAnd the X-axis coordinate value sigma of point B_i+1Mean value as rock long-term strength σ_∞Value, i.e.

Long term strength σ_∞See fig. 9. It should be noted that: if necessary to increase the long-term strength σ_∞The creep stress increment delta sigma of each stage can be adjusted according to the requirement. Wherein, delta sigma is sigma_i-σ_i-1。

Example 2

2.1 preparation of Standard rock test pieces

Cylindrical rock test pieces with the diameter of 50mm and the height of 100mm are prepared according to the Standard of engineering rock testing methods (GB/T50266-2013), and are shown in figure 10.

2.2 Acoustic emission seismic source positioning test in rock creep process

2.2.1 instruments and apparatus

The test loading instrument, namely the rigid pressure, adopts a GDS VIS 400kN HPTAS triaxial rheometer, the acoustic emission positioning is completed by a PCI-2 acoustic emission system, and meanwhile, a Nano30 type acoustic emission sensor is matched, and the rock longitudinal wave velocity test adopts an RSM-RCT (B) acoustic wave instrument. The main equipment is shown in figure 11.

2.2.2 Standard Cylinder relative coordinate compilation

In order to facilitate the installation and positioning of the acoustic emission sensor and the calculation of the space coordinates of the seismic source, the relative coordinates of the standard cylinder are compiled. The method comprises the following steps:

(1) and establishing a space coordinate system by taking the center of the bottom surface of the test piece as a coordinate origin, the lower end surface of the test piece as an X-Y plane and the axial direction of the test piece as a Z axis.

(2) And taking the X axis as a starting point, marking the X axis as a 0-degree scale mark, and drawing parallel lines of the Z axis at intervals of 30 degrees along the surface of the test piece anticlockwise.

(3) Taking the X-Y plane as a starting point, and making circumference lines every 10mm along the Z-axis direction.

The relative coordinates of the test piece are compiled and are shown in fig. 12.

2.2.3 Acoustic emission sensor arrangement

The method comprises the following steps of symmetrically arranging 8 acoustic emission sensors in total:

(1) the pencil is used to make a straight line L1 along the axial direction of the surface of the test piece. And precisely measuring points which are 10mm away from the upper end surface and the lower end surface along the linear direction by using a vernier caliper, and taking the two points (the point No. 2 and the point No. 6) as the central points of the arrangement positions of the acoustic emission sensors.

(2) And taking the axis of the test piece as a symmetrical line L2 of L1, and taking symmetrical points of No. 2 point and No. 6 point as the arrangement center points of No. 4 and No. 8 sensors.

(3) Similarly, straight lines L3 and L4 are drawn along the surface of the test piece respectively, the plane formed by L3 and L4 is perpendicular to the plane formed by L1 and L2, and the arrangement center points of the remaining sensors No. 1 and No. 5, and No. 3 and No. 7 are determined.

(4) And finally, respectively calculating and recording the coordinates of the arrangement center points of the 8 sensors by taking the center of the bottom surface of the test piece as a coordinate origin. The seismic source location sensor arrangement is schematically shown in FIG. 13.

2.2.4 rock longitudinal wave velocity test

And (3) testing the longitudinal wave velocity of the rock by using an RSM-RCT (B) sound wave instrument for not less than 5 times, and taking an average value as a calculation parameter for seismic source positioning. Test procedure, see fig. 14.

2.2.5 implementation of acoustic emission seismic source positioning test in rock creep process

The acoustic emission seismic source positioning is completed by a GDS VIS 400kN HPTAS triaxial rheometer and a PCI-2 acoustic emission system. The loading mode of the positioning test of the creeping acoustic emission seismic source adopts graded loading, and the loading rate is 0.1 MPa/s. Taking red sandstone as an example, the rock average uniaxial compressive strength is about 60.35MPa and the fracture initiation stress is about 30.00MPa according to a uniaxial compression test. In the test, the graded creep stress is 23MPa, 27MPa, 31MPa, 35MPa, 39MPa, 42MPa and 45MPa respectively, and the values are about 0.80, 0.90, 1.03, 1.16, 1.30, 1.40 and 1.50 times of the initiation stress respectively. Acoustic emission parameter settings, see table 1. The calculation of the space coordinates of the seismic source is completed by a PCI-2 acoustic emission system. FIG. 15 shows the positioning results of the seismic source under a certain creep stress condition.

2.3 moment tensor solution

And screening out 6 and more waveform files corresponding to the seismic sources on the basis of acoustic emission seismic source positioning. The Chichi information principle (AIC) takes the minimum point of the AIC function as the arrival time t of the P wave_iWith t_iThen the first maximum point in the amplitude is used as the initial motion amplitude A_iThe value of (c).

Taking 6 waveform files corresponding to a certain seismic source as an example, the calculation results are shown in table 2. Wherein each sensor actually receives a signal time T_iIs equal to the time T recorded by the acoustic emission instrument_jAnd the arrival time t of P wave_iThe difference between them.

TABLE 2P wave arrival time and initial motion amplitude calculation results

The moment tensor M six independent components are solved according to equation (6):

in the formula: a (x) -is the initial motion amplitude;

r, R is the distance between the sound source and the sensor and the direction cosine thereof, which can be calculated by the sensor coordinate and the seismic source coordinate;

C_Sthe sensor sensitivity correlation coefficient can be calibrated in a lead breaking mode;

ref (t, r) -reaction coefficient, which can be calibrated by the lead-breaking test, usually taken as 2.

The solution result is shown in formula (7):

2.4 Source type identification

The normalized characteristic value of equation (7) is [ -0.3510.0141.597 ]. The source type is identified as per equation (8). The calculation result shows that: wherein the relative proportion of X is 22.865%, the relative proportion of Y is 50.833%, and the relative proportion of Z is 26.302%. Thus, the seismic source is a tension type seismic source.

Corresponding to FIG. 15 as an example, FIGS. 16-18 show the identification results of shear, tension and hybrid seismic sources under a certain creep stress condition.

2.5 Long-term Strength σ_∞Determining

2.5.1 identifying dominant acoustic emission seismic source type in creep rupture process

(1) And counting the number of shearing seismic sources, tensioning seismic sources and mixed seismic sources in the creep process of each stage. Note S_iZFor tensioning the seismic source number, S, in the i-th stage creep process_iJShearing the number of seismic sources during i-stage creep, S_iHThe number of mixed sources in the i-th stage creep process.

(2) In the whole creep process, a shearing seismic source, a tensioning seismic source and a mixed seismic source are countedThe number of the cells. Note S_ZFor tensioning the number of seismic sources, S, during the entire creep_JShearing the number of seismic sources, S, for the entire creep process_HThe number of sources is blended throughout the creep process. Corresponding calculation, see formula (9):

in the formula: m is the grading times.

(3) Comparison S_Z、S_J、S_HThe value is the maximum value max (S)_Z,S_J,S_H) The corresponding acoustic emission source of some type is the dominant source.

The number of each type of acoustic emission seismic source under all levels of creep stress conditions is shown in table 3, and the shear type seismic sources are the most. Therefore, a shear-open type seismic source is an advantageous seismic source.

TABLE 3 number of acoustic emission sources of each type under creep stress conditions of each stage

2.5.2 dominant acoustic emission seismic source absolute energy pickup

Table 2 shows that a seismic source signal is acquired by 6 acoustic emission sensors, and 6 waveform files are correspondingly generated. As can be seen from table 2: p-wave arrival time t through 6 waveform files generated by 6 sensors_iIs calculated and recorded by the PCI-2 acoustic emission system as time T_jThe actual signal receiving time of the 3# sensor is 12.3597278s as the minimum. Therefore, the absolute energy collected by the 3# sensor is selected asIs the absolute energy scale of the source.

2.5.3 calculation of mean absolute energy of dominant acoustic emission seismic source in each stage of creep process

And counting the number and absolute energy of dominant acoustic emission sources in each stage of creep process. Note N_YiFor dominant acoustic emission source number, E, during i-stage creep_YiThe sum of the energy of the dominant acoustic emission source in the ith stage creep process is the average absolute energy of the dominant acoustic emission source in each stage creep processCan be calculated from equation (10):

2.5.4 drawing of mean absolute energy curve of dominant acoustic emission seismic source under all levels of creep stress conditions

At each stage creep stress σ_iIs an X axis, and the average absolute energy of the acoustic emission seismic source in the process of each stage of creep is taken as the dominant acoustic emissionFor the Y-axis, a creep stress-dominant acoustic emission source mean absolute energy curve is plotted, as shown in fig. 19.

2.5.4 Long-term Strength σ_∞Determining

FIG. 19 shows that the dominant acoustic emission source mean absolute energy progressively decreases with increasing creep stress when the creep stress is 39MPa or less; when the creep stress is more than or equal to 39MPa, the average absolute energy of the dominant acoustic emission seismic source is gradually increased along with the increase of the creep stress; the mean absolute energy of the dominant acoustic emission source is the smallest at a creep of 39MPa, which is about 39 aJ.

(1) And taking the minimum value of the average absolute energy curve of the creep stress-dominant acoustic emission source as the point A.

(2) And taking the first data point after the A point of the average absolute energy curve of the creep stress-dominant acoustic emission source as B.

(3) Get the point AThe average value of the X-axis coordinate value and the X-axis coordinate value of the point B is used as the long-term strength sigma of the rock_∞Value, i.e.As an example, the long-term intensity σ_∞See fig. 20.

By way of comparison, FIG. 21 shows the steady state creep rate method long term strength σ_∞The result was 39.6 MPa. The difference between the two is 0.9MPa, further explaining the long-term strength sigma provided by the invention_∞A determination method is feasible.

The above disclosure is only for a few specific embodiments of the present invention, however, the present invention is not limited to the above embodiments, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.