阅读说明：本技术 一种基于矩张量分析的岩石声发射参数确定方法及系统 (Rock acoustic emission parameter determination method and system based on moment tensor analysis ) 是由 翟梦阳 薛雷 步丰畅 黄晓林 张珂 许超 于 2021-10-18 设计创作，主要内容包括：本发明涉及一种基于矩张量分析的岩石声发射参数确定方法及系统,该方法包括：根据宏观力学参数构建待测试岩石试样的数值模型；通过PFC软件加载数值模型,模拟待测试岩石试样的破坏过程,在PFC软件加载数值模型的过程中识别各微裂纹的破裂时间和位置；在PFC软件加载数值模型的过程中,若依次产生的两个微裂纹的岩石晶粒中有共同的岩石晶粒,且两个微裂纹产生的时间间隔小于当前声发射事件的持续时间,则两个微裂纹为同一声发射事件；将声发射事件的空间范围内的所有微裂纹位置的几何中心作为对应声发射事件的震源位置；根据矩张量分析的方法确定各声发射事件的声发射参数。本发明能够确定各声发射事件的震源位置和声发射参数。(The invention relates to a rock acoustic emission parameter determination method and a system based on moment tensor analysis, wherein the method comprises the following steps: constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; loading a numerical model through PFC software, simulating the damage process of the rock sample to be tested, and identifying the fracture time and position of each microcrack in the process of loading the numerical model through the PFC software; in the process of loading the numerical model by the PFC software, if the rock grains of the two sequentially generated microcracks have a common rock grain and the time interval generated by the two microcracks is less than the duration of the current acoustic emission event, the two microcracks are the same acoustic emission event; taking the geometric centers of all microcrack positions within the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event; and determining the acoustic emission parameters of each acoustic emission event according to a moment tensor analysis method. The method can determine the seismic source position and the acoustic emission parameters of each acoustic emission event.)

1. A rock acoustic emission parameter determination method based on moment tensor analysis is characterized by comprising the following steps:

acquiring macroscopic mechanical parameters of a rock sample to be tested;

constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model comprises a plurality of rock crystal grains, and the rock crystal grains are bonded through a cementing material;

loading the numerical model through PFC software, simulating the damage process of the rock sample to be tested, and identifying the fracture time and position of each microcrack in the process of loading the numerical model through the PFC software; the fracture of each bonding point among all rock crystal grains represents a micro-crack in the process of loading the numerical model by the PFC software;

in the process of loading the numerical model by the PFC software, if the rock grains of the two sequentially generated microcracks have a common rock grain and the time interval generated by the two microcracks is less than the duration time of the current acoustic emission event, the two microcracks are the same acoustic emission event; the initial duration of the current acoustic emission event is the duration of generation of the first microcrack of the current acoustic emission event, the duration of generation of the microcrack is the propagation time of the crack in the larger diameter of the two rock grains generating the microcrack, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested;

taking the spatial range covered by all the microcracks corresponding to one acoustic emission event as the spatial range corresponding to the acoustic emission event, and taking the geometric centers of all the microcrack positions in the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event;

and determining the acoustic emission parameters of each acoustic emission event according to a moment tensor analysis method.

2. The method for determining rock acoustic emission parameters based on moment tensor analysis according to claim 1, wherein the determining acoustic emission parameters of each acoustic emission event according to the method for moment tensor analysis specifically comprises:

in the process of loading the numerical model by the PFC software, after initial microcrack generation, determining each component of a microcrack moment tensor according to the variation of contact force between rock crystal grains of the generated microcrack and the contact position at each set time step;

determining a scalar moment of the microcracks from the components of the microcrack moment tensor;

taking the value of the largest scalar moment among all microcracks within a range of acoustic emission events as the scalar moment corresponding to the acoustic emission event;

an acoustic emission parameter of the acoustic emission event is determined from a scalar moment of the acoustic emission event.

3. The method for determining an acoustic emission parameter of a rock based on a moment tensor analysis as set forth in claim 2, wherein the determining an acoustic emission parameter of an acoustic emission event from a scalar moment of the acoustic emission event specifically includes:

determining a magnitude of the acoustic emission event from a scalar moment of the acoustic emission event;

the energy of the acoustic emission event is determined from the magnitude of the acoustic emission event.

4. The method of moment tensor analysis-based rock acoustic emission parameter determination as claimed in claim 1, wherein the macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, poisson's ratio, and shear wave velocity.

5. The method for determining rock acoustic emission parameters based on moment tensor analysis according to claim 1, wherein the constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters specifically comprises:

constructing a numerical model of the rock sample to be tested based on PFC software;

and calibrating the microscopic parameters of the contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

6. A rock acoustic emission parameter determination system based on moment tensor analysis, comprising:

the macroscopic mechanical parameter obtaining module is used for obtaining the macroscopic mechanical parameters of the rock sample to be tested;

the numerical model building module is used for building a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model comprises a plurality of rock crystal grains, and the rock crystal grains are bonded through a cementing material;

the fracture time and position determining module of each microcrack is used for identifying the fracture time and position of each microcrack in the process of loading the numerical model through PFC software; the fracture of each bonding point among all rock crystal grains represents a micro-crack in the process of loading the numerical model by the PFC software;

the same acoustic emission event determining module is used for determining that the two microcracks are the same acoustic emission event if the rock grains of the two microcracks which are sequentially generated have the same rock grain and the time interval generated by the two microcracks is less than the duration time of the current acoustic emission event in the process of loading the numerical model by the PFC software; the initial duration of the current acoustic emission event is the duration of generation of the first microcrack of the current acoustic emission event, the duration of generation of the microcrack is the propagation time of the crack in the larger diameter of the two rock grains generating the microcrack, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested;

the system comprises a spatial range and seismic source position determining module, a seismic source position determining module and a data processing module, wherein the spatial range and the seismic source position determining module are used for taking the spatial range covered by all microcracks corresponding to one acoustic emission event as the spatial range corresponding to the acoustic emission event, and taking the geometric centers of all microcrack positions in the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event;

and the acoustic emission parameter determining module is used for determining the acoustic emission parameters of each acoustic emission event according to the moment tensor analysis method.

7. The moment tensor analysis-based rock acoustic emission parameter determination system as claimed in claim 6, wherein the acoustic emission parameter determination module specifically comprises:

the component determination unit of the microcrack moment tensor is used for determining components of the microcrack moment tensor according to the variation of the contact force between the rock crystal grains of the generated microcrack and the contact position at each set time step after the initial microcrack is generated in the process of loading the numerical model by the PFC software;

a scalar moment determination unit for the microcracks, for determining the scalar moment of the microcracks from the components of the microcrack moment tensor;

a scalar moment determination unit of the acoustic emission event for taking the value of the largest scalar moment among all microcracks within a range of the acoustic emission event as the scalar moment corresponding to the acoustic emission event;

an acoustic emission parameter determination unit for determining an acoustic emission parameter of an acoustic emission event from a scalar moment of the acoustic emission event.

8. The system for determining acoustic emission parameters of rock based on moment tensor analysis according to claim 7, wherein said acoustic emission parameter determining unit comprises:

a magnitude determination subunit, configured to determine a magnitude of the acoustic emission event from the scalar moment of the acoustic emission event;

an energy determination subunit for determining the energy of the acoustic emission event from the magnitude of the acoustic emission event.

9. The moment tensor analysis-based rock acoustic emission parameter determination system as recited in claim 6, wherein the macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, Poisson's ratio, and shear wave velocity.

10. The moment tensor analysis-based rock acoustic emission parameter determination system as claimed in claim 6, wherein the numerical model construction module specifically comprises:

the numerical model building unit is used for building a numerical model of the rock sample to be tested based on PFC software;

and the calibration unit is used for calibrating microscopic parameters of contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

Technical Field

The invention relates to the technical field of acoustic emission monitoring, in particular to a rock acoustic emission parameter determination method and system based on moment tensor analysis.

Background

Rock is a typical heterogeneous material, deformation failure of which occurs progressively, and understanding the progressive failure process of rock is of great importance to many projects. However, progressive damage to rock material is caused by initiation, propagation, and penetration of microcracks, which are difficult to directly observe and quantify, and for this reason, researchers and engineers need to conduct research by other means. Acoustic emission monitoring is widely applied to the fields of rock mechanics and engineering as a nondestructive monitoring technology. The acoustic emission is an elastic wave generated by the release of strain energy in the process of breaking the rock, various acoustic emission parameters including acoustic emission count, acoustic emission energy, b value and the like can be obtained through further analysis of the elastic wave, and the parameters can be used for quantifying the damage degree of the rock, capturing rock instability precursors and the like.

In view of the defects existing in indoor rock acoustic emission experiments, the numerical simulation method for reproducing the rock acoustic emission phenomenon becomes a powerful means for researching the rock progressive fracture process. In various numerical simulation methods, a particle Flow dispersion unit program PFC (particle Flow code) can reproduce the whole processes of microcrack initiation, expansion and penetration in the rock progressive fracture process through a Bonded-particle model BPM (Bonded-particle model), can directly simulate large deformation of rock materials, and becomes one of mainstream software in the field of rock mechanics. The BPM simulates rock grains by using rigid circular particles with non-uniform sizes, and simulates cementing behaviors among the rock grains by using bonding contacts, the bonding contacts are endowed with certain rigidity and strength, the movement of the particles meets Newton's second law, the force and the moment borne by each bonding contact are updated along with the movement of the particles, when the contact force exceeds the contact strength, microcracks are generated, and the microcracks continuously crack and cluster along with the loading, and finally the model is damaged.

In natural earthquake and microseismic monitoring, moment tensor theory is often adopted to obtain information of an earthquake source through inversion when dynamic waves released by the earthquake source are recorded, and in PFC simulation, the moment tensor can be obtained through recording the change of the contact force around the earthquake source when adhesion is damaged, so that the magnitude and the energy of acoustic emission are obtained. At present, the seismic source position and the number of contained microcracks of a single acoustic emission event cannot be determined by adopting a moment tensor analysis method.

Disclosure of Invention

The invention aims to provide a rock acoustic emission parameter determination method and system based on moment tensor analysis, which can determine the seismic source position and acoustic emission parameters of each acoustic emission event.

In order to achieve the purpose, the invention provides the following scheme:

a rock acoustic emission parameter determination method based on moment tensor analysis comprises the following steps:

acquiring macroscopic mechanical parameters of a rock sample to be tested;

constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model comprises a plurality of rock crystal grains, and the rock crystal grains are bonded through a cementing material;

loading the numerical model through PFC software, simulating the damage process of the rock sample to be tested, and identifying the fracture time and position of each microcrack in the process of loading the numerical model through the PFC software; the fracture of each bonding point among all rock crystal grains represents a micro-crack in the process of loading the numerical model by the PFC software;

in the process of loading the numerical model by the PFC software, if the rock grains of the two sequentially generated microcracks have a common rock grain and the time interval generated by the two microcracks is less than the duration time of the current acoustic emission event, the two microcracks are the same acoustic emission event; the initial duration of the current acoustic emission event is the duration of generation of the first microcrack of the current acoustic emission event, the duration of generation of the microcrack is the propagation time of the crack in the larger diameter of the two rock grains generating the microcrack, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested;

taking the spatial range covered by all the microcracks corresponding to one acoustic emission event as the spatial range corresponding to the acoustic emission event, and taking the geometric centers of all the microcrack positions in the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event;

and determining the acoustic emission parameters of each acoustic emission event according to a moment tensor analysis method.

Optionally, the determining acoustic emission parameters of each acoustic emission event according to the method of moment tensor analysis specifically includes:

in the process of loading the numerical model by the PFC software, after initial microcrack generation, determining each component of a microcrack moment tensor according to the variation of contact force between rock crystal grains of the generated microcrack and the contact position at each set time step;

determining a scalar moment of the microcracks from the components of the microcrack moment tensor;

taking the value of the largest scalar moment among all microcracks within a range of acoustic emission events as the scalar moment corresponding to the acoustic emission event;

an acoustic emission parameter of the acoustic emission event is determined from a scalar moment of the acoustic emission event.

Optionally, the determining an acoustic emission parameter of an acoustic emission event according to a scalar moment of the acoustic emission event specifically includes:

determining a magnitude of the acoustic emission event from a scalar moment of the acoustic emission event;

the energy of the acoustic emission event is determined from the magnitude of the acoustic emission event.

Optionally, the macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, poisson's ratio, and shear wave velocity.

Optionally, the constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters specifically includes:

constructing a numerical model of the rock sample to be tested based on PFC software;

and calibrating the microscopic parameters of the contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

The invention also discloses a rock acoustic emission parameter determination system based on moment tensor analysis, which comprises the following steps:

the macroscopic mechanical parameter obtaining module is used for obtaining the macroscopic mechanical parameters of the rock sample to be tested;

the numerical model building module is used for building a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model comprises a plurality of rock crystal grains, and the rock crystal grains are bonded through a cementing material;

the fracture time and position determining module of each microcrack is used for loading the numerical model through PFC software, simulating the damage process of the rock sample to be tested, and identifying the fracture time and position of each microcrack in the process of loading the numerical model through the PFC software; the fracture of each bonding point among all rock crystal grains represents a micro-crack in the process of loading the numerical model by the PFC software;

the same acoustic emission event determining module is used for determining that the two microcracks are the same acoustic emission event if the rock grains of the two microcracks which are sequentially generated have the same rock grain and the time interval generated by the two microcracks is less than the duration time of the current acoustic emission event in the process of loading the numerical model by the PFC software; the initial duration of the current acoustic emission event is the duration of generation of the first microcrack of the current acoustic emission event, the duration of generation of the microcrack is the propagation time of the crack in the larger diameter of the two rock grains generating the microcrack, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested;

the system comprises a spatial range and seismic source position determining module, a seismic source position determining module and a data processing module, wherein the spatial range and the seismic source position determining module are used for taking the spatial range covered by all microcracks corresponding to one acoustic emission event as the spatial range corresponding to the acoustic emission event, and taking the geometric centers of all microcrack positions in the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event;

and the acoustic emission parameter determining module is used for determining the acoustic emission parameters of each acoustic emission event according to the moment tensor analysis method.

Optionally, the acoustic emission parameter determining module specifically includes:

the component determination unit of the microcrack moment tensor is used for determining components of the microcrack moment tensor according to the variation of the contact force between the rock crystal grains of the generated microcrack and the contact position at each set time step after the initial microcrack is generated in the process of loading the numerical model by the PFC software;

a scalar moment determination unit for the microcracks, for determining the scalar moment of the microcracks from the components of the microcrack moment tensor;

a scalar moment determination unit of the acoustic emission event for taking the value of the largest scalar moment among all microcracks within a range of the acoustic emission event as the scalar moment corresponding to the acoustic emission event;

an acoustic emission parameter determination unit for determining an acoustic emission parameter of an acoustic emission event from a scalar moment of the acoustic emission event.

Optionally, the acoustic emission parameter determining unit specifically includes:

a magnitude determination subunit, configured to determine a magnitude of the acoustic emission event from the scalar moment of the acoustic emission event;

an energy determination subunit for determining the energy of the acoustic emission event from the magnitude of the acoustic emission event.

Optionally, the macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, poisson's ratio, and shear wave velocity.

Optionally, the numerical model building module specifically includes:

the numerical model building unit is used for building a numerical model of the rock sample to be tested based on PFC software;

and the calibration unit is used for calibrating microscopic parameters of contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

according to the method, a numerical model of the rock sample to be tested is constructed according to macroscopic mechanical parameters, a failure process of the numerical model is simulated through PFC software, microcracks with similar generation time and generation position are determined as the same acoustic emission event in a loading process, so that the position of an acoustic emission seismic source is determined, and acoustic emission parameters of each acoustic emission event are calculated through a moment tensor analysis method.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic flow chart of a rock acoustic emission parameter determination method based on moment tensor analysis according to the present invention;

FIG. 2 is a schematic illustration of a rock sample according to the present invention;

FIG. 3 is a schematic view of a numerical model of the present invention;

FIG. 4 is a comparative illustration of rock samples and numerical model fractures according to the present invention;

FIG. 5 is a graph comparing stress-strain curves of a rock sample and a numerical model according to the present invention;

FIG. 6 is a schematic diagram illustrating the evolution of an acoustic emission event according to the present invention;

FIG. 7 is a schematic structural diagram of a rock acoustic emission parameter determination system based on moment tensor analysis.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention aims to provide a rock acoustic emission parameter determination method and system based on moment tensor analysis, which can determine the seismic source position and acoustic emission parameters of each acoustic emission event.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Fig. 1 is a schematic flow diagram of a method for determining a rock acoustic emission parameter based on moment tensor analysis, and as shown in fig. 1, the method for determining a rock acoustic emission parameter based on moment tensor analysis includes the following steps:

step 101: and acquiring macroscopic mechanical parameters of the rock sample to be tested.

Macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, poisson's ratio, and shear wave velocity. The macroscopic mechanical parameters of the rock sample to be tested are obtained through indoor tests.

Step 102: constructing a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model includes a plurality of rock grains, each rock grain being bonded to another by a cement.

Wherein, step 102 specifically comprises:

and constructing a numerical model of the rock sample to be tested based on PFC software.

And calibrating the microscopic parameters of the contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

Taking shale as a specific example, a numerical model of a rock sample is constructed based on a particle flow dispersion unit Program (PFC). The rock sample is shown in figure 2, the numerical model of the rock sample is shown in figure 3, the microscopic parameters of particles and contact in the numerical model are calibrated by a trial and error method according to the macroscopic mechanical parameters of the rock sample obtained in the previous step, and the macroscopic mechanical response characteristics of the rock sample are reproduced as shown in tables 1 and 2 and shown in figures 4 and 5. Where contact refers to particle-to-particle contact, i.e., the bond between the individual rock grains.

TABLE 1 microscopic parameters of rock grains and contacts

Microscopic parameters of particles	Numerical value	Contact microscopic parameters	Numerical value
				Density [ kg/m ]3]	3000	Modulus of elasticity for bonding [ GPa]	22
Elastic modulus [ GPa ]]	22	Ratio of bond stiffness	1.5
				Stiffness ratio	1.5	Contact tensile strength [ MPa ]]	170
Coefficient of friction	0.8	Contact cohesion [ MPa ]]	150
				Damping coefficient	0.7	Contact internal friction angle [ ° ]]	40

TABLE 2 microscopic parameters of rock bedding

Fig. 5 is three sets of parallel experiments, wherein 0-1, 0-2 and 0-3 respectively represent stress-strain curves of different shale samples under the same condition, and stress-strain curve data of the shale samples are determined through the three sets of parallel experiments, so that errors of acquired parameters are reduced.

Step 103: loading a numerical model through PFC software, simulating the damage process of the rock sample to be tested, and identifying the fracture time and position of each microcrack in the process of loading the numerical model through the PFC software; the fracture of each bond between rock grains during loading of the numerical model by the PFC software represents a microcrack.

Wherein, step 103 specifically comprises: based on a fish language built in PFC software, a program is written, and the fracture of each bonding contact of the numerical model in the loading process is regarded as the generation of one-time microcrack, so that the microcracks generated in the loading process of the rock numerical model are identified, and the fracture time and position of the microcracks are recorded. The generated microcracks are shown in fig. 4, wherein the left side in fig. 4 is a real fracture diagram of a rock sample, and the right side is a numerical model fracture diagram.

When the stress applied to the bonding contact exceeds the corresponding strength, the contact is broken to generate micro-cracks, and at the moment, the model operation time, namely the micro-crack generation time (fracture time), can be recorded in PFC software through a built-in function mech.

Step 104: in the process of loading the numerical model by the PFC software, if the rock grains of the two sequentially generated microcracks have a common rock grain and the time interval generated by the two microcracks is less than the duration of the current acoustic emission event, the two microcracks are the same acoustic emission event; the initial duration of the current acoustic emission event is the duration of the first microcrack generation of the current acoustic emission event, the duration of microcrack generation is the propagation time of the crack in the larger diameter of the two rock grains in which the microcrack is generated, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested.

Wherein, the step 104 specifically comprises: in the process of loading the numerical model by PFC software, judging whether the rock grains of the two generated microcracks have a common rock grain and whether the time interval generated by the two microcracks is less than the duration of the current acoustic emission event or not in sequence, if the rock grains of the two sequentially generated microcracks have a common rock grain and the time interval generated by the two microcracks is less than the duration of the current acoustic emission event, determining that the two microcracks are the same acoustic emission event; the initial duration of the current acoustic emission event is the duration of the first microcrack generation of the current acoustic emission event, the duration of microcrack generation is the propagation time of the crack in the larger diameter of the two rock grains in which the microcrack is generated, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested.

If the rock grains of the two sequentially generated microcracks do not have a common rock grain or the time interval generated by the two microcracks is greater than or equal to the duration of the current acoustic emission event, the two microcracks are not the same acoustic emission event, and the microcracks generated in the two microcracks are used as initial microcracks of a new acoustic emission event, so that the two microcracks are classified into different acoustic emission events.

The principle of determining the same acoustic emission event is to regard the microcracks with similar fracture time and fracture position as the same acoustic emission event according to the fracture time and the fracture position of the microcracks.

Step 105: and taking the spatial range covered by all the microcracks corresponding to one acoustic emission event as the spatial range corresponding to the acoustic emission event, and taking the geometric centers of all the microcrack positions in the spatial range of the acoustic emission event as the seismic source positions corresponding to the acoustic emission event.

Wherein, the step 104-105 specifically comprises: 1) based on the crack propagation velocity and the shear wave velocity of the rock materialThe relationship between the two determines the duration of an acoustic emission event, from which the duration of an acoustic emission event can be determined assuming that the crack propagation velocity is half the shear wave velocity of the rock materialt _d(ii) a 2) The particles that created the initial microcracks were defined as "trigger particles" (large crack-producing particles identified at S1 in FIG. 6), and the bond contacts around them (small bond contact points around large particles identified at S2 in FIG. 6) were defined as "affected contacts", for the duration of the acoustic emission eventt _dIf the "affected contact" breaks, a new micro-crack is created, which becomes part of the same acoustic emission event, and at the same time the particle that created the micro-crack becomes a new "trigger particle", the acoustic emission duration is recalculated, updated with the recalculated acoustic emission durationt _d(ii) a 3) When in acoustic emission durationt _dInner, "affected contact" does not break to produce microcracks, and this acoustic emission event is considered to be over; 4) the geometric center of all the microcrack locations contained by the acoustic emission event is taken as the acoustic emission source location.

FIG. 6 is a schematic view of the evolution of an acoustic emission event of the present invention, wherein an acoustic emission event of FIG. 6 includes three microcracks. In FIG. 6, (a) corresponds to the timet ₁In FIG. 6, (b) corresponds to the timet ₂In FIG. 6, (c) corresponds to the timet ₃，t ₂-t ₁<t _dAnd ist ₃-t ₂<t _d(t _dIs the acoustic emission duration, updated according to the increase in microcracks).

Step 106: and determining the acoustic emission parameters of each acoustic emission event according to a moment tensor analysis method.

The acoustic emission parameters include magnitude and energy.

Wherein, step 106 specifically includes:

in the process of loading the numerical model by PFC software, after initial microcrack generation, determining each component of the microcrack moment tensor according to the variation of the contact force between rock crystal grains of the generated microcrack and the contact position at each set time step.

M _ij=∑ΔF _i R _j （1）

In the formula:M _ijthe individual components of the moment tensor are represented,ΔF _iis the amount of change in contact forceiThe number of the components is such that,R _jis the first between the contact location and the center of the acoustic emission eventjThe components, in mathematical terms, the contact location and the acoustic emission event center may represent two points, respectively, the distance between the two points is calculated,R _ja jth component representing the distance between two points, wherein the magnitude of the contact force and the contact position can be obtained by a built-in fish language.

The magnitude of the contact force can be obtained by a built-in function contact.

The scalar moment of the microcracks is determined from the individual components of the microcrack moment tensor.

From equation (1), the moment tensor component of an acoustic emission event can be calculated at each time step after the initial microcrack generation, and the scalar moment is determined as:

（2）

in the formula:m _j is the moment tensorM _ijTo (1) ajThe value of the characteristic is used as the characteristic value,M ₀representing a scalar moment. Considering that recording the moment tensor and the scalar moment at each time step consumes memory, the value of the largest scalar moment in the acoustic emission event is generally taken as the actual value, and the time when the value is generated is the occurrence time of the acoustic emission event.

And taking the value of the maximum scalar moment in all the microcracks in the acoustic emission event range as the scalar moment corresponding to the acoustic emission event, wherein the occurrence time of the microcracks corresponding to the maximum scalar moment is the occurrence time of the acoustic emission event.

An acoustic emission parameter of the acoustic emission event is determined from a scalar moment of the acoustic emission event.

Wherein, determining an acoustic emission parameter of an acoustic emission event according to a scalar moment of the acoustic emission event specifically comprises:

determining a magnitude of the acoustic emission event from the scalar moment of the acoustic emission event.

The magnitude of an acoustic emission event is:

（3）

the energy of the acoustic emission event is determined from the magnitude of the acoustic emission event.

（4）

In the formula:M _Wthe magnitude of the shock is represented by,Eis the acoustic emission energy in joules.

Fig. 7 is a schematic structural diagram of a rock acoustic emission parameter determination system based on moment tensor analysis according to the present invention, and as shown in fig. 7, a rock acoustic emission parameter determination system based on moment tensor analysis includes:

and the macroscopic mechanical parameter obtaining module 201 is used for obtaining the macroscopic mechanical parameters of the rock sample to be tested.

The numerical model building module 202 is used for building a numerical model of the rock sample to be tested according to the macroscopic mechanical parameters; the numerical model includes a plurality of rock grains, each rock grain being bonded to another by a cement.

The fracture time and position determining module 203 for each microcrack is used for identifying the fracture time and position of each microcrack in the process of loading the numerical model through PFC software; the fracture of each bond between rock grains during loading of the numerical model by the PFC software represents a microcrack.

The same acoustic emission event determining module 204 is configured to, in the process of loading the numerical model by the PFC software, if there is a common rock grain in rock grains of two sequentially generated microcracks and a time interval between two microcracks is less than a duration of a current acoustic emission event, determine that the two microcracks are the same acoustic emission event; the initial duration of the current acoustic emission event is the duration of the first microcrack generation of the current acoustic emission event, the duration of microcrack generation is the propagation time of the crack in the larger diameter of the two rock grains in which the microcrack is generated, and the propagation speed of the crack is half of the shear wave speed of the rock sample to be tested.

The spatial range and source location determination module 205 is configured to use the spatial range covered by all the microcracks corresponding to an acoustic emission event as the spatial range corresponding to the acoustic emission event, and use the geometric center of all the microcrack locations within the spatial range of the acoustic emission event as the source location corresponding to the acoustic emission event.

And the acoustic emission parameter determining module 206 is configured to determine an acoustic emission parameter of each acoustic emission event according to a moment tensor analysis method.

The acoustic emission parameter determining module 206 specifically includes:

and the component determination unit of the microcrack moment tensor is used for determining components of the microcrack moment tensor according to the variation of the contact force between the rock crystal grains of the generated microcrack and the contact position at each set time step after the initial microcrack is generated in the process of loading the numerical model by the PFC software.

A scalar moment determination unit of the microcracks for determining the scalar moment of the microcracks from the components of the microcrack moment tensor.

A scalar moment determination unit of the acoustic emission event for taking the value of the largest scalar moment among all microcracks within a range of the acoustic emission event as the scalar moment corresponding to the acoustic emission event.

An acoustic emission parameter determination unit for determining an acoustic emission parameter of an acoustic emission event from a scalar moment of the acoustic emission event.

The acoustic emission parameter determination unit specifically includes:

a magnitude determination subunit for determining a magnitude of the acoustic emission event from the scalar moment of the acoustic emission event.

An energy determination subunit for determining the energy of the acoustic emission event from the magnitude of the acoustic emission event.

Macroscopic mechanical parameters include uniaxial compressive strength, elastic modulus, poisson's ratio, and shear wave velocity.

The numerical model building module 202 specifically includes:

and the numerical model construction unit is used for constructing a numerical model of the rock sample to be tested based on PFC software.

And the calibration unit is used for calibrating microscopic parameters of contact between the rock grains in the numerical model by a trial and error method according to the macroscopic mechanical parameters.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.