Coal rock mass main fracture precursor rock sound information analysis method

Abstract

The invention discloses a coal rock mass main fracture precursor rock sound information analysis method. The method comprises the following steps: acquiring multiple groups of coal rock samples by adopting a core drilling mode, and processing the coal rock samples to form coal rock standard samples; placing the coal rock standard sample in a loading control system, and receiving an acoustic emission signal in the loading process of the coal rock standard sample through loading of a servo hydraulic machine; extracting a plurality of main frequency characteristic frequency bands in the received acoustic emission signal; analyzing each extracted main frequency characteristic frequency band to obtain the change rate of each main frequency characteristic frequency band; and according to the change rate of each main frequency characteristic frequency band, carrying out early warning grade division on the main fracture of the coal and rock mass. By means of the method, the problems that the sound emission impact number and energy are always located at high values due to mixing of multiple main frequencies, and the report rate is reduced are solved, meanwhile, early warning is conducted according to the main frequency characteristic frequency bands, and the sound emission early warning effect is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine monitoring, and particularly relates to a method for analyzing the acoustic emission information of the precursor of the main fracture of coal and rock mass. Background Technique

[0002] In recent years, with the increasing depth of coal mine exploitation, more and more coal mines are threatened by rock bursts. In order to effectively prevent and control rock burst accidents, experts and scholars have carried out research on various types of rock burst monitoring and early warning methods, which can be divided into two categories: rock mechanics methods and geophysical methods according to the monitoring objectives and principles. Acoustic emission is a kind of geophysical method, which is an instantaneous elastic wave generated by the rapid release of local strain energy inside the material. The acoustic emission signals generated during the fracture of coal and rock mass contain a lot of information, which is used to study the fracture law of coal and rock mass and explore the precursor information of the occurrence of the main fracture.

[0003] The main methods of acoustic emission research can be divided into characteristic parameter analysis method and waveform analysis method. The characteristic parameter analysis method is to analyze the damage and failure characteristics of materials by recording and analyzing the characteristic parameters of acoustic emission signals, such as amplitude, energy, duration, ring count, number of events, etc. The waveform analysis method refers to recording and analyzing the waveform of acoustic emission signals to obtain the frequency spectrum and correlation functions of the signals. By analyzing the frequency spectrum characteristics of the damage caused by different stages and different mechanisms of materials, the damage characteristics of materials can be obtained.

[0004] However, during the loading and failure process of coal and rock specimens, different acoustic emission main frequencies correspond to different types of microscopic failure forms of rocks, and the acoustic emission main frequency will change with the fracture process of load and deformation. If the characteristic parameters of different main frequency bands are superimposed and analyzed together, it will cause the mixing of multiple main frequencies, resulting in the acoustic emission impact number and energy always being at high values, resulting in poor acoustic emission early warning effect and reduced reporting accuracy, and unable to reflect the relationship between a certain main frequency band and the fracture mechanism of coal and rock specimens. Summary of the Invention

[0005] In order to solve the above technical problems, the present application proposes the following technical solutions:

[0006] In the first aspect, an embodiment of the present application provides a method for analyzing the acoustic emission information of the precursor of the main fracture of coal and rock mass, including:

[0007] Obtaining multiple groups of coal and rock specimens by core drilling and then processing the coal and rock specimens to form standard coal and rock specimens;

[0008] Placing the standard coal and rock specimens in a loading control system, and receiving the acoustic emission signals during the loading of the standard coal and rock specimens through the loading of a servo hydraulic press;

[0009] Extracting multiple main frequency characteristic bands in the received acoustic emission signals;

[0010] Analyze each extracted main frequency characteristic band to obtain the change rate of each main frequency characteristic band;

[0011] Classify the early warning levels of the main fractures of coal and rock masses according to the change rates of each main frequency characteristic band.

[0012] In a possible implementation manner, after obtaining multiple groups of coal and rock specimens by the core drilling method and processing the coal and rock specimens to form standard coal and rock specimens, it includes:

[0013] Collect multiple groups of coal and rock specimens from the roof by the core drilling method;

[0014] Process the coal and rock specimens into cylindrical specimens of a preset specification through the sawing, drilling, and grinding processes of a sawing machine, a diamond drilling machine, and a grinding machine;

[0015] Place the cylindrical specimens in a dryer with water at the bottom for humidification to form standard coal and rock specimens.

[0016] In a possible implementation manner, the loading control system includes: a servo hydraulic press, with a standard coal and rock specimen arranged between two press head modules of the servo hydraulic press, acoustic emission sensors arranged at both ends of the standard coal and rock specimen, and the signals collected by the acoustic emission sensors are input to a preamplifier for amplification and then transmitted to an acoustic emission acquisition system, and a press loading control module is used to control the pressure loading of the press head module.

[0017] In a possible implementation manner, extracting multiple main frequency characteristic bands from the received acoustic emission signals includes:

[0018] Determine the main frequency characteristic band information of multiple standard coal and rock specimens;

[0019] Regard the bands with a relatively large proportion in different standard coal and rock specimens as the main frequency characteristic bands, where the main frequency characteristic bands include low-frequency characteristic bands and high-frequency characteristic bands.

[0020] In a possible implementation manner, analyzing each extracted main frequency characteristic band to obtain the change rate of each main frequency characteristic band includes:

[0021] Respectively determine the change rates of the impact numbers and energy change rates of the low-frequency characteristic bands and high-frequency characteristic bands, and the calculation formulas are:

[0022]

[0023] Where: For Δ ijis the change rate of the number of impacts or the change rate of energy in the high-frequency characteristic frequency band or the low-frequency characteristic frequency band. When i = 1 and j = 1, it is the change rate of the number of impacts in the low-frequency characteristic frequency band. When i = 2 and j = 1, it is the change rate of energy in the low-frequency characteristic frequency band. When i = 1 and j = 2, it is the change rate of the number of impacts in the high-frequency characteristic frequency band. When i = 2 and j = 2, it is the change rate of energy in the high-frequency characteristic frequency band. When i = 1, p i is the cumulative value of the number of acoustic emission impacts per current unit time, is the average value of the number of acoustic emission impacts per preset number of unit times before the current time. When i = 2, p i is the cumulative value of the acoustic emission energy per current unit time, is the average value of the acoustic emission energy per preset number of unit times before the current time;

[0024] Select the maximum value from the change rate of the number of impacts and the change rate of energy as the change rate of the low-frequency characteristic frequency band or the high-frequency characteristic frequency band. The calculation formula is: W j = max{Δ 1j , Δ 2j}, when j = 1, W j is the change rate of the low-frequency characteristic frequency band. When j = 2, W j is the change rate of the high-frequency characteristic frequency band.

[0025] In a possible implementation, it further includes analyzing the acoustic emission impacts and acoustic emission energy of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band respectively, including:

[0026] Conduct acoustic emission tests on different coal and rock standard specimens and draw corresponding axial force - acoustic emission impact number diagrams and axial force - acoustic emission energy diagrams;

[0027] Determine the change trends of the acoustic emission impacts and acoustic emission energy of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of different coal and rock standard specimens from the compaction stage, elastic stage, and plastic stage respectively according to the axial force - acoustic emission impact number diagrams and axial force - acoustic emission energy diagrams.

[0028] In a possible implementation, determining the change trends of the acoustic emission impacts and acoustic emission energy of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of different coal and rock standard specimens from the compaction stage, elastic stage, and plastic stage respectively according to the axial force - acoustic emission impact number diagrams and axial force - acoustic emission energy diagrams includes:

[0029] During the compaction stage, when the strength of the standard coal and rock specimen is relatively high, both the number of AE hits and the AE energy in the low-frequency characteristic frequency band are higher than those in the high-frequency characteristic frequency band; or, when the strength of the standard coal and rock specimen is relatively low, the number of AE hits in the low-frequency characteristic frequency band is lower than that in the high-frequency characteristic frequency band; the AE energy in the low-frequency characteristic frequency band is initially higher than that in the high-frequency characteristic frequency band, and in the later stage of the stage, the AE energy in the low-frequency characteristic frequency band is lower than that in the high-frequency characteristic frequency band;

[0030] During the elastic stage, both the number of AE hits and the AE energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band remain at a relatively low level;

[0031] During the plastic stage, both the number of AE hits and the AE energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band increase with the increase of the axial force, and rise to the maximum value when approaching the maximum axial force.

[0032] In a possible implementation manner, the early warning level division of the main fracture of the coal and rock mass according to the change rate of each main frequency characteristic frequency band includes:

[0033] Obtain the preset value of the energy start judgment value;

[0034] Under the condition of the energy start judgment value limit, calculate the change rates of the high-frequency characteristic frequency band and the low-frequency characteristic frequency band;

[0035] Carry out early warning level division of the main fracture of the coal and rock mass according to the change rates of the high-frequency characteristic frequency band and the low-frequency characteristic frequency band.

[0036] In a possible implementation manner, the calculation formula for obtaining the preset value of the energy start judgment value is:

[0037]

[0038] where E i is the cumulative value of the AE energy per unit statistical time in the plastic stage of the AE test, and n is the number of unit statistical times.

[0039] In a possible implementation manner, the formula for carrying out early warning level division of the main fracture of the coal and rock mass is:

[0040]

[0041] where W 1 is the change rate of the low-frequency characteristic frequency band, and W 2 is the change rate of the high-frequency characteristic frequency band.

[0042] Compared with the prior art, the beneficial effects of this application are:

[0043] The acoustic emission data analysis method adopted in this application extracts the main frequency characteristic bands in the acoustic emission test of the specimen, and then separately analyzes the characteristics of the impact numbers and acoustic emission energies in different characteristic bands (low-frequency characteristic band and high-frequency characteristic band), avoiding the problem of the mixing of multiple main frequencies, which leads to the impact numbers and energies of acoustic emission always being at high values and causing the reduction of the reporting accuracy rate. At the same time, early warning is carried out according to the main frequency characteristic band, further improving the effect of acoustic emission early warning. Description of the Drawings

[0044] Figure 1 It is a schematic flow chart of a method for analyzing the precursor ground sound information of the main fracture of coal and rock mass provided by an embodiment of this application;

[0045] Figure 2 It is a schematic diagram of a standard coal and rock specimen provided by an embodiment of this application;

[0046] Figure 3 It is a schematic structural diagram of a loading control system provided by an embodiment of this application;

[0047] Figure 4 It is a main frequency characteristic diagram of acoustic emission during uniaxial compression of a coarse sandstone specimen provided by an embodiment of this application;

[0048] Figure 5 It is a main frequency characteristic diagram of acoustic emission during uniaxial compression of a siltstone specimen provided by an embodiment of this application;

[0049] Figure 6 It is a main frequency characteristic diagram of acoustic emission during uniaxial compression of a coal specimen provided by an embodiment of this application;

[0050] Figure 7 It is an axial force - acoustic emission impact number diagram of a coarse sandstone specimen provided by an embodiment of this application;

[0051] Figure 8 It is an axial force - acoustic emission energy diagram of a coarse sandstone specimen provided by an embodiment of this application;

[0052] Figure 9 It is an axial force - acoustic emission impact number diagram of a siltstone specimen provided by an embodiment of this application;

[0053] Figure 10 It is an axial force - acoustic emission energy diagram of a siltstone specimen provided by an embodiment of this application;

[0054] Figure 11 It is an axial force - acoustic emission impact number diagram of a coal specimen provided by an embodiment of this application;

[0055] Figure 12 It is an axial force - acoustic emission energy diagram of a coal specimen provided by an embodiment of this application.

[0056] Among them, Figure 3The symbols in the figure are as follows: 1 - servo hydraulic press, 2 - acoustic emission sensor, 3 - preamplifier, 4 - acoustic emission acquisition system, 5 - press loading control module, 6 - standard coal and rock specimen. Specific implementation manner

[0057] The present solution will be described below in conjunction with the accompanying drawings and specific implementation manners.

[0058] Figure 1 It is a schematic flow chart of a method for analyzing the precursor ground sound information of the main fracture of coal and rock mass provided by an embodiment of the present application. Refer to Figure 1 A method for analyzing the precursor ground sound information of the main fracture of coal and rock mass in this embodiment includes:

[0059] S101, obtaining multiple groups of coal and rock specimens by core drilling and then processing the coal and rock specimens to form standard coal and rock specimens.

[0060] In this embodiment, the coal and rock specimens are taken from Jining No. 3 Mine. The coal samples are directly collected from the roof of the roadway side by core drilling, and a total of two roof core drilling holes are constructed. During sampling, the requirements for coal and rock sampling in GB / T23561.1 - 2009 are met. The coal and rock specimens are wrapped with plastic wrap, and the coal and rock specimens should be kept in the original fracture state as much as possible. In this reception, 6 boxes of roof cores from Hole 1 with a hole depth of 35m and 6 boxes of roof cores from Hole 2 with a hole depth of 35m are received. The sample processing uses diamond machines, sawing machines and grinding machines of GCTS in the United States. Among them, the diamond machine: the core diameter is 20mm - 200mm, the maximum core length is 400mm, automatic drilling, and tap water cooling. The sawing machine: the saw blade diameter is 600mm, the cutting sample size is less than 250mm×250mm×250mm, automatic cutting. The grinding machine: the grinding wheel diameter is 200mm, the grinding sample size is less than 25mm - 200mm, manual plus automatic feed tap water cooling, and the parallelism at both ends is less than 0.05mm.

[0061] In this embodiment, according to the requirements specified in the coal industry standard MT38 - 48 - 87 "Determination Method for Physical and Mechanical Properties of Coal and Rock": The coal and rock specimens are processed into cylindrical specimens with a specification of φ50mm×100mm by sawing, drilling and grinding processes. Under the same state of the same group of rocks, the number of specimens for each parameter is generally not less than 3.

[0062] Since underground coal and rock mostly contain bedding and joints, in the test, some specimens use hydraulic cutting to prefabricate fractures on the complete specimens to simulate the original weak planes in coal and rock. The sample processing meets the requirements that the parallelism deviation of both ends of the specimen shall not be greater than 0.005cm, the size deviation of both ends of the specimen shall not be greater than 0.02cm, and both ends of the specimen shall be perpendicular to the specimen axis. The completion situation of the processing of the standard coal and rock specimens is as Figure 2As shown, according to the requirements of the experimental project, the natural water content state is selected: that is, after the coal-rock standard specimen is prepared, it is placed in a desiccator with water at the bottom for 24 - 48 hours to maintain a certain humidity, and the coal-rock standard specimen shall not contact the water surface.

[0063] S102. Place the coal-rock standard specimen in the loading control system, and receive the acoustic emission signals during the loading of the coal-rock standard specimen through the loading of the servo hydraulic press.

[0064] See Figure 3 , in this embodiment, the loading control system includes a servo hydraulic press 1. A coal-rock standard specimen 6 is arranged between two press head modules of the servo hydraulic press 1. Acoustic emission sensors 2 are arranged at both ends of the coal-rock standard specimen 6. The signals collected by the acoustic emission sensors 2 are input to the preamplifier 3 for amplification and then transmitted to the acoustic emission acquisition system 4. The press loading control module 5 is used to control the pressure loading of the press head module. In this embodiment, the loading control system selects HUT_A-OM-202208B produced by Wance Company. The testing machine uses different fixtures and can complete the mechanical property tests of various materials under tensile, compressive and other states. The TestPilot test software can automatically collect and process test data, and display test data, stress-strain curves, load-strain curves and other various test curves in real time. The acoustic emission acquisition system uses an acoustic emission acquisition card based on the PCI-Express bus, adopts the brand-new Express bus technology. Each Express card has 8 acoustic emission channels, more than 500 freely combinable digital filters, 16-bit A / D accuracy, and a sampling rate of 10 MHz. The acoustic emission sensor uses MINI-30 produced by Wusheng Technology. The sensitivity of this sensor is -73.38 dB, and the peak frequency is 300 kHz.

[0065] In this embodiment, in order to simulate the scenario of gradually increasing mine pressure during the working face production process, a displacement control grading loading method is adopted. The loading rate is constant at 0.2 mm / min, the loading stage lasts for 1.5 minutes, and the displacement holding stage lasts for 1 minute. After the press head contacts the coal-rock standard specimen, start the loading and start each data acquisition system; through the loading of the servo hydraulic press on the coal-rock specimen block, receive the acoustic emission signals during the loading of the coal-rock specimen block.

[0066] S103. Extract multiple main frequency characteristic frequency bands from the received acoustic emission signals.

[0067] In this embodiment, determine the main frequency characteristic frequency band information of multiple coal-rock standard specimens, and use the frequency band with a relatively large proportion in different coal-rock standard specimens as the main frequency characteristic frequency band, where the main frequency characteristic frequency band includes a low-frequency characteristic frequency band and a high-frequency characteristic frequency band.

[0068] In this embodiment, select coarse sandstone specimens, siltstone specimens and coal specimens, seeFigures 4 - 6 , in terms of the main frequency distribution, the coal and rock specimens show a concentration of multiple main frequencies. One or more frequency bands with a relatively large proportion of the main frequency are collectively referred to as the main frequency characteristic bands. Among them, the main frequency characteristic bands of each channel of the acoustic emission of the coarse sandstone specimens are mainly concentrated in the range of 60 - 100 kHz and 250 - 310 kHz. The main frequency characteristic bands of each channel of the acoustic emission of the siltstone specimens are mainly concentrated in the range of 60 - 90 kHz and 250 - 300 kHz. The main frequency characteristic bands of each channel of the acoustic emission of the coal specimens are mainly concentrated in the range of 60 - 80 kHz and 250 - 290 kHz. Since the main frequency characteristic bands of the above specimens are not very different, for better analysis of the main frequency, the main frequency characteristic bands are divided into a high-frequency characteristic band (250 - 300 kHz) and a low-frequency characteristic band (60 - 90 kHz).

[0069] S104. Analyze each extracted main frequency characteristic band to obtain the change rate of each main frequency characteristic band.

[0070] In this embodiment, the change rates of the impact numbers and energy change rates of the low-frequency characteristic band and the high-frequency characteristic band are determined respectively. The calculation formulas are as follows:

[0071]

[0072] Among them: For Δ ij is the change rate of the impact number or energy change rate of the high-frequency characteristic band or the low-frequency characteristic band. When i = 1 and j = 1, it is the change rate of the impact number of the low-frequency characteristic band. When i = 2 and j = 1, it is the energy change rate of the low-frequency characteristic band. When i = 1 and j = 2, it is the change rate of the impact number of the high-frequency characteristic band. When i = 2 and j = 2, it is the energy change rate of the high-frequency characteristic band. When i = 1, p i is the cumulative value of the acoustic emission impact numbers in the current unit time, is the average value of the acoustic emission impact numbers in the preset number of unit times before the current time. When i = 2, p i is the cumulative value of the acoustic emission energy in the current unit time, is the average value of the acoustic emission energy in the preset number of unit times before the current time. In this embodiment, the cumulative values of the acoustic emission impact numbers or energy in the first 10 unit times are taken. The calculation formula is:

[0073] Among them, p m is the cumulative value of the acoustic emission impact numbers or the cumulative value of the acoustic emission energy in the previous ten (excluding the current) unit times.

[0074] Select the maximum value from the change rate of the impact number and the energy change rate as the change rate of the low-frequency characteristic band or the high-frequency characteristic band. The calculation formula is: W j = max{Δ 1j ,Δ 2j}, when j = 1, W j is the change rate of the low-frequency characteristic frequency band. When j = 2, W j is the change rate of the high-frequency characteristic frequency band.

[0075] Analyze the acoustic emission impact number and acoustic emission energy of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band respectively. In this embodiment, conduct acoustic emission tests on different coal and rock standard specimens, draw the corresponding axial force - acoustic emission impact number diagram and axial force - acoustic emission energy diagram, and determine the change trends of the acoustic emission impact number and acoustic emission energy of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of different coal and rock standard specimens from the compaction stage, elastic stage, and plastic stage according to the axial force - acoustic emission impact number diagram and axial force - acoustic emission energy diagram.

[0076] See Figure 7 and Figure 9 and Figure 11 . From the specimen axial force - acoustic emission impact number diagram, in the compaction stage (O - A), the original pores and microcracks inside the specimen are gradually compressed tightly with the increase of the test load. There are fewer newly generated fracture sources, and only a few microcracks initiate, mainly dominated by the compaction closure of the original defects. In this embodiment, due to the higher strength of the coarse sandstone and siltstone specimens, the impact number of the low-frequency characteristic frequency band is higher than that of the high-frequency characteristic frequency band in the acoustic emission characteristic frequency band. However, due to the lower strength of the coal specimen, the impact number of the high-frequency characteristic frequency band is higher than that of the low-frequency characteristic frequency band in the acoustic emission characteristic frequency band. In the elastic stage (A - B), the impact numbers of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of the coarse sandstone specimen, siltstone specimen, and coal specimen all remain at a low level. In the plastic stage (B - C), as the load continuously increases to near the peak stress, the acoustic emission activity is frequent, the impact numbers of each acoustic emission channel and the energy values of each acoustic emission channel begin to increase, and the main frequency distribution range of the acoustic emission signal changes from being relatively concentrated to a complex and discrete direction, indicating that the cracks have expanded and aggregated, and new cracks are continuously generated. Especially in the later stage of the plastic stage, the low-frequency characteristic frequency band and the high-frequency characteristic frequency band coexist in the same time period, and the main frequency distribution range is larger and the number is more than before, indicating that the fracture situation of the rock mass in this stage is more complex. As the test time progresses, larger-scale microfractures in the specimen increase, and the fracture surfaces inside the specimen gradually connect to form the final fracture surface, and the acoustic emission energy rises to the maximum value when the specimen fails. In this embodiment, the impact numbers of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of the coarse sandstone specimen, siltstone specimen, and coal specimen increase with the increase of the axial force and rise to the maximum value when approaching the maximum axial force. When the axial force remains stable, the impact numbers of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of the coarse sandstone specimen, siltstone specimen, and coal specimen all decrease to a lower value.

[0077] See Figure 8 and Figure 10 andFigure 12 From the axial force - acoustic emission energy diagram of the specimens, it can be seen that during the compaction stage (O - A), the energy of the low - frequency characteristic frequency band of the coarse sandstone specimens and siltstone specimens is greater than that of the high - frequency characteristic frequency band. For the coal specimens, the energy of the low - frequency characteristic frequency band is greater than that of the high - frequency characteristic frequency band at the initial stage of the compaction stage, and is less than that of the high - frequency characteristic frequency band at the later stage of the compaction stage. During the elastic stage (A - B), the energies of the low - frequency and high - frequency characteristic frequency bands of the coarse sandstone specimens, siltstone specimens, and coal specimens are all maintained at a relatively low level. During the plastic stage (B - C), the energies of the low - frequency and high - frequency characteristic frequency bands of the coarse sandstone specimens, siltstone specimens, and coal specimens increase with the increase of the axial force, and rise to the maximum value when approaching the maximum axial force. Before the main fracture, for the coarse sandstone specimens, the energies of both the low - frequency and high - frequency characteristic frequency bands increase simultaneously; for the siltstone specimens, the energy of the high - frequency characteristic frequency band increases first and then the energy of the low - frequency characteristic frequency band increases; for the coal specimens, the energy of the low - frequency characteristic frequency band increases first and then the energy of the high - frequency characteristic frequency band increases. When the axial force remains stable, the energies of the low - frequency and high - frequency characteristic frequency bands of all specimens decrease to relatively low values.

[0078] S105, classify the early warning levels of the main fractures of coal and rock masses according to the change rates of each main frequency characteristic frequency band.

[0079] During the uniaxial compression test of the specimens, the acoustic emission hit numbers and energies are mainly at relatively high values during the compaction stage and plastic stage. The data are discrete, and the maximum value often appears in the later stage of the plastic stage. Since high - frequency signals are prone to attenuation, and the values of acoustic emission hit numbers and energies of different lithologies often vary, the hit numbers and energy values cannot be used as precursor information for main fractures. Using the change rates of acoustic emission hit numbers and energies as precursor information for main fractures can also show the trend of increasing acoustic emission values. However, since the high - frequency signal occurrence events of specimen failure are earlier, it is easy to meet the magnification condition, and at this time, there is still a certain time for the specimen to fail under continuous loading. This will inevitably cause false alarms in the compaction stage or the early stage of the plastic stage, resulting in poor early warning effects. In this embodiment, to improve the reporting accuracy, based on the change - rate early warning index, an energy starting judgment value is set to filter out the high - change - rate situations in the compaction stage and the early stage of the plastic stage. Among them, the calculation formula for obtaining the preset value of the energy starting judgment value is:

[0080]

[0081] Among them, E i is the cumulative value of the acoustic emission energy per unit statistical time in the plastic stage of the acoustic emission test, and n is the number of unit statistical times.

[0082] Under the condition of setting the energy threshold value, calculate the change rates of the high-frequency characteristic frequency band and the low-frequency characteristic frequency band, and divide the early warning levels of the main fracture of the coal and rock mass according to the change rates of the high-frequency characteristic frequency band and the low-frequency characteristic frequency band.

[0083] In this embodiment, the formula for dividing the early warning levels of the main fracture of the coal and rock mass is:

[0084]

[0085] Wherein, W 1 is the change rate of the low-frequency characteristic frequency band, and W 2 is the change rate of the high-frequency characteristic frequency band. However, if the accumulated energy value per unit time is less than the energy threshold value at present, and max{w 1 , w 2}≥1, then max{w 1 , w 2}=0.99.

[0086] In the embodiments of the present application, "a plurality of" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent the situations of A existing alone, A and B existing simultaneously, and B existing alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0087] It should be noted that in this article, the terms "including", "comprising" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0088] The above is only the specific implementation manner of the present application. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the said claims.

Claims

1. A method for analyzing geoacoustic information of coal rock mass main fracture precursor, characterized in that: include: After obtaining multiple groups of coal and rock samples by core drilling, the coal and rock samples are processed to form coal and rock standard samples; The coal rock standard sample is placed in a loading control system, and the acoustic emission signal of the coal rock standard sample during loading is received by the servo hydraulic press; Extracting multiple main frequency characteristic frequency bands from the received acoustic emission signal; Analyze each extracted main frequency characteristic frequency band to obtain the change rate of each main frequency characteristic frequency band; The warning level of main fracture of coal rock mass is divided according to the change rate of each main frequency characteristic band.

2. The method for analyzing the geoacoustic information of the main fracture precursor of coal and rock mass according to claim 1 is characterized in that: The method of obtaining a plurality of groups of coal and rock samples by means of core drilling and then processing the coal and rock samples to form coal and rock standard samples comprises: Multiple groups of coal and rock samples were collected from the roof by core drilling; Processing the coal rock sample into a cylindrical sample of preset specifications through sawing, drilling and grinding processes of a stone sawing machine, a diamond machine and a stone grinding machine; The cylindrical sample is placed in a dryer with water at the bottom for humidification to form a coal rock standard sample.

3. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 1, characterized in that: The loading control system includes: a servo hydraulic press, a coal rock standard sample is arranged between two pressure head modules of the servo hydraulic press, acoustic emission sensors are arranged at both ends of the coal rock standard sample, the acoustic emission sensor inputs the collected signal into the preamplifier for amplification and then transmits it to the acoustic emission collection system, and the press loading control module is used to control the pressure loading of the pressure head module.

4. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 1, characterized in that: The extracting of multiple main frequency characteristic frequency bands in the received acoustic emission signal includes: Determine the main frequency characteristic frequency band information of multiple coal and rock standard samples; The frequency band that accounts for a larger proportion in different coal rock standard samples is taken as the main frequency characteristic frequency band, wherein the main frequency characteristic frequency band includes a low frequency characteristic frequency band and a high frequency characteristic frequency band.

5. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 1, characterized in that: The step of analyzing each extracted main frequency characteristic frequency band to obtain the change rate of each main frequency characteristic frequency band includes: Determine the impact number change rate and energy change rate of the low-frequency characteristic frequency band and the high-frequency characteristic frequency band respectively, and the calculation formula is: Where: For Δ ij is the impact number change rate or energy change rate of the high-frequency characteristic frequency band or the low-frequency characteristic frequency band. When i=1 and j=1, it is the impact number change rate of the low-frequency characteristic frequency band. When i=2 and j=1, it is the energy change rate of the low-frequency characteristic frequency band. When i=1 and j=2, it is the impact number change rate of the high-frequency characteristic frequency band. When i=2 and j=2, it is the energy change rate of the high-frequency characteristic frequency band. When i is 1, p i is the cumulative value of the acoustic emission impact number per unit time, is the average number of acoustic emission impacts per unit time before the current time. When i is 2, p i is the current cumulative value of acoustic emission energy per unit time, The average value of acoustic emission energy per unit time of a preset number of times before the current time; The maximum value is selected from the impact number change rate and the energy change rate as the change rate of the low-frequency characteristic frequency band or the high-frequency characteristic frequency band, and the calculation formula is: W j =max{Δ 1j ,Δ 2j }, when j = 1, W j is the rate of change of the low-frequency characteristic band. When j=2, W j is the change rate of the high-frequency characteristic band.

6. The method for analyzing the geoacoustic information of the main fracture precursor of coal and rock mass according to claim 5, characterized in that: It also includes the analysis of the acoustic emission impact number and acoustic emission energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band, including: Conduct coal-rock sample acoustic emission tests on different coal-rock standard samples and draw corresponding axial force-acoustic emission impact number diagrams and axial force-acoustic emission energy diagrams; According to the axial force-acoustic emission impact number diagram and the axial force-acoustic emission energy diagram, the changing trends of the acoustic emission impact number and the acoustic emission energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of different coal and rock standard samples are determined from the compaction stage, elastic stage and plastic stage respectively.

7. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 6, characterized in that: According to the axial force-acoustic emission impact number diagram and the axial force-acoustic emission energy diagram, the change trends of the acoustic emission impact number and the acoustic emission energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band of different coal and rock standard samples are determined from the compaction stage, the elastic stage and the plastic stage, respectively, including: In the compaction stage, when the strength of the coal rock standard sample is high, the number of acoustic emission impacts and the acoustic emission energy in the low-frequency characteristic frequency band are higher than those in the high-frequency characteristic frequency band; or, when the strength of the coal rock standard sample is low, the number of acoustic emission impacts in the low-frequency characteristic frequency band is lower than that in the high-frequency characteristic frequency band; the acoustic emission energy in the low-frequency characteristic frequency band is higher than that in the high-frequency characteristic frequency band at the initial stage, and in the later stage, the acoustic emission energy in the low-frequency characteristic frequency band is lower than that in the high-frequency characteristic frequency band; In the elastic stage, the number of AE impacts and AE energy in both the low-frequency characteristic band and the high-frequency characteristic band remain at a low level; In the plastic stage, the number of AE impacts and AE energy in the low-frequency characteristic frequency band and the high-frequency characteristic frequency band increase with the increase of axial force, and rise to the maximum value when approaching the maximum axial force.

8. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 1, characterized in that: The early warning level classification of the main fracture of the coal rock mass according to the change rate of each main frequency characteristic frequency band includes: Obtain the preset value of the energy starting value; Under the limited condition of energy starting value, the change rate of high-frequency characteristic frequency band and low-frequency characteristic frequency band is calculated; The warning levels of main fractures in coal and rock mass are divided according to the change rates of high-frequency characteristic frequency bands and low-frequency characteristic frequencies.

9. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 8, characterized in that: The calculation formula for obtaining the preset value of the energy starting value is: Among them, E i It is the accumulated value of acoustic emission energy per unit statistical time in the plastic stage of acoustic emission test, and n is the number of unit statistical time.

10. The method for analyzing the geoacoustic information of coal rock main fracture precursor according to claim 8, characterized in that: The formula for classifying the early warning levels of the main fractures of coal and rock mass is: Among them, W1 is the change rate of the low-frequency characteristic frequency band, and W2 is the change rate of the high-frequency characteristic frequency band.

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