Coal body adsorption micro-fracture detection experiment system and method and coal mining safety monitoring system

Abstract

This invention discloses a coal body adsorption micro-fracture detection experimental system, method, and coal mining safety monitoring system. Addressing the issue that existing coal mine outburst prevention assessments primarily rely on single gas indicators such as gas content and gas pressure, which are insufficient to reflect the "low-indicator outburst" problem caused by the deterioration of coal body mechanical properties during gas desorption, this invention constructs a multi-parameter collaborative monitoring platform comprising a high-pressure adsorption chamber, gas injection and pressure control, and strain and wave emission acquisition subsystems. Combined with DIC technology, it achieves synchronous collaborative monitoring of strain, full-field displacement, and elastic waves under high-pressure gas injection conditions. This invention utilizes the inverse quality factor Q... ‑1 Multidimensional joint verification of surface optical DIC and microscopic local strain quantifies the evolution of differential shrinkage of coal micro-components and macroscopic mechanical damage, and calibrates specific safe desorption and extraction thresholds for target coal seams. This makes up for the shortcomings of traditional macroscopic indicators in the stability evaluation of heterogeneous coal seams and provides reliable physical and mechanical criteria for the prevention and control of coal mine dynamic disasters.

Description

Technical Field

[0001] This invention belongs to the field of coal mechanical property testing technology, specifically relating to a coal adsorption micro-crushing detection experimental system, method, and coal mining safety monitoring system. Background Technology

[0002] After coal adsorbs or desorbs gases (such as methane and carbon dioxide), its internal pore structure and macroscopic mechanical properties undergo significant evolution. Currently, coal mine outburst prevention in my country mainly relies on the "Detailed Rules for the Prevention and Control of Coal and Gas Outbursts," which typically uses residual methane content below 8 m³ / t and residual methane pressure below 0.74 MPa as the criteria for eliminating outburst risks.

[0003] However, in deep coal seam mining practice, a phenomenon known as "low-index outburst" often occurs, where gas levels have dropped below national standard limits, yet dynamic disasters still occur. From a rock mechanics perspective, coal and gas outbursts are not only controlled by gas pressure but also closely related to the mechanical strength of the coal itself. During gas drainage and pressure reduction, the heterogeneity of the internal micro-components of the coal leads to inconsistent and differential shrinkage of the coal matrix. This mismatch in local deformation triggers frictional displacement of internal micro-cracks and residual stress concentration, resulting in a hidden deterioration of the macroscopic mechanical strength of the coal. Gas content or pressure alone cannot accurately reflect whether the coal has truly reached the mechanical stability required to resist outbursts.

[0004] In existing technologies, such as Chinese invention patent CN108458950A, a device and method for measuring the amount of adsorbed / desorbed gas during the loading and fracturing process of coal and rock are disclosed. This device measures the amount of gas injected and the amount of adsorption / desorption through a quantitative bottle. However, it has the following technical problems: First, the acoustic emission probe is directly bonded to the side of the coal and rock specimen. Under the action of high pressure infiltration and coal body expansion and contraction deformation, the coupling interface between the probe and the specimen is easy to loosen, resulting in signal attenuation or distortion. Second, the data processing only focuses on the superficial correlation between gas quantity, displacement and acoustic emission ring count, without deeply exploring the quantitative relationship between elastic wave velocity, attenuation and other characteristics and the microscopic damage and macroscopic stiffness deterioration inside the coal body. It is difficult to accurately reveal the microcrack evolution mechanism of the coal body during the adsorption / desorption process.

[0005] Therefore, there is an urgent need to develop a multi-parameter collaborative synchronous monitoring system to accurately capture the dynamic evolution characteristics of microscopic fractures and surface strain in coal seams, and to formulate specific safety thresholds for heterogeneous coal seams in order to solve the early warning problem of prominent low indicators in deep coal mines. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the first aspect of this invention is to provide an experimental system for detecting micro-fractures in coal adsorption. The second aspect, based on the same inventive concept, is to provide a method for detecting micro-fractures in coal adsorption. The third aspect, based on the same inventive concept, is to provide a coal mining safety monitoring system.

[0007] In this embodiment of the invention, the coal adsorption micro-fracture detection experimental system includes a high-pressure adsorption chamber subsystem, a gas injection and pressure control subsystem, a strain subsystem, and a wave emission acquisition subsystem. The high-pressure adsorption chamber subsystem is the pressure-bearing core, including a chamber for accommodating coal and rock samples and providing a high-airtightness testing environment, and a wave emission guide rod extending into the chamber through the chamber wall. The chamber wall is also provided with a gas injection interface for connecting to an external gas source pipeline. The output end of the gas injection and pressure control subsystem is connected to the gas injection interface through a pipeline to provide a controllable gas environment to the chamber. The strain subsystem is used to capture the strain changes generated by the adsorption of gas by the coal and rock samples. The wave emission acquisition subsystem includes a wave emitter, a piezoelectric ceramic, and a wave emission receiver. The piezoelectric ceramic and the wave emission guide rod are respectively attached to the surfaces of both ends of the coal sample. The wave emitter periodically emits elastic waves, which are transmitted by the wave emission guide rod. The piezoelectric ceramic receives the wave signal and transmits it to the wave emission receiver. The wave emission receiver synchronously captures the micro-fracture wave emission signal and the elastic wave waveform.

[0008] The detection method of this invention embodiment is based on the above-mentioned coal adsorption micro-fracture detection experimental system, and includes the following steps: S1, preparing and grinding coal and rock specimens, attaching strain gauges of the strain system to the ground surface of the coal and rock specimens, and completing the connection of the strain gauge wires and the wiring ports; S2, installing piezoelectric ceramics inside the cavity, completing the connection of the piezoelectric ceramic wires and the wiring ports, placing the coal and rock specimens on the upper surface of the piezoelectric ceramics and fitting them tightly, adjusting the position of the wave emitting guide rod so that the upper surface of the coal and rock specimens fits properly with the lower surface of the wave emitting guide rod; S3, sealing the cavity, connecting the gas injection interface to the output end of the gas injection and pressure control subsystem, and tightly fitting the wave emitter head to the top of the wave emitting guide rod; S4, starting the strain subsystem and zeroing the strain data before starting recording, turning on the wave emitter and setting the wave properties, recording the wave data, and then turning off the wave emitter; S5, injecting the material to be adsorbed into the cavity through the gas injection and pressure control subsystem. The gas is applied to place the coal and rock sample in a high-pressure gas environment. The gas pressure is adjusted to the preset first pressure value and maintained until the coal and rock sample reaches adsorption equilibrium, after which the gas source is turned off. S6: The wave transmitter is started to emit elastic waves into the coal and rock sample in the high-pressure gas environment. The wave data penetrating the coal and rock sample is recorded and the wave transmitter is turned off. This step is repeated at set time intervals to complete the wave data acquisition at the corresponding pressure level. S7: The gas pressure in the cavity is adjusted to multiple incremental pressure values ​​in sequence. The pressure value of each level increases sequentially. After each pressure value is adjusted to a certain level and stabilized, step S6 is repeated to complete the wave data acquisition at the corresponding pressure level. S8: After the wave data acquisition at all pressure levels is completed, the strain data recording is stopped, the pressure in the cavity is released, and the strain data and wave data of the entire adsorption process are exported. S9: By analyzing the small changes in the wave velocity, attenuation, or tail wave characteristics of the elastic waves, the microstructural evolution inside the coal and rock sample is inverted.

[0009] The coal mining safety monitoring system of this invention includes an indoor parameter calibration terminal, a field wave emission acquisition terminal, and a safety early warning control terminal. The indoor parameter calibration terminal uses the experimental system of Embodiment 1 to perform the detection methods of Embodiments 2 and 3 on coal and rock samples taken from the working face of the target coal seam to obtain the adverse quality factor of the target coal seam during the adsorption of high-pressure gas. Evolution curves, and the expansion of differences in micro-components leading to The slope value at the time of abrupt change is extracted as a specific safety warning threshold for the target coal seam. The field wave emission acquisition end includes a wave emission probe and a wave receiving probe deployed in the field borehole of the target coal seam. The wave emission probe emits active elastic waves into the coal seam, and the wave receiving probe captures the field elastic wave waveform after penetrating the coal seam and transmits it to the safety warning control end. The safety warning control end has a processing module set to extract the tail wave segment of the field elastic wave waveform, and uses time-domain waveform stacking imaging technology to denoise the one-dimensional time-series tail wave signal and transform it into a striped image with alternating bright and dark stripes. The time drift Δt of the striped image is extracted and combined with the waveform amplitude attenuation to calculate the current status of the field coal seam in real time. Change in slope; when the scene When the slope of change reaches or exceeds the exclusive safety warning threshold, a safety warning is triggered before macroscopic dynamic failure of the coal seam occurs.

[0010] Compared with the prior art, the advantages of the superior technical solution of the present invention include:

[0011] 1. This invention constructs a multi-parameter collaborative synchronous monitoring mechanism of "high-pressure gas injection-strain-DIC-elastic wave". By using a unified timestamp, it achieves precise alignment of strain signals, wave emission signals and elastic wave waveforms. The parameters have good synchronization and are adapted to high-pressure environments. It can establish the coupling relationship between micro-parameters and macro-mechanical properties, and fully capture the dynamic evolution correlation of each parameter during the coal adsorption process, providing comprehensive data support for the analysis of coal micro-fracture mechanism.

[0012] 2. This invention integrates a high-pressure adsorption chamber sealing and wave emission coupling structure. It employs a V-shaped gasket to seal the wave emission guide rod and a limiting pressure plate + epoxy resin composite seal for the wiring ports. This achieves direct and tight contact between the piezoelectric ceramic, the wave emission guide rod, and the sample, effectively avoiding signal coupling instability and mechanical interference. This enables low-loss direct capture of the wave emission signal. Simultaneously, it ensures airtightness under high pressure, balancing signal acquisition accuracy and high-pressure adaptability, thus improving the reliability of monitoring data. The sapphire glass viewing window integrated into the front cover allows for real-time visualization of macroscopic cracks on the surface of the coal and rock specimens. This complements the strain data and wave emission signal, providing multi-dimensional data support for a comprehensive analysis of the coal adsorption micro-fracture evolution mechanism, enhancing the completeness and reliability of the test results.

[0013] 3. The mechanical properties of coal and rock change after absorbing gas (at the microscale, the micro-components of the coal body undergo mutual compression and stretching, potentially leading to stress concentration in certain areas, resulting in a decrease in the mechanical properties of the coal after gas adsorption). This is a significant contributing factor to coal and gas outbursts or rockbursts. This invention, through active elastic wave detection, can detect minute changes and the accumulation of cracks within the coal body before macroscopic deformation occurs. This provides early warning of coal body failure under high gas pressure, offering a longer warning window. Furthermore, by monitoring elastic wave waveform changes, it can assess whether the coal body undergoes micro-crack damage due to excessive expansion during gas injection, ensuring that injected gas does not leak and guaranteeing the safety of geological sealing.

[0014] 4. This invention achieves cross-scale coupled monitoring from microscopic component deformation to macroscopic media damage. Unlike traditional single-dimensional monitoring, this experimental system constructs a rigorous three-dimensional architecture: at the microscopic scale, strain gauges are arranged on specific microscopic components (such as inert groups) and bedding directions in coal and rock to capture the non-uniform expansion effect at the microscopic scale during adsorption; on the macroscopic surface, sapphire viewing windows and DIC technology are combined to observe surface crack propagation at the macroscopic scale; within the macroscopic interior, wake interferometry of active elastic waves is used to quantify the evolution of porosity and stiffness degradation at the macroscopic scale. This three-dimensional monitoring architecture can reveal the physical mechanism of macroscopic damage induced by the mismatch between microscopic component adsorption and expansion in coal, solving the problem that traditional methods struggle to explain the microscopic causes of adsorption damage in coal.

[0015] 5. This invention uses elastic wave tail wave analysis to process data and combines it with active elastic wave excitation technology. To address the problem of difficulty in identifying minute changes in elastic wave waveforms, it converts them into stripe images through MATLAB programming. By utilizing the cumulative effect of wave velocity differences in the tail wave stage, the change characteristics are amplified, which improves the accuracy of capturing minute changes in the macroscopic mechanical properties of coal. It can accurately invert the evolution law of coal mechanical properties under different gas pressures and different adsorption times, providing a precise data analysis method for the study of coal adsorption damage mechanism.

[0016] 6. This invention enables the cross-scale transfer of laboratory microscopic mechanisms to macroscopic engineering applications in mines. Addressing the differences in testing environments between small-sized rock cores and large-scale coal bodies in the field, this invention clarifies a physical mechanism equivalent to the pressure relief height during in-situ mining during the indoor calibration stage. It also establishes a rigorous optical quantitative criterion of "maximum principal strain gradient difference reduced to below 0.05%", eliminating the subjectivity of traditional manual interpretation. Simultaneously, in field applications, it incorporates cross-hole transmission detection technology with a low frequency band of 1–10 kHz and a spacing of 5–15 m, effectively overcoming the high attenuation characteristics of complex coal and rock media in the field. This significantly improves the operability of laboratory calibration parameters in engineering field applications and the absolute reliability of the results.

[0017] 7. This invention constructs a dual-dimensional safety monitoring system covering the entire lifecycle of coal mine production, from pre-mining to mining. It overcomes the limitations of traditional outburst prevention assessments that rely solely on gas concentration. This system obtains two independent thresholds through indoor calibration: before mining, a dedicated safety desorption threshold serves as a rigid physical threshold for meeting outburst prevention and drainage standards, fundamentally eliminating the risk of "low-index outbursts" from a mechanical perspective; during mining, a dedicated disaster early warning threshold acts as a dynamic radar, monitoring in real-time abnormal ruptures induced by mining disturbances. This system is logically self-consistent and clearly prioritizes key elements, constructing an all-weather, blind-spot-free defense line for the safe mining of deep, complex, and heterogeneous coal seams.

[0018] 8. Addressing the issue that existing coal mine outburst prevention assessments primarily rely on single gas indicators such as gas content and pressure, which are insufficient to reflect the "low-indicator outburst" problem caused by the deterioration of coal's mechanical properties during gas desorption, this invention constructs a multi-parameter collaborative monitoring platform comprising a high-pressure adsorption chamber, gas injection and pressure control, and strain and wave emission acquisition subsystems. Combined with DIC technology, it achieves synchronous collaborative monitoring of strain, full-field displacement, and elastic waves under high-pressure gas injection conditions. This invention utilizes the "internal elastic wave inverse quality factor"... The multi-dimensional joint verification of "+surface optical DIC+microscopic local strain" quantitatively analyzes the evolution law of differential shrinkage of coal micro-components and macroscopic mechanical damage, and calibrates the exclusive safe desorption and extraction threshold for the target coal seam. This makes up for the shortcomings of traditional macroscopic indicators in the stability evaluation of heterogeneous coal seams and provides reliable physical and mechanical criteria for the prevention and control of coal mine dynamic disasters. Attached Figure Description

[0019] Figure 1 This is the coal adsorption microfracture detection experimental system in the embodiments.

[0020] Figure 2 This is an exploded view of the high-pressure adsorption chamber subsystem in the embodiment.

[0021] Figure 3 This is a partial exploded view of the high-pressure adsorption chamber subsystem in the embodiment.

[0022] Figure 4 This is a schematic diagram showing the connection between the piezoelectric ceramic and the sample tray in the embodiment.

[0023] Figure 5 This is a schematic diagram of the V-shaped washer fitted outside the wave-emitting guide rod in the embodiment.

[0024] Figure 6 This is a schematic diagram of the structure of the wire lead-out static sealing unit in the embodiment.

[0025] Figure 7 This is a diagram showing the state of the coal and rock specimen inside the chamber after the adsorption experiment.

[0026] Figure 8 This is a schematic diagram of strain changing over time.

[0027] Figure 9 This is the elastic wave waveform diagram of the nitrogen adsorption experiment at 2.5 MPa.

[0028] Figure 10 This is the elastic wave waveform diagram of the carbon dioxide adsorption experiment at 1.5 MPa.

[0029] Figure 11 This is the elastic wave waveform diagram of the carbon dioxide adsorption experiment at 2.5 MPa.

[0030] Figure 12 The results are from the tail wave analysis of the coal body waveform under nitrogen adsorption conditions of 2.5 MPa.

[0031] Figure 13 The results are from the tail wave analysis of the coal body waveform under carbon dioxide adsorption conditions of 1.5 MPa.

[0032] Figure 14 The results are from the tail wave analysis of the coal body waveform under carbon dioxide adsorption conditions of 2.5 MPa.

[0033] Figure 15 This is a graph showing the curve changes of the specific disaster early warning threshold in Example 4.

[0034] Figure 16 This is an evolution curve of the proprietary safe desorption threshold in Example 4.

[0035] Figure 17 This is a flowchart of the step-by-step slow depressurization process for simulating on-site gas extraction in Example 4.

[0036] The reference numerals in the accompanying drawings include: high-pressure adsorption chamber subsystem 100, chamber 10, chamber body 11, front cover plate 12, rear cover plate 13, front cover plate sealing ring 14, rear cover plate sealing ring 15, guide rod hole 16, wave emission guide rod 20, guide rod dynamic sealing unit (V-shaped gasket) 40, wire lead-out static sealing unit 50, auxiliary sealing gasket group 51, polyethylene gasket 511, metal gasket 512, potting body 52, limiting pressure plate 53, branch hole 531, wire passage hole 54, sample tray 60, mounting groove 61, elastic element 62, wire passage groove 63, viewing window 70, stepped groove 71, viewing window sealing ring 72, pressure cap 73, buffer gasket 74, pressure sensor 80, gas injection and pressure control subsystem 200, strain gauge 300, wave emitter 410, piezoelectric ceramic 420, wave emission receiver 430, coal and rock specimen A. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] Example 1

[0039] This embodiment provides an experimental system for detecting micro-fractures in coal adsorption, such as... Figure 1 As shown, in a preferred embodiment, the detection system includes a high-pressure adsorption chamber subsystem 100, a gas injection and pressure control subsystem 200, a strain subsystem, and a wave emission acquisition subsystem.

[0040] The high-pressure adsorption chamber subsystem 100 is the pressure-bearing core, including a chamber 10 for accommodating coal and rock samples and providing a highly airtight testing environment, and a wave-emitting guide rod 20 extending into the chamber 10 through its wall. A wiring port is pre-installed inside the chamber 10, sealed using a combination of pressure plates and epoxy resin. A V-shaped washer is added to the middle of the wave-emitting guide rod 20 to ensure low-loss signal transmission while maintaining the airtightness of the equipment. A high-strength glass viewing window 70 is integrated on the front of the chamber 10 for auxiliary observation; an injection port for connecting to an external gas source pipeline is also provided on the rear of the chamber 10 to inject adsorbed gas into the chamber 10 and maintain the pressure environment. Preferably, the chamber 10 is also equipped with a pressure sensor 80 for monitoring its internal pressure, and a pressure relief valve (not shown in the drawings) for rapid pressure relief inside the chamber 10.

[0041] The output of the gas injection and pressure control subsystem 200 is connected to the gas injection interface via a pipeline, which is used to provide a controllable gas environment to the cavity 10. The gas injection and pressure control subsystem 200 includes a high-purity gas source, a gas supply pipeline connected to the gas source, a pressure reducing valve installed on the gas supply pipeline, and a high-precision pressure measuring instrument. The outlet end of the gas supply pipeline is connected to the gas injection interface, forming a closed gas injection and pressure testing environment, which can accurately control the gas injected into the cavity 10 to maintain a stable pressure environment inside the cavity 10.

[0042] A strain gauge system is used to capture strain changes caused by adsorbed gases in coal and rock samples. The strain gauge system consists of several strain gauges that can be attached to the surface of the coal and rock sample. Figure 7As shown in the diagram, a strain gauge 300 is connected to the signal output terminal of the strain gauge, and the strain gauge 300 is connected to a computer terminal. The main working process of the strain subsystem is as follows: the coal and rock sample adsorbs gas and deforms; the strain gauge senses this deformation and converts it into an electrical signal; the electrical signal is transmitted back to the strain gauge 300 via a transmission line; the strain gauge 300 calculates the changes at each measuring point in real time; the data, along with a timestamp, is uploaded to the computer terminal for storage and display; the image results of strain changing over time are shown in the diagram. Figure 8 As shown.

[0043] The wave emission detection subsystem is a module for capturing the dynamic process of micro-fractures inside the coal body. It includes a wave emitter 410 (such as a CTS-8077PR waveform exciter), a piezoelectric ceramic 420 (installed inside the cavity 10), and a wave emission receiver 430. The piezoelectric ceramic 420 and the wave emission guide rod 20 are respectively attached to the surfaces of both ends of the coal sample (specifically: the lower surface of the coal sample A is in contact with and tightly attached to the piezoelectric ceramic 420, and the upper surface of the coal sample A is in contact with and tightly attached to the inner end of the wave emission guide rod 20 that extends into the cavity 10; preferably, a small amount of petroleum jelly is applied to the upper and lower surfaces of the coal sample A to ensure sufficient adhesion). The upper end of the wave emitting guide rod 20 extends outside the cavity 10 to connect to the external wave emitter 410. The wave emitter 410 periodically emits elastic waves, which are transmitted to the coal sample by the wave emitting guide rod 20. The piezoelectric ceramic 420 receives the wave signal, amplifies it, and then transmits it to the wave emitting receiver 430. The wave emitting receiver 430 simultaneously captures the coal micro-fracture wave emission signal and the elastic wave waveform, and transmits the signal to the computer terminal for storage and display.

[0044] In this embodiment, the wave transmitter 410 may be, for example, a piezoelectric ceramic transducer or a magnetostrictive transducer, which is coaxially fixed to the outer end of the elastic waveguide rod 20 by means of threads or adhesive, and is used to generate elastic wave signals.

[0045] It should be noted that in this invention, the piezoelectric ceramic 420 is not only used to receive the active detection wave signal from the elastic waveguide rod 20, but also to passively receive the acoustic emission signal radiated when the coal and rock specimen A generates micro-fractures during the adsorption process. This signal is led out to an external amplifier and acoustic emission acquisition system through the same wire, thereby realizing the integrated function of active wave detection and passive micro-fracture monitoring.

[0046] like Figures 1-3 As shown, in this invention, the cavity 10 includes a cavity body 11 with openings at both the front and rear ends, and an internal cavity for placing the coal and rock specimen A. A front cover plate 12 is detachably fixed to the front end of the cavity body 11 by bolts, and the front cover plate 12 and the cavity body 11 are sealed together by a front cover plate sealing ring 14. A rear cover plate 13 is detachably fixed to the rear end of the cavity body 11 by bolts, and the rear cover plate 13 and the cavity body 11 are sealed together by a rear cover plate sealing ring 15.

[0047] like Figure 1 and Figure 5 As shown, in this invention, the guide rod hole 16 is located at the top of the cavity body 11. The wave emitting guide rod 20 can slide axially (vertically) relative to the guide rod hole 16 and be sealed by the guide rod dynamic sealing unit 40. The guide rod dynamic sealing unit 40 includes a V-shaped washer disposed in the guide rod hole 16 of the cavity 10. The V-shaped washer 40 can be sleeved on the outside of the wave emitting guide rod 20, and the V-shaped opening end of the V-shaped washer 40 faces the high-pressure side inside the cavity 10, achieving a self-tightening seal using gas pressure. The V-shaped washer 40 is made of elastic rubber or polymer. Under high pressure, the V-shaped opening of the V-shaped washer 40 is opened by pressure and fits the outer wall of the wave emitting guide rod 20 and the inner wall of the guide rod hole 16. Moreover, because the V-shaped washer 40 has a certain elastic deformation capacity, it also allows the wave emitting guide rod 20 to adapt to axial displacement as the coal and rock specimen A is adsorbed and expanded.

[0048] The above technical solution uses a V-shaped washer 40 fitted in the middle of the wave emitting guide rod 20, with the opening of the V-shaped washer 40 facing the inside of the cavity (high pressure side), to achieve a self-tightening seal by means of air pressure. This structure reduces the radial clamping force on the wave emitting guide rod 20 while ensuring air tightness, and realizes low-damping transmission of acoustic signals.

[0049] like Figure 2 and Figure 6 As shown, in this invention, the multi-channel wires of the strain gauge pass through the wall of the cavity 10 and are sealed by the wire lead-out static sealing unit 50. The wires of the piezoelectric ceramic 30 also pass through the wall of the cavity 10 and are sealed by the wire lead-out static sealing unit 50. Multiple wires are simultaneously led out through the wire lead-out static sealing unit 50 to form a multi-channel electrical signal wiring port (hereinafter referred to as wiring port). Preferably, multiple wiring ports are provided, and the wiring ports are located on the side wall of the cavity body 11 or on the rear cover plate 13. The wire lead-out static sealing unit 50 includes a wire passage hole 54 disposed on the wall of the cavity 10, an auxiliary sealing gasket assembly 51 filled in the wire passage hole 54, a potting body 52 (epoxy resin potting body 52) covering the outside of the auxiliary sealing gasket assembly 51, and a limiting pressure plate 53 made of metal. The wire passage hole 54 is a stepped hole and communicates with the inside of the cavity 10. The inner end of the auxiliary sealing gasket assembly 51 is limited by the step. The auxiliary sealing gasket is composed of several polyethylene gaskets 511 and several metal gaskets 512 stacked together. The limiting pressure plate 53 is fixed to the outer wall of the cavity 10 by bolts and applies an axial limiting force to the potting body 52 and the auxiliary sealing gasket assembly 51. The limiting pressure plate 53 has a branch hole 531 for multi-channel wires to pass through. The auxiliary sealing gasket assembly 51 is provided between the limiting pressure plate 53 and the cavity 10 to prevent high-pressure gas from leaking along the interface between the epoxy resin potting body 52 and the wall of the wire passage hole 54.

[0050] The above technical solution, for sealing the electrical signal wiring port, adopts a combination of epoxy resin potting body 52 and mechanical limiting pressure plate 53 for the micro wire bundle connecting the internal strain gauge / piezoelectric ceramic 30. After the wire passes through the wiring port, it is filled with epoxy resin, and the external limiting pressure plate 53 and bolts are used for limiting and fixing to prevent high pressure gas from pushing the epoxy resin potting body 52 out.

[0051] like Figure 4 As shown, in another preferred embodiment, a sample tray 60, which is a metal block, is provided inside the cavity 10. The piezoelectric ceramic 30 is elastically connected to the mounting groove 61 of the sample tray 60 via an elastic element 62. The upper surface of the piezoelectric ceramic 30 is slightly higher than the upper surface of the sample tray 60. The elastic element 62 is a columnar spring or silicone rubber, so that the center of the lower surface of the coal and rock specimen A after installation maintains physical contact coupling with the upper end face of the piezoelectric ceramic 30 used to receive wave signals. The sample tray 60 is also provided with a wire groove 63 communicating with the mounting groove 61, so that the wire (shielded wire) of the piezoelectric ceramic 30 can pass through the wire groove 63 and exit the sample tray 60.

[0052] like Figure 1 and Figure 2 As shown, in another preferred embodiment, a viewing window 70 made of sapphire glass is also provided on the front side of the cavity 10. Sapphire glass combines high strength and high light transmittance. This viewing window 70 is located on the front cover plate 12, facing the side surface of the coal and rock specimen A. External imaging equipment can directly observe the macroscopic crack propagation and matrix expansion of the internal coal and rock specimen A. Specifically, a stepped groove 71 is formed on the front side of the cavity 10. A viewing window sealing ring 72 is fitted at the step of the stepped groove 71. The viewing window 70 is embedded in the stepped groove 71 and the viewing window sealing ring 72 is pressed tightly. Then, it is axially pressed and sealed by the pressure cap 73 outside the cavity 10. Preferably, a buffer gasket 74 is also provided between the viewing window 70 and the pressure cap 73 to provide buffer protection.

[0053] Initially, the cavity 10 is in the open state, and the front cover 12 and the rear cover 13 are not installed.

[0054] The process of using the high-pressure adsorption device is as follows: First, a coal and rock specimen A is prepared. The surface is polished and strain gauges are attached in the direction parallel to the bedding plane and perpendicular to the bedding plane. When attaching, high-temperature resistant (150℃) epoxy resin adhesive is used to bond the strain gauge substrate to the surface of the coal and rock specimen A. A layer of silicone rubber protective layer is coated on the surface to prevent the high-pressure adsorption gas (such as methane) from corroding or short-circuiting the strain gauge. The strain gauge wire and the piezoelectric ceramic 30 shield wire are passed through the wire hole 54 in the wall of the cavity 10 to complete the epoxy resin potting to form the potting body 52 and locked and fixed by the limiting pressure plate 53. The coal and rock specimen A is placed on the specimen tray 60 inside the cavity body 11, with the lower surface of the coal and rock specimen A in close contact with the upper surface of the piezoelectric ceramic 30. The rear cover plate 13 is fixed to the rear side of the cavity body 11. The wave emitting guide rod 20 is adjusted so that its end face is in close contact with the upper surface of the coal and rock specimen A. At this time, the V-shaped washer 40 is in a pre-installed state. Then, the front cover plate 12 is fixed to the front side of the cavity body 11 to form the cavity 10. The gas injection interface is connected to the external pipeline and high-pressure gas is injected. As the internal pressure of the cavity 10 increases, the V-shaped washer 40 automatically clamps the wave emitting guide rod 20 under the action of gas pressure to achieve a seal. The macroscopic cracks on the surface of the coal and rock specimen A are recorded using the sapphire glass viewing window 70, and strain data is collected simultaneously. Active elastic wave detection is performed using the wave emitting guide rod 20. By analyzing the small changes in wave velocity, the microstructural evolution inside the coal and rock body is inverted.

[0055] Example 2

[0056] This embodiment provides a method for detecting the emission of adsorbed micro-fracture waves in coal, based on the coal adsorption micro-fracture detection experimental system of Embodiment 1, and includes the following steps:

[0057] S1. Prepare coal and rock specimen A. The experiment uses a rectangular coal block sample of 50mm*25mm*25mm for testing. Grind the side of the specimen into two planes, observe the grinding profile, find the inert group and bedding direction, and attach strain gauges at the inert group position and in the direction parallel to and perpendicular to the bedding. Complete the strain gauge wire connection, specifically by welding the strain gauge wire to the wire passing through the wiring port of the rear cover plate 13.

[0058] S2. Place the piezoelectric ceramic 420 into the sample tray 60, supported by the elastic element 62 so that the surface of the piezoelectric ceramic 420 is slightly higher than the surface of the sample tray 60. Install the sample tray 60 containing the piezoelectric ceramic 420 into the cavity 10. Lead the piezoelectric ceramic 420 wire through the wire groove 63 of the sample tray 60 to prevent interference caused by squeezing the wire. Complete the connection between the piezoelectric ceramic 420 wire and the wiring port. Specifically, weld the piezoelectric ceramic 420 wire to the shielded wire passing through the wiring port of the rear cover plate 13. Apply a small amount of Vaseline to the upper and lower surfaces of the coal and rock specimen A. Place the coal and rock specimen A on the sample tray 60, making the lower surface of the coal and rock specimen A fully fit with the upper surface of the piezoelectric ceramic 420. Adjust the position of the wave emitting guide rod 20 so that the upper surface of the coal and rock specimen A fits with the lower surface of the wave emitting guide rod 20. At this time, the V-shaped washer is in the pre-installation state.

[0059] S3. Install the front and rear cover plates 13 of the cavity body 11, and tighten the bolts to seal the inside of the cavity 10, thus closing the cavity 10; connect the gas injection port to the output end of the gas injection and pressure control subsystem 200, that is, connect the gas injection port to a high-purity gas source through a pressure reducing valve, a gas pipeline, and a high-precision gas pressure measuring instrument; apply Vaseline to the generating head of the wave generator and make it adhere tightly to the top of the wave emitting guide rod 20 of the cavity 10. Connect the strain wire outside the wiring port of the rear cover plate 13 to the strain gauge 300, connect the strain gauge 300 to the computer terminal for recording, and connect the piezoelectric ceramic 420 shielded wire outside the wiring port of the rear cover plate 13 to the wave emitting receiver 430. The wave emitting receiver 430 is connected to the computer terminal through an aviation plug. The connection of the wiring outside the wiring port can be done in this step S3, or in step S1, or initially; the industrial camera can be installed outside the viewing window 70 in this step S3, or in step S1, or initially.

[0060] S4. Before the experiment, open the strain data recording software and oscilloscope software on the computer terminal, then turn on the strain subsystem, zero the strain data, and start recording the strain data; turn on the wave transmitter 410, select the appropriate wave properties, record the received wave data through the computer terminal, and turn off the wave transmitter 410 after recording is complete.

[0061] S5. Open the air pressure recording software on the computer terminal, inject gas into the cavity 10 through the gas injection and pressure control subsystem 200, so that the coal and rock sample is in a high-pressure gas environment, adjust the air pressure inside the cavity 10 to the first pressure value (e.g., 0.5MPa), maintain this pressure state until the adsorption of the coal and rock sample reaches equilibrium, and then turn off the gas source of the gas injection and pressure control subsystem 200.

[0062] S6. Simultaneously, start the wave transmitter 410 to emit elastic waves to the coal and rock sample in the high-pressure gas environment, record the wave data that penetrates the coal and rock sample, and then turn off the wave transmitter 410. Repeat this step at the set time interval to complete the wave data acquisition at this pressure level. Specifically, repeat this step at intervals of 5, 10, 20, 30, 40, 50, 60, and 70 minutes from the time interval of recording the previous set of data.

[0063] S7. When the internal air pressure of cavity 10 reaches the first pressure value (0.5MPa), the data recording is completed. Turn on the air source of the air injection and pressure control subsystem 200 and adjust the pressure to stabilize the internal air pressure of cavity 10 at a second pressure value (e.g., 1.5MPa) that is greater than the first pressure value. Turn off the air source and repeat step S6. After the end, adjust the internal air pressure of cavity 10 to a third pressure value (e.g., 2.5MPa) and a fourth pressure value (e.g., 3.5MPa) that are even greater. Repeat step S6 to complete the wave data acquisition at the corresponding pressure level.

[0064] S8. After all the wave data tests at all pressure levels have been completed and recorded, stop recording the strain data, depressurize the cavity 10 (for example, open the pressure relief valve on the cavity 10 to depressurize the cavity 10), and export the strain data and wave data of the entire adsorption process.

[0065] S9. By analyzing minute changes in the wave velocity, attenuation, or tail wave characteristics of elastic waves, the microstructural evolution inside coal and rock samples is inverted.

[0066] In this invention, when performing step S1, since the coal and rock specimen is black, it is preferable to spray a very thin layer of white matte paint as a base color (white background) on the observation surface of the coal and rock specimen A. The matte finish is to prevent reflection. Black spots are sprayed on the white background so that each tiny area (sub-area) on the surface of the coal and rock specimen has a unique grayscale characteristic. The spots should be uniform in size (the diameter of the spots is recommended to be around 0.05-0.1 mm), randomly distributed, and have high contrast.

[0067] During the experiment, when recording macroscopic cracks on the surface of coal and rock specimen A using the sapphire glass viewing window 70, a high-resolution industrial camera (such as a CCD camera with over 5 megapixels) was placed outside the cavity, directly facing the viewing window 70. The optical axis of the industrial camera must be perpendicular to both the viewing window 70 and the surface of coal and rock specimen A to eliminate perspective errors. The industrial camera used a high-brightness LED cold light source. Because sapphire glass is reflective, it is preferable to install polarizing filters (CPL) in front of the lens and the light source of the industrial camera to eliminate specular reflections from the glass surface and ensure that the industrial camera clearly captures the surface of the coal and rock specimen inside.

[0068] In step S4 (no gas injection, no pressurization), the industrial camera takes the first photo through the viewing window 70 as a zero-strain reference image. In steps S5-S7 (gas injection and pressurization process), the industrial camera is set to be triggered uniformly by the control system, and the photos taken are deformed images. Whenever the wave emitter emits an elastic wave or the strain gauge records data, the industrial camera simultaneously takes a photo, ensuring that each contour image corresponds to a specific wave velocity value.

[0069] The control system processes the images captured by the industrial camera (specifically, this can be done using dedicated DIC software):

[0070] 1) Divide the reference image into multiple small squares, called sub-regions;

[0071] 2) Search for the sub-region in the deformed image that is most similar to the gray-level distribution in the reference image. Specifically, you can calculate the difference between the gray-level values ​​of the corresponding pixels in the two sub-regions, then take the absolute value and sum them, and select the sub-region with the smallest sum.

[0072] 3) After finding the matching position, calculate the displacement vector of the center point of the sub-region in the deformed image relative to its position in the reference image;

[0073] 4) Result Generation (Full-field Strain Contour Map, DIC Contour Map): By differentiating the displacement field, the horizontal tensile or compressive strain ε of the strain field is obtained. x (Reflecting matrix expansion), vertical deformation ε y (Reflecting axial force), shear deformation γ xy (The easiest time to detect the onset of cracks).

[0074] After gas absorption, coal and rock specimen A does not expand uniformly. Some areas, such as the vitrinite, are in a high-strain state, while others, such as the inertinite, remain in a low-strain state. Before cracks are visible to the naked eye, a thin, bright high-strain band will appear on the DIC contour map; this is a precursor to microcrack initiation and fracture. When the bright band appears on the DIC contour map, examining the wave velocity data at that moment reveals a sharp drop in wave velocity, indicating an abrupt change. This is precisely because the uneven expansion of the microstructure components (as seen in the DIC contour map) leads to the formation of microcracks, which in turn blocks sound wave propagation, resulting in a decrease in macroscopic wave velocity (as measured by elastic waves).

[0075] This invention monitors the evolution of adsorption microfractures in coal bodies from three levels: microscopic, macroscopic surface, and macroscopic interior.

[0076] 1) Microscopic observation (strain gauge): By attaching strain gauges to specific microscopic coal and rock components (such as inert group / vitrinite group) and specific bedding directions in coal and rock specimen A, the differential adsorption expansion caused by material inhomogeneity inside the coal body can be accurately captured. This is the root cause of internal stress and micro-fractures.

[0077] 2) Macroscopic Surface (DIC-assisted Verification): Through a sapphire glass viewing window, combined with digital image correlation (DIC) technology, the evolution of strain field and crack initiation path on the coal surface are observed in real time to verify the local damage caused by microscopic expansion differences.

[0078] 3) Macroscopic internal (overall elastic wave inversion): Using active elastic wave / wake wave interferometry, the porosity and damage evolution of full-size specimens are measured.

[0079] In this invention, the specific method for inverting the microstructural evolution inside a coal and rock sample by analyzing minute changes in the wave velocity, attenuation, or tail wave characteristics of elastic waves is as follows:

[0080] 1) Obtaining porosity changes in coal and rock samples by measuring the wave velocity of elastic waves.

[0081]

[0082] in, Porosity is the porosity of a coal and rock sample, which is the proportion of pore volume to the total volume in the coal and rock sample. The reference wave velocity for elastic waves, i.e., the elastic wave velocity, is obtained by analyzing the wake waveform, as detailed in Example 3. The slope coefficient is measured using a standard sample; For the time difference, Figures 12-14 The amount of misalignment in; For the duration of transmission, this stripe is in Figures 12-14 The position on the horizontal axis.

[0083] As porosity increases, the overall wave velocity decreases. In adsorption experiments, the decrease in the velocity of each elastic wave can be converted into an increase in the porosity of the coal and rock sample. The porosity of the coal and rock samples increases. As the voltage increases, the attenuation of the elastic wave will increase significantly. If the peak voltage of the waveform decreases significantly, it indicates that the elastic wave has encountered more crack interfaces during propagation, resulting in scattering and energy loss.

[0084] 2) Obtaining the attenuation of elastic waves through the amplitude of elastic waves

[0085]

[0086]

[0087] in, The inverse quality factor is a direct representation of elastic wave attenuation. The attenuation coefficient is... For elastic wave velocity, It is the frequency of the input wave. The initial amplitude of the elastic wave (the initial amplitude measured in step S4). The amplitude of the elastic wave measured at a certain moment (the amplitude measured at a certain moment in step S6). The length of the coal and rock sample (e.g., 50 mm);

[0088] pass and get Further, the inverse quality factor was obtained. The curves showing changes with gas injection and time accurately characterize the energy dissipation capacity inside the coal and rock samples. Abrupt changes in the curves (such as the moment when the inverse quality factor (first derivative) first exceeds 5% of the average change rate in the stable stage) can be used to determine the time when damage occurs in the coal and rock samples, thus revealing the subtle changes in the coal body during the adsorption process.

[0089] It should be noted that, regarding the attenuation coefficient The calculation formula is obtained as follows:

[0090] The core form of the Beer-Lambert law in wave physics is that the intensity / amplitude of a wave decays exponentially with the distance it travels, as follows: The result of the transformation is: .

[0091] Because the mechanical properties of coal and rock change after absorbing methane, this is a significant contributing factor to coal and gas outbursts or rockbursts. This invention, through active elastic wave detection, can detect minute changes and the accumulation of cracks within the coal body before macroscopic deformation occurs. This allows for early warning of coal body failure under high methane pressure, providing a longer warning window. Furthermore, by detecting changes in the elastic wave waveform, it can assess whether excessive expansion of the coal body during gas injection causes micro-cracks, ensuring that injected gas does not leak and guaranteeing the safety of geological sealing.

[0092] Example 3

[0093] This embodiment uses the coal adsorption micro-fracture detection experimental system of Embodiment 1 and the detection method of Embodiment 2 to conduct coal adsorption elastic wave detection experiments. For example, nitrogen adsorption experiments at 2.5 MPa, carbon dioxide adsorption experiments at 1.5 MPa, and carbon dioxide adsorption experiments at 2.5 MPa are performed. Elastic waves are emitted every 5, 10, 20, 30, 40, 60, and 70 minutes during the adsorption process, and the elastic wave waveforms are acquired through the wave emission acquisition subsystem. The elastic wave waveforms under the three experimental conditions are as follows: Figure 9 , Figure 10 and Figure 11 As shown.

[0094] from Figure 9 , Figure 10 and Figure 11 As can be seen, the elastic wave waveform changes to some extent during coal adsorption under different adsorption conditions. However, due to the small amount of change, it is difficult to accurately calculate the impact of different adsorption conditions on the mechanical properties of coal by directly calculating the changes in the mechanical parameters of coal during adsorption using the initial elastic wave arrival time. Therefore, this invention uses the wake wave analysis method to reprocess the waveform data obtained at different time periods.

[0095] The elastic wave tail waves under three experimental conditions were transformed using MATLAB programming. The transformation results are as follows: Figure 12 , Figure 13 and Figure 14 As shown, the transformed waveform forms alternating light and dark stripes, where dark stripes represent wave peaks and light stripes represent wave troughs. The specific transformation process is as follows: First, the elastic wave tailwave signals under different experimental conditions are filtered and denoised to remove interference noise and retain the effective waveform. Then, through time-domain waveform stacking imaging, the denoised one-dimensional time-domain waveforms are arranged row by row along the vertical axis according to the absolute time sequence of the experiment. The horizontal axis represents the propagation time of the elastic wave, and the vertical axis represents the experimental process time, visualized using grayscale mapping. The wave peaks and troughs correspond to the dark and light areas in the image, respectively, and the difference between the light and dark stripes at different times represents the wave velocity difference between the previous and subsequent elastic waves.

[0096] from Figures 12-14 As can be seen, the difference between bright and dark fringes is not significant under different adsorption times in the initial stage of the elastic wave. However, significant differences in bright and dark fringes appear under different adsorption times in the wake stage. This is because the increased propagation distance of the elastic wave leads to a cumulative increase in the difference in wave velocity. Therefore, it can be seen that the wake wave can effectively capture the subtle changes in the macroscopic mechanical properties of the coal body during adsorption.

[0097] Calculate how much time has passed since a certain dark stripe shifted to the right from its initial position. According to the principles of wave physics, the rate of change of wave speed is inversely proportional to the rate of time shift. The elastic wave speed can be obtained using the following formula. :

[0098]

[0099] in, for The elastic wave velocity at any given moment; This is the change in wave speed; The propagation time is the current position of the stripe on the horizontal axis. This represents the amount of time drift (i.e., the time difference in the movement of the stripes).

[0100] Example 4

[0101] This embodiment provides a coal mining safety monitoring system, which includes an indoor parameter calibration terminal, a field wave emission acquisition terminal, and a safety early warning control terminal.

[0102] Among them, the indoor parameter calibration end adopts the experimental system of Example 1 to conduct desorption and decompression experiments on coal and rock samples taken from the working face of the target coal seam, extracting the exclusive disaster early warning threshold characterizing the acceleration of micro-fractures in the coal body, and the exclusive safety desorption threshold characterizing the elimination of internal residual expansion stress.

[0103] The field wave transmission and acquisition end includes a wave transmission probe and a wave receiving probe deployed in the field detection borehole of the target coal seam, used to transmit active elastic waves to the coal seam and capture the field elastic wave waveform.

[0104] The safety early warning control terminal is used to assess the anti-outburst extraction compliance of the target coal seam based on the exclusive safety desorption threshold before mining. During mining operations, it uses time-domain waveform stacking imaging technology to extract the time drift Δt and amplitude attenuation of the elastic waves at the site, and calculates the inverse quality factor at the site in real time. Evolutionary characteristics, when they reach or exceed the specific disaster early warning threshold, trigger an advanced safety warning.

[0105] In response to the extremely heterogeneous characteristics of deep coal seams, this coal mining safety monitoring system overcomes the limitations of traditional single static gas concentration or pressure indicators. It constructs a comprehensive safety monitoring system covering the entire coal mining process, from indoor parameter calibration to pre-mining desorption compliance assessment to dynamic early warning during mining. Its specific implementation and working mechanism are as follows:

[0106] Phase 1: Indoor Parameter Calibration

[0107] Before mining the target coal seam, coal samples were extracted on-site and placed in the high-pressure adsorption chamber subsystem of Example 1. After the samples were saturated with adsorbed gas and reached in-situ stress equilibrium, the following parameter calibration experiments were conducted:

[0108] 1) Obtaining a specific disaster early warning threshold: Simulating rapid depressurization conditions in front of the coal mining face, by rapidly releasing the cavity pressure, inducing the expansion and ionization of high-pressure gas inside the specimen and generating micro-fractures. For example... Figure 15 As shown, during the depressurization process, when the reverse quality factor... When the evolution curve shows a sudden increase in slope (for example, the moment when the first derivative of the inverse quality factor evolution curve first exceeds 5% of the average rate of change in the stable phase is the break-off point), and micro-crack precursors are captured on the specimen surface through the viewing window, this moment is extracted. The abrupt change slope characteristic value is set as the exclusive disaster early warning threshold for the target coal seam.

[0109] 2) Obtain a dedicated safe desorption threshold: such as Figure 16and Figure 17 As shown, this simulates the gradual, step-by-step depressurization process during on-site gas extraction. Acoustic and optical monitoring are simultaneously activated when… When the evolution curve enters the low-level stable region, and the DIC full-field strain cloud map meets the quantitative dissipation criterion for the strain concentration zone (i.e., the maximum principal strain gradient difference across the entire field drops below 0.05%), it is determined that the residual expansion stress inside the coal seam has been substantially eliminated. The critical desorption pressure and residual gas concentration in the cavity at this time are extracted and set as the exclusive safe desorption threshold for the target coal seam.

[0110] Phase Two: Pre-Mining Phase (Assessment of Outburst Prevention and Drainage Standards)

[0111] Before formal mining of the target coal seam, regional gas pre-drainage is required. This system uses the specific safe desorption threshold obtained in the first stage as the benchmark for judging whether the drainage meets the standards, comparing the residual gas concentration or gas pressure measured on-site with this specific safe desorption threshold. If the measured on-site indicators do not drop below the specific safe desorption threshold, it indicates that the residual stress inside the coal seam skeleton has not been completely eliminated, and there is still a risk of outburst due to micro-fractures. Gas drainage and pressure reduction operations must continue until the measured on-site indicators drop below the specific safe desorption threshold before mining operations can proceed, thereby preventing the hidden danger of outburst due to low indicators from the source.

[0112] Phase 3: Mining Phase (24 / 7 Dynamic Early Warning)

[0113] After the target coal seam passes the above-mentioned anti-outburst compliance assessment and enters mining operations, the mining disturbance will cause depressurization of the coal seam in front of the working face, which can easily trigger the free expansion of residual gas inside the coal body and local micro-fractures. The physical mechanism of this on-site depressurization fracture is equivalent to the first-stage indoor rapid depressurization calibration condition. Online dynamic monitoring is fully implemented using on-site wave emission acquisition terminals and safety early warning control terminals.

[0114] (1) The wave transmitting probe and the wave receiving probe are arranged in the detection borehole in front of the working face using a cross-hole transmission method. In order to overcome the high attenuation characteristics of the coal and rock medium in the field, the borehole spacing is set to 5 to 15 m, and a low-frequency elastic wave probe of 1 to 10 kHz is selected for the transmission and reception of elastic waves.

[0115] (2) The safety early warning control terminal extracts the tail wave band from the elastic wave waveform at the site, and uses time-domain waveform stacking imaging technology to convert it into a two-dimensional bright and dark striped image. The time drift Δt and waveform amplitude attenuation characteristics are extracted from it, and the current adverse quality factor of the coal seam at the site is calculated in real time. The slope of change.

[0116] (3) The system will calculate the data in real time on site. The slope of change is compared on a rolling basis with the specific disaster early warning threshold calibrated in the first stage. When on-site measurements are performed... When the slope of change reaches or exceeds the exclusive disaster warning threshold, it is determined that the mining disturbance and pressure relief have induced the accelerated accumulation of micro-fractures in the coal body. Before the occurrence of macro-dynamic disasters in the coal body, the safety warning control terminal automatically triggers audible and visual warning signals to guide on-site workers to evacuate and take targeted pressure relief and anti-outburst measures.

[0117] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A coal adsorption micro-fracture detection experimental system, characterized in that, It includes a high-pressure adsorption chamber subsystem, a gas injection and pressure control subsystem, a strain subsystem, and a wave emission acquisition subsystem; The high-pressure adsorption chamber subsystem is the pressure-bearing core, including a chamber for accommodating coal and rock samples and providing a high airtightness testing environment, and a wave emitting guide rod that extends through the chamber wall into its interior. The chamber wall is also provided with an injection port for connecting an external gas source pipeline. The output of the gas injection and pressure control subsystem is connected to the gas injection interface via a pipeline, which is used to provide a controllable gas environment in the cavity; The strain subsystem is used to capture strain changes caused by adsorbed gas in the coal and rock sample; The wave emission acquisition subsystem includes a wave emitter, a piezoelectric ceramic, and a wave emission receiver. The piezoelectric ceramic and the wave emission guide rod are respectively attached to the surfaces at both ends of the coal sample. The wave emitter periodically emits elastic waves, which are transmitted by the wave emission guide rod. The piezoelectric ceramic receives the wave signal and transmits it to the wave emission receiver. The wave emission receiver synchronously captures the micro-fracture wave emission signal and the elastic wave waveform.

2. The coal adsorption micro-fracture detection experimental system according to claim 1, characterized in that, The wave-emitting guide rod can slide axially relative to the guide rod hole of the cavity and be sealed by the guide rod dynamic sealing unit. The multi-channel wire of the strain gauge system passes through the cavity wall and is sealed by the wire leading out of the static sealing unit. The wire of the piezoelectric ceramic passes through the cavity wall and is also sealed by the wire leading out of the static sealing unit. The guide rod dynamic sealing unit includes a V-shaped washer disposed in the guide rod hole of the cavity. The V-shaped washer can be sleeved on the outside of the wave emitting guide rod, and the V-shaped open end of the V-shaped washer faces the high-pressure side inside the cavity, so as to achieve a self-tightening seal by using gas pressure. The wire lead-out static sealing unit includes a wire passage hole disposed in the cavity wall, an auxiliary sealing gasket group filled in the wire passage hole, a potting body covering the outside of the auxiliary sealing gasket group, and a limiting pressure plate. The limiting pressure plate is fixed to the outer wall of the cavity and applies an axial limiting force to the potting body.

3. The coal adsorption micro-fracture detection experimental system according to claim 2, characterized in that, The V-shaped washer is made of elastic rubber or polymer. Under high pressure, the V-shaped opening of the V-shaped washer is opened by pressure and fits the outer wall of the wave emitting guide rod and the inner wall of the guide rod hole.

4. The coal adsorption microfracture detection experimental system according to any one of claims 1-3, characterized in that, The cavity is equipped with a sample tray, and the piezoelectric ceramic is elastically connected to the mounting groove of the sample tray through an elastic element. And / or the front side of the cavity is also provided with a high-strength viewing window facing the side surface of the coal and rock specimen. The front side of the cavity is provided with a groove, and the bottom of the groove is provided with a sealing ring. The viewing window is embedded in the groove and is axially pressed and sealed by an external pressure cap. A buffer gasket is also provided between the viewing window and the pressure cap. And / or the cavity includes a cavity body with openings at both the front and rear ends, a front cover plate is detachably fixed to the front end of the cavity body, a rear cover plate is detachably fixed to the rear end of the cavity body, and the front cover plate and the rear cover plate are sealed to the cavity body by sealing rings.

5. A method for detecting micro-fractures in coal adsorption, implemented based on the coal adsorption micro-fracture detection experimental system according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Prepare and grind the coal and rock specimen, attach the strain gauges of the strain system to the ground surface of the coal and rock specimen, and complete the connection between the strain gauge wires and the wiring ports. S2. Install the piezoelectric ceramic inside the cavity, complete the connection between the piezoelectric ceramic wire and the wiring port, place the coal and rock specimen on the upper surface of the piezoelectric ceramic and fit it tightly, adjust the position of the wave emitting guide rod so that the upper surface of the coal and rock specimen fits properly with the lower surface of the wave emitting guide rod. S3, a sealed cavity, connecting the gas injection port to the output of the gas injection and pressure control subsystem, and tightly fitting the wave transmitter head to the top of the wave emission guide rod; S4. Start the strain subsystem and zero the strain data before starting to record. Turn on the wave emitter and set the wave properties. Record the wave data and then turn off the wave emitter. S5. Inject the gas to be adsorbed into the cavity through the gas injection and pressure control subsystem, so that the coal and rock sample is in a high-pressure gas environment. Adjust the gas pressure to the preset first pressure value, maintain this pressure state until the coal and rock sample adsorption is balanced, and then shut off the gas source. S6. Start the wave transmitter to emit elastic waves to the coal and rock sample in the high-pressure gas environment, record the wave data that penetrates the coal and rock sample, and turn off the wave transmitter. Repeat this step at the set time interval to complete the wave data acquisition at this pressure level. S7. Adjust the air pressure in the cavity to multiple increasing pressure values ​​in sequence. The pressure value of each level increases in sequence. After each pressure value is adjusted to a level and stabilized, repeat step S6 to complete the wave data acquisition at the corresponding pressure level. S8. After the wave data acquisition at all pressure levels is completed, stop the strain data recording, depressurize the cavity, and export the strain data and wave data of the entire adsorption process. S9. By analyzing minute changes in the wave velocity, attenuation, or tail wave characteristics of elastic waves, the microstructural evolution inside coal and rock samples is inverted.

6. The detection method according to claim 5, characterized in that, When no gas is injected in step S4, and during the gas injection and pressurization process in steps S5-S7, the industrial camera synchronously captures images through the viewing window on the front side of the cavity. The control system processes the images captured by the industrial camera using DIC technology to generate a full-field strain cloud map - DIC cloud map.

7. The detection method according to claim 5, characterized in that, The specific method for inverting the evolution of the microstructure inside a coal and rock sample by analyzing minute changes in the wave velocity, attenuation, or tail wave characteristics of elastic waves is as follows: 1) Obtaining porosity changes in coal and rock samples by measuring the wave velocity of elastic waves. in, Porosity refers to the porosity of a coal and rock sample, which is the proportion of pore volume to the total volume of the sample. The reference wave velocity for elastic waves, i.e., the elastic wave velocity, is obtained by analyzing the wake waveform. The slope coefficient is measured using a standard sample; This represents the amount of time shift; For the duration of transmission; In the adsorption experiment, every decrease in the measured elastic wave velocity can be converted into an increase in the porosity of the coal and rock sample. With the increase of porosity in the coal and rock sample With the increase of the , the attenuation of elastic waves will increase significantly, indicating that elastic waves encounter more crack interfaces during propagation, resulting in scattering and energy loss. 2) Obtaining the attenuation of elastic waves through the amplitude of elastic waves in, The inverse quality factor is a direct representation of elastic wave attenuation. The attenuation coefficient is... For elastic wave velocity, It is the frequency of the input wave. The initial amplitude of the elastic wave. The amplitude of the elastic wave measured at a certain moment. The length of the coal and rock sample; pass and get Further, the inverse quality factor was obtained. The curves showing changes with gas injection and time accurately characterize the energy dissipation capacity inside the coal and rock sample, and the abrupt changes in the curves reveal the time at which damage occurs in the coal and rock sample.

8. The detection method according to claim 7, characterized in that, The method for obtaining the elastic wave velocity by analyzing the wake waveform is as follows: The tail waves of elastic waves under different experimental conditions were transformed, and after transformation, alternating bright and dark stripes were formed. The dark stripes represent wave crests and the light stripes represent wave troughs. The difference between the bright and dark stripes at different times represents the difference in wave velocity between the previous elastic wave and the next elastic wave. According to the principles of wave physics, the rate of change of wave speed is inversely proportional to the rate of time drift. The elastic wave speed can be obtained using the following formula. : in, for The elastic wave velocity at any given moment; This is the change in wave speed; The propagation time is the current position of the stripe on the horizontal axis. This represents the amount of time drift.

9. A coal mining safety monitoring system, characterized in that, This includes an indoor parameter calibration terminal, a field wave emission acquisition terminal, and a safety early warning control terminal; The indoor parameter calibration terminal uses the experimental system described in any one of claims 1-4 to conduct desorption and decompression experiments on coal and rock samples taken from the target coal seam working face, extracting a specific disaster early warning threshold characterizing the acceleration of micro-fractures in the coal body, and a specific safety desorption threshold characterizing the elimination of internal residual expansion stress. The field wave transmission and acquisition end includes a wave transmission probe and a wave receiving probe deployed in the field detection borehole of the target coal seam, used to transmit active elastic waves to the coal seam and capture the field elastic wave waveform; The safety early warning control terminal is used to assess the anti-outburst extraction compliance of the target coal seam before mining, based on the exclusive safety desorption threshold. During mining operations, it uses time-domain waveform stacking imaging technology to extract the time drift Δt and amplitude attenuation of the elastic wave at the site, and calculates the inverse quality factor at the site in real time. Evolutionary characteristics, when they reach or exceed the specific disaster early warning threshold, trigger an advanced safety warning.

10. The coal mining safety monitoring system according to claim 9, characterized in that, The coal mining safety monitoring system employs a two-stage safety monitoring method, specifically including the following steps: 1) Indoor parameter calibration: After the coal and rock samples loaded into the high-pressure adsorption chamber subsystem are saturated with adsorption, the coal body fracturing process induced by mining and decompression is simulated, and the parameters are extracted. The abrupt change in the slope of the curve serves as the specific disaster early warning threshold; simulated on-site sampling is performed using a stepped depressurization and desorption method, when... When the curve enters the low-level stable region and the DIC cloud map meets the quantitative dissipation criterion of the strain concentration zone, the critical desorption pressure and residual gas concentration in the cavity at this time are extracted as the exclusive safe desorption threshold. 2) Pre-mining outburst prevention compliance assessment: If the on-site pre-drainage gas index has not dropped below the exclusive safety desorption threshold before mining operations, it is determined that the internal expansion stress of the coal body has not been substantially eliminated, and drainage and pressure reduction must continue. 3) Dynamic early warning during mining: During mining operations, the on-site wave emission acquisition terminal performs cross-hole transmission monitoring, and the safety early warning control terminal calculates the on-site situation in real time. When the evolution slope reaches or exceeds the exclusive disaster early warning threshold, it is determined that the mining disturbance has induced abnormal coal body rupture and triggered an advanced safety early warning.

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