Method for preventing rock burst

Abstract

The invention discloses a method for preventing rock burst, and belongs to the technical field of coal mining safety. Comprising the following steps: selecting a coal seam of a to-be-solved dangerous rock burst mine, measuring the gas pressure of the coal seam, and drilling a coal sample for coal body impact energy index test; evaluating the impact risk grade of the target coal seam according to the target coal seam gas pressure and the impact energy index of the coal body; if the impact risk of the target coal seam is higher than the set level, an alternating magnetic field transmitting device is arranged at the set position of the target coal seam to conduct gas desorption on the coal seam. According to the invention, through dual parameter measurement of the gas pressure and the impact energy index, accurate assessment of the impact risk is realized, movement and desorption of gas molecules in the coal body are promoted by using the magnetic field effect, the action range is wide, no mechanical disturbance exists, and the desorption efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of coal mining safety technology, specifically to a method for preventing rockbursts. Background Technology

[0002] As the scale of coal mining in my country continues to expand, the mining depth is also increasing year by year. Against this backdrop, the threat of rock bursts during coal resource mining is becoming increasingly severe, and has become one of the main dynamic hazards restricting the safe and efficient mining of deep coal mines.

[0003] Existing research indicates that coal seam gas and coal hardness are key factors influencing the risk of rockbursts. On the one hand, high-pressure gas generated by coal seam desorption provides the impetus for rockbursts; different coal seam gas contents correspond to different rockburst risks, with higher gas contents often resulting in greater probability and intensity of rockbursts. On the other hand, coal hardness is positively correlated with rockburst risk; the harder the coal, the stronger its elastic energy storage capacity, making it more prone to sudden energy release under stress concentration conditions, leading to rockburst accidents.

[0004] Currently, the industry has adopted various technical means to prevent rockbursts, such as pressure relief blasting, borehole pressure relief, and water injection softening. However, these methods have problems such as insufficient targeting, limited effectiveness, or complex construction. For example, pressure relief blasting may cause local stress redistribution, borehole pressure relief is not well adapted to high-gas coal seams, and water injection softening is not ideal for softening hard coal bodies. Summary of the Invention

[0005] The technical problem this invention aims to solve is that existing methods for preventing rockbursts are not effective enough. Therefore, this invention proposes a highly efficient and safe method for preventing rockbursts based on the action of a magnetic field.

[0006] To address the aforementioned technical problems, the present invention provides the following technical solution: A method for preventing rockbursts includes the following steps: Select the coal seam of the mine to be protected against rock bursts, measure the gas pressure of the coal seam, and drill coal samples to test the coal body impact energy index. The impact hazard level of the target coal seam is assessed based on the gas pressure and impact energy index of the coal body. If the impact hazard of the target coal seam is higher than the set level, an alternating magnetic field emission device is deployed at a set location in the target coal seam to desorb gas from the coal seam.

[0007] In some embodiments of the present invention, the determination of gas pressure in a coal seam includes: drilling at least one set of test holes in the target coal seam, placing a pressure measuring tube in the test holes and sealing the test holes, wherein a pressure sensor is provided inside the pressure measuring tube, and after a set time, the pressure value of the test hole is obtained based on the detection signal of the pressure sensor.

[0008] In some embodiments of the present invention, at least three sets of test holes are drilled along the upper and lower roadways toward the target coal seam. The three sets of test holes are arranged at intervals in the vertical direction, and the distance between the test holes and the working face is greater than 100m.

[0009] In some embodiments of the present invention, the coal sample drilling and coal impact energy index test includes: extracting at least two groups of coal samples spaced apart along the height direction, and preparing each group of coal samples into a standard specimen for uniaxial compression test to measure the stress-strain curve of the coal sample, and obtaining the impact energy index based on the stress-strain curve of the coal sample.

[0010] In some embodiments of the present invention, the impact energy index is obtained from the stress-strain curve of the coal sample using the following formula:

[0011] in, K E Impact energy index; A 1 represents the deformation energy accumulated before the peak of the stress-strain curve; A 2 represents the deformation energy lost after the peak value of the stress-strain curve.

[0012] In some embodiments of the present invention, if the impact hazard of the target coal seam is higher than a set level, mounting holes for installing the alternating magnetic field emitting device are drilled along the upper and lower roadways into the target coal seam, wherein the distance between the mounting holes and the working face is greater than 10m.

[0013] In some embodiments of the present invention, the number and location of the alternating magnetic field emitting device are determined based on the target coal seam thickness and the working face width.

[0014] In some embodiments of the present invention, the setting parameters of the alternating magnetic field emitting device are determined based on the coal impact energy index of the target coal seam.

[0015] In some embodiments of the present invention, the setting parameters include one or more of the alternating magnetic field transmitter power, amplitude, and frequency.

[0016] In some embodiments of the present invention, after the alternating magnetic field emitting device is turned on for a set time, a coal sample is drilled again to test the coal impact energy index, and the alternating magnetic field emitting device is used to determine whether to continue operating based on the test results.

[0017] The technical solution of the present invention has the following technical effects compared with the prior art: The method for preventing rockbursts provided by this invention achieves accurate assessment of rockburst risk by measuring both gas pressure and rockburst energy index, overcoming the limitations of single-parameter assessment. It uses an alternating magnetic field emission device for gas desorption, utilizing the magnetic field to promote the movement and desorption of gas molecules inside the coal body. Compared with traditional depressurization methods, it has advantages such as wide range of application, no mechanical disturbance, and high desorption efficiency.

[0018] Furthermore, this invention achieves precise targeting of the target coal seam through the targeted design of the magnetic field emitting device's arrangement and parameters, avoiding energy waste. Combined with a closed-loop monitoring mechanism, it ensures that the hazard mitigation effect meets safety standards, providing continuous protection for safe production in the mine. Attached Figure Description

[0019] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, which will help to understand the purpose and advantages of the present invention, wherein: Figure 1 This is a plan view of the working face of a mine prone to rock bursts. Figure 2 This is a schematic diagram of a borehole used to measure the gas pressure in a coal seam in the method for preventing ground pressure shock of the present invention. Figure 3 This is a diagram showing the arrangement of mounting holes for installing the alternating magnetic field emitting device in the method for preventing ground pressure impact of the present invention; Figure 4 This is a schematic diagram of a specific embodiment of the alternating magnetic field transmitting device of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The method for preventing rockbursts according to the present invention will be described in detail below with reference to a specific implementation scenario. This embodiment takes the 2453 working face of a rockburst-prone mine as the application object. The average thickness of the coal seam is 3.5m, and the working face width is 80m. The specific implementation steps for preventing rockbursts are as follows: S1. Procedure for determining coal seam parameters First, based on the mine's geological exploration data, mining face layout map, and historical records of rockbursts, working face 10 of mine 2453, which is prone to rockbursts, was selected as the target area for mitigating the potential rockburst hazard. Two key parameters were measured in this area: coal seam gas pressure and coal body impact energy index. Accurate acquisition of these crucial parameters provides a direct basis for subsequent rockburst hazard assessment, avoiding misjudgments due to missing or inaccurate parameters.

[0024] The specific implementation methods for measuring coal seam gas pressure and testing coal body impact energy index are as follows: like Figure 2 As shown, six sets of test holes 11 were drilled into the target coal seam in the transport roadway (lower roadway 20) and return airway (upper roadway 30) of working face 2453. Two test holes 11 were arranged horizontally, with a horizontal distance of 2-3 meters between them; three were arranged vertically at intervals, with a vertical distance of 1 meter between adjacent sets of test holes 11, corresponding to the upper, middle, and lower regions of the coal seam, respectively. All boreholes had a diameter of Φ60mm and extended to the middle of the coal seam. Simultaneously, the distance between all test holes 11 and working face 2345 was controlled at 120 meters to avoid the influence zone of the advanced support pressure of working face 10. This arrangement can comprehensively obtain the gas pressure distribution characteristics at different heights of the coal seam and is far from the disturbance area of ​​working face 10, ensuring that the measured parameters reflect the original gas occurrence state of the coal seam and providing spatial dimension assurance for the representativeness of subsequent evaluation results.

[0025] After drilling is completed, a pressure testing tube with a built-in pressure sensor (accuracy ±0.01MPa) equipped with a filter is immediately inserted into the borehole. The end of the pressure testing tube is connected to the data acquisition instrument via a sealing joint. Subsequently, the borehole opening section (2m in length) is sealed with a mixture of expansive cement and polyurethane to ensure isolation from outside air. After sealing, the data acquisition instrument is set to record pressure data once per hour. Once the pressure value has remained stable for 72 consecutive hours with fluctuations not exceeding 0.05MPa, the gas pressure value of test hole 11 is read and recorded. This implementation method, by optimizing the sealing material and data acquisition cycle, effectively avoids pressure measurement errors caused by gas leakage, ensuring the authenticity and reliability of the gas pressure data. For example, the gas pressure values ​​of the six holes are 3.71MPa, 3.44MPa, 3.51MPa, 3.88MPa, 3.96MPa, and 3.86MPa, with an average value of 3.73MPa. The coal seam gas pressure is greater than 3.5MPa, meeting the technical application requirements.

[0026] During the construction of the six sets of test wells 11, coal samples were extracted from the upper, middle, and lower parts of the coal seam, and five sets of standard coal samples were prepared from each sample. More specifically, the coal samples from the upper, middle, and lower parts of the coal seam were prepared into standard cylindrical specimens of Φ50mm×100mm, with five parallel specimens prepared for each set of samples to reduce experimental error. A uniaxial compression test was conducted on the standard specimens using an electro-hydraulic servo pressure testing machine, with the loading rate set to 0.5mm / min, and stress-strain curve data were collected simultaneously. By testing the mechanical properties of coal samples from different areas, the longitudinal impact energy distribution law of the coal seam can be fully understood, avoiding characteristic deviations caused by sampling from a single location.

[0027] The impact energy index, obtained from stress-strain curve data, is calculated using the following formula:

[0028] in, K E Impact energy index; A 1 represents the deformation energy accumulated before the peak of the stress-strain curve (i.e., the area below the line connecting the peak point of the curve and the origin). A 2 represents the deformation energy lost after the peak of the stress-strain curve (i.e., the area enclosed by the curve peak point to the residual strength point and the horizontal axis).

[0029] By integrating the stress-strain curves obtained from the experiment, the results for each group of specimens were obtained. K E The value is calculated by taking the average of five parallel samples in each group as the impact energy index for that region. This calculation method directly reflects the energy accumulation and release characteristics of the coal body during the stress process, providing a quantitative basis for the classification of impact hazard levels.

[0030] S2. Impact Hazard Level Assessment Procedure The impact hazard level of the target coal seam is assessed based on the gas pressure and the impact energy index of the coal body.

[0031] Specifically, when the coal seam impact energy index K < 3 and the gas pressure P < 0.74 MPa, it is classified as a low-risk level. Under this level, the coal seam has weak energy accumulation capacity, low gas occurrence pressure, and an extremely low probability of rockburst. It only needs to be managed according to conventional mining safety measures and does not require special hazard mitigation treatment.

[0032] When any of the following conditions are met: "3≤K<5 and P<1.0MPa", "K<3 and 1.0MPa≤P<1.5MPa", or "3≤K<5 and 1.0MPa≤P<1.5MPa", the coal seam is classified as medium-risk. At this level, the coal seam possesses a certain energy accumulation capacity or the gas pressure is at a critical state, posing a potential impact risk, requiring the initiation of targeted mitigation measures.

[0033] When the coal seam impact energy index K≥5 and the gas pressure P≥1.5MPa, it is classified as a high-risk condition. Under this level, the coal seam has a strong energy accumulation capacity, high gas pressure, and an extremely high risk of rockburst. It is necessary to immediately stop the 10-day longwall mining operation, implement enhanced mitigation measures, and reassess the safety status.

[0034] By using a dual-indicator collaborative assessment, the one-sidedness of a single parameter judgment is avoided, and the degree of coal seam impact risk can be reflected more accurately, providing a scientific basis for the selection of subsequent mitigation measures.

[0035] S3. Alternating magnetic field gas desorption steps When the impact hazard level of the target coal seam is medium or higher, an alternating magnetic field gas desorption step is performed. For example, if the impact hazard level of the target coal seam at working face 10 is assessed to be higher than the set medium hazard level, installation holes 12 are drilled along the upper roadway 30 and lower roadway 20 of working face 10 towards the target coal seam. The arrangement of the installation holes 12 is selected according to the coal seam thickness: for example, when the coal seam thickness is ≤3.5m (medium-thick coal seam), a single row of holes is used with a hole spacing of 5m; when the coal seam thickness is 3.5-8m (thick coal seam), a double row of holes is used, with the upper and lower rows of holes staggered; when the coal seam thickness is ≥8m (super-thick coal seam), a multi-row of holes is used. In this embodiment, the average coal seam thickness is 3.5m, which is a medium-thick coal seam, so a single row of holes is used. Figure 3(As shown). The specific parameters of mounting hole 12 are: hole diameter Φ94mm, located 10m in front of working face 10, and the depth of mounting hole 12 is 25% of the width of working face 10 (working face 10 is 80m wide, so the hole depth is 20m). This mounting hole arrangement can adapt to the optimal hole type according to the coal seam thickness. Combined with precise hole position and depth design, it provides a basic guarantee for the uniform action of the magnetic field and subsequent gas extraction.

[0036] Ten alternating magnetic field emitting devices 40 are arranged along the upper roadway 30 and lower roadway 20 according to the hole spacing requirements, ensuring that each device corresponds to one mounting hole 12. When installing the devices, the magnetic field direction is made to point from the upper roadway 30 to the lower roadway 20 to ensure that the direction of the magnetic field is matched with the coal seam direction, improve the penetration and coverage uniformity of the magnetic field inside the coal seam, and avoid mutual interference of magnetic fields to form blind spots.

[0037] like Figure 4 As shown, the alternating magnetic field transmitting device 40 includes a sealed protective housing 41 and a transmitting assembly located within the sealed protective housing 41. The transmitting assembly includes an iron core 42 and a transmitting coil 43. The transmitting coil 43 is made of high-conductivity copper core enameled wire, and the number of coil turns is designed to match the set magnetic field strength. It is the core actuator for generating the alternating magnetic field. It also includes a power supply module 44 and a control module 45 electrically connected to the transmitting assembly. The power supply module 44 uses an explosion-proof DC power supply, which can convert the AC power from the mine power supply system into stable DC power, providing a continuous and reliable energy supply for the device, meeting the underground explosion-proof safety requirements. The control module 45 has a built-in microprocessor and an adjustment knob 451, which can receive control signals in real time and adjust the frequency and amplitude of the output current to achieve precise setting of the alternating magnetic field amplitude, frequency, and power.

[0038] The alternating magnetic field emitting device 40 applies a periodically changing magnetic field to the coal seam, altering the interaction state between the coal and gas molecules at the microscopic level, thereby promoting gas desorption. On one hand, the alternating magnetic field induces forced vibrations in the coal lattice. These vibrations are transmitted to the pore structure inside the coal, causing minute displacements of the pore walls and disrupting the adsorption equilibrium of gas molecules on the pore surface. On the other hand, the magnetic field increases the kinetic energy of the gas molecules, intensifying their thermal motion and enabling more gas molecules to overcome the adsorption energy on the coal surface, transforming them from an adsorbed state to a free state. Furthermore, the periodically changing magnetic field generates an induced electric field in the coal, which exerts a directional driving force on the polarized gas molecules, accelerating the migration of free gas molecules towards the borehole. The magnetic field vibration can also clear micro-cracks inside the coal, expanding gas seepage channels and reducing gas migration resistance. Through the aforementioned multi-dimensional effects, the alternating magnetic field significantly enhances the desorption rate and amount of coal seam gas, creating favorable conditions for subsequent gas extraction. In turn, by reducing gas pressure and coal energy accumulation, the risk of rockburst can be effectively controlled.

[0039] The setting parameters of the alternating magnetic field emission device 40 are determined based on the coal impact energy index of the target coal seam.

[0040] When K is in the weak impact level (1.5≤K<5), the amplitude is set to 10KV / m, the frequency to 3-4MHz, and the power to 1000W; when K≥5 is the strong impact level, the amplitude is set to 20KV / m, the frequency to 6-8MHz, and the power to 2000W. By precisely matching the magnetic field parameters according to the risk level, efficient energy utilization and targeted improvement of disaster relief effects are achieved.

[0041] By linking the device parameters with the impact energy characteristics of the coal body, targeted adjustment of the parameters is achieved, avoiding energy waste or insufficient effect, and ensuring a balance between gas desorption effect and device operating efficiency.

[0042] S4. Steps for Monitoring and Judging the Operation Effect of the Equipment After the alternating magnetic field emitting device 40 is turned on and a magnetic field is applied for 24 hours, gas extraction is performed on the target coal seam (the extraction negative pressure is set to 40 kPa). Subsequently, a coal sample is drilled again at the original coal sample extraction location to retest the impact energy index K. If the retest results show that the reduction in K is insufficient, for example, K ≥ 1.5, the magnetic field parameters (amplitude, frequency, power) are increased by 20%, and the above magnetic field application-gas extraction-retest process is repeated until K < 1.5, reaching the safety level. This optimized effect verification process can track the progress of risk mitigation more quickly, and the dynamic parameter enhancement mechanism ensures that the impact risk is completely eliminated.

[0043] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preventing rockbursts, characterized in that, Includes the following steps: Select the coal seam of the mine to be protected against rock bursts, measure the gas pressure of the coal seam, and drill coal samples to test the coal body impact energy index. The impact hazard level of the target coal seam is assessed based on the gas pressure and impact energy index of the coal body. If the impact hazard of the target coal seam is higher than the set level, an alternating magnetic field emission device is deployed at a set location in the target coal seam to desorb gas from the coal seam.

2. The method for preventing rockbursts according to claim 1, characterized in that, The method for determining the gas pressure of a coal seam includes: drilling at least one set of test holes in the target coal seam, placing a pressure measuring tube in the test hole and sealing the test hole, wherein a pressure sensor is installed inside the pressure measuring tube, and after a set time, the pressure value of the test hole is obtained based on the detection signal of the pressure sensor.

3. The method for preventing rockbursts according to claim 1, characterized in that, At least three sets of test holes are drilled along the upper and lower roadways toward the target coal seam. The three sets of test holes are arranged at intervals in the vertical direction, and the distance between the test holes and the working face is greater than 100m.

4. The method for preventing rockbursts according to claim 1, characterized in that, The coal impact energy index test of the drilled coal samples includes: extracting at least two groups of coal samples spaced apart along the height direction of the target coal sample, and making each group of coal samples into a standard specimen for uniaxial compression test to measure the stress-strain curve of the coal sample, and obtaining the impact energy index based on the stress-strain curve of the coal sample.

5. A method for preventing rockbursts according to claim 1, characterized in that, The impact energy index is obtained from the stress-strain curve of the coal sample using the following formula: in, K E Impact energy index; A 1 represents the deformation energy accumulated before the peak of the stress-strain curve; A 2 represents the deformation energy lost after the peak value of the stress-strain curve.

6. A method for preventing rockbursts according to claim 5, characterized in that, If the impact hazard of the target coal seam is higher than the set level, installation holes for installing the alternating magnetic field emitting device are drilled along the upper and lower roadways into the target coal seam, wherein the distance between the installation hole and the working face is greater than 10m.

7. The method for preventing rockbursts according to claim 1, characterized in that, The number and location of the alternating magnetic field emitting devices are determined based on the target coal seam thickness and the working face width.

8. A method for preventing rockbursts according to claim 4, characterized in that, The setting parameters of the alternating magnetic field emitting device are determined based on the coal impact energy index of the target coal seam.

9. A method for preventing rockbursts according to claim 8, characterized in that, The set parameters include one or more of the alternating magnetic field transmitter power, amplitude, and frequency.

10. A method for preventing rockbursts according to claim 1, characterized in that, After the alternating magnetic field emitting device is turned on for a set time, a coal sample is drilled again to test the coal impact energy index. The test results determine whether the alternating magnetic field emitting device should continue to operate.

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