Roof cutting and pressure relief method for fractured rock mass based on ultrasonic vibration excitation

Abstract

The invention provides a broken rock mass roof cutting pressure relief method based on ultrasonic vibration excitation, which comprises the following steps of: 1, determining data of a working face roof and a coal seam according to the geological condition of a coal mine working face; 2, a target rock stratum is determined, and the ultrasonic vibration crushing range is determined; 3, the inherent frequency of the rock at the top cutting position is measured; 4, upward drilling is conducted on a top plate of the to-be-tunneled coal seam according to a preset angle; 5, an ultrasonic excitation device is placed in the pressure relief drill hole and fixed; 6, under the combined action of ultrasonic excitation and impact load, tiny cracks on the surface of the target rock stratum continuously develop and rapidly expand and penetrate through; and seventhly, ultrasonic vibration treatment is conducted on the preset pressure relief drill holes for multiple times. According to the method for top cutting and pressure relief of the fractured rock mass based on ultrasonic vibration excitation, the pressure relief range is large, and the problems that the stress of a top plate above an untunneled coal seam is too large, and a hydraulic support cannot be normally pushed forwards can be effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of equipment related to coal mining, and in particular to a method for top cutting and pressure relief of broken rock mass based on ultrasonic vibration excitation. Background Art

[0002] With the continuous development and consumption of shallow coal resources in my country, my country's coal mining is developing deeper and deeper. The original rock stress of deep mines is high, and the hardness is high. There is a hard and thick roof with strong integrity, high strength, large thickness, and undeveloped joints and fissures above the coal seam. It is difficult to collapse in time during mining, and it is easy to form a large area of ​​hanging roof, causing high stress concentration to deform the roadway, resulting in the inability of the working face support to move forward normally. If the hard and thick roof suddenly breaks during mining, it will cause a large impact ground pressure on the working face, damage the roadway and mining equipment, and even cause casualties, which will seriously threaten the safe production of coal mines. Therefore, it is necessary to crush, split and relieve the pressure of the hard and thick roof to avoid its sudden collapse.

[0003] In recent years, coal mining technology has gradually improved. At present, the most commonly used methods of roof cutting and pressure relief are blasting and hydraulic fracturing. The blasting method has complex construction technology, poor blasting efficiency, large loss of machinery and materials, time-consuming and labor-intensive, and has many safety hazards. The vibration generated by the blasting of explosives will disturb the surrounding rock of the mining area. At the same time, if the amount of explosives used for blasting is large, the impact formed by the blasting will also be harmful to the gas control of the working face. The amount of explosives used for blasting is small and cannot achieve the preset effect. The amount of explosives is difficult to control. The method of hydraulic fracturing to break the hard roof avoids the main shortcomings of the blasting technology, but its breaking effect depends on the extension range and direction of the cracks. In actual application, it is affected by the size of the ground stress and the state of the roof rock layer. The direction and diffusion range of hydraulic fracturing are difficult to control. The effect of hydraulic fracturing is not very ideal, and it cannot effectively break the hard and thick roof of the working face on a large scale.

[0004] Therefore, based on the above problems, the present invention provides a method for top cutting and pressure relief of broken rock mass based on ultrasonic vibration excitation. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for top cutting and pressure relief of broken rock mass based on ultrasonic vibration excitation, which solves the problems mentioned in the background technology.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for removing pressure by cutting off the top of a broken rock mass based on ultrasonic vibration excitation comprises the following steps:

[0008] Step 1: Determine the data of the working face roof and coal seam according to the geological conditions of the coal mine working face;

[0009] Step 2: Determine the target rock layer, determine the ultrasonic vibration crushing range, and determine the location of the drill hole in order to determine the drilling angle and depth;

[0010] Step 3: Measure the natural frequency of the rock at the top cutting position, and adjust the ultrasonic generator to resonate with the rock according to the natural frequency of the target rock formation;

[0011] Step 4: drilling upwards at a preset angle on the roof of the coal seam to be excavated, and drilling multiple times at preset intervals along the advancing direction of the tunnel to obtain multiple parallel arranged pressure relief boreholes;

[0012] Step 5: Place the ultrasonic excitation device in the pressure relief borehole and fix it. First, ultrasonic excitation pre-crack the target rock formation to cause fine cracks on its surface to reduce the strength of the rock. When the rock is in a resonant state, apply the impact load.

[0013] Step 6: Under the combined effect of ultrasonic excitation and impact load, the micro cracks on the surface of the target rock layer continue to develop, expand rapidly and penetrate, so that the target layer rock is quickly broken;

[0014] Step 7: Perform ultrasonic vibration treatments on the preset pressure relief boreholes for multiple times to complete the crushing of all preset positions of the entire roof, thereby crushing the roof and causing it to collapse.

[0015] Preferably, in step three, when the frequency of the ultrasonic generator is further adjusted to be the same as the natural frequency of the rock itself, the rock will resonate under the excitation of the ultrasonic wave, and the amplitude of the particles inside the rock will be amplified to the maximum extent. At this time, the rock is extremely unstable and is most likely to be damaged under the resonance condition. At this time, applying an impact helps to accelerate the crushing of the rock.

[0016] Preferably, in the step four, further, in the laneway, holes are drilled multiple times at preset angles into the roof above the coal seam with preset spacing and preset depth to obtain the multiple parallel arranged pressure relief drill holes.

[0017] Preferably, the multiple drillings at preset intervals along the forward direction of the tunnel adopt directional pressure relief drilling with a spacing of 10m.

[0018] Preferably, in step five, when the target rock formation is pre-cracking by ultrasonic excitation, the frequency and power of the ultrasonic wave emitted by the ultrasonic generator are adjusted according to the hardness of the target rock formation, so that the output frequency of the ultrasonic wave excited by the transducer is equal to the natural frequency of the rock, and the target rock formation is pre-cracking by ultrasonic excitation to cause fine cracks to appear on its surface to reduce the strength of the rock, and the impact load is applied when the rock is in a resonant state.

[0019] Preferably, in step 6, when ultrasonic excitation and impact load are applied to the target rock formation, the step further includes: adjusting the ultrasonic generator so that the ultrasonic output frequency is equal to the natural frequency of the rock, and under ultrasonic excitation, the rock can be destroyed with a load much smaller than that of conventional methods;

[0020] When an impact load is applied to the target rock formation, the ultrasonic fracturing device will spray high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local excessive temperature, and avoid accidents such as gas explosions. When ultrasonic excitation and impact load act together, fine cracks on the surface of the target rock formation continue to develop, and quickly expand and penetrate into the adjacent pressure relief boreholes, causing the target layer of rock to be quickly broken.

[0021] Preferably, in step seven, when ultrasonic vibration treatment is performed on the preset pressure relief boreholes respectively, it includes: after the rock at the target rock formation fracturing point is crushed under the combined action of ultrasonic excitation and impact load, the position of the ultrasonic fracturing device is replaced, and the above crushing step is repeated;

[0022] The preset pressure relief boreholes are subjected to ultrasonic vibration excitation treatment respectively until all preset positions of the entire roof are cracked, thereby breaking the roof and causing it to collapse, ensuring that the working face support can be pushed forward.

[0023] The invention provides a method for top cutting and pressure relief of broken rock mass based on ultrasonic vibration excitation.

[0024] Compared with the prior art, it has the following beneficial effects:

[0025] 1. The present invention pre-cracks the hard and thick roof overlying the coal seam tunnel to be excavated, thereby breaking and removing the sunken roof, ensuring the normal advancement of the working face support, and also making the tunnel excavation tunnel covered by ultrasonic vibration cracking and the tunnel in a low stress zone during use, ensuring that the mining workers are in an effectively protected state, so that coal mining can be carried out in a safe and orderly manner;

[0026] 2. The method of ultrasonic vibration cutting roof pressure relief adopted in the present invention avoids the shortcomings of blasting technology and hydraulic fracturing technology. Ultrasonic vibration cutting roof pressure relief technology has the advantages of good directionality, concentrated energy, and strong penetration ability. It can effectively solve the problem of excessive stress on the roof in front of the working face and difficulty in advancing the working face support. It is not only simple, safe, and low-cost, but also has a large pressure relief range and good effect. It can effectively avoid coal mining safety accidents and ensure the normal advancement of the working face. It has important practical engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 A flowchart of a method for removing pressure from a rock mass by cutting the top based on ultrasonic vibration excitation is shown in the present invention;

[0029] Figure 2 The front and rear support pressure distribution diagram of the working face of the tunnel to be excavated according to the present invention is shown;

[0030] Figure 3 The present invention is shown Figure 3 This is a physical model diagram of a "wedge-shaped" rock formation;

[0031] Figure 4 The mechanical model diagram of the present invention under the combined action of ultrasonic excitation and impact load is shown;

[0032] Figure 5 A schematic diagram of an ultrasonic vibration excitation crushing structure for a thick hard rock layer overlying a tunnel to be excavated according to the present invention is shown;

[0033] Figure 6 A schematic diagram of the overall connection structure in a method for top cutting and pressure relief of a crushed rock mass based on ultrasonic vibration excitation of the present invention is shown;

[0034] Figure 7 A schematic diagram showing the structure of an ultrasonic fracturing device in a method for crushing rock mass by top cutting and pressure relief based on ultrasonic vibration excitation of the present invention;

[0035] Figure 8 A schematic diagram of an ultrasonic vibration-stimulated weakened roof plate for top cutting and pressure relief of a crushed rock mass based on ultrasonic vibration excitation according to the present invention;

[0036] As shown in the figure: 1. Coal seam; 2. Tunnel; 3. Hard roof; 4. Target rock layer; 5. Pressure relief borehole; 6, 7, 8, 9. Hydraulic cutting surface; 10. Ultrasonic transducer; 11. Drill rod; 12. Ultrasonic fracturing device; 13. Ultrasonic generating device; 14. High-pressure water pump. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example

[0039] In order to solve the technical problems in the background technology, a method for removing pressure by cutting the top of the crushed rock mass based on ultrasonic vibration excitation is provided as follows:

[0040] Combination Figure 1-8 As shown, the present invention provides a method for removing pressure from a rock mass by cutting the top based on ultrasonic vibration excitation, comprising the following steps:

[0041] Step 1: Determine the data of the working face roof and coal seam according to the geological conditions of the coal mine working face;

[0042] Step 2: Determine the target rock layer, determine the ultrasonic vibration crushing range, and determine the location of the drill hole in order to determine the drilling angle and depth;

[0043] The coal mine working face production geological condition data includes the physical and structural data of the working face roof, rock layer and coal seam. The structural data of the working face roof is determined based on the comprehensive columnar stratification diagram of the mining area working face or through observation with a borehole peephole instrument.

[0044] The calculation formulas for the drilling angle and depth are as follows:

[0045] The calculation formula of the drilling angle θ is as follows:

[0046] tanθ=H 切 / L1

[0047] Where θ is the angle between the drilling axis and the horizontal direction; H 切 is the cutting height of the roof rock layer, m; L1 is the horizontal distance from the peak pressure in front of the working face to the working face, m;

[0048] The top rock layer cutting height H 切 The calculation formula is as follows:

[0049] H 切 =M0 / (K P -1)

[0050] In the formula, H 切 is the cutting height of the roof rock layer, m; M0 is the thickness of the coal seam, m; KP is the average expansion coefficient of the broken rock mass, and the average expansion coefficient of the broken rock mass is 1.25;

[0051] The calculation formula of the drilling depth L is as follows:

[0052] L=KH 切 / sinθ

[0053] Where, L is the drilling depth, m; K is the redundancy factor, ranging from 1.1 to 1.3; H 切 is the cutting height of the roof rock layer, m; θ is the angle between the drilling axis and the horizontal direction.

[0054] Step 3: Measure the natural frequency of the rock at the top cutting position, and adjust the ultrasonic generator to resonate with the rock according to the natural frequency of the target rock formation;

[0055] In the step three, when the frequency of the ultrasonic generator is further adjusted to be the same as the natural frequency of the rock itself, the rock will resonate under the excitation of the ultrasonic wave, and the amplitude of the particles inside the rock will be amplified to the maximum extent. At this time, the rock is extremely unstable and is most likely to be damaged under the resonance condition. At this time, applying an impact helps to accelerate the crushing of the rock.

[0056] Step 4: drilling upwards at a preset angle on the roof of the coal seam to be excavated, and drilling multiple times at preset intervals along the advancing direction of the tunnel to obtain multiple parallel arranged pressure relief boreholes;

[0057] In the step four, further, in the laneway, holes are drilled multiple times at preset angles into the roof above the coal seam with preset spacing and preset depth to obtain the multiple parallel arranged pressure relief drill holes.

[0058] The multiple drillings are performed at preset intervals along the forward direction of the tunnel, using directional pressure relief drilling with a spacing of 10m.

[0059] Specifically, in step 1 to step 4, in order to ensure that the structural data of the roof of the coal seam 1 is reasonable and accurate, the physical parameters and structural data of the rock layer strength, rock layer thickness and other physical parameters of the hard roof 3 of the coal mine working face can be determined by taking a comprehensive columnar layered diagram of the working face or observing with a borehole peep instrument through drilling, determining the target rock layer 4, determining the ultrasonic vibration crushing range, and determining the parameters such as the drilling angle and depth;

[0060] According to the data of the hard roof 3 and coal seam 1 obtained in step one, the target rock layer 4 is found, and a hole is drilled upward at a preset angle toward the roof of the coal mine tunnel 2. The working face width is relatively wide. At this time, multiple holes are drilled at preset intervals along the forward direction of the tunnel 2 to obtain multiple parallel-arranged pressure relief boreholes 5. In order to ensure the accurate positioning of each pressure relief borehole 5, directional drilling is performed with a preset spacing of 10m and a preset depth of Lm.

[0061] Step 5: Place the ultrasonic excitation device in the pressure relief borehole and fix it. First, ultrasonic excitation pre-crack the target rock formation to cause fine cracks on its surface to reduce the strength of the rock. When the rock is in a resonant state, apply the impact load.

[0062] In the step five, when the target rock formation is ultrasonically excited for pre-cracking, the frequency and power of the ultrasonic wave emitted by the ultrasonic generator are adjusted according to the hardness of the target rock formation, so that the output frequency of the ultrasonic wave excited by the transducer is equal to the natural frequency of the rock, and the target rock formation is ultrasonically excited for pre-cracking to cause fine cracks to appear on its surface to reduce the strength of the rock, and the impact load is applied when the rock is in a resonant state.

[0063] Step 6: Under the combined effect of ultrasonic excitation and impact load, the micro cracks on the surface of the target rock layer continue to develop, expand rapidly and penetrate, so that the target layer rock is quickly broken;

[0064] In the step 6, when the target rock formation is subjected to ultrasonic excitation and impact load, the step further includes: adjusting the ultrasonic generator so that the ultrasonic output frequency is equal to the natural frequency of the rock, and under ultrasonic excitation, the rock can be destroyed with a load much smaller than that of conventional methods;

[0065] When an impact load is applied to the target rock formation, the ultrasonic fracturing device will spray high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local excessive temperature, and avoid accidents such as gas explosions. When ultrasonic excitation and impact load act together, fine cracks on the surface of the target rock formation continue to develop, and quickly expand and penetrate into the adjacent pressure relief boreholes, causing the target layer of rock to be quickly broken.

[0066] Step 7: Perform ultrasonic vibration treatments on the preset pressure relief boreholes for multiple times to complete the crushing of all preset positions of the entire roof, thereby crushing the roof and causing it to collapse.

[0067] In the step 7, when the preset pressure relief boreholes are subjected to ultrasonic vibration treatment respectively, the steps include: after the rock at the fracture point of the target rock formation is crushed under the combined action of ultrasonic excitation and impact load, the position of the ultrasonic fracturing device is replaced, and the above crushing step is repeated;

[0068] The preset pressure relief boreholes are subjected to ultrasonic vibration excitation treatment respectively until all preset positions of the entire roof are cracked, thereby breaking the roof and causing it to collapse, ensuring that the working face support can be pushed forward.

[0069] For specific steps 5 to 7, see Figure 5-8As shown, the hard top plate of the target rock layer 4 is ultrasonically excited for pre-cracking. By adjusting the frequency and power of the ultrasonic wave emitted by the ultrasonic generator, the ultrasonic wave output frequency excited by the transducer is equal to the natural frequency of the rock. The target rock layer 4 is ultrasonically excited for pre-cracking, the strength of the rock is reduced, and fine cracks appear on its surface. The ultrasonic excitation pre-cracking process is performed at multiple preset distances on each pressure relief borehole 5 to form multiple pre-crack surfaces.

[0070] In order to ensure the accurate positioning of the ultrasonic excitation pre-crack surface on each pressure relief borehole 5, the preset spacing between each pre-crack surface is 5m, so that the borehole with a length of L m forms four crack surfaces 6, 7, 8 and 9 respectively, the crack surface 9 is 2m away from the bottom of the borehole, and the spacing between the pre-crack surfaces is 5m, which weakens the thick hard roof;

[0071] When the target rock layer 4 is in a resonant state, an impact load is applied. The impact force applied by the ultrasonic transducer 10 to the rock is short in action time, and the energy density of the loading stress wave is high. The rock is subjected to high-frequency cyclic vibration impact, and the cracks inside the rock gradually expand and penetrate. The rock performance continues to decline, and the damage accumulates rapidly until the fatigue failure limit is reached, and the rock is broken.

[0072] Taking the fracture surface 6 as an example, the ultrasonic fracturing device 12 is fixed to the fracture surface 6 of the borehole through the drill rod 11, and then the ultrasonic generating device 13 is adjusted so that the ultrasonic output frequency is equal to the natural frequency of the rock. Under ultrasonic excitation, a small vibration load can cause the rock to be destroyed. When an impact load is applied to the fracture surface 6, the ultrasonic fracturing device 12 will spray high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent the local temperature from being too high, and avoid accidents such as gas explosion. Under the combined action of ultrasonic excitation and impact load, the tip of the fracture surface 6 continues to develop, and quickly expands and penetrates to the adjacent pressure relief borehole, so that the rock is quickly broken and closed. The ultrasonic fracturing device 12 and the high-pressure water pump 14 complete the fracturing of the fracture surface 6, and the position of the ultrasonic fracturing device 12 is changed, and the above-mentioned crushing steps are repeated. The same method is used to perform ultrasonic vibration excitation treatment on the fracture surfaces 7, 8 and 9, respectively, to achieve the effect of crushing the target rock layer 4. The preset pressure relief boreholes 5 are subjected to ultrasonic vibration excitation treatment respectively until the fracturing of all preset positions of the entire target rock layer 4 is completed, thereby crushing the roof and causing the roof to collapse. During the excavation process, when there is still a certain distance from the overlying roof that needs to be cut off to relieve pressure, directional drilling is performed again, and the above-mentioned operations are continued until the roof is completely crushed and the working face support can be pushed forward normally.

[0073] To sum up, the present invention is aimed at the situation where the top plate stress is too large in the area to be excavated and settlement occurs, resulting in the inability of the working face support to advance normally. Directional drilling can be used to perform ultrasonic vibration excitation to cut the top and relieve pressure on the thick hard top plate on the tunnel. By repeatedly executing directional drilling construction and performing ultrasonic vibration treatment on the directional pre-cracking drilling holes, the thick hard top plate on the tunnel can be pre-cracked continuously to achieve the effect of layered crushing to cause the top plate to collapse, thereby ensuring that the working face support can advance normally. After the thick hard top plate above the tunnel is relieved of pressure, the tunnel is excavated within the coverage range of ultrasonic vibration fracturing and is in a low stress zone during the use of the tunnel, so that the mining workers are in an effectively protected state.

[0074] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing pressure from broken rock mass by cutting top based on ultrasonic vibration excitation, characterized in that: The steps include: Step 1: Determine the data of the working face roof and coal seam according to the geological conditions of the coal mine working face; Step 2: Determine the target rock layer, determine the ultrasonic vibration crushing range, and determine the location of the drill hole in order to determine the drilling angle and depth; Step 3: Measure the natural frequency of the rock at the top cutting position, and adjust the ultrasonic generator to resonate with the rock according to the natural frequency of the target rock formation; Step 4: drilling upwards at a preset angle on the roof of the coal seam to be excavated, and drilling multiple times at preset intervals along the advancing direction of the tunnel to obtain multiple parallel arranged pressure relief boreholes; Step 5: Place the ultrasonic excitation device in the pressure relief borehole and fix it. First, ultrasonic excitation pre-crack the target rock formation to cause fine cracks on its surface to reduce the strength of the rock. When the rock is in a resonant state, apply the impact load. Step 6: Under the combined effect of ultrasonic excitation and impact load, the micro cracks on the surface of the target rock layer continue to develop, expand rapidly and penetrate, so that the target layer rock is quickly broken; Step 7: Perform ultrasonic vibration treatments on the preset pressure relief boreholes for multiple times to complete the crushing of all preset positions of the entire roof, thereby crushing the roof and causing it to collapse.

2. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: The coal mine working face production geological condition data includes the physical and structural data of the working face roof, rock layer and coal seam. The structural data of the working face roof is determined based on the comprehensive columnar stratification diagram of the mining area working face or through observation with a borehole peephole instrument.

3. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 2 is characterized in that: The calculation formulas for the drilling angle and depth are as follows: The calculation formula of the drilling angle θ is as follows: tanθ=H 切 / L1 Where θ is the angle between the drilling axis and the horizontal direction; H 切 is the cutting height of the roof rock layer, m; L1 is the horizontal distance from the peak pressure in front of the working face to the working face, m; The top rock layer cutting height H 切 The calculation formula is as follows: H 切 =M0 / (K P -1) In the formula, H 切 is the cutting height of the roof rock layer, m; M0 is the thickness of the coal seam, m; KP is the average expansion coefficient of the broken rock mass, and the average expansion coefficient of the broken rock mass is 1.25; The calculation formula of the drilling depth L is as follows: L=KH 切 / sinθ Where, L is the drilling depth, m; K is the redundancy factor, ranging from 1.1 to 1.3; H 切 is the cutting height of the roof rock layer, m; θ is the angle between the drilling axis and the horizontal direction.

4. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: In the step three, when the frequency of the ultrasonic generator is further adjusted to be the same as the natural frequency of the rock itself, the rock will resonate under the excitation of the ultrasonic wave, and the amplitude of the particles inside the rock will be amplified to the maximum extent. At this time, the rock is extremely unstable and is most likely to be damaged under the resonance condition. At this time, applying an impact helps to accelerate the crushing of the rock.

5. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: In the step four, further, in the laneway, holes are drilled multiple times at preset angles into the roof above the coal seam with preset spacing and preset depth to obtain the multiple parallel arranged pressure relief drill holes.

6. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 5 is characterized in that: The multiple drillings are performed at preset intervals along the forward direction of the tunnel, using directional pressure relief drilling with a spacing of 10m.

7. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: In the step five, when the target rock formation is ultrasonically excited for pre-cracking, the frequency and power of the ultrasonic wave emitted by the ultrasonic generator are adjusted according to the hardness of the target rock formation, so that the output frequency of the ultrasonic wave excited by the transducer is equal to the natural frequency of the rock, and the target rock formation is ultrasonically excited for pre-cracking to cause fine cracks to appear on its surface to reduce the strength of the rock, and the impact load is applied when the rock is in a resonant state.

8. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: In the step 6, when the target rock formation is subjected to ultrasonic excitation and impact load, the step further includes: adjusting the ultrasonic generator so that the ultrasonic output frequency is equal to the natural frequency of the rock, and under ultrasonic excitation, the rock can be destroyed with a load much smaller than that of conventional methods; When an impact load is applied to the target rock formation, the ultrasonic fracturing device will spray high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local excessive temperature, and avoid accidents such as gas explosions. When ultrasonic excitation and impact load act together, fine cracks on the surface of the target rock formation continue to develop, and quickly expand and penetrate into the adjacent pressure relief boreholes, causing the target layer of rock to be quickly broken.

9. The method for removing pressure from the top of a rock mass by ultrasonic vibration excitation according to claim 1 is characterized in that: In the step 7, when the preset pressure relief boreholes are subjected to ultrasonic vibration treatment respectively, the steps include: after the rock at the fracture point of the target rock formation is crushed under the combined action of ultrasonic excitation and impact load, the position of the ultrasonic fracturing device is replaced, and the above crushing step is repeated; The preset pressure relief boreholes are subjected to ultrasonic vibration excitation treatment respectively until all preset positions of the entire roof are cracked, thereby breaking the roof and causing it to collapse, ensuring that the working face support can be pushed forward.

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