A method for breaking rock mass and cutting roof and releasing pressure based on ultrasonic vibration excitation

Abstract

The application provides a method for cutting roof and pressure relief based on ultrasonic vibration excitation and rock breaking, which comprises the following steps: step one, determining the data of the working face roof and coal seam according to the geological conditions of the coal mine working face; step two, determining the target rock stratum and the ultrasonic vibration breaking range; step three, measuring the natural frequency of the rock at the cutting roof position; step four, drilling a hole upward at a preset angle on the roof of the coal seam to be excavated; step five, placing the ultrasonic excitation device into the pressure relief borehole and fixing it; step six, under the combined action of ultrasonic excitation and impact load, the fine cracks on the surface of the target rock stratum continuously develop and rapidly expand and penetrate; step seven, repeatedly performing ultrasonic vibration treatment on the preset pressure relief borehole. The method for cutting roof and pressure relief based on ultrasonic vibration excitation and rock breaking not only has a large pressure relief range, but also can effectively solve the problem that the roof stress above the unexcavated coal seam is too large and the hydraulic support cannot normally advance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining related equipment, and particularly relates to a method for cutting roof and pressure relief based on ultrasonic vibration excitation and breaking rock mass. BACKGROUND

[0002] With the continuous development and consumption of shallow coal resources in China, coal mining in China is increasingly developing towards the deep part. The original rock stress of deep mine is high, the hardness is high, and there is a hard and thick roof above the coal seam, which has high integrity, high strength, large thickness and underdeveloped joint fissure. The hard and thick roof is difficult to collapse in time during mining, and is easy to form a large area of suspended roof, causing high stress concentration phenomenon to make the roadway deformed, resulting in that the working face support cannot normally advance forward. If the hard and thick roof suddenly breaks during mining, it will cause great rock pressure bumping to the working face, damage the roadway and mining equipment, and even cause personnel casualties, which will seriously threaten the safety production of coal mine. Therefore, the hard and thick roof needs to be broken, segmented and relieved to avoid the phenomenon of sudden collapse.

[0003] In recent years, the coal mining technology has gradually improved. At present, the most commonly used method for cutting roof and pressure relief is mainly blasting roof breaking and hydraulic fracturing. The blasting roof breaking method has complex construction technology, poor blasting efficiency, large loss of machines and materials, and is time-consuming and laborious. It has many safety hazards. The vibration generated by blasting will disturb the surrounding rock of the stope. At the same time, if the blasting roof breaking uses large amount of explosives, the impact formed by blasting will also be harmful to the gas control of the working face. If the blasting roof breaking uses small amount of explosives, it cannot achieve the preset effect. It is difficult to control the amount of explosives. The method of hydraulic fracturing breaking hard roof avoids the main shortcomings of the blasting roof breaking technology. However, the breaking effect of hydraulic fracturing depends on the crack propagation range and direction. In the actual application process, the direction and diffusion range of hydraulic fracturing are difficult to control due to the influence of ground stress and the state of roof rock stratum. The effect of hydraulic fracturing cutting roof is not very ideal, and it cannot effectively break the hard and thick roof of the working face in a large range.

[0004] Therefore, based on the above problems, the present application provides a method for cutting roof and pressure relief based on ultrasonic vibration excitation and breaking rock mass. SUMMARY

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

[0006] To achieve the above object, the present application is implemented by the following technical scheme:

[0007] A method for cutting roof and pressure relief based on ultrasonic vibration excitation and breaking rock mass, comprising the following steps:

[0008] Step one: according to the geological conditions of the coal mining face, the data of the roof and coal seam of the working face are determined.

[0009] Step two: determine the target rock stratum, determine the range of ultrasonic vibration breaking, determine the position of the borehole, so as to determine the angle and depth of the borehole;

[0010] Step three: measure the natural frequency of the rock at the top cutting position, adjust the ultrasonic generator to resonate with the rock according to the natural frequency of the target rock stratum;

[0011] Step four: drilling a hole upward at a preset angle in the roof of the coal seam to be excavated, and drilling multiple holes at a preset distance along the advancing direction of the roadway to obtain multiple parallel pressure relief boreholes;

[0012] Step five: placing the ultrasonic excitation device into the pressure relief borehole and fixing it, first performing ultrasonic excitation pre-cracking on the target rock stratum to cause fine cracks on the surface of the target rock stratum and reduce the strength of the rock, and then applying an impact load when the rock is in a resonant state;

[0013] Step six: under the combined action of ultrasonic excitation and impact load, the fine cracks on the surface of the target rock stratum continuously develop and rapidly expand and penetrate, causing the target rock stratum to be rapidly broken;

[0014] Step seven: performing multiple ultrasonic vibration treatments on the preset pressure relief boreholes to complete the breaking of all preset positions in the roof, thereby breaking the roof and causing the roof to collapse.

[0015] Preferably, in step three, the frequency of the ultrasonic generator is further adjusted to be the same as the natural frequency of the rock, the rock will resonate under the excitation of the ultrasonic wave, and the amplitude of the rock internal particles will be maximally amplified, at this time the rock is extremely unstable, and the rock is most likely to be damaged under the action of resonance, at this time the impact helps to accelerate the breaking of the rock.

[0016] Preferably, in step four, further drilling multiple holes at a preset distance and a preset depth in the roof above the coal seam in the roadway at a preset angle to obtain the multiple parallel pressure relief boreholes.

[0017] Preferably, the multiple drilling holes at a preset distance along the advancing direction of the roadway adopt directional pressure relief boreholes with a spacing of 10m.

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

[0019] Preferably, in step six, when the target rock stratum is subjected to ultrasonic excitation and impact load, further comprising: adjusting the ultrasonic wave generating device to make the ultrasonic wave output frequency equal to the natural frequency of the rock, and under the ultrasonic excitation, the rock can be destroyed with a much smaller load than the conventional method.

[0020] When the impact load is applied to the target rock stratum, the ultrasonic cracking device sprays high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local temperature from being too high, and avoid gas explosion and other accidents, and when the ultrasonic excitation and the impact load act together, the fine cracks on the surface of the target rock stratum continue to develop and rapidly expand and penetrate to the adjacent pressure relief borehole, so that the target rock stratum is quickly crushed.

[0021] Preferably, in step seven, when the preset pressure relief borehole is subjected to ultrasonic vibration treatment, further comprising: after the rock at the cracking point of the target rock stratum is crushed under the action of ultrasonic excitation and impact load, the position of the ultrasonic cracking device is replaced, and the above crushing step is repeated.

[0022] The preset pressure relief borehole is subjected to ultrasonic vibration excitation treatment until the cracking of all preset positions of the entire roof is completed, thereby breaking the roof and causing the roof to collapse, ensuring that the working face support advances forward.

[0023] The application provides a method for cutting and pressure releasing of roof based on ultrasonic vibration excitation and rock crushing.

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

[0025] 1. The application realizes the crushing and cutting of the sinking roof by pre-cracking the hard and thick roof over the roadway to be excavated in the coal seam, ensures the normal advancement of the working face support, and also enables the ultrasonic vibration cracking coverage range of the roadway to be excavated and the roadway during use to be in a low stress area, thereby effectively protecting the mining personnel and enabling the coal mining to be carried out in a safe and orderly manner.

[0026] 2. The application adopts the method of ultrasonic vibration cutting and roof pressure releasing, which avoids the shortcomings of the blasting technology and the hydraulic fracturing technology, and has the advantages of good directionality, concentrated energy, strong penetration ability, etc., can effectively solve the problem of excessive stress of the roof in front of the working face and the difficulty of advancing the working face support, is simple in process, safe and low in cost, has a large pressure releasing range and good effect, can effectively avoid coal mining safety accidents, and ensures the normal advancement of the working face, and has important engineering practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0028] Figure 1 A flow step block diagram of a method for cutting roof and pressure relief of rock mass based on ultrasonic vibration excitation of the present application is shown.

[0029] Figure 2 A front and rear support pressure distribution diagram of a roadway working face to be excavated of the present application is shown.

[0030] Figure 3 A physical model diagram of a "wedge-shaped" rock mass of the present application is shown. Figure 3

[0031] Figure 4 A mechanical model diagram under the combined action of ultrasonic excitation and impact load of the present application is shown.

[0032] Figure 5 A schematic diagram of ultrasonic vibration excitation and crushing structure of an overlying thick hard rock layer of a roadway to be excavated of the present application is shown.

[0033] Figure 6 A schematic diagram of an overall connecting structure in a method for cutting roof and pressure relief of rock mass based on ultrasonic vibration excitation of the present application is shown.

[0034] Figure 7 A schematic diagram of the working structure of an ultrasonic cracking device in a method for cutting roof and pressure relief of rock mass based on ultrasonic vibration excitation of the present application is shown.

[0035] Figure 8 A schematic diagram of ultrasonic vibration excitation and weakening of roof in a method for cutting roof and pressure relief of rock mass based on ultrasonic vibration excitation of the present application is shown.

[0036] The diagram shows: 1, coal seam; 2, roadway; 3, hard roof; 4, target rock mass; 5, pressure relief borehole; 6, 7, 8, 9, hydraulic cutting surface; 10, ultrasonic transducer; 11, drill rod; 12, ultrasonic cracking device; 13, ultrasonic generating device; 14, high-pressure water pump. DETAILED DESCRIPTION

[0037] ​In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0038] Embodiments

[0039] To solve the technical problems in the background art, the following method for cutting roof and relieving pressure of broken rock mass based on ultrasonic vibration excitation is given:

[0040] In combination with Figures 1-8 The present application provides a method for cutting roof and relieving pressure of broken rock mass based on ultrasonic vibration excitation, which comprises the following steps:

[0041] Step 1: determining the data of the roof and coal seam of the coal mining face according to the geological conditions of the coal mining face;

[0042] Step 2: determining the target rock stratum, determining the range of ultrasonic vibration breaking, and determining the position of the borehole so as to determine the angle and depth of the borehole;

[0043] The geological condition data of the coal mining face production includes the physical and structural data of the roof, rock stratum and coal seam of the coal mining face, and the structural data of the roof of the coal mining face is determined according to the comprehensive columnar stratification diagram of the coal mining face or by observing with a borehole peeping instrument or other methods.

[0044] The calculation formula of the angle and depth of the borehole is as follows:

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

[0046] tanθ=H 切 / L1

[0047] In the formula, θ is the included angle between the axis of the borehole and the horizontal direction; H 切 is the roof rock stratum cutting height, m; L1 is the horizontal distance from the pressure peak in front of the coal mining face to the coal mining face, m;

[0048] The calculation formula of the roof rock stratum cutting height H 切 is as follows:

[0049] H 切 =M0 / (K P -1)

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

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

[0052] L=KH 切 / sinθ

[0053] In the formula, L is the drilling depth, m; K is the surplus coefficient, the value range is 1.1-1.3; H 切 The height of the roof rock cutting, m; θ is the angle between the drilling axis and the horizontal direction.

[0054] Step three: measure the natural frequency of the rock at the cutting position, adjust the ultrasonic generator to resonate with the rock according to the natural frequency of the target rock layer;

[0055] In step three, further, adjust the frequency of the ultrasonic generator to the same as the natural frequency of the rock itself, the rock will resonate under the excitation of the ultrasonic wave, the amplitude of the rock internal particle will be amplified to the maximum extent, at this time the rock is extremely unstable, the rock is most likely to be damaged under the action of resonance condition, at this time the impact helps to accelerate the rock breaking.

[0056] Step four: drill a hole upward at the roof of the coal seam to be excavated at a preset angle, and drill a hole multiple times at a preset distance along the advancing direction of the roadway to obtain multiple parallel pressure relief boreholes;

[0057] In step four, further, multiple holes are drilled upward at the roof of the coal seam in the roadway at a preset angle with a preset interval and a preset depth to obtain the multiple parallel pressure relief boreholes.

[0058] The multiple holes drilled at a preset distance along the advancing direction of the roadway are directional pressure relief boreholes with an interval of 10m.

[0059] Specifically, steps one to four, in order to ensure that the structure data of the roof of the coal seam 1 is reasonable and accurate, the rock layer strength, rock layer thickness and other physical parameters and structure data of the hard roof 3 of the coal mine working face can be determined according to the comprehensive columnar stratification diagram of the working face or by observing with a borehole peeping instrument, the target rock layer 4 is determined, the ultrasonic vibration breaking range is determined, and the drilling angle, depth and other parameters are determined;

[0060] According to the data of the hard roof 3 and the coal seam 1 obtained in step one, the target rock layer 4 is found, a hole is drilled upward at the roof of the coal mine roadway 2 at a preset angle, the working face width is wide, a hole is drilled multiple times at a preset distance along the advancing direction of the roadway 2 to obtain multiple parallel pressure relief boreholes 5, and directional drilling is performed at a preset interval of 10m and a preset depth of Lm to ensure accurate positioning of each pressure relief borehole 5.

[0061] Step five: the ultrasonic excitation device is placed into the pressure relief borehole and fixed, the target rock is first pre-cracked by ultrasonic excitation, fine cracks appear on the surface of the target rock to reduce the strength of the rock, when the rock is in a resonant state, an impact load is applied;

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

[0063] Step six: under the combined action of ultrasonic excitation and impact load, the fine cracks on the surface of the target rock continuously develop, rapidly expand and penetrate, so that the target rock is quickly broken;

[0064] In step six, when the target rock is subjected to the combined action of ultrasonic excitation and impact load, the ultrasonic wave output frequency is adjusted to be equal to the natural frequency of the rock, so that the rock can be damaged under a smaller load than the conventional method under ultrasonic excitation;

[0065] When the impact load is applied to the target rock, the ultrasonic cracking device sprays high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local temperature from being too high, and avoid accidents such as gas explosion. When the ultrasonic excitation and the impact load act together, the fine cracks on the surface of the target rock continuously develop, rapidly expand and penetrate to the adjacent pressure relief borehole, so that the target rock is quickly broken.

[0066] Step seven: the preset pressure relief borehole is subjected to ultrasonic vibration treatment for multiple times, and the breaking of all preset positions of the entire roof is completed, so that the roof is broken and collapsed.

[0067] In step seven, when the preset pressure relief borehole is subjected to ultrasonic vibration treatment, the position of the ultrasonic cracking device is changed after the rock at the cracking point of the target rock is broken under the combined action of ultrasonic excitation and impact load, and the above breaking steps are repeated;

[0068] The preset pressure relief borehole is subjected to ultrasonic vibration excitation treatment until the cracking of all preset positions of the entire roof is completed, so that the roof is broken and collapsed, and the working face support is ensured to advance.

[0069] Specific steps five to seven, further, see Figures 5-8As shown, the hard roof of the target rock stratum 4 is subjected to ultrasonic excitation pre-splitting, and the frequency and power of the ultrasonic wave generator are adjusted so that the output frequency of the ultrasonic wave excited by the transducer is equal to the natural frequency of the rock. The target rock stratum 4 is subjected to ultrasonic excitation pre-splitting, the strength of the rock is reduced, and fine cracks appear on the surface of the rock. Ultrasonic excitation pre-splitting treatment is performed at multiple preset distances on each pressure relief borehole 5, and multiple pre-split fracture surfaces are formed.

[0070] In order to accurately position the ultrasonic excitation pre-split fracture surface on each pressure relief borehole 5, the distance between each pre-split fracture surface is preset to 5 m, so that the L m long borehole forms 6, 7, 8 and 9 four fracture surfaces respectively. The fracture surface 9 is 2 m away from the bottom of the borehole, and the pre-split fracture surface has a distance of 5 m between each other, which forms a weakening effect on the thick and hard roof.

[0071] When the target rock stratum 4 is in a resonant state, an impact load is applied, the impact force of the ultrasonic transducer 10 acting on the rock is short in time, the loading stress wave energy density is high, the rock is subjected to high frequency cyclic vibration impact, the internal cracks of the rock gradually expand and penetrate, the rock performance continuously decreases, the damage rapidly accumulates, and the rock is broken when reaching the fatigue failure limit;

[0072] Taking the fracture surface 6 as an example, the ultrasonic cracking device 12 is fixed at the fracture surface 6 of the borehole through the drill pipe 11, and then the ultrasonic wave generating device 13 is adjusted so that the output frequency of the ultrasonic wave is equal to the natural frequency of the rock. Under the excitation of ultrasonic wave, a small vibration load can cause the rock to be damaged. When the impact load is applied to the fracture surface 6, the ultrasonic cracking device 12 will spray high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent 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 continuously develops and rapidly expands and penetrates into the adjacent pressure relief borehole, so that the rock is quickly broken. The ultrasonic cracking device 12 and the high-pressure water pump 14 are turned off, the fracture of the fracture surface 6 is completed, the position of the ultrasonic cracking device 12 is replaced, and the above breaking steps are repeated. The fracture surface 7, 8 and 9 are subjected to ultrasonic vibration excitation treatment in the same way, and the target rock stratum 4 is broken. The preset pressure relief borehole 5 is subjected to ultrasonic vibration excitation treatment, until the cracking of all preset positions of the entire target rock stratum 4 is completed, so as to break the roof and make the roof collapse. During the tunneling process, when the overlying roof still has a certain distance to be cut and pressure relieved, directional drilling is performed again, and the above operation is continued until the roof is broken, and the working face support can normally advance.

[0073] In summary, the present application is aimed at the situation that the roof stress is too large to cause the working face support to fail to advance normally, and the directional drilling can be used to perform ultrasonic vibration excitation cutting and pressure relief on the thick and hard roof over the roadway, the continuous pre-splitting of the thick and hard roof over the roadway can be performed by repeatedly performing the construction directional drilling and performing ultrasonic vibration treatment on the directional pre-splitting drilling, the effect of layering and crushing to make the roof collapse is achieved, the working face support is ensured to advance normally, and the thick and hard roof over the roadway is relieved, so that the mining staff is in the state of being effectively protected.

[0074] It should be noted that, in this document, the terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or equipment including the element.

[0075] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent ones; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for cutting the roof of a rock mass and releasing pressure based on ultrasonic vibration excitation, characterized in that: It comprises the following steps: Step one: according to the geological conditions of the coal mine working face, the data of the working face roof and coal seam are determined; Step two: the target rock stratum is determined, the ultrasonic vibration breaking range is determined, and the position of the drill hole is determined so as to determine the angle and depth of the drill hole; Step three: the natural frequency of the rock at the top cutting position is measured, and the ultrasonic wave generating device is adjusted to resonate with the rock according to the natural frequency of the target rock stratum; Step four: drill holes are drilled upward at a preset angle on the roof of the coal seam to be excavated, and multiple drill holes are drilled at a preset distance along the advancing direction of the roadway, thereby obtaining multiple parallel pressure relief drill holes; Step five: the ultrasonic wave generating device is placed in the pressure relief drill hole and fixed, the target rock stratum is first subjected to ultrasonic excitation pre-cracking, the surface of the target rock stratum is made to have fine cracks to reduce the strength of the rock, and when the rock is in a resonant state, an impact load is applied; In step five, when the target rock stratum is subjected to ultrasonic excitation pre-cracking, the frequency and power of the ultrasonic wave generating device are adjusted according to the hardness of the target rock stratum, the output frequency of the ultrasonic wave excited by the ultrasonic wave transducer is equal to the natural frequency of the rock, the target rock stratum is subjected to ultrasonic excitation pre-cracking, the surface of the target rock stratum is made to have fine cracks to reduce the strength of the rock, and when the rock is in a resonant state, an impact load is applied; Step six: under the combined action of ultrasonic excitation and impact load, the fine cracks on the surface of the target rock stratum continuously develop and rapidly expand and penetrate, so that the target rock stratum is rapidly broken; In step six, when the target rock stratum is subjected to the combined action of ultrasonic excitation and impact load, the ultrasonic wave generating device is adjusted so that the output frequency of the ultrasonic wave is equal to the natural frequency of the rock, and under the ultrasonic excitation, the rock can be damaged with a much smaller load than in the conventional method; When the impact load is applied to the target rock stratum, the ultrasonic wave generating device sprays high-pressure water, which can effectively reduce the temperature of the device and the rock, prevent local temperature from being too high, and avoid gas explosion accidents, under the combined action of ultrasonic excitation and impact load, the fine cracks on the surface of the target rock stratum continuously develop and rapidly expand and penetrate into adjacent pressure relief drill holes, so that the target rock stratum is rapidly broken; Step seven: the preset pressure relief drill holes are subjected to multiple ultrasonic vibration treatments, the entire roof at all preset positions is broken, and the roof is broken to make the roof collapse.

2. The method according to claim 1, wherein the method is characterized in that: The coal mine working face production geological condition data includes physical and structural data of the working face roof, rock stratum and coal seam, and the structural data of the working face roof is determined according to a working face comprehensive columnar stratification diagram or by observing the method of a drill hole peeping instrument.

3. The method according to claim 2, wherein the method is characterized in that: The calculation formula of the drill hole angle θ is as follows: The calculation formula of the drill hole angle θ is as follows: θ is the angle between the drilling axis and the horizontal direction; is the roof rock cutting height, m; is the horizontal distance from the pressure peak in front of the working face to the working face, m; the roof rock cutting height The calculation formula is as follows: θ is the angle between the drilling axis and the horizontal direction; is the roof rock cutting height, m; is the coal seam thickness, m; is the average broken rock mass crushing coefficient, the average broken rock mass crushing coefficient is 1.25; the drilling depth The calculation formula is as follows: θ is the angle between the drilling axis and the horizontal direction; is the drilling depth, m; is the surplus coefficient, the value range is 1.1-1.3; is the roof rock cutting height, m; θ is the angle between the drilling axis and the horizontal direction.

4. The method according to claim 1, wherein the method is characterized in that: In step three, further, the frequency of the ultrasonic wave generating device is adjusted to be the same as the natural frequency of the rock, the rock will resonate under the excitation of the ultrasonic wave, the amplitude of the rock internal particles will be maximally amplified, the rock is extremely unstable at this time, the rock is most likely to be damaged under the action of the resonance condition, and the impact load at this time helps to accelerate the breaking of the rock.

5. The method according to claim 1, wherein the method is characterized in that: In the fourth step, further, the roof above the coal seam is perforated at a preset angle at a preset interval and a preset depth multiple times in the roadway to obtain the plurality of parallel pressure relief boreholes.

6. The method according to claim 5, wherein the method is characterized in that: The multiple boreholes in the advancing direction of the roadway at a preset distance are directional pressure relief boreholes with an interval of 10 m.

7. The method according to claim 1, wherein the method is characterized in that: In the seventh step, when the preset pressure relief boreholes are respectively subjected to ultrasonic vibration treatment, the following steps are included: under the combined action of ultrasonic excitation and impact load, after the rock at the target rockburst point is broken, the position of the ultrasonic wave generating device is replaced, and the above breaking step is repeated; The preset pressure relief boreholes are respectively subjected to ultrasonic vibration excitation treatment until the cracking of all preset positions of the entire roof is completed, thereby breaking the roof, causing the roof to collapse, and ensuring the forward advancement of the working face support.

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