A safety mining method for preventing rock bursts during coal quarrying and coal caving in coal seams prone to rock bursts

Abstract

This application relates to the technical field of safe coal seam mining, and particularly to a method for preventing rock bursts and safely mining coal in a rock burst-prone coal seam, which includes the following steps: S1. Arrange the return airway of the rock stratum working face in the coal seam and the rock stratum. The length of the rock stratum working face is not less than 100 m. The rock stratum includes the direct bottom rock stratum and the old bottom rock stratum; S2. Mine the rock stratum, and the mining height is not more than 3 m; S3. Convey the mined rock to the underground waste rock chamber or the waste rock filling working face; S4. Use the top coal caving technology for the coal seam above the rock stratum, and it will collapse by itself under the action of mine pressure. The coal after collapse is conveyed above the ground. By arranging the return airway in the rock stratum and arranging the working face in the rock stratum, transforming the traditional "coal mining" working face into a "rock quarrying" working face, and using the coal seam as the "roof" of the rock stratum working face, the coal is mined after it collapses by itself, so as to realize the intrinsic safety mining of the rock burst-prone coal seam.

Description

Technical Field

[0001] This application relates to the technical field of safe coal seam mining, and particularly relates to a method for preventing rock bursts and safely mining coal in a coal seam prone to rock bursts by quarrying and coal caving. Background Art

[0002] Rock burst refers to the dynamic phenomenon of sudden and violent destruction of the coal body around the mine roadway or working face in a coal mine due to the instantaneous release of elastic deformation energy, which is one of the main factors restricting the safe mining of deep coal resources in China. Statistical data shows that more than 90% of the rock burst manifestations in the mining project of coal seams prone to rock bursts occur in the return air roadway of the working face. The main method of coal seam mining in China is longwall retreating mining, that is, two return air roadways are arranged in the coal seam, and coal mining is carried out by means of shearer cutting or blasting. With the deterioration of the coal mine geological conditions and the intensification of stress concentration, the risks faced by the mining of some coal seams prone to rock bursts are increasing. Even with comprehensive pressure relief and danger elimination measures such as coal seam, roof, and floor pressure relief, the roadways and working faces arranged in the coal seams prone to rock bursts are always in the risk of rock bursts, and it is impossible to achieve the "source control" and "disaster source elimination" in the true sense.

[0003] The main anti-rock burst technologies for the safe mining of coal seams prone to rock bursts are "regional first" and "local follow-up". "Regional first" means mining the protective seam, reasonably arranging the coal seam roadways, selecting the appropriate coal mining method, reducing the mining disturbance, etc. "Local follow-up" means carrying out pressure relief and danger elimination treatment on the mined coal seam in the mining space, such as coal seam borehole pressure relief, coal seam unloading blasting, coal seam water injection, roof deep hole pre-splitting blasting, roof hydraulic fracturing, floor borehole pressure relief and blasting, etc. For the above methods, whether it is full height mining at one time, top coal caving or slicing mining, the working space is in the coal seam, that is, the working face is arranged in the coal seam, and the return air roadway directly serving the working face is also arranged in the coal seam. Limited by the current coal seam mining layout method, the staff are always working in the coal seam prone to rock bursts and face the risk of rock bursts. Summary of the Invention

[0004] In order to improve the safety of the mining process of coal seams prone to rock bursts, this application provides a method for preventing rock bursts and safely mining coal in a coal seam prone to rock bursts by quarrying and coal caving.

[0005] This application provides a method for preventing rock bursts and safely mining coal in a coal seam prone to rock bursts by quarrying and coal caving, adopting the following technical solutions:

[0006] A method for preventing rock bursts and safely mining coal in a coal seam prone to rock bursts includes the following steps:

[0007] S1. Arrange the return air roadway of the rock layer working face in the coal seam and the rock layer, the length of the rock layer working face is not less than 100 m, and the rock layer includes the direct bottom rock layer and the old bottom rock layer;

[0008] S2. Mine the rock stratum with a mining height not greater than 3m;

[0009] S3. Convey the mined rock to the underground waste rock chamber or the waste rock filling working face;

[0010] S4. For the coal seam above the rock stratum, adopt the top coal caving technology, and it will collapse automatically under the action of mine pressure. The coal after collapse is conveyed above the ground.

[0011] Optionally, in step S1, it further includes:

[0012] When the coal seam has weak impact risk, half of the return airway of the rock stratum working face is arranged in the coal seam, and the other half is arranged in the rock stratum below the coal seam;

[0013] When the coal seam has medium impact risk, the return airway of the rock stratum working face is arranged in the rock stratum below the coal seam, and the roof of the roadway is the coal seam;

[0014] When the coal seam has strong impact risk, the return airway of the rock stratum working face is arranged in the old floor rock stratum, and the distance between the roof of the roadway and the coal seam is not less than 2m;

[0015] When the coal seam has impact risk and the coal seam has coal and gas outburst risk, the return airway of the rock stratum working face is arranged in the old floor rock stratum, and the distance between the roof of the roadway and the coal seam is not less than 5m.

[0016] Optionally, in step S2, it further includes:

[0017] Determine the mining height during the mining of the rock stratum according to the coal seam thickness;

[0018] When the coal seam thickness is not greater than 3.5m, the mining height is not greater than 2m;

[0019] When the coal seam thickness is greater than 3.5m, the mining height is 2 - 3m.

[0020] Optionally, in step S2, it further includes:

[0021] Determine the assisted rock breaking method for fracturing the rock stratum working face according to the uniaxial compressive strength of the rock stratum in the rock stratum working face;

[0022] When the uniaxial compressive strength of the rock stratum in the rock stratum working face is not greater than 30MPa, adopt the direct cutting method of the shearer for mechanized mining;

[0023] When the uniaxial compressive strength of the rock stratum in the rock stratum working face is greater than 30MPa and not greater than 60MPa, adopt blasting-assisted rock breaking;

[0024] When the uniaxial compressive strength of the rock stratum in the rock stratum working face is greater than 60MPa, adopt directional slotting orthogonal hydraulic fracturing-assisted rock breaking.

[0025] Optionally, during the process of using blasting to assist in rock breaking, it further includes:

[0026] Arrange a number of blasting holes in the middle of the mined rock formation. The blasting holes are arranged in a straight line. The charging depth is the sum of twice the daily mining advance and the hole sealing length, and the hole sealing length is not less than one-third of the total hole length. The hole diameter is not more than 42 mm, the spacing between adjacent holes is 5 - 10 m, and the charge amount per hole is not more than 10 kg.

[0027] Optionally, during the process of using directional slotting and orthogonal hydraulic fracturing to assist in rock breaking, it further includes:

[0028] Construct perpendicular holes to the mined rock formation through a drill rig in the lower flat roadway of the rock formation working face and within the rock formation working face. Then, use a slotting device to form directional pre - cracks in the holes. Finally, use a hole - sealing device to seal the space closer to the pre - cracks and conduct high - pressure water injection operations to expand the pre - cracks.

[0029] Optionally, construction is carried out at the middle position of the mining height within the rock formation working face and at the middle positions of the two roadways of the rock formation working face; the hole diameter is 45 - 65 mm; the hole depth is greater than 100 m; the hole spacing is 10 - 50 m; the pre - crack slotting is more than twice the hole diameter; the pre - crack spacing at different positions within the same hole is 5 - 10 m; the length of the hole - sealing device depends on the pre - crack interval and is set to 1 - 2 m; the holes are parallel to the rock formation bedding plane; the hydraulic fracturing pressure range is: 10 - 40 Mpa;

[0030] Among them, the estimated value of the starting pressure required for hydraulic fracturing is calculated as:

[0031] ; (1)

[0032] In formula (1), p is the estimated value of the starting pressure required for hydraulic fracturing, with the unit of Mpa, b is the minor semi - axis length of the pre - crack, with the unit of m, a is the major semi - axis length of the pre - crack, with the unit of m, is the maximum principal stress in the fracturing working face area, is the minimum principal stress in the fracturing working face area, is the tensile strength of the rock formation at the fracturing point, with the unit of Mpa.

[0033] Optionally, in step S3, it further includes:

[0034] Convey the mined rock through the front scraper conveyor, transfer conveyor, and belt conveyor to the underground waste rock chamber or the waste rock filling working face in sequence.

[0035] Optionally, in step S4, it further includes:

[0036] After the coal collapses, it is successively conveyed by the rear scraper conveyor and the transfer conveyor to the crusher for crushing, and then conveyed to the coal bunker through the belt conveyor, and then lifted to the ground through the main shaft.

[0037] In summary, the present application includes at least one of the following beneficial technical effects:

[0038] 1. By arranging the mining roadway in the rock stratum, arranging the working face in the rock stratum, transforming the traditional "coal mining" working face into a "rock quarrying" working face, taking the coal seam as the "roof" of the rock stratum working face, and through the method of mine pressure or artificial fracturing, the coal collapses by itself and is mined out, so as to realize the intrinsic safety mining of the rock burst coal seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic flow chart of a safety mining method for preventing rock burst in a rock quarrying and coal caving of a rock burst coal seam.

[0040] Figure 2 is a schematic diagram of the rock stratum working face for showing the embodiment of the present application.

[0041] Figure 3 is Figure 2 the schematic cross-sectional view A-A in

[0042] Figure 4 is Figure 2 the schematic cross-sectional view B-B in

[0043] Figure 5 is a layout plan of the mining roadway of the rock stratum working face when the coal seam in the embodiment of the present application has weak rock burst danger.

[0044] Figure 6 is a layout plan of the mining roadway of the rock stratum working face when the coal seam in the embodiment of the present application has medium rock burst danger.

[0045] Figure 7 is a layout plan of the mining roadway of the rock stratum working face when the coal seam in the embodiment of the present application has strong rock burst danger.

[0046] Figure 8 is a layout plan of the mining roadway of the rock stratum working face when the coal seam in the embodiment of the present application has rock burst danger and coal and gas outburst danger.

[0047] Figure 9 is a schematic diagram of the working of directional slotting and orthogonal hydraulic fracturing assisted rock breaking for showing the embodiment of the present application.

[0048] Description of the reference numerals: 1, shearer; 2, hydraulic support; 3, front scraper conveyor; 4, rear scraper conveyor; 5, end support; 6, transfer conveyor; 7, crusher; 8, belt conveyor. Detailed implementation mode

[0049] The following further elaborates on this application in conjunction with all the attached drawings.

[0050] Refer to Figures 1-9 , this embodiment of the application discloses a safety mining method for preventing rock bursts during quarrying and coal caving in coal seams prone to rock bursts.

[0051] A safety mining method for preventing rock bursts during quarrying and coal caving in coal seams prone to rock bursts includes the following steps:

[0052] S1. Arrange the gob-side entry of the rock stratum working face in the coal seam and the rock stratum. The length of the rock stratum working face is not less than 100 m. The rock stratum includes the immediate floor rock stratum and the old floor rock stratum;

[0053] S2. Mine the rock stratum, and the mining height is not greater than 3 m;

[0054] S3. Transport the mined rock to the underground waste rock chamber or the waste rock filling working face;

[0055] S4. For the coal seam above the rock stratum, adopt the top coal caving technology, and it will collapse automatically under the action of mine pressure. The coal after collapse is transported above the ground.

[0056] Among them, in step S1, that is, when arranging the gob-side entry of the rock stratum working face in the coal seam and the rock stratum, the gob-side entry of the rock stratum working face is supported by the hydraulic support 2 and the end support 5.

[0057] Furthermore, in step S1, that is, when arranging the gob-side entry of the rock stratum working face in the coal seam and the rock stratum, according to the evaluation results of the impact risk of different coal seams, determine the layout horizon Li (i = 1, 2, 3, 4) of the gob-side entry of the rock stratum working face. The height of the gob-side entry of the rock working face is H, with the unit of m, and the coal seam thickness is , with the unit of m.

[0058] When the coal seam has weak impact risk, half of the gob-side entry of the rock stratum working face is arranged in the coal seam, and the other half is arranged in the rock stratum below the coal seam. The roof of the roadway is the coal seam, that is: , if the coal seam thickness h is less than , then L1 = ;

[0059] When the coal seam has medium impact risk, the gob-side entry of the rock stratum working face is arranged in the rock stratum below the coal seam, and the roof of the roadway is the coal seam, that is: L2 = 0;

[0060] When the coal seam has strong impact risk, the gob-side entry of the rock stratum working face is arranged in the old floor rock stratum, and the distance between the roof of the roadway and the coal seam is not less than 2 m, that is: m;

[0061] When the coal seam has impact hazard and coal and gas outburst hazard, the roadway for extracting the rock stratum working face is arranged in the old rock stratum, and the distance between the roadway roof and the coal seam is not less than 5m, that is: m.

[0062] Among them, the impact hazard level of the coal seam is determined according to the comprehensive impact hazard index and the comprehensive impact hazard index is calculated as follows:

[0063] , (i = 1, 2, 3, 4... 8, 9).

[0064] Specifically, the parameters of the comprehensive impact hazard index include:

[0065] : The historical occurrence times N of rock bursts;

[0066] : The mining depth H;

[0067] : The coal seam thickness ;

[0068] : The elastic energy index of the coal;

[0069] : The impact tendency of the coal;

[0070] : The thickness distance relationship (M, d) between the hard thick rock stratum and the coal seam;

[0071] : The characteristic parameter of the roof rock stratum thickness ;

[0072] : The complexity degree of the geological structure;

[0073] The evaluation indexes corresponding to each parameter of the comprehensive impact hazard index can be obtained through analysis and calculation, as shown in Table 1 below:

[0074]

[0075] Calculate , and determine the impact hazard level of the coal seam through the comprehensive impact hazard index ;

[0076] When the comprehensive impact hazard index is not greater than 0.25, the impact hazard level is none;

[0077] When the comprehensive impact hazard index is greater than 0.25 and not greater than 0.5, the impact hazard level is weak impact;

[0078] When the comprehensive impact hazard index is greater than 0.5 and not less than 0.75, the impact hazard level is medium impact;

[0079] When the comprehensive impact hazard index is greater than 0.75, the impact hazard level is strong impact.

[0080] The method for determining the impact hazard of coal seams through the comprehensive impact hazard index and the evaluation index corresponding to all comprehensive impact hazard index parameters are prior arts, which can be obtained through the "Interim Measures for the Identification of Rock Burst Mines", and will not be specifically described in this application.

[0081] Among them, in step S2, that is, during the mining of rock strata, it also includes determining the mining height during the mining of rock strata according to the coal seam thickness , and determining the mining height .

[0082] When the coal seam thickness is not greater than 3.5 m, m, the mining height is not greater than 2 m, that is: m;

[0083] When the coal seam thickness is greater than 3.5 m, m, the mining height is 2 - 3 m, that is: .

[0084] Furthermore, in step S2, according to the uniaxial compressive strength R of the rock strata in the rock strata working face, the method of assisted rock breaking by fracturing the rock strata working face is determined.

[0085] When the uniaxial compressive strength of the rock strata in the rock strata working face is not greater than 30 MPa, Mpa, the mechanized mining is carried out by directly cutting with a shearer.

[0086] When the uniaxial compressive strength of the rock strata in the rock strata working face is greater than 30 MPa and not greater than 60 MPa, MPa, the blasting-assisted rock breaking is adopted.

[0087] Specifically, a number of blasting holes are arranged in the middle of the mined rock strata. The blasting holes are arranged in a straight line. Among them, the charging depth is the sum of twice the daily mining advance and the hole sealing length, and the hole sealing length is not less than one-third of the total hole length. The hole diameter is not greater than 42 mm, the spacing between adjacent holes is 5 - 10 m, and the charge amount per hole is not greater than 10 kg.

[0088] When the uniaxial compressive strength of the rock strata in the rock strata working face is greater than 60 MPa, MPa, and directional slotted orthogonal hydraulic fracturing is used to assist in rock breaking.

[0089] Specifically, in the lower crossheading of the rock stratum working face and within the rock stratum working face, drill holes perpendicular to each other into the exploited rock stratum through a drill rig. Then, form directional pre-cracks in the drill holes through a slotting device. Finally, seal the space closer to the pre-cracks with a packer and perform high-pressure water injection operations to achieve the expansion of the pre-cracks.

[0090] Among them, construction is carried out at the middle position of the mining height within the rock stratum working face and at the middle positions of the two crossheadings of the rock stratum working face; the drill hole diameter is 45 - 65 mm; the drill hole depth is greater than 100 m; the drill hole spacing is 10 - 50 m; the pre-crack cutting groove is more than twice the drill hole diameter; the pre-crack spacing at different positions within the same drill hole is 5 - 10 m; the length of the packer depends on the pre-crack interval and is set to 1 - 2 m; the drill hole is parallel to the rock stratum bedding plane; the water pressure fracturing pressure range is 10 - 40 MPa.

[0091] Calculate the estimated value of the starting pressure required for hydraulic fracturing:

[0092] ; (1)

[0093] In formula (1):

[0094] —Estimated value of the starting pressure required for hydraulic fracturing, MPa;

[0095] —Minor semi-axis of the pre-crack, m;

[0096] —Major semi-axis of the pre-crack, m;

[0097] —Maximum principal stress in the fracturing working face area;

[0098] —Minimum principal stress in the fracturing working face area;

[0099] —Tensile strength of the rock stratum at the fracturing point, MPa.

[0100] Among them, the main operation process of directional slotted orthogonal hydraulic fracturing assisted rock breaking includes drilling, slitting, hole sealing, and water injection fracturing, etc. During drilling, the drilling diameter is mainly required to be maintained at 45 - 65 mm, and an error within 2 mm is allowed due to the rock formation characteristics during this process. After the drill pipe drills to a certain depth, the drill pipe is withdrawn and the drill bit is replaced with a slitting tool, and then the slitting tool is sent to the bottom of the drill hole. After starting the drill rig for directional slitting, first, the drill tool is idled to flush out the rock powder. After the rock powder in the drill hole is washed clean, the drill pipe is slowly pushed to rotate, causing the drill pipe to move forward along the axis. Under the action of the spring, the blades continuously extend, thus cutting out directional cracks in the drill hole. As the drill pipe rotates, the slitting tool will form pre-cracks perpendicular to the axial direction of the drill hole in the drill hole, and its cross-section is approximately elliptical. Repeat this process and keep moving forward to form multiple pre-cracks perpendicular to the drill hole axis. After all the directional cracks are cut, the fracturing work is carried out. The hole is sealed at the outer end of the drill hole through a hole sealer, and the hole sealer is placed at a position 5 - 10 m away from the first directional crack, and then high-pressure water injection operation is carried out into the sealed drill hole. The water injection operation requires a water injection pressure of 10 - 40 Mpa to cause the fracturing and extension of all the directional cracks in the drill hole. After the fracturing work is completed in the roadway, similarly, it is necessary to carry out drilling, slitting, and fracturing work on the rock formation along the working face advancing direction at the coal mining face. The specific operation method is the same as the above process. The fracture zone formed during the construction in the working face is orthogonal to the fracture zone formed by fracturing in the roadway. After multiple rounds of operations, a fracture zone that penetrates and is orthogonal to each other is formed in the rock formation to achieve the purpose of regional rock mass fracturing.

[0101] Furthermore, in step S3, that is, transporting the mined rock to the underground waste rock chamber or the waste rock filling working face, it also includes drilling mutually perpendicular holes into the mined rock formation through a drill rig in the lower flat roadway of the rock formation working face and within the rock formation working face, then forming directional pre-cracks in the drill holes through a slitting device, and finally sealing the space closer to the pre-cracks through a hole sealer and carrying out high-pressure water injection operation to achieve the expansion of the pre-cracks. The water injection operation requires a water injection pressure of 10 - 40 Mpa.

[0102] Furthermore, in step S4, that is, the coal seam above the rock formation adopts the top coal caving technology and collapses spontaneously under the action of the mine pressure. After collapse, the coal is transported above the ground. It also includes that after collapse, the coal is successively transported to the crusher 7 through the rear scraper conveyor 4 and the transfer conveyor 6 for crushing, and then transported to the coal bunker through the belt conveyor 8 and then lifted to the ground through the main shaft.

[0103] The implementation principle of a safety mining method for preventing rock bursts during coal quarrying and coal caving in a coal seam prone to rock bursts in an embodiment of this application is as follows: The mining roadway is arranged in the rock stratum, a working face is arranged in the rock stratum, the traditional "coal mining" working face is transformed into a "coal quarrying" working face, the coal seam is regarded as the "roof" of the rock stratum working face, and through the method of mine pressure or artificial fracturing, the coal collapses by itself and is then mined out, thereby realizing the intrinsically safe mining of the coal seam prone to rock bursts. The above are all preferred embodiments of this application, and the protection scope of this application is not limited accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application shall be covered within the protection scope of this application.

Claims

1. A method for safe mining in rock burst coal seam quarrying and coal caving to prevent impact, characterized by: The steps include: S1. Arrange the mining tunnel of the rock layer working face in the coal seam and rock layer. The length of the rock layer working face shall not be less than 100m. The rock layer includes the direct bottom rock layer and the old bottom rock layer. In step S1, it also includes: When the coal seam has a weak impact hazard, half of the mining tunnel of the rock face is arranged in the coal seam, and the other half is arranged in the rock layer below the coal seam; When the coal seam has a medium impact hazard, the rock face mining tunnel is arranged in the rock layer below the coal seam, and the tunnel roof is the coal seam; When the coal seam has a strong impact hazard, the mining tunnel of the rock working face is arranged in the old bottom rock layer, and the distance between the tunnel roof and the coal seam is not less than 2m; When the coal seam has the danger of impact and the coal seam has the danger of coal and gas outburst, the mining tunnel of the rock layer working face is arranged in the old bottom rock layer, and the distance between the tunnel roof and the coal seam is not less than 5m; S2. Mining the rock layer with a mining height of no more than 3m; S3, transporting the mined rock to the underground gangue chamber or gangue filling working face; S4. The coal seam above the rock layer adopts the top coal caving technology, which collapses automatically under the action of mine pressure, and the collapsed coal is transported to the ground.

2. The method for safe mining in rock burst coal seam quarrying and coal caving to prevent rock burst according to claim 1, characterized in that: In step S2, it also includes: According to the thickness of coal seam, determine the mining height during the mining process; When the thickness of the coal seam is not more than 3.5m, the mining height shall not exceed 2m; When the coal seam thickness is greater than 3.5m, the mining height is 2-3m.

3. The method for safe mining in rock burst coal seam quarrying and coal caving to prevent rock burst according to claim 1, characterized in that: In step S2, it also includes: According to the uniaxial compressive strength of the rock formation working face, determine the auxiliary rock breaking method of the rock formation working face; When the uniaxial compressive strength of the rock stratum at the working face is not greater than 30 MPa, mechanized mining is carried out by using a coal mining machine (1) to directly cut the rock stratum; When the uniaxial compressive strength of the rock stratum at the working face is greater than 30MPa and not greater than 6MPa, blasting is used to assist in rock breaking; When the uniaxial compressive strength of the rock formation at the working face is greater than 60MPa, directional slit orthogonal hydraulic fracturing is used to assist in rock breaking.

4. The method for preventing rock burst and coal caving in rock burst coal seam according to claim 3 is characterized in that: The process of using blasting to assist rock breaking also includes: Several blasting holes are arranged in the middle of the mined rock stratum in a straight line. The charging depth is the sum of twice the daily mining footage and the sealing length, and the sealing length is not less than one third of the total length of the borehole. The borehole diameter is not greater than 42mm, the distance between adjacent boreholes is 5-10m, and the charging amount of a single hole is not more than 10kg.

5. The method for safe mining in rock burst coal seam quarrying and coal caving to prevent rock burst according to claim 3, characterized in that: The process of using directional slotted orthogonal hydraulic fracturing to assist in rock breaking also includes: In the horizontal tunnels below the rock working face and in the rock working face, a drilling rig is used to construct perpendicular holes into the mined rock layer, and then a directional pre-crack is formed in the drill hole through a cutting device. Finally, the space close to the pre-crack is sealed by a sealer and high-pressure water injection is performed to expand the pre-crack.

6. A rock burst coal seam quarrying and coal caving anti-bumping safety mining method according to claim 5, characterized in that: The construction is carried out in the middle of the mining height in the mining stratum working face and in the middle of the two lanes of the rock stratum working face; the diameter of the borehole is 45-65mm; the depth of the borehole is greater than 100m; the spacing between boreholes is 10-50m; the pre-crack cutting groove is greater than 2 times the diameter of the borehole; the spacing between pre-cracks at different positions in the same borehole is 5-10m; the length of the hole sealer depends on the pre-crack spacing and is set to 1-2m; The borehole is parallel to the rock layer; hydraulic fracturing pressure range: 10-40Mpa; Among them, the estimated starting pressure required for hydraulic fracturing is: Where p is the estimated starting pressure required for hydraulic fracturing, in MPa, b is the short semi-axis length of the pre-crack, in m, a is the long semi-axis length of the pre-crack, in m, is the maximum principal stress in the fracture working surface area, is the minimum principal stress in the fracture working surface area, It is the tensile strength of rock formation at the fracture point, in MPa.

7. The method for safe mining in rock burst coal seam quarrying and coal caving to prevent rock burst according to claim 1, characterized in that: In step S3, it also includes: The mined rock is transported to an underground gangue chamber or a gangue filling working face via a front scraper conveyor (3), a transfer machine (6) and a belt conveyor in sequence.

8. The method for safe mining in rock burst coal seam quarrying and coal caving to prevent rock burst according to claim 1, characterized in that: In step S4, it also includes: The collapsed coal is transported to the crusher (7) through the rear scraper conveyor (4) and the transfer machine (6) for crushing, and then transported to the coal bunker through the belt conveyor (8) and lifted to the ground through the main shaft.

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