Composite hard and thick coal seam top coal weakening method

Abstract

The invention discloses a composite hard and thick coal seam top coal weakening method, which comprises the following steps that S1, blasting drill hole groups are constructed on a composite hard and thick coal seam on an air return crossheading and an air inlet crossheading in the length direction of the crossheading at intervals of 5-10 m at the position not less than 30 m away from a mining line of a coal face, each group comprises 3-5 drill holes, the distance between hole opening points is 0.3-0.5 m, and the height of hole distribution positions in the vertical direction is 2-3 m; s2, drilling, charging and mud sealing are conducted, a radial air column non-coupling axial continuous forward charging mode is adopted as the charging mode, the charging linear density of each hole is 2.4 Kg / m, and the mud sealing length is not smaller than one third of the depth of a shot hole; s3, blasting is carried out; and S4, a water injection softening device is connected to the drill hole, water is supplied through a coal mine underground dustproof water pipeline, the water is filtered through a filtering water tank and then enters a liquid injection pump to be pressurized, and high-pressure multi-hole water injection and drill hole water injection softening fracturing are conducted on the blasted top coal weakening hole.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining methods, and in particular to a method for weakening top coal in a composite hard and thick coal seam. Background Art

[0002] Composite hard and thick coal seams have the characteristics of complete structure, high hardness, high compressive and tensile strength, and high shear strength. During the mining process of the coal mining face using the top coal caving mining method, the top coal is not easy to be damaged, the fractured hinge surface is not easy to slide off, it is easy to break and fall into large pieces, and it is not easy to break, which increases the difficulty of top coal caving and reduces the recovery rate of the top coal.

[0003] The existing loosening blasting method has poor practical effect on solving the problem of low top coal recovery rate in composite hard and thick coal seams and cannot fundamentally solve the problem.

[0004] Therefore, a top coal weakening method for composite hard and thick coal seams is proposed. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a method for weakening the top coal of a composite hard and thick coal seam.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: A composite hard and thick coal seam top coal weakening method comprises the following steps: S1. At a distance of not less than 30m from the mining face, on the return air chute and the inlet air chute, a blasting drilling group is constructed every 5-10m along the length of the chute, towards the composite hard and thick coal seam. Each group has 3-5 holes, of which 1-2 holes are also used as guide holes, with a hole diameter of 75-100mm and a depth of 15-50m. Each blasting drilling group is arranged in a fan shape in the composite hard and thick coal seam, with a hole spacing of 0.3-0.5m and a vertical hole arrangement height of 2-3m. S2. Drilling, charging and sealing. The charging method is radial air column uncoupled axial continuous forward charging. The charging line density of each hole is 2.4 kg / m. The charging is Φ50×1.5m long special relay wooden baton. The detonation method is electric detonator detonating detonating cord, detonating index explosives, and the sealing length shall not be less than one third of the blasthole depth; S3, blasting, the blasting method adopts the alternate blasting method of the air inlet chute and the return air chute, that is, drilling and blasting are carried out in the air inlet chute on the same day, and drilling and blasting are carried out in the return air chute on the next day; S4. Connect a water injection and softening device to the borehole, use the dust-proof water pipeline in the coal mine to supply water, and after being filtered in the filter water tank, enter the injection pump for pressurization. Perform high-pressure multi-porous water injection on the weakened holes of the top coal after blasting, and perform water injection softening and fracturing on the borehole.

[0007] Wherein, in step S1, the included angle between the drilling direction and the working surface advancement direction is 90°.

[0008] Among them, in the step S1, the explosive is the third-level emulsion explosive permitted in coal mines, the specification of the explosive roll is Φ50×500mm, the weight of each section is 1.2kg, the detonator is the digital electronic detonator permitted in coal mines, the detonating cord is the third-level waterproof detonating cord permitted in coal mines, and the blasting is detonated by MBH-200B detonator.

[0009] Wherein, in the step S1, the boreholes in each blasting drill hole group of the return air chute are numbered 1 to 5, and the boreholes in each blasting drill hole group of the inlet air chute are numbered 6 to 10; The No. 1 borehole, which also serves as a guide hole, is located at a height of 2.2m, a horizontal angle of 2°, and a depth of 50m; the No. 2 borehole is located at a height of 2.5m, a horizontal angle of 8°, and a depth of 47m; the No. 3 borehole is located at a height of 2.8m, a horizontal angle of 14°, and a depth of 33m; the No. 4 borehole, which also serves as a guide hole, is located at a height of 2.8m, a horizontal angle of 24°, and a depth of 22m; the No. 5 borehole is located at a height of 2.8m, a horizontal angle of 42°, and a depth of 15m; Drill hole No. 1 also serves as a guide hole, with a hole layout height of 2.2m, a horizontal angle of 12°, and a depth of 50m; drill hole No. 7 has a hole layout height of 2.5m, a horizontal angle of 18°, and a depth of 47m; drill hole No. 8 has a hole layout height of 2.8m, a horizontal angle of 25°, and a depth of 33m; drill hole No. 9 also serves as a guide hole, with a hole layout height of 2.8m, a horizontal angle of 35°, and a depth of 22m; drill hole No. 10 has a hole layout height of 2.8m, a horizontal angle of 50°, and a depth of 15m.

[0010] Among them, the charging length of No. 1 borehole is 23m, and the sealing length is 27m; the charging length of No. 2 borehole is 21m, and the sealing length is 26m; the charging length of No. 3 borehole is 15m, and the sealing length is 18m; the charging length of No. 4 borehole is 10m, and the sealing length is 12m; the charging length of No. 5 borehole is 7m, and the sealing length is 8m; the charging length of No. 6 borehole is 20m, and the sealing length is 30m; the charging length of No. 7 borehole is 19m, and the sealing length is 28m; the charging length of No. 8 borehole is 13m, and the sealing length is 20m; the charging length of No. 9 borehole is 9m, and the sealing length is 13m; the charging length of No. 10 borehole is 6m, and the sealing length is 9m.

[0011] Among them, the technical parameters of water injection softening are: water injection pressure 18~20MPa; water injection time 0.5~1h; use of sealer to seal the hole, the sealing depth is 20m; dynamic pressure fracturing is 0.7~2.0m³ / h; fracturing volume per hole is 1m³.

[0012] Among them, in step S1, in order to prevent loosening blasting from causing rock damage on the coal seam roof, causing excessive roof caving and coal gangue mixing to affect coal quality, the normal distance between each drilling end point and the coal seam roof should be controlled to be no less than 1m.

[0013] Among them, in the step S2, in order to achieve the expected blasting goal and taking into account the need to protect the working face roof, the normal distance range of 0 to 4.0 m upward from the working face roof is determined as the blasting gap zone, and charging and blasting are not allowed in the boreholes within this range; the normal distance range of 4.0 to 9.7 m upward from the working face roof is determined as the blasting zone, and charging and blasting are only allowed in the boreholes within this range.

[0014] The beneficial effects of the present invention are: 1. The method of the present invention systematically analyzes and studies the crushing and cavability of the composite hard and thick coal seam on the working face, implements the corresponding top coal weakening project, solves the problems of top coal crushing and recovery rate in comprehensive top coal caving mining, further improves the top coal recovery rate, and ensures the maximum recovery of coal resources.

[0015] 2. The present invention is a top coal weakening process that combines deep hole blasting pre-cracking with water injection softening fracturing. The advanced pre-cracking technology adopts the working face deep hole blasting technology as the main body and water injection softening as the auxiliary advanced top coal weakening technology. It determines the key layer of coal rock weakening in the fully-mechanized caving working face, coordinates the coal-breaking effect of the advanced supporting pressure of the fully-mechanized caving working face, controls the size and crack evolution law of the top coal in the fully-mechanized caving mining from time and space, and realizes the purpose of timely collapse of the top coal of the working face and venting as it is mined.

[0016] 3. The present invention combines blasting and water injection. The entire implementation process is a superposition of the blasting fracturing effect and the water injection fracturing and softening effect, a superposition of long-term and short-term effects, and a superposition of blasting stress waves, explosion gas pressure, and pore water pressure. This can further increase the number and density of cracks, increase the blasting fracturing effect and the water injection fracturing and softening effect, improve the crushability of top coal, and increase the recovery rate of top coal.

[0017] 4. The present invention determines the deep hole blasting location based on mining technical factors such as the burial depth of the composite hard and thick coal seam, coal rock characteristics, coal caving technology, roof disaster-causing laws, etc., combined with the actual on-site conditions such as the requirements for top coal crushing, coal body block size control and construction schedule.

[0018] 5. The present invention is based on the observation of tunnel deformation, and manifests itself in accordance with the changes in mining depth and the law of mine pressure. Usually, drilling holes are arranged at a safe location 30m away from the mining face and outside the influence range of the mining pressure of the air inlet and return air chute, and deep hole charging pre-splitting blasting is carried out to pre-splitting and fissure transformation of the coal seam. The effect of the explosive gas generated when the explosive explodes is utilized to form cavities, crushing circles and pre-splitting circles in the coal body, thereby pre-breaking and loosening the coal body, reducing its strength, and causing it to collapse in medium and small pieces when the top coal is caving, thereby improving the recovery rate.

[0019] 6. Through the application of the present invention during the mining process of the working face, a top coal weakening process method combining deep hole blasting pre-cracking and water injection softening fracturing is adopted to weaken the top coal, improve the top coal stress environment, enhance the coal breaking effect of mine pressure, and realize safe and efficient mining of hard and thick composite coal seams.

[0020] 7. The application of the present invention reduces the particle size of lump coal during top coal caving at the working face, making most of them reach below 40cm×40cm×40cm, thereby increasing the caving performance of the top coal at the working face.

[0021] 8. The application of the present invention reduces the firmness of coal (rock) layers and improves the resource recovery rate, with the top coal recovery rate reaching more than 86%.

[0022] 9. The application of the present invention can recover more coal resources, increase profits, and have considerable economic benefits.

[0023] 10. The application of the present invention reduces the dust concentration in the working area, and the total dust concentration is reduced to below 1.0 mg / m³, thus creating a clean production working environment and providing conditions for preventing spontaneous combustion of gas and coal seams.

[0024] 11. The application of the present invention reduces the failure rate of working face equipment and improves the equipment startup rate.

[0025] 12. The application of the present invention effectively solves the problems of poor top coal crushing and caving performance during top coal caving at the working face, and at the same time develops new technologies, processes and methods specifically for crushing and caving performance of fully mechanized top coal caving in composite hard and thick coal seams.

[0026] 13. The application of the present invention provides practical support for establishing a technical innovation system for clean and efficient top coal mining, and provides technical guarantee for the future top coal caving working face of composite hard and thick coal seams and multi-coal seam combined mining working face mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a schematic elevation diagram of the arrangement of the blasting drilling group of the present invention.

[0028] Figure 2 It is a schematic plan view of the arrangement of the blasting drilling group of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0030] According to the key influencing factors such as the buried depth of the composite hard and thick coal seam of 90-150m; the 2 layers of mineable coal seams contain 2.2-3m of interlayer gangue; the hardness coefficient of interlayer gangue is 5.8; the hardness coefficient of the coal seam is 3; the 2 layers of coal are mined together; the thickness of the coal seam is 13.5m; the inclined length of the working face is 150m; the mining height is 2.8m, the top coal caving height is 10.7m, and the mining and caving ratio is 1:3.8; there is no impact, no protrusion, etc., combined with the actual situation that the working face is within the initial mining range of 40m, because the coal seam is hard, the cracks are not developed, the ground stress is low, the natural collapse height of the top coal is only 2-3m, and the average recovery rate is only 23%, it is determined to adopt this method Example 1 like Figure 1 and Figure 2 As shown, a composite hard thick coal seam top coal weakening method comprises the following steps: S1. At a distance of not less than 30m from the mining face 3, on the return air chute 1 and the inlet air chute 5, a blasting drill hole group 4 is constructed every 5m along the length of the chute, toward the composite hard and thick coal seam 2. Each group of 5 drill holes, of which 1-2 drill holes are also used as guide holes, with a hole diameter of 75mm and a depth of 15m. Each blasting drill hole group 4 is arranged in a fan shape in the composite hard and thick coal seam 2, with a hole opening point spacing of 0.3m and a hole arrangement position height of 2m in the vertical direction; S2. Drilling, charging and sealing. The charging method is radial air column uncoupled axial continuous forward charging. The charging line density of each hole is 2.4 kg / m. The charging is Φ50×1.5m long special relay wooden baton. The detonation method is electric detonator detonating detonating cord, detonating index explosives, and the sealing length shall not be less than one third of the blasthole depth; S3, blasting, the blasting method adopts the alternate blasting method of the air inlet chute and the return air chute, that is, drilling and blasting are carried out in the air inlet chute on the same day, and drilling and blasting are carried out in the return air chute on the next day; S4. Connect a water injection and softening device to the borehole, use the dust-proof water pipeline in the coal mine to supply water, and after being filtered in the filter water tank, enter the injection pump for pressurization. Perform high-pressure multi-porous water injection on the weakened holes of the top coal after blasting, and perform water injection softening and fracturing on the borehole.

[0031] Wherein, in step S1, the included angle between the drilling direction and the working surface advancement direction is 90°.

[0032] Among them, in the step S1, the explosive is the third-level emulsion explosive permitted in coal mines, the specification of the explosive roll is Φ50×500mm, the weight of each section is 1.2kg, the detonator is the digital electronic detonator permitted in coal mines, the detonating cord is the third-level waterproof detonating cord permitted in coal mines, and the blasting is detonated by MBH-200B detonator.

[0033] Wherein, in the step S1, the boreholes in each blasting drill hole group 4 of the return air chute 1 are numbered 1 to 5, and the boreholes in each blasting drill hole group 4 of the inlet air chute 5 are numbered 6 to 10; The No. 1 borehole, which also serves as a guide hole, is located at a height of 2.2m, a horizontal angle of 2°, and a depth of 50m; the No. 2 borehole is located at a height of 2.5m, a horizontal angle of 8°, and a depth of 47m; the No. 3 borehole is located at a height of 2.8m, a horizontal angle of 14°, and a depth of 33m; the No. 4 borehole, which also serves as a guide hole, is located at a height of 2.8m, a horizontal angle of 24°, and a depth of 22m; the No. 5 borehole is located at a height of 2.8m, a horizontal angle of 42°, and a depth of 15m; Drill hole No. 1 also serves as a guide hole, with a hole layout height of 2.2m, a horizontal angle of 12°, and a depth of 50m; drill hole No. 7 has a hole layout height of 2.5m, a horizontal angle of 18°, and a depth of 47m; drill hole No. 8 has a hole layout height of 2.8m, a horizontal angle of 25°, and a depth of 33m; drill hole No. 9 also serves as a guide hole, with a hole layout height of 2.8m, a horizontal angle of 35°, and a depth of 22m; drill hole No. 10 has a hole layout height of 2.8m, a horizontal angle of 50°, and a depth of 15m.

[0034] Among them, the charging length of No. 1 borehole is 23m, and the sealing length is 27m; the charging length of No. 2 borehole is 21m, and the sealing length is 26m; the charging length of No. 3 borehole is 15m, and the sealing length is 18m; the charging length of No. 4 borehole is 10m, and the sealing length is 12m; the charging length of No. 5 borehole is 7m, and the sealing length is 8m; the charging length of No. 6 borehole is 20m, and the sealing length is 30m; the charging length of No. 7 borehole is 19m, and the sealing length is 28m; the charging length of No. 8 borehole is 13m, and the sealing length is 20m; the charging length of No. 9 borehole is 9m, and the sealing length is 13m; the charging length of No. 10 borehole is 6m, and the sealing length is 9m.

[0035] Among them, the technical parameters of water injection softening are: water injection pressure 18MPa; water injection time 0.5h; use of sealer to seal the hole, the sealing depth is 20m; dynamic pressure fracturing is 0.7m³ / h; fracturing volume per hole is 1m³.

[0036] Among them, in step S1, in order to prevent loosening blasting from causing rock damage on the coal seam roof, causing excessive roof caving and coal gangue mixing to affect coal quality, the normal distance between each drilling end point and the coal seam roof should be controlled to be no less than 1m.

[0037] Among them, in step S2, in order to achieve the expected blasting goal and taking into account the need to protect the working face roof, the normal distance range of 0 to 4.0 m upward from the working face roof is determined as the blasting gap zone, and charging and blasting are not allowed in the boreholes within this range; the normal distance range of 4.0 m upward from the working face roof is determined as the blasting zone, and charging and blasting are only allowed in the boreholes within this range.

[0038] Example 2 like Figure 1 and Figure 2 As shown, a composite hard thick coal seam top coal weakening method comprises the following steps: S1. At a distance of not less than 30m from the mining face 3, on the return air chute 1 and the inlet air chute 5, a blasting drill hole group 4 is constructed towards the composite hard and thick coal seam 2 every 10m along the length direction of the chute. Each group has 5 drill holes, of which 1 to 2 drill holes are also used as guide holes with a hole diameter of 100mm and a depth of 50m. Each blasting drill hole group 4 is arranged in a fan shape in the composite hard and thick coal seam 2, with a hole opening point spacing of 0.5m and a vertical hole arrangement position height of 3m; S2. Drilling, charging and sealing. The charging method is radial air column uncoupled axial continuous forward charging. The charging line density of each hole is 2.4 kg / m. The charging is Φ50×1.5m long special relay wooden baton. The detonation method is electric detonator detonating detonating cord, detonating index explosives, and the sealing length shall not be less than one third of the blasthole depth; S3, blasting, the blasting method adopts the alternate blasting method of the air inlet chute and the return air chute, that is, drilling and blasting are carried out in the air inlet chute on the same day, and drilling and blasting are carried out in the return air chute on the next day; S4. Connect a water injection and softening device to the borehole, use the dust-proof water pipeline in the coal mine to supply water, and after being filtered in the filter water tank, enter the injection pump for pressurization. Perform high-pressure multi-porous water injection on the weakened holes of the top coal after blasting, and perform water injection softening and fracturing on the borehole.

[0039] Wherein, in step S1, the included angle between the drilling direction and the working surface advancement direction is 90°.

[0040] Among them, in the step S1, the explosive is the third-level emulsion explosive permitted in coal mines, the specification of the explosive roll is Φ50×500mm, the weight of each section is 1.2kg, the detonator is the digital electronic detonator permitted in coal mines, the detonating cord is the third-level waterproof detonating cord permitted in coal mines, and the blasting is detonated by MBH-200B detonator.

[0041] Wherein, in the step S1, the boreholes in each blasting drill hole group 4 of the return air chute 1 are numbered 1 to 5, and the boreholes in each blasting drill hole group 4 of the inlet air chute 5 are numbered 6 to 10; The No. 1 borehole, which also serves as a guide hole, is located at a height of 2.2m, a horizontal angle of 2°, and a depth of 50m; the No. 2 borehole is located at a height of 2.5m, a horizontal angle of 8°, and a depth of 47m; the No. 3 borehole is located at a height of 2.8m, a horizontal angle of 14°, and a depth of 33m; the No. 4 borehole, which also serves as a guide hole, is located at a height of 2.8m, a horizontal angle of 24°, and a depth of 22m; the No. 5 borehole is located at a height of 2.8m, a horizontal angle of 42°, and a depth of 15m; Drill hole No. 1 also serves as a guide hole, with a hole layout height of 2.2m, a horizontal angle of 12°, and a depth of 50m; drill hole No. 7 has a hole layout height of 2.5m, a horizontal angle of 18°, and a depth of 47m; drill hole No. 8 has a hole layout height of 2.8m, a horizontal angle of 25°, and a depth of 33m; drill hole No. 9 also serves as a guide hole, with a hole layout height of 2.8m, a horizontal angle of 35°, and a depth of 22m; drill hole No. 10 has a hole layout height of 2.8m, a horizontal angle of 50°, and a depth of 15m.

[0042] Among them, the charging length of No. 1 borehole is 23m, and the sealing length is 27m; the charging length of No. 2 borehole is 21m, and the sealing length is 26m; the charging length of No. 3 borehole is 15m, and the sealing length is 18m; the charging length of No. 4 borehole is 10m, and the sealing length is 12m; the charging length of No. 5 borehole is 7m, and the sealing length is 8m; the charging length of No. 6 borehole is 20m, and the sealing length is 30m; the charging length of No. 7 borehole is 19m, and the sealing length is 28m; the charging length of No. 8 borehole is 13m, and the sealing length is 20m; the charging length of No. 9 borehole is 9m, and the sealing length is 13m; the charging length of No. 10 borehole is 6m, and the sealing length is 9m.

[0043] Among them, the technical parameters of water injection softening are: water injection pressure 20MPa; water injection time 1h; use of sealer to seal the hole, the sealing depth is 20m; dynamic pressure fracturing is 2.0m³ / h; fracturing volume per hole is 1m³.

[0044] Among them, in step S1, in order to prevent loosening blasting from causing rock damage on the coal seam roof, causing excessive roof caving and coal gangue mixing to affect coal quality, the normal distance between each drilling end point and the coal seam roof should be controlled to be no less than 1m.

[0045] Among them, in step S2, in order to achieve the expected blasting goal and taking into account the need to protect the working face roof, the normal distance range of 0 to 4.0 m upward from the working face roof is determined as the blasting gap zone, and charging and blasting are not allowed in the boreholes within this range; the normal distance range of 9.7 m upward from the working face roof is determined as the blasting zone, and charging and blasting are only allowed in the boreholes within this range.

[0046] In the above embodiment, after comparative analysis after the mining was completed, the top coal recovery rate increased by 66% to 89%; nearly 320,000 tons more coal resources were recovered than normal mining, and after removing the additional costs such as explosives, electricity, labor, materials, and accessories during the implementation of the method, the profit per ton of coal was 328 yuan, and the increased profit reached over 100 million yuan; the total dust concentration of the working face was reduced from the original 3.2 mg / m³ to 0.8 mg / m³; there was no local accumulation and over-limit of gas; there was no spontaneous combustion of coal seams; and the equipment start-up rate was increased from the original 75% to 87%.

[0047] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A composite hard and thick coal seam top coal weakening method, characterized in that: The following steps are involved: S1. At a distance of not less than 30 m from the mining face (3) to the mining line, on the return air chute (1) and the inlet air chute (5), a blasting drill hole group (4) is constructed towards the composite hard and thick coal seam (2) every 5 to 10 m along the length direction of the chute. Each group has 3 to 5 drill holes, of which 1 to 2 drill holes also serve as guide holes, with a hole diameter of 75 to 100 mm and a depth of 15 to 50 m. Each blasting drill hole group (4) is arranged in a fan shape in the composite hard and thick coal seam (2), with a hole opening point spacing of 0.3 to 0.5 m and a hole arrangement height of 2 to 3 m in the vertical direction; S2. Drilling, charging and sealing. The charging method is radial air column uncoupled axial continuous forward charging. The charging line density of each hole is 2.4 kg / m. The charging is Φ50×1.5m long special relay wooden baton. The detonation method is electric detonator detonating detonating cord, detonating index explosives, and the sealing length shall not be less than one third of the blasthole depth; S3, blasting, the blasting method adopts the alternate blasting method of the air inlet chute and the return air chute, that is, drilling and blasting are carried out in the air inlet chute on the same day, and drilling and blasting are carried out in the return air chute on the next day; S4. Connect a water injection and softening device to the borehole, use the dust-proof water pipeline in the coal mine to supply water, and after being filtered in the filter water tank, enter the injection pump for pressurization. Perform high-pressure multi-porous water injection on the weakened holes of the top coal after blasting, and perform water injection softening and fracturing on the borehole.

2. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In step S1, the included angle between the drilling direction and the working surface advancement direction is 90°.

3. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In step S1, the explosive is the third-grade emulsion explosive permitted in coal mines, the explosive roll specification is Φ50×500mm, each section weighs 1.2kg, the detonator is the digital electronic detonator permitted in coal mines, the detonating cord is the third-grade waterproof detonating cord permitted in coal mines, and the blasting is initiated by the MBH-200B detonator.

4. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In the step S1, the boreholes in each blasting borehole group (4) of the return air chute (1) are numbered 1 to 5, and the boreholes in each blasting borehole group (4) of the inlet air chute (5) are numbered 6 to 10; The No. 1 borehole, which also serves as a guide hole, is located at a height of 2.2m, a horizontal angle of 2°, and a depth of 50m; the No. 2 borehole is located at a height of 2.5m, a horizontal angle of 8°, and a depth of 47m; the No. 3 borehole is located at a height of 2.8m, a horizontal angle of 14°, and a depth of 33m; the No. 4 borehole, which also serves as a guide hole, is located at a height of 2.8m, a horizontal angle of 24°, and a depth of 22m; the No. 5 borehole is located at a height of 2.8m, a horizontal angle of 42°, and a depth of 15m; Drill hole No. 1 also serves as a guide hole, with a hole layout height of 2.2m, a horizontal angle of 12°, and a depth of 50m; drill hole No. 7 has a hole layout height of 2.5m, a horizontal angle of 18°, and a depth of 47m; drill hole No. 8 has a hole layout height of 2.8m, a horizontal angle of 25°, and a depth of 33m; drill hole No. 9 also serves as a guide hole, with a hole layout height of 2.8m, a horizontal angle of 35°, and a depth of 22m; drill hole No. 10 has a hole layout height of 2.8m, a horizontal angle of 50°, and a depth of 15m.

5. A composite hard and thick coal seam top coal weakening method according to claim 4, characterized in that: In the step S2, the charge length of No. 1 borehole is 23m, and the sealing length is 27m; the charge length of No. 2 borehole is 21m, and the sealing length is 26m; the charge length of No. 3 borehole is 15m, and the sealing length is 18m; the charge length of No. 4 borehole is 10m, and the sealing length is 12m; the charge length of No. 5 borehole is 7m, and the sealing length is 8m; the charge length of No. 6 borehole is 20m, and the sealing length is 30m; the charge length of No. 7 borehole is 19m, and the sealing length is 28m; the charge length of No. 8 borehole is 13m, and the sealing length is 20m; the charge length of No. 9 borehole is 9m, and the sealing length is 13m; the charge length of No. 10 borehole is 6m, and the sealing length is 9m.

6. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In step S4, the water injection softening technical parameters are as follows: water injection pressure 18-20 MPa; water injection time 0.5-1 h; using a sealer to seal the hole, the sealing depth is 20 m; dynamic pressure fracturing is 0.7-2.0 m³ / h; the fracturing volume per hole is 1 m³.

7. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In step S1, in order to prevent loosening blasting from damaging the coal seam roof rock, causing excessive roof caving and coal gangue mixing to affect coal quality, the normal distance between each drilling end point and the coal seam roof should be controlled to be no less than 1m.

8. A composite hard and thick coal seam top coal weakening method according to claim 1, characterized in that: In step S2, in order to achieve the expected blasting goal and taking into account the need to protect the top plate of the working face, the normal distance range of 0 to 4.0 m upward from the top plate of the working face is determined as the blasting gap zone, and charging and blasting are not allowed in the boreholes within this range; the normal distance range of 4.0 to 9.7 m upward from the top plate of the working face is determined as the blasting zone, and charging and blasting are only allowed in the boreholes within this range.

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