Roof cutting and pressure relief method for end of coal face

Abstract

The invention relates to the technical field of mine safety devices, in particular to a coal face end top cutting pressure relief method which mainly comprises the steps that A, rock core sampling is conducted, and the thickness of a top plate layer is determined according to the rock core structure; b, grouting holes are drilled, specifically, a plurality of grouting holes are drilled in the position close to the coal face from the lower portion of the top plate; c, water injection holes and nitrogen filling holes are drilled, and a plurality of water injection holes and a plurality of nitrogen filling holes are drilled upwards in a top plate on the side, away from the coal face, of the grouting hole; d, grouting is conducted, specifically, a rock stratum gap above the coal face is filled with slurry; e, water injection is conducted, specifically, water is injected into a rock stratum gap between the top plate and the rock stratum above the top plate; f, filling liquid nitrogen, namely filling the liquid nitrogen into a rock stratum gap between the top plate and the rock stratum above the top plate. According to the scheme, the drilling density is small, the drilling number is small, the construction time is short, construction is safe, pre-supporting is not needed during drilling operation, the fracturing process is slow and stable, gas explosion accidents cannot be caused, and the applicability is wide.

Description

Technical Field

[0001] The invention relates to the technical field of mine safety devices, and in particular to a method for removing pressure by cutting the top of a coal mining working face. Background Art

[0002] In underground coal mining, rock control is the core of safe and efficient coal mining, especially when a hard roof exists. Because the hard roof is strong and not easy to break, a large area of ​​the hard roof hangs over the working face, causing continuous stress concentration in the working face, serious deformation and damage to the tunnel, and other problems. After the coal mining working face is mined, the hard roof is difficult to collapse in time and is prone to form a cantilever structure. After the basic roof breaks, the cantilever structure will rotate and sink, causing the surrounding rock stress of the adjacent tunnels to increase, the adjacent working face tunnels to deform seriously, and cause violent vibration of the working face rock mass and impact mine pressure and coal and gas outbursts and other dynamic disasters.

[0003] In view of the serious deformation of surrounding rock and the difficulty of controlling the roof in the goaf-side tunnel, it is impossible to effectively control the deformation of surrounding rock by strengthening the support of tunnel with traditional anchor rods and anchor cables. Only by cutting off the cantilever roof in the goaf and releasing the elastic potential energy accumulated in the roof can the stress concentration caused by the roof on the surrounding rock of the goaf-side tunnel be fundamentally eliminated, thereby improving the stability of the surrounding rock of the goaf-side tunnel. The commonly used technical methods include blasting top cutting pressure relief technology, hydraulic fracturing weakened top cutting pressure relief technology, and composite perforation top cutting pressure relief technology. However, the blasting top cutting and pressure relief technology uses explosive blasting, which is only suitable for low-gas mines. High-gas mines require strict technical requirements for use, and top cutting blasting may cause the roof in the tunnel to fall prematurely, making it difficult to manage the roof. Conventional hydraulic fracturing weakened top cutting and pressure relief technology uses high-pressure water to create and expand cracks inside the roof to weaken the roof structure, causing the roof to collapse under its own weight, achieving the solution of top cutting and pressure relief. However, this method requires the equipment to have extremely high pressure output performance in order to press out cracks in the roof, which has high equipment requirements, complex processes, and poor adaptability to natural conditions in the tunnel. There are also schemes in the prior art that use dense drilling methods to cut the roof and relieve pressure. For example, the prior art with publication number CN110966002 B discloses a method for cutting the roof and relieving pressure based on dense drilling. This scheme destroys the roof structure by densely drilling holes on the roof that forms a cantilever, and the roof automatically collapses under the influence of the roof's own weight and mining. However, this method requires too many holes to be drilled, the drilling time is too long, and the collapse time of the roof cannot be predicted. In addition, due to the high density of drilling holes, there may be a risk of sudden collapse of the roof during the drilling process. Based on this, it is an urgent problem to study a method for cutting the roof and relieving pressure at the end of a coal mining face. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a method for top cutting and pressure relief at the end of a coal mining working face to solve the above-mentioned problems in the prior art.

[0005] In order to solve the above technical problems, a basic solution adopted by the present invention is a method for removing pressure by cutting the top of a coal mining working face, comprising the following steps: Step A: core sampling, drill cores upward from multiple points on the roof where holes are to be drilled, and determine the thickness of the roof layer based on the core structure to determine the drilling depth; Step B: drilling grouting holes, drilling a plurality of grouting holes from the bottom of the roof upward near the coal mining working face, wherein the plurality of grouting holes are arranged in sequence in a direction parallel to the coal mining working face, and the drilling depth of the grouting holes exceeds the thickness of the roof; Step C: drilling water injection holes and nitrogen filling holes, and drilling a plurality of water injection holes and a plurality of nitrogen filling holes in an alternating arrangement upward in a direction parallel to the coal mining working face on the roof plate on the side of the grouting hole away from the coal mining working face, and the drilling depth exceeds the thickness of the roof plate; Step D: grouting, using grouting equipment to fill slurry into the rock stratum gap above the coal mining working face through the grouting hole; Step E: water injection, using the water injection device to inject water into the rock stratum gap between the top plate and the rock stratum above the top plate through the water injection hole so that the water body is enriched in the rock stratum gap between the top plate and the rock stratum above the top plate; Step F: Filling with liquid nitrogen: Liquid nitrogen is filled into the rock stratum gap between the top plate and the rock stratum above the top plate through the nitrogen filling hole through the nitrogen filling device.

[0006] In the above scheme, water is injected into the cracks of the rock formation above the goaf-side tunnel, and then liquid nitrogen is introduced into the cracks of the rock formation. The vaporization of the liquid nitrogen causes the water in the cracks of the rock formation to freeze quickly and expand to press the roof downwards, so that the weakened zone formed by the water injection holes and the nitrogen filling holes on the roof is broken, thereby achieving the purpose of top cutting and pressure relief. In this scheme, compared with forming the weakened zone of the roof by densely drilling holes, the water injection holes and nitrogen filling holes in this scheme also form a weakened zone on the roof, but the drilling density of this scheme is small, and the water in the cracks of the rock formation is frozen before nitrogen is filled. Before the ice expands, the roof will not break, the construction is highly safe, and no pre-support is required during drilling operations. In this scheme, grouting is first injected into the rock stratum gap between the roof above the coal mining face and the rock stratum above the roof, and then water is injected into the rock stratum gap above the gob tunnel. This can effectively prevent water from entering the rock stratum gap above the coal mining face, forcing the injected water to gather in the rock stratum gap above the gob tunnel, effectively preventing excessive pressure on the coal pillar when the water body is frozen and expanded by nitrogen filling, thereby reducing the risk of collapse of the coal pillar edge.

[0007] Furthermore, the upper end of the grouting hole is inclined by 5 to 15 degrees toward the coal mining working face.

[0008] Furthermore, the water injection device includes a water injection pipe and a water pump, the water injection pipe is a hard pipe with one end open, a water outlet connecting the inner cavity of the water injection pipe with the external space of the water injection pipe is arranged on the wall of the water injection pipe near the closed end of the water injection pipe, the water injection pipe is connected to the water pump through a pipe, one end of the pipe is connected to the open sealed end of the water injection pipe, and the other end of the pipe is connected to the water pump, the water pump is connected to an external water source, and a sealing component is arranged on the outer wall of the water injection pipe near the closed end of the water injection pipe to prevent water from flowing back from the water injection hole.

[0009] Furthermore, the blocking member 1 includes an annular air bag 1 sleeved on the outer wall of the water injection pipe, and the inner cavity of the annular air bag 1 is connected to an external air pump 1 through an air pipe 1.

[0010] Furthermore, the nitrogen charging device includes a nitrogen charging pipe for charging liquid nitrogen into the rock formation gaps, a liquid nitrogen tank for storing liquid nitrogen, and a nitrogen charging pump for pumping the nitrogen in the liquid nitrogen tank into the nitrogen charging pipe. The nitrogen charging pipe is a hard pipe with one end open, and a water outlet 2 is provided on the wall of the nitrogen charging pipe near the closed end of the nitrogen charging pipe, which connects the inner cavity of the nitrogen charging pipe with the external space of the nitrogen charging pipe. The nitrogen charging pipe is connected to the nitrogen charging pump through a pipeline 2, one end of the pipeline 2 is connected to the open sealed end of the nitrogen charging pipe, and the other end of the pipeline 2 is connected to the nitrogen charging pump. A valve body 2 is provided on the pipeline 2, the nitrogen charging pump is connected to the liquid nitrogen tank, and a plugging component 2 is provided on the outer wall of the nitrogen charging pipe near the closed end of the nitrogen charging pipe to prevent liquid nitrogen from flowing back from the nitrogen charging hole.

[0011] Furthermore, the second sealing member comprises a second annular airbag sleeved on the outer wall of the nitrogen filling tube, and the inner cavity of the second annular airbag is connected to a second external air pump through a second air pipe.

[0012] Furthermore, the nitrogen filling device also includes a pressurizing unit for accelerating the rapid expansion of the liquid nitrogen in the nitrogen filling pipe so that the liquid nitrogen in the nitrogen filling pipe can be quickly filled into the cracks in the rock formation.

[0013] Furthermore, the pressurizing unit includes an electric heating layer attached to the inner wall of the nitrogen filling tube, and the electric heating layer is electrically connected to a power source of an external device through a power line.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Compared with forming a weakened zone on the roof through dense drilling, the water injection holes and nitrogen filling holes in this scheme also form a weakened zone on the roof, but the drilling density of this scheme is small. Before the water in the rock stratum cracks freezes and expands due to nitrogen filling, the roof will not break, the construction safety is high, and no pre-support is required during drilling operations; 2 In this scheme, the injected water is confined to the rock stratum gap above the roof away from the coal pillar side by pre-sealing, preventing the injected water and liquid nitrogen from entering the rock stratum gap above the coal pillar, preventing excessive pressure on the coal pillar when the water freezes and expands due to nitrogen filling, and reducing the risk of collapse of the coal pillar edge.

[0015] 3. The fracturing pressure relief of this scheme has a slow and stable fracturing speed compared with blasting pressure relief, and will not cause gas explosion.

[0016] 4. Compared with the existing hydraulic fracturing weakening and cutting top pressure relief technology, which requires the equipment to have extremely high pressure output, high equipment requirements, complex process, and poor adaptability to natural conditions in the tunnel, the injection pressure required for injecting water into the rock formation gaps in this solution is relatively smaller than that of conventional hydraulic fracturing weakening and cutting top pressure relief. It does not require complex high-pressure water injection equipment, has low requirements for equipment, simple process, and high site adaptability.

[0017] 5. In this scheme, water and nitrogen can be injected into the rock stratum cracks in steps according to the degree of deformation and fracture of the roof to achieve gradual fracturing of the roof, and the fracturing and pressure relief of the roof are highly controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 A schematic diagram of the vertical structure of a method for removing pressure by cutting the top of a coal mining face end according to the present invention Figure 1 .

[0019] Figure 2 The present invention is a schematic diagram of the planar structure of a method for top cutting and pressure relief at the end of a coal mining working face.

[0020] Figure 3 A schematic diagram of the vertical structure of a method for removing pressure by cutting the top of a coal mining face end according to the present invention Figure 2 .

[0021] Figure 4 Schematic diagram of the water injection pipe structure.

[0022] Figure 5 This is a schematic diagram of the nitrogen filling pipe structure.

[0023] Figure 6 This is a schematic diagram of the structure of the nitrogen filling device.

[0024] Figure 7 The present invention is a flow chart of a method for top cutting and pressure relief at the end of a coal mining working face.

[0025] The meanings of the symbols in the accompanying drawings are: Coal mining face-10; roof-11; goaf-12; goaf-13; rock stratum gap-14; coal pillar-15; Water injection hole-21; nitrogen filling hole-22; grouting hole-23; Water injection pipe-31; water outlet-311; pipeline-32; annular air bag-312; air pipe-33; Nitrogen filling pipe-41; water outlet 2-411; annular air bag 2-412; liquid nitrogen tank-42; nitrogen filling pump-43; pipeline 2-44; valve body 2-441; air pipe 2-45; electric heating layer-46; power cord-47. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] like Figure 7 As shown, a method for removing pressure by cutting the top of a coal mining face end in this scheme mainly includes the following steps: Step A: core sampling, drilling cores upward from multiple points on the roof 11 where holes are to be drilled, and determining the thickness of the roof 11 based on the core structure to determine the drilling depth; Step B: drilling grouting holes 23, drilling a plurality of grouting holes 23 upward from the bottom of the roof 11 near the coal mining working face 10, wherein the plurality of grouting holes 23 are arranged in sequence in a direction parallel to the coal mining working face 10, and the drilling depth of the grouting holes 23 exceeds the thickness of the roof 11; Step C: Drilling water injection holes 21 and nitrogen filling holes 22, drilling a plurality of water injection holes 21 and a plurality of nitrogen filling holes 22 in an alternating arrangement upwardly in a direction parallel to the coal mining face 10 on the roof 11 on the side of the grouting hole 23 away from the coal mining face 10, and the drilling depth exceeds the thickness of the roof 11; Step D: grouting, using grouting equipment to fill slurry into the rock stratum gap 14 above the coal mining working face 10 through the grouting hole 23; Step E: injecting water through the water injection device from the water injection hole 21 into the rock stratum gap 14 between the top plate 11 and the rock stratum above the top plate 11, so that water is enriched in the rock stratum gap 14 between the top plate 11 and the rock stratum above the top plate 11; Step F: Filling with liquid nitrogen: Liquid nitrogen is filled into the rock gap 14 between the top plate 11 and the rock layer above the top plate 11 through the nitrogen filling hole 22 by the nitrogen filling device.

[0029] In step A of the present scheme, core sampling is performed at multiple points in the pre-drilling area, and then the thickness of the roof 11 above the empty tunnel 13 is analyzed and determined based on the structure of the sampled core, thereby determining the specific location of the rock stratum gap 14 between the roof 11 and the rock stratum above the roof 11, and further determining the depth of the upward drilling, so that water and liquid nitrogen can be accurately injected into the rock stratum gap 14. Specifically, conventional core sampling equipment can be used to reasonably select multiple sampling points within the area of ​​the grouting holes 23, water injection holes 21 and nitrogen filling holes 22 to be drilled on the roof 11 to drill cores upwards. Conventional core sampling tools can be used, and after drilling the core, the sampled rock column is observed. The place where obvious stratification and fracture appear on the rock column is the location of the rock stratum gap 14 on the rock column. The distance from the end of the sampled rock column to the obvious stratification on the rock column is the thickness of the roof 11 at the sampling point, and this thickness is also That is, the depth of the rock stratum crack 14 at the sampling point from the lower surface of the roof 11. After obtaining multiple depth data through multi-point sampling measurement, the direction of the rock stratum crack 14 in the drilling area and the distance from the lower surface of the roof 11 at that location can be preliminarily determined. When drilling the grouting holes 23, water injection holes 21 and nitrogen filling holes 22 subsequently, the drilling depth should be appropriately greater than the preliminarily determined depth distance to ensure that grouting, water injection and nitrogen filling can be effectively performed in the rock stratum crack 14 above the grouting holes 23, water injection holes 21 and nitrogen filling holes 22 at that location.

[0030] Combination Figure 1 , Figure 2 As shown, during the drilling of the grouting hole 23 in step B of the present scheme, the upper end of the grouting hole 23 is inclined 5 to 15 degrees, preferably 10 degrees, toward the direction close to the coal mining working face 10, so that the filled slurry is located in the rock stratum gap 14 above the coal pillar 15, preventing the water added later from entering the rock stratum gap 14 above the coal pillar 15 and allowing the rock stratum gap 14 above the empty tunnel 13 to be filled with water as much as possible.

[0031] During the drilling process of step C of the present scheme, a plurality of water injection holes 21 and a plurality of nitrogen filling holes 22 are alternately arranged in sequence along a direction parallel to the coal mining face 10 at a position of the roof 11 close to the coal mining face 10, and the depths of the water injection holes 21 and the nitrogen filling holes 22 both exceed the thickness of the roof 11 upwards, so that water can be injected and liquid nitrogen can be filled into the rock formation gaps 14 through the water injection device and the nitrogen filling device.

[0032] In step D of this scheme, a conventional grouting pump and a grouting pipe are used to inject slurry into the rock formation gap 14. The slurry can be cement slurry or organic grouting material such as polyurethane, propylene hydrochloric acid, etc., preferably cement slurry.

[0033] After the slurry to be filled solidifies, water is injected into the rock stratum gap 14 above the gob tunnel through the water injection hole by the water injection device. Figure 4 As shown, the water injection device used in step E includes a water injection pipe 31 and a water pump (not shown), the water injection pipe 31 is a hard pipe with an open end, and a water outlet 311 is provided on the pipe wall of the water injection pipe 31 near the closed end of the water injection pipe 31, which connects the inner cavity of the water injection pipe 31 with the external space of the water injection pipe 31, the water injection pipe 31 is connected to the water pump through a pipe 32, one end of the pipe 32 is connected to the open sealed end of the water injection pipe 31, and the other end of the pipe 32 is connected to the water pump. In actual setting, a water outlet main pipe 1 is provided on the water outlet of the water pump, and the pipe 132 on each water injection pipe 31 is sealed and connected to the water outlet main pipe 1, and the water can be synchronously supplied to the water pump by controlling the on and off of the water outlet main pipe 1. Water is introduced into each water injection pipe 31, and the water pump is connected to an external water source. A sealing member is provided on the outer wall of the water injection pipe 31 near the closed end of the water injection pipe 31 to prevent water from flowing back from the water injection hole 21 to the outside of the water injection hole 21. The sealing member includes an annular air bag 312 sleeved on the outer wall of the water injection pipe 31. Specifically, the annular air bag 312 is located below the water outlet 311. The annular air bag 312 is sleeved on the outer wall of the water injection pipe 31 and is fixedly connected to the water injection pipe 31. The inner cavity of the annular air bag 312 is connected to an external air pump 1 (not shown) through an air pipe 33. The water pump and the air pump 1 are both conventional ordinary equipment and will not be repeated here.

[0034] After water is injected through the water injection hole 21, liquid nitrogen is injected into the rock stratum gap 14 above the gob tunnel through the nitrogen filling hole 22 by the nitrogen filling device. Figure 5 , Figure 6As shown, the nitrogen charging device used in step F includes a nitrogen charging pipe 41 for charging liquid nitrogen into the rock formation gap 14, a liquid nitrogen tank 42 for storing liquid nitrogen, and a nitrogen charging pump 43 for charging the nitrogen in the liquid nitrogen tank 42 into the nitrogen charging pipe 41, a plugging member 2 and a pressurizing unit. The nitrogen charging pipe 41 is a hard pipe with an open end. A water outlet 2 411 is provided on the wall of the nitrogen charging pipe 41 near the closed end of the nitrogen charging pipe 41, which connects the inner cavity of the nitrogen charging pipe 41 with the external space of the nitrogen charging pipe 41. The pipe 41 is connected to the nitrogen filling pump 43 through the second pipe 44. One end of the second pipe 44 is connected to the open sealed end of the nitrogen filling pipe 41, and the other end of the second pipe 44 is connected to the nitrogen filling pump 43. A valve body 441 is provided on the second pipe 44. The valve body 441 can control the opening and closing of the corresponding second pipe 44 separately. When actually set, a water outlet main pipe 44 is provided on the water outlet of the nitrogen filling pump 43. The second pipe 44 on each nitrogen filling pipe 41 is sealed and connected to the second water outlet main pipe. The opening and closing of the second water outlet main pipe can be controlled by controlling the opening and closing of the second water outlet main pipe. To synchronously introduce liquid nitrogen into each nitrogen filling pipe 41, the nitrogen filling pump 43 is connected to the liquid nitrogen tank 42 through a pipeline, and the second plugging member is arranged on the outer wall of the nitrogen filling pipe 41 near the closed end of the nitrogen filling pipe 41 to prevent liquid nitrogen from flowing back from the nitrogen filling hole 22 to the outside of the nitrogen filling hole 22. Specifically, the second plugging member includes an annular airbag 412 sleeved on the outer wall of the nitrogen filling pipe 41, the annular airbag 412 is located below the water outlet 411, and the annular airbag 412 is fixed to the outer wall of the nitrogen filling pipe 41. The inner cavity of the annular airbag 412 is connected to the external air pump 2 (not shown) through the air pipe 45. The pressurizing unit is used to accelerate the rapid expansion of the liquid nitrogen in the nitrogen filling pipe 41 so that the liquid nitrogen in the nitrogen filling pipe 41 can be quickly filled into the rock formation gap 14. The pressurizing unit includes an electric heating layer 46 attached to the inner wall of the nitrogen filling pipe 41. The electric heating layer 46 can be set as an electric heating sheet attached to the inner wall of the nitrogen pipe 41. The electric heating layer 46 is electrically connected to the external power supply through a power line 47. The air pump 2 and the nitrogen filling pump 43 are both conventional common equipment and will not be repeated here.

[0035] In the above scheme, after the drilling position and depth are determined by core sampling, the grouting hole 23 is drilled upward and the water injection hole 21 and the nitrogen filling hole 22 are drilled in sequence. After grouting is injected into the rock stratum gap 14 above the coal pillar 15 through the grouting hole 23, the water injection pipe 31 and the nitrogen filling pipe 41 are respectively inserted into the corresponding water injection hole 21 and the nitrogen filling hole 22, so that the water outlet 1 311 on the water injection pipe 31 and the water outlet 2 411 on the nitrogen filling pipe 41 are both located at the same position. At the rock formation gap 14, air is inflated into the inner cavity of the annular airbag 312 by air pump 1 so that the annular airbag 312 expands and presses against the inner wall of the water injection hole 21, thereby preventing the water above the annular airbag 312 from flowing downward out of the water injection hole 21; air is inflated into the inner cavity of the annular airbag 412 by air pump 2 so that the annular airbag 412 expands and presses against the inner wall of the nitrogen filling hole 22, thereby preventing the liquid nitrogen above the annular airbag 412 from flowing downward out of the nitrogen filling hole 22.

[0036] First, water is repeatedly injected into the rock formation cracks 14 through the water outlet main pipe 1 through each water injection pipe 31. After the water outlet main pipe 1 is closed, the nitrogen filling pump 43 is operated to inject liquid nitrogen into each nitrogen filling pipe 41 respectively. After the liquid nitrogen fills the inner cavity of the nitrogen filling pipe 41, the water outlet main pipe 2 is closed, and the electric heating layer 46 is connected to the power supply of the external device. The electric heating layer 46 heats the liquid nitrogen in the nitrogen filling pipe 41. The liquid nitrogen near the electric heating layer 46 vaporizes rapidly and expands rapidly to generate high pressure, squeezing the remaining liquid nitrogen into the rock formation cracks 14, vaporizing in the rock formation cracks 14 and absorbing heat. Figure 3 As shown, the water in the rock stratum cracks 14 absorbs heat from the vaporized liquid nitrogen and then expands to squeeze the top plate 11 downward, causing the top plate 11 to break at the weakened zone formed by the water injection holes 21 and the nitrogen filling holes 22. In this solution, water can be injected into the rock stratum cracks 14 and high-pressure nitrogen can be filled multiple times until the top plate 11 is squeezed and broken.

[0037] The above are only embodiments of the present invention, and the common knowledge such as the known specific structures and characteristics in the scheme are not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for relieving pressure by cutting off the top of a coal mining face, characterized in that: The following steps are involved: Step A: core sampling, drill cores upward from multiple points on the roof where holes are to be drilled, and determine the thickness of the roof layer based on the core structure to determine the drilling depth; Step B: drilling grouting holes, drilling a plurality of grouting holes from the bottom of the roof upward near the coal mining working face, wherein the plurality of grouting holes are arranged in sequence in a direction parallel to the coal mining working face, and the drilling depth of the grouting holes exceeds the thickness of the roof; Step C: drilling water injection holes and nitrogen filling holes, and drilling a plurality of water injection holes and a plurality of nitrogen filling holes in an alternating arrangement upward in a direction parallel to the coal mining working face on the roof plate on the side of the grouting hole away from the coal mining working face, and the drilling depth exceeds the thickness of the roof plate; Step D: Grouting, using grouting equipment to fill slurry into the rock stratum gap above the coal mining working face through the grouting holes; Step E: injecting water, injecting water into the gap between the top plate and the rock layer above the top plate through the water injection hole through the water injection device so that the water is enriched in the gap between the top plate and the rock layer above the top plate; Step F: Filling with liquid nitrogen: Liquid nitrogen is filled into the rock stratum gap between the top plate and the rock stratum above the top plate through the nitrogen filling hole through the nitrogen filling device.

2. The method for relieving pressure by cutting off the top of the coal mining face according to claim 1, characterized in that: The upper end of the grouting hole is inclined 5 to 15 degrees toward the coal mining working face.

3. The method for relieving pressure by cutting off the top of the coal mining face according to claim 1, characterized in that: The water injection device includes a water injection pipe and a water pump. The water injection pipe is a hard pipe with one end open. A water outlet that connects the inner cavity of the water injection pipe with the external space of the water injection pipe is arranged on the wall of the water injection pipe near the closed end of the water injection pipe. The water injection pipe is connected to the water pump through a pipe. One end of the pipe is connected to the open sealed end of the water injection pipe, and the other end of the pipe is connected to the water pump. The water pump is connected to an external water source. A sealing component that prevents water from flowing back from the water injection hole is arranged on the outer wall of the water injection pipe near the closed end of the water injection pipe.

4. The method for relieving pressure by cutting off the top of the coal mining face according to claim 3, characterized in that: The blocking member 1 includes an annular air bag 1 sleeved on the outer wall of the water injection pipe, and the inner cavity of the annular air bag 1 is connected with an external air pump 1 through an air pipe 1.

5. The method for relieving pressure by cutting off the top of the coal mining working face according to claim 1, characterized in that: The nitrogen charging device comprises a nitrogen charging pipe for charging liquid nitrogen into the rock formation gap, a liquid nitrogen tank for storing liquid nitrogen and a nitrogen charging pump for pumping the nitrogen in the liquid nitrogen tank into the nitrogen charging pipe. The nitrogen charging pipe is a hard pipe with one end open. A water outlet 2 for connecting the inner cavity of the nitrogen charging pipe with the external space of the nitrogen charging pipe is arranged on the wall of the nitrogen charging pipe near the closed end of the nitrogen charging pipe. The nitrogen charging pipe is connected with the nitrogen charging pump through a pipeline 2. One end of the pipeline 2 is connected with the open sealed end of the nitrogen charging pipe, and the other end of the pipeline 2 is connected with the nitrogen charging pump. A valve body 2 is arranged on the pipeline 2. The nitrogen charging pump is connected with the liquid nitrogen tank. A plugging member 2 for preventing liquid nitrogen from flowing back from the nitrogen charging hole is arranged on the outer wall of the nitrogen charging pipe near the closed end of the nitrogen charging pipe.

6. The method for relieving pressure by cutting off the top of the coal mining face according to claim 5, characterized in that: The second blocking member comprises a second annular airbag sleeved on the outer wall of the nitrogen filling tube, and the inner cavity of the second annular airbag is connected with a second external air pump through a second air pipe.

7. The method for relieving pressure by cutting off the top of the coal mining face according to claim 6, characterized in that: The nitrogen filling device also includes a pressurizing unit for accelerating the rapid expansion of the liquid nitrogen in the nitrogen filling pipe so that the liquid nitrogen in the nitrogen filling pipe can be quickly filled into the cracks in the rock formation.

8. The method for relieving pressure by cutting off the top of the coal mining face according to claim 7, characterized in that: The pressurizing unit comprises an electric heating layer attached to the inner wall of the nitrogen filling tube, and the electric heating layer is electrically connected to a power source of an external device through a power line.

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