A combined pre-splitting and extraction method for double-hard and extra-thick coal seam roof

Abstract

The present invention discloses a combined pre-splitting and extraction method for the roof of a double-hard and extra-thick coal seam, which belongs to the field of roof pre-splitting blasting and gas extraction in fully-mechanized caving mining of thick coal seams, and includes two roof pre-splitting and extraction stages and four types of blasting pre-splitting and extraction drilling holes. The first stage is used to reduce the hanging roof area during initial mining and initial caving, reduce the loss of top coal during initial caving, and perform gas pre-drainage of the top coal and roof; the second stage is the normal mining and caving roof pre-splitting and extraction stage, which includes the construction arrangement of blasting pre-splitting and extraction drilling holes for the coal seam roof in the leading area of the working face and blasting pre-splitting and extraction drilling holes for the roof of two lanes in the leading area of the working face, blasting pre-splitting and gas extraction, and is used to ensure timely and sufficient roof collapse and coal caving effect during normal mining and caving, and perform gas pre-drainage of the top coal and roof. It can achieve the purpose of roof crushing and cutting and gas pre-drainage, ensure that the roof collapses as mining progresses, optimize the top coal caving effect, and ensure safe production at the working face.

Description

Technical Field

[0001] The invention belongs to the field of roof pre-splitting blasting and gas extraction in fully-mechanized caving mining of thick coal seams, and in particular relates to a combined pre-splitting and gas extraction method for the roof of a double-hard and extra-thick coal seam. Background Art

[0002] Coal, my country's primary energy source, boasts abundant reserves, growing demand and consumption year after year, and significant annual mining output. Thick coal seams account for approximately 44% of my country's total coal reserves, and annual underground production from thick seams accounts for over 45% of total coal production. With the advancement of mining technology and processes, and the rapid improvement of mechanization and automation, fully mechanized top-coal caving (LCC) has become one of the most important mining methods for thick and extra-thick coal seams in my country, thanks to its wide range of applications, high production efficiency, and high degree of mechanization. However, fully mechanized top-coal caving in double-hard, extra-thick coal seams often presents safety hazards such as hanging roofs and roof gas outbursts, and the caving results are unstable. Therefore, developing an effective combined roof pre-splitting and extraction method for fully mechanized top-coal caving in double-hard, extra-thick coal seams has become a pressing issue for some mines. Summary of the Invention

[0003] The present invention provides a combined pre-splitting and drainage method for the roof of a double-hard, extra-thick coal seam, aiming to ensure that the roof collapses as it is mined, optimize the top coal venting effect, achieve roof gas pre-drainage, and ensure safe production at the working face. To achieve the above objectives, the present invention provides a combined pre-splitting and drainage method for the roof of a double-hard, extra-thick coal seam, comprising the following steps:

[0004] A combined pre-splitting and extraction method for the roof of a double-hard and extra-thick coal seam is used for double-hard and extra-thick coal seams with potential safety hazards such as suspended roofs and roof gas outbursts, and comprises two roof pre-splitting and extraction stages and four blasting pre-splitting drilling holes (10); the two roof pre-splitting and extraction stages include an initial mining and initial caving roof pre-splitting and extraction stage and a normal mining and caving roof pre-splitting and extraction stage, and the roof of the working face is blasted and pre-splitting in stages; the four blasting pre-splitting drilling holes (10) include a roof blasting and extraction stage in an opening hole of the working face, a roof blasting and extraction stage in a opening hole of the working face, and a roof blasting and extraction stage in a opening hole of the working face. Pre-splitting and extraction drilling hole a, pre-splitting and extraction drilling hole b at the end of the working face roof, pre-splitting and extraction drilling hole c at the coal seam roof in the advanced area of the working face, and pre-splitting and extraction drilling hole d at the roof of the two lanes in the advanced area of the working face; the four types of pre-splitting and extraction drilling holes (10) complete the combined pre-splitting and extraction of gas in the two roof pre-splitting and extraction stages, and achieve the purpose of roof crushing and gas pre-extraction, ensure that the roof collapses as it is mined, optimize the top coal venting effect, and ensure safe production of the working face;

[0005] The specific steps are as follows:

[0006] During the initial mining and caving roof pre-splitting and drainage phase, prior to mining at the working face, multiple blasting pre-splitting and drainage drill holes a are arranged at intervals along the working face cut in the inner roof. Multiple blasting pre-splitting and drainage drill holes b are arranged at the working face end roof at the end of the drift below the working face and at the end of the drift above the working face. Subsequently, the blasting pre-splitting and drainage drill holes a in the working face cut and the blasting pre-splitting and drainage drill holes b at the working face end roof are synchronously pre-splitting to reduce the hanging roof area during the initial mining and caving period, minimize top coal caving losses, and perform gas pre-drainage from the top coal and roof.

[0007] During the normal roof pre-splitting and drainage stage of mining and caving, multiple coal seam roof blasting pre-splitting and drainage drill holes c in the working face advance area and multiple coal seam roof blasting pre-splitting and drainage drill holes d in the two-lane roof blasting pre-splitting and drainage drill holes d in the working face advance area are constructed in the working face lower drift and working face drift on both sides of the mining and caving working face. The two-lane roof blasting pre-splitting and drainage drill holes d in the working face advance area and the coal seam roof blasting pre-splitting and drainage drill holes c in the working face advance area are arranged in groups in the same drilling site. Afterwards, the coal seam roof blasting pre-splitting and drainage drill holes c in the working face advance area and the two-lane roof blasting pre-splitting and drainage drill holes d in the working face advance area in the same drilling site are used for synchronous blasting pre-splitting to ensure timely and sufficient roof collapse and coal caving effect during normal mining and caving, and simultaneous gas pre-drainage of top coal and roof is carried out.

[0008] Furthermore, the sealing lengths of the four types of blasting pre-splitting boreholes (10) are all not less than I / 3, where I is the length of the blasting pre-splitting borehole (10), clay material is selected as the sealing material, and the sealing method is a hole sealer or manual sealing; the blasting pre-splitting borehole (10) adopts a detonator connection form of parallel connection within the hole and series connection between holes, which has higher blasting safety, and a detonator is arranged every 2 to 3 meters in the hole and detonated simultaneously.

[0009] Furthermore, the drilling site gas extraction device used for gas extraction is a gas collecting and slag discharge box, which includes an inlet, an outlet and a drain port. The inlet of the gas collecting and slag discharge box is provided with a branch pipe outlet ball valve, and the outlet is provided with a main pipe inlet ball valve. The blasting pre-splitting borehole (10) is used as an extraction borehole for gas extraction. The inlet of the gas collecting and slag discharge box is connected to the extraction borehole through a borehole extraction branch pipe. The borehole extraction branch pipe is arranged along the cut eye or the slot roof, wherein the borehole extraction branch pipe is connected to the extraction borehole. The orifice seal is connected with a straight-through and an air inlet guide pipe. The air inlet guide pipe is connected to the drilling pumping branch pipe through a pipe clamp. A branch pipe inlet ball valve is provided between the straight-through and the air inlet guide pipe. An air outlet guide pipe is connected between the drilling pumping branch pipe and the gas gathering and slag box through a pipe clamp. The outlet of the gas gathering and slag box is connected to the chute pumping pipeline through the drilling site pumping main pipe. A main pipe pressure gauge is provided on the drilling site pumping main pipe, a gas gathering box pressure gauge is provided on the gas gathering and slag box, and a water drainer is provided on the water outlet of the gas gathering and slag box.

[0010] Furthermore, the gas collecting and slag discharge box can be connected to multiple drilling extraction branch pipes and a drilling field extraction main pipe at the same time to remove slag and collect gas from multiple extraction boreholes in the same drilling field; the drilling extraction branch pipe is made of steel wire hose, and both ends are connected to the guide pipe through pipe clamps.

[0011] Furthermore, multiple roof blasting pre-splitting and drainage drill holes a in the working face cut are arranged in the working face cut, and the multiple roof blasting pre-splitting and drainage drill holes a in the working face cut are marked as a1~an in sequence. A row of roof blasting pre-splitting and drainage drill holes a in the working face cut are arranged 1 m away from the coal wall in front of and behind the rack respectively. Each row of roof blasting pre-splitting and drainage drill holes a in the working face cut consists of alternating 10 m long drill holes and 5 m short drill holes. The two rows of roof blasting pre-splitting and drainage drill holes a in the working face cut are arranged opposite to each other in front of and behind the rack, n=(L-1) / 3, L is the length of the working face cut, the drill hole spacing is 3~5 m, the angle with the coal wall is 90°, and the angle with the roof is 60°~80°.

[0012] Furthermore, the working face end roof blasting pre-splitting extraction drill holes b are divided into two groups of five, which are respectively arranged perpendicular to the working face direction at the end of the chute below the working face and the end of the chute above the working face. The working face end roof blasting pre-splitting extraction drill holes b pass through the coal seam roof 20~30m, the borehole spacing within the group is 0.3~0.5m, and the angle with the coal wall is 90°. The working face end roof blasting pre-splitting extraction drill holes in each group away from the working face coal body are defined as initial boreholes b. The initial borehole b has an angle of 90° with the roof, and the subsequent angles decrease by 10~15° successively, and are arranged in a fan shape.

[0013] Furthermore, the coal seam roof blasting pre-splitting and extraction drill holes c in the working face advance area are divided into two groups of five, which are respectively arranged on the roof of the heading below the working face and the heading above the working face. They are arranged every 10 to 20 meters in the heading perpendicular to the working face. The drill holes pass through the coal seam roof for 20 to 30 meters. The spacing between the drill holes in the group is 0.3 to 0.5 meters, and the angle with the coal wall is 90 degrees. The coal seam roof blasting pre-splitting and extraction drill holes in the working face advance area close to the working face coal body in each group are defined as initial drill holes c. The angle between the initial drill hole c and the roof is 30 degrees, and the subsequent angles increase by 5 to 8 degrees successively, and are arranged in a fan shape.

[0014] Furthermore, the two-lane roof blasting pre-splitting and extraction drill holes d in the working face advance area are divided into two groups of four, which are respectively arranged on the roof of the lower drift and the drift above the working face. The drift is arranged every 10 to 20 meters perpendicular to the working face. The drill holes are 5 to 10 meters long, the drill hole spacing within the group is 0.3 to 0.5 meters, and the angle with the coal wall is 90°. The two-lane roof blasting pre-splitting and extraction drill holes in the working face advance area away from the working face coal body in each group are defined as initial drill holes d. The initial drill hole d has an angle of 90° with the roof, and the subsequent angles increase by 5 to 8° successively, and are arranged in a fan shape.

[0015] Furthermore, the blasting pre-splitting drilling hole (10) first uses a probe tube, which is a connectable plastic tube, to conduct a blasting and complete the drilling cleaning; after the blasting is completed, the hole is immediately charged and sealed to ensure that the hole is sealed tightly and solid, and then the blasting is carried out; 30 minutes after the blasting, the roof blasting pre-splitting extraction drilling hole a in the working face opening eye and the roof blasting pre-splitting extraction drilling hole b at the end of the working face are pre-splitting before the working face is mined; the coal seam roof blasting pre-splitting extraction drilling hole c in the working face advance area and the roof blasting pre-splitting extraction drilling hole d in the two lanes in the working face advance area are blasted 50m away from the working face.

[0016] Beneficial effects

[0017] The present invention includes two roof pre-splitting and extraction stages and four blasting pre-splitting and extraction drilling holes. The two roof pre-splitting and extraction stages run through the entire mining and venting operation of the working face. The four blasting pre-splitting and extraction drilling holes are arranged in different forms at different positions, and blasting pre-splitting and gas extraction are completed at different stages to achieve the purpose of roof crushing and cutting and gas pre-extraction, ensure that the roof collapses as it is mined, optimize the top coal venting effect, and ensure safe production of the working face. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the layout diagram of the blasting pre-splitting extraction drilling holes in the initial mining and initial blasting stage of the present invention.

[0019] Figure 2 This is the layout diagram of the blasting pre-splitting extraction drilling in the normal mining and release stage of the present invention.

[0020] Figure 3 This is a cross-sectional view of the Ⅰ-Ⅰ arrangement of blasting pre-splitting extraction drilling holes in the normal mining and release stage of the present invention.

[0021] Figure 4 This is a structural diagram of the blasting pre-splitting drilling charging and sealing method of the present invention.

[0022] Figure 5 This is a structural diagram of the drilling site gas extraction device of the present invention.

[0023] Figure: a-blasting pre-splitting and drainage drilling holes for roof in the working face opening; b-blasting pre-splitting and drainage drilling holes for roof at the end of the working face; c-blasting pre-splitting and drainage drilling holes for roof in the coal seam in the area ahead of the working face; d-blasting pre-splitting and drainage drilling holes for roof in two lanes in the area ahead of the working face; 1-working face opening; 2-end of the drift below the working face; 3-end of the drift above the working face; 4-drift below the working face; 5-drift above the working face; 6-mining and caving working face; 7-top coal; 8-direct roof; 9-basic roof; 10-blasting pre-splitting drilling holes ;11-explosives;12-detonator;13-water cannon mud;14-clay cannon mud;15-slot top plate;16-extraction drilling hole;17-straight-through;18-branch pipe inlet ball valve;19-air inlet guide pipe;20-pipe clamp;21-drilling extraction branch pipe;22-air outlet guide pipe;23-branch pipe outlet ball valve;24-gas collecting and slag discharge box;25-gas collecting box pressure gauge;26-water drain;27-main pipe inlet ball valve;28-main pipe pressure gauge;29-drilling field extraction main pipe;30-slot extraction pipeline. DETAILED DESCRIPTION

[0024] The following describes in detail a combined pre-splitting and extraction method for a double-hard and extra-thick coal seam roof according to the present invention with reference to the accompanying drawings and examples.

[0025] like Figure 1 and Figure 2 As shown, taking the working face mining of a double-hard, extra-thick coal seam at a certain mine as an example, the working face is 110m deep, 155m long, with an advanceable length of 1,284m. The average coal thickness is 8.6m. Fully mechanized caving is used, with a mechanized mining height of 4m and a top coal caving height of 4.6m. The mining-caving ratio is 1:1.15, and the upper and lower trenches are 5.0m wide and 2.9m high. The immediate roof 8 of the coal seam is primarily composed of fine siltstone, and the immediate roof 9, in some sections, transitions to contact with the old roof coarse sandstone and fine sandstone. The old roof is composed of fine sandstone, medium sandstone, and gravelly coarse sandstone. There is no false roof.

[0026] The specific implementation is as follows:

[0027] S1: Blasting pre-splitting extraction drilling construction layout, such as Figure 3 As shown,

[0028] The aforementioned roof blasting pre-splitting and extraction drill holes a1-an in the cut hole are arranged in the cut hole of the working face, and are arranged in a row 1 m away from the coal wall in front of and behind the rack respectively. 10 m long drill holes and 5 m short drill holes are arranged alternately in each row. Two drill holes in each row are arranged as a group, and a total of 51 groups of 2 are arranged in each group. The drill holes are spaced 3 m apart, with an angle of 90° to the coal wall and an angle of 75° to the roof.

[0029] The blasting pre-splitting extraction drill holes b1 to b10 at the end of the working face roof are arranged on the roof of the two ends of the working face, with a group of 5 holes arranged perpendicular to the working face at each end. The drill holes penetrate 28m of the coal seam roof, and the spacing between the drill holes in the group is 0.3m. The angle between the holes and the coal wall is 90°. The initial drill holes b1 and b6 are at 90° with the roof, and the angles of the subsequent holes decrease by 10°, forming a fan-shaped arrangement.

[0030] The coal seam roof blasting pre-splitting and extraction drill holes c1 to c10 in the advance area of the working face are arranged on the roof of the two drifts of the working face. A group of 5 holes is arranged every 10 meters perpendicular to the working face in the drift. The drill holes penetrate 20 meters through the coal seam roof. The spacing between drill holes in a group is 0.3 meters. The angle with the coal wall is 90 degrees. The initial drill holes c1 and c6 are at a 30 degree angle with the roof. The angle of subsequent drill holes increases by 5 degrees in sequence, forming a fan-shaped arrangement.

[0031] The blasting pre-splitting and extraction drill holes d1 to d8 for roof blasting in the two lanes in the advance area of the working face are arranged on the roof of the two drifts of the working face. A group of 4 holes is arranged every 10m perpendicular to the working face in the drift. The drill holes are 10m long, the spacing between the drill holes in the group is 0.3m, and the angle with the coal wall is 90°. The initial drill holes d1 and d5 are at 90° with the roof, and the angles of the subsequent drill holes increase by 5° in sequence, forming a fan-shaped arrangement.

[0032] S2: Blasting pre-splitting extraction drilling pre-splitting blasting

[0033] The blasting pre-splitting drilling hole 10 first uses a probe tube, which is a connectable plastic tube, to conduct a probe hole and complete the drilling cleaning; after the drilling is completed, the explosive is immediately charged and sealed to ensure that the drill hole is sealed firmly and solidly, and then the blasting is carried out; 30 minutes after the blasting, the tile inspector and safety supervisor will conduct a safety inspection to eliminate the danger;

[0034] The sealing length of the blasting pre-splitting borehole 10 is not less than 1 / 3, where 1 is the length of the blasting pre-splitting borehole 10. The sealing material is yellow mud, and the sealing method is a hole sealer or manual sealing. The blasting pre-splitting borehole 10 adopts a connection form of detonators 12 in parallel in the hole and in series between holes, which has higher blasting safety, and the detonators in the hole are arranged every 2 to 3 meters and detonated at the same time. The blasting pre-splitting borehole 10, explosives 11 detonators 12, water cannon mud 13 and clay cannon mud 14 are sequentially connected, such as Figure 4 As shown;

[0035] The aforementioned roof blasting pre-splitting extraction drilling holes a1 to an in the opening eye and the roof blasting pre-splitting extraction drilling holes b1 to b10 at the end of the working face are pre-splitting blasted before the working face is mined;

[0036] The coal seam roof blasting pre-splitting and extraction drilling holes c1 to c10 in the working face advance area and the two lane roof blasting pre-splitting and extraction drilling holes d1 to d8 in the working face advance area are blasted 50m away from the working face;

[0037] S3: blasting pre-splitting gas extraction through boreholes

[0038] The end of the extraction borehole 16 is connected to the drilling site gas extraction device, and the gas enters the borehole extraction branch pipe 21 through the straight-through 17, the branch pipe inlet ball valve 18 and the air inlet guide pipe 19. The end of the borehole extraction branch pipe 21 is connected to the air outlet guide pipe 22 and the branch pipe outlet ball valve 23, and the gas is introduced into the gas collecting and slag discharge box 24, and the gas is deslagging and collected; the gas after deslagging flows out of the gas collecting and slag discharge box 24 through the main pipe air inlet valve 27 and the main pipe air pressure gauge 28, and enters the chute extraction pipeline 30.

[0039] The drilling extraction branch pipe 21 is made of a steel hose, and its two ends are connected to the air inlet guide pipe 19 and the air outlet guide pipe 22 through a pipe clamp 20; the gas collecting and slag discharge box 24 is simultaneously connected to multiple drilling extraction branch pipes 21 and a drilling field extraction main pipe 29 to remove slag and collect gas from multiple extraction boreholes 16 in the same drilling field.

[0040] like Figure 5 As shown, the drilling site gas extraction device for gas extraction operation is a gas collecting and slag box 24, which includes an inlet, an outlet and a drain port. The inlet of the gas collecting and slag box 24 is provided with a branch pipe outlet ball valve 23, and the outlet is provided with a main pipe inlet ball valve 27. The blasting pre-splitting borehole 10 is used as an extraction borehole 16 for gas extraction. The inlet of the gas collecting and slag box 24 is connected to the extraction borehole 16 through a borehole extraction branch pipe 21. The borehole extraction branch pipe 21 is arranged along the cut eye or the groove top plate 15, wherein the borehole extraction branch pipe 21 is sealed with the orifice of the extraction borehole 16 by a straight The through-hole 17 and the air inlet guide pipe 19 are connected to the drilling extraction branch pipe 21 through a pipe clamp 20. A branch pipe inlet ball valve 18 is provided between the through-hole 17 and the air inlet guide pipe 19. An air outlet guide pipe 22 is connected between the drilling extraction branch pipe 21 and the gas collecting and slag discharge box 24 through a pipe clamp 20. The outlet of the gas collecting and slag discharge box 24 is connected to the chute extraction pipeline 30 through the drilling site extraction main pipe 29. A main pipe pressure gauge 28 is provided on the drilling site extraction main pipe 29, a gas collecting box pressure gauge 25 is provided on the gas collecting box 24, and a water discharge device 26 is provided on the water discharge port of the gas collecting and slag discharge box 24. The gas collecting and slag discharge box 24 can be connected to multiple drilling extraction branch pipes 21 and a drilling field extraction main pipe 29 at the same time to remove slag and collect gas from multiple extraction boreholes 16 in the same drilling field; the drilling extraction branch pipe 21 is made of steel wire hose, and both ends are connected to the diversion pipe through pipe clamps 20.

Claims

1. A combined pre-splitting and drainage method for double-hard and extra-thick coal seam roof, characterized by: The invention is used for double-hard and extra-thick coal seams with potential safety hazards such as hanging roof and roof gas outburst, and includes two roof pre-splitting and extraction stages and four blasting pre-splitting drilling holes (10); the two roof pre-splitting and extraction stages include the initial mining and initial caving roof pre-splitting and extraction stage and the normal mining and caving roof pre-splitting and extraction stage, and the working face roof is blasted and pre-splitting in stages; the four blasting pre-splitting drilling holes (10) include a roof blasting pre-splitting and extraction drilling hole a in the working face opening eye, a roof blasting pre-splitting and extraction drilling hole b at the end of the working face, a coal seam roof blasting pre-splitting and extraction drilling hole c in the working face advance area, and a roof blasting pre-splitting and extraction drilling hole d in the two lanes in the working face advance area; the four blasting pre-splitting drilling holes (10) respectively complete the combined blasting pre-splitting and gas extraction in the two roof pre-splitting and extraction stages, and achieve the purpose of roof crushing and gas pre-extraction, ensure that the roof collapses as it is mined, optimize the top coal caving effect, and ensure safe production of the working face; The specific steps are as follows: In the initial mining and initial caving roof pre-splitting and extraction stage, before the working face is mined, multiple working face opening eye inner roof blasting pre-splitting and extraction drilling holes a are arranged at intervals on the inner roof along the working face opening eye (1), and multiple working face end roof blasting pre-splitting and extraction drilling holes b are arranged on the top of the working face lower chute end (2) and the working face upper chute end (3), and then the working face opening eye inner roof blasting pre-splitting and extraction drilling holes a and the working face end roof blasting pre-splitting and extraction drilling holes b are synchronously blasted and pre-splitting to reduce the hanging roof area during the initial mining and initial caving period, reduce the loss of top coal in the initial caving, and pre-drain the top coal and roof gas through the working face opening eye inner roof blasting pre-splitting and extraction drilling holes a and the working face end roof blasting pre-splitting and extraction drilling holes b; During the normal mining and caving roof pre-splitting and extraction stage, multiple coal seam roof blasting pre-splitting and extraction drilling holes c in the working face advance area and multiple coal seam roof blasting pre-splitting and extraction drilling holes d in the two lanes in the working face advance area are constructed in the working face lower drift (4) and the working face drift (5) on both sides of the mining and caving working face (6). The coal seam roof blasting pre-splitting and extraction drilling holes d in the two lanes in the working face advance area and the coal seam roof blasting pre-splitting and extraction drilling holes c in the working face advance area are arranged in the same drilling site as a group. Then, synchronous blasting pre-splitting is performed using the coal seam roof blasting pre-splitting and extraction drilling holes c in the working face advance area and the coal seam roof blasting pre-splitting and extraction drilling holes d in the two lanes in the working face advance area in the same drilling site to ensure timely and sufficient roof collapse and coal caving effect during normal mining and caving, and top coal and roof gas are pre-extracted through the coal seam roof blasting pre-splitting and extraction drilling holes c in the working face advance area and the two lanes in the working face advance area. Multiple roof blasting pre-splitting and extraction drilling holes a in the working face cut-eye are arranged in the working face cut-eye (1). The multiple roof blasting pre-splitting and extraction drilling holes a in the working face cut-eye are marked as a1~an in sequence. A row of roof blasting pre-splitting and extraction drilling holes a in the working face cut-eye is arranged 1m away from the coal wall in front of the frame and behind the frame respectively. Each row of roof blasting pre-splitting and extraction drilling holes a in the working face cut-eye consists of 10m long drilling holes and 5m short drilling holes arranged alternately. The two rows of roof blasting pre-splitting and extraction drilling holes a in the working face cut-eye in front of the frame and behind the frame are arranged opposite to each other. The spacing between the drilling holes is 3~5m, and the angle between the drilling holes and the coal wall is 90°, and the angle between the drilling holes and the roof is 60°~80°. The working face end roof blasting pre-splitting extraction drilling holes b are divided into two groups of five, and are respectively arranged perpendicular to the working face at the working face lower chute end (2) and the working face upper chute end (3). The working face end roof blasting pre-splitting extraction drilling holes b pass through the coal seam roof by 20 to 30 m, and the borehole spacing within the group is 0.3 to 0.5 m. The angle between the drilling holes and the coal wall is 90 degrees. The working face end roof blasting pre-splitting extraction drilling holes in each group that are far away from the working face coal body are defined as initial drilling holes b. The initial drilling hole b1 has an angle of 90 degrees with the roof, and the angles of the subsequent drilling holes decrease by 10 to 15 degrees in sequence, forming a fan-shaped arrangement. The coal seam roof blasting pre-splitting extraction drilling holes c in the working face advance area are divided into two groups of five, which are respectively arranged on the roof of the working face lower chute (4) and the working face upper chute (5). The holes are arranged every 10 to 20 m in the chute perpendicular to the working face. The holes penetrate the coal seam roof 20 to 30 m. The spacing between the holes in the group is 0.3 to 0.5 m. The angle with the coal wall is 90 degrees. The coal seam roof blasting pre-splitting extraction drilling holes in the working face advance area close to the working face coal body in each group are defined as initial holes c. The angle between the initial hole c1 and the roof is 30 degrees. The angles of the subsequent holes increase by 5 to 8 degrees in sequence, and they are arranged in a fan shape. The blasting pre-splitting extraction drilling holes d for the roof of the two lanes in the working face advance area are divided into two groups of four, which are respectively arranged on the roof of the working face lower drift (4) and the working face drift (5). The drilling holes are arranged every 10 to 20 meters perpendicular to the working face direction in the drift. The length of the drilling holes is 5 to 10 meters, the spacing between the drilling holes in the group is 0.3 to 0.5 meters, and the angle with the coal wall is 90 degrees. The blasting pre-splitting extraction drilling holes for the roof of the two lanes in the working face advance area far away from the working face coal body in each group are defined as the initial drilling holes d. The angle between the initial drilling hole d1 and the roof is 90 degrees, and the angles of the subsequent drilling holes increase by 5 to 8 degrees in sequence, forming a fan-shaped arrangement.

2. The combined pre-splitting and drainage method for double-hard and extra-thick coal seam roof according to claim 1, characterized in that: The sealing lengths of the four types of blasting pre-splitting boreholes (10) are all not less than I / 3, where I is the length of the blasting pre-splitting borehole (10). Clay material is selected as the sealing material, and the sealing method is a hole sealer or manual sealing. The blasting pre-splitting boreholes (10) adopt a detonator connection form of parallel connection within the hole and series connection between holes, which has higher blasting safety, and a detonator is arranged every 2 to 3 meters in the hole and detonated simultaneously.

3. The combined pre-splitting and drainage method for double-hard and extra-thick coal seam roof according to claim 1, characterized in that: The drilling site gas extraction device for gas extraction is a gas collecting and slag discharge box (24), which includes an inlet, an outlet and a drain port. The inlet of the gas collecting and slag discharge box (24) is provided with a branch pipe outlet ball valve (23), and the outlet is provided with a main pipe inlet ball valve (27). The blasting pre-cracking borehole (10) is used as an extraction borehole (16) for gas extraction. The inlet of the gas collecting and slag discharge box (24) is connected to the extraction borehole (16) through a borehole extraction branch pipe (21). The borehole extraction branch pipe (21) is arranged along the cut eye or the slot top plate (15), wherein the borehole extraction branch pipe (21) is sealed with the orifice of the extraction borehole (16) by a straight-through (17) and an air inlet guide. The flow pipe (19) is connected to the drilling extraction branch pipe (21) through a pipe clamp (20), a branch pipe inlet ball valve (18) is provided between the straight-through (17) and the air extraction branch pipe (19), an air outlet pipe (22) is connected to the gas collecting and slag box (24) through a pipe clamp (20), and the outlet of the gas collecting and slag box (24) is connected to the flue extraction pipeline (30) through the drilling site extraction main pipe (29), wherein the drilling site extraction main pipe (29) is provided with a main pipe pressure gauge (28), the gas collecting and slag box (24) is provided with a gas collecting box pressure gauge (25), and the water outlet of the gas collecting and slag box (24) is provided with a water discharger (26).

4. The combined pre-splitting and drainage method for double-hard and extra-thick coal seam roof according to claim 3 is characterized by: The gas collecting and slag discharge box (24) can be connected to multiple drilling hole extraction branch pipes (21) and a drilling field extraction main pipe (29) at the same time to remove slag from gas gas from multiple extraction drilling holes (16) in the same drilling field; the drilling hole extraction branch pipe (21) is made of a steel wire hose, and both ends are connected to the guide pipe through a pipe clamp (20).

5. The method for combined pre-splitting and drainage of double-hard and extra-thick coal seam roof according to claim 1, characterized in that: The blasting pre-splitting drilling hole (10) first uses a probe tube, which is a plastic tube that can be connected, to conduct a blasting and complete the drilling cleaning; after the blasting is completed, the hole is immediately charged and sealed to ensure that the hole is sealed tightly and solid, and then the blasting is carried out; 30 minutes after the blasting, the roof blasting pre-splitting and extraction drilling hole a in the working face opening eye and the roof blasting pre-splitting and extraction drilling hole b at the end of the working face are pre-splitting blasted before the working face is mined; the coal seam roof blasting pre-splitting and extraction drilling hole c in the working face advance area and the roof blasting pre-splitting and extraction drilling hole d in the two lanes in the working face advance area are blasted 50m away from the working face.

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