A top-laying device and method for directional cutting of top plates by front-mixed abrasive water jet

Abstract

The present invention belongs to the technical field of coal mining field and tunnel surrounding rock control technology, and specifically discloses a top-laying device and method for directional cutting of a roof plate by a pre-mixed abrasive water jet. The top-laying device includes a water supply tank and an anchor-type agitator installed in the water supply tank. A water pump is provided on the top of the water supply tank. Abrasive water inside the water supply tank is pumped into a mud pump through a water outlet pipe by the water pump. A pressure gauge is provided on the water outlet pipe of the mud pump. The outlet of the water outlet pipe is connected to a directional drill rod. A drill rod transmission device is provided at the inlet end of the directional drill rod, a drill rod direction control device is provided at the outlet end of the directional drill rod, and a slit drill bit is provided at the outlet of the directional drill rod. The present invention has the advantages of being easy to use and safe to use.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining field and tunnel surrounding rock control technology, and in particular relates to a top caving device and method for directional cutting of a top plate by a pre-mixed abrasive water jet. Background Art

[0002] The occurrence conditions of coal seams in my country are complex, among which one-third of the coal seams have hard roofs that are difficult to collapse. This type of roof has high rock strength, large thickness and strong integrity. It is difficult to collapse naturally after coal seam mining, which will cause air leakage in the goaf. In addition, the sudden collapse of the roof will bring gas from the goaf to the working face, causing gas excessive, and will increase the intensity of the initial pressure, damaging the working face and even causing tunnel collapse. Therefore, the research on the method of controlling the roof collapse of the hard roof of coal seams is of great significance.

[0003] The main methods currently used for cutting coal seam roof are: hydraulic cutting, blasting cutting, dense drilling cutting, and cutting machine cutting. Among them, hydraulic cutting has the problem of too high operating pressure and too shallow cutting, which is not easy to apply on site; blasting cutting has an adverse effect on underground gas control work and mining area surrounding rock during charging and detonation, and is very dangerous; although dense drilling cutting has obvious effects, the cost is too high and it is not easy to promote and use on a large scale; cutting machine cutting has the current situation that the cutting machine equipment is bulky, difficult to move, the cutting depth is shallow, a large amount of dust is generated, causing pollution, and it is impossible to effectively cut the roof surrounding rock above the tunnel.

[0004] The use of abrasive water jets can solve the problem of high water pressure and shallow cutting depth in high-pressure water jet cutting and increase the safety of the entire system. It is safer and more reliable than blasting cutting, more economical and easier than intensive drilling cutting, better than cutting machines and no dust pollution. Abrasive water jets can be further divided into pre-mixed abrasive water and post-mixed abrasive water jets. Compared with post-mixed abrasive water jets, pre-mixed abrasive water jets have a more complete and uniform mixture of water and abrasive, and the abrasive particles have a longer acceleration time and higher energy, which has a more prominent effect on rock cutting. Therefore, under the same conditions, pre-mixed abrasive water jets have better effects. The current method of directional roof cutting is mainly directional blasting for cutting. This method has an adverse effect on underground gas control work and surrounding rock in the process of charging and detonation, and is very dangerous. Currently, there is no safer method for directional roof cutting. Summary of the invention

[0005] The purpose of the present invention is to provide a device and method for directional cutting of roof plates by a pre-mixed abrasive water jet. The device can use a pre-mixed high-pressure abrasive water jet pressurized by a mud pump to adjust the direction of the cutting nozzle through a drill pipe direction control device in the drill hole constructed at the opening point, thereby realizing directional cutting of the roof to form predetermined directional cracks. After sealing the hole, a directional hydraulic fracturing method is used to form a crack network on the roof to control the roof release, realize the collapse of the roof, reduce the initial pressure strength of the old roof, and ensure the safety of the working face.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A top-laying device for directional cutting of top plates by pre-mixed abrasive water jet comprises a water supply tank and an anchor-type agitator installed in the water supply tank. A water pump is provided on the top of the water supply tank. Abrasive water inside the water supply tank is pumped into a mud pump through a water outlet pipe by the water pump. A pressure gauge is provided on the water outlet pipe of the mud pump. The outlet of the water outlet pipe is connected to a directional drill rod. A drill rod transmission device is provided at the inlet end of the directional drill rod. A drill rod direction control device is provided at the outlet end of the directional drill rod. A slit drill bit is provided at the outlet of the directional drill rod.

[0008] Furthermore, the drill rod transmission device includes two support piers arranged in parallel on the left and right, each support pier is provided with a horizontal through hole on the top and bottom, and two upper and lower parallel screw rods are provided between the two support piers. Both ends of the screw rod are rotatably connected to the support piers through support bearings installed in the through holes, and the leftmost end of each screw rod is driven to rotate by a motor. A directional drill rod mounting hole is also provided in the middle of each support pier, and the directional drill rod passes through the directional drill rod mounting hole. The drill rod transmission device also includes a transmission plate arranged vertically with the screw rod, and the transmission plate and the upper and lower screw rods are movably connected by a circular thread provided on the back of the transmission plate, and the thread is threadedly connected to the screw rod. A positioning hoop movably connected to the directional drill rod is also provided in the middle of the back of the transmission plate, and a bolt is also provided on the positioning hoop.

[0009] Furthermore, the directional drill rod is composed of multiple sections of drill rods connected end to end, each section of the drill rod is provided with a side wing on both sides, the two side wings are arranged along the axial direction of the drill rod, each section of the drill rod is provided with a U-shaped female joint on the left side, and a male joint matching the female joint is provided on the right side of the drill rod, each female joint is provided with a groove on the upper and lower inner sides, each male joint is provided with an annular groove, a sealing ring is provided in the annular groove, and an annular protrusion is provided on the left side of the annular groove, and adjacent drill rods are mutually clamped and sealed through the annular protrusion on the male joint and the groove on the female joint.

[0010] Furthermore, the drill rod direction control device includes a flange, a circular turntable is provided on the upper surface of the middle part of the flange, a T-shaped boss is provided on the bottom of the circular turntable, and an annular groove is also provided on the upper surface of the flange. The T-shaped boss is located in the annular groove and drives the circular turntable to rotate along the annular groove. Two handles are provided in the radial direction of the circular turntable, and the angle between the line connecting the two handles and the normal of the circular turntable is 90°. Bolt holes are also provided on the flange, and expansion bolts pass through the bolt holes to fix the flange on the wall at a specified position. Positioning grooves are provided on the circular turntable and the flange, and the directional drill rod enters the drill hole from the positioning groove.

[0011] Furthermore, two slitting nozzles are radially provided at the end of the slitting drill bit, and the two slitting nozzles are symmetrically arranged along the side wall axis of the slitting drill bit. The connecting line of the two slitting nozzles is perpendicular to the axis direction of the drill pipe. The two nozzles are respectively on the extension lines of the two side wings of the directional drill pipe. The slitting nozzle adopts a conical convergent nozzle, and the nozzle throat diameter is 3mm.

[0012] A method for placing a top plate by directional cutting of a top plate by a front-mixed abrasive water jet, comprising the following steps:

[0013] 1) After the wall opening is completed and before the coal seam working face is mined, a row of holes is drilled on the roof behind the hydraulic support using a drilling rig. The angle between the axis of the holes and the horizontal direction is 90°, and the spacing between adjacent holes is 10m. Drilling is stopped 1m above the overlying rock layer after the old roof is penetrated.

[0014] 2) Use a roof placing device based on abrasive water jet directional cutting of the roof to perform directional slitting in the pre-drilled borehole to cut the old roof. By adjusting the drill rod direction control device, the plane formed by the two slitting nozzles of the slitting drill bit and the directional drill rod connected thereto is parallel to the working surface. By adjusting the drill rod transmission device, the drill rod is gradually retreated. The slitting is symmetrically performed on both sides of the borehole 16 in a backward manner. The slitting is stopped at the junction of the direct roof and the old roof 1m upward along the axis;

[0015] 3) After the slitting is completed, the capsule sealer is used to seal the drilled hole with the directional slitting completed. The sealing is carried out within 1m along the axial direction from the bottom of the hole and within 1m upward along the axial direction from the junction of the direct top and the old top. The sealing depth is at least 1m;

[0016] 4) After the hole is sealed, high-pressure water is used for directional fracturing to achieve the purpose of weakening the roof and controlling the roof release.

[0017] Furthermore, in the step 1), the wall surface consists of horizontal coal seam, direct roof, old roof and overlying rock layer from bottom to top.

[0018] Furthermore, in step 2), the high-pressure abrasive water pressure is 30 MPa, the mass ratio of abrasive to water in the water tank is 13%, and the high-pressure abrasive water jet starts cutting along the axial direction of the borehole from 1.5 m away from the bottom of the hole.

[0019] Furthermore, in step 4), the formula for calculating the self-weight stress of the rock mass is: , severe , burial depth , the self-weight stress and horizontal stress of the old roof can be calculated Self-weight stress Half of the hydraulic fracturing pressure of the rock formation is calculated according to the formula: , where the lateral pressure coefficient , For the borehole radius, the old roof fracturing pressure can be calculated. Hydraulic fracturing uses a high-pressure water pump. The water pump inlet is connected to static water, and the water outlet is connected to a high-pressure hose. The other end of the high-pressure hose is connected to the water injection pipe. After the connection is correct, first pass water through the high-pressure water pump and then turn on the power to inject water. Slowly increase the pressure and record the readings of the water pump pressure gauge and the manual pump pressure gauge. Continue to increase the pressure until the predetermined directional cracks crack. At this time, the water pressure will suddenly drop, and continue to maintain the pressure and inject water. Maintain the pressure for 0.5h to allow the cracks to continue to expand so that the cracks in the hydraulic fracturing of adjacent boreholes can be connected to form a crack network, thereby achieving the purpose of weakening the roof and controlling the top release.

[0020] The present invention has the advantages that:

[0021] 1. This device uses a stirrer to mix abrasive and water evenly, and then pressurizes it into a high-pressure abrasive water flow through a mud pump. Then the high-pressure abrasive water flow passes through a directional drill pipe and then through a drill pipe transmission device to realize the movement of the drill pipe in the borehole. The drill pipe and drill bit directions are adjusted by a drill pipe direction control device to realize the directional cutting of the roof by a front-mixed high-pressure abrasive water jet to form a pre-determined directional crack, and then a capsule sealer is used to seal the hole, and then high-pressure water is used for directional hydraulic fracturing, so that the cut gaps in adjacent boreholes are connected through the fracturing gaps to form a crack network, thereby realizing the purpose of controlling the roof and weakening the roof;

[0022] 2. By using a water pump to transport abrasive water to the mud pump, the stable and continuous supply of the mud pump can be achieved, ensuring the stability of the formed front-mixed abrasive water jet, thereby ensuring its good rock breaking effect;

[0023] 3. Use a mud pump to pressurize the mixed low-pressure abrasive water. The high-pressure abrasive water pressurized by the mud pump has the characteristics of high static pressure and low dynamic pressure. The high-pressure abrasive water with this characteristic will greatly reduce the wear on the pipeline;

[0024] 4. Compared with the post-mixing abrasive water jet, the abrasive and water are fully and evenly mixed in the front-mixing abrasive water jet, the acceleration time of the abrasive particles is long, the energy obtained is high, the cutting effect on the rock is more prominent, and the working pressure can be greatly reduced;

[0025] 5. Compared with hydraulic cutting, blasting cutting, intensive drilling cutting, and cutting machine cutting, the method of using pre-mixed abrasive water jet to directional cut the top plate has deeper cutting effects and better results. It is safe, efficient, easy to operate, and easy to promote.

[0026] 6. The drill pipe direction control device can control the direction of the conical convergent nozzle on the slot drill bit through the directional drill pipe, realize directional pre-mixed high-pressure abrasive water jet slotting, and thus produce prefabricated directional cracks. After the directional cracks are formed, it is easier to implement high-pressure hydraulic fracturing in the slotted borehole, and the cracks formed by hydraulic fracturing can be used to the greatest extent to form a crack network to control the roof caving to achieve the purpose of weakening the roof. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the device of the present invention;

[0028] Figure 2 It is a plan view of the drill rod transmission device of the present invention;

[0029] Figure 3 It is a cross-sectional view of the drill rod transmission device of the present invention;

[0030] Figure 4 It is a schematic diagram of the directional drill rod structure of the present invention;

[0031] Figure 5 It is a plan view of the drill rod direction control device of the present invention;

[0032] Figure 6 It is a cross-sectional view of the drill pipe direction control device of the present invention;

[0033] Figure 7 is a cross-sectional view of a slot drill bit of the present invention;

[0034] Figure 8 It is a cross-sectional view of the implementation method of the present invention;

[0035] Fig. 9 It is a plan view of the implementation method of the present invention;

[0036] 1. Anchor stirrer; 2. Water tank; 3. Water pump; 4. Pipeline; 5. Mud pump; 6. Pressure gauge; 7. Transmission device; 7.1. Support pier; 7.2. Motor; 7.3. Bearing; 7.4. Transmission plate; 7.5. Thread; 7.6. Positioning hoop; 7.7. Screw rod; 7.8. Bolt; 8. Directional drill pipe; 8.1. Flank; 8.2. Slot; 8.3. Female joint; 8.4. Annular protrusion; 8.5. Annular groove; 8.6, male joint; 9, direction control device; 9.1, expansion bolt; 9.2, flange plate; 9.3, handle 9.4, circular turntable; 9.5, positioning groove; 9.6, annular groove; 9.7, T-shaped boss; 10, slot drill bit; 10.1, conical convergent nozzle; 11, overlying strata; 12, old roof; 13, direct roof; 14, hydraulic support; 15, mining coal seam; 16, drilling. DETAILED DESCRIPTION

[0037] like Figure 1, 2, 3, 4, 5, 6, 7 show a top-laying device for directional cutting of top plates by front-mixing abrasive water jets, the device comprising an anchor stirrer 1, a water supply tank 2, a water pump 3, a pipeline 4, a mud pump 5, a pressure gauge 6, a drill rod transmission device 7, a directional drill rod 8, a drill rod direction control device 9, a slotting drill bit 10, etc.; the drill rod transmission device 7 comprises two left and right parallel supporting piers 7.1, each supporting pier 7.1 is provided with a transverse through hole at the top and bottom, and two upper and lower parallel screw rods 7.7 are provided between the two supporting piers 7.1, and both ends of the screw rod 7.7 are rotatably connected to the supporting pier 7.1 through supporting bearings 7.3 installed in the through holes, and each screw rod 7.7 The leftmost end is driven to rotate by a motor 7.2. A directional drill rod mounting hole is also provided in the middle of each support pier 7.1. The directional drill rod passes through the directional drill rod mounting hole. The drill rod transmission device 7 also includes a transmission plate 7.4 vertically arranged with the screw rod 7.7. The transmission plate 7.4 is movably connected to the upper and lower screw rods 7.7 through a circular thread 7.5 arranged on the back of the transmission 7.4. The thread 7.5 is threadedly connected to the screw rod 7.7. A positioning hoop 7.6 movably connected to the directional drill rod 8 is also provided in the middle of the back of the transmission plate 7.4. Bolts 7.8 are also provided on the positioning hoop 7.6. The directional drill rod 8 is composed of multiple sections of drill rods connected end to end, and each section of the drill rod is provided with a side wing 8 on both sides. .1, two side wings 8.1 are arranged along the axial direction of the drill pipe, a U-shaped female joint 8.3 is arranged on the left side of each drill pipe section, a male joint 8.6 matching with the female joint 8.3 is arranged on the right side of the drill pipe, each female joint 8.3 is provided with a clamping groove 8.2 on the upper and lower inner sides, each male joint 8.6 is provided with an annular groove 8.5, a sealing ring is arranged in the annular groove 8.5, an annular protrusion 8.4 is arranged on the left side of the annular groove 8.5, and adjacent drill pipes are mutually clamped and sealed through the annular protrusion 8.4 on the male joint 8.6 and the clamping groove 8.2 on the female joint 8.3; further, the drill pipe direction control device 9 includes a flange plate 9.2, the upper middle part of the flange plate 9.2 A circular turntable 9.4 is provided on the surface, a T-shaped boss 9.7 is provided at the bottom of the circular turntable 9.4, an annular groove 9.6 is also provided on the upper surface of the flange plate 9.2, the T-shaped boss 9.7 is located in the annular groove 9.6 and drives the circular turntable 9.4 to rotate along the annular groove 9.6, the circular turntable 9.4 is provided with two handles 9.3 along the radial direction, the connecting line of the two handles 9.3 and the normal of the circular turntable 9.4 form an angle of 90°, the flange plate 9.2 is also provided with bolt holes, the expansion bolts 9.1 pass through the bolt holes to fix the flange plate 9.2 on the wall surface at the designated position, the circular turntable 9.4 and the flange plate 9.2 are both provided with positioning grooves 9.5, and the directional drill rod 8 is inserted from the positioning grooves 9.5 enters the borehole; further, the end of the slot drill bit 10 is provided with two slot nozzles in the radial direction, the two slot nozzles are arranged symmetrically along the side wall of the slot drill bit, the connecting line of the two slot nozzles is perpendicular to the axis direction of the drill pipe, the two nozzles are respectively on the extension lines of the two flanks of the directional drill pipe 8, the slot nozzle adopts a conical convergent nozzle 10.1, and the nozzle throat diameter is 3mm; when used specifically, the water and abrasive in the water supply tank 2 are fully mixed and uniformly through the stirring of the anchor stirrer 1, the mixed abrasive water is pumped into the mud pump 5 through the pipeline 4 by the water pump 3 to be pressurized to form a high-pressure abrasive water flow, the high-pressure abrasive water flow enters the directional drill pipe 8 after passing through the pressure gauge 6, and the directional Side wings 8.1 are arranged on both sides of the drill pipe. The ends of the drill pipe along the axial direction of the two side wings are slit nozzles arranged on the slit drill bit 10. The slit nozzle adopts a conical convergent nozzle 10.1, so the directional drill pipe 8 can be controlled to realize the directional cutting of the top plate by front-mixed abrasive water jet. The directional drill pipes 8 are connected by a quick connector, wherein the front part of the male connector 8.6 is provided with an annular groove 8.5, and the groove has a built-in sealing ring to ensure the air tightness of the connection between the drill pipes. The rear part of the annular groove is provided with an annular protrusion 8.4, and the card groove 8.2 arranged on the drill pipe female connector 8.3 and the annular protrusion 8.4 on the male connector are fixed by a U-shaped card to ensure the tightness of the connection between the drill pipes. The rod 8 realizes the movement of the directional drill rod in the borehole through the drill rod transmission device 7. The drill rod transmission device realizes the forward and backward movement of the transmission plate 7.4 by the rotation of the motor 7.2, thereby driving the rotation of the screw rod 7.7. The screw rod and the transmission plate are connected by a thread 7.5. A positioning hoop 7.6 is provided on the transmission plate. The positioning hoop fixes the directional drill rod 8 through a bolt 7.8. The directional drill rod enters the drill rod direction control device 9 after passing through the drill rod transmission device. The drill rod direction control device fixes a square flange plate 9.2 on the wall surface by using an expansion bolt 9.1. The square flange plate 9.2 is provided with an annular groove 9.6. A circular turntable 9.4 is provided above the square flange plate 9.2. The lower part of the circular turntable is provided with a T-shaped boss 9.7. The square flange plate 9.2 and the circular turntable 9.4 are connected through an annular groove 9.6 and a T-shaped boss 9.7. The circular turntable is provided with two handles 9.3 along the radial direction. The angle between the connecting line of the two handles and the normal line of the circular turntable is 90°. The circular turntable and the square flange plate are provided with positioning grooves 9.5. The directional drill rod enters the borehole from the positioning groove. By controlling the handle on the circular turntable and rotating the drill rod to observe the position of the flank of the directional drill rod, the direction of the slotting nozzle at the end of the drill rod can be determined. The slotting drill bit 10 is connected to the end of the directional drill rod. The high-pressure abrasive water inside the drill rod is transported to the slotting drill bit and passes through the conical convergent nozzle 10.1. The slit nozzle further accelerates the ejection of high-pressure abrasive water to form a pre-mixed high-pressure abrasive water jet to directional slit the rock mass to form a pre-determined directional crack. After the rock mass forms a pre-determined directional crack under the action of the slit nozzle, the same slit treatment is performed on the next position of the borehole. After all are completed, the slit borehole is sealed with a capsule sealer, and then high-pressure water is used to perform directional hydraulic fracturing in the roof, so that the slit gaps in adjacent boreholes are connected through the fracturing gaps, and a crack network is formed on the roof to control the roof caving to achieve the purpose of weakening the roof. .

[0038] like Figure 1 , 8, 9 show a method for cutting a slit of a top-laying device for directional cutting of a roof by a pre-mixed abrasive water jet. In a horizontal coal seam 15 (2.5 m thick), a direct roof 13 (4 m thick mudstone), an old roof 12 (10 m thick dense sandstone), and an overlying rock layer 11 (200 m buried depth), after the opening of the cut hole is completed and before the working face of the coal seam 15 is mined, a row of holes is drilled on the roof behind the hydraulic support 14 using a drill rig. The angle between the axis of the hole and the horizontal direction is 90°, and the spacing between adjacent holes is 10 m. The drilling is stopped at 1 m from the old roof through the overlying rock layer (e.g. Figure 8 As shown), a top-dropping device based on abrasive water jet directional cutting of the old top is then used, wherein the high-pressure abrasive water pressurized by the mud pump can reach up to 30MPa, and directional slitting is performed in the pre-drilled borehole 16 to cut the old top; when the high-pressure abrasive water jet is slitting, the drill pipe direction control device is adjusted so that the plane formed by the two slitting nozzles of the slitting drill bit and the directional drill pipe connected thereto is parallel to the working surface to achieve the best fracturing effect in the later stage, and the high-pressure abrasive water jet starts slitting along the axial direction of the borehole from 1.5m away from the bottom of the hole, and the drill pipe transmission device is adjusted to gradually retreat the drill pipe, and the slitting is symmetrically performed on both sides of the borehole 16 in a backward manner (when the high-pressure abrasive water pressure is 30MPa and the mud pump flow rate is 80m 3 / h, when the mass ratio of abrasive and water in the water tank reaches 13%, the cutting effect is best and the cutting depth can reach 1m), the cutting stops at 1m upward along the axis from the junction of the direct top and the old top.

[0039] After the slotting is completed, the capsule sealer is used to seal the drilled hole with the directional slotting completed. The hole is sealed within 1m along the axial direction from the bottom of the hole and within 1m upward along the axial direction from the junction of the direct top and the old top. The sealing depth is at least 1m. After the sealing is completed, high-pressure water is used for directional fracturing. According to the self-weight stress calculation formula of the rock mass: , severe , burial depth , it can be calculated that the self-weight stress on the old roof is 6MPa, and the horizontal stress Self-weight stress Half of the original value. According to the calculation formula of hydraulic fracturing pressure of rock formation: , where the lateral pressure coefficient , = ...

Claims

1. A method for directional cutting of a top plate by a pre-mixed abrasive water jet, implemented using a top placing device, characterized in that: The top release device includes a water supply tank and an anchor agitator installed in the water supply tank. A water pump is provided on the top of the water supply tank. The abrasive water inside the water supply tank is pumped into the mud pump through the water outlet pipe by the water pump. A pressure gauge is provided on the water outlet pipe of the mud pump. The outlet of the water outlet pipe is connected with the directional drill rod. A drill rod transmission device is provided at the inlet end of the directional drill rod. A drill rod direction control device is provided at the outlet end of the directional drill rod. A slit drill bit is provided at the outlet of the directional drill rod. The directional drill rod is composed of a plurality of sections of drill rod connected end to end. A flank is provided on both sides of each section of the drill rod, and the two flanks are arranged along the axial direction of the drill rod. A U-shaped female joint is provided on the left side of each section of the drill rod, and a male joint matching with the female joint is provided on the right side of the drill rod. A slot is provided on the upper and lower inner sides of each female joint, and an annular groove is provided on each male joint. A sealing ring is provided in the groove, and an annular protrusion is provided on the left side of the annular groove. Adjacent drill rods are mutually clamped and sealed through the annular protrusion on the male joint and the clamping groove on the female joint; the drill rod direction control device comprises a flange, a circular turntable is provided on the upper surface of the middle part of the flange, a T-shaped boss is provided on the bottom of the circular turntable, and an annular groove is also provided on the upper surface of the flange. The T-shaped boss is located in the annular groove and drives the circular turntable to rotate along the annular groove. Two handles are provided in the radial direction of the circular turntable, and the angle between the connecting line of the two handles and the normal line of the circular turntable is 90°. Bolt holes are also provided on the flange, and expansion bolts pass through the bolt holes to fix the flange on the wall at the specified position. Positioning grooves are provided on the circular turntable and the flange, and the directional drill rod enters the borehole from the positioning groove; the method comprises the following steps: 1) After the wall opening is completed and before the coal seam working face is mined, a row of holes is drilled on the roof behind the hydraulic support using a drilling rig. The angle between the axis of the holes and the horizontal direction is 90°, and the spacing between adjacent holes is 10m. Drilling is stopped 1m above the overlying rock layer after the old roof is penetrated; 2) Use a roof placing device based on abrasive water jet directional cutting of the roof to perform directional slitting in the pre-drilled borehole to cut the old roof. By adjusting the drill pipe direction control device, the plane formed by the two slitting nozzles of the slitting drill bit and the directional drill pipe connected thereto is parallel to the working surface. By adjusting the drill pipe transmission device, the drill pipe is gradually retreated, and the slitting is symmetrically performed on both sides of the borehole in a backward manner. The slitting is stopped at the junction of the direct roof and the old roof 1m upward along the axis; 3) After the slitting is completed, the capsule sealer is used to seal the drilled hole that has completed the directional slitting. The sealing is carried out within 1m along the axial direction from the bottom of the hole and within 1m upward along the axial direction from the junction of the direct top and the old top. The sealing depth is at least 1m; 4) After the hole is sealed, high-pressure water is used for directional fracturing to achieve the purpose of weakening the roof and controlling the roof release.

2. The method for directional cutting of a top plate by a pre-mixed abrasive water jet according to claim 1, characterized in that: The drill rod transmission device includes two supporting piers arranged in parallel on the left and right, each supporting pier is provided with a horizontal through hole on the top and bottom, and two upper and lower parallel screw rods are provided between the two supporting piers. Both ends of the screw rod are rotatably connected to the supporting piers through supporting bearings installed in the through holes, and the leftmost end of each screw rod is driven to rotate by a motor. A directional drill rod mounting hole is also provided in the middle of each supporting pier, and the directional drill rod passes through the directional drill rod mounting hole. The drill rod transmission device also includes a transmission plate arranged vertically with the screw rod, and the transmission plate and the upper and lower screw rods are movably connected by a circular thread provided on the back of the transmission plate, and the thread is threadedly connected to the screw rod. A positioning hoop movably linked to the directional drill rod is also provided in the middle of the back of the transmission plate, and a bolt is also provided on the positioning hoop.

3. The method for directional cutting of a top plate by a pre-mixed abrasive water jet according to claim 2, characterized in that: Two slotting nozzles are radially arranged at the end of the slotting drill bit. The two slotting nozzles are symmetrically arranged along the side wall axis of the slotting drill bit. The connecting line of the two slotting nozzles is perpendicular to the axis direction of the drill pipe. The slotting nozzle adopts a conical convergent nozzle. The two nozzles are respectively on the extension lines of the two side wings of the directional drill pipe, and the nozzle throat diameter is 3mm.

4. The method for directional cutting of a top plate by a pre-mixed abrasive water jet according to claim 3, characterized in that: In the step 1), the wall surface consists of horizontal coal seam, direct roof, old roof and overlying rock layer from bottom to top.

5. The method for directional cutting of a top plate by a pre-mixed abrasive water jet according to claim 1, characterized in that: In the step 2), the high-pressure abrasive water pressure is 30 MPa, the mass ratio of abrasive to water in the water tank is 13%, and the high-pressure abrasive water jet starts cutting along the axial direction of the borehole from 1.5 m away from the bottom of the hole.

6. The method for directional cutting of a top plate by a pre-mixed abrasive water jet according to claim 1, characterized in that: In step 4), the self-weight stress calculation formula of the rock mass is: z =γH, heavy γ=30kN / m 3 , burial depth H = 200m, the self-weight stress on the old top can be calculated, and the horizontal stress σ x ,σ y is the self-weight stress σ z Half of the hydraulic fracturing pressure of the rock formation is calculated according to the formula: p = (3-λ)σ z +R t , where the lateral pressure coefficient λ = 1.5, R t For the borehole radius, the old roof fracturing pressure can be calculated. Hydraulic fracturing uses a high-pressure water pump. The water pump inlet is connected to static water, and the water outlet is connected to a high-pressure hose. The other end of the high-pressure hose is connected to the water injection pipe. After the connection is correct, first pass water through the high-pressure water pump and then turn on the power to inject water. Slowly increase the pressure and record the readings of the water pump pressure gauge and the manual pump pressure gauge. Continue to increase the pressure until the predetermined directional cracks crack. At this time, the water pressure will suddenly drop, and continue to maintain the pressure and inject water. Maintain the pressure for 0.5h to allow the cracks to continue to expand so that the cracks in the hydraulic fracturing of adjacent boreholes can be connected to form a crack network, thereby achieving the purpose of weakening the roof and controlling the top release.

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