Large-diameter drill hole protection pipe connecting device in coal body prone to hole collapse and protection pipe laying method

Abstract

The invention belongs to the technical field of coal mine gas control, and particularly relates to a large-diameter drill hole protection pipe connecting device in a coal body prone to hole collapse and a protection pipe laying method. The device comprises a drill bit connector, a tension converter, a plug and a bearing, the axis of the drill bit connector is parallel to the axis of a drill bit, and one side of the drill bit connector is connected with the drill bit; one side of the tension converter is hollow and internally provided with a bearing, the other side of the tension converter is provided with protective pipe connecting threads used for being connected with a protective pipe, and a plug penetrates through the bearing to be connected with the other side of the drill bit connector. The protection pipe laying method comprises the steps of drilling construction; assembling a protective tube connecting device; mounting a protective pipe connecting device; laying a first section of protective pipe; laying a protective pipe on the whole hole section; and sealing the hole. The one-way movement of the protective pipe in the drill hole is changed into the forward and backward two-way movement, so that the hole collapse treatment difficulty is reduced; according to the laying method, a traditional jacking-in type protection pipe laying mode is changed into a pull-out type protection pipe laying mode, the protection pipe is laid while the drill rod is withdrawn, and coal cinder and collapsed coal briquettes in the hole can be brought out through rotation and withdrawing of the drill rod.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine gas control, and in particular relates to a large-diameter borehole protective pipe connecting device in a coal body prone to hole collapse and a protective pipe laying method. Background Art

[0002] In order to solve the problem of excessive gas in the corners of the mining face, some mines use large-diameter drilling in the coal pillar between the return air lane and the extraction lane, bury a protective pipe of a certain diameter in it, and then connect it to the extraction system, which solves the problem of excessive gas in the corners of the working face. The current general process of laying protective pipes is: after the drilling construction is in place, the drill is withdrawn, and the thrust of the drilling rig is used to push the protective pipe into the borehole section by section to complete the installation of the protective pipe.

[0003] Due to the different occurrence conditions of coal seams in different regions, large-diameter boreholes completed in soft coal areas collapse during the drilling process or within a few hours after drilling, and the protective pipe cannot be pushed into the borehole, resulting in drilling failure. Although the current solution to the problem of borehole collapse is to pre-grout in the large-diameter drilling construction area to strengthen the strength of the coal body in the drilling area in advance, and to improve the drill structure and construction technology, and to lay protective pipes while drilling. However, in actual underground coal mine operations, affected by the occurrence conditions of coal seams and drilling layout parameters, the bedding, joints and various geological structures in the coal seams are extremely rich. During pre-grouting of the borehole, the distribution range of the slurry is unpredictable, and it is difficult for the grouting area to evenly cover the large-diameter drilling construction area. Especially when the borehole is long, the hole protection effect is not ideal, which limits the effect and application scenarios of grouting to prevent borehole collapse. At the same time, when the coal seam is too soft or the soft and hard layers are oblique to the direction of the drilling, the drill cuttings and coal slag will block or the hard layer fragments will get stuck between the drill rod and the casing and between the casing and the hole wall, causing the drilling to be difficult to advance and retreat, seriously affecting the drilling efficiency. The casing is generally made of iron, and the high-speed rotation of the drill rod in the casing will inevitably produce friction sparks with the inner wall of the casing, which will pose a great threat to coal mine safety.

[0004] Affected by the above factors, the application of large-diameter drilling technology to control gas in the upper corner of the working face will be limited. Therefore, it is necessary to seek new methods to prevent hole collapse and the process of laying protective pipes to improve the success rate of laying protective pipes and the safety during the construction process. Summary of the invention

[0005] In view of the above problems, the present invention provides a large-diameter borehole protective pipe connecting device in a coal body prone to hole collapse, which is used to change the connection mode between the protective pipe and the drill bit and the movement state of the protective pipe in the borehole. When the protective pipe is traditionally pushed in, the drill bit only makes horizontal displacement and cannot perform rotational movement. The present invention reduces the friction resistance between the drill bit and the hole wall, and the rotational backward movement can also play a slag removal role to prevent hole blockage. In addition, the present invention adopts the device to provide a method for laying protective pipes, which changes the traditional top-in type of laying protective pipes into a pull-out type, and is ultimately used to ensure that protective pipes can be quickly and reliably laid in large-diameter boreholes in coal bodies prone to hole collapse and when soft and hard stratifications are obliquely intersected with the borehole, thereby improving the drilling hole formation rate and achieving the purpose of upper corner gas control.

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

[0007] A protective tube connection device for drilling large diameter holes in coal bodies prone to collapse comprises a drill bit connector, a tension converter, a plug and a bearing. The axis of the drill bit connector is parallel to the axis of the drill bit. One side of the drill bit connector is connected to the drill bit. One side of the tension converter is hollow with a built-in bearing and the other side is provided with a protective tube connection thread. The protective tube connection thread is used to connect the protective tube. The plug passes through the bearing and is connected to the other side of the drill bit connector. The drill bit connector and the tension converter are connected to form an integral device through the bearing and the plug.

[0008] Furthermore, the middle part of the drill bit connector is a gear device, which includes one or more spiral blades with full pitch and multiple movable gears; the spiral blades are fixedly connected to the drill bit connector; the gears are connected to the outside of the spiral blades and are evenly arranged along the circumferential direction; the total outer diameter of the gear device is larger than the outer diameter of the protective tube and smaller than the drill bit diameter.

[0009] Furthermore, the bearing built into the tension converter includes: a high-pressure wear-resistant sealing ring, a lubricating fluid, and a ball; the bearing is provided with a plurality of concave ball rings; the number of the ball rings is not single;

[0010] Two high-pressure wear-resistant sealing rings 10 are arranged at both ends of the bearing 4, a plurality of balls are placed in the ball ring, and lubricating fluid is injected into the ball ring; the high-pressure wear-resistant sealing ring and the lubricating fluid constitute a sealing system.

[0011] Furthermore, the plug is a solid cylinder with a baffle at one end. The connecting end of the plug and the tension converter is connected to the inner ring part of the bearing. A hole vertical to the plug is set near the vertical surface of the bearing, and its horizontal movement is restricted by a pin.

[0012] Furthermore, the drill bit connector is a solid cylinder, one side of which is detachably connected to the drill bit, and the other side of which is detachably connected to the joint of the plug.

[0013] Furthermore, the outer diameter of the protective tube connection thread end on one side of the tension converter is the same as the inner diameter of the protective tube, the protective tube is internally threaded, the protective tube connection thread has the same pitch as the internal thread of the protective tube port, and can be threadedly connected.

[0014] A method for laying protective pipes in large-diameter boreholes, the method using a large-diameter borehole protective pipe connection device in a coal body prone to collapse, and the specific method includes the following steps:

[0015] Step 1: Drilling construction;

[0016] Use a drilling rig to drill a large diameter hole in the coal seam between the return air tunnel and the extraction tunnel. The drill bit penetrates the coal pillar and stops drilling when a certain length is exposed.

[0017] Step 2: Assemble the protective tube connection device;

[0018] The inner ring of the bearing that is connected to the plug and the tension converter is first covered with a matching high-pressure wear-resistant sealing ring. After the plug is passed through the bearing, the inner ring and outer ring of the bearing are correctly matched, and balls are put in to fill the ball ring formed between the inner ring and the outer ring. Lubricating fluid is injected, and another high-pressure wear-resistant sealing ring is installed at the end of the plug. A pin is inserted into the vertical hole at the exposed end to fix and restrict its horizontal movement, so that the tension converter and the plug are both axially perpendicular to the ground, and the plug is connected to the drill connector;

[0019] Step 3: Installation of protective pipe connection device;

[0020] The drill bit connector of the device is firmly connected to the connecting head of the drill bit, and the protective tube connecting thread of the tension converter is connected to the internal thread end of the first section of the threaded protective tube;

[0021] Step 4: Lay the first section of protective pipe;

[0022] Start the drilling rig to withdraw the drill, adjust the drilling rig's withdrawal speed and the drill rod rotation speed, so that the drill bit slowly and evenly withdraws, and use the drilling rig's withdrawal action to pull the protective tube into the borehole section by section, and stop drilling when only the protective tube connection end is exposed;

[0023] Step 5: Laying protective pipe in the whole hole section;

[0024] Add a new protective pipe to connect it to the first section of protective pipe in the hole, repeat step 4, and then repeat the protective pipe connection and step 4 in a cycle until the protective pipe laying to the specified depth is completed;

[0025] Step 6: Sealing the hole;

[0026] After the protective pipe is laid in the entire drilling section, the drilling rig is shut down, the protective pipe connection device is removed, and the large-diameter drilling and sealing work is carried out at both ends of the coal pillar.

[0027] Furthermore, in step 6, the large-diameter borehole sealing is selected by a combined sealing method of cement sealing and bag-type grouting sealing according to the actual situation of the drilling construction.

[0028] Furthermore, in step 3, the corresponding protective tube is selected according to the diameter of the large-diameter drilling hole; the diameter of the large-diameter drilling hole is ≧220mm; in step 1, the drill bit is processed and modified in advance, and a detachable connector is installed at the center axis position of the drill bit.

[0029] Furthermore, in step 5, the protective pipes are connected by insert bolts or threads; during the drill withdrawal process, the drill withdrawal speed and the advance or retreat of the drill bit are adjusted in time according to the collapse of the hole wall in the large-diameter borehole and the resistance encountered during the drill withdrawal, and the cones on the spiral drill rod and the protective pipe connecting device are used to cut, destroy and discharge the collapsed coal blocks; when the hole wall is relatively intact and the drill bit retreat resistance is small, the drill withdrawal speed is accelerated to quickly complete the connection and laying of the protective pipe; when there is a lot of coal slag in the hole and the drill bit retreat resistance is large, the drilling rig is operated to move forward and backward to clear the coal slag blocking the hole, and the drill is slowly withdrawn to complete the connection and laying of the protective pipe.

[0030] The beneficial effects of the present invention are:

[0031] The entire protective tube connection device is a detachable bearing-type movable connection. The two ends of the connector are connected as a whole through high-strength bearings and plugs. One end is fixed to the drill bit and rotates with the drill rod, and the other end is connected to the protective tube. Due to the tension conversion and transmission effect of the tension converter, the protective tube is restricted from axial rotation in the borehole and only horizontal displacement, thereby reducing the torque of the drilling rig operation, that is, from a contact connection to a fixed connection, and from a smooth moving state to a rotating forward state. By changing the connection method, the protective tube changes from unidirectional movement in the borehole to bidirectional movement that can move forward and backward, reducing the difficulty of handling collapsed holes; changing the movement state of the drill bit in the borehole; at the same time, the protective tube connection device is designed with a set of threaded blades and cones with a complete pitch near the outer edge of the drill bit side, which can roll and break coal when the drill rod is withdrawn to lay the protective tube, eliminating the phenomenon of coal block stuck in the drill. In addition, the protective pipe can be laid out by pulling out the drill rig and laying the protective pipe while retracting the drill. On the one hand, the drill rod that has not been withdrawn in the borehole can be used to temporarily support the completed hole wall, reducing the risk of hole collapse. On the other hand, the re-drilling action of the drill rod during the rotation and withdrawal of the drill can be used to remove the residual drill cuttings in the borehole and the coal slag dropped from the partially collapsed hole, reducing the adverse effects of the hole collapse. The two work together to facilitate the smooth movement of the protective pipe in the hole. This invention device and the method for laying protective pipes change the traditional process of first withdrawing all drill rods after drilling a large diameter hole, then inserting the protective pipe, and then reinstalling the drill rod to push the protective pipe in turn. It solves the problem of failure of drilling due to the collapse of the hole when using large diameter drilling to extract gas in coal bodies prone to hole collapse, and improves work efficiency and the success rate of laying protective pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural cross-sectional view of a large-diameter drilling protection pipe connection device in a coal body prone to hole collapse according to the present invention;

[0033] Figure 2 It is a schematic diagram of the connection between the protective tubes of the present invention;

[0034] Figure 3 It is a cross-sectional view of the invented plug structure;

[0035] Figure 4 It is a structural schematic diagram of the use of the present invention for laying protective pipe operations;

[0036] Figure numerals: 1. drill bit connector; 2. tension converter; 3. plug; 4. bearing; 5. baffle; 6. joint; 7. spiral blade; 8. gear; 9. drill bit connecting thread; 10. high-pressure wear-resistant sealing ring; 11. lubricating fluid; 12. ball; 13. pin; 14. protective tube connecting thread; 15. protective tube; 16. bolt eye; 17. bolt; 18. coal seam; 19. large diameter drilling hole; 20. drilling rig; 21. drill rod; 22. drill bit. DETAILED DESCRIPTION

[0037] In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention are described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0038] like Figure 1-Figure 4 As shown, the protective tube connection device for drilling large diameter holes in a coal body prone to collapse provided in this embodiment comprises: a drill connector 1, a tension converter 2, a plug 3, and a bearing 4. The axis of the drill connector 1 is parallel to the axis of the drill bit 22. One side of the drill connector 1 is connected to the drill bit 22. The middle part of the drill connector 1 is a cone device, which includes a spiral blade 7 with a full pitch and a plurality of movable cones 8. One side of the tension converter 2 is hollow with a built-in bearing 4, and the other side is provided with a protective tube connection thread 14, which is used to connect a protective tube 15. The plug 3 passes through the bearing 4 and is connected to the other side of the drill connector 1. The drill connector 1 and the tension converter 2 are connected to form an integral device through the plug 3 and the bearing 4.

[0039] Specifically, the drill connector 1 is a solid cylinder, one side of which is detachably connected to the drill bit 22, for example, by means of threads, latches or buckles. In this embodiment, the drill connector 1 is connected to the drill bit 22 via the drill connecting threads 9 thereon; the other side is detachably connected to the plug 3, for example, by means of threads, latches or buckles. In this embodiment, threaded connection is preferred. The drill connecting threads 9 in the drill connector 1 are rotated and dragged by the power provided by the drill bit 22, driving the drill connector 1 and the spiral blades 7 and the gear 8 fixed thereon to perform spiral forward motion in the drill hole, and the axial spiral forward motion of the drill connector 1 is converted into horizontal displacement forward motion via the bearing 4. The bearing 4 drives the tension converter 2 to perform horizontal displacement forward motion, and the tension converter 2 drives the protective tube 15 to perform horizontal displacement forward motion via the protective tube connecting threads 14;

[0040] As a preferred solution, the spiral blade 7 in the drill bit connector 1 is firmly connected to 1 by welding, and the spiral blade 7 includes one or more spiral blades 7 with a full pitch, and in this embodiment, it is a spiral blade 7 with a full pitch;

[0041] A plurality of cones 8 are welded to the outside of the spiral blades 7 and are evenly arranged along the circumferential direction; the total outer diameter of the cones 8 and the spiral blades 7 is larger than the outer diameter of the protective tube 15 and smaller than the diameter of the drill bit 22;

[0042] The bearing 4 built into the tension converter 2 includes: a high-pressure wear-resistant sealing ring 10, a lubricating liquid 11, and balls 12; the bearing 4 is provided with a plurality of ball tracks, and the number of the ball tracks is not singular; two high-pressure wear-resistant sealing rings 10 are arranged at both ends of the bearing 4, a plurality of balls 12 are placed in the ball tracks, and the lubricating liquid 11 is injected into the ball tracks; the high-pressure wear-resistant sealing ring 10 and the lubricating liquid 11 form a sealing system, which plays a role in lubrication and isolating external gas from entering the interior of the rolling component; the bearing 4 is constituted by the bearing 4 built into the tension converter 2 and the plug 3 together to form an entity.

[0043] As a preferred solution, the plug 3 is a solid cylinder with a baffle 5 at one end. The connecting end of the plug 3 and the tension converter 2 is the inner ring part connected to the bearing 4, which is exposed for a certain length after passing through the bearing 4. A hole perpendicular to the plug 3 is set near the vertical plane of the bearing 4, and its horizontal movement is fixed by a pin 13. In this way, under the joint action of the baffle 5 and the pin 13, the plug 3 is tightly connected to the tension converter 2 to realize the conversion of the power state; the other end of the plug 3 serves as a joint 6 and is detachably connected to the drill connector 1, for example, by a threaded, pin or snap-on connection or other feasible methods. In this embodiment, a threaded connection is preferred.

[0044] Specifically, the outer diameter of the protective tube connection thread 14 on one side of the tension converter 2 is the same as the inner diameter of the protective tube 15, the protective tube 15 has internal threads, and the protective tube connection thread 14 is consistent with the internal thread pitch of the protective tube 15 port, and can be threadedly connected; the subsequent protective tubes 15 are connected by insert bolts or threads; in this embodiment, the insert bolt 17 is preferably inserted into the bolt eye 16 for connection, and threaded connection can be used in other scenarios according to needs.

[0045] In addition, if Figure 4 As shown, this embodiment utilizes the above-mentioned large-diameter drilling protection pipe connection device in the easily collapsed coal body, and also provides a large-diameter drilling protection pipe laying method, and the specific method includes the following steps:

[0046] Step 1: Drilling construction;

[0047] A large diameter borehole 19 is constructed in the coal seam 18 between the return air tunnel and the extraction tunnel by using a drilling machine 20, and the drill bit 22 penetrates the coal pillar and stops drilling after a certain length is exposed;

[0048] Step 2: Assemble the protective tube connection device;

[0049] The inner ring of the bearing 4 connected with the plug 3 and the tension converter 2 is first covered with a suitable high-pressure wear-resistant sealing ring 10, and then the plug 3 is passed through the bearing 4 to make the inner ring and the outer ring of the bearing 4 match correctly, and the balls 12 are put in to fill the ball ring formed between the inner ring and the outer ring. The balls occupy more than 80% of the ball ring, and the lubricating fluid 11 is injected. Another high-pressure wear-resistant sealing ring 10 is installed at the end of the plug 3, and the pin 13 is inserted into the vertical hole at the exposed end to fix and limit its horizontal movement. This operation step makes the tension converter 2 and the plug 3 keep the axial direction perpendicular to the ground, and then the plug 3 is reliably connected to the drill connector 1 through the joint 6; the tension converter 2 and the plug 3 need to be assembled in the vertical direction to facilitate the work of placing the balls and adding the lubricating fluid;

[0050] Step 3: Installation of protective pipe connection device;

[0051] The drill bit connector 1 of the device is firmly connected to the drill bit 22, and the protective tube connecting thread 14 of the tension converter 2 is connected to the internal thread end of the first threaded protective tube 15;

[0052] Step 4: Lay the first section of protective pipe;

[0053] Start the drilling rig 20 to do the drilling withdrawal operation, adjust the drilling rig 20 drilling withdrawal speed and the drill rod 21 rotation speed, ensure that the drill bit 22 slowly and evenly withdraws, use the drilling rig 20 drilling withdrawal action to pull the protective tube 15 into the large diameter borehole 19 section by section, and stop drilling when only the protective tube connection end of the protective tube 15 is exposed.

[0054] Step 5: Laying protective pipe in the whole hole section;

[0055] Add a new protective pipe 15 and fix it to the first section of protective pipe in the hole, repeat step 4, and then repeat the protective pipe connection and step 4 in a loop until the protective pipe laying to the specified depth is completed;

[0056] Step 6: Sealing the hole;

[0057] After the protective pipe 15 is laid in the entire drilling section, the drilling machine 20 is turned off, the protective pipe connection device is disassembled, and the large-diameter drilling and sealing work is carried out at both ends of the coal pillar.

[0058] In the above step 1, the large diameter drill bit 22 needs to be processed and modified in advance, and a detachable connector is installed at the central axis position of the drill bit 22;

[0059] In the above step 3, the corresponding protective tube is selected according to the diameter of the large-diameter drill hole 19; the diameter of the large-diameter drill hole is ≧220 mm; when the diameter of the large-diameter drill hole 19 is 550 mm, the diameter of the protective tube 15 is 426 mm.

[0060] In the above step 5, the protective tubes 15 are connected by insert bolts 17; in some scenarios, the protective tubes are connected by threads;

[0061] During the drilling withdrawal process, according to the collapse of the borehole wall in the large-diameter borehole 19 and the resistance encountered during drilling withdrawal, the drilling withdrawal speed and the advance or retreat of the drill bit 22 are adjusted in time, and the cone 8 on the spiral drill rod 21 and the protective tube connection device is used to cut, destroy and discharge the collapsed coal blocks to ensure the completion of the task of laying the protective tube 15. When the borehole wall is relatively intact and the resistance to drilling bit 22 withdrawal is relatively small, the drilling withdrawal speed can be accelerated to quickly complete the connection and laying of the protective tube 15; when there is a lot of coal slag in the hole and the resistance to drilling bit 22 withdrawal is relatively large, the drilling rig 20 can be operated to move forward and backward to clear the coal slag blocking the hole, and then slowly withdraw the drill to complete the connection and laying of the protective tube 15;

[0062] In the above step 6, the large diameter borehole 19 can be sealed by a combined sealing method of cement sealing and bag grouting sealing according to the actual situation of the drilling construction.

[0063] The above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which are all covered by the protection scope of the present invention.

Claims

1. A large diameter borehole protection pipe connection device for a coal body prone to collapse, characterized in that: It includes a drill connector, a tension converter, a plug, and a bearing. The axis of the drill connector is parallel to the axis of the drill. One side of the drill connector is connected to the drill. One side of the tension converter is hollow with a built-in bearing, and the other side is provided with a protective tube connecting thread. The protective tube connecting thread is used to connect the protective tube. The plug passes through the bearing and is connected to the other side of the drill connector. The drill connector and the tension converter are connected to form an integral device through the bearing and the plug.

2. The large diameter drilling protection pipe connection device for coal bodies prone to collapse according to claim 1 is characterized in that: The middle part of the drill bit connector is a gear unit, which includes one or more spiral blades with full pitch and multiple movable gears; the spiral blades are fixedly connected to the drill bit connector; the gears are connected to the outside of the spiral blades and are evenly arranged along the circumferential direction; the total outer diameter of the gear unit is larger than the outer diameter of the protective tube and smaller than the drill bit diameter.

3. The large diameter drilling protection pipe connection device for coal bodies prone to collapse according to claim 1 is characterized in that: The bearing built into the tension converter includes: a high-pressure wear-resistant sealing ring, a lubricating fluid, and a ball; the bearing is provided with a plurality of concave ball rings; the number of the ball rings is not single; Two high-pressure wear-resistant sealing rings are arranged at both ends of the bearing, a plurality of balls are placed in the ball ring, and lubricating fluid is injected into the ball ring; the high-pressure wear-resistant sealing ring and the lubricating fluid form a sealing system.

4. The large diameter drilling protection pipe connection device for coal bodies prone to collapse according to claim 3 is characterized in that: The plug is a solid cylinder with a baffle at one end. The connecting end of the plug and the tension converter is connected to the inner ring part of the bearing. A hole vertical to the plug is set near the vertical surface of the bearing, and a pin is used to fix it to limit its horizontal movement.

5. The large diameter drilling protection pipe connection device for coal bodies prone to collapse according to claim 1 is characterized in that: The drill bit connector is a solid column, one side of which is detachably connected to the drill bit, and the other side of which is detachably connected to the joint of the plug.

6. The large diameter drilling protection pipe connection device for coal bodies prone to collapse according to claim 1 is characterized in that: The outer diameter of the protective tube connection thread end on one side of the tension converter is the same as the inner diameter of the protective tube, the protective tube is internally threaded, the protective tube connection thread is consistent with the internal thread pitch of the protective tube port, and can be threadedly connected.

7. A method for laying protective pipes in large-diameter boreholes, the method using the large-diameter borehole protective pipe connection device in a coal body prone to collapse as claimed in any one of claims 1 to 6, characterized in that: The specific method includes the following steps: Step 1: Drilling construction; Use a drilling rig to drill a large diameter hole in the coal seam between the return air tunnel and the extraction tunnel. The drill bit penetrates the coal pillar and stops drilling when a certain length is exposed. Step 2: Assemble the protective tube connection device; The inner ring of the bearing where the plug is connected to the tension converter is first covered with a matching high-pressure wear-resistant sealing ring. Then, after the plug is passed through the bearing, the inner ring and outer ring of the bearing are correctly matched. Balls are put in to fill the ball ring formed between the inner ring and the outer ring. Lubricating fluid is injected. Another high-pressure wear-resistant sealing ring is installed at the end of the plug. A pin is inserted into the vertical hole at the exposed end to fix and restrict its horizontal movement. The tension converter and the plug are kept axially perpendicular to the ground. The plug is connected to the drill connector. Step 3: Installation of protective pipe connection device; The drill bit connector of the device is firmly connected to the connecting head of the drill bit, and the protective tube connecting thread of the tension converter is connected to the internal thread end of the first section of the threaded protective tube; Step 4: Lay the first section of protective pipe; Start the drilling rig to withdraw the drill, adjust the drilling rig's withdrawal speed and the drill rod rotation speed, so that the drill bit slowly and evenly withdraws, and use the drilling rig's withdrawal action to pull the protective tube into the borehole section by section, and stop drilling when only the protective tube connection end is exposed; Step 5: Laying protective pipe in the whole hole section; Add a new protective pipe to connect it to the first section of protective pipe in the hole, repeat step 4, and repeat the protective pipe connection and step 4 in a cycle until the protective pipe laying to the specified depth is completed; Step 6: Sealing the hole; After the protective pipe is laid in the entire drilling section, the drilling rig is shut down, the protective pipe connection device is removed, and the large-diameter drilling and sealing work is carried out at both ends of the coal pillar.

8. A method for laying protective pipes in large-diameter drilling holes according to claim 7, characterized in that: In step 6, a combined sealing method of cement sealing and bag grouting sealing is selected for large-diameter drilling holes according to the actual situation of the drilling construction.

9. A method for laying protective pipes in large-diameter drilling holes according to claim 7, characterized in that: In step 3, select the corresponding protective tube according to the diameter of the large-diameter drilling hole; the diameter of the large-diameter drilling hole is ≧220mm; in step 1, the drill bit is processed and modified in advance, and a detachable connector is installed at the center axis position of the drill bit.

10. A method for laying protective pipes in large-diameter drilling holes according to claim 7, characterized in that: In step 5, the protective pipes are connected by plug-in bolts or threads; during the drill withdrawal process, the drill withdrawal speed and the advance or retreat of the drill bit are adjusted in time according to the collapse of the hole wall in the large-diameter borehole and the resistance to drill withdrawal, and the cones on the spiral drill rod and the protective pipe connecting device are used to cut, destroy and discharge the collapsed coal blocks; when the hole wall is relatively intact and the drill bit retreat resistance is small, the drill withdrawal speed is accelerated to quickly complete the connection and laying of the protective pipe; when there is a lot of coal slag in the hole and the drill bit retreat resistance is large, the drill rig is operated to move forward and backward to clear the coal slag blocking the hole, and the drill is slowly withdrawn to complete the connection and laying of the protective pipe.

Images