Large-diameter drill hole casing pipe connecting device and casing pipe laying method in easy-collapsing coal body

Abstract

This invention belongs to the field of coal mine gas control technology, and particularly relates to a connection device and method for laying protective casing in large-diameter boreholes in easily collapsed coal seams. The device includes a drill bit connector, a force 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 force converter has a hollow interior bearing, and the other side has a protective casing connection thread for connecting the protective casing. The plug passes through the bearing and connects to the other side of the drill bit connector. The method for laying the protective casing includes drilling; assembling the protective casing connection device; installing the protective casing connection device; laying the first section of protective casing; laying the protective casing throughout the entire borehole; and sealing the borehole. The protective casing in this invention changes from unidirectional movement within the borehole to bidirectional movement that allows for both forward and backward movement, reducing the difficulty of handling collapsed boreholes. The laying method changes the traditional top-insertion method to a pull-out method, laying the protective casing while retracting the drill rod, which can utilize the rotation and retraction of the drill rod to remove coal slag and collapsed coal blocks from the borehole.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas control technology, and particularly relates to a connection device for large-diameter borehole protective pipes and a method for laying protective pipes in easily collapsed coal bodies. Background Technology

[0002] To address the issue of excessive gas levels in the upper corner of the working face, some mines have adopted a method of drilling large-diameter boreholes in the coal pillar between the return airway and the extraction roadway, embedding protective pipes of a certain diameter within them, and then connecting them to the extraction system. This has solved the problem of excessive gas levels in the upper corner of the working face. The currently common procedure for laying protective pipes is as follows: after drilling to the designated position, the drill is withdrawn, and the thrust of the drilling rig is used to push the protective pipes section by section into the borehole, completing the installation of the protective pipes.

[0003] Due to varying coal seam conditions in different regions, large-diameter boreholes completed in areas with softer coal often collapse during or within hours of drilling withdrawal, preventing the installation of the casing and causing borehole failure. While current solutions to borehole collapse include pre-grouting in the large-diameter borehole construction area to strengthen the coal seam before drilling, and improving drilling structure and construction techniques by laying casing as drilling progresses, actual underground coal mine operations are hampered by coal seam conditions and borehole layout parameters. The abundance of bedding, joints, and various geological structures within the coal seam makes grout distribution unpredictable during pre-grouting. It's difficult to evenly cover the large-diameter borehole construction area, especially with longer boreholes, resulting in inadequate protection and limiting the effectiveness and application of grouting in preventing borehole collapse. Meanwhile, during the drilling and laying process, when the coal seam is too soft or the soft and hard strata are obliquely intersecting the borehole direction, drill cuttings and coal slag can clog the connection between the drill rod and the casing, or between the casing and the borehole wall, causing the drilling to become uncontrolled and severely affecting drilling efficiency. The casing is generally made of iron, and the high-speed rotation of the drill rod inside the casing inevitably generates frictional sparks with the inner wall of the casing, posing a significant threat to coal mine safety.

[0004] The aforementioned factors limit the application of gas control technology in the upper corner of large-diameter boreholes. Therefore, new methods for preventing borehole collapse and new processes for laying protective casings are needed to improve the success rate of casing laying and the safety of the construction process. Summary of the Invention

[0005] To address the above problems, this invention provides a large-diameter borehole casing connection device for easily collapsible coal seams. This device changes the connection method between the casing and the drill bit, as well as the movement state of the casing within the borehole. Traditionally, when inserting the casing, the drill bit only makes horizontal displacement and cannot rotate. This invention reduces the frictional resistance between the drill bit / drill rod and the borehole wall, and the rotating and retracting motion also serves to remove slag, preventing borehole blockage. Furthermore, this invention uses the device to provide a casing laying method, changing the traditional top-insertion method to a pull-out method. Ultimately, this ensures rapid and reliable casing laying within large-diameter boreholes in easily collapsible coal seams and when soft and hard strata intersect with the borehole, improving borehole formation rate and achieving the goal of controlling gas in the upper corner.

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

[0007] A large-diameter borehole casing connection device for easily collapsible coal seams includes a drill bit connector, a force 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 force converter has a hollow built-in bearing, and the other side has a casing connection thread for connecting the casing. The casing connection thread is used to connect the casing. The plug passes through the bearing and connects to the other side of the drill bit connector. The drill bit connector and the force converter are connected as a whole device through the bearing and the plug.

[0008] Furthermore, the drill bit connector has a roller cone assembly in the middle, which includes one or more helical blades with a complete pitch and multiple movable roller cones; the helical blades are fixedly connected to the drill bit connector; the roller cones are connected to the outside of the helical blades and are evenly arranged along the circumference; the total outer diameter of the roller cone assembly is larger than the outer diameter of the casing and smaller than the diameter of the drill bit.

[0009] Furthermore, the bearing built into the force converter includes: a high-pressure wear-resistant seal ring, lubricant, and balls; the bearing has several concave ball raceways; the number of ball raceways is not singular;

[0010] Two high-pressure wear-resistant sealing rings 10 are set at both ends of the bearing 4, multiple balls are placed in the ball ring channel, and lubricant is injected into the ball ring channel; the high-pressure wear-resistant sealing rings and lubricant form a sealing system.

[0011] Furthermore, the plug is a solid cylinder with a baffle at one end. The connection end between the plug and the force converter is the inner ring part of the bearing. A hole for 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, with one side detachably connected to the drill bit and the other side detachably connected to the plug connector.

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

[0014] A method for laying protective casing in large-diameter boreholes, comprising the following steps: (The method utilizes a large-diameter borehole protective casing connection device in easily collapsible coal seams.)

[0015] Step 1: Drilling;

[0016] In the coal seam between the return airway and the extraction roadway, a large-diameter borehole is drilled using a drilling rig. The drill bit penetrates the coal pillar and stops drilling when a certain length is exposed.

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

[0018] First, fit a suitable high-pressure wear-resistant seal ring onto the inner ring of the bearing that connects the plug to the force converter. After passing the plug through the bearing, ensure that the inner and outer rings of the bearing are correctly matched. Insert ball bearings to fill the ball bearing channel formed between the inner and outer rings, inject lubricant, install another high-pressure wear-resistant seal ring at the end of the plug, and insert a pin into the vertical hole at the exposed end to fix and restrict its horizontal movement, so that both the force converter and the plug remain axially perpendicular to the ground. Connect the plug to the drill bit connector.

[0019] Step 3: Install the protective pipe connection device;

[0020] Securely connect the drill bit connector of the device to the drill bit connector, and connect the threaded end of the protective tube of the tension converter to the internal thread end of the first threaded protective tube.

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

[0022] Start the drilling rig to perform the retraction operation, adjust the retraction speed of the drilling rig and the rotation speed of the drill rod, so that the drill bit retracts slowly and at a constant speed. Use the retraction action of the drilling rig to pull the casing into the borehole section by section. Stop drilling when only the casing connection end is exposed.

[0023] Step 5: Lay the protective pipe along the entire borehole section;

[0024] Connect the new protective pipe to the first section of the protective pipe in the hole, repeat step 4, and then repeat the process of adding the protective pipe and step 4 in a cycle until the protective pipe is laid to the specified depth.

[0025] Step 6: Seal the holes;

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

[0027] Furthermore, in step 6, the sealing of large-diameter boreholes is carried out by selecting a combination of cement sealing and bag-type grouting sealing methods based on the actual drilling conditions.

[0028] Furthermore, in step 3, a corresponding protective casing is selected based on the diameter of the large-diameter borehole; the diameter of the large-diameter borehole is ≥220mm; in step 1, the drill bit is pre-processed and modified, and a detachable connector is installed at the center axis position of the drill bit.

[0029] Furthermore, in step 5, the casings are connected by internal bolts or by threads. During the retraction process, the retraction speed and the forward or backward movement of the drill bit are adjusted in a timely manner according to the collapse of the borehole wall in the large-diameter borehole and the resistance encountered during retraction. The toothed cones on the auger rod and casing connection device are used to cut and destroy the collapsed coal blocks. When the borehole wall is relatively intact and the resistance of the drill bit retraction is small, the retraction speed is increased to quickly complete the connection and laying of the casing. When there is a lot of coal slag in the borehole and the resistance of the drill bit retraction is large, the drilling rig is operated to move forward and backward to clear the coal slag blocking the borehole, and the drill is slowly retracted to complete the connection and laying of the casing.

[0030] The beneficial effects of this invention are:

[0031] The entire casing connection device is a detachable bearing-type movable connection. The connector ends are integrated via high-strength bearings and plugs. One end is fixed to the drill bit and rotates with the drill rod, while the other end connects to the casing. Due to the force conversion and transmission function of the force converter, the casing does not rotate axially within the borehole, only moving horizontally. This reduces the torque force on the drilling rig, changing the connection from a contact type to a fixed type, and from smooth movement to a rotating forward movement. This change in connection method transforms the casing's movement within the borehole from unidirectional to bidirectional (forward and backward) movement, reducing the difficulty of handling borehole collapse. It also changes the drill bit's movement within the borehole. Furthermore, the casing connection device features a series of threaded blades and rollers with complete pitches near the outer edge of the drill bit side. These allow for rolling and breaking of coal during casing installation, eliminating coal block jamming. Furthermore, utilizing the drilling rig's retraction motion to pull out and lay the protective casing simultaneously with drilling retraction serves two purposes. First, the remaining drill rods inside the borehole provide temporary support to the completed borehole wall, reducing the risk of borehole collapse. Second, the retraction motion of the drill rods during retraction removes residual drill cuttings and some coal slag that has fallen due to borehole collapse, mitigating the adverse effects of collapse. These two combined effects facilitate smooth movement of the protective casing within the borehole. This invention and its protective casing laying method change the traditional process of retracting all drill rods after completing a large-diameter borehole, then inserting the protective casing, and then reinstalling the drill rods to push the casing in sequentially. It solves the problem of borehole failure in easily collapsible coal seams where large-diameter boreholes used for gas extraction cannot smoothly insert the protective casing due to borehole collapse, thus improving work efficiency and the success rate of protective casing laying. Attached Figure Description

[0032] Figure 1 This is a structural cross-sectional view of the large-diameter borehole casing connection device in easily collapsed coal seams according to the present invention;

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

[0034] Figure 3 Cross-sectional view of the plug structure for the invention;

[0035] Figure 4 This is a schematic diagram of the structure used when laying protective pipes using the present invention;

[0036] Reference numerals: 1. Drill bit connector; 2. Force converter; 3. Plug; 4. Bearing; 5. Baffle; 6. Joint; 7. Helical blade; 8. Roller cone; 9. Drill bit connection thread; 10. High-pressure wear-resistant sealing ring; 11. Lubricating fluid; 12. Ball bearing; 13. Pin; 14. Threaded connection of protective tube; 15. Protective tube; 16. Bolt eye; 17. Bolt; 18. Coal seam; 19. Large-diameter borehole; 20. Drilling rig; 21. Drill rod; 22. Drill bit. Detailed Implementation

[0037] To better explain and facilitate understanding of the present invention, the technical solution and effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] like Figures 1-4 As shown in the figure, the large-diameter borehole casing connection device for easily collapsed coal seams provided in this embodiment includes: a drill bit connector 1, a tension converter 2, a plug 3, and a bearing 4. The axis of the drill bit connector 1 is parallel to the axis of the drill bit 22. One side of the drill bit connector 1 is connected to the drill bit 22. The middle part of the drill bit connector 1 is a roller device, which includes a spiral blade 7 with a complete pitch and multiple movable rollers 8. The tension converter 2 has a hollow bearing 4 built into one side and a casing connection thread 14 on the other side. The casing connection thread 14 is used to connect the casing 15. The plug 3 passes through the bearing 4 and is connected to the other side of the drill bit connector 1. The drill bit connector 1 and the tension converter 2 are connected into a whole device through the plug 3 and the bearing 4.

[0039] Specifically, the drill bit connector 1 is a solid cylinder. One side is detachably connected to the drill bit 22, for example, by threads, pins, or snap-fits. In this embodiment, the drill bit connector 1 is connected to the drill bit 22 via the drill bit connecting thread 9. The other side is detachably connected to the plug 3, for example, by threads, pins, or snap-fits. In this embodiment, a threaded connection is preferred. The drill bit connector 1 is rotated by the power provided by the drill bit 22 via the drill bit connecting thread 9, causing the drill bit connector 1 and its fixedly connected helical blades 7 and rollers 8 to perform a helical forward motion in the borehole. The bearing 4 converts the axial helical forward motion of the drill bit connector 1 into a horizontal forward motion. The bearing 4 drives the force converter 2 to perform a horizontal forward motion, and the force converter 2 drives the protective tube 15 to perform a horizontal forward motion via the protective tube connecting thread 14.

[0040] As a preferred embodiment, the helical blade 7 in the drill bit connector 1 is firmly connected to 1 by welding. The helical blade 7 includes one or more helical blades 7 with a complete pitch. In this embodiment, it is a helical blade 7 with a complete pitch.

[0041] Multiple roller cones 8 are welded to the outside of the spiral blades 7 and are evenly arranged along the circumference; the total outer diameter of the roller cones 8 and the spiral blades 7 is greater 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 force converter 2 includes: a high-pressure wear-resistant seal ring 10, a lubricant 11, and balls 12; the bearing 4 has several ball ring channels, and the number of ball ring channels is not singular; two high-pressure wear-resistant seal rings 10 are set at both ends of the bearing 4, multiple balls 12 are placed in the ball ring channels, and the lubricant 11 is injected into the ball ring channels; the high-pressure wear-resistant seal rings 10 and the lubricant 11 form a sealing system, which plays the role of lubricating and isolating external gas from entering the interior of the rolling assembly; the bearing 4 is a solid entity composed of the bearing 4 built into the force converter 2 and the plug 3.

[0043] As a preferred embodiment, the plug 3 is a solid cylinder with a baffle 5 at one end. The end of the plug 3 that connects to the force converter 2 is the inner ring of the bearing 4. After passing through the bearing 4, it protrudes to a certain length. A hole is set in the plug 3 vertically near the vertical surface of the bearing 4. The horizontal movement of the plug is restricted by the pin 13. In this way, under the combined action of the baffle 5 and the pin 13, the plug 3 is tightly connected to the force converter 2, realizing the conversion of the power state. The other end of the plug 3 serves as a connector 6 and is detachably connected to the drill bit connector 1. For example, it can be connected by threads, pins, or snap-fit ​​connections or other feasible methods. In this embodiment, a threaded connection is preferred.

[0044] Specifically, the outer diameter of the threaded end of the protective tube 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 thread pitch of the connecting thread 14 and the internal thread at the port of the protective tube 15 are the same, and they can be connected by threads. Subsequently, the protective tubes 15 are connected by internal bolts or by threads. In this embodiment, it is preferred to insert the internal bolt 17 into the bolt eye 16 for connection. In other scenarios, threads can be used as needed.

[0045] In addition, such as Figure 4 As shown, this embodiment utilizes the aforementioned large-diameter borehole casing connection device in easily collapsible coal seams, and also provides a method for laying casing in large-diameter boreholes. The specific method includes the following steps:

[0046] Step 1: Drilling;

[0047] In the coal seam 18 between the return airway and the extraction roadway, a large-diameter borehole 19 is drilled using a drilling rig 20. The drill bit 22 penetrates the coal pillar and stops drilling when a certain length is exposed.

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

[0049] First, a suitable high-pressure wear-resistant seal ring 10 is fitted onto the inner ring of the bearing 4, which is connected to the plug 3 and the force converter 2. Then, after the plug 3 passes through the bearing 4, the inner ring and outer ring of the bearing 4 are correctly matched. Balls 12 are inserted to fill the ball annular channel formed between the inner and outer rings, with the balls occupying more than 80% of the ball annular channel. Lubricant 11 is injected. Another high-pressure wear-resistant seal ring 10 is installed at the end of the plug 3. A pin 13 is inserted into the vertical hole at the exposed end to fix and restrict its horizontal movement. This operation step keeps the force converter 2 and the plug 3 axially perpendicular to the ground. Then, the plug 3 is reliably connected to the drill bit connector 1 through the joint 6. The force converter 2 and the plug 3 need to be assembled in the vertical direction to facilitate the placement of balls and the addition of lubricant.

[0050] Step 3: Install the protective pipe connection device;

[0051] Securely connect the drill bit connector 1 of the device to the drill bit 22, and connect the protective tube connection thread 14 of the tension converter 2 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 perform the retraction operation. Adjust the retraction speed of the drilling rig 20 and the rotation speed of the drill rod 21 to ensure that the drill bit 22 retracts slowly and at a constant speed. Use the retraction action of the drilling rig 20 to pull the protective casing 15 into the large-diameter borehole 19 section by section. Stop drilling when only the protective casing 15 is exposed at the connection end of the protective casing.

[0054] Step 5: Lay the protective pipe along the entire borehole section;

[0055] Add a new protective tube 15 and fix it to the first section of the protective tube in the hole. Repeat step 4. Then repeat the process of adding the protective tube and step 4 in a cycle until the protective tube is laid to the specified depth.

[0056] Step 6: Seal the holes;

[0057] After the protective casing 15 is laid in the entire borehole section, the drilling rig 20 is shut down, the protective casing connection device is removed, and the large-diameter borehole sealing work at both ends of the coal pillar is carried out.

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

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

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

[0061] During the retraction process, the retraction speed and the forward or backward movement of the drill bit 22 are adjusted in a timely manner according to the collapse of the inner wall of the large-diameter borehole 19 and the resistance encountered during retraction. The rollers 8 on the auger rod 21 and the casing connection device are used to cut, break, and remove the collapsed coal blocks, ensuring the completion of the casing 15 laying task. When the borehole wall is relatively intact and the retraction resistance of the drill bit 22 is small, the retraction speed can be increased to quickly complete the connection and laying of the casing 15. When there is a lot of coal slag in the borehole and the retraction resistance of the drill bit 22 is large, the drilling rig 20 can be operated to move forward and backward to clear the coal slag blocking the borehole, and then the drill can be slowly retracted to complete the connection and laying of the casing 15.

[0062] In step 6 above, the sealing of the large-diameter borehole 19 can be achieved by a combination of cement sealing and bag-type grouting sealing, depending on the actual drilling conditions.

[0063] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, are covered within the scope of protection of the present invention.

Claims

1. A connection device for large-diameter borehole casing in easily collapsed coal seams, characterized in that, The device includes a drill bit connector, a force 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 force converter has a hollow built-in bearing, and the other side is provided with a protective tube connection thread for connecting a protective tube. The plug passes through the bearing and connects to the other side of the drill bit connector. The drill bit connector and the force converter are connected as a whole device through the bearing and the plug. The drill bit connector has a roller cone assembly in the middle, which includes one or more helical blades with a complete pitch and multiple movable roller cones; the helical blades are fixedly connected to the drill bit connector; the roller cones are connected to the outside of the helical blades and are evenly arranged along the circumference. The total outer diameter of the roller cone assembly is larger than the outer diameter of the casing but smaller than the drill bit diameter. The bearing built into the tension converter includes: a high-pressure wear-resistant seal ring, lubricant, and balls; the bearing has several concave ball annular channels; the number of ball annular channels is not singular; Two high-pressure wear-resistant seals are placed at both ends of the bearing, and multiple balls are placed in the ball ring channel. Lubricant is injected into the ball ring channel; the high-pressure wear-resistant seals and lubricant form a sealing system. The plug is a solid cylinder with a baffle at one end. The connection end between the plug and the force converter is the inner ring part of the bearing. A hole for the plug is set near the vertical surface of the bearing, and its horizontal movement is restricted by a pin.

2. The large-diameter borehole casing connection device for easily collapsible coal seams according to claim 1, characterized in that, The drill bit connector is a solid cylinder, with one side detachably connected to the drill bit and the other side detachably connected to the plug connector.

3. The large-diameter borehole casing connection device for easily collapsible coal seams according to claim 1, characterized in that, The outer diameter of the threaded end of the protective tube on one side of the tension converter is the same as the inner diameter of the protective tube. The protective tube has an internal thread, and the pitch of the connecting thread of the protective tube is the same as that of the internal thread of the protective tube port, and they can be threaded together.

4. A method for laying protective pipes in large-diameter boreholes, wherein the method employs the large-diameter borehole protective pipe connection device in easily collapsible coal seams as described in any one of claims 1-3, characterized in that, The specific method includes the following steps: Step 1: Drilling; In the coal seam between the return airway and the extraction roadway, a large-diameter borehole is drilled using a drilling rig. The drill bit penetrates the coal pillar and stops drilling when a certain length is exposed. Step 2: Assemble the protective pipe connection device; First, fit a suitable high-pressure wear-resistant seal ring onto the inner ring of the bearing that connects the plug to the force converter. Then, after the plug passes through the bearing, ensure that the inner and outer rings of the bearing are correctly matched. Insert ball bearings to fill the ball bearing channel formed between the inner and outer rings, inject lubricant, install another high-pressure wear-resistant seal ring at the end of the plug, and insert a pin into the vertical hole at the exposed end to fix and restrict its horizontal movement, so that both the force converter and the plug remain axially perpendicular to the ground. Connect the plug to the drill bit connector. Step 3: Install the protective pipe connection device; Securely connect the drill bit connector of the device to the drill bit connector, and connect the threaded end of the protective tube of the tension converter to the internal thread end of the first threaded protective tube. Step 4: Lay the first section of protective pipe; Start the drilling rig to perform the retraction operation, adjust the retraction speed of the drilling rig and the rotation speed of the drill rod, so that the drill bit retracts slowly and at a constant speed. Use the retraction action of the drilling rig to pull the casing into the borehole section by section. Stop drilling when only the casing connection end is exposed. Step 5: Lay the protective pipe along the entire borehole section; Connect the new protective pipe to the first section of the protective pipe in the hole, repeat step 4, and repeat the process of adding the protective pipe and step 4 in a cycle until the protective pipe is laid to the specified depth. Step 6: Seal the holes; After the protective casing is laid in the entire borehole section, the drilling rig is shut down, the protective casing connection device is removed, and the large-diameter borehole sealing work at both ends of the coal pillar is carried out.

5. The method for laying protective pipes in large-diameter boreholes according to claim 4, characterized in that, In step 6, for large-diameter borehole sealing, a combination of cement sealing and bag-type grouting sealing is selected based on the actual drilling conditions.

6. The method for laying protective pipes in large-diameter boreholes according to claim 4, characterized in that, In step 3, select the appropriate protective casing according to the diameter of the large-diameter borehole; the diameter of the large-diameter borehole is ≥220mm; in step 1, process and modify the drill bit in advance, and install a detachable connector at the center axis of the drill bit.

7. The method for laying protective pipes in large-diameter boreholes according to claim 4, characterized in that, In step 5, the casing pipes are connected by internal bolts or threads. During the retraction process, the retraction speed and the forward or backward movement of the drill bit are adjusted in a timely manner according to the collapse of the borehole wall in the large-diameter borehole and the resistance encountered during retraction. The toothed cones on the auger rod and casing pipe connection device are used to cut and destroy the collapsed coal blocks. When the borehole wall is relatively intact and the resistance of the drill bit retraction is small, the retraction speed is increased to quickly complete the connection and laying of the casing pipe. When there is a lot of coal slag in the borehole and the resistance of the drill bit retraction is large, the drilling rig is operated to move forward and backward to clear the coal slag blocking the borehole, and the drill is slowly retracted to complete the connection and laying of the casing pipe.

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