Method for improving coal recovery rate of screw drill based on directional reaming

Abstract

The application discloses a method for improving the coal extraction rate of a spiral drill based on directional reaming, and belongs to the technical field of coal mining, and aims to solve the problem that the existing process is limited in the coal extraction rate due to a large number of isolated coal pillars. The method comprises the following steps: driving a drilling machine to drill in a straight line, stopping at a safe distance L1 away from the air return roadway, reserving the roadway side solid coal and forming an initial borehole with an initial solid isolated coal pillar; in the process of reaming out, a deflection mechanism is activated to make the drill bit deflect by an angle alpha for lateral cutting and reaming; after combined monitoring inside and outside the borehole, when the drill bit is reamed out to a safe distance L2 away from the machine rail roadway, the drill bit resumes a straight line state to stop reaming, and the roadway side protective coal pillar is reserved; after the drill is withdrawn, a built-in rib flexible mold bag is used to block the borehole. The application integrates reaming into the reaming-out process, accurately cuts and reserves the solid isolated coal pillar in a plastic yield state, realizes the partial controllable recovery of the isolated coal pillar under the premise of safety, and significantly improves the coal extraction rate.

Description

Technical Field

[0001] This invention belongs to the field of coal mining and relates to a high-extraction mining method for thin and extremely thin coal seams, specifically a method for improving the extraction rate of spiral drilling coal mining based on directional borehole enlargement. Background Technology

[0002] Spiral drilling is a specialized coal mining technique suitable for recovering thin coal seams, marginal coal seams, and irregular coal pillars. Its core process involves using a high-powered spiral drilling machine to drive the drill rod and drill bit through the coal seam between two parallel roadways. Simultaneously, rotating spiral blades continuously transport the broken coal into the roadway. This method offers advantages such as low equipment investment, relatively simple process, low roadway excavation rate, and no need for personnel to enter the goaf. However, to prevent air leakage from the working face, gas and water inrush from the goaf, or roadway collapse due to borehole breakthrough, and to ensure mining safety, current spiral drilling techniques require the extensive use of inter-bore isolation coal pillars. These conservatively placed pillars, for safety reasons, typically limit the overall extraction rate of the working face, resulting in valuable coal resources being permanently left underground.

[0003] Although improving extraction rate is a long-term goal pursued by the industry, the existing auger drilling coal mining method has obvious bottlenecks: on the one hand, reducing the coal pillar by optimizing the borehole layout spacing is limited by the mechanical properties of the roof rock, and there is a safety limit to the reduction of the spacing, which cannot be reduced indefinitely; on the other hand, although improving the drilling rig power or drilling depth can increase the output per hole, it does not change the mining mode and cannot fundamentally solve the technical problem of "how to safely recover the isolated coal pillar".

[0004] Therefore, there is an urgent need in this field for an innovative technical solution that can partially and controllably recover the reserved isolation coal pillars while strictly ensuring the safety and stability of roadways and goaf areas, thereby finding the best balance between technical feasibility and economic efficiency and achieving efficient and high-recovery mining of thin coal seams. Summary of the Invention

[0005] To overcome the above shortcomings, the present invention provides a method for improving the coal extraction rate of auger drilling based on directional borehole enlargement.

[0006] This invention is applicable to thin or extremely thin coal seams with a thickness of 0.3m-1.3m, targeting conventional thin coal seam mining conditions where the roof is moderately to stable, there are no strict surface settlement control requirements, and the goal is to achieve minimal processes and the lowest mining costs. This invention requires no additional equipment; instead, it directly utilizes the spiral drilling rig's own system to achieve simultaneous retreat and mining. Specifically, during the drilling retreat process, the drill bit is controlled to laterally cut and enlarge the initial borehole, partially thinning and recovering the initial solid isolation coal pillars that must be left over a large area in traditional processes. While strictly preserving the solid coal in the roadway sides, the protective coal pillars in the roadway sides, and the solid isolation coal pillars in the hole-hole state under plastic yielding conditions, this invention ensures the sealing of the goaf and the stability of the surrounding rock in the roadway, achieving a dual improvement in safety and extraction rate.

[0007] This invention provides a method for improving the coal extraction rate of auger drilling based on directional borehole enlargement, comprising the following steps: A. Arrange a machine track roadway and a return air roadway in the thin coal seam working face, and place the spiral drilling coal mining machine and its supporting equipment in the machine track roadway; B. Start the spiral drilling coal mining machine and drive the drill bit to drill into the coal body in a straight line. At the same time, the crushed coal is continuously transported into the machine track roadway until the drill bit tip is at the first preset safety distance L1 from the side of the return air roadway, and then stop drilling to form an initial borehole. According to the mining design, an initial solid isolation coal pillar with a width of D is left between the initial borehole and the adjacent planned borehole. C. After stopping drilling, begin retracting the drill bit; during the retraction process, the main control console on the auger coal mining machine sends a command to activate the deflection mechanism of the drill bit, causing the drill bit axis to deflect at a preset angle α relative to the initial borehole axis, and relying on the deflection posture to perform lateral cutting and enlarging of the side coal wall of the initial borehole. D. During the directional reaming process, the drill bit attitude and position are monitored in real time by a monitoring device; when the drill bit retracts to the second preset safety distance L2 from the side of the machine track roadway, the main control console sends a return signal, the drill bit returns to a straight state, and the reaming stops; E. After the drill string is completely withdrawn, immediately seal the borehole opening. F. Repeat steps B to E, and perform drilling, enlargement, and plugging operations on each borehole in sequence along the working face advance direction until the entire working face is mined out.

[0008] Furthermore, in step A, the auger coal mining machine is a multi-axis auger coal mining machine that includes multiple parallel drilling tools; the auger coal mining machine also includes a displacement sensor and a measurement while drilling (MWD) probe.

[0009] This invention customizes the front-end drilling tool assembly of existing spiral drilling coal mining machines. Multiple parallel drilling tools, i.e., the front-end drilling tool assembly, include 1-2 rigid linear drilling tools in the middle and articulated directional drilling tools at the left and right ends. Each drilling tool includes a drill bit and a drill rod. The drill bit of the rigid linear drilling tool is connected to the rear spiral drill rod via a rigid coupling, maintaining a straight line throughout the operation and serving as a stable base for lateral deflection thrust. The drill bit of the articulated directional drilling tool is connected to the rear spiral drill rod via a universal joint coupling.

[0010] The deflection operation of the articulated directional drilling tool is achieved by a deflection mechanism. This mechanism uses conventional components, primarily including a hydraulic thrust mechanism and an electro-hydraulic control valve assembly installed between the non-rotating support sleeves of adjacent drilling tools. The electro-hydraulic control valve assembly is communicatively connected to the main control console in the drilling rig roadway via a control cable laid during drilling, and is used to receive and execute deflection or return-to-center commands. The "universal joint coupling + non-rotating support sleeve + hydraulic thrust mechanism" proposed in this invention is a specially designed combined structure.

[0011] The displacement sensor is mounted on the push-pull slide of the auger coal mining machine in the track roadway and is used to measure the depth distance of the drill bit. The measurement-while-drilling (MWD) probe is arranged in the drill pipe cavity to obtain the attitude and position of the drill bit.

[0012] Furthermore, in step B, the value range of the first preset safety distance L1 is 2m-5m; the hole width of the initial borehole is determined by the drill bit size and arrangement of the spiral drilling coal mining machine, and its hole width ranges from 0.3m to 3.0m; the value range of the width D of the initial solid isolation coal pillar is 0.4m-2.0m.

[0013] Further, in step C, the preset angle α ranges from 2° to 10°; the lateral cutting and reaming is continuously implemented for each borehole within the working face, and its specific implementation process is as follows: after the operator issues a command through the main control console, the electro-hydraulic control valve group drives the hydraulic thrust mechanism to extend outward, using the adjacent un-deflected drill bit in the middle as a support base, forcing the edge articulated directional drill bit to deflect outward relative to the borehole center axis by a preset angle α in a plane parallel to the coal seam; this edge articulated directional... During the retraction and rotation of the drill bit, the drill bit continuously performs lateral cutting on the initial solid isolation coal pillar with a width of D. This isolation coal pillar is thinned by cutting on one side when each of the two adjacent boreholes is retracted and enlarged. By precisely controlling the unilateral deflection cutting amount of the current borehole, it is ensured that a solid isolation coal pillar with a thickness of M of 0.2m-1.0m is always maintained between the current enlarged section and the adjacent mined goaf. This isolation coal pillar with a thickness of M is in a plastic yielding state and acts as an isolation zone to prevent air leakage from the goaf.

[0014] Furthermore, in step D, the real-time monitoring is achieved through combined in-hole and out-of-hole monitoring. In-hole monitoring specifically involves integrating a measurement while drilling (MWD) probe into the non-magnetic drill rod cavity adjacent to the drill bit. The probe contains an inclinometer and an azimuth sensor, and transmits the real-time deflection attitude of the drill bit to the main control console via signal transmission to verify whether the deflection angle has reached the preset α value. Out-of-hole monitoring specifically involves installing a displacement sensor on the push-pull slide of the auger coal mining machine main unit, and calculating the depth position of the drill bit in the hole in real time by recording the slide's movement stroke.

[0015] Furthermore, in steps C and D, the control system of the main control console includes a PLC module. To prevent excessive hole enlargement and damage to the roadway walls due to human error or delay in judgment, when the PLC module determines, based on data from the external displacement sensor, that the current retraction depth has reached the second preset safety distance L2, the PLC module transmits a return-to-center signal to the electro-hydraulic control valve group inside the hole via the control cable. Upon receiving the signal, the electro-hydraulic control valve group drives the hydraulic thrust mechanism to retract, restoring the articulated directional drill bit at the edge to a straight state and stopping the hole enlargement. Simultaneously, the control system is compatible with manual return-to-center commands issued by the operator.

[0016] Furthermore, in step E, for the large-span flat borehole formed by the multi-axis spiral drilling coal mining machine, a double-layer flexible formwork bag with built-in tie rods matching the borehole cross-section is adopted. The built-in tie rods refer to high-strength flexible tension members connecting the upper and lower inner walls within the formwork bag, and the ends of the formwork bag are equipped with grouting pipes and venting pipes.

[0017] The specific method of sealing is as follows: a long-distance mechanized pumping sealing technology is employed. In the machine-railway roadway, the flexible manhole cover is pushed into the borehole to a predetermined depth using a feeding rod. Subsequently, a grouting pump within the roadway is connected, pumping a highly fluid grout without coarse aggregate into the manhole cover. The manhole cover expands under the pressure of the grout. Internal reinforcing bars tighten when the grout expands, limiting excessive vertical expansion and deformation of the manhole cover, forcing it to extend laterally in all directions, ensuring a tight conformity to the flat and irregular roof and floor slabs and the coal seams on both sides. After the grout solidifies, a high-strength, full-section solid seal is formed. Furthermore, the highly fluid grout includes, but is not limited to, pure cement grout, cement-fly ash grout, or high-water filling materials. A grout mix with micro-expansion and low-shrinkage characteristics is preferred to ensure that no shrinkage gaps form at the top of the manhole cover after solidification, ensuring a tight and continuous fit with the roof slab.

[0018] In step A, the first preset safety distance L1 ensures that the integrity of the coal wall in the return airway will not be damaged due to drilling or mining pressure; in step C, the width M retained is 0.2-1.0m to isolate the coal pillar, preventing direct connection between the enlarged borehole area and the adjacent goaf, and avoiding the risk of gas and water inrush; in step D, the second preset safety distance L2 ensures that sufficient coal pillars are retained to protect the sidewalls of the machine track roadway, preventing stress concentration, spalling, or damage to the support system caused by excessive borehole enlargement; in step E, the sealing and plugging prevents air leakage from the goaf, leakage of harmful gases, and spontaneous combustion of coal.

[0019] The beneficial effects of this invention are: (1) This invention uses directional borehole expansion technology to partially recover the isolation coal pillars that cannot be extracted in traditional processes. Without increasing the additional roadway engineering, the coal extraction rate can be increased by 5%-15%, which greatly saves coal resources.

[0020] (2) By precisely controlling the start and end positions of the borehole expansion, key isolation coal pillars and roadway protection coal pillars are preserved. This double insurance effectively prevents connection with adjacent goaf areas and roadway instability, keeping all operational risks within a known and controllable range.

[0021] (3) The hole enlargement process is integrated into the conventional drilling withdrawal process. Combined with the existing measurement while drilling technology and hydraulic deflection actuator, there is no need for complicated auxiliary special equipment. The construction efficiency is high and it is easy to promote and apply in existing mines. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic plan view of the mining area layout when the present invention is applied; Figure 3 This is a schematic diagram of the drilling pattern when the present invention is applied; Figure 4 This is a schematic diagram of the articulated directional drill bit used for linear drilling in the application of the present invention; Figure 5 This is a schematic diagram of the deflection and reaming of the articulated directional drill bit when the present invention is applied; Figure 6 This is a block diagram illustrating the monitoring and control system principle of the present invention during application; Figure 7 This is a schematic diagram illustrating the orifice sealing process of the present invention during application; Figure 8 for Figure 7 Top view.

[0023] In the diagram: 1. Drilling and mining face track roadway; 2. Drilling and mining face return airway; 3. Spiral drilling coal mining machine; 4. Solid coal in the roadway side; 5. Solid isolation coal pillar; 6. Protective coal pillar in the roadway side; 7. Drilling and mining goaf; 8. Sealed structure; 9. Hydraulic thrust mechanism; 10. Rigid coupling; 11. Universal joint coupling; 12. Drill bit; 13. Non-rotating support sleeve; 14. Spiral drill rod; 15. Roof plate; 16. Floor plate; 17. Flexible formwork bag; 18. Filling grout; 19. Internal tie rod; 20. Grouting pipe; 21. Exhaust pipe. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. Example 1

[0026] This embodiment takes a conventional thin coal seam working face in a coal mine as an example. The mine has no strict requirements for surface settlement control, and the mine owner pursues the simplest coal mining process and the lowest mining cost. The working face mines a thin coal seam with an average thickness of 0.8m and a dip angle of 5° (belonging to a near-horizontal gently dipping coal seam). Its immediate roof is fine sandstone (belonging to a moderately stable to hard roof).

[0027] Based on the aforementioned geological and engineering conditions, the method of this invention is employed for mining, aiming to maximize the recovery of coal resources without compromising roof stability. See details below. Figure 1 The process flow diagram shown includes the following implementation steps: A. As Figure 2As shown, a drilling and mining face machine track roadway 1 and a drilling and mining face return air roadway 2 are excavated and arranged on both sides of the thin coal seam working face, with a distance of 60m between the two roadways. A three-axis multi-spindle auger coal mining machine 3 and its supporting pump station, control system, etc. are arranged in the drilling and mining face machine track roadway 1.

[0028] Combination Figure 3 , Figure 4 and Figure 5 As shown, the triple-axis multi-spindle auger coal mining machine used in this embodiment includes three parallel drilling tools, with each drill bit having a diameter of 0.8m. The three drill bits are arranged in an alternating pattern, and the initial borehole width is 2.0m. Specifically, the drilling tools include: a rigid linear drilling tool located in the middle, whose drill bit 12 is connected to the rear auger drill rod 14 via a rigid coupling 10, maintaining a straight line throughout the drilling operation and serving as a stable base for lateral deflection thrust; and two articulated directional drilling tools located at the left and right ends, whose drill bits 12 are connected to the rear auger drill rod 14 via universal joint couplings 11. A hydraulic thrust mechanism 9 is horizontally installed between the non-rotating support sleeves 13 of the adjacent rigid linear drilling tools and the articulated directional drilling tools, and this mechanism is driven by the system's electro-hydraulic control valve group.

[0029] The deflection operation of the articulated directional drilling tool is achieved by an added deflection mechanism. The components of this mechanism are conventional in the field, mainly including a hydraulic thrust mechanism and an electro-hydraulic control valve assembly installed between the non-rotating support sleeves of adjacent drilling tools. The electro-hydraulic control valve assembly is communicatively connected to the main control console in the drilling track via a control cable laid during drilling, and is used to receive and execute deflection or return-to-center commands. The "universal joint coupling + non-rotating support sleeve + hydraulic thrust mechanism" proposed in this invention is a specially designed combined structure. By combining and installing these components between the non-rotating support sleeves of adjacent drilling tools, the directional deflection mechanism of this invention is formed, achieving directional deflection.

[0030] B. Start the spiral drilling coal mining machine 3. The rotational torque output by the main unit is transmitted to the three drill bits 12 through the spiral drill rod 14. At this time, the hydraulic thrust mechanism 9 is in the retracted state, and the three drill bits maintain a parallel straight line and drill into the solid coal seam 4 of the roadway. In the 0.8m thick coal seam, the drill bits continuously break the coal body, and the falling coal is continuously transported to the machine track roadway 1 of the drilling and mining face by the rotating spiral drill rod 14.

[0031] During drilling, the depth is monitored in real time. When the drill tip advances to the first preset safety distance L1 (3m in this embodiment) from the sidewall of the return airway 2 of the opposite drilling and mining face, drilling stops, forming an initial borehole with a width of 2.0m. According to the mining design, an initial solid coal pillar for supporting the roof is left between this initial borehole and the adjacent planned borehole, with a designed width D of 1.5m. The 3m solid coal pillar 4 of the sidewall effectively prevents the drill bit from penetrating the return airway and prevents damage to the integrity of the return airway sidewall due to mine pressure manifestation.

[0032] C. After drilling stops, the auger coal mining machine 3 begins to rotate and retract. (Refer to...) Figure 5 The deflection principle works as follows: In the initial stage of drill retraction, the operator issues a deflection and reaming command via the main control console. The electro-hydraulic control valve group drives the hydraulic thrust mechanism 9 inside the hole to extend outward. The hydraulic thrust mechanism 9 uses the non-rotating support sleeve 13 of a rigid linear drill bit in the middle as a solid base, pushing the hinged directional drill bits on both sides horizontally outward. The drill bits 12 on both sides deflect around the universal joint coupling 11 by a preset angle α, which is 5° in this embodiment.

[0033] At this time, the main unit continues to provide rotational power, and the drill bits 12, which deflect on both sides, perform lateral cutting and enlarging of the sidewall coal wall of the initial drill hole, continuously extracting the initial solid isolation coal pillar with a designed width D of 1.5m. Since this initial solid isolation coal pillar is subjected to cutting from one side during the retraction and enlarging of each of the two adjacent drill holes, in this embodiment, the single-sided deflection cutting amount of the current drill hole is precisely controlled to be 0.25m. Figure 3 As shown, after the borehole enlargement operation, a solid isolation coal pillar 5 with a thickness of M of 1.0m is ultimately retained between the current borehole and the adjacent mined goaf 7. This solid isolation coal pillar 5 with a thickness of M of 1.0m enters a plastic yielding state under the compaction of the roof, preventing direct connection between the enlarged borehole area and the adjacent goaf, and avoiding the risk of gas and water inrush.

[0034] D. Combination Figure 6 As shown, the system performs real-time monitoring of both the inside and outside of the hole throughout the entire process of hole enlargement and drilling withdrawal.

[0035] Displacement sensors are installed on the push-pull carriage of the auger coal mining machine in the machine track roadway to measure the depth of the drill bit. Measurement-while-drilling (MWD) probes are arranged inside the drill pipe cavity to acquire the attitude and position of the drill bit. The MWD probes inside the borehole feed back the deflection attitude of the drill bits on both sides to the PLC module of the main control panel in real time; simultaneously, displacement sensors outside the borehole record the retraction stroke of the auger coal mining machine's carriage in real time.

[0036] When drill bit 12 retracts to the second preset safety distance L2 (4m in this embodiment) from the sidewall of the machine track roadway, the PLC monitors the drill bit position based on the displacement sensor signal and sends a return signal to the electro-hydraulic control valve group inside the hole via the control cable. After receiving the signal, the electro-hydraulic control valve group directly drives the hydraulic thrust mechanism 9 to retract, and the drill bits on both sides return to a straight state, stopping the lateral cutting and hole enlargement. This operation strictly preserves the 4m wide protective coal pillar 6 of the roadway sidewall, fundamentally avoiding stress concentration and roof collapse accidents caused by excessive hole enlargement.

[0037] E. After the auger rod 14 and drill bit 12 have completely withdrawn from the borehole, immediately perform a sealing and plugging operation on the borehole opening. For example... Figure 7 and Figure 8 As shown, in this embodiment, a double-layer flexible mold bag 17 with built-in reinforcing bars is used to seal the flat borehole formed by the triple-axis multi-axis auger coal mining machine. Figure 7 This is a schematic diagram of the orifice sealing observed from the side of the track roadway.

[0038] The aforementioned double-layer flexible mold bag with built-in reinforcing ribs, the built-in reinforcing ribs 19 refer to high-strength flexible tensile members that connect the upper and lower inner walls inside the mold bag, and the mold bag ends are provided with grouting pipes 20 and venting pipes 21.

[0039] The specific method of sealing is as follows: In the machine track roadway, an uninflated flexible formwork bag 17 is pushed into the orifice to a depth of about 1.0m using a feeding rod. Then, filling grout 18 is pumped into the formwork bag through the grouting pipe 20. The filling grout 18 is a high-flowability grout without coarse aggregate (preferably cement-fly ash grout in this embodiment), which has excellent flowability, micro-expansion and low shrinkage characteristics. Under grouting pressure, the flexible formwork bag 17 expands in all directions. The internally distributed reinforcing bars 19 are stretched when the grout expands under pressure, limiting the excessive expansion and deformation of the formwork bag in the vertical direction, forcing the formwork bag to extend laterally in all directions, and tightly conforming to the 0.8m high roof 15, floor 16 and the irregular coal pillars 6 on both sides of the roadway. Air is discharged through the exhaust pipe 21. After the grout solidifies, a full-section, high-strength sealed wall is formed at the orifice, completely eliminating the risk of gas escape and spontaneous combustion in the goaf.

[0040] F. Repeat steps B to E above, moving the auger coal mining machine 3 forward one hole distance along the machine track roadway. The hole distance is the initial hole width plus the initial isolation coal pillar width. In this embodiment, the initial hole width of the triple-axis auger coal mining machine is 2.0m, and the designed initial solid isolation coal pillar width D is 1.5m. Therefore, the hole distance for this relocation is clearly set to 3.5m. After the machine is in place, the straight drilling, lateral cutting and enlargement, and exit sealing operations of the next borehole begin until the entire thin coal seam working face is safely and efficiently mined with a high recovery rate.

[0041] Through the above implementation process, the present invention successfully completed directional reaming during the drill retraction stage. As described in the above steps and... Figure 3 As shown, within the effective enlargement section of 53m (total working face length 60m, minus the safety distances of 3m at the return airway end and 4m at the machine rail roadway end), the initial solid isolation coal pillar with a design width D of 1.5m, which originally needed to be reserved, was effectively mined out by 0.5m, ultimately retaining a solid isolation coal pillar with a thickness M of 1.0m. This approach, while strictly ensuring the integrity of the return airway and machine rail roadway, allows for the recovery of an additional 53m in length, 0.5m in width, and 0.8m in height from a single borehole. Calculations show that the overall extraction rate of this working face has significantly increased from the traditional approximately 65.1% to approximately 74.1%. Simultaneously, the retained isolation coal pillar with a thickness M of 1.0m enters a plastic yield state under roof compaction, avoiding brittle failure due to excessive stress concentration and providing excellent sealing and buffering effects.

[0042] The above description is merely a preferred embodiment 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, should be covered within the scope of protection of the present invention.

Claims

1. A method for improving the coal extraction rate of auger drilling based on directional borehole enlargement, characterized in that... Includes the following steps: A. Arrange a machine track roadway and a return air roadway in the thin coal seam working face, and place the spiral drilling coal mining machine and its supporting equipment in the machine track roadway; B. Start the spiral drilling coal mining machine and drive the drill bit to drill into the coal body in a straight line. At the same time, the crushed coal is continuously transported into the machine track roadway until the drill bit tip is at the first preset safety distance L1 from the side of the return air roadway, and then stop drilling to form an initial borehole. According to the mining design, an initial solid isolation coal pillar with a width of D is left between the initial borehole and the adjacent planned borehole. C. After stopping drilling, begin retracting the drill bit; during the retraction process, the main control console on the auger coal mining machine sends a command to activate the deflection mechanism of the drill bit, causing the drill bit axis to deflect at a preset angle α relative to the initial borehole axis, and relying on the deflection posture to perform lateral cutting and enlarging of the side coal wall of the initial borehole. D. During the directional reaming process, the drill bit attitude and position are monitored in real time by a monitoring device; when the drill bit retracts to the second preset safety distance L2 from the side of the machine track roadway, the main control console sends a return signal, the drill bit returns to a straight state, and the reaming stops; E. After the drill string is completely withdrawn, immediately seal the borehole opening. F. Repeat steps B to E, and perform drilling, enlargement, and plugging operations on each borehole in sequence along the working face advance direction until the entire working face is mined out.

2. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, The thickness of the thin coal seam is 0.3m-1.3m.

3. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, In step A, the spiral drilling coal mining machine is a multi-axis spiral drilling coal mining machine containing multiple parallel drilling tools; the spiral drilling coal mining machine also includes a displacement sensor and a measurement while drilling (MWD) probe; the displacement sensor is arranged on the push-pull slide of the spiral drilling coal mining machine main unit in the machine track roadway and is used to calculate the depth distance of the drill bit; the MWD probe is arranged in the drill pipe cavity and is used to obtain the attitude and position of the drill bit.

4. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 3, characterized in that, Multiple drill bits are arranged side-by-side, including a rigid linear drill bit in the middle and articulated directional drill bits at the left and right ends; the drill bits include drill bits and drill rods; the drill bit of the rigid linear drill bit is connected to the auger drill rod behind it by a rigid coupling, maintaining a straight line throughout the operation and serving as a stable base for lateral deflection thrust; the drill bit of the articulated directional drill bit is connected to the auger drill rod behind it by a universal joint coupling; the deflection operation of the articulated directional drill bit is achieved by a deflection mechanism, which includes a hydraulic thrust mechanism and an electro-hydraulic control valve assembly installed between the non-rotating support sleeves of adjacent drill bits.

5. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 3, characterized in that, In step D, the real-time monitoring is achieved through a combination of in-hole and out-of-hole monitoring. In-hole monitoring specifically involves integrating a Measurement While Drilling (MWD) probe into the non-magnetic drill rod cavity adjacent to the drill bit. The probe contains an inclinometer and an azimuth sensor, and transmits the real-time deflection attitude of the drill bit to the main control console via signal transmission to verify whether the deflection angle has reached the preset α value. Out-of-hole monitoring specifically involves installing a displacement sensor on the push-pull slide of the auger coal mining machine main unit, and calculating the depth position of the drill bit in the hole in real time by recording the slide's movement stroke.

6. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, In step B, the first preset safety distance L1 ranges from 2m to 5m; the hole width of the initial borehole is determined by the size of the drill bit of the spiral drilling coal mining machine and its arrangement, and its hole width ranges from 0.3m to 3.0m; the width D of the initial solid isolation coal pillar ranges from 0.4m to 2.0m.

7. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, In step C, the preset angle α ranges from 2° to 10°. The lateral cutting and reaming are continuously implemented for each borehole in the working face. The specific implementation process is as follows: after the operator issues a command through the main control console, the electro-hydraulic control valve group drives the hydraulic thrust mechanism to extend outward, using the adjacent undeflected drill bit in the middle as a support base, forcing the edge articulated directional drill bit to deflect outward relative to the borehole center axis by a preset angle α. During the rotation and retraction process, the drill bit of the edge articulated directional drill bit continuously performs lateral cutting on the initial solid isolation coal pillar with a width of D. When the two adjacent boreholes are retracted and reamed, the isolation coal pillar is thinned by cutting on one side. By precisely controlling the unilateral deflection cutting amount of the current borehole, it is ensured that a solid isolation coal pillar with a thickness of M of 0.2m-1.0m is always maintained between the current reaming section and the adjacent completed goaf. The isolation coal pillar with a thickness of M is in a plastic yielding state and acts as an isolation zone to prevent air leakage from the goaf.

8. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, In steps C and D, the main control console is equipped with a PLC module. When the PLC module determines, based on the data from the external displacement sensor, that the current retraction depth has reached the second preset safety distance L2, the PLC module transmits a return-to-center signal to the electro-hydraulic control valve group inside the hole via the control cable. After receiving the signal, the electro-hydraulic control valve group drives the hydraulic thrust mechanism to retract, restoring the articulated directional drill bit at the edge to a straight state and stopping the hole enlargement. At the same time, the control system is compatible with operators manually issuing return-to-center commands.

9. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 1, characterized in that, In step E, for the large-span flat borehole formed by the multi-axis spiral drilling coal mining machine, a double-layer flexible mold bag with built-in reinforcing bars that matches the borehole cross-section is adopted; the specific method of sealing is as follows: a long-distance mechanized pumping sealing technology is adopted; in the machine track roadway, the flexible mold bag is pushed into the borehole opening to a predetermined depth by a feeding rod; then the grouting pump in the roadway is connected to pump a high-flowability slurry without coarse aggregate into the mold bag.

10. The method for improving the coal extraction rate of auger drilling based on directional borehole enlargement according to claim 9, characterized in that, The aforementioned double-layer flexible mold bag with built-in reinforcing bars refers to a high-strength flexible tensile component that connects the upper and lower inner walls inside the mold bag, and the mold bag ends are equipped with grouting pipes and venting pipes.

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