Advanced diversion prevention and control method for roof composite water disasters in close-range coal seam lower group coal mining

Abstract

The invention provides an advanced diversion control method for roof composite water disasters in mining of lower group coal of a close-range coal seam, which utilizes the water diversion performance of a caving zone after mining of upper group coal, adopts an upper drainage and lower drainage combined dredging mode, and eliminates the problem that drilling cannot be completely constructed in a fractured stratum; water drainage and drainage drill holes are reserved in suspected water accumulation areas of the underground upper group coal goaf, and it is guaranteed that newly-supplied water in the goaf can flow out smoothly after flow guide of ground water drainage holes. According to the method, threats of water damage of a water-bearing layer in a lower-group coal mining area and water accumulation composite water damage of an upper-group coal goaf in the lower-group coal mining process can be eliminated in advance, and safe mining of the working face is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine water control, and relates to a method for preventing and controlling compound water disasters, specifically to a method for advanced diversion and prevention of roof compound water disasters in the mining of the lower coal seam of closely spaced coal seams. Background Art

[0002] After the upper coal seam of the closely spaced coal seam group in the coal mine is mined, local water accumulation will occur due to the uncoordinated deformation of the strata. At the same time, the water - resistant layer between the coal seam and the main aquifer will re - close under the long - term soaking effect, making the mining process of the lower coal seam often face the threats of roof aquifer, inter - layer separation water, and water accumulation in the overlying goaf at the same time, forming a hidden danger of compound water disasters. The conventional water control method is to use underground boreholes to drain the roof aquifer or separated - layer water accumulation, reduce the local water accumulation in the inter - layer separation and the water accumulation in the local water - rich abnormal area in the aquifer, so as to achieve the purpose of reducing peaks and filling valleys, and ensure that the water inflow is relatively stable during the face mining process.

[0003] However, under the condition that the upper coal seam of the closely spaced coal seam group has been mined, the overlying strata of the coal seam roof are relatively broken, the construction difficulty of underground boreholes is high, the hole - forming rate is extremely low, and the borehole trajectory is affected by fissures in the strata, making it difficult to accurately construct to the designed position. At the same time, the aquifer continuously replenishes the goaf, resulting in the inability to drain the water in the goaf. Coupled with the influence of the broken strata, the exploration difficulty of the overlying inter - layer separation water accumulation and the water - rich abnormal area in the aquifer is also relatively high, and the scope that can be revealed by underground inclined boreholes is extremely limited, and the overall drainage effect is poor. Therefore, for the roof compound water disasters in the mining of the lower coal seam of closely spaced coal seams, the method of passively increasing the drainage system is mostly adopted, which not only causes waste in the configuration of the drainage system, but also cannot completely avoid the occurrence of roof water inrush accidents. Summary of the Invention

[0004] Aiming at the defects and deficiencies existing in the prior art, the purpose of the present invention is to provide a method for advanced diversion and prevention of roof compound water disasters in the mining of the lower coal seam of closely spaced coal seams, and solve the technical problems that the aquifer and inter - layer separation water disasters in the prior art cannot be explored and the water accumulation in the goaf cannot be drained completely.

[0005] In order to solve the above - mentioned technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] A method for advanced diversion and prevention of roof compound water disasters in the mining of the lower coal seam of closely spaced coal seams, the method specifically includes the following steps:

[0007] Step 1, determining the potential water - accumulation area of the overlying goaf: According to the undulation condition of the coal seam revealed during the mining process of the upper coal seam, select the local lowest point and demarcate it as the potential water - accumulation area of the overlying goaf.

[0008] Step 2, construct underground water drainage holes: Select a suitable position in the roadway of the lower coal seam working face near the plane position of the potential water accumulation area in the overlying goaf as the drill site, and construct underground water drainage holes in the selected drill site area. The underground water drainage holes need to cover the potential water accumulation area in the overlying goaf; after the end hole position of the underground water drainage hole enters the floor of the upper coal seam mining area, ream the hole and install a water stop casing. After ensuring that the water stop casing is well consolidated, install an orifice gate valve and a U-shaped pipe at the orifice in sequence, and open the orifice gate valve to continuously drain the accumulated water in the overlying upper coal seam goaf.

[0009] Step 3, layout surface water drainage holes: Calculate and obtain the influence radius R of the aquifer in the lower coal seam mining area using Formula Ⅰ, and then take half of the influence radius R of the aquifer in the lower coal seam mining area as the spacing r between two adjacent surface water drainage holes; the Formula Ⅰ is as follows:

[0010]

[0011] R represents the influence radius of the aquifer in the lower coal seam mining area, with the unit of m.

[0012] S w represents the average water level drawdown in the stable section, with the unit of m.

[0013] H 0 represents the initial water level of the aquifer in the lower coal seam mining area, with the unit of m.

[0014] K represents the permeability coefficient of the aquifer in the lower coal seam mining area, with the unit of m / d.

[0015] Step 4, construct surface water drainage holes: Construct surface water drainage holes on the ground corresponding to the plane position of the suspected water accumulation area in the upper coal seam, and layout the surface water drainage holes along both sides of the working face trend at the interval r determined in Step 3 until the influence range can cover the entire range of the lower coal seam working face; after the surface water drainage hole enters the caving zone of the upper coal seam, lower a water stop casing and cement it in the strata above the aquifer in the lower coal seam mining area.

[0016] Step 5, lower the diversion pipe: Lower the diversion pipe into the constructed surface water drainage hole. Seal the pipe orifice during the lowering process of the diversion pipe, and use the pressure difference on the pipe wall during the water flow process to smoothly lower the diversion pipe to the bottom of the hole; a self-expanding rubber barrel is sleeved outside the upper part of the diversion pipe.

[0017] Step 6, lower the water level observation device: Lower the water level observation device from the surface water drainage hole, and install a double-threaded sealing cover at the orifice of the surface water drainage hole; the double-threaded sealing cover has internal threads and external threads. The internal threads are used to connect the water stop casing, and the external threads are used to connect the diversion pipe. A through-wire pipe is provided at the center of the inner diameter of the double-threaded sealing cover for passing out the cable of the water level observation device.

[0018] Step 7, hydrophobic diversion: By using the ground drainage holes, the groundwater in the aquifer of the lower coal seam mining area is made to enter the gob area of the upper coal seam along the boreholes, further enter the underground along the underground water drainage holes, and finally be discharged by the underground drainage system.

[0019] The present invention also has the following technical features:

[0020] Step 8, plugging treatment of the ground drainage holes: If the water level in the ground drainage holes rises, indicating that the inside of the ground drainage holes has collapsed and become blocked, the water level observation device in the hole is taken out, and a surface drill is used for through-hole operation until the ground drainage holes show the phenomenon of air suction and water drainage again.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] (Ⅰ) The present invention makes full use of the water-conducting performance of the caving zone after the upper coal seam is mined, adopts the combined dredging method of upper drainage and lower drainage, and eliminates the problem that it is impossible to construct boreholes completely in the broken strata; by leaving water drainage boreholes in the suspected water accumulation areas in the gob area of the upper coal seam underground, it is ensured that the newly replenished water in the gob area can also flow out smoothly after the ground drainage holes conduct water. The present invention can eliminate in advance the threat of the combined water disaster of the aquifer water disaster in the lower coal seam mining area and the water accumulation in the gob area of the upper coal seam during the mining process of the lower coal seam, and ensure the safe mining of the working face.

[0023] (Ⅱ) The present invention installs a water-stop casing in the underground water drainage borehole to fix the pipe, and installs a U-shaped pipe at the hole opening, which can avoid the secondary accident of coal spontaneous combustion caused by air leakage from the water drainage borehole.

[0024] (Ⅲ) The present invention uses a diversion pipe made of PVC material in the ground drainage holes to ensure that the boreholes will not be blocked due to the collapse of the broken strata, and guarantees the continuous water drainage effect.

[0025] (Ⅳ) The present invention adopts the structure of a double-threaded sealing cover at the hole opening and a self-expanding rubber barrel in the hole, combined with the water level automatic monitoring mode, and uses the dynamic water level to scientifically identify the plugging situation of the borehole, avoiding the secondary disaster of coal spontaneous combustion caused by air suction on the ground of the borehole. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a plane layout diagram of the advanced diversion boreholes for the roof composite water disaster in the lower coal seam of the close-distance coal seams; Figure 1 In it: The orange lines represent the contour lines of the coal seam floor.

[0027] Figure 2 It is a schematic cross-sectional view of the advanced diversion boreholes for the roof composite water disaster in the lower coal seam of the close-distance coal seams; Figure 2 In it: The blue lines represent the water level lines, and the blue arrows represent the water flow direction.

[0028] Figure 3Schematic diagram of the connection structure of the water stop casing, orifice gate valve and U-shaped pipe.

[0029] Figure 4 Schematic diagram of the connection structure of the double-threaded sealing cover, diversion pipe and self-expanding rubber barrel; Figure 4 In the figure: the blue line represents the water level line, and the blue arrow represents the water flow direction.

[0030] Figure 5 Schematic diagram of the structure of the ground drainage hole; Figure 5 b - is Figure 5 A - A' sectional view of a-.

[0031] The meanings of each label in the figure are as follows: 1 - underground drainage hole, 2 - ground drainage hole, 3 - goaf of the upper coal seam, 4 - roadway of the lower coal seam working face, 5 - aquifer in the lower coal seam mining area, 6 - water - resisting layer, 7 - upper coal seam, 8 - lower coal seam, 9 - caving zone of the upper coal seam, 10 - water - conducting fissure zone of the upper coal seam, 11 - water stop casing, 12 - orifice gate valve, 13 - U - shaped pipe, 14 - water level observation device, 15 - double - threaded sealing cover, 16 - diversion pipe, 17 - self - expanding rubber barrel.

[0032] The technical solutions of the present invention will be further described below in conjunction with embodiments. Specific embodiments

[0033] It should be noted that all the components, devices and systems used in the present invention, without special instructions, are all components, devices and systems known in the art. For example: the water level observation device 14 adopts a conventional water level observation device known in the prior art. The underground drainage system adopts a conventional underground drainage system known in the prior art.

[0034] The research background of the present invention is as follows: As Figure 3 shown, during the mining construction of a certain coal mine, after the upper coal seam 7 of the coal mine is mined, the lower coal seam 8 is ready to be mined. During the mining process of the upper coal seam 7, although the water - conducting fissure zone 10 of the upper coal seam extends to the bottom of the aquifer 5 in the lower coal seam mining area of the coal seam roof, due to the long interval of up to four years between the mining of the two working faces, the fissures in the fractured water - resisting layer 6 within the fissure zone are basically closed, resulting in a certain amount of water accumulation in the goaf 3 of the upper coal seam, and the aquifer 5 in the lower coal seam mining area above is re - water - rich. During the mining process of the lower coal seam working face, it faces the threats of water accumulation in the goaf 3 of the upper coal seam and water hazards from the aquifer 5 in the lower coal seam mining area of the roof. Based on the above situation, the present invention proposes a method for advanced diversion prevention and control of compound water hazards in the roof during the mining of the lower coal seam in close - distance coal seams, as shown in the embodiments.

[0035] Following the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and any equivalent transformation based on the technical solution of this application falls within the protection scope of the present invention.

[0036] Embodiment:

[0037] This embodiment provides a method for preventing and controlling the advanced diversion of composite water hazards in the roof during the mining of the lower group of coal seams at close range. As Figures 1 to 5 shown, the method specifically includes the following steps:

[0038] Step 1: Determine the potential water accumulation area in the overlying goaf:

[0039] Based on the distribution of the floor contour line of the No. 7 coal seam in the upper group of coal seams and the measurement data during the cutting of the coal body by the shearer during the mining of the No. 7 coal seam in the upper group of coal seams, it is determined that the local low-lying point in the goaf 3 of the upper group of coal seams is located in the middle of the working face, and this area is determined as the potential water accumulation area in the overlying goaf.

[0040] Step 2: Construct underground water drainage holes:

[0041] Near the plane position of the potential water accumulation area in the overlying goaf, select a suitable position in the roadway 4 of the working face of the lower group of coal seams as a drill site, and construct underground water drainage holes 1 in the selected drill site area. The underground water drainage holes 1 need to cover the potential water accumulation area in the overlying goaf, and the number of drill holes constructed in each drill site is dynamically adjusted according to the on-site water inflow situation (generally three drill holes are constructed). During the drilling process, record the drill pressure every 2 m and take rock powder. When the drill pressure starts to increase significantly and the sticking phenomenon occurs, and the rock powder is mixed with mudstone in the goaf 3 of the upper group of coal seams, foam or yellow mud for fire prevention and filling, it is considered that the drill hole has entered the goaf 3 of the upper group of coal seams; continue to construct the drill hole to ensure that the final hole position enters more than 4 m below the floor of the mining of the No. 7 coal seam in the upper group of coal seams. Then ream the hole and install a water-stop casing 11. After ensuring that the water-stop casing 11 is well consolidated, install a hole gate valve 12 and a U-shaped pipe 13 at the hole mouth in sequence, and open the hole gate valve 12 to continuously drain the accumulated water in the overlying goaf 3 of the upper group of coal seams.

[0042] As a specific solution in this embodiment, the inner diameter of the underground water drainage hole 1 is 153 mm, the inner diameter of the water-stop casing 11 is 127 mm. The upper part of the water-stop casing 11 enters the goaf 3 of the upper group of coal seams and this section is a slotted pipe, and the lower part of the water-stop casing 11 is buried in the formation and this section is a seamless steel pipe, and the hole section of the seamless steel pipe is fixed with cement slurry.

[0043] Step 3: Layout surface drainage holes according to the influence radius of the aquifer in the mining area of the lower group of coal seams:

[0044] According to the exploration data of the hydrogeological conditions of the main water - filled aquifers in the mine, the formula for calculating the influence radius of the unconfined aquifer (Kusakin formula) is selected to determine the influence radius during the surface water drainage process, as follows:

[0045]

[0046] R represents the influence radius of the aquifer in the lower - group coal mining area, with the unit of m.

[0047] Sw represents the average water - level drawdown in the stable section, with the unit of m.

[0048] H 0 represents the initial water level of the aquifer in the lower - group coal mining area, with the unit of m.

[0049] K represents the permeability coefficient of the aquifer in the lower - group coal mining area, with the unit of m / d.

[0050] In this embodiment, the thickness of the aquifer 5 in the lower - group coal mining area is 85m, and H 0 is selected as 85m; through previous pumping test calculations, the permeability coefficient K of the aquifer 5 in the lower - group coal mining area is 0.4517m / d; the maximum water - level drawdown of the aquifer 5 in the lower - group coal mining area monitored during the maximum water inrush of the previous working face is 35m. Therefore, Sw is determined to be 34m, and finally R = 676m is calculated (it should be noted that when using formula Ⅰ for calculation, it is a dimensionless calculation). To ensure the dewatering effect of the aquifer, it is necessary to ensure that the drawdown funnels of two adjacent surface water - drainage holes 2 overlap to ensure their final drawdown. Therefore, the spacing r between two adjacent surface water - drainage holes 2 is finally determined to be 1 / 2 of the influence radius of the aquifer in the lower - group coal mining area, that is, 338m.

[0051] Step Four, construct surface water - drainage holes:

[0052] Construct surface water - drainage holes 2 on the ground corresponding to the plane position of the suspected water - accumulation area of the upper - group coal 7, and arrange the surface water - drainage holes 2 along both sides of the working - face strike at an interval of r = 338m until the influence range can cover the entire range of the lower - group coal 8 working face.

[0053] As a specific scheme of this embodiment, the borehole of the surface water - drainage hole 2 adopts a two - stage structure, with the upper diameter of 311mm and the lower diameter of 133mm. In this embodiment, the reasons for adopting the two - stage structure are as follows: First, for safety, staged cementing can prevent the collapse of the wellbore and control the formation pressure. Second, for layered isolation, to avoid the inter - flow of fluids in different formations. Third, to adapt to complex geology, and flexibly adjust parameters according to the formation characteristics at different depths.

[0054] As a specific solution of this embodiment, during the construction process, the situation of drill pipe jamming and drilling fluid leakage needs to be recorded every 2 m of construction. When obvious drill pipe jamming and sticking occur, almost all of the drilling fluid leaks, and air suction phenomenon appears, it indicates that the ground drainage hole 2 has entered the caving zone 9 of the upper coal seam group; continue the construction to ensure that the ground drainage hole 2 enters more than 5 m within the caving zone 9 of the upper coal seam group, and lower a water-stop casing 11 in the loose formation above the aquifer 5 in the main mining area of the lower coal seam group and cement it in place.

[0055] As a specific solution of this embodiment, the material of the water-stop casing 11 should be selected as seamless steel pipe with a wall thickness of more than 15 mm, a diameter of 219 mm, and screw threads are left on the inner side of the orifice part.

[0056] Step Five, lower the diversion pipe:

[0057] Lower a diversion pipe 16 into the constructed ground drainage hole 2. The diversion pipe 16 is made of PVC material. During the lowering process of the diversion pipe 16, the pipe orifice is closed, and the diversion pipe 16 is smoothly lowered to the bottom of the hole by the pressure difference on the pipe wall during the water flow process; a self-expanding rubber barrel 17 is sleeved on the outer side of the upper part of the diversion pipe 16.

[0058] As a specific solution of this embodiment, the diameter of the diversion pipe 16 should be more than 10 mm smaller than the diameter of the ground drainage hole 2. In this embodiment, the diameter of the diversion pipe 16 is 98 mm.

[0059] As a specific solution of this embodiment, the lower part (aquifer section) of the diversion pipe 16 is a slotted pipe, and the upper part (seamless steel pipe section) of the diversion pipe 16 is a solid pipe. The solid pipe has a non-porous structure, which can prevent the migration of pollutants or formation interference, and can be used in combination with the slotted pipe to meet complex geological and engineering requirements.

[0060] As a specific solution of this embodiment, the self-expanding rubber barrel 17 is made of water-swellable rubber (made with butyl rubber, chloroprene rubber or ethylene propylene diene monomer rubber as the matrix and adding sodium polyacrylate resin), polyurethane-based composite material, water-absorbing resin composite polymer (made by mixing sodium polyacrylate resin with thermoplastic elastomer or polyethylene), modified cellulose material (such as carboxymethyl cellulose). In this embodiment, the self-expanding rubber barrel 17 can achieve a volume expansion of 100% - 500%, and after expansion, it has certain compressive and shear resistance, does not decompose under long-term immersion, and has good durability.

[0061] Step Six, lower the water level observation device:

[0062] Lower the water level observation device 14 into the ground drainage hole 2. Install a double-threaded sealing cover 15 at the orifice of the ground drainage hole 2, and pass the cable of the water level observation device 14 through the central hole of the double-threaded sealing cover 15. The double-threaded sealing cover 15 has an inner and outer double-threaded structure, and is respectively screwed and fixed to the internal threads of the water-stop casing 11 and the diversion pipe 16. A wire passing pipe is provided at the center of the inner diameter of the double-threaded sealing cover 15 for passing out the cable of the water level observation device 14.

[0063] Step Seven, hydrophobic diversion:

[0064] Utilize the ground drainage hole 2 to enable the groundwater in the aquifer 5 of the lower coal mining area to enter the goaf 3 of the upper coal group along the borehole, further enter the underground along the underground water drainage hole 1, and finally be discharged by the underground drainage system.

[0065] Step Eight, plugging treatment of the ground drainage hole:

[0066] If the water level in the ground drainage hole 2 rises, indicating that the inside of the ground drainage hole 2 has collapsed and plugged, then take out the water level observation device 14 in the hole and use a surface drill to conduct through-hole operation until the ground drainage hole 2 reappears the phenomenon of air suction and water drainage.

Claims

1. A method for preventing and controlling composite water hazards in the roof of a coal mining group under a close-range coal seam, characterized in that: The method specifically comprises the following steps: Step 1: Identify potential waterlogging areas in the overlying goaf: According to the coal seam fluctuations revealed during the mining process of the upper coal group, the local lowest point is selected and delineated as the potential water accumulation area of ​​the overlying goaf; Step 2: Construction of underground drainage holes: A suitable location is selected as a drilling site in the lower coal working face tunnel (4) near the plane position of the potential water accumulation area of ​​the overlying goaf area, and an underground drainage hole (1) is constructed in the selected drilling site area. The underground drainage hole (1) needs to cover the potential water accumulation area of ​​the overlying goaf area; after the terminal hole position of the underground drainage hole (1) enters the mining floor of the upper coal group (7), the hole is expanded and a water stop casing (11) is lowered. After ensuring that the water stop casing (11) is well consolidated, an orifice gate valve (12) and a U-shaped pipe (13) are installed in sequence at the orifice, and the orifice gate valve (12) is opened to continuously drain the accumulated water in the overlying upper coal group goaf area (3); Step 3: Lay out ground drainage holes: Formula I is used to calculate and obtain the influence radius R of the aquifer in the lower coal mining area, and then half of the influence radius R of the aquifer in the lower coal mining area is taken as the spacing r between two adjacent surface drainage holes; the formula I is as follows: R represents the influence radius of the aquifer in the lower group coal mining area; S w It indicates the average water level drop in the stable period; H0 represents the initial water level of the aquifer in the mining area of ​​the lower group coal; K represents the permeability coefficient of the aquifer in the lower group coal mining area; Step 4: Construction of ground drainage holes: A surface drainage hole (2) is constructed on the ground corresponding to the plane position of the suspected water accumulation area of ​​the upper group coal (7), and the surface drainage holes (2) are arranged on both sides along the working face according to the interval r determined in step 3 until the affected range can cover the entire range of the working face of the lower group coal (8); after the surface drainage hole (2) enters the upper group coal collapse zone (9), a water stop casing (11) is lowered into the stratum above the aquifer (5) in the lower group coal mining area and cemented; Step 5: Lower the flow guide pipe: A guide pipe (16) is lowered into the constructed ground drainage hole (2), and the pipe opening of the guide pipe (16) is closed during the lowering process, and the guide pipe (16) is smoothly lowered to the bottom of the hole by utilizing the pressure difference of the pipe wall during the water flow process; a self-expanding rubber barrel (17) is sleeved on the outer side of the upper part of the guide pipe (16); Step 6: Lower the water level observation device: A water level observation device (14) is lowered into the ground drainage hole (2), and a double-threaded sealing cover (15) is installed at the opening of the ground drainage hole (2); the double-threaded sealing cover (15) has an internal thread and an external thread, the internal thread is used to connect to the water stop sleeve (11), and the external thread is used to connect to the guide pipe (16), and a wire pipe is reserved at the center of the inner diameter of the double-threaded sealing cover (15) for passing the cable of the water level observation device (14). Step 7: Drainage and diversion: By using the surface drainage holes (2), groundwater in the aquifer (5) in the lower coal mining area flows through the drill holes into the upper coal mining area (3), further flows through the underground drainage holes (1) into the underground, and finally is discharged by the underground drainage system.

2. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step 2, the upper part of the water-stopping sleeve (11) enters the upper coal mining area (3), and the upper part of the water-stopping sleeve (11) is a flower pipe; the lower part of the water-stopping sleeve (11) is buried in the stratum; the lower part of the water-stopping sleeve (11) is a seamless steel pipe, and the hole section of the seamless steel pipe is fixed with cement slurry.

3. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 2, characterized in that: In step 2, cement slurry is used to fix the seamless steel pipe hole section at the bottom of the water stop sleeve (11).

4. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step 2, during the construction of the underground drainage hole (1), the drilling pressure is recorded and rock powder is collected after each construction distance. When the drilling pressure begins to increase significantly and the drill becomes stuck, and the rock powder is mixed with mudstone from the upper coal goaf (3), foam or yellow mud for fire prevention and extinguishing filling, it is considered that the borehole has entered the upper coal goaf (3); the drilling is continued until the final hole position enters the upper coal (7) mining floor.

5. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step 4, the ground drainage hole (2) is drilled using a two-opening structure.

6. The method for preventing and controlling composite water hazards in the roof of a coal mining group under a close-range coal seam according to claim 1, characterized in that: In step 4, during the construction process, the drill bit sticking and drilling fluid leakage conditions need to be recorded once every construction distance. When the drill bit is obviously stuck, the drilling fluid is almost completely lost, and air suction occurs, the ground drainage hole (2) has entered the upper coal collapse zone (9); continue construction until the ground drainage hole (2) enters the upper coal collapse zone (9).

7. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step 4, the material of the water-stop sleeve (11) is a seamless steel pipe with a wall thickness of 15 to 50 mm.

8. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step 5, the flow guide tube (16) is made of polyvinyl chloride.

9. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: In step five, the lower part of the guide pipe (16) enters the aquifer (5) in the lower coal mining area and is a flower pipe, and the upper part of the guide pipe (16) is a seamless steel pipe and is a solid pipe.

10. The method for preventing and controlling composite water hazards in roof of coal mining under close-range coal seams according to claim 1, characterized in that: The method further includes step eight, treating the ground drainage hole for blocking: if the water level in the ground drainage hole (2) rises, indicating that the ground drainage hole (2) has collapsed and blocked, the water level observation device (14) in the hole is removed, and a ground drilling machine is used to perform a hole drilling operation until the ground drainage hole (2) re-appears to absorb air and drain water.

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