A method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining face

Abstract

The present invention discloses a method for filling abandoned tunnels with multiphase materials in a self-igniting coal seam mining working face, comprising the following steps: S1, determining the sealed position of the abandoned tunnel; S2, drilling and laying a gas production pipe next to the abandoned tunnel; S3, building an inner sealed wall in the abandoned tunnel and arranging a gas injection pipe; S4, injecting CO2 gas into the abandoned tunnel inside the inner sealed wall through the gas injection pipe, and performing a sealing test, etc. The abandoned tunnel of the present invention only uses two sealed walls for sealing and gravel filling within a range of 30m close to the coal mining working face. The present invention injects CO2 gas into the abandoned tunnel. After the roof rock of the goaf continues to collapse, the goaf is continuously re-compacted, and liquid CO2 is then injected into the abandoned tunnel to achieve permanent sealing. By drilling holes around the abandoned tunnels and sampling the gas in the holes through gas sampling pipes, the diffusion range of CO2 gas in the abandoned tunnels can be detected to ensure that the liquid CO2 in the abandoned tunnels will not leak.

Description

Technical Field

[0001] The present invention relates to the technical field of treatment of abandoned underground coal mine tunnels, and in particular to a method for filling abandoned tunnels of a spontaneous combustion coal seam mining working face with multiphase materials. Background Art

[0002] Most coal mines in my country are underground mines, primarily mining underground coal seams. Due to geological conditions, the occurrence conditions of most coal seams are relatively complex, and faults, folds, and other geological structures may exist. This poses significant challenges to the excavation of underground tunnels and the layout of coal mining faces. A complete coal mining face generally consists of an intake tunnel, a return tunnel, and a working face. The working face is the core area of ​​coal mining operations. Initially, it consists of a tunnel excavated along the coal seam and connecting the intake and return tunnels. This tunnel, also known as an open cut, forms an independent ventilation system with the intake and return tunnels. Under normal circumstances, the open cut is perpendicular to the return tunnel and intake tunnel, meaning that the intake tunnel is parallel to the return tunnel, and the endpoints of the two tunnels deep into the coal seam are collinear. However, due to factors such as geological conditions and mining plans, after one tunnel (the first tunnel) of the coal mining face is excavated, the other tunnel (the second tunnel) may encounter geological structures, abnormal gas outburst areas, etc. during the excavation process, making it impossible to continue excavating the tunnel. In this case, the excavation of the tunnel is generally stopped, and excavation is directly carried out from one end of the tunnel to the other tunnel (the first tunnel) until it is connected with the other and forms an independent ventilation system. This will cause the inner section of the first tunnel to become a useless tunnel, that is, a scrapped tunnel, such as Figure 1 shown.

[0003] Currently, abandoned underground coal mine tunnels are typically treated by building a sealed wall within the tunnel or by filling the entire tunnel with materials such as loess. The former is prone to damage and air leakage under the influence of mining stresses; the latter requires transporting relevant materials from the surface to the underground, which increases the workload of underground scheduling. If the abandoned tunnel is long, the engineering workload will be very large, seriously affecting the mining plan of the coal face. Furthermore, if the tunnel is partially filled, that is, there are unfilled sections within the abandoned tunnel, when the coal seam is at risk of spontaneous combustion and certain conditions are met, the coal wall or residual coal in the unfilled section may spontaneously combust, posing a significant threat to the safe production of the coal face. At this time, if gas accumulates in the unfilled section, in the presence of high-temperature heat sources, gas explosions are highly likely to occur, potentially causing significant casualties and economic losses to the mine. Therefore, existing methods for treating abandoned underground coal mine tunnels are no longer sufficient to safely handle such abandoned tunnels. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a method for filling abandoned tunnels with multi-phase materials in a spontaneous combustion coal seam mining working face.

[0005] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: a method for filling a scrapped roadway with multiphase material in a spontaneous combustion coal seam mining working face, which specifically comprises the following steps:

[0006] S1. Determination of sealed location of scrapped tunnel:

[0007] Two closed walls are built in the abandoned roadway, namely the inner closed wall and the outer closed wall. The outer closed wall is built at the connection between the abandoned roadway and the cut hole, and the inner closed wall is built on the inner side of the abandoned roadway at a distance L from the outer closed wall.

[0008] S2. Drill holes next to the abandoned roadway and lay out the gas production pipe:

[0009] On the side of the abandoned roadway adjacent to the inner closed wall and away from the cut-eye, several boreholes are constructed in the coal seam outside the abandoned roadway away from the cut-eye. A gas production pipe is placed in each borehole, and each borehole is sealed with a plugging material. The gas production pipe is fixed, and the outer end of the plugging material is flush with the borehole opening. A gap is left between the inner end of the plugging material and the bottom of the borehole, which serves as a gas production chamber. The head end of the gas production pipe is placed in the gas production chamber. An L-shaped elbow pipe is provided at the opening of each borehole, and the tail end of the gas production pipe passes through the L-shaped elbow pipe;

[0010] S3. Build an inner closed wall in the abandoned tunnel and arrange the gas injection pipe;

[0011] S4. Inject CO2 gas into the scrapped tunnel on the inner side of the sealed wall through the gas injection pipe and perform a tightness test;

[0012] S5. Fill gravel along the outer side of the inner sealed wall from the inside to the outside. During the gravel filling process, connect the extended gas injection pipe and gas production pipe in sequence, and lay the grouting pipe;

[0013] S6. Build the outer closed wall and arrange the gas injection pipe and grouting pipe;

[0014] S7. injecting grouting material into the abandoned roadway filled with crushed stone and hardening it;

[0015] S8, coal working face mining, connect the extended gas injection pipe and gas production pipe in sequence, and observe the CO2 gas pressure in the abandoned roadway. If the pressure drops, add CO2 gas;

[0016] S9. Liquid CO2 filling: When the goaf roof continues to collapse and compact the goaf, connect the tail end of the gas injection pipe to the external gas injection hose. Before injection, all the gas pipe openings must be sealed first. Then, inject liquid CO2 into the abandoned tunnel on the inner side of the closed wall, and connect the tail end of the gas injection pipe to the 1-inch pipeline through a reducer.

[0017] S10. CO2 gas diffusion range detection: As the coal mining face continues to advance, the 1-inch pipeline and the gas production pipe inside it are continuously connected, and the gas in each borehole is sampled through the gas production pipe to detect the CO2 gas concentration, thereby realizing the detection of the CO2 gas diffusion range. When the CO2 gas concentration in the gas sample in a certain borehole is detected to be more than 50% for three consecutive days, it is considered that CO2 gas has diffused to the borehole, and the gas production pipe in the borehole is blocked. In the future, CO2 gas detection and gas production pipe extension will no longer be carried out on the borehole, and this cycle will be repeated until the coal mining face is recovered.

[0018] Furthermore, the inner sealed wall includes a first inner wall, a first filler, and a first outer wall, and an air injection pipe is inserted through the first inner wall, the first filler, and the first outer wall; the outer sealed wall includes a second inner wall, a second filler, and a second outer wall, and an air injection pipe and a grouting pipe are inserted through the second inner wall, the second filler, and the second outer wall; L=30m;

[0019] The total thickness of the inner sealed wall is 3.0m, the thickness of the first inner wall and the first outer wall are both 0.37m, and the thickness of the first filler is 2.26m; the total thickness of the outer sealed wall is 2.0m, the thickness of the second inner wall and the second outer wall are both 0.37m, and the thickness of the second filler is 1.26m.

[0020] Furthermore, in step S2, the specific steps of constructing a plurality of boreholes on the sidewall of the abandoned roadway adjacent to the inner sealed wall and in the coal seam outside the abandoned roadway away from the cutting hole are as follows:

[0021] Construct multiple holes on the side of the abandoned roadway adjacent to the inner closed wall and away from the cut-off eye, with the horizontal distance between each hole along the roadway direction being 0.5m, and then construct a drill hole in the coal seam outside the abandoned roadway away from the cut-off eye at each hole; the diameter of the drill hole is 75mm, and the horizontal distance between the line connecting the position of the end hole of each drill hole and the inner wall of the inner closed wall is 10m, the spacing between the positions of the end holes of each drill hole is 2m, the drill hole closest to the side of the abandoned roadway is 4m away from the side of the abandoned roadway; the straight-line distance k between the drill hole closest to the abandoned roadway wall and the outer edge of the inner outer wall of the inner closed wall is not less than 1m;

[0022] Height of the drill hole: If the coal seam thickness is less than the roadway height, the final hole position is half the coal seam thickness; if the coal seam thickness is higher than the roadway height, the final hole position is half the roadway height.

[0023] Furthermore, in step S2, the total length d of the plugging material in the borehole is not less than 15m, and the length l of the gas production chamber is 20cm-50cm; the gas production pipe is a stainless steel capillary tube, and the outer diameter of the stainless steel capillary tube is 2mm-3mm.

[0024] Furthermore, in step S3, the specific steps of building the inner closed wall and arranging the gas injection pipe are as follows:

[0025] Cutting: Cutting is carried out around the abandoned roadway at a distance of 30m from the opening of the coal mining face. First, the axial cutting width of the two sides of the abandoned roadway is 1.0m, and the cutting depth is 50cm; then the axial cutting width of the bottom plate is 1.0m, and the cutting depth is 50cm when the bottom plate is a coal seam, and the cutting depth is 30cm when the bottom plate is a rock layer; finally, the axial cutting width of the top plate is 1.0m, and the cutting depth is 50cm when the top plate is a coal seam, and the cutting depth is 30cm when the top plate is a rock layer;

[0026] Build the first inner wall: After the trenching is completed, use bricks or stones to build the first inner wall. When building the first inner wall, insert the gas injection pipe horizontally. The front end of the gas injection pipe passes through the first inner wall and penetrates 2.0m into the scrapped roadway. The rear end of the gas injection pipe passes through the first filling and the first outer wall in sequence. After the first inner wall is built, continue to trench the scrapped roadway according to the above trenching sequence. The trench width is 2.0m and the trench depth remains unchanged.

[0027] Filling the first filling material and building the first outer wall: when loess is used as the first filling material, bricks or stones are used to build the first outer wall at the position of the first outer wall, and loess is filled between the first outer wall and the first inner wall as the first outer wall is built; when fluid concrete is used as the first filling material, after the first inner wall is built, the scrapped tunnel is continued to be grooved according to the above-mentioned groove order, the groove depth remains unchanged, and the groove width is 2.0m. Then, bricks or stones are used to build the first outer wall at the position of the first outer wall. During the construction, a grouting pipe is additionally left on the first outer wall. After the first outer wall is built, fluid concrete is injected between the first inner wall and the first outer wall through the grouting pipe. After the fluid concrete hardens, the grouting pipe is removed and the grouting pipe installation position is sealed.

[0028] Furthermore, in step S4, the specific steps of injecting CO2 gas into the scrapped tunnel on the inner side of the inner sealed wall through the gas injection pipe and performing a tightness test are as follows:

[0029] The tail end of the gas injection pipe on the outside of the first outer wall is connected to the external gas injection hose in the scrapped tunnel. In order to prevent gas from entering the stainless steel capillary, it is necessary to seal the openings of each gas production pipe before gas injection. CO2 gas is injected into the scrapped tunnel inside the inner closed wall through the external gas injection hose and the gas injection pipe until the gas pressure in the scrapped tunnel exceeds 20% of the coal seam gas pressure and remains unchanged for 24 hours. At this time, the sealing of the inner closed wall meets the requirements; after the sealing test is completed, the external gas injection hose is removed from the gas injection pipe.

[0030] Furthermore, the specific steps of step S5 are:

[0031] The crushed stone produced by the excavation of the rock tunnel is directly transported to the scrapped tunnel, and the crushed stone is filled from the inside to the outside along the outer side of the inner closed wall. During the filling process of the crushed stone, multiple gas injection pipes are connected in sequence at the tail end of the gas injection pipe. When the gas injection pipe is laid to the vicinity of the four adjacent boreholes, four tees are installed on the gas injection pipe in sequence, and respectively connected to the L-shaped elbow pipes on the four boreholes, so that the gas production pipe enters the gas injection pipe through the tees. The gas injection pipe is installed on the outermost tee to continue filling with crushed stone. The gas injection pipe and all gas production pipes are continuously connected and extended outward along with the gravel filling; when the gravel filling is to a distance of 15m from the first inner wall, the grouting pipe is laid along with the gravel filling. The gas injection pipe, grouting pipe and all gas production pipes are continuously connected and extended until the gravel filling is completed.

[0032] Furthermore, in step S6, the specific steps of building the outer closed wall and arranging the gas injection pipe and the grouting pipe are as follows:

[0033] Grooving: Build the outer closed wall from the inside out at a distance of 28m from the first inner wall. When building the outer closed wall, first, groove the surrounding areas of the abandoned roadway. First, the axial groove width of the two sides of the abandoned roadway is 1.0m, and the groove depth is 50cm. Then, the axial groove width of the bottom plate is 1.0m, and the groove depth is 50cm when the bottom plate is a coal seam, and the groove depth is 30cm when the bottom plate is a rock layer. Finally, the axial groove width of the top plate is 1.0m, and the groove depth is 50cm when the top plate is a coal seam, and the groove depth is 30cm when the top plate is a rock layer.

[0034] Build the second inner wall: After the trenching is completed, use bricks or stones to build the second inner wall. When building the second inner wall, insert the air injection pipe and grouting pipe in the horizontal direction. The front ends of the air injection pipe and grouting pipe are respectively connected to the air injection pipe and grouting pipe laid during the gravel filling. The rear ends of the air injection pipe and grouting pipe must be exposed from the second outer wall. After the second inner wall is built, continue to trench the scrapped roadway according to the above trenching sequence. The trench width is 1.0m and the trench depth remains unchanged.

[0035] Filling the second filling material and building the second outer wall: when loess is used as the second filling material, bricks or stones are used to build the second outer wall at the position of the second outer wall, and loess is filled between the second outer wall and the second inner wall as the second outer wall is built; when fluid concrete is used as the second filling material, after the second inner wall is built, the scrapped tunnel is continued to be grooved in accordance with the above-mentioned groove order, and the groove depth and width remain unchanged, and then bricks or stones are used to build the first outer wall at the position of the second outer wall. During the construction, a grouting pipe is additionally left on the first outer wall. After the first outer wall is built, fluid concrete is injected between the first inner wall and the first outer wall through the grouting pipe. After the fluid concrete hardens, the grouting pipe is removed and the grouting pipe installation position is sealed.

[0036] Furthermore, the specific steps of step S7 are:

[0037] Connect the tail end of the grouting pipe on the outer closed wall to the feed pipe in the scrapped tunnel for inputting grouting materials. Connect the feed pipe to the grouting pump. Use the grouting pump to inject the grouting material into the scrapped tunnel filled with gravel through the feed pipe and the grouting pipe, and fill it up. After the grouting is completed, wait for it to harden.

[0038] Furthermore, the specific steps of step S8 are:

[0039] As the coal mining face is continuously mined, the roof of the goaf will collapse periodically. While the coal mining face is being mined, the gas injection pipe outside the outer closed wall and the gas production pipe inside it are continuously connected;

[0040] Each time the gas injection pipe is connected, it is necessary to connect the gas injection pipe to the external gas injection hose on one side of the coal mining working face. The external gas injection hose is equipped with a pressure gauge and a valve. The pressure gauge value must be checked each time a connection is made. When it is observed that the CO2 gas pressure in the scrapped tunnel has dropped by 10% compared with the pressure in step S2, it is necessary to replenish CO2 gas through the gas injection pipe to restore its pressure to 120% of the gas pressure in the coal seam.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention builds two closed walls in the abandoned tunnel and fills the space between the two closed walls with crushed stones. The closed walls are simple to construct and have strong adaptability. Each closed wall consists of two walls and a filling material. It has a stable structure and a strong pressure-bearing capacity. It can effectively prevent the penetration of moisture and gas, and maintain the stability of the internal environment of the abandoned tunnel.

[0043] (2) The scrapped tunnel of the present invention is sealed and filled with two closed walls only within 30m of the coal mining working face, and the filling section of the tunnel is filled with only crushed stones excavated from the rock tunnel, which effectively reduces the scheduling workload of the entire mine, and the overall construction difficulty is low and the construction steps are simple.

[0044] (3) The present invention first injects CO2 gas into the abandoned tunnel, which can effectively reduce the oxygen content of the air inside it, inhibit the spontaneous combustion of coal, and ensure the construction safety during the sealing period of the abandoned tunnel; the inert gas has good stability, is environmentally friendly and pollution-free, and has low economic cost; and it can be used to detect the sealing of the closed wall.

[0045] (4) In the present invention, after the roof rock of the goaf continuously collapses, the goaf is continuously re-compacted. At this time, liquid CO2 is injected into the abandoned tunnel to achieve permanent sealing, thereby helping to reduce greenhouse gas emissions and achieve the reuse of abandoned tunnels.

[0046] (5) The present invention constructs a drilling hole around the abandoned roadway, samples the gas in the borehole through the gas sampling pipe, and detects the diffusion range of CO2 gas in the abandoned roadway. It can provide a reference for the reasonable coal pillar between the abandoned coal mining working face and the adjacent coal mining working face, and at the same time provide a reference for the support measures in the roadway of the adjacent working face, thereby effectively ensuring that the liquid CO2 in the abandoned roadway will not leak. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the location of the abandoned underground tunnel of the present invention.

[0048] Figure 2 This is a schematic diagram of the inner closed wall, outer closed wall and drilling arrangement in the scrapped tunnel of the present invention.

[0049] Figure 3 This is a schematic diagram of the installation structure of the gas production pipe and L-shaped elbow in the drill hole of the present invention.

[0050] Figure 4 This is a schematic diagram of the structure of the inner sealed wall of the present invention built in a scrapped tunnel.

[0051] Figure 5 This is a schematic diagram of the structure of the outer closed wall of the present invention built in a scrapped tunnel.

[0052] Figure 6 It is a structural diagram of the present invention after completing steps S1-S7 in a scrapped tunnel before mining at a coal working face.

[0053] Figure 7 This is a construction schematic diagram of injecting liquid CO2 into an abandoned tunnel during the coal mining face recovery process of the present invention.

[0054] Figure 8 This is a schematic diagram of the installation of the gas injection pipe, tee, L-shaped elbow pipe and gas production pipe of the present invention.

[0055] Description of reference numerals:

[0056] 1. Abandoned tunnel; 2. Inner sealed wall; 21. First inner wall; 22. First filling material; 23. First outer wall; 3. Outer sealed wall; 31. Second inner wall; 32. Second filling material; 33. Second outer wall; 4. Cutting hole; 5. Gas injection pipe; 6. Grouting pipe; 7. Drill hole; 8. Gas production pipe; 9. Sealing material; 10. Gas production chamber; 11. L-shaped elbow pipe; 12. CO2 gas; 13. Gravel; 14. Tee; 15. Liquid CO2; 16. Goaf;

[0057] 100, return air tunnel; 200, intake air tunnel; 300, auxiliary transport tunnel in mining area; 400, belt tunnel in mining area; 500, return air tunnel in mining area. DETAILED DESCRIPTION

[0058] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0059] Example

[0060] Reference Figures 1-8 A method for filling abandoned tunnels with multiphase materials in a self-igniting coal seam mining working face. The abandoned tunnel 1 is longer than 30m. The layout of the abandoned tunnels in the mine is as follows: Figure 1 As shown, the cut hole 4 is perpendicular to the return air tunnel 100 and the air inlet tunnel 200. A mining area auxiliary transport tunnel 300, a mining area belt tunnel 400, and a mining area return air tunnel 500 are also arranged underground. The scrapped tunnel 1 is located on the inner side of the cut hole 4. The specific steps include:

[0061] S1. Determination of the sealed position of scrapped tunnel 1:

[0062] Reference Figure 2 , build two closed walls in the abandoned tunnel 1, namely the inner closed wall 2 and the outer closed wall 3. The outer closed wall 3 is built at the connection between the abandoned tunnel 1 and the cut hole 4, and the inner closed wall 2 is built in the abandoned tunnel 1 at a distance of L from the outer closed wall 3, L = 30m;

[0063] The inner sealed wall 2 includes a first inner wall 21, a first filler 22, and a first outer wall 23, and an air injection pipe 5 is inserted through the first inner wall 21, the first filler 22, and the first outer wall 23; the outer sealed wall 3 includes a second inner wall 31, a second filler 32, and a second outer wall 33, and an air injection pipe 5 and a grouting pipe 6 are inserted through the second inner wall 31, the second filler 32, and the second outer wall 33;

[0064] The total thickness of the inner sealed wall 2 is 3.0m, the thickness of the first inner wall 21 and the first outer wall 23 are both 0.37m, and the thickness of the first filler 22 is 2.26m; the total thickness of the outer sealed wall 3 is 2.0m, the thickness of the second inner wall 31 and the second outer wall 33 are both 0.37m, and the thickness of the second filler 32 is 1.26m;

[0065] S2. Drill a hole 7 next to the abandoned tunnel 1 and lay out the gas production pipe 8:

[0066] On the sidewall of the abandoned roadway 1 adjacent to the inner closed wall 2 and away from the cutting eye, several boreholes 7 are constructed in the outer coal seam of the abandoned roadway 1 away from the cutting eye 4. The specific steps are: construct multiple holes on the sidewall of the abandoned roadway 1 adjacent to the inner closed wall 2 and away from the cutting eye 4, with a horizontal distance of 0.5m between each hole along the direction of the roadway, and then construct a borehole 7 in the outer coal seam of the abandoned roadway 1 away from the cutting eye 4 at each hole; the diameter of the borehole 7 is 75mm, and the horizontal distance between the line where the end hole of each borehole 7 is located and the inner wall of the inner closed wall 2 is 10m, and the spacing between the end hole positions of each borehole 7 is 2m, the borehole 7 closest to the sidewall of the abandoned roadway 1 is 4m away from the sidewall of the abandoned roadway 1; the straight-line distance k between the borehole 7 closest to the wall of the abandoned roadway 1 and the outer edge of the outer wall of the inner closed wall 2 is not less than 1m;

[0067] The height of the borehole 7 is as follows: if the coal seam thickness is less than the roadway height, the final hole position is half the coal seam thickness; if the coal seam thickness is greater than the roadway height, the final hole position is half the roadway height;

[0068] In this embodiment, the number of boreholes 7 is 4, and the horizontal distance between the final position of each of the four boreholes 7 and the inner wall of the inner closed wall 2 is 10m. The distances between the final position of each borehole 7 and the sidewall of the abandoned tunnel 1 are 4m, 6m, 8m, and 10m, respectively.

[0069] Reference Figure 3 , a gas production pipe 8 is placed in each borehole 7, and each borehole 7 is sealed with a plugging material 9. The gas production pipe 8 is fixed, and the outer end of the plugging material 9 is flush with the borehole 7 orifice, and a gap is left between the inner end of the plugging material 9 and the bottom of the borehole 7, which serves as a gas production chamber 10. The head end of the gas production pipe 8 is placed in the gas production chamber 10. An L-shaped elbow pipe 11 is provided at the orifice of each borehole 7 for connecting to a tee 14. The tail end of the gas production pipe 8 passes through the L-shaped elbow pipe 11;

[0070] Preferably, the total length d of the plugging material 9 in the borehole 7 is not less than 15 m, and the length l of the gas extraction chamber 10 is 20 cm to 50 cm;

[0071] The gas sampling pipe 8 is a stainless steel capillary tube, and the outer diameter of the stainless steel capillary tube is 2mm-3mm;

[0072] S3. Build an inner closed wall 2 in the abandoned tunnel 1 and arrange gas injection pipes 5. In this embodiment, the gas injection pipes 5 are all 2-inch pipes, and the length of a single gas injection pipe 5 is 1m-1.5m. When extending, the gas injection pipes 5 are connected to each other;

[0073] Reference Figure 4 The specific steps for constructing the inner closed wall 2 are as follows:

[0074] Cutting: Cutting is carried out around the abandoned roadway 1 at a distance of 30m from the opening 4 of the coal mining face. First, the axial cutting width of the two sides of the abandoned roadway 1 is 1.0m, and the cutting depth is 50cm. Then, the axial cutting width of the bottom plate is 1.0m, and the cutting depth is 50cm when the bottom plate is a coal seam, and the cutting depth is 30cm when the bottom plate is a rock layer. Finally, the axial cutting width of the top plate is 1.0m, and the cutting depth is 50cm when the top plate is a coal seam, and the cutting depth is 30cm when the top plate is a rock layer.

[0075] Building the first inner wall 21: After the trenching is completed, the first inner wall 21 is built using bricks or stones. When building the first inner wall 21, the gas injection pipe 5 is inserted horizontally. The front end of the gas injection pipe 5 passes through the first inner wall 21 and penetrates 2.0 m into the scrapped tunnel 1. The rear end of the gas injection pipe 5 passes through the first filling material 22 and the first outer wall 23 in sequence. After the first inner wall 21 is built, the scrapped tunnel 1 is further trenched according to the above trenching sequence. The trench width is 2.0 m and the trench depth remains unchanged.

[0076] Filling the first filling material 22 and building the first outer wall 23: When loess is used as the first filling material 22, bricks or stones are used to build the first outer wall 23 at the position of the first outer wall 23. As the first outer wall 23 is built, loess is filled between the first outer wall 23 and the first inner wall 21. When fluid concrete is used as the first filling material 22, after the first inner wall 21 is built, the scrapped tunnel 1 is further excavated according to the above-mentioned excavation sequence. The excavation depth remains unchanged and the excavation width is 2.0 m. Then, bricks or stones are used to build the first outer wall 23 at the position of the first outer wall 23. During the construction, a grouting pipe 6 (not shown in the figure) is additionally provided on the first outer wall 23. After the first outer wall 23 is built, fluid concrete is injected into the space between the first inner wall 21 and the first outer wall 23 through the grouting pipe 6. After the fluid concrete hardens, the grouting pipe 6 is removed and the installation position of the grouting pipe 6 is sealed.

[0077] S4, injecting CO2 gas 12 into the scrapped tunnel 1 on the inner side of the inner closed wall 2 through the gas injection pipe 5, and performing a tightness test. The specific steps are as follows:

[0078] Reference Figure 6 , connect the tail end of the gas injection pipe 5 outside the first outer wall 23 to the external gas injection hose in the scrapped tunnel 1, and inject CO2 gas 12 into the scrapped tunnel 1 inside the inner closed wall 2 (to prevent gas from entering the stainless steel capillary tubes, it is necessary to seal the openings of each stainless steel capillary tube before gas injection) until the gas pressure in the scrapped tunnel 1 exceeds 20% of the coal seam gas pressure (for example, if the coal seam gas pressure is 0.5 MPa, the gas pressure in the tunnel after the CO2 gas 12 is injected should be no less than 0.6 MPa), and remain unchanged for 24 hours. At this time, the sealing of the inner closed wall 2 meets the requirements; after the sealing test is completed, remove the external gas injection hose from the gas injection pipe 5;

[0079] S5, filling gravel 13 along the outer side of the inner closed wall 2 from the inside to the outside. During the filling process of the gravel 13, the extended gas injection pipe 5 and the gas production pipe 8 are connected in sequence, and the grouting pipe 6 is laid. The specific implementation steps are as follows:

[0080] Reference Figure 6 and Figure 8 The crushed stones 13 produced by the excavation of the rock tunnel are directly transported to the abandoned tunnel 1, and the crushed stones 13 are filled from the inside to the outside along the outside of the first outer wall 23 of the inner closed wall 2. During the filling process of the crushed stones 13, the crushed stones 13 with smaller blocks are placed on the upper part of the abandoned tunnel 1. During the filling process of the crushed stones 13, multiple gas injection pipes 5 are connected in sequence at the tail end of the gas injection pipe 5. When the gas injection pipe 5 is laid to the vicinity of the openings of the four adjacent boreholes 7, four tees 14 are installed in sequence on the gas injection pipe 5, which are connected to the four drill holes 7 respectively. Connect the L-shaped elbow pipe 11 on the hole 7, install the gas injection pipe 5 on the outermost tee 14, and let the stainless steel capillary enter the gas injection pipe 5 through the tee 14. Continue to fill the gravel 13. The gas injection pipe 5 and all the gas production pipes 8 are continuously connected and extended outward as the gravel 13 is filled. When the gravel 13 is filled to a distance of 15m from the first inner wall 21, start laying the grouting pipe 6 as the gravel 13 is filled. The gas injection pipe 5, the grouting pipe 6 and all the gas production pipes 8 are continuously connected and extended until the gravel 13 is filled.

[0081] S6, build the outer closed wall 3 and arrange the gas injection pipe 5 and the grouting pipe 6, the specific steps are:

[0082] Reference Figure 5 , Grooving: Build the outer closed wall 3 from the inside to the outside at a distance of 28m from the first inner wall 21. When building the outer closed wall 3, first, grooves are cut around the abandoned tunnel 1. First, the axial groove width of the two sides of the abandoned tunnel 1 is 1.0m, and the groove depth is 50cm; then, the axial groove width of the bottom plate is 1.0m, and the groove depth is 50cm when the bottom plate is a coal seam, and the groove depth is 30cm when the bottom plate is a rock layer; finally, the axial groove width of the top plate is 1.0m, and the groove depth is 50cm when the top plate is a coal seam, and the groove depth is 30cm when the top plate is a rock layer;

[0083] Building the second inner wall 31: After the trenching is completed, the second inner wall 31 is built using bricks or stones. When building the second inner wall 31, the air injection pipe 5 and the grouting pipe 6 are inserted horizontally. The front ends of the air injection pipe 5 and the grouting pipe 6 are respectively connected to the air injection pipe 5 and the grouting pipe 6 laid when filling the gravel 13. The tail ends of the air injection pipe 5 and the grouting pipe 6 must be exposed from the second outer wall 33. After the second inner wall 31 is built, the scrapped tunnel 1 is further trenched according to the above trenching sequence. The trenching width is 1.0 m and the trenching depth remains unchanged.

[0084] Filling the second filling material 32 and building the second outer wall 33: When loess is used as the second filling material 32, bricks or stones are used to build the second outer wall 33 at the position of the second outer wall 33. Between the second outer wall 33 and the second inner wall 31, loess is filled as the second outer wall 33 is built. When fluid concrete is used as the second filling material 32, after the second inner wall 31 is built, the scrapped tunnel 1 is further grooved according to the above-mentioned groove cutting sequence, and the groove cutting depth and width remain unchanged. Then, bricks or stones are used to build the first outer wall 23 at the position of the second outer wall 33. During the construction, a grouting pipe 6 (not shown in the figure) is additionally provided on the first outer wall 23. After the first outer wall 23 is built, fluid concrete is injected into the space between the first inner wall 21 and the first outer wall 23 through the grouting pipe 6. After the fluid concrete hardens, the grouting pipe 6 is removed, and the installation position of the grouting pipe 6 is sealed.

[0085] S7, injecting grouting material into the abandoned tunnel 1 filled with crushed stone 13 and hardening it:

[0086] Connect the tail end of the grouting pipe 6 on the outer closed wall 3 to the feed pipe for inputting grouting material in the scrapped tunnel 1, connect the feed pipe to the grouting pump, and use the grouting pump to inject the grouting material into the scrapped tunnel 1 filled with gravel 13 through the feed pipe and the grouting pipe 6, and fill it up. After the grouting is completed, wait for it to harden;

[0087] S8, coal working face mining, sequentially connect the extended gas injection pipe 5 and the gas production pipe 8, and observe the pressure of the CO2 gas 12 in the abandoned roadway 1. If the pressure drops, replenish the CO2 gas 12. The specific steps include:

[0088] As the coal mining face is continuously mined, the roof of the goaf 16 will periodically collapse. While the coal mining face is being mined, the gas injection pipe 5 outside the outer closed wall 3 and the gas production pipe 8 inside it are continuously connected;

[0089] Each time the gas injection pipe 5 is connected, it is necessary to connect the gas injection pipe 5 to the external gas injection hose on the side of the coal mining working face. The external gas injection hose is provided with a pressure gauge and a valve. The pressure gauge value must be checked each time the connection is made. When the pressure of the CO2 gas 12 in the scrapped roadway 1 is observed to drop by 10% compared with the pressure in step S2, it is necessary to replenish the CO2 gas 12 through the gas injection pipe 5 to restore its pressure to 120% of the gas pressure in the coal seam.

[0090] S9, Liquid CO215 filling:

[0091] Reference Figure 7, when the top plate of the goaf 16 continues to collapse and compact the goaf 16 (in this embodiment, the top plate of the goaf 16 completes 5 collapses), the tail end of the gas injection pipe 5 is connected to the external gas injection hose. Before injection, it is still necessary to seal the pipe openings of all gas production pipes 8, and then inject liquid CO215 into the scrapped tunnel 1 on the inner side of the inner closed wall 2 until the pressure of the liquid CO215 in the scrapped tunnel 1 reaches 12MPa. At this time, the valve on the external gas injection hose is closed and the pressure gauge is removed, and the external gas injection hose is disassembled from the gas injection pipe 5; since it is no longer necessary to inject CO2 gas 12 into the scrapped tunnel 1, the tail end of the gas injection pipe 5 is connected to the 1-inch pipeline through a reducer. On the one hand, the 1-inch pipeline can be used to protect the gas production pipe 8, and on the other hand, the construction cost can be reduced;

[0092] S10, CO2 gas 12 diffusion range detection:

[0093] As the coal mining face continues to advance, the 1-inch pipeline and the gas production pipe 8 inside it are continuously connected, and the gas in each borehole 7 is sampled through the gas production pipe 8 at least once a day to observe the diffusion radius of the CO2 gas 12 around the scrapped tunnel 1. When the CO2 gas 12 concentration in the gas sample in a certain borehole 7 is detected to be more than 50% for three consecutive days, it is considered that the CO2 gas 12 has diffused to that place and the gas production pipe 8 in the borehole 7 is blocked, and it will no longer be tested or extended in the future; this cycle is repeated until the coal mining face is recovered.

[0094] The above content is only a preferred embodiment of the present invention. For ordinary technicians in this field, according to the concept of the present invention, many changes can be made in the specific implementation method and application scope. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of the present invention.

Claims

1. A method for filling abandoned tunnels with multiphase materials in a self-igniting coal seam mining working face, characterized in that: The specific steps include: S1. Determination of sealed location of scrapped tunnel: Two closed walls are built in the abandoned roadway, namely the inner closed wall and the outer closed wall. The outer closed wall is built at the connection between the abandoned roadway and the cut hole, and the inner closed wall is built on the inner side of the abandoned roadway at a distance L from the outer closed wall. The inner sealed wall includes a first inner wall, a first filler, and a first outer wall, and an air injection pipe is inserted through the first inner wall, the first filler, and the first outer wall; the outer sealed wall includes a second inner wall, a second filler, and a second outer wall, and an air injection pipe and a grouting pipe are inserted through the second inner wall, the second filler, and the second outer wall; L = 30m; The total thickness of the inner sealed wall is 3.0m, the thickness of the first inner wall and the first outer wall are both 0.37m, and the thickness of the first filler is 2.26m; the total thickness of the outer sealed wall is 2.0m, the thickness of the second inner wall and the second outer wall are both 0.37m, and the thickness of the second filler is 1.26m; S2. Drill holes next to the abandoned roadway and lay out the gas production pipe: On the side of the abandoned roadway adjacent to the inner closed wall, several boreholes are constructed in the coal seam outside the abandoned roadway away from the cutting eye. A gas production pipe is placed in each borehole, and each borehole is sealed with a plugging material. The gas production pipe is fixed, and the outer end of the plugging material is flush with the borehole opening. A gap is left between the inner end of the plugging material and the bottom of the borehole, which serves as a gas production chamber. The head end of the gas production pipe is placed in the gas production chamber. An L-shaped elbow pipe is provided at the opening of each borehole, and the tail end of the gas production pipe passes through the L-shaped elbow pipe; S3. Build an inner closed wall in the abandoned tunnel and arrange the gas injection pipe; S4. Inject CO2 gas into the scrapped tunnel on the inner side of the sealed wall through the gas injection pipe and perform a tightness test; S5. Fill gravel along the outer side of the inner sealed wall from the inside to the outside. During the gravel filling process, connect the extended gas injection pipe and gas production pipe in sequence, and lay the grouting pipe; S6. Build the outer closed wall and arrange the gas injection pipe and grouting pipe; S7. injecting grouting material into the abandoned roadway filled with crushed stone and hardening it; S8, coal working face mining, connect the extended gas injection pipe and gas production pipe in sequence, and observe the CO2 gas pressure in the abandoned roadway. If the pressure drops, add CO2 gas; S9. Liquid CO2 filling: When the goaf roof continues to collapse and compact the goaf, connect the tail end of the gas injection pipe to the external gas injection hose. Before injection, all the gas pipe openings must be sealed first. Then, inject liquid CO2 into the abandoned tunnel on the inner side of the closed wall, and connect the tail end of the gas injection pipe to the 1-inch pipeline through a reducer. S10. CO2 gas diffusion range detection: As the coal mining face continues to advance, the 1-inch pipeline and the gas production pipe inside it are continuously connected, and the gas in each borehole is sampled through the gas production pipe to detect the CO2 gas concentration, thereby realizing the detection of the CO2 gas diffusion range. When the CO2 gas concentration in the gas sample in a certain borehole is detected to be more than 50% for three consecutive days, it is considered that CO2 gas has diffused to the borehole, and the gas production pipe in the borehole is blocked. In the future, CO2 gas detection and gas production pipe extension will no longer be carried out on the borehole, and this cycle will be repeated until the coal mining face is recovered.

2. A method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: In step S2, the specific steps of constructing a plurality of boreholes on the side of the abandoned roadway adjacent to the inner closed wall and away from the cut-hole, and into the outer coal seam of the abandoned roadway away from the cut-hole are as follows: Construct multiple holes on the side of the abandoned roadway adjacent to the inner closed wall, with the horizontal distance between each hole along the direction of the roadway being 0.5m, and then construct a hole in the coal seam outside the abandoned roadway away from the cut eye at each hole; the diameter of the hole is 75mm, and the horizontal distance between the line connecting the position of the end hole of each hole and the inner wall of the inner closed wall is 10m, the spacing between the positions of the end holes of each hole is 2m, the hole closest to the side of the abandoned roadway is 4m away from the side of the abandoned roadway; the straight-line distance k between the hole closest to the abandoned roadway wall and the outer edge of the inner outer wall of the inner closed wall is not less than 1m; Height of the drill hole: If the coal seam thickness is less than the roadway height, the final hole position is half the coal seam thickness; if the coal seam thickness is higher than the roadway height, the final hole position is half the roadway height.

3. The method for filling abandoned tunnels with multiphase materials in a self-igniting coal seam mining working face according to claim 1, characterized in that: In step S2, the total length d of the plugging material in the borehole is not less than 15m, and the length l of the gas collection chamber is 20cm-50cm; the gas collection pipe is a stainless steel capillary tube, and the outer diameter of the stainless steel capillary tube is 2mm-3mm.

4. The method for filling abandoned tunnels with multiphase materials in a self-igniting coal seam mining working face according to claim 1, characterized in that: In step S3, the specific steps of building the inner closed wall and arranging the gas injection pipe are as follows: Cutting: Cutting is carried out around the abandoned roadway at a distance of 30m from the opening of the coal mining face. First, the axial cutting width of the two sides of the abandoned roadway is 1.0m, and the cutting depth is 50cm; then the axial cutting width of the bottom plate is 1.0m, and the cutting depth is 50cm when the bottom plate is a coal seam, and the cutting depth is 30cm when the bottom plate is a rock layer; finally, the axial cutting width of the top plate is 1.0m, and the cutting depth is 50cm when the top plate is a coal seam, and the cutting depth is 30cm when the top plate is a rock layer; Build the first inner wall: After the trenching is completed, use bricks or stones to build the first inner wall. When building the first inner wall, insert the gas injection pipe horizontally. The front end of the gas injection pipe passes through the first inner wall and penetrates 2.0m into the scrapped roadway. The rear end of the gas injection pipe passes through the first filling and the first outer wall in sequence. After the first inner wall is built, continue to trench the scrapped roadway according to the above trenching sequence. The trench width is 2.0m and the trench depth remains unchanged. Filling the first filling material and building the first outer wall: when loess is used as the first filling material, bricks or stones are used to build the first outer wall at the position of the first outer wall, and loess is filled between the first outer wall and the first inner wall as the first outer wall is built; when fluid concrete is used as the first filling material, after the first inner wall is built, the scrapped tunnel is continued to be grooved according to the above-mentioned groove order, the groove depth remains unchanged, and the groove width is 2.0m. Then, bricks or stones are used to build the first outer wall at the position of the first outer wall. During the construction, a grouting pipe is additionally left on the first outer wall. After the first outer wall is built, fluid concrete is injected between the first inner wall and the first outer wall through the grouting pipe. After the fluid concrete hardens, the grouting pipe is removed and the grouting pipe installation position is sealed.

5. The method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: In step S4, the specific steps of injecting CO2 gas into the scrapped tunnel on the inner side of the inner closed wall through the gas injection pipe and performing a tightness test are as follows: The tail end of the gas injection pipe on the outside of the first outer wall is connected to the external gas injection hose in the scrapped tunnel. In order to prevent gas from entering the stainless steel capillary, it is necessary to seal the openings of each gas production pipe before gas injection. CO2 gas is injected into the scrapped tunnel inside the inner closed wall through the external gas injection hose and the gas injection pipe until the gas pressure in the scrapped tunnel exceeds 20% of the coal seam gas pressure and remains unchanged for 24 hours. At this time, the sealing of the inner closed wall meets the requirements; after the sealing test is completed, the external gas injection hose is removed from the gas injection pipe.

6. The method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: The specific steps of step S5 are: The crushed stone produced by the excavation of the rock tunnel is directly transported to the scrapped tunnel, and the crushed stone is filled from the inside to the outside along the outer side of the inner closed wall. During the filling process of the crushed stone, multiple gas injection pipes are connected in sequence at the tail end of the gas injection pipe. When the gas injection pipe is laid to the vicinity of the four adjacent boreholes, four tees are installed on the gas injection pipe in sequence, and respectively connected to the L-shaped elbow pipes on the four boreholes, so that the gas production pipe enters the gas injection pipe through the tees. The gas injection pipe is installed on the outermost tee to continue filling with crushed stone. The gas injection pipe and all gas production pipes are continuously connected and extended outward along with the gravel filling; when the gravel filling is to a distance of 15m from the first inner wall, the grouting pipe is laid along with the gravel filling. The gas injection pipe, grouting pipe and all gas production pipes are continuously connected and extended until the gravel filling is completed.

7. The method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: In step S6, the specific steps of building the outer closed wall and arranging the gas injection pipe and the grouting pipe are as follows: Grooving: Build the outer closed wall from the inside out at a distance of 28m from the first inner wall. When building the outer closed wall, first, groove the surrounding areas of the abandoned roadway. First, the axial groove width of the two sides of the abandoned roadway is 1.0m, and the groove depth is 50cm. Then, the axial groove width of the bottom plate is 1.0m, and the groove depth is 50cm when the bottom plate is a coal seam, and the groove depth is 30cm when the bottom plate is a rock layer. Finally, the axial groove width of the top plate is 1.0m, and the groove depth is 50cm when the top plate is a coal seam, and the groove depth is 30cm when the top plate is a rock layer. Build the second inner wall: After the trenching is completed, use bricks or stones to build the second inner wall. When building the second inner wall, insert the air injection pipe and grouting pipe in the horizontal direction. The front ends of the air injection pipe and grouting pipe are respectively connected to the air injection pipe and grouting pipe laid during the gravel filling. The rear ends of the air injection pipe and grouting pipe must be exposed from the second outer wall. After the second inner wall is built, continue to trench the scrapped roadway according to the above trenching sequence. The trench width is 1.0m and the trench depth remains unchanged. Filling the second filling material and building the second outer wall: when loess is used as the second filling material, bricks or stones are used to build the second outer wall at the position of the second outer wall, and loess is filled between the second outer wall and the second inner wall as the second outer wall is built; when fluid concrete is used as the second filling material, after the second inner wall is built, the scrapped tunnel is continued to be grooved in accordance with the above-mentioned groove order, and the groove depth and width remain unchanged, and then bricks or stones are used to build the first outer wall at the position of the second outer wall. During the construction, a grouting pipe is additionally left on the first outer wall. After the first outer wall is built, fluid concrete is injected between the first inner wall and the first outer wall through the grouting pipe. After the fluid concrete hardens, the grouting pipe is removed and the grouting pipe installation position is sealed.

8. The method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: The specific steps of step S7 are: Connect the tail end of the grouting pipe on the outer closed wall to the feed pipe in the scrapped tunnel for inputting grouting materials. Connect the feed pipe to the grouting pump. Use the grouting pump to inject the grouting material into the scrapped tunnel filled with gravel through the feed pipe and the grouting pipe, and fill it up. After the grouting is completed, wait for it to harden.

9. The method for filling abandoned tunnels with multiphase materials in a spontaneous combustion coal seam mining working face according to claim 1, characterized in that: The specific steps of step S8 are as follows: as the coal mining face is continuously mined, the roof of the goaf will periodically collapse, and while the coal mining face is being mined, the gas injection pipe outside the outer sealed wall and the gas production pipe inside the wall are continuously connected; Each time the gas injection pipe is connected, it is necessary to connect the gas injection pipe to the external gas injection hose on one side of the coal mining working face. The external gas injection hose is equipped with a pressure gauge and a valve. The pressure gauge value must be checked each time a connection is made. When it is observed that the CO2 gas pressure in the scrapped tunnel has dropped by 10% compared with the pressure in step S2, it is necessary to replenish CO2 gas through the gas injection pipe to restore its pressure to 120% of the gas pressure in the coal seam.

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