Method for passing over an adjacent layer remaining coal pillar above a coal mining face

Abstract

The present application belongs to the field of coal mining, and particularly relates to a method for passing over an upper adjacent layer residual coal pillar in a coal mining face. First, based on the distance between the upper adjacent layer residual coal pillar and the lower production coal seam and the relationship between the lower production coal seam and the water-conducting fractured zone, the treatment measures are determined, that is, the treatment measures are determined according to the risk degree, so that the treatment effect and the treatment efficiency can be considered. When the water-conducting fractured zone developed after the mining of the lower production coal seam reaches the residual coal pillar of the upper adjacent coal seam, the upper adjacent layer residual coal pillar is partially mined, and the residual coal pillar is creeped and weakened to support the overburden strata, the average thickness of the residual coal pillar after the creep and weakening is equal to the total thickness of the crushing and swelling of the caving zone of the upper adjacent layer, so that the overburden strata of the upper adjacent coal seam uniformly subsides, and the stress concentration problem of the residual coal pillar is completely eliminated. In addition, when passing over the residual coal pillar, the working face inclination adjusting measures are taken, so that the support capacity of the upper external coal pillar of the lower production coal seam to the overburden strata, especially the overburden strata above the residual coal pillar, can be improved.

Description

Technical Field

[0001] This invention belongs to the field of coal mining, specifically relating to a method for leaving coal pillars in adjacent layers above a coal mining face. Background Technology

[0002] Coal seams typically exist underground in multiple layers, varying in thickness. Some seams have stable thickness and distribution, making them highly mineable, while others have highly variable and discontinuous thicknesses, resulting in poor mineability. Currently, coal mining generally employs fully mechanized mining technology, which involves huge investments. The hydraulic supports used must be matched to the mining height of the coal seam. Furthermore, considering the significant challenges in managing and producing multiple coal seams simultaneously, even if multiple mineable coal seams exist in the mining area, generally only one seam is mined at a time.

[0003] For multi-seam coal mines, the commonly chosen mining sequence is a top-down, downward mining method. Early fully mechanized coal mining typically used protective pillars between working faces, resulting in significant coal loss. However, due to its high safety profile, this method was widely used. Currently, with continuous improvements in mining technology, this low-recovery-rate mining method has been largely phased out. As the upper coal seam is mined and its resources are gradually depleted, the mine will begin mining the lower coal seams. At this point, it is necessary to consider the impact of residual coal pillars from the upper seam (commonly including protective pillars and fault pillars) on the mining of the lower coal seam. These residual pillars act as support columns, bearing the weight of the strata above them, exceeding their surface area. This causes stress concentration at the pillar location. During the mining of the lower coal seam below these pillars, the mining of the underlying coal body will be affected. The mining of the lower coal seam should minimize the transmission of this stress concentration to the working face to avoid accidents such as collapse and impacts, which could disrupt normal mine production and safety.

[0004] like Figure 1As shown, a sister mine under our group company faces the aforementioned problem. The upper first mineable coal seam has been mined out, and production is currently continuing through the lower second mineable coal seam. During the mining of the upper first mineable coal seam, protective coal pillars and fault pillars were left behind. Due to the close proximity of the two coal seams, there are concerns that mining the second mineable coal seam 1 may result in accidents such as pressure buildup and impacts when passing over the remaining coal pillar 6. In response, our group company conducted extensive research on similar construction projects, including on-site investigations and literature reviews. We found that the most common solution is to use hydraulic fracturing boreholes to fracture the remaining coal pillar, thereby reducing stress concentration. While this method can reduce stress concentration, the degree of reduction is not suitable for all working conditions, and pressure buildup and impacts can still occur. Production safety is paramount. Therefore, based on summarizing the advantages of previous methods, we have made some innovations and explored a method to ensure the safe passage of the mining face over the remaining coal pillars of adjacent seams. This method has been put into engineering practice and has yielded beneficial results. Summary of the Invention

[0005] To address the problem of incomplete stress concentration caused by residual coal pillars in adjacent layers in existing technologies, this invention partially mines out the residual coal pillars and weakens them through creep to support the overlying strata. The average thickness of the weakened residual coal pillars is equal to the total thickness of the caving zone of the adjacent layer above, thereby causing the overlying strata to subside uniformly and completely eliminating the stress concentration problem caused by the residual coal pillars. Specifically, this invention studies a method for mining faces passing through residual coal pillars in adjacent layers above, which is particularly suitable for situations where the residual coal pillars are perpendicular to the direction of face advancement. The main steps include:

[0006] S1. Determine the height of the water-conducting fracture zone after the mining of the lower production coal seam and compare it with the thickness of the bedrock between the production coal seam and the remaining coal pillar; if the water-conducting fracture zone after the mining of the lower production coal seam has not developed to the remaining coal pillar of the upper adjacent coal seam, construct a hydraulic fracturing borehole on the construction surface to the remaining coal pillar, hydraulically fracturing the rock strata within the caving zone of the upper adjacent coal seam directly above the remaining coal pillar, and then carry out coal face mining; otherwise, proceed to steps S2-S6;

[0007] S2. When the water-conducting fracture zone develops to the coal pillar of the upper adjacent coal seam after the lower production coal seam is mined, determine the total thickness n of the caving zone in the fully mined area of ​​the upper adjacent coal seam, and then determine the subsidence s of the strata above the caving zone in the fully mined area of ​​the upper adjacent coal seam, s=mn, where m is the average mining height of the upper adjacent coal seam.

[0008] S3. Determine the fragmentation coefficient k of the adjacent coal seam, and calculate the extraction rate a of the remaining coal pillar based on the formula k·(1-a)·m=n;

[0009] S4. A measure roadway parallel to the remaining coal pillar is excavated below it. Several rows of underground fracturing boreholes are arranged along the measure roadway. The remaining coal pillar is fracturing through the underground fracturing boreholes, and the coal body within the fracturing range is extracted by hydraulic flushing. The proportion of coal extracted by hydraulic flushing to the remaining coal pillar is a.

[0010] Preferably, the haulage level and return air level are excavated, and then the measures roadway is excavated from the haulage level to the return air level.

[0011] Preferably, hydraulic jet fracturing is performed through downhole fracturing boreholes, or mechanical enlargement of the borehole is used with enlarged drilling tools to create large-scale fracturing and leave coal pillars.

[0012] Preferably, the hydraulic flushing extraction method for the remaining coal pillars is a checkerboard pattern or a strip pattern.

[0013] S5. Utilize hydraulic power to recover the coal body from the remaining coal pillars and use the backfilling measures in the roadway;

[0014] S6. Based on the basic roof periodic failure step distance, determine the first basic roof periodic failure position after passing the residual coal pillar, and define the production coal seam between it and the critical advance support pressure position as the adjustment zone. When the coal mining face is mined back to the adjustment zone, adjustment mining is carried out; at the same time, the basic roof is artificially broken by drilling the roof fracture borehole, so that the rock block after the basic roof is broken is parallel to the working face after adjustment.

[0015] Preferably, the inclination adjustment is completed before the coal face reaches the critical advanced support pressure position, and the adjustment work begins after the first basic top cycle failure position after the remaining coal pillar has been completely mined.

[0016] The beneficial technical effects of this invention are as follows: This invention addresses the problem of coal pillars left over adjacent layers in coal mining faces. First, it proposes to determine treatment measures based on the relationship between the distance between the coal pillars left over adjacent layers and the lower production coal seam and the water-conducting fracture zone of the lower production coal seam. That is, treatment measures are determined according to the degree of danger, which can take into account both treatment effect and treatment efficiency.

[0017] Secondly, this invention creatively extracts some of the coal pillars left over from the adjacent upper layers and weakens the residual coal pillars through creep to support the overlying strata. The average thickness of the residual coal pillars after creep weakening is equal to the total thickness of the caving zone of the adjacent upper layers, thereby causing the overlying strata of the adjacent upper coal seam to sink uniformly and completely eliminating the stress concentration problem of the residual coal pillars. The checkerboard-style scheme for recovering the residual coal pillars is more conducive to achieving the above-mentioned technical objectives.

[0018] Finally, this invention creatively proposes a measure for adjusting the angle of the working face during mining using residual coal pillars. This can improve the supporting capacity of the external coal pillars above the lower production coal seam on the overlying strata, especially the overlying strata above the residual coal pillars, and prevent rotation around the dip direction at the residual coal pillars, which would pose a danger to the coal mining face. A reasonable method for determining the adjustment range is also provided. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the stratigraphic profile of the coal seam and the coal pillars left by the adjacent upper layer in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of a coal pillar left over from surface fracturing;

[0021] Figure 3 This is a schematic diagram of a cross-section during the recovery of a residual coal pillar underground;

[0022] Figure 4 This is a schematic diagram of the cross-section of the remaining coal pillar after it becomes unstable following the recovery of the coal pillar underground.

[0023] Figure 5 yes Figure 3 Plan view of the remaining coal pillar;

[0024] Figure 6 This is a schematic diagram of the coal seam layout in an embodiment of the present invention;

[0025] In the diagram, 1 is the producing coal seam; 2 is the bedrock between the producing coal seam and the adjacent coal seam above; 3 is the goaf (collapse zone) of the adjacent coal seam above; 4 is the water-conducting fracture zone of the adjacent coal seam above; 5 is the key layer (the bottom layer of the bending subsidence zone); 6 is the remaining coal pillar; 7 is the surface hydraulic fracturing borehole; 8 is the hydraulic fracture; 9 is the fracturing roadway; 10 is the underground fracturing borehole; 11 is the coal pillar recovery zone; 12 is the residual coal pillar; 13 is the critical advance support pressure zone; 14 is the location of the first basic roof cycle failure after passing the remaining coal pillar; 15 is the face tilt adjustment; 16 is the coal mining face; 17 is the transport roadway; 18 is the return air roadway; and 19 is the starting position of the critical advance support pressure. Detailed Implementation

[0026] like Figure 1As shown, a brother mine under the group company to which our mine belongs has its production continuing to the second minable coal seam below, namely the currently producing coal seam 1. The adjacent first minable coal seam above has been mined out, forming the goaf (collapse zone) 3 and the water-conducting fracture zone 4 of the adjacent coal seam above. Some areas have residual coal pillars 6. The residual coal pillars 6 involved in this embodiment extend along the dip as a whole. The coal mining face 16 of the lower producing coal seam 1 is to be arranged along the strike, that is, the coal mining face 16 of the producing coal seam 1 will vertically pass through the residual coal pillars 6 during the advancement process. The remaining coal pillar 6, located in the upper adjacent coal seam, is approximately 30m wide and 3.6m high on average, with a length that can traverse the entire mining face 16. The distance between the remaining coal pillar 6 and the production coal seam 1 is between 36-42m, meaning the bedrock 2 between the production coal seam and the upper adjacent coal seam is 36-42m thick. The average mining height of the production coal seam 1 is 4.0m. Based on engineering experience, accidents such as frame collapse and impacts may occur when the mining face 16 advances to the vicinity of the remaining coal pillar 6. The solutions we have adopted are as follows:

[0027] A method for handling coal pillars left over adjacent layers in a coal mining face includes the following steps:

[0028] Based on the stratigraphic lithology and reference to coal mine mining regulations, and taking into account existing measured data from the mine, the height of the water-conducting fracture zone after the mining of the production coal seam 1 is comprehensively estimated and compared with the thickness of the bedrock 2 between the production coal seam and the remaining coal pillar. If the water-conducting fracture zone after the mining of the lower production coal seam 1 does not develop to the remaining coal pillar 6 of the adjacent upper coal seam, it indicates that after the mining of the lower production coal seam 1, there will be a complete, unbroken rock stratum between the lower production coal seam 1 and the remaining coal pillar 6 of the adjacent upper stratum. This complete rock stratum will act as a slab beam, supporting the overlying rock stratum and transferring the stress to the distant coal seam and the goaf below. At this time, the stress concentration of the remaining coal pillar 6 will be shared and weakened by this complete rock stratum, having a smaller impact on the production of the lower production coal seam 1. Therefore, surface hydraulic fracturing boreholes 7 can be drilled on the surface, such as... Figure 2 As shown, the ground hydraulic fracturing borehole 7 is constructed into the abandoned coal pillar 6, and hydraulic fracturing is used to hydraulically fracture the abandoned coal pillar 6 and the rock strata within the caving zone 3 of the adjacent upper coal seam directly above the abandoned coal pillar 6, generating hydraulic fracturing fractures 8. This weakens the abandoned coal pillar 6 of the adjacent upper coal seam and the rock strata above it. This construction measure is quite similar to the existing technology. It mainly weakens the stress concentration capacity of the abandoned coal pillar 6 by weakening the abandoned coal pillar 6 of the adjacent upper coal seam. At the same time, combined with the isolation and weakening effect of the intact rock strata between the lower production coal seam 1 and the abandoned coal pillar 6, it enables the safe mining of the production coal seam 1 and avoids accidents such as crushing and impact.

[0029] In this embodiment, the average mining height of the production coal seam 1 is 4.0m, the expected caving zone height is 12m, and the water-conducting fracture zone height is 48m (including the 12m caving zone). The distance between the remaining coal pillar 6 and the production coal seam 1 is between 36-42m. After the lower coal seam 1 is mined, the water-conducting fracture zone will penetrate to the upper adjacent coal seam goaf 3. After the lower coal seam 1 is mined, there is no complete rock layer between it and the remaining coal pillar 6. Therefore, the remaining coal pillar 6 has a significant impact on the production of the lower production coal seam 1, especially when the lower production coal seam 1 is mined into the range of influence of the remaining coal pillar 6. Therefore, it is not advisable to adopt the traditional scheme of only constructing hydraulic fracturing boreholes to fracturing the remaining coal pillar 6.

[0030] In the case where the water-conducting fracture zone of the lower coal seam 1 will penetrate into the goaf 3 of the upper adjacent coal seam after mining, the total thickness n of the caving zone 3 in the fully mined area of ​​the upper adjacent coal seam, measured by the construction exploration borehole, can be obtained by subtracting the elevation of the bottom plate of the upper adjacent coal seam from the basic elevation after mining, and then subtracting the original bedrock thickness of the caving zone. Based on the total thickness n of the caving zone 3 of the upper adjacent coal seam and the average mining height m of the upper adjacent coal seam, the subsidence s = mn of the strata above the caving zone 3 in the fully mined area of ​​the upper adjacent coal seam can be determined. In this embodiment, the original bedrock thickness of the caving zone 3 of the upper adjacent coal seam is 10.2m. After mining the upper adjacent coal seam, the original bedrock of the caving zone 3 of the upper adjacent coal seam is broken, and the thickness of the caving zone 3 after caving is 12.4m, the total thickness n of caving is about 2.2m, the average caving coefficient is 1.2157, and the subsidence s = mn = 3.6 - 2.2 = 1.4m of the strata above the caving zone 3 of the upper adjacent coal seam. In addition, those skilled in the art can also refer to the previously measured calving coefficient of the adjacent coal seam caving zone in the mine, and calculate the subsidence s of the rock strata above the adjacent coal seam caving zone 3 based on the original bedrock thickness of the adjacent coal seam caving zone 3.

[0031] The drilling reached the remaining coal pillar 6. After core sampling, the coefficient of rupture of the adjacent coal seam was measured to be k = 1.1. The extraction rate of the remaining coal pillar 6 was determined so that after a portion of the remaining coal pillar was extracted, the average height of the remaining coal pillar 12 was equal to the total rupture thickness n, i.e., 2.2m. This ensured that the subsidence of the overlying strata of the remaining coal pillar 6 was the same as that of the overlying strata of the caving zone 3 of the adjacent coal seam, resulting in a gentle strata in the overall area and eliminating stress concentration at the remaining coal pillar 6. In this embodiment, the extraction height of the remaining coal pillar was 3.6m. Based on the formula k·(1-a)·m = n, the extraction rate a = 44.4% could be calculated. That is, for the adjacent coal seam with an extraction height of 3.6m, the average thickness of the extracted portion was equivalent to 1.6m, and the average height of the remaining coal was 2.0m. Considering its rupture coefficient, the height of the remaining ruptured coal body was 2.2m. In addition, those skilled in the art can also refer to the previously measured rupture coefficient of the adjacent coal seam in this mine.

[0032] like Figure 3-4As shown in Figure 6, a production working face 16 is arranged, and a transport roadway 17 and a return air roadway 18 are excavated simultaneously. When the excavation reaches below the remaining coal pillar 6, a measure roadway 9 is excavated from the transport roadway 17 to the return air roadway 18. The measure roadway 9 is parallel to the length direction of the remaining coal pillar 6 and is located below the middle of the remaining coal pillar 6. Several rows of underground fracturing boreholes 10 are arranged along the measure roadway 9. The remaining coal pillar 6 is hydraulically fracturing using the underground fracturing boreholes 10 or mechanically enlarged within the remaining coal pillar using enlarged drilling tools. Then, the coal body within the corresponding fracturing range of each underground fracturing borehole 10 is hydraulically flushed to recover part of the remaining coal pillar 6, forming a coal pillar recovery zone 11 and a residual coal pillar 12 within the remaining coal pillar. The recovery method of the remaining coal pillar 6 is a checkerboard (room-pillar) type, as shown in Figure 6. Figure 6 As shown. In this embodiment of the invention, several rows of underground fracturing boreholes 10 are arranged along the measure roadway 9, each row including 3 underground fracturing boreholes 10. The 3 underground fracturing boreholes 10 are constructed at equal intervals into the remaining coal pillar 6. The underground fracturing borehole 10 located in the middle is constructed vertically upwards. Along the measure roadway 9 from the return air level roadway 18 to the transport level roadway 17, the remaining coal pillar 6 is recovered by fracturing each row of underground fracturing boreholes 10. After each underground fracturing borehole 10 recovers the remaining coal pillar 6, a coal pillar recovery area 11 with a range of 6.36m × 6.36m is formed. The entire coal seam height of the coal pillar recovery area 11 is recovered. Small coal pillars with a width of 2.73m are left between the coal pillar recovery areas 11 and between the coal pillar recovery area 11 and the upper adjacent coal seam goaf 3, forming residual coal pillars 12. Figure 4 As shown, due to the small width of the residual coal pillar 12, it continuously creeps and deforms over a period of time, filling the coal pillar recovery area 11 to form a residual coal pillar 4 with uniform thickness and a reduced thickness of 2.2m; if the coal body has high strength, it can also be artificially destroyed.

[0033] As an alternative, the recovery method for the remaining coal pillar 6 is a strip-type method, such as... Figure 6 As shown, in this embodiment of the invention, several rows of underground fracturing boreholes 10 are arranged along the measure roadway 9, each row including 3 underground fracturing boreholes 10. The 3 underground fracturing boreholes 10 are constructed at equal intervals into the remaining coal pillar 6. The underground fracturing borehole 10 located in the middle is constructed vertically upwards. Along the measure roadway 9 from the return air level roadway 18 to the transport level roadway 17, the remaining coal pillar 6 is recovered by fracturing each row of underground fracturing boreholes 10. After the remaining coal pillar 6 is recovered by the underground fracturing boreholes 10, 3 spaced coal pillar recovery areas 11 are formed. The entire coal seam height of the coal pillar recovery area 11 is recovered, the width is 4.44m, and the length is parallel to the length of the measure roadway 9 and the remaining coal pillar 6. Small coal pillars with a width of 4.17m are left between the coal pillar recovery areas 11 and between the coal pillar recovery area 11 and the upper adjacent coal seam goaf 3, forming residual coal pillars 12. Figure 4As shown, due to the small width of the residual coal pillar 12, it continuously creeps and deforms over a period of time, filling the coal pillar recovery area 11 to form a residual coal pillar with uniform thickness and a thickness reduced to 2.2m; if the coal body has high strength, it can also be artificially destroyed.

[0034] For the coal pillars left by hydraulic recovery, part of the coal is used to fill the backfill in the measures roadway 9 after the water seepage is removed. The coal is gradually piled up and filled along the measures roadway 9 from the return air level roadway 18 to the transport level roadway 17 to facilitate the water seepage of the backfilled coal body. The other part of the coal pillars left by hydraulic recovery is transported to the surface through the underground transport and hoisting system.

[0035] The longwall face 16 is mined, and the longwall face 16 is advanced along the strike. The range of advance support pressure and the basic top cycle failure step distance of the longwall face 16 are measured to determine the critical advance support pressure zone 13 of the remaining coal pillar 6. That is, when the longwall face advances to this critical advance support pressure zone 13, the advance support pressure affects the area of ​​the remaining coal pillar 6. Based on the basic top cycle failure step distance, the first basic top cycle failure position 14 after passing the remaining coal pillar 16 is determined. The production coal seam 1 between the first basic top cycle failure position 14 after passing the remaining coal pillar 6 and the critical advance support pressure position 19 (the far boundary of the critical advance support pressure zone 13 relative to the remaining coal pillar 6) is defined as the tilt adjustment area. When the working face 16 is mined to the adjustment zone, adjustment mining must be carried out so that the working face is oblique to the length direction or extension direction of the remaining coal pillar instead of being parallel. It is preferable to complete the adjustment work before the coal mining working face reaches the advanced critical advanced support pressure position 19. Adjustment work should begin after the first basic roof cycle failure position 14 after the remaining coal pillar 16 has been completely mined. In the adjustment zone, the basic roof is artificially broken by drilling the roof fracturing borehole so that the rock block after the basic roof failure is parallel to the adjusted working face along the dip direction instead of perpendicular to it, that is, not parallel to the extension direction of the remaining coal pillar 6. It is also preferable to use hydraulic fracturing to artificially adjust the angle and break the rock block at the first basic roof cycle failure position 14 after the remaining coal pillar 6. In this embodiment, the measured width of the advance support pressure of the coal mining face 16 is about 40m, the basic top cycle failure step distance is 25m, the horizontal distance between the critical advance support pressure position 19 and the remaining coal pillar 6 is 40m, and the horizontal distance between the first basic top cycle failure position 14 after passing the remaining coal pillar 16 and the remaining coal pillar 6 is 15m. That is, the entire tilt adjustment area is 85m long along the strike. The tilt adjustment work is completed before the coal mining face 16 reaches the critical advance support pressure position 19. The tilt adjustment angle is 7-10°, that is, the angle between the working face after tilt adjustment and the strike of the production coal seam 1 and the transport roadway changes from the original 90° to 80-83°. When passing through the remaining coal pillars of adjacent coal seams, this invention proposes to adjust the inclination of the working face and cut off the basic roof by drilling a crack in the roof during construction. This avoids the basic roof breaking parallel to the extension direction of the remaining coal pillar, which can improve the support capacity of the external coal pillars in the transport roadway 17 and return air roadway 18 for the overlying strata and prevent rotation around the dip direction at the remaining coal pillar, thus avoiding danger to the coal mining face.

[0036] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A method for a coal face passing over an adjacent layer with a coal pillar remaining, wherein the remaining coal pillar is perpendicular to the direction of advance of the coal face, characterized in that, Includes the following steps: S1. Determine the height of the water-conducting fracture zone after the mining of the lower production coal seam and compare it with the thickness of the bedrock between the production coal seam and the remaining coal pillar; if the water-conducting fracture zone after the mining of the lower production coal seam has not developed to the remaining coal pillar of the upper adjacent coal seam, construct a hydraulic fracturing borehole on the construction surface to the remaining coal pillar, hydraulically fracturing the rock strata within the caving zone of the upper adjacent coal seam directly above the remaining coal pillar, and then carry out coal face mining; otherwise, proceed to steps S2-S6; S2. When the water-conducting fracture zone develops to the coal pillar of the upper adjacent coal seam after the lower production coal seam is mined, determine the total thickness n of the caving zone in the fully mined area of ​​the upper adjacent coal seam, and then determine the subsidence s of the strata above the caving zone in the fully mined area of ​​the upper adjacent coal seam, s=mn, where m is the average mining height of the upper adjacent coal seam. S3. Determine the fragmentation coefficient k of the adjacent coal seam, and calculate the extraction rate a of the remaining coal pillar based on the formula k·(1-a)·m=n; S4. A measure roadway parallel to the remaining coal pillar is excavated below it. Several rows of underground fracturing boreholes are arranged along the measure roadway. The remaining coal pillar is fracturing through the underground fracturing boreholes, and the coal within the fracturing range is hydraulically flushed out. The proportion of coal hydraulically flushed out to the remaining coal pillar is a. The hydraulic flushing out of the remaining coal pillar is carried out in a checkerboard pattern or a strip pattern. S5. Utilize hydraulic power to recover the coal body from the remaining coal pillars and use the backfilling measures in the roadway; S6. Based on the basic roof periodic failure step distance, determine the first basic roof periodic failure position after passing the remaining coal pillar, and define the production coal seam between it and the critical advance support pressure position as the adjustment zone. When the coal mining face is mined back to the adjustment zone, adjustment mining is carried out; at the same time, the basic roof is artificially broken by drilling the roof fracturing borehole, so that the rock block interface along the dip after the basic roof failure is parallel to the adjusted working face; the adjustment work is completed before the coal mining face reaches the critical advance support pressure position, and the adjustment work begins after the first basic roof periodic failure position after the remaining coal pillar has been completely mined.

2. The method for leaving coal pillars in adjacent layers above a coal mining face according to claim 1, characterized in that, In step S4, the transport level and return air level are excavated, and then the measures tunnel is excavated from the transport level to the return air level.

3. The method for leaving coal pillars in adjacent layers above a coal mining face according to claim 1, characterized in that, In step S4, hydraulic jet fracturing is performed through downhole fracturing boreholes, or mechanical enlargement of the borehole is used to create large-scale fracturing and leave coal pillars.

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