Coal mining method of coordinating rock burst prevention and roof height control

Abstract

The present application relates to the technical field of coal mining, and more particularly to a coal mining method for the coordination of rock burst prevention and roof height control. For rock burst coal seams with a thickness greater than the maximum support height of a hydraulic support, the present application proposes, in the advanced support pressure zone, at the bottom of the coal seam, the construction of two rows of crossheading pressure relief boreholes in a quincunx pattern, and the reaming of the pressure relief boreholes to form liberation boreholes with a large diameter and a small spacing. Under the action of strata pressure, the liberation boreholes continuously undergo plastic deformation and instability collapse, which approximates the mining of the bottom of the coal seam, similar to the mining of a liberation layer, and achieves the pressure relief of the full height range of the coal seam. At the same time, the similar mining of the liberation layer causes the creep displacement of the superimposed coal seam towards the hydraulic support, which reduces the mining height of the coal seam to meet the support range of the hydraulic support, thereby achieving safe mining.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, and in particular to a coal mining method that coordinates rockburst prevention and roof height control. Background Technology

[0002] Rockburst is a geological hazard in coal mining, generally occurring at greater coal seam depths. One common approach to address this hazard is to drill pressure relief boreholes from the longwall face into the coal seam. Typically, hydraulic fracturing is then performed on the coal seam following the drilling to further enhance the pressure relief effect. This method addresses both the rockburst problem and the high pressure exerted on the advance support under rockburst conditions. However, a drawback is that for thick fully mechanized longwall faces, the hydraulic fracturing range may not cover the entire coal seam height, resulting in insufficient pressure relief.

[0003] Furthermore, coal seam geological conditions are complex, with significant variations in thickness. When selecting hydraulic supports, the selection is generally based on the overall thickness of the coal seam in the mine. Although the support height of hydraulic supports can be adjusted within a certain range, it's still impossible to avoid situations where the coal seam mining height in some working faces exceeds the maximum support height of the hydraulic supports. For example, if the actual coal seam thickness is 6.0m, but the maximum support height of the hydraulic supports is only 5.5m, then 0.5m of coal seam thickness in the roof or floor will be unminable. This leads to resource waste. On the other hand, if... Figure 1 As shown, when there is unminable coal seam in the roof (the top 0.5m is not mined), due to the low strength of the coal, cracks will form during the continuous movement of the hydraulic supports, making it extremely unstable. If it falls, it will cause personnel safety and the risk of roof collapse. When there is unminable coal seam in the floor (the bottom 0.5m is not mined), due to the low strength of the coal, cracks are easily formed under the pressure of the scraper conveyor, making it difficult to move the hydraulic supports.

[0004] Therefore, how to solve the problem of coal seam thickness exceeding the maximum mining limit of hydraulic supports and control rockburst during thick coal seam mining has become a major technical challenge in the mining field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a coal mining method that coordinates rockburst prevention and roof height control, comprising the following steps: S1: Determine the range of the advanced support pressure zone and designate the area that reaches the set pressure threshold as the drilling release layer construction zone; S2: Drilling the release layer in the drilling release layer construction area: Drilling two rows of staggered pressure relief boreholes along the layer near the coal seam floor; enlarging the pressure relief boreholes to form release boreholes, wherein the diameter and spacing of the release boreholes meet the following requirements: each release borehole in the upper row overlaps with the two release boreholes in the lower row that are adjacent to it in the vertical direction, and the release boreholes can be guaranteed not to become unstable immediately after construction. S3: The diameter and spacing of the Liberation boreholes also meet the following requirements: in the range from the peak pressure zone of the advance support to the coal wall of the longwall face, the Liberation boreholes exhibit instability and collapse, while the coal body near the Liberation boreholes in other locations of the Liberation layer mainly undergoes plastic deformation. S4: If the remaining height of the coal seam is still greater than the maximum support height of the hydraulic support, and the roof can continue to move downward appropriately without breaking, then a portion of the coal body should be pre-excavated in the decompression zone. S5: As the longwall mining face advances, the borehole liberation layer construction area moves forward continuously. Refer to step S2 to carry out borehole liberation layer construction in the newly added borehole liberation layer construction area.

[0006] Preferably, in step S1, the location where the advance support pressure reaches 1.2 times the original rock stress ahead of the peak advance support pressure is determined, and the range from this location to the coal face of the longwall mining face is designated as the drilling liberation layer construction area.

[0007] Preferably, in step S2, each pressure relief borehole in the upper row is located between the two adjacent pressure relief boreholes in the lower row, and the pressure relief boreholes along the coal seam are constructed parallel to the coal seam and perpendicular to the working face advancing direction.

[0008] Preferably, in step S2, the lower row of pressure relief boreholes is 0.5-0.8m away from the coal seam floor, the row spacing between the upper row of pressure relief boreholes and the lower row of pressure relief boreholes is 0.6m, and the spacing between adjacent pressure relief boreholes 5 in the same row is 0.6m; the diameter of the pressure relief borehole is 150mm, and the diameter of the release borehole is 400mm.

[0009] Preferably, in step S2, the construction method of the relief borehole includes: using a spiral drill to enlarge the pressure relief borehole, and the drilled coal is discharged from the borehole along the spiral blades; or using an enlarging drill bit and a polished drill rod to enlarge the borehole, with water flowing from the center of the drill rod to the enlarging drill bit and then discharged to the bottom of the hole, and then carrying the broken coal drilled down by the enlarging drill bit out of the borehole.

[0010] Preferably, in step S3, the diameter and spacing of the liberation boreholes further satisfy the following: deformation, instability, or collapse of the liberation boreholes in the liberation layer causes the roof to sink in the coal face of the longwall mining face, which is basically consistent with the diameter of the liberation boreholes.

[0011] Preferably, in step S4, a wedge is cut out in the decompression zone. The wedge has a triangular cross-section, with a wider side near the coal wall and a tapering shape as it advances toward the working face.

[0012] Invention Points and Beneficial Effects: For rockburst coal seams where the seam thickness exceeds the maximum support height of the hydraulic supports, this invention creatively proposes constructing two rows of pressure-relief boreholes in a quincunx pattern at the bottom of the coal seam within the pre-support pressure zone. These pressure-relief boreholes are then enlarged to form larger-diameter, more closely spaced release boreholes. Under the influence of ground pressure, these release boreholes continuously undergo plastic deformation and instability, effectively mimicking the mining of the bottom of the coal seam, similar to release layer mining, thus achieving pressure relief across the entire height range of the coal seam. Simultaneously, due to the superimposed creep displacement of the coal seam towards the hydraulic supports, similar to release layer mining, the coal seam recovery height is reduced to meet the support range of the hydraulic supports, thereby enabling safe mining. Attached Figure Description

[0013] When considered in conjunction with the accompanying drawings, the invention will be more fully and better understood, and many of its accompanying beneficial effects will become readily apparent, through the following detailed description. However, the accompanying drawings, which are provided to further illustrate the invention and form part of this invention, and the illustrative embodiments thereof, together with their descriptions, are used to explain the invention and do not constitute an undue limitation thereof, wherein: Figure 1 —A diagram showing the coal seam thickness exceeding the maximum mining limit of the hydraulic support; Figure 2 —A schematic diagram of the drilling and liberation layer construction in the coal mining method of this invention; Figure 3 —A schematic diagram of the drilling construction and surrounding coal transport in the borehole liberation layer of this invention; Figure 4 —A schematic diagram of roof rotation and wedge construction in the coal mining method of this invention; Explanation of reference numerals in the attached diagram: 1. Coal seam; 2. Roof; 3. Hydraulic support; 4. Goaf; 5. Pressure relief borehole; 6. Liberation borehole; 7. Wedge block. Detailed Implementation

[0014] The specific embodiments of the present invention will now be described in conjunction with the accompanying drawings.

[0015] like Figure 2-4 As shown, this invention proposes a coal mining method that coordinates rockburst prevention and roof height control, comprising the following steps: S1: Determine the range of the advanced support pressure zone and the advanced support pressure value along the working face advance direction; determine the position where the advanced support pressure reaches 1.2 times the original rock stress in front of the peak of the advanced support pressure, and take the range from this position to the coal wall of the longwall mining face as the drilling liberation layer construction area; In this embodiment, the thickness of coal seam 1 is 6.0m, and the ultimate support height of hydraulic support 3 is 5.5m; the range of the advance support pressure zone is about 90m along the working face advance direction of the coal wall of the mining face; among them, the position where the advance support pressure in front of the peak reaches 1.2 times the original rock stress is about 65m away from the coal wall of the mining face.

[0016] S2: Drilling is carried out in the drilling liberation layer construction area. Specifically, two rows of pressure relief boreholes 5 are constructed along the coal seam near the bottom plate. The two rows of pressure relief boreholes 5 are arranged in a quincunx pattern, that is, in the working face advancement direction, each pressure relief borehole 5 in the upper row is located in the middle of the two adjacent pressure relief boreholes in the lower row. The pressure relief boreholes 5 are constructed parallel to the coal seam and perpendicular to the working face advancement direction. The pressure relief boreholes 5 are enlarged to form liberation boreholes 6. The diameter and spacing of the liberation boreholes 6 meet the following requirements: each liberation borehole 6 in the upper row overlaps with the two adjacent liberation boreholes 6 in the lower row in the vertical direction, and the liberation boreholes 6 do not immediately become unstable after construction.

[0017] In this embodiment, the lower row of pressure relief boreholes 5 is 0.5-0.8m away from the coal seam floor. The row spacing between the upper row of pressure relief boreholes 5 and the lower row of pressure relief boreholes 5 is approximately 0.6m. The spacing between adjacent pressure relief boreholes 5 in the same row is 0.6m. The release borehole 6 is constructed coaxially with the pressure relief boreholes 5. The diameter of the pressure relief borehole 5 is 150mm, and the diameter of the release borehole 6 is 400mm. The distances are based on the borehole center.

[0018] In this embodiment, the construction method of the liberation borehole 6 includes: using a spiral drill to enlarge the pressure relief borehole 5, and the drilled coal is discharged from the borehole along the spiral blades; or using an enlarging drill bit (with a smooth drill rod) to enlarge the borehole, water flows from the center of the drill rod to the enlarging drill bit and is discharged to the bottom of the hole, and then carries the broken coal drilled down by the enlarging drill bit out of the borehole.

[0019] S3: As Figures 2-3 As shown, under the continuous action of the advance support pressure, the Liberation Borehole 6 will deform, become unstable, or collapse to varying degrees. Generally, within the range from the peak of the advance support pressure to the coal wall of the longwall face, the Liberation Borehole 6 exhibits instability and collapse. In other locations within the Liberation Borehole 6, the coal body near the Liberation Borehole 6 undergoes primarily plastic deformation. That is, the borehole diameter and spacing of the Liberation Borehole 6 also satisfy the following conditions: within the range from the peak of the advance support pressure to the coal wall of the longwall face, the Liberation Borehole 6 exhibits instability and collapse, while in other locations within the Liberation Borehole 6, the coal body near the Liberation Borehole 6 undergoes primarily plastic deformation.

[0020] like Figures 3 to 4As shown, the construction of the liberated layer through drilling will have two beneficial effects: First, similar to the pressure relief principle of liberated layer mining, after the liberated borehole 6 is drilled at the bottom of the thick coal seam 1, it will deform, become unstable, or collapse due to the pressure of the advance support (similar to mining a coal seam with a thickness of 0-400mm at this point). The coal seam above the liberated borehole 6 will then shift downwards, creating a pressure relief effect. Furthermore, because the liberated borehole 6 is drilled close to the bottom of the coal seam, it will also relieve pressure on the bottom coal seam. The pressure relief effect generated by the liberated layer mining is far greater than that of the pressure relief borehole itself and the pressure relief effect generated by hydraulic fracturing using pressure relief drilling; it can relieve pressure across the entire height of the coal seam.

[0021] Secondly, due to the construction similar to the mining of the liberation layer at the bottom of the thick coal seam 1, and because each liberation borehole 6 in the upper row overlaps with the two adjacent liberation boreholes 6 in the lower row in the vertical direction, and the deformation, instability or collapse of the liberation borehole 6 is more severe as it gets closer to the working face along the working face advance direction (similar to mining a coal seam with a thickness of 0-400mm here, 400mm from the coal wall of the working face, and the position where the advance support pressure reaches 1.2 times the original rock stress in front of the peak of the advance support pressure is close to 0, and increases approximately linearly), the roof 2 on the coal seam 1 will undergo rotational deformation under the action of the formation pressure. The starting point of the rotational deformation is at the position where the advance support pressure reaches 1.2 times the original rock stress in front of the peak of the advance support pressure (the front boundary of the borehole liberation layer). The roof 2 above the borehole liberation layer is similar to a cantilever beam, and the whole body flexes and sinks. At the location of the hydraulic support 3 in the longwall face, the coal seam thickness decreases, the roof 2 descends, and because the borehole-liberated layer is relatively long in the working face advance direction, the approximately 400mm subsidence of the roof can ensure that it does not break. In addition, the coal seam at the coal wall of the longwall face is in the decompression zone, and the coal body will deform to a certain extent in the direction of the hydraulic support 3 under the pressure of the roof 2. These deformations will lead to a further decrease in the height of the coal seam, for example, a decrease of about 100mm. At this time, the coal seam will only have a height of 5.5m, which is consistent with the maximum support height of the hydraulic support 3. This allows for full-thickness mining of the coal seam, while also enabling the hydraulic support to directly support the roof, solving the problems of personnel safety caused by coal seam collapse and the danger of roof breakage.

[0022] Preferably, the diameter and spacing of the liberation boreholes 6 should satisfy the following: deformation, instability or collapse of the liberation boreholes in the liberation layer should cause the roof to sink in the coal face of the longwall mining face to be approximately the same as the diameter of the liberation boreholes.

[0023] S4: If the remaining height of the coal seam is still slightly greater than the maximum support height of the hydraulic support 3 (for example, the coal seam height decrease caused by the deformation of the coal body in the decompression zone towards the hydraulic support position is less than 100mm, or the original height of the coal seam is 6.1m), and the roof 2 can still move appropriately without breaking, then a wedge 7 is cut out in the decompression zone. The wedge 7 has a triangular overall cross-section, with a larger width on the side near the coal wall and a pointed front end that advances towards the working face. Thus, under the action of the advance support pressure or the roof pressure, the wedge 7 will move towards the working face / hydraulic support 3, thereby increasing the amount of movement of the coal body in the decompression zone towards the working face / hydraulic support 3, further reducing the coal seam height until the hydraulic support reaches its limit support height.

[0024] The wedge 7 can be cut using a wire saw, and the specific construction method is not limited.

[0025] S5: As the longwall face advances, the borehole-liberation layer construction area moves forward continuously. Referring to step S2, borehole-liberation layer construction is carried out in the newly added borehole-liberation layer construction area. The roof collapses behind the longwall face to form goaf 4.

[0026] 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 coal mining method that coordinates rockburst prevention and roof height control, characterized in that, Includes the following steps: S1: Determine the range of the advanced support pressure zone and designate the area that reaches the set pressure threshold as the drilling release layer construction zone; S2: Drilling the release layer in the drilling release layer construction area: Drilling two rows of staggered pressure relief boreholes along the layer near the coal seam floor; enlarging the pressure relief boreholes to form release boreholes, wherein the diameter and spacing of the release boreholes meet the following requirements: each release borehole in the upper row overlaps with the two release boreholes in the lower row that are adjacent to it in the vertical direction, and the release boreholes can be guaranteed not to become unstable immediately after construction. S3: The diameter and spacing of the Liberation boreholes also meet the following requirements: in the range from the peak pressure zone of the advance support to the coal wall of the longwall face, the Liberation boreholes exhibit instability and collapse, while the coal body near the Liberation boreholes in other locations of the Liberation layer mainly undergoes plastic deformation. S4: If the remaining height of the coal seam is still greater than the maximum support height of the hydraulic support, and the roof can continue to move downward appropriately without breaking, then a portion of the coal body should be pre-excavated in the decompression zone. S5: As the longwall mining face advances, the borehole liberation layer construction area moves forward continuously. Refer to step S2 to carry out borehole liberation layer construction in the newly added borehole liberation layer construction area.

2. The coal mining method according to claim 1, characterized in that, In step S1, the location where the advance support pressure reaches 1.2 times the original rock stress ahead of the peak advance support pressure is determined, and the range from this location to the coal face of the longwall mining face is designated as the drilling liberation layer construction area.

3. The coal mining method according to claim 1, characterized in that, In step S2, each pressure relief borehole in the upper row is located between the two adjacent pressure relief boreholes in the lower row. The pressure relief boreholes along the coal seam are constructed parallel to the coal seam and perpendicular to the working face advance direction.

4. The coal mining method according to claim 1, characterized in that, In step S2, the lower row of pressure relief boreholes is 0.5-0.8m away from the coal seam floor, the row spacing between the upper row of pressure relief boreholes and the lower row of pressure relief boreholes is 0.6m, and the spacing between adjacent pressure relief boreholes 5 in the same row is 0.6m; the diameter of the pressure relief borehole is 150mm, and the diameter of the release borehole is 400mm.

5. The coal mining method according to claim 1, characterized in that, In step S2, the construction method of the relief borehole includes: using a spiral drill to enlarge the pressure relief borehole, and the drilled coal is discharged from the borehole along the spiral blades; or using an enlarging drill bit and a polished drill rod to enlarge the borehole, with water flowing from the center of the drill rod to the enlarging drill bit and then discharged to the bottom of the hole, and then carrying the broken coal drilled down by the enlarging drill bit out of the borehole.

6. The coal mining method according to any one of claims 1-5, characterized in that, In step S3, the diameter and spacing of the liberation boreholes further satisfy the following: the deformation, instability or collapse of the liberation boreholes in the liberation layer cause the roof to sink in the coal face of the longwall mining face to be basically consistent with the diameter of the liberation boreholes.

7. The coal mining method according to any one of claims 1-5, characterized in that, In step S4, a wedge is cut out in the decompression zone. The wedge has a triangular cross-section, with a wider side near the coal wall and a tapering point towards the working face.

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