Method for controlling pressure cracking of surrounding rock in mining roadway in close distance coal seam mining intersection area

Abstract

The present application discloses a method for controlling the fracturing of surrounding rock in a mining roadway in a close-distance coal seam mining intersection area. The method calculates the stress superposition influence range of the intersection area when the close-distance coal seams are mined in opposite directions, and arranges fracturing boreholes to transfer the fracturing stress of the roof and interlayer hard rock in the mining intersection range. In the stress superposition influence range of the mining intersection, the overlying hard roof is cut off by fracturing in the mining roadway of the upper coal seam, which reduces the weighting step distance and intensity of the roof breakage and the mining-induced stress transmitted to the mining roadway of the lower coal seam; the interlayer hard rock is cut off by fracturing in the track high drainage roadway of the lower coal seam, which blocks the stress transmission, weakens the mining-induced stress superposition of the mining of the upper coal seam working face and the mining of the roadway of the lower coal seam, and reduces the stress concentration degree of the mining intersection area. The present application reduces the influence of the mining-induced stress superposition in the close-distance coal seam mining intersection area on the mining of the roadway of the lower coal seam and the mining of the working face of the upper coal seam, and ensures the normal mining of the working face of the upper coal seam and the normal mining of the roadway of the lower coal seam.

Description

Technical Field

[0001] This invention relates to a method for controlling the fracturing of surrounding rock in tunnels in close coal seam mining intersection areas, belonging to the field of mining technology. Background Technology

[0002] Coal mining is gradually moving towards deeper levels, and deep mining presents a typical problem of controlling the surrounding rock in high-stress, dynamic-pressure roadways. In close-range coal seam mining at depths of over 1,000 meters, as the mining activity continues to expand, the impact of mining dynamic pressure increases, leading to roadway rock fracturing, difficulty in controlling rock deformation, frequent roof falls, and endangering the safe and efficient production of coal mines.

[0003] In the mining of closely spaced coal seams, to achieve efficient production, the mining of the working face and the tunneling of the lower or adjacent coal seams often need to be carried out simultaneously. However, when the upper and lower coal seams adopt a mining layout of mining or tunneling in opposite directions, especially in coal and gas outburst-prone coal seams, the problem of mutual disturbance between mining and tunneling operations is particularly prominent. When mining and tunneling of closely spaced coal seams proceed in opposite directions, the overlying strata undergo periodic fracturing during the mining of the upper coal seam working face. The strain energy accumulated in the strata is suddenly released, generating strong mining stress. This stress is transmitted to the lower coal and rock strata through the strong and integral interlayer strata. When the tunneling face of the lower coal seam approaches or enters the mining influence zone of the upper strata, the disturbance stress generated by the tunneling operation in the lower strata will be superimposed with the mining stress transmitted from the upper strata. This leads to an increase in the stress concentration of the coal and rock mass in the area where the mining and tunneling operations are close (the confrontation point) and within a certain range before and after it, far exceeding the impact of a single operation. This can easily cause large deformation and instability of the surrounding rock in the tunnel, induce the risk of coal and gas outbursts, and force the interruption of tunneling operations. Such stress-induced tunneling interruptions disrupt planned mining succession schemes, causing tension in the working face and severely limiting safe and efficient mine production. Therefore, in-depth research on the stress superposition mechanism, impact range, and control measures under near-distance coal seam group facing mining conditions is of significant engineering importance for ensuring safe production and maintaining normal mining succession.

[0004] Traditional methods for controlling surrounding rock in deep roadways typically rely on near-surface support measures to address deformation control at the end of the roadway. However, these methods struggle to solve the problem of large deformations under high stress in deep mining, resulting in limited effectiveness. Roof fracturing is an effective method for weakening and blocking mining-induced stress in deep mines. In recent years, fracturing has seen rapid development in treating thick, hard roofs, and field practice has proven its effectiveness in roof control. Fracturing involves injecting high-pressure water into boreholes. Under fluid-structure interaction, the borehole walls fracture and propagate, altering the properties of the rock mass and reducing the overall strength of the roof rock. It has been widely applied in areas such as hydraulic fracturing control of hard roofs, weakening of hard top coal, coal seam permeability enhancement, and prevention of rockbursts, achieving good results. However, currently, there is a lack of fracturing control methods specifically addressing the challenge of controlling surrounding rock deformation in the intersection zone of mining faces under conditions of close proximity to coal seams. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a method for controlling the fracturing of surrounding rock in tunnels in close-range coal seam mining intersection zones. This method reduces the impact of working face mining on the tunneling of adjacent coal seams, thereby ensuring the safe and efficient mining of close-range coal seams. During the mining of close-range coal seam groups, when coal seam mining proceeds in opposite directions, the overlying strata undergo periodic fracturing during the mining of the upper coal seam face, generating strong mining-induced stress. This stress is transmitted to the lower coal and rock strata through strong, well-integrated interlayer strata. When the tunneling face of the lower coal seam approaches or enters the upper mining-induced stress zone, the disturbance stress generated by the tunneling operation will superimpose with the upper mining-induced stress, leading to an increased stress concentration in the coal and rock mass within the mining intersection zone. This presents a challenge to controlling the stability of the surrounding rock in the tunneling roadways, severely restricting the safe and efficient production of the mine.

[0006] Preferably, the present invention provides a method for controlling the fracturing of surrounding rock in tunnels in close coal seam mining intersection areas, comprising:

[0007] S1. Core samples are taken from the high-level hard rock strata of the upper coal seam mining face, the low-level hard rock strata of the upper coal seam mining face, and the hard rock strata between nearby coal seams. Rock mechanical property tests are then conducted to obtain the mechanical properties of the hard rock strata of the roof. The hard rock strata of the roof that need to be fracturing are determined, and the periodic fracturing step distance and fracturing intensity of the hard roof of the upper coal seam mining face are collected.

[0008] S2. Calculate the range of influence of coal seam mining stress, the range of influence of mining stress laterally, and the range of influence of roadway excavation stress. The superimposed area of ​​the range of influence of coal seam mining stress, the range of influence of mining stress laterally, and the range of influence of roadway excavation stress is taken as the mining-excavation confrontation area.

[0009] S3. The final position of the fracturing borehole in the high-extraction roadway of the adjacent working face of the lower coal seam mining face is the hard rock layer between the close coal seam determined in step S1. The arrangement range of the fracturing borehole in the high-extraction roadway is within the mining-excavation intersection area, and the fracturing cuts off the hard rock layer between the close coal seam above the lower coal seam transport roadway excavation face.

[0010] S4. Arrange roof fracturing boreholes in a fan shape in the transport roadway of the upper coal seam mining face. The final position of the roof fracturing boreholes is the high-level hard rock strata of the upper coal seam mining face determined in step S1. Fracturing is performed on the high-level hard rock strata and the low-level hard rock strata of the upper coal seam mining face to form a weak structural surface of the high-level hard rock strata and a structural surface of the low-level hard rock strata of the upper coal seam mining face.

[0011] S5. In the fracturing system, the fracturing fluid in the water tank is pressurized by the high-pressure pump and then flows to the high-pressure sealed drill pipe through the high-pressure hose. The high-pressure hose is depressurized through the pressure relief valve. The flow rate and water pressure in the fracturing system are monitored in real time by the fracturing control instrument.

[0012] S6. Push the one-way valve group and the sealing device to the high-pressure sealing drill pipe to the fracturing borehole in the high-pressure extraction roadway and perform fracturing. Use a high-pressure pump to inject high-pressure water into the hard rock layer between the nearby coal seams.

[0013] S7. If the water pressure collected in real time by the fracturing monitoring and control instrument is less than 5MPa and the duration exceeds the preset duration threshold, or if the water outflow duration of the adjacent borehole of the fracturing borehole in the high-pressure extraction roadway exceeds the preset time threshold, then the high-pressure pump is shut down and the pressure relief valve is opened to depressurize the high-pressure pipeline; if there are multiple layers of hard rock between closely spaced coal seams, then the high-pressure sealing drill rod is used to move the one-way valve group and the sealing device to other hard rock between closely spaced coal seams to continue fracturing.

[0014] S8. Repeat step S7 until all high-level extraction roadway fracturing boreholes are completed; perform fracturing on the roof fracturing boreholes so that the high-level hard rock strata and the low-level hard rock strata of the roof of the upper coal seam mining face collapse as the upper coal seam mining face is mined, thereby reducing the dynamic pressure of the upper coal seam mining face; repeat step S8 until the roof fracturing boreholes in the mining-excavation intersection area are completed.

[0015] Prioritize that, in step S2, the calculation of the advance influence range of coal seam mining stress, the lateral influence range of mining stress, and the influence range of roadway excavation stress includes: calculating the advance influence range of coal seam mining stress, including: calculating the advance influence distance of the upper coal seam mining face L1=D / tanβ+ξM; calculating the lateral influence range of mining stress, including: calculating the boundary distance of the lateral influence of the upper coal seam mining face L2=KDcotβ;

[0016] Calculating the stress influence range during tunnel excavation includes: calculating the stress influence radius R of the tunnel. d =r0(2P / σ c ) 1 / 2 The unit is m; where D is the interlayer spacing between the upper and lower coal seams, M is the thickness of the coal seam in the upper coal seam mining face, ξ is the lithology coefficient, K is the mining stress increase coefficient, β is the mining influence angle, r0 is the equivalent radius of the lower coal seam transport roadway excavation face, P is the roadway support resistance, and σ c It is the uniaxial compressive strength of the coal body in the lower coal seam.

[0017] Preferably, in step S2, the mining conflict zone satisfies L0 ≤ L2 + R d And Δy≤L1+R d Where Δy is the distance between the upper coal seam mining face and the lower coal seam tunneling and haulage roadway along the advancing direction of the upper coal seam mining face, and L0 is the horizontal misalignment between the upper coal seam mining face and the lower coal seam tunneling face; based on the mining speed of the upper coal seam mining face, the daily advance rate of the lower coal seam tunneling face, and the horizontal distance between the upper coal seam mining face and the lower coal seam tunneling face, the range of the mining-tunneling intersection zone is determined; fracturing operations are carried out on the hard roof strata in the mining-tunneling intersection zone.

[0018] Prioritize that, in step S3, if the mining of the adjacent working face of the lower coal seam mining face has not yet ended and the high-speed extraction roadway of the adjacent working face of the lower coal seam mining face is in use, then high-speed extraction roadway fracturing boreholes are arranged in the high-speed extraction roadway of the adjacent working face of the lower coal seam mining face. Before the lower coal seam transport roadway excavation face enters the mining-excavation intersection area, the hard rock layer between the nearby coal seams is fractured and cut off, thereby blocking the propagation of mining stress from the upper coal seam mining face towards the lower coal seam transport roadway excavation face.

[0019] Preferably, in step S4, the spacing between the final holes of the roof fracturing boreholes in the high-level hard rock strata of the upper coal seam mining face is 15-20m, the spacing between each group of roof fracturing boreholes is 20-30m, and the spacing between each group of roof fracturing boreholes is less than the periodic pressure step distance of the hard roof in the high-level hard rock strata of the upper coal seam mining face; the line connecting the final hole positions of each group of roof fracturing boreholes is perpendicular to the advancing direction of the upper coal seam mining face.

[0020] Preferably, in step S4, the arrangement range of the roof fracturing boreholes is within the mining intersection area, and all of the roof fracturing boreholes in each group are arranged in the transport roadway or track roadway of the upper coal seam mining face, or, each group of roof fracturing boreholes are symmetrically arranged in the transport roadway and track roadway of the upper coal seam mining face.

[0021] Preferably, in step S4, if the mining of the adjacent working face of the lower coal seam mining face is completed and the high-extraction roadway of the adjacent working face of the lower coal seam mining face is closed, then negative-angle floor fracturing boreholes are arranged in the transport roadway of the upper coal seam mining face. The hard rock strata between the closely spaced coal seams are fracturing through the floor fracturing boreholes. The floor fracturing boreholes arranged in the transport roadway of the upper coal seam mining face and the roof fracturing boreholes arranged in the transport roadway of the upper coal seam mining face are used intermittently for fracturing.

[0022] Preferably, in step S6, the fracturing time is determined based on the mechanical properties of the rock strata.

[0023] The beneficial effects achieved by this invention are as follows: First, this invention calculates the range of stress superposition between coal and rock masses during the mining of closely spaced coal seams. Then, it designs a hydraulic fracturing scheme. Within the range of stress superposition between mining operations, fracturing the hard roof of the upper coal seam working face reduces the mining stress, and fracturing the hard rock layers between layers blocks stress transmission. This reduces the superposition of mining stress between the upper coal seam working face and the lower coal seam roadway excavation, and reduces the impact of the dynamic pressure of the upper coal seam mining on the lower coal seam roadway excavation. The first stage of fracturing involves drilling boreholes in the high-extraction roadway adjacent to the lower coal seam mining face to the hard interlayer rock. By fracturing the interlayer rock, the propagation path of mining stress from the upper coal seam working face towards the tunneling roadway is cut off, reducing the superposition of mining stress and minimizing the impact of the upper coal seam mining on the tunneling of the lower coal seam working face. The second stage of fracturing involves drilling fan-shaped roof fracturing boreholes in the upper coal seam mining roadway towards the hard roof rock. By fracturing and cutting off the target hard roof, the pressure step distance and pressure intensity of the roof fracture are reduced, thereby reducing the mining dynamic pressure of the upper coal seam working face and further reducing the mining stress transmitted to the tunneling roadway of the lower coal seam. At the same time, the impact of mining stress on the mining roadway of the working face is also reduced.

[0024] This invention addresses the engineering challenges of strong mine pressure manifestation, large deformation of surrounding rock in roadways, and difficulty in stability control caused by the superposition of mining-induced stress in close-range coal seam mining areas. First, this invention calculates and determines the influence range of both coal seam mining-induced stress and roadway excavation stress. The stress superposition zone between these two areas is designated as the mining-in-excavation conflict zone. Fracturing boreholes are designed and deployed to cut and relieve pressure on the target rock strata within the conflict zone. Focusing on the hard roof strata in the mining-in-excavation conflict zone, the invention pre-fracturing the hard roof strata between layers in the high-speed extraction roadway blocks the propagation of mining-induced stress from the upper coal seam mining face towards the lower coal seam roadway, reducing the superposition of mining-induced stress between the upper coal seam mining face and the lower coal seam roadway excavation. By fracturing and cutting the hard roof of the mining face, the invention reduces the pressure step distance and intensity of roof fracture, further reducing the mining-induced stress transmitted to the lower coal seam roadway, minimizing the damage to the roadway caused by mining-induced stress, and ensuring that the lower coal seam roadway excavation is not affected by mining. The above measures achieve stability control of the surrounding rock in the mining and excavation intersection area, and also play a certain protective role in the mining roadway of the upper coal seam working face, ensuring the normal mining of the upper coal seam working face and the normal excavation of the roadway of the lower coal seam working face. It has the characteristics of being simple, efficient, easy to construct, low cost and pollution-free. Attached Figure Description

[0025] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a three-dimensional schematic diagram of the method for controlling the fracturing of the surrounding rock in the tunneling area of ​​the coal seam mining intersection zone, where fracturing boreholes can be drilled in both the upper coal seam mining face mining transport roadway and the high-extraction roadway of the lower coal seam mining face.

[0027] Figure 2 This is a schematic diagram of the borehole layout for the method of controlling the surrounding rock of the tunneling roadway in the close coal seam mining intersection area, where fracturing boreholes can be drilled in both the upper coal seam mining face mining transport roadway and the high-extraction roadway of the lower coal seam mining face.

[0028] Figure 3 yes Figure 2 A schematic diagram of the borehole profile in the advancing direction of the upper coal seam mining face in the AA direction.

[0029] Figure 4 This is a three-dimensional schematic diagram of the method for controlling the fracturing of the surrounding rock in the tunneling area of ​​the coal seam mining intersection zone in this invention, which is only used for fracturing drilling in the transport roadway of the upper coal seam mining face.

[0030] Figure 5This is a schematic diagram of the borehole layout for the method of controlling the fracturing of the surrounding rock in the tunneling area of ​​the coal seam mining intersection zone in the present invention, which is only used for fracturing boreholes in the transport roadway of the upper coal seam mining face.

[0031] Figure 6 yes Figure 5 A schematic diagram of the borehole profile perpendicular to the advancing direction of the upper coal seam mining face in the BB section.

[0032] In the diagram, 1-Transport roadway of the upper coal seam mining face; 2-Track roadway of the upper coal seam mining face; 3-High-speed extraction roadway adjacent to the lower coal seam mining face; 4-Less coal seam transport roadway excavation face; 5-Less coal seam track roadway excavation face; 6-Track roadway adjacent to the lower coal seam mining face; 7-Transport roadway adjacent to the lower coal seam mining face; 8-Upper coal seam mining face; 9-Lower coal seam mining face; 10-Adjacent to the lower coal seam mining face; 11-Goaf; 12-Design stop line of the working face; 13-Mining-excavation intersection area; 14-Meeting point of mining-excavation intersection. 15-Roof fracturing borehole; 16-High-level extraction roadway fracturing borehole; 17-Floor fracturing borehole; 18-High-level hard rock strata in the roof of the upper coal seam mining face; 19-Low-level hard rock strata in the roof of the upper coal seam mining face; 20-Hard rock strata between closely spaced coal seams; 21-Weak structural surface of fracturing high-level hard rock strata in the roof of the upper coal seam mining face; 22-Structural surface of fracturing low-level hard rock strata in the roof of the upper coal seam mining face; 23-Weak structural surface of fracturing hard rock strata between closely spaced coal seams; 24-Direction of lower coal seam transport roadway excavation; 25-Direction of upper coal seam mining face advance; 26-Upper coal seam; 27-Lower coal seam. Detailed Implementation

[0033] During the mining of closely spaced coal seams, when coal seam mining proceeds in opposite directions, the overlying strata undergo periodic fracturing during the mining of the upper coal seam face, generating strong mining stress. This stress is transmitted to the lower coal and rock strata through the strong and well-integrated interlayer strata. When the lower coal seam transport roadway face 4 approaches or enters the upper mining-affected zone along the lower coal seam transport roadway direction 24, the disturbance stress generated by the tunneling operation will be superimposed with the upper mining stress, resulting in an increased stress concentration in the coal and rock mass within the mining-excavation intersection zone. This leads to difficulties in controlling the stability of the surrounding rock in the tunneling roadway, severely restricting the safe and efficient production of the mine.

[0034] To address the aforementioned problems, this invention provides a method for controlling the fracturing of surrounding rock in roadways in areas of close-range coal seam mining and excavation. Two embodiments are provided: Embodiment 1 involves jointly arranging fracturing boreholes in the mining transport roadway of the upper coal seam mining face and the high-speed extraction roadway of the adjacent working face when the lower coal seam mining face has not yet been mined or when mining has not yet ended; Embodiment 2 involves arranging fracturing boreholes entirely in the transport roadway of the upper coal seam mining face when mining has ended in the adjacent working face of the lower coal seam mining face. The invention details the method for controlling the fracturing of surrounding rock in roadways in areas of close-range coal seam mining and excavation.

[0035] Example 1

[0036] like Figure 1 , Figure 2 and Figure 3 As shown, for situations where adjacent working faces in the lower coal seam mining face have not yet completed mining, the method for controlling the fracturing of the surrounding rock in the tunneling roadway in the close-range coal seam mining intersection area provided by this invention has the following specific implementation steps:

[0037] S1. Conduct core sampling and mechanical testing: Core samples were taken from the hard roof strata corresponding to the transport roadway 1, track roadway 2, high-extraction roadway 3 adjacent to the lower coal seam mining face, and the lower coal seam transport roadway excavation face 4, and rock mechanical property tests were conducted to obtain the mechanical properties of the roof at different strata; the hard roof strata requiring fracturing were identified, and data on the periodic fracturing step distance and fracturing intensity of the hard roof at the upper coal seam mining face 8 were collected. The lower coal seam transport roadway excavation face 4 and the lower coal seam track roadway excavation face 5 are located in the lower coal seam mining face 9, and the track roadway 6 and the transport roadway 7 adjacent to the lower coal seam mining face are located in the adjacent working face 10.

[0038] S2. Determine the mining-excavation intersection area between the upper coal seam mining face and the lower coal seam transport roadway excavation face: Calculate the advance influence range of coal seam mining stress, the lateral influence range of mining stress, and the influence range of roadway excavation stress. The superimposed area of ​​stress influence range is taken as the mining-excavation intersection area 13. Subsequently, fracturing boreholes are arranged in the mining-excavation intersection area 13 to cut off and relieve pressure on the hard rock strata of the roof of the mining-excavation intersection area 13.

[0039] The calculation of the advance and lateral influence range of coal seam mining stress, as well as the influence range of roadway excavation stress, includes: calculating the advance influence distance L1=D / tanβ+ξM of the upper coal seam longwall face 8 (in meters); calculating the lateral influence boundary distance L2=KDcotβ of the upper coal seam longwall face 8 (in meters); and calculating the stress influence radius R of the excavated roadway. d =r0(2P / σ c ) 1 / 2The unit is m; where D is the interlayer spacing between the upper coal seam 26 and the lower coal seam 27, M is the thickness of the upper coal seam longwall face 8, ξ is the lithology coefficient, with a value range of 1~1.2, K is the mining stress increase coefficient, with a value range of 1.5~2.5; β is the mining influence angle, calculated based on the assumption that the interlayer strata between the closely spaced coal seams are medium-hard strata, with a value range of 45°~55°; r0 is the equivalent radius of the lower coal seam transport roadway face 4, P is the roadway support resistance, σ c It is the uniaxial compressive strength of coal seam 27 in the lower coal seam.

[0040] Mining conflict zone 13 needs to satisfy the condition L0≤L2+R d And Δy≤L1+R d Where Δy is the distance along the strike between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4, and L0 is the horizontal offset between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4; combined with the mining speed of the upper coal seam mining face 8, the daily advance of the lower coal seam transport roadway excavation face 4, and the horizontal distance between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4, the mining-excavation encounter position 14 and the range of the mining-excavation encounter area 13 are determined, and the hard rock strata of the roof in the mining-excavation encounter area 13 are subjected to fracturing construction.

[0041] S3. Arrange high-extraction roadway fracturing boreholes 16 in the high-extraction roadway 3 adjacent to the lower coal seam mining face: The final position of the high-extraction roadway fracturing boreholes 16 arranged in the high-extraction roadway 3 adjacent to the lower coal seam mining face is the hard rock layer 20 between the close coal seams determined in step S1. The arrangement range of the boreholes is the mining-excavation intersection area. By fracturing, the hard rock layer 20 between the close coal seams above the lower coal seam transport roadway excavation face 4 is cut off, forming a weak structural surface 23 of the hard rock layer between the close coal seams. This blocks the propagation of mining stress from the upper coal seam mining face 8 to the lower coal seam transport roadway excavation face 4, reduces the degree of mining stress superposition, reduces the damage of mining stress to the lower coal seam transport roadway excavation face 4, and ensures that the excavation of the lower coal seam transport roadway excavation face 4 is not affected by the mining of the upper coal seam mining face 8.

[0042] When the adjacent working face 10 of the lower coal seam mining face has not yet been mined to the designed stop line 12, and the high-speed extraction roadway 3 of the adjacent working face is in use, high-speed extraction roadway fracturing boreholes 16 can be arranged in the high-speed extraction roadway 3 of the adjacent working face to pre-fracture and cut off the hard rock strata 20 between the nearby coal seams, thereby blocking the propagation of mining stress from the upper coal seam mining face 8 towards the lower coal seam transport roadway excavation face 4. Fracturing can select multiple rock strata in the roof as target hard rock strata, and perform retreating fracturing on each hard rock strata in the roof.

[0043] S4. In the transport roadway 1 of the upper coal seam mining face, roof fracturing boreholes 15 are arranged in a fan shape. The final position of the roof fracturing boreholes 15 is the high-level hard rock layer 18 of the upper coal seam mining face determined in step S1. By fracturing the high-level hard rock layer 18 and the low-level hard rock layer 19 of the upper coal seam mining face, weak structural surfaces 21 and 22 of the high-level hard rock layer and the low-level hard rock layer of the upper coal seam mining face are formed. This allows the hard roof to collapse in time as the upper coal seam mining face is mined, reducing the pressure step distance and pressure intensity of the hard rock layer fracture, thereby reducing the dynamic pressure of the upper coal seam mining face and reducing the degree of stress superposition.

[0044] The roof fracturing boreholes 15 arranged in the transport roadway of the upper coal seam mining face have a final hole spacing of 15-20m between each borehole in each group of roof fracturing boreholes 15 and the hard rock strata 18 at the high position of the roof of the upper coal seam mining face. The spacing between each group of roof fracturing boreholes 15 is 20m-30m, which should be less than the hard roof cycle of the hard rock strata 18 at the high position of the roof of the upper coal seam mining face. The line connecting the final hole positions of each group of roof fracturing boreholes 15 is perpendicular to the advancing direction 25 of the upper coal seam mining face.

[0045] The arrangement range of the roof fracturing boreholes 15 is the mining intersection area. Each group of roof fracturing boreholes 15 can be arranged entirely in the transport roadway 1 or the track roadway 2 of the upper coal seam mining face, or they can be arranged symmetrically towards each other in the transport roadway 1 and the track roadway 2 of the upper coal seam mining face. The arrangement method and the specific opening position are determined according to the on-site construction conditions. The fan-shaped hole arrangement in the transport roadway 1 of the upper coal seam mining face can reduce the drilling rig stabilization and relocation time, which is conducive to improving the drilling and fracturing construction efficiency.

[0046] In step S4, the high-speed extraction roadway fracturing borehole 16 and the roof fracturing borehole 15 in step S3 are staggered in the horizontal direction. The spacing between the high-speed extraction roadway fracturing borehole 16 in step S4 is 20m~30m, and the spacing between the high-speed extraction roadway fracturing borehole 16 in step S4 and the adjacent roof fracturing borehole 15 in step S3 in the horizontal direction is 15m. The final hole spacing of each borehole in this group at the target fracturing layer is 15~20m, and the line connecting the final hole positions of each group of boreholes is parallel to the working face advance direction.

[0047] S5. Arrange the existing fracturing system: The fracturing fluid in the water tank is pressurized by the high-pressure pump and flows to the high-pressure sealed drill pipe through the high-pressure hose. The high-pressure hose is depressurized through the pressure relief valve. The flow rate and water pressure in the fracturing system are monitored in real time by the fracturing monitoring and control instrument. The fracturing system includes a high-pressure pump, water tank, high-pressure hose, high-pressure sealed drill pipe, pressure relief valve, fracturing monitoring and control instrument, sealing device, one-way valve group, reverse one-way valve, adapter, and U-shaped water tail.

[0048] S6. Target Key Rock Layer for Fracturing: Push the one-way valve group and the sealing device into the fracturing borehole 16 in the high-pressure extraction roadway through the high-pressure sealing drill rod under the operation of the drilling rig. Turn on the high-pressure pump to inject high-pressure water into the hard rock layer 20 between the nearby coal seams. The fracturing time is determined according to the mechanical properties of the rock layer. The fracturing time of the top plate of the thick and hard sandstone layer is usually 20 to 30 minutes.

[0049] S7. After the fracturing of the high-extraction roadway fracturing borehole 16 in the high-extraction roadway 3 of the adjacent working face of the lower coal seam mining face is completed, the pipeline is depressurized: if the water pressure collected in real time by the fracturing monitoring and control instrument is less than 5MPa and the duration exceeds the preset duration threshold, or if the duration of water discharge in the adjacent boreholes in each group of high-extraction roadway fracturing boreholes 16 of the high-extraction roadway of the adjacent working face of the lower coal seam mining face exceeds the preset time threshold of 5 minutes, then the high-pressure pump is shut down and the pressure relief valve is opened to depressurize the high-pressure pipeline; if there are multiple layers of hard rock strata 20 between closely spaced coal seams, then retreating segmented fracturing is adopted, and the retreating high-pressure sealing drill rod is used to retreat the one-way valve group and the sealing device to other hard rock strata to continue fracturing.

[0050] S8. Repeat step S7 until all fracturing of the high-extraction roadway fracturing boreholes 16 arranged in the high-extraction roadway 3 of the adjacent working face of the lower coal seam mining face is completed; fracturing of the roof fracturing boreholes 15 arranged in the transport roadway 1 of the upper coal seam mining face in step S4 is performed so that the high-level hard rock layer 18 and the low-level hard rock layer 19 of the roof of the upper coal seam mining face collapse in time as the working face is mined, thereby reducing the dynamic pressure of mining in the upper coal seam mining face 8; repeat step S8 until the fracturing of the roof fracturing boreholes in the mining-excavation intersection area is completed.

[0051] Example 2

[0052] like Figure 4 , Figure 5 , Figure 6 As shown, for a situation where the adjacent working face of the lower coal seam mining face has been mined out, forming a goaf 11, and the lower coal seam transport roadway is being excavated while the upper coal seam mining face has begun mining, the method for controlling the fracturing of the surrounding rock in the tunneling roadway in the close coal seam mining intersection area provided by this invention has the following specific implementation steps:

[0053] S1. Conduct core sampling and mechanical testing: Core samples were taken from the hard roof strata corresponding to the transport roadway 1, track roadway 2, high-extraction roadway 3 adjacent to the lower coal seam mining face, and the lower coal seam transport roadway excavation face 4. Rock mechanical property tests were conducted to obtain the mechanical properties of the roof at different strata, determine the hard roof strata requiring fracturing, and collect data on the periodic fracturing step distance and fracturing intensity of the hard roof at the upper coal seam mining face 8. The lower coal seam transport roadway excavation face 4 and the lower coal seam track roadway excavation face 5 are located in the lower coal seam mining face 9. The track roadway 6 and the transport roadway 7 adjacent to the lower coal seam mining face are located in the adjacent working face 10.

[0054] S2. Determine the mining-excavation intersection zone between the upper coal seam longwall face and the lower coal seam transport roadway face: Calculate the advance influence range of coal seam mining stress, the lateral influence range of mining stress, and the influence range of roadway excavation stress. The superimposed area of ​​stress influence ranges is designated as the mining-excavation intersection zone 13. Subsequently, fracturing boreholes are arranged in the mining-excavation intersection zone to cut and relieve pressure on the hard roof strata in the mining-excavation intersection zone.

[0055] The calculation of the advance and lateral influence range of coal seam mining stress, as well as the influence range of roadway excavation stress, includes: calculating the advance influence distance L1=D / tanβ+ξM of the upper coal seam longwall face 8 (in meters); calculating the lateral influence boundary distance L2=KDcotβ of the upper coal seam longwall face 8 (in meters); and calculating the stress influence radius R of the excavated roadway. d =r0(2P / σ c ) 1 / 2 The unit is m; where D is the interlayer spacing between the upper coal seam 26 and the lower coal seam 27, M is the thickness of the upper coal seam longwall face 8, ξ is the lithology coefficient, with a value range of 1~1.2, K is the mining stress increase coefficient, with a value range of 1.5~2.5; β is the mining influence angle, calculated based on the assumption that the interlayer strata between the closely spaced coal seams are medium-hard strata, with a value range of 45°~55°; r0 is the equivalent radius of the lower coal seam transport roadway face 4, P is the roadway support resistance, σ c It refers to the uniaxial compressive strength of coal seam 27 in the lower coal seam; the mining-excavation intersection zone needs to meet the condition L0≤L2+R. d And Δy≤L1+R dWhere Δy is the distance along the strike between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4, and L0 is the horizontal offset between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4; combined with the mining speed of the upper coal seam mining face 8, the daily advance of the lower coal seam transport roadway excavation face 4, and the horizontal distance between the upper coal seam mining face 8 and the lower coal seam transport roadway excavation face 4, the mining-excavation encounter position 14 and the mining-excavation encounter area 13 are determined, and the hard rock strata of the roof in the mining-excavation encounter area are subjected to fracturing construction.

[0056] S3. Fracturing by arranging floor holes in the mining roadway of the upper coal seam: After the mining of the adjacent working face 10 of the lower coal seam is completed, the high-extraction roadway 3 of the adjacent working face of the lower coal seam is closed, and it is impossible to construct the high-extraction roadway fracturing borehole 16 in the high-extraction roadway 3 of the adjacent working face of the lower coal seam. Then, floor fracturing boreholes 17 are arranged in the transport roadway 1 of the upper coal seam to fracture the hard rock layer 20 between the nearby coal seams. The floor fracturing boreholes 17 and the roof fracturing boreholes 15 are arranged at intervals in the mining intersection area for fracturing construction. Hydraulic fracturing can select multiple rock layers in the roof as target hard rock layers and perform retreat fracturing on each hard rock layer.

[0057] The final position of the bottom plate fracturing borehole 17 is the hard rock stratum 20 between the adjacent coal seams determined in step S1. The arrangement range of the bottom plate fracturing borehole 17 in the transport roadway 1 of the upper coal seam mining face is the mining-excavation intersection area. By fracturing and cutting off the hard rock stratum 20 between the adjacent coal seams above the lower coal seam transport roadway excavation face 4, a weak structural surface 23 of the hard rock stratum between the adjacent coal seams is formed by fracturing. This blocks the propagation of mining stress from the upper coal seam mining face 8 to the lower coal seam transport roadway excavation face 4, reduces the degree of superposition of mining stress, and reduces the impact of the mining of the upper coal seam mining face 8 on the excavation of the lower coal seam transport roadway excavation face 4.

[0058] S4. In the transport roadway 1 of the upper coal seam mining face, roof fracturing boreholes 15 are arranged in a fan shape. The final position of the roof fracturing boreholes 15 is the high-level hard rock layer 18 of the upper coal seam mining face determined in step S1. By fracturing the high-level hard rock layer 18 and the low-level hard rock layer 19 of the upper coal seam mining face, weak structural surface 21 and structural surface 22 of the high-level hard rock layer and the low-level hard rock layer of the upper coal seam mining face are formed. This allows the hard roof to collapse in time as the upper coal seam mining face is mined, reducing the pressure step distance and pressure intensity of the hard rock layer of the working face roof fracture, thereby reducing the mining dynamic pressure of the upper coal seam mining face and reducing the degree of mining dynamic stress superposition.

[0059] The roof fracturing boreholes 15 arranged in the transport roadway of the upper coal seam mining face have a final hole spacing of 15-20m between each borehole in each group of roof fracturing boreholes 15 and the hard rock strata 18 at the high position of the roof of the upper coal seam mining face. The spacing between each group of roof fracturing boreholes 15 is 20m-30m, which should be less than the hard roof cycle of the hard rock strata 18 at the high position of the roof of the upper coal seam mining face. The line connecting the final hole positions of each group of roof fracturing boreholes 15 is perpendicular to the advancing direction 25 of the upper coal seam mining face.

[0060] The boreholes are arranged in the mining and excavation intersection area. Each group of roof fracturing boreholes 15 can be arranged entirely in the transport roadway 1 or the track roadway 2 of the upper coal seam mining face, or they can be arranged symmetrically towards each other in the transport roadway 1 and the track roadway 2 of the upper coal seam mining face. The arrangement method and specific opening positions are determined according to the on-site construction conditions. The fan-shaped hole arrangement in the transport roadway 1 of the upper coal seam mining face can reduce the drilling rig stabilization and relocation time, which is conducive to improving the drilling and fracturing construction efficiency.

[0061] In step S4, the top plate fracturing borehole 15 and in step S3, the bottom plate fracturing borehole 17 are staggered in the horizontal direction. The distance between adjacent top plate fracturing boreholes 15 in S4 is 20m to 30m, and the distance between the bottom plate fracturing borehole 17 in step S4 and the adjacent top plate fracturing borehole 15 in step S3 in the horizontal direction is 15m. The final hole spacing of each borehole in this group at the target fracturing layer is 15 to 20m, and the line connecting the final hole positions of each group of boreholes is parallel to the working face advancement direction.

[0062] S5. Fracturing System Setup: The fracturing fluid in the water tank is pressurized by a high-pressure pump and flows to the high-pressure sealed drill pipe through a high-pressure hose. The high-pressure hose is depressurized through a pressure relief valve. The flow rate and water pressure in the fracturing system are monitored in real time by a fracturing control instrument. The fracturing system includes a high-pressure pump, water tank, high-pressure hose, high-pressure sealed drill pipe, pressure relief valve, fracturing control instrument, perforator, one-way valve group, reverse one-way valve, adapter, and U-shaped water tail.

[0063] S6. Target Key Rock Layer for Fracturing: Push the one-way valve group and the sealing device to the bottom plate fracturing borehole 17 through the high-pressure sealing drill rod under the operation of the drilling rig, and start the high-pressure pump to inject high-pressure water into the hard rock layer 20 between the nearby coal seam layers; The fracturing time is determined according to the mechanical properties of the rock layer. The fracturing time of the top plate of the thick and hard sandstone layer is usually 20~30 minutes.

[0064] S7. After the fracturing of the bottom plate fracturing borehole 17 in the transport roadway 1 of the upper coal seam mining face is completed, the pipeline is depressurized: if the water pressure collected in real time by the fracturing monitoring and control instrument is less than 5MPa and the duration exceeds the preset duration threshold, or if the water outflow duration of the adjacent boreholes in the bottom plate fracturing borehole 17 group in the transport roadway 1 of the upper coal seam mining face exceeds the preset time threshold of 5 minutes, then the high-pressure pump is shut down and the pressure relief valve is opened to depressurize the high-pressure pipeline; if there are multiple layers of hard rock strata 20 between closely spaced coal seams, then retreating segmented fracturing is adopted, and the retreating high-pressure sealing drill rod is used to retreat the one-way valve group and the sealing device to other hard rock strata to continue fracturing.

[0065] S8. Repeat step S7 until all floor fracturing boreholes 17 arranged in the transport roadway 1 of the upper coal seam longwall face are completed. Fracturing the roof fracturing boreholes 15 arranged in the transport roadway of the upper coal seam longwall face in step S4 is performed so that the high-level hard rock strata 18 and the low-level hard rock strata 19 of the roof of the upper coal seam longwall face collapse in time as the face is mined, thereby reducing the dynamic pressure of the upper coal seam longwall face 8 during mining. Repeat step S8 until the roof fracturing boreholes 15 in the mining-excavation intersection area are completed.

[0066] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0067] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention described herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not invented herein. The specification and embodiments are to be considered exemplary only.

[0068] The above specific embodiments further illustrate the purpose, technical solution and beneficial effects of this application. It should be understood that the above are only specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of this application should be included within the scope of protection of this application.

Claims

1. A method for controlling fracturing of surrounding rock in tunnels in close-range coal seam mining intersection areas, characterized in that, include: Step S1: After core sampling of the high-level hard rock strata (18) of the upper coal seam mining face, the low-level hard rock strata (19) of the upper coal seam mining face, and the hard rock strata (20) between the nearby coal seams, rock mechanical property tests are carried out to obtain the mechanical properties of the hard rock strata of the roof; determine the hard rock strata of the roof that need to be fracturing, and collect the periodic fracturing step distance and fracturing intensity of the hard roof of the upper coal seam mining face (8); Step S2: Calculate the range of influence of coal seam mining stress, the range of influence of mining stress laterally, and the range of influence of roadway excavation stress. The superimposed area of ​​the range of influence of coal seam mining stress, the range of influence of mining stress laterally, and the range of influence of roadway excavation stress is taken as the mining-excavation confrontation area (13). Step S3: The final position of the high-extraction roadway fracturing borehole (16) arranged in the high-extraction roadway (3) of the adjacent working face of the lower coal seam mining face is the hard rock layer (20) between the nearby coal seam layers. The arrangement range of the high-extraction roadway fracturing borehole (16) is within the mining and excavation intersection area. The fracturing cuts the hard rock layer (20) between the nearby coal seam layers above the lower coal seam transport roadway excavation face (4), forming a fracturing weak structural surface (23) between the hard rock layer between the nearby coal seam layers. Step S4: Arrange roof fracturing boreholes (15) in a fan shape in the transport roadway (1) of the upper coal seam mining face. The final position of the roof fracturing boreholes (15) is the high-level hard rock layer (18) of the upper coal seam mining face determined in step S1. Fracturing is performed on the high-level hard rock layer (18) and the low-level hard rock layer (19) of the upper coal seam mining face to form a weak structural surface (21) of the high-level hard rock layer and a weak structural surface (22) of the low-level hard rock layer of the upper coal seam mining face. Step S5: In the fracturing system, the fracturing fluid in the water tank is pressurized by the high-pressure pump and flows to the high-pressure sealed drill pipe through the high-pressure hose. The high-pressure hose is depressurized through the pressure relief valve. The flow rate and water pressure in the fracturing system are monitored in real time by the fracturing control instrument. Step S6: Push the one-way valve group and the sealing device to the high-pressure sealing drill rod to the high-pressure extraction roadway fracturing borehole (16) and perform fracturing. Use a high-pressure pump to inject high-pressure water into the hard rock layer (20) between the close coal seams to form a weak structural surface (23) of the hard rock layer between the close coal seams. Step S7: If the water pressure collected in real time by the fracturing control instrument is less than 5MPa and the duration exceeds the preset duration threshold, or if the water outflow duration of the adjacent borehole of the currently fracturing high-pressure drainage roadway fracturing borehole (16) exceeds the preset time threshold, then the high-pressure pump is shut down; if there are multiple layers of hard rock strata (20) between closely spaced coal seams that have not been fractured, then the one-way valve group and the sealing device are moved to other hard rock strata (20) between closely spaced coal seams using the high-pressure sealing drill rod to continue fracturing. Step S8: Repeat step S7 until all high-level extraction roadway fracturing boreholes (16) are completed; fracturing the roof fracturing boreholes (15) so that the high-level hard rock strata (18) and the low-level hard rock strata (19) of the roof of the upper coal seam mining face collapse as the upper coal seam mining face is mined, reducing the mining dynamic pressure of the upper coal seam mining face (8); repeat step S8 until the roof fracturing boreholes (15) of the mining-excavation intersection area (13) are completed.

2. The method for controlling the fracturing of surrounding rock in roadways in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S2, the influence range of coal seam mining stress, the lateral influence range of mining stress, and the influence range of roadway excavation stress are calculated, including: Calculate the range of the leading impact of coal seam mining stress, including: Calculate the advance influence distance L1 of the upper coal seam mining face (8) L1 = D / tanβ + ξM; Calculate the lateral influence range of mining-induced stress, including: Calculate the lateral influence boundary distance L2=KDcotβ for the upper coal seam mining face (8); The calculation of the stress influence range during tunnel excavation includes: Calculate the radius of influence R of stress in the tunnel. d =r0(2P / σ c ) 1 / 2 Where D is the interlayer spacing between the upper coal seam (26) and the lower coal seam (27), M is the thickness of the coal seam in the upper coal seam mining face (8), ξ is the lithology coefficient, K is the mining stress increase coefficient, β is the mining influence angle, r0 is the equivalent radius of the lower coal seam transport roadway excavation face (4), P is the roadway support resistance, σ c It is the uniaxial compressive strength of the coal body in the lower coal seam (27).

3. The method for controlling the fracturing of surrounding rock in roadways in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S2, the mining conflict zone satisfies L0 ≤ L2 + R d And Δy≤L1+R d Δy is the distance between the upper coal seam mining face (8) and the lower coal seam transport roadway excavation face (4) along the advancing direction (25) of the upper coal seam mining face, and L0 is the horizontal misalignment between the upper coal seam mining face (8) and the lower coal seam transport roadway excavation face (4). Based on the mining speed of the upper coal seam mining face (8), the daily advance of the lower coal seam transport roadway excavation face (4), and the horizontal distance between the upper coal seam mining face (8) and the lower coal seam transport roadway excavation face (4), the range of the mining-excavation intersection area is determined. Fracturing construction is carried out on the hard rock strata of the roof in the mining-excavation intersection area.

4. The method for controlling the fracturing of surrounding rock in roadways in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S3, if the mining of the adjacent working face (10) of the lower coal seam mining face has not yet ended and the high-extraction roadway (3) of the adjacent working face of the lower coal seam mining face is in use, then a high-extraction roadway fracturing borehole (16) is arranged in the high-extraction roadway (3) of the adjacent working face of the lower coal seam mining face. Before the lower coal seam transport roadway excavation face (4) enters the mining-excavation confrontation area (13), the hard rock layer (20) between the nearby coal seam layers is fractured and cut off, blocking the propagation of the mining stress of the upper coal seam mining face (8) towards the lower coal seam transport roadway excavation face (4).

5. The method for controlling fracturing of surrounding rock in tunnels in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S4, the final hole spacing of the roof fracturing boreholes (15) in the high-level hard rock strata (18) of the upper coal seam mining face is 15~20m, the spacing between each group of roof fracturing boreholes (15) is 20m~30m, and the spacing between each group of roof fracturing boreholes (15) is less than the periodic pressure step distance of the hard roof strata (18) of the upper coal seam mining face; the line connecting the final hole positions of each group of roof fracturing boreholes (15) is perpendicular to the advancing direction (25) of the upper coal seam mining face.

6. The method for controlling the fracturing of surrounding rock in roadways in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S4, the arrangement range of the roof fracturing boreholes (15) is within the mining intersection area (13). Each group of roof fracturing boreholes (15) is arranged in the transport roadway (1) or the track roadway (2) of the upper coal seam mining face. Alternatively, each group of roof fracturing boreholes (15) is symmetrically arranged in the transport roadway (1) and the track roadway (2) of the upper coal seam mining face.

7. The method for controlling the fracturing of surrounding rock in tunnels in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S4, if the mining of the adjacent working face (10) of the lower coal seam mining face is completed and the high-extraction roadway (3) of the adjacent working face of the lower coal seam mining face is closed, then a negative-angle bottom plate fracturing borehole (17) is arranged in the transport roadway (1) of the upper coal seam mining face. The hard rock layer (20) between the nearby coal seams is fracturing through the bottom plate fracturing borehole (17). The bottom plate fracturing borehole (17) arranged in the transport roadway (1) of the upper coal seam mining face and the top plate fracturing borehole (15) arranged in the transport roadway (1) of the upper coal seam mining face are used for fracturing at intervals.

8. The method for controlling fracturing of surrounding rock in tunnels in close-range coal seam mining intersection areas according to claim 1, characterized in that, In step S6, the fracturing time is determined based on the mechanical properties of the rock strata.

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