Roadway driving method for thick coal seam based on advanced pressure relief and gas extraction

Abstract

The present application belongs to the field of coal mine roadway tunneling, and particularly relates to a thick coal seam roadway tunneling method based on advanced pressure relief and gas extraction; the present application constructs pressure relief boreholes parallel to the roadway on both sides of the roadway before roadway tunneling, and controls the pressure relief range of the pressure relief boreholes outside the plastic zone of the roadway, then performs roadway tunneling after extracting gas by the pressure relief boreholes; and performs grouting reinforcement on the hydraulic fracturing fissures in the section coal pillar by the pressure relief boreholes after roadway tunneling, to restore the bearing capacity of the section coal pillar. The present application can extract gas in the coal seam near the roadway, reduce the amount of gas entering the roadway during roadway tunneling, realize the synergistic effect of advanced pressure relief and gas extraction, and eliminate the risk of rock burst and gas outburst during roadway tunneling. Reserving an elastic zone between the roadway and the pressure relief range of the pressure relief boreholes and performing grouting reinforcement later is beneficial to roadway support, reduces the cost of roadway support, and effectively controls the large deformation of the roadway later.

Description

Technical Field

[0001] This invention belongs to the field of coal mine roadway excavation, specifically relating to a method for excavating thick coal seam roadways based on advanced pressure relief and gas extraction. Background Technology

[0002] As coal mining depths continue to increase, the coexistence of high ground stress and high gas levels becomes increasingly prominent, especially during the excavation of thick coal seams, where the conflict between controlling the surrounding rock and managing gas becomes more pronounced. Thick coal seams themselves have high gas content and poor permeability. In addition, the excavation area is affected by the mining activities of adjacent working faces, resulting in high stress concentration in the coal pillars and coal bodies of the roadway sides. This makes them prone to dynamic disasters such as rock bursts and coal and gas outbursts, seriously threatening excavation safety and construction efficiency.

[0003] For the problem of tunneling in high-gas, thick coal seams, the conventional approach is to implement decompression and gas extraction separately. For example, methods such as blasting decompression and large-diameter borehole decompression are used to reduce surrounding rock stress, while pre-extraction of gas is performed through in-seam or cross-seam boreholes before tunneling. However, this approach has the following shortcomings: First, decompression measures and gas extraction lack coordinated design. Decompression boreholes do not fully consider gas extraction needs, while extraction boreholes have limited effect on regulating the surrounding rock stress field, leading to insufficient decompression or poor extraction results. Second, the bearing capacity of the coal pillars and coal seams in the roadway sides decreases significantly after decompression, resulting in large roadway deformation and difficult maintenance in the later stages, with a lack of effective means to restore the bearing capacity of the coal pillars. Third, in terms of construction procedures, most methods only perform supplementary decompression or extraction after roadway excavation, failing to achieve proactive intervention before excavation and making it difficult to fundamentally eliminate the risk of stress concentration and gas outbursts during the excavation process.

[0004] Therefore, there is an urgent need for a method for tunneling thick coal seams that can achieve advanced pressure relief and efficient gas extraction, while ensuring the stability of the coal pillar in the later stages. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for tunneling thick coal seams based on advanced pressure relief and gas extraction, comprising the following steps: S1: Calculate the width R1 of the plastic zone of the coal pillar near the roadway in the calculation section; S2: Calculate the width R2 of the plastic zone around the roadway after the excavation of the transport roadway and return air roadway; S3: Take 1.5 times R1 as the safety boundary width M1 of the coal pillar section; take 1.5 times R2 as the safety boundary width M2 of the coal wall; in the coal pillar section, the pressure relief range of the pressure relief borehole is completely controlled within the elastic zone between the safety boundaries of the coal pillar section; in the working face, the pressure relief range of the pressure relief borehole is completely controlled within the elastic zone outside the safety boundary of the coal wall. S4: Decompression boreholes are constructed in the coal pillar section and on the side of the first working face near the coal pillar section. The decompression boreholes are parallel to the transport roadway of the first working face, and the decompression range of adjacent decompression boreholes overlaps by a safety margin. S5: Hydraulic fracturing is performed through pressure relief boreholes, and gas is extracted through the pressure relief boreholes using a gas extraction system. S6: The transport roadway of the first working face is excavated. The first roadway support is carried out during the excavation of the transport roadway. Then, the hydraulic fracturing fractures in the coal pillar of the section are reinforced by grouting through pressure relief boreholes. After the grouting reinforcement is stabilized, the transport roadway is supplemented with support. Then the first working face is mined. S7: The side of the second working face near the section coal pillar is its return airway. Based on the construction parameters determined in steps S3 and S4, pressure relief boreholes are constructed on the side of the second working face near the section coal pillar. The pressure relief boreholes are parallel to the return airway of the second working face. S8: Refer to step S5 to perform hydraulic fracturing and gas extraction on the pressure relief boreholes in the second working face; carry out the excavation of the return airway in the second working face, and provide roadway support during the excavation of the return airway.

[0006] Preferably, the section between the first working face and the second working face is a coal pillar. The first working face is mined first, and the second working face is mined later. The side of the first working face closest to the coal pillar is its transport roadway, and the side of the second working face closest to the coal pillar is its return air roadway.

[0007] Preferably, in step S3, assuming the depressurization radius of a single depressurization borehole is R, and the distance between the center of the depressurization borehole adjacent to the safety boundary of the coal pillar section and the safety boundary of the coal pillar section is D1, then D1≥R+M1.

[0008] Preferably, in step S3, the distance between the center of the pressure relief borehole adjacent to the safety boundary of the coal wall and the safety boundary of the coal wall is D2, then D2≥R+M2.

[0009] Preferably, in step S4, the pressure relief drilling is carried out to the same end as the transport tunnel.

[0010] Preferably, in step S4, one or more rows of pressure relief boreholes are constructed according to the thickness of the coal seam and the pressure relief radius of the pressure relief boreholes.

[0011] Preferably, in step S5, the pressure relief borehole is depressurized along its entire axial length or at intervals, and proppant is injected into the fracture after depressurization.

[0012] Preferably, in step S6, the grouting material is a cement-based binder grout or a chemical binder grout.

[0013] Preferably, in step S7, the pressure relief drilling is carried out to the same end as the return airway.

[0014] Preferably, it also includes S9: referring to the above construction, the thick coal seam roadway excavation based on advanced pressure relief and gas extraction is carried out on the transport roadway and return air roadway on both sides of the coal pillar in the subsequent section.

[0015] The beneficial effects of this invention are as follows: Before tunnel excavation, pressure relief boreholes parallel to the tunnel are constructed on both sides of the tunnel, and the pressure relief range of the boreholes is controlled outside the plastic zone of the tunnel. Gas is then extracted using these boreholes before tunnel excavation. On one hand, this extracts gas from the coal seams near the tunnel (mainly those within the pressure relief range of the boreholes), reducing the amount of gas entering the tunnel during excavation (the gas content in the tunnel and the coal seams between it and the pressure relief range of the boreholes is limited and easy to control), achieving a synergistic effect of pre-emptive pressure relief and gas extraction, and eliminating the risks of rockbursts and gas outbursts during tunnel excavation. On the other hand, maintaining an elastic zone between the tunnel and the pressure relief range of the boreholes facilitates tunnel support and reduces support costs. Furthermore, after tunnel excavation, grouting is performed through the pressure relief boreholes to reinforce the hydraulic fracturing fissures in the coal pillar section, thereby restoring the bearing capacity of the coal pillar section and effectively controlling large deformations in the later stages of tunnel excavation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the cross-sectional structure of the advanced depressurization and gas extraction in the first working face transport tunnel of the present invention; Figure 2 This is a schematic diagram of the planar structure of the first working face transport tunnel for advanced depressurization and gas extraction in this invention. Figure 3 This is a schematic diagram of the cross-sectional structure of the advanced depressurization and gas extraction in the return airway of the second working face of the present invention. Figure 4 This is a schematic diagram of the planar structure of the return airway and gas extraction system in the second working face of the present invention. In the diagram: 1-First working face; 2-Pressure relief borehole; 3-Transportation level; 4-Coal seam; 5-Second working face; 6-Section coal pillar; 7-Rock strata; 8-Goaf; 9-Return airway; 10-Pressure relief range. Detailed Implementation

[0017] To illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to the accompanying drawings.

[0018] like Figure 1As shown, this invention proposes a method for tunneling thick coal seams based on advanced pressure relief and gas extraction, applied to the tunneling of a deep, high-stress, rockburst-prone thick coal seam. A section coal pillar 6 is left between the first working face 1 and the second working face 5. The first working face 1 is mined first, followed by the second working face 5. The side of the first working face 1 closest to the section coal pillar 6 is its transport roadway 3, and the side of the second working face 5 closest to the section coal pillar 6 is its return airway 9. This arrangement is well-known in the art and will not be described in detail here. The method includes the following steps: S1: Calculate the width of the plastic zone of coal pillar 6 near the roadway; specifically, use the following formula for calculation:

[0019] In the formula, R1 is the width of the plastic zone of coal pillar 6 near the roadway, in meters; n This indicates the mining thickness of coal seam 4, in meters, which is 10 meters in this embodiment. x is the triaxial stress coefficient of coal seam 4, which is dimensionless and is 4 in this embodiment; f Here is the friction coefficient of coal seam 4, which is dimensionless and is 0.21 in this embodiment; k is the stress concentration factor of section coal pillar 6, which is dimensionless and is 2 in this embodiment; c The unit weight of rock stratum 7 is kN / m³, and in this embodiment it is 25 kN / m³. H The coal seam is buried at a depth of 4 meters, which is 600 meters in this embodiment. C The cohesion of coal seam 4 is 1.14 MPa in this embodiment. f The internal friction angle of coal seam 4 is °, which is 28.15° in this embodiment; P i The stress is the horizontal stress of coal seam 4, in MPa, and in this embodiment it is 3 MPa.

[0020] Section coal pillar 6 is the unmined part of coal seam 4. After substituting the above parameters, the width R1 of the plastic zone of section coal pillar 6 near the roadway can be determined to be 2.65m.

[0021] S2: Calculate the width of the plastic zone around the roadway after excavation of transport roadway 3 and return air roadway 9; specifically, the following formula is used for calculation:

[0022] In the formula, R2 is the width of the plastic zone around the tunnel, in meters; r 0 represents the equivalent radius of a rectangular cross-section tunnel, in meters. r 0=( l + h ) / 4, l Indicates the width of the tunnel, in meters (m). h The height of the tunnel is indicated in meters (m). In this embodiment, both the transport tunnel 3 and the return air tunnel 9 are rectangular cross-section tunnels with a width of [missing information].l All are 6.5m high. h All are 4.8m; P Vertical stress, MPa .

[0023] Substituting the above parameters, the width R2 of the plastic zone around the roadway can be determined to be 3.89m.

[0024] S3: Take 1.5 times the width of the plastic zone R1 of the section coal pillar 6 near the roadway as the safety boundary width M1 of the section coal pillar 6 (with 0.5 times R1 as the elastic zone). In this embodiment, M1=1.5×R1=1.5×2.65=3.975m; Take 1.5 times the width of the plastic zone R2 around the roadway as the safety boundary width M2 of the coal wall (with 0.5 times R2 as the elastic zone). In this embodiment, M2=1.5×R2=5.835m.

[0025] In section coal pillar 6, the pressure relief range 10 of the pressure relief borehole 2 is completely controlled within the elastic zone between the safety boundaries of section coal pillar 6. Assuming the pressure relief radius of a single borehole 2 is R (in meters), which is 4 meters in this embodiment, and the distance between the center of the pressure relief borehole 2 adjacent to the safety boundary of section coal pillar 6 and the safety boundary of section coal pillar 6 is D1, then D1 ≥ R + M1, that is, D1 should not be less than 7.975 meters. In this embodiment, it can be taken as 8 meters. In the working face, the pressure relief range 10 of the pressure relief borehole 2 is completely controlled within the elastic zone outside the safety boundary of the coal wall. The distance between the center of the pressure relief borehole 2 adjacent to the safety boundary of the coal wall and the safety boundary of the coal wall is D2, then D2 ≥ R + M2, which should not be less than 9.835 meters. In this embodiment, it can be taken as 10 meters.

[0026] S4: Decompression boreholes 2 are constructed in the coal pillar 6 and on the side of the first working face 1 near the coal pillar 6. The decompression boreholes 2 are parallel to the transport roadway 3 of the first working face 1, and preferably constructed to the same end as the transport roadway 3. Depending on the thickness of the coal seam 4 and the decompression radius of the decompression boreholes 2, one or more rows of decompression boreholes 2 can be constructed. In the same row or column, the center distance between adjacent decompression boreholes 2 is... ; The overlap safety margin of the pressure relief range 10 of adjacent pressure relief boreholes 2 is in meters, not less than 1.0m, and is taken as 2.0m in this embodiment. The center distance D of adjacent pressure relief boreholes 2 is 6m. In this embodiment, a row of pressure relief boreholes 2 is constructed at the center of the coal seam 4 in the height direction. In this embodiment, the width of the section coal pillar 6 is 22m, two pressure relief boreholes 2 are constructed in the section coal pillar 6, and three pressure relief boreholes 2 are constructed on the side of the first working face 1 near the section coal pillar 6.

[0027] S5: Hydraulic fracturing is performed through pressure relief borehole 2; after a stable and continuous fracture network is formed by hydraulic fracturing in pressure relief borehole 2, i.e., sufficient pressure relief is achieved and gas extraction conditions are met, the gas extraction system is started, and gas is efficiently extracted through pressure relief borehole 2. During extraction, the gas concentration and extraction rate are continuously monitored to ensure that the extraction meets the standards; the pressure relief borehole 2 is used for full-length axial pressure relief or intermittent pressure relief; when intermittent pressure relief is used, the fracturing segment length L s =β·R, taking the piecewise coefficient β=0.9, we can calculate L. s =0.9×4=3.6m; Segment spacing L m =α·L f Taking the interval coefficient α = 0.6, we calculate L. m =0.6×4=2.4m; generally β=0.8-1.0, α=0.6-0.8. During hydraulic fracturing, high-pressure water injection is performed until fractures appear in the borehole wall. Water pressure is then continued to propagate the fractures. When the water pressure reaches the rated injection pressure... p inj =1.2 (3) s h - s H + s t When the pressure stabilizes or the flow rate suddenly increases, continue injection for 10-30 minutes, then stop injection and depressurize. s h The minimum horizontal principal stress of coal seam 4 is 18 MPa in this embodiment. s H The maximum horizontal principal stress of coal seam 4 is 28 MPa in this embodiment. s t Given the tensile strength of coal seam 4 (MPa), which is 1.2 MPa in this embodiment, the rated injection pressure is... p inj =32.64MPa; furthermore, proppant was injected into the fracture.

[0028] S6: The transport roadway 3 of the first working face 1 is excavated. During the excavation of the transport roadway 3, the first roadway support is carried out. Then, grouting is performed to reinforce the hydraulically fractured fissures in the coal pillar 6 through the pressure relief borehole 2. After the grouting reinforcement is stabilized, supplementary support is provided for the transport roadway 3. Then, the first working face 1 is mined. After mining, the upper rock strata 7 of the first working face 1 collapses and fractures, forming a goaf 8. The grouting material is a cement-based binder grout or a chemical binder grout. The grout diffuses, fills, and binds in the fracture network, systematically reinforcing the hydraulically fractured fissures.

[0029] S7: The return airway 9 is located on the side of the second working face 5 near the section coal pillar 6. Based on the construction parameters determined in steps S3 and S4, pressure relief boreholes 2 are constructed on the side of the second working face 5 near the section coal pillar 6. The pressure relief boreholes 2 are parallel to the return airway 9 of the second working face 5, and preferably constructed to the same end as the return airway 9. In this embodiment, three pressure relief boreholes 2 are constructed on the side of the second working face 5 near the section coal pillar 6.

[0030] S8: Referring to step S5, hydraulic fracturing and gas extraction are carried out on the pressure relief borehole 2 in the second working face 5; the return airway 9 of the second working face 5 is excavated, and roadway support is carried out during the excavation of the return airway 9.

[0031] S9: Referring to the above construction steps, the thick coal seam 4 roadway will be excavated on both sides of the coal pillar 6 in the subsequent section, based on advanced pressure relief and gas extraction.

[0032] In this invention, the transport roadway 3 and the return air roadway 9 are excavated along the bottom plate of the coal seam 4.

[0033] This invention is not limited to the above embodiments. Any modifications or equivalent substitutions made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for tunneling thick coal seams based on advanced pressure relief and gas extraction, characterized in that, Includes the following steps: S1: Calculate the width R1 of the plastic zone of the coal pillar near the roadway in the calculation section; S2: Calculate the width R2 of the plastic zone around the roadway after the excavation of the transport roadway and return air roadway; S3: Take 1.5 times R1 as the safety boundary width M1 of the coal pillar section; take 1.5 times R2 as the safety boundary width M2 of the coal wall; in the coal pillar section, the pressure relief range of the pressure relief borehole is completely controlled within the elastic zone between the safety boundaries of the coal pillar section; in the working face, the pressure relief range of the pressure relief borehole is completely controlled within the elastic zone outside the safety boundary of the coal wall. S4: Decompression boreholes are constructed in the coal pillar section and on the side of the first working face near the coal pillar section. The decompression boreholes are parallel to the transport roadway of the first working face, and the decompression range of adjacent decompression boreholes overlaps by a safety margin. S5: Hydraulic fracturing is performed through pressure relief boreholes, and gas is extracted through the pressure relief boreholes using a gas extraction system. S6: The transport roadway of the first working face is excavated. The first roadway support is carried out during the excavation of the transport roadway. Then, the hydraulic fracturing fractures in the coal pillar of the section are reinforced by grouting through pressure relief boreholes. After the grouting reinforcement is stabilized, the transport roadway is supplemented with support. Then the first working face is mined. S7: The side of the second working face near the section coal pillar is its return airway. Based on the construction parameters determined in steps S3 and S4, pressure relief boreholes are constructed on the side of the second working face near the section coal pillar. The pressure relief boreholes are parallel to the return airway of the second working face. S8: Refer to step S5 to perform hydraulic fracturing and gas extraction on the pressure relief boreholes in the second working face; carry out the excavation of the return airway in the second working face, and provide roadway support during the excavation of the return airway.

2. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, The section between the first working face and the second working face is a coal pillar. The first working face is mined first, and the second working face is mined later. The side of the first working face closest to the coal pillar is its transport roadway, and the side of the second working face closest to the coal pillar is its return airway.

3. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 2, characterized in that, In step S3, assuming the pressure relief radius of a single pressure relief borehole is R, and the distance between the center of the pressure relief borehole adjacent to the safety boundary of the coal pillar section and the safety boundary of the coal pillar section is D1, then D1≥R+M1.

4. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 3, characterized in that, In step S3, the distance between the center of the pressure relief borehole adjacent to the safety boundary of the coal wall and the safety boundary of the coal wall is D2, then D2≥R+M2.

5. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, In step S4, the pressure relief borehole is constructed to the same end as the transport tunnel.

6. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, In step S4, one or more rows of pressure relief boreholes are constructed according to the thickness of the coal seam and the pressure relief radius of the pressure relief boreholes.

7. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, In step S5, the pressure relief borehole is depressurized along its entire axial length or at intervals, and proppant is injected into the fracture after depressurization.

8. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, In step S6, the grouting material is a cement-based binder grout or a chemical binder grout.

9. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to claim 1, characterized in that, In step S7, the pressure relief drilling is carried out to the same end as the return airway.

10. The thick coal seam roadway excavation method based on advanced pressure relief and gas extraction according to any one of claims 1-9, characterized in that, It also includes S9: thick coal seam roadway excavation based on advanced pressure relief and gas extraction for the transport and return air horizontal roadways on both sides of the subsequent coal pillar.

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