Large and long tunnel gas pre-extraction method based on surrounding rock pressure relief principle

Abstract

The invention provides a large and long tunnel gas pre-extraction method based on a surrounding rock pressure relief principle, and belongs to the technical field of tunnel construction. Drilling from the earth surface to the central area of the tunnel and coal seam intersecting surface to form a footrill; a main roadway is tunneled from the tail end of the footrill, and the trend is adjusted to be parallel to the coal seam inclination direction at the position close to the coal seam; auxiliary roadway networks are tunneled towards the two sides on the basis of the main roadway, and a manual pressure relief space is formed to replace a protective layer; dense crossing drilling holes are constructed in the coal seam in the auxiliary roadway, and hydraulic slotting pressure relief and permeability increase are carried out; and gas is extracted through the roadway network until the standard is reached, and finally grouting plugging is conducted. Complete parallel operation of gas extraction and tunneling is achieved through ground roadway engineering independent of a tunnel main hole, and the construction period is greatly shortened. The gas extraction efficiency and safety of the low-permeability coal seam are improved by combining the manual pressure relief space with hydraulic slotting, and the method is suitable for large and long tunnel engineering penetrating through gently-inclined and inclined high-gas coal seams.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel construction, in particular to a long tunnel pre-drainage gas method based on the principle of surrounding rock pressure relief. BACKGROUND

[0002] With the development of China's transportation industry, the possibility of building tunnels in coal seam and gas area is increasing, and long tunnels crossing multiple coal seams and high gas areas are becoming more common. In order to ensure the smooth construction of the tunnel, the tunnel crossing the coal seam needs to be constructed with coal seam prevention during the construction process.

[0003] The existing long tunnel pre-drainage gas method mainly has the following deficiencies: 1. Most of them are based on optimization of the coal seam process, and few can be separated from the traditional coal seam process, with limited efficiency improvement; 2. The cost of intelligent equipment is high, and the maintenance is complex, and the actual application faces the problems of complex technology integration and poor equipment coordination; 3. The extraction efficiency of some outburst prevention measures applied in low permeability coal seams is low, and the gas control and outburst prevention effect is unstable, which is greatly affected by geological conditions. SUMMARY

[0004] The present application aims to solve the technical problems of low extraction efficiency in low permeability coal seams and unstable gas control and outburst prevention effect in the prior art, and proposes a long tunnel pre-drainage gas method based on the principle of surrounding rock pressure relief.

[0005] The present application provides a long tunnel pre-drainage gas method based on the principle of surrounding rock pressure relief, comprising: S1, determining the thickness, inclination angle a and gas parameter of the target coal seam through advanced geological exploration, setting the protection range, adit position and direction, arrangement parameters of the main lane and auxiliary lane, and the coal seam cutting direction angle β, wherein the coal seam cutting direction angle β is the circumferential angle of the cutting head of the high-pressure hydraulic cutting device in the plane perpendicular to the drilling axis relative to the initial direction; S2, installing a directional drilling machine on the ground surface corresponding to the coal seam section where the tunnel is to pass through, drilling from the ground surface to the center point area of the designed intersection surface between the tunnel axis and the coal seam to form a flat adit straight from the ground surface to the top of the coal measure stratum; S3, excavating the main lane from the end of the flat adit towards the coal seam, and adjusting the excavation direction of the main lane when excavating to a preset distance from the coal seam roof, so that the strike direction is parallel to the inclination direction of the coal seam; S4, taking the main lane as a reference, excavating multiple auxiliary lanes in the upward and downward directions along the normal direction of the coal seam at an acute angle with the main lane to form a lane network distributed on both sides of the main lane, and the adjacent auxiliary lanes are kept at a preset distance; the lane network of the main lane and the auxiliary lane forms an artificial pressure relief space above the target coal seam. S5, drilling a through-hole in the target coal seam in the auxiliary lane, the hole extending along the strike of the coal seam after entering the coal seam; a high-pressure hydraulic slotting device is used to cut the coal seam section in the hole radially to form a slot, wherein the pressure range of the high-pressure hydraulic slotting device is 30-100 MPa; S6, pre-draining the coal seam area through the adit, the main lane and the auxiliary lane until the evaluation is a non-outburst dangerous area; after the tunnel is excavated to the safety warning position and the re-measurement is qualified, the lane network is grouted and plugged.

[0006] Further, in step S4, the included angle between the auxiliary lane and the main lane is between 10° and 20°.

[0007] Further, in step S5, the single slot formed by the high-pressure hydraulic slotting device has a depth of 0.5-1 m and an axial length of 3-5 m along the hole, and the axial spacing between adjacent slots in the coal seam section of a single hole is not greater than 2 m.

[0008] Further, the equivalent mining thickness M of the artificial pressure relief space is calculated by dividing the total volume of the main lane and the auxiliary lane network by the projection area in the coal seam inclination direction, which is used to verify the effectiveness of the lower protective layer; when the equivalent mining thickness M is less than or equal to 0.5 m, the drilling hole needs to be constructed after drainage to verify the protection effect.

[0009] Further, the method for verifying the effectiveness of the lower protective layer comprises: calculating the minimum allowable interlayer spacing H=KMcosα, wherein K is a roof management coefficient, and is taken as 5-12; calculating the maximum effective pressure relief vertical distance wherein is the theoretical effective vertical distance, is the mining influence coefficient, is the interlayer hard rock content coefficient; the actual vertical distance of the main lane from the coal seam is required to be greater than H, and the coal seam is required to be within the range of

[0010] Further, in S5, the high-pressure hydraulic slotting device is periodically rotated in the coal seam section to change the slotting direction angle β in the coal seam within the range of 0° to 45°, thereby forming uniformly distributed slots in the circumferential direction of the hole.

[0011] Further, in S3, the main lane direction is adjusted by a steering device installed on the excavation equipment.

[0012] Further, the cross section of the main lane and the auxiliary lane is arched or rectangular, the net height of the main lane is not less than 2.5 m, the net width is not less than 2.6 m, and the diameter of the auxiliary lane is not less than 1.8 m. ​​​

[0013] Furthermore, in S6, the safety warning position is 10-15m away from the coal seam at the tunnel excavation face.

[0014] Furthermore, in S5, the diameter of the cross-layer boreholes drilled into the target coal seam in the auxiliary roadway is not less than 75mm, and the end position of all boreholes is located 12m outside the tunnel outline.

[0015] The technical advantages of the gas pre-drainage method for long tunnels based on the principle of surrounding rock decompression disclosed in this invention are as follows: the roadway network engineering required for gas drainage is independent of the main tunnel and can be constructed in advance on the ground, allowing it to be carried out simultaneously with tunnel excavation. This eliminates the bottleneck of gas control occupying the critical path construction period in traditional methods, enabling parallel processes and significantly shortening the construction period. By simulating protective layer mining through artificial roadway network, a large-scale decompression effect is generated on the lower coal seam, significantly increasing the permeability of the coal seam. Combined with dense boreholes and circumferentially uniform hydraulic slits, the gas desorption and flow channels are greatly increased, resulting in a significantly higher total gas drainage volume in the same time period compared to traditional face borehole drainage methods. Attached Figure Description

[0016] Figure 1 A schematic flowchart of a method for pre-draining gas from long tunnels based on the principle of surrounding rock decompression, provided in an embodiment of the present invention; Figure 2 yes Figure 1 A three-dimensional schematic diagram of the section of the tunnel that passes through the coal seam using the method shown. Figure 3 yes Figure 1 Axial plan view of the method shown; Figure 4 yes Figure 3 Enlarged detail of A; Figure 5 yes Figure 1 A magnified view of a section showing the method of tunneling through a coal seam; Figure 6 This is a schematic diagram of the layout of the main tunnel and auxiliary tunnels as shown in the diagram.

[0017] Explanation of reference numerals in the attached diagram: 1-rock stratum; 2-coal seam; 3-tunnel; 4-adit; 5-protective layer; 6-main roadway; 7-auxiliary roadway; 8-drill hole; 9-slot. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of the present invention, exemplary embodiments of the present invention are described below in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0019] A method for pre-draining gas from long tunnels based on the principle of surrounding rock pressure relief, referenced Figures 1 to 6 As shown, the specific steps include: S1: Geological Exploration and Scheme Design Before Tunnel Excavation: Assuming the actual tunnel diameter is 12m and the excavation speed is 100m per month, the tunnel needs to pass through a 2m thick coal seam. Before tunnel construction, a geological survey of the coal seam was conducted, revealing a dip angle α of 30°, a pressure relief angle δ1 of 69°, and δ2 of 90°. Advanced geological testing and analysis determined the original gas content of the coal seam to be 15m³. 3 Based on the original gas content, the estimated time required for gas drainage is at least 3 months. Before tunnel excavation, advanced geological exploration and analysis are needed to determine coal seam parameters such as the original gas content and gas pressure. Based on parameters such as coal seam thickness and dip angle α, the optimal drilling locations and depths for the protection zone, adits, main roadways, and auxiliary roadways, as well as the internal cutting direction angle β of the slotted pipe, are determined to form a construction plan. The internal cutting direction angle β is defined as the circumferential rotation angle of the cutting nozzle of the high-pressure hydraulic cutting device relative to the starting direction in a plane perpendicular to the borehole axis; that is, the turning angle of the slotted pipe, which is a conventional technical method in this field.

[0020] Before the formal excavation of Tunnel 3, advanced geological prediction was conducted using methods such as seismic wave exploration and core drilling. It was determined that the coal seam 2 to be traversed was 3m thick, with a dip angle α=25°, and an initial gas content of 18m³. 3 / t, gas pressure is 1.2MPa. According to the "Regulations for Prevention and Control of Coal and Gas Outbursts", the design protection range is 12m beyond the tunnel outline. The adit 4 is calculated to be driven from the surface, with the target point being 8m outside the intersection of the tunnel axis and the coal seam roof (i.e., the center of the intersection surface). The main roadway 6 is designed to run parallel to the coal seam dip direction, and the auxiliary roadway 7 is designed to be at an angle of 15° to the main roadway, arranged vertically along the normal direction of the coal seam. The normal spacing between the upper and lower auxiliary roadways on the same side is designed to be 15m. Based on the cross-sectional dimensions (main roadway: 2.8m wide × 2.6m high; auxiliary roadway: 2m diameter), length, and spacing of the main and auxiliary roadways, the network volume is calculated, and its projected area on the coal seam dip is calculated. Dividing the two yields the equivalent mining thickness M≈0.4m. The nozzle is defined to face upwards when the cutting direction angle β is 0°. When designing the cutting, β is periodically varied between 0° and 40° to ensure the cutting coverage area.

[0021] S2: Surface Adit Construction: A drilling rig and gas pre-extraction device are installed on a surface with stable terrain and closest to the coal seam in a selected section. A directional drilling rig is used to drill from the most suitable location on the hillside towards the center of the intersection of Tunnel 3 and the coal seam, forming the adit 4. The end of the adit is located at least 12m outside the tunnel's designed outline and, along the tunnel excavation direction, at least 5m in front of the center point of the intersection of the tunnel axis and the coal seam.

[0022] On the surface corresponding to the tunnel mileage, select a flat site and install a high-power directional drilling rig. Drill a 350mm diameter pilot hole from this point toward the target point designed for S1, and then enlarge the hole to a diameter of 3m to form adit 4, which will serve as a transportation channel for personnel, equipment and materials.

[0023] S3: Main Roadway Construction and Orientation: Based on the "Technical Specifications for Protective Layer Mining" and actual conditions, the distribution parameters of main roadway 6 and auxiliary roadway 7 were determined. At a distance of 12m from the coal seam, a steering device was used to adjust the direction, ensuring that main roadway 6 was as parallel as possible to the dip direction of the coal seam. Starting from the bottom of adit 4, main roadway 6 was excavated towards the coal seam using the drill-and-blast method. Its cross-section is a straight-walled semi-circular arch, with a net width of 2.8m and a net height of 2.6m. When drilling measurements revealed a vertical distance of 12m from the coal seam roof, the hydraulic steering system installed on the tunneling machine was activated to gradually adjust the orientation, ensuring that the subsequent section of main roadway 6 maintained consistency with the pre-surveyed dip direction of the coal seam (25° dip angle).

[0024] S4: Auxiliary roadway network construction: Based on the main roadway, multiple auxiliary roadways are excavated upwards and downwards along the coal seam normal direction at acute angles to the main roadway, forming a roadway network distributed on both sides of the main roadway; the distance between two adjacent auxiliary roadways on the same side of the main roadway and along the coal seam normal direction is 12-18m; the network formed by the main roadway and auxiliary roadways creates a continuous artificial pressure relief space above the target coal seam, simulating the pressure relief effect of the lower protective layer.

[0025] Auxiliary tunnels are excavated to the left and right sides of the main tunnel at a certain angle, with a 15m interval between the upper and lower auxiliary tunnels. This replaces the protective layer, preventing rock collapse due to excavation while still providing pressure relief and accelerating gas release. On the sidewall of the main tunnel 6, openings are made at regular intervals (e.g., 20m), and auxiliary tunnels 7 are excavated upwards at a 15° angle to the designed height. Similarly, the lower auxiliary tunnels are excavated downwards at a 15° angle. The vertical spacing between the upper and lower auxiliary tunnels is controlled at 15m. All auxiliary tunnels 7 have a diameter of approximately 2m. This tunnel network forms a continuous pressure relief zone, i.e., a protective layer 5, above the coal seam.

[0026] Based on the main roadway, auxiliary roadways are excavated to the left and right sides at a certain angle. The diameter of the auxiliary roadway is 2m, and the interval between the upper and lower auxiliary roadways is 15m. When the coal seam boundary and the auxiliary roadway form a pressure relief angle, the excavation stops. The constructed main roadway and auxiliary roadway replace the protective layer, and the remaining rock pillars play a supporting role. This can prevent the rock layer from collapsing due to excavation, while still playing a pressure relief role and accelerating the gas release speed.

[0027] S5: Coal Seam Drilling and Hydraulic Slotting for Permeability Enhancement: Select a suitable location on auxiliary roadway 7. After the drill bit reaches the coal seam from auxiliary roadway 7, drill along the coal seam strike. The drill rod is withdrawn after reaching the designated position in the coal seam. Repeat this operation at intervals. For paths drilled deep into the coal seam, use a hydraulic slotting device to slot and depressurize the coal seam 2 until slots are evenly distributed throughout the coal seam 2, forming clustered slots 9. A drilling site is arranged at 5m intervals in each auxiliary roadway 7. Use a tunnel drilling rig to construct through-layer boreholes 8. The borehole first penetrates the remaining rock pillar into coal seam 2, then continues drilling along the coal seam strike for 20-30m. The borehole diameter is 94mm. After completion, a high-pressure hydraulic slotting device is lowered into each borehole. This device includes a high-pressure water pump, drill rod, in-hole motor, and directional nozzle. In the coal seam section of the borehole, the in-hole motor is started, driving the nozzle to rotate uniformly at a speed of approximately 5-10 rpm, while simultaneously pumping in high-pressure water at ≥30MPa. The nozzle rotation causes the cutting direction angle β to continuously change from 0° to 360°, thereby cutting radial slots 9 in the coal body around the borehole. The design depth of a single slot is approximately 0.8m, and the length is approximately 4m. By controlling the advance speed, the axial spacing between adjacent slots is kept to approximately 1.5m, achieving full coverage of the coal seam section and uniform "cluster-like" cutting. Here, "cluster-like" means that within a single borehole, the slots are closely arranged axially; in the three-dimensional network formed by all boreholes, the slot groups are distributed in a cluster-like pattern within the coal seam.

[0028] S6: Gas extraction and sealing: The gas is pre-extracted from the formation by using a surface gas extraction pump. The equivalent of the extracted gas is monitored in real time until the area is a no-outburst hazard zone. Then, ventilation continues until the tunnel construction reaches 12m from the coal seam. The data is re-tested. After the standard is met, grout is injected into the reserved pipeline in the roadway to seal it. The pre-extraction of gas in the tunnel is completed.

[0029] All tunnels and boreholes were connected to a centralized surface extraction pumping station via pipelines. The extraction pumps were activated to forcefully extract gas from the target area. The gas flow rate and concentration in each branch pipe were monitored in real time. After 60 days of continuous extraction, the residual gas content in the area was assessed to have decreased to 6 mg / m³. 3 Below a certain value (e.g., t / t), the gas level meets the standard for a no-outburst hazard zone. At this point, the main tunnel face of Tunnel 3 is still 100m away from the coal seam (far greater than the 12m warning line). When the tunnel reaches 12m from the coal seam, the gas parameters are measured again to confirm safety. Finally, high-grade cement grout is injected into the main roadway 6, auxiliary roadway 7, and borehole 8 through pre-embedded grouting pipes for permanent sealing.

[0030] By conducting gas extraction operations completely synchronously with the main tunnel excavation, at least three months of separate gas control time were saved during tunnel construction. Through roadway network depressurization combined with hydraulic fracturing, gas extraction efficiency was increased by approximately three times, ensuring coal seam safety. For long tunnel construction, the distance from the starting construction point to the center of the intersection is much shorter than the distance from the tunnel's starting mileage to the traditional coal seam anti-outburst mileage. This method ensures that boreholes are not damaged during tunnel excavation, allowing for simultaneous gas extraction and tunnel excavation.

[0031] A further proposed solution, in another tunnel project, involves a coal seam dip angle α = 40° and a designed mining (pressure relief) thickness M (i.e., the equivalent height of the pressure relief space formed by the main and auxiliary roadway network) of 0.4m. Its effectiveness as a "lower protective layer" needs to be verified. For gently dipping and inclined coal seams, the protective effect of the main and auxiliary roadways replaces that of the lower protective layer, with the maximum effective distance... : ; Among them, S′ 下 For the theoretical effective vertical distance, This is the influence coefficient during mining. The coefficient representing the content of hard rock (sandstone, limestone) between layers; When α < 60°, the minimum interlayer distance H that prevents the upper protected layer from being damaged during mining is: H=KMcosα; Where H is the minimum permissible interlayer spacing, M is the mining thickness, α is the coal seam dip angle, and K is the roof management coefficient.

[0032] Calculate the minimum permissible floor spacing H = KMcosα. In this example, we take the roof management coefficient K = 10 (for a rigid roof). In the actual design, the main roadway is 12m away from the coal seam, which is much larger than 3.06m, and is safe from the perspective of the inter-layer spacing.

[0033] Based on the protective layer mining theory, the maximum effective pressure relief distance S needs to be calculated. The theoretical effective vertical distance S′下 Take 50m (based on experience). Mining impact coefficient. Take 1.1 (strong pressure relief), interlayer hard rock content coefficient Take 0.9 (high sandstone content). Then... This means that coal seams within a 49.5m radius below the tunnel network can be effectively depressurized and protected. In this case, the coal seam traversed by the tunnel is within this range, and the protection is effective. With proper planning, the main and auxiliary tunnels can replace the lower protective layer in providing depressurization and protection, which not only reduces the workload but also effectively avoids the problem of rock collapse caused by excavation.

[0034] Since the equivalent extraction thickness M=0.4<0.5, three verification boreholes were drilled from the surface to the treated area during the later stages of extraction. The measured residual gas pressure was below 0.4 MPa, and the drill cuttings gas desorption index was [not specified]. All values ​​were less than the critical value, confirming that the hazard had been eliminated.

[0035] Through specific calculations and verifications, it has been proven that the "main tunnel + auxiliary tunnel" network in this invention can be scientifically equivalent to a "lower protective layer". Through rigorous parameter verification and effect verification, the theoretical reliability and safety of engineering applications have been ensured.

[0036] A further step in the design process involves strictly controlling the spatial scope according to requirements: the terminal target point of adit 4 is designed 15m outside the design outline of tunnel 3, and 8m in front of the center point of the intersection of the tunnel axis and the coal seam (along the tunnel excavation direction). This ensures that the extraction range completely covers the coal seam area that the tunnel will traverse, while leaving sufficient safety boundaries.

[0037] The hydraulic slotting operation specifically involves using a hydraulic slotting device equipped with a high-precision in-hole orientation instrument. Once the device enters the coal seam section, it is slowly rotated, causing the orientation of the slotting nozzle (i.e., the slotting direction angle β) to periodically change between 0° and 40° (less than 45°), thereby cutting asymmetrical but uniformly distributed slots 9 around the borehole. This turning angle of less than 45° avoids excessive concentration of slots in one direction, which could lead to stress concentration or cutting blind spots. Twelve cross-seam boreholes 8 were drilled from each auxiliary roadway 7 into the coal seam, and the aforementioned slotting was performed, forming a highly uniform "cluster-like" permeability enhancement network.

[0038] By strictly controlling the spatial location of the adit endpoint (extending outward by 12m and advancing axially by more than 5m), the gas control area was ensured to be free of blind spots. By limiting β and ensuring a sufficient number of boreholes, the uniformity and efficiency of coal seam depressurization and permeability enhancement were achieved, laying a solid foundation for rapid extraction.

[0039] Hydraulic cutting of the coal seam can achieve uniform pressure relief. Due to the influence of gas density and pressure difference, the gas will accumulate in the upper part of the adit and main roadway, which improves the gas drainage efficiency, reduces the time required for gas drainage, and realizes gas drainage in coal-bearing strata, which can reduce the construction period for tunnel construction.

[0040] A further refinement involves drilling a borehole with a diameter of no less than 75mm into the target coal seam within the auxiliary roadway in section S5, ensuring that the end of each borehole is located 12m outside the tunnel outline. A 90mm diameter drill bit is typically used. The coordinates of all borehole endpoints are precisely calculated and verified to ensure that even in the most unfavorable locations, the borehole end remains at a safe distance of 12m outside the tunnel outline. The sufficiently large borehole diameter guarantees the effectiveness of the hydraulic cutting and the subsequent gas flow, while strict endpoint control ensures that a well-prepared safety barrier always exists ahead of the tunnel face.

[0041] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A method for pre-draining gas from long tunnels based on the principle of surrounding rock pressure relief, characterized in that, include: S1. The thickness, dip angle α, and gas parameters of the target coal seam are determined through advanced geological exploration. The protection range, adit location and direction, layout parameters of main roadway and auxiliary roadway, and the cutting direction angle β in the coal seam are set. The cutting direction angle β in the coal seam is the circumferential rotation angle of the cutting nozzle of the high-pressure hydraulic cutting device relative to the starting direction in a plane perpendicular to the borehole axis. S2, on the surface corresponding to the section of the coal seam that the tunnel is to pass through, a directional drilling rig is installed and drills from the surface to the center point of the intersection between the tunnel axis and the designed coal seam, forming a tunnel that runs directly from the surface to the coal-bearing strata above. S3, the main roadway is excavated from the end of the adit towards the coal seam. When the excavation reaches a preset distance from the top of the coal seam, the excavation direction of the main roadway is adjusted so that its direction is parallel to the dip direction of the coal seam. S4. Based on the main roadway, multiple auxiliary roadways are excavated upwards and downwards along the coal seam normal direction at an acute angle to the main roadway, forming a roadway network distributed on both sides of the main roadway, with adjacent auxiliary roadways maintaining a preset distance; the roadway network of the main roadway and auxiliary roadways forms an artificial pressure relief space above the target coal seam. S5, drilling a cross-layer borehole into the target coal seam in the auxiliary roadway, the borehole extending along the coal seam direction after entering the coal seam; using a high-pressure hydraulic cutting device to radially cut the coal seam section in the borehole to form a slot; wherein the pressure range of the high-pressure hydraulic cutting device is 30Mpa~100Mpa. S6. The coal seam area is pre-extracted through the adit, main roadway and auxiliary roadway until it is evaluated as a non-outburst danger zone; after the tunnel is excavated to a safe warning position and the retest is qualified, the roadway network is grouted and sealed.

2. The method according to claim 1, characterized in that, In step S4, the angle between the auxiliary lane and the main lane is between 10° and 20°.

3. The method according to claim 1, characterized in that, In step S5, the depth of a single slot formed by the high-pressure hydraulic slotting device is 0.5-1m, the length along the borehole axis is 3-5m, and the axial distance between adjacent slots within the coal seam section of a single borehole is no greater than 2m.

4. The method according to claim 1, characterized in that, The equivalent mining thickness M of the artificial decompression space is calculated by dividing the total volume of the main roadway and auxiliary roadway network by the projected area in the dipping direction of the coal seam, and is used to verify the effectiveness of the lower protective layer. When the equivalent mining thickness M ≤ 0.5m, a verification borehole needs to be constructed after extraction to verify the protective effect.

5. The method according to claim 4, characterized in that, Methods for verifying the effectiveness of the lower protective layer include: calculating the minimum allowable interlayer spacing H=KMcosα, where K is the roof management coefficient, which is taken as 5-12; Calculate the maximum effective pressure relief vertical distance : ； in For the theoretical effective vertical distance, The mining impact coefficient, This is the interlayer hard rock content coefficient; it requires that the actual vertical distance between the main roadway and the coal seam is greater than H, and that the coal seam is in... Within the range.

6. The method according to claim 1, characterized in that, In step S5, the high-pressure hydraulic slitting device rotates periodically within the coal seam section, causing the slitting direction angle β within the coal seam to vary within the range of 0° to 45°, thereby forming uniformly distributed slots around the borehole.

7. The method according to claim 1, characterized in that, In S3, the direction of the main tunnel is adjusted by a steering device installed on the tunneling equipment.

8. The method according to claim 1, characterized in that, The main lane and auxiliary lane have arched or rectangular cross-sections. The main lane has a clear height of not less than 2.5m and a clear width of not less than 2.6m. The auxiliary lane has a diameter of not less than 1.8m.

9. The method according to claim 1, characterized in that, In S6, the safety warning position is 10-15m away from the coal seam at the tunnel excavation face.

10. The method according to claim 1, characterized in that, In S5, the diameter of the cross-layer boreholes drilled into the target coal seam in the auxiliary roadway is not less than 75mm, and the end position of all boreholes is located 12m outside the tunnel outline.

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