Multi-disaster cooperative prevention and control method and system for fracturing in advance hole exploration area of heading face coal seam under complex geological conditions

Abstract

The invention relates to a multi-disaster cooperative prevention and control method and system for fracturing of a heading face coal seam advanced hole exploration area under complex geological conditions, and belongs to the field of mine disaster prevention and control. According to the method, an integrated process of drilling, exploring, pressing and pumping is adopted, and geological exploration is completed through advanced hole exploring construction bedding drilling; on the basis of a segmented retreating type hydraulic fracturing technology, pressure relief and permeability increase of a coal body are achieved in combination with a recoverable packer device; and after fracturing, a gas extraction system is connected by adopting a process of two-plugging one-injection and hole sealing under pressure, and the stability of the roadway is enhanced through an anchor net cable beam supporting system. The matched fracturing system comprises a water tank, a water injection pump, an ultrahigh pressure hydraulic hose, a fracturing sealing pipe column and an integrated monitoring device. Through multi-disaster collaborative design, repeated drilling construction and resource waste are reduced; the anchor net cable beam supporting system enhances the stability of the roadway under the complex geological condition. The scheme has high adaptability and popularization value, and provides reliable technical support for safe mining of coal mines.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine disaster prevention and control, and relates to a method and system for coordinated prevention and control of multiple disasters caused by fracturing in an advance exploration area of ​​a coal seam at a tunneling working face under complex geological conditions. Background Art

[0002] In the field of underground coal mine disaster prevention and control, especially in tunneling operations under complex geological conditions, the coordinated management of multiple hazards such as gas accumulation, rock bursts, water damage, and dust has always been a technical challenge. Currently, prevention and control technologies for these hazards are typically implemented independently: gas extraction requires the deployment of dedicated extraction boreholes to reduce the gas content of the coal seam; anti-blowout pressure relief requires stress relief in the coal rock through independent boreholes; and exploration of geological structures and hydrological conditions relies on separate geophysical boreholes. While this decentralized approach can partially mitigate the risks of individual hazards, it has significant limitations. On the one hand, the independent construction of multiple boreholes results in the duplication of equipment, manpower, and time resources, and the close spacing of boreholes can easily cause interference and reduce drilling efficiency. On the other hand, the fragmented functions of various operations and the lack of coordination mechanisms make it difficult to achieve coordinated and optimized disaster prevention and control within the limited space of roadways (such as belt conveyor lanes). In addition, existing technologies mostly rely on a single monitoring method (such as water injection pressure or flow monitoring) to evaluate the fracturing effect, and are unable to provide comprehensive feedback on multi-dimensional parameters such as coal seam crack expansion, stress distribution, and gas seepage, resulting in difficulty in accurately controlling the pressure relief and permeability enhancement effect.

[0003] In the existing technology, although some solutions have attempted to integrate some functions into the same borehole (for example, using the borehole for both gas extraction and water injection to prevent dust), its scope of application is limited and it has failed to effectively solve the core problem of coordinated management of multiple disasters. For example, such solutions do not combine advanced exploration technology, making it difficult to achieve accurate geological exploration under complex geological conditions; the fracturing process mostly uses a single-stage water injection, lacking a staged backward fracturing design, resulting in insufficient fracturing range and coal body modification effect; the sealing process and extraction pipeline layout also have defects. Traditional sealing materials are prone to leakage due to the development of coal body cracks, and irregular operations such as laying pipelines and cables on the same side may cause secondary safety hazards. These problems seriously restrict the efficiency and safety of coal mine disaster management, especially in deep mining or complex structural areas, where the limitations of existing technologies are more prominent. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an efficient method that can integrate geological exploration, staged fracturing, gas extraction and multi-hazard coordinated control. By optimizing drilling design, strengthening monitoring methods and innovating process connections, it solves the bottleneck problems of resource waste, insufficient coordination and low control accuracy in existing technologies, and provides reliable technical support for safe and efficient mining of coal mines under complex geological conditions.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for coordinating the prevention and control of multiple hazards in the advanced exploration area of ​​coal seams in a tunneling working face under complex geological conditions adopts a "drilling-exploration-pressure-extraction" working procedure, specifically including the following steps:

[0007] S1 Geological Exploration: Geological exploration is carried out through long-hole drilling operations and in-hole geophysical exploration operations;

[0008] The long drilling operation includes drilling holes in the belt conveyor tunnel excavation working face along the working face strike direction in the drilling field;

[0009] The in-hole geophysical exploration operation includes fixing a transient electromagnetic measurement device, a natural gamma logging device and a borehole radar device on a drill pipe, pushing them into the borehole by a drilling rig for detection, and avoiding the metal casing area during the detection process;

[0010] S2 staged hydraulic fracturing: The hydraulic fracturing system is used to perform backward staged fracturing on the borehole. The initial fracturing position is the bottom of the bedding borehole, and the fracturing is carried out stage by stage according to the preset pressure range and spacing.

[0011] During the fracturing process, the fracturing effect is comprehensively tested through water injection pressure, microseismicity, ground sound, stress monitoring and resistivity 3D imaging;

[0012] S3 connected borehole drainage: After fracturing, gas leakage is detected by tracer gas testing and borehole leakage attenuation testing. The borehole is then sealed and connected to the gas drainage system for gas extraction.

[0013] The sealing operation adopts the "two blocking and one injection, pressure sealing" process, the sealing device is a bag, and the sealing tube is an antistatic sealing tube;

[0014] The belt conveyor tunnel adopts a rectangular cross-section and the support form is anchor mesh cable beam support.

[0015] Optionally, the specific process of the in-hole geophysical exploration operation in S1 is as follows:

[0016] During the pushing process, in-hole radar detection is carried out. After reaching the measuring point, the drill pipe is fixed and transient electromagnetic and natural gamma ray logging detection are carried out in sequence. The pushing and detection are repeated until the entire measuring range is completed.

[0017] Optionally, the hydraulic fracturing system in S2 includes:

[0018] a water tank connected to the inlet end of the water injection pump through a water inlet pipe, and used for storing and supplying fracturing fluid;

[0019] The water injection pump, whose outlet end is connected to the fracturing sealing pipe string device through an ultra-high pressure hydraulic hose wrapped with multiple layers of steel wire, is used to pressurize the fracturing fluid to a preset pressure;

[0020] The fracturing sealing string device includes a retrievable packer device, the front end of which is rigidly connected to the special fracturing orifice device through a threaded interface, and the rear end receives the high-pressure fracturing fluid delivered by the water injection pump through an ultra-high-pressure hydraulic hose;

[0021] A special orifice device for fracturing, fixed at the borehole mouth, with a diversion channel inside, used to directionally inject fracturing fluid into the target fracturing section;

[0022] The retrievable packer device is integrated into the fracturing sealing string device, and realizes the sealing and switching of staged fracturing through hydraulic control of setting and contraction.

[0023] Optionally, the specific operations of the staged hydraulic fracturing are:

[0024] Push the fracturing sealing string with a retrievable packer to the designed position and then set the packer;

[0025] After completing the target section fracturing, shut down the water injection pump and release the pressure. After the packer shrinks, withdraw to the next fracturing section and repeat the fracturing.

[0026] Optionally, the resistivity 3D imaging monitoring system in S2 is used to monitor the fracturing effect of the belt conveyor lane roof in real time.

[0027] Optionally, the tracer gas test method in S3 uses SF6 tracer gas with a purity of ≥99.99%. The test equipment includes SF6 gas cylinder, pressure reducing valve, flow meter, TD500-SH-SF6 detector and CFZ22(A) negative pressure sampler.

[0028] Optionally, the anchor mesh beam support includes threaded steel anchor rods, steel braided mesh, steel strand anchor cables and matching resin drug roll anchoring;

[0029] The threaded steel anchor bolts are anchored to the coal wall through K2360 resin coils. Two coils are used to fill the drill hole and solidify to form the anchoring section for each bolt.

[0030] The steel woven mesh is covered between adjacent anchor rods and fixed to the anchor rod support plate through flat iron strips to form a continuous support surface;

[0031] The steel strand anchor cable is anchored deep in the coal wall through K2360 resin coils. Each anchor cable uses three coils, and the end of the anchor cable passes through the pressure ring and is connected to the anchor cable beam.

[0032] The anchor cable beam is arranged transversely along the roadway and perpendicular to the roadway direction. The steel strands are fixed at both ends through anchor cable support plates and pressure rings to form a bidirectional bearing structure.

[0033] The anchor rod support plate and the anchor cable support plate are both made of Q345 steel and are rigidly connected to the flat iron steel belt and the anchor cable beam by bolts to ensure the overall stability of the support system.

[0034] Optionally, the gas drainage system pipeline laying requirements include:

[0035] The pipeline shall not be laid on the same side as the cable, and the turning angle of the pipeline shall not exceed 50°;

[0036] The manifolds are connected with seamless steel pipes and the use of extraction hoses is prohibited.

[0037] A fracturing system for the above method, comprising:

[0038] The water tank is connected to the water injection pump through an ultra-high pressure hydraulic hose wrapped with multiple layers of steel wire;

[0039] A water injection pump connected to the fracturing sealing string device is used to inject high-pressure fracturing fluid into the borehole;

[0040] A fracturing sealing string device, including a retrievable packer, is connected to a dedicated fracturing orifice device via an ultra-high pressure hydraulic hose;

[0041] A special orifice device for fracturing, fixed at the borehole, used to seal and guide the fracturing fluid;

[0042] The resistivity 3D imaging monitoring system is integrated with the fracturing sealing string device to monitor the resistivity changes in the fracturing area in real time.

[0043] A supporting structure for the above method, comprising:

[0044] Threaded steel anchor rods are arranged at intervals along the roadway and anchored to the coal wall through resin coils;

[0045] The steel strand anchor cable is installed in conjunction with the anchor beam and the pressure ring, with the direction perpendicular to the direction of the roadway;

[0046] The steel woven mesh is covered between the anchor rods and anchor cables to form a continuous support surface.

[0047] The beneficial effects of the present invention are:

[0048] The present invention provides a method and system for coordinated prevention and control of multiple hazards in the advanced exploration area of ​​coal seams in tunneling working faces under complex geological conditions. By integrating the full process of "drilling-exploration-fracturing-extraction" and combining it with a multi-hazard coordinated design concept, it significantly improves the coordination and overall efficiency of underground disaster prevention and control. This is specifically reflected in the following aspects:

[0049] Improved multi-hazard collaborative management capabilities: Through the "one hole, multiple uses" technology, gas extraction, anti-blowout and pressure relief, and geological exploration functions are integrated into the same borehole, avoiding resource waste and operation interference caused by the independent construction of multiple types of boreholes. At the same time, hydraulic fracturing is used to achieve multiple goals such as coal modification and pressure relief, permeability enhancement and extraction, and dust reduction, fundamentally solving the problem of fragmented disaster management functions in traditional technologies.

[0050] Optimization of construction efficiency and resource utilization: The staged retreat hydraulic fracturing process, combined with a recoverable packer device, realizes single-hole multi-stage fracturing operations, significantly reducing the number of drilling holes and repeated construction cycles; through comprehensive monitoring methods (microseismic, geoacoustic, stress and resistivity three-dimensional imaging), real-time feedback on fracturing effects is provided, and fracturing parameters are precisely controlled to improve coal seam pressure relief and permeability enhancement efficiency, thereby shortening the disaster management cycle.

[0051] Enhanced safety and reliability: The innovative "two blocking and one injection, pressure sealing" process and anti-static sealing tubes are used, combined with the tracer gas method and leakage attenuation test method to double-check the sealing quality, effectively reducing the risk of gas leakage; the standardized design of extraction pipelines and cables laying on different sides, seamless steel pipe confluence, etc., further avoids the hidden dangers of electrical fire sources and pipeline failure, and ensures the long-term stable operation of the extraction system.

[0052] Enhanced support structure stability: Based on the anchor mesh cable beam support system, through the synergistic effect of high-strength threaded steel anchor rods, steel strand anchor cables and steel woven mesh, combined with the lateral load-bearing design of the pressure ring and anchor beam, the tunnel's anti-deformation capacity and overall stability under complex geological conditions are significantly improved, providing a safe environment for fracturing and extraction operations.

[0053] The technical adaptability and promotion value are outstanding: this method is not only suitable for narrow working spaces such as belt conveyor tunnels, but can also adapt to different coal seam occurrence conditions by adjusting drilling parameters, fracturing spacing and support schemes, and has wide engineering applicability; its integrated design concept and modular devices (such as fracturing systems) provide a reusable technical paradigm for other mine disaster prevention and control projects, and have significant industry promotion value.

[0054] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0056] Figure 1It is a schematic diagram of the multi-hazard coordinated prevention and control process for rock burst coal seams of the present invention.

[0057] Figure 2 This is a schematic diagram of the plane position of the 1012006 working surface in the present invention.

[0058] Figure 3 This is the geological structure distribution map of the 1012006 working face in the present invention.

[0059] Figure 4 This is a division diagram of the rock burst danger zone during excavation of the 1012006 working face in the present invention.

[0060] Figure 5 This is a schematic cross-sectional view of the belt conveyor lane of the 1012006 working face in the present invention.

[0061] Figure 6 This is a schematic diagram of the support plane of the belt conveyor lane of the 1012006 working face in the present invention.

[0062] Figure 7 This is a plan view of the drilling arrangement trajectory in the present invention.

[0063] Figure 8 It is a cross-sectional schematic diagram of the drilling trajectory in the present invention.

[0064] Figure 9 Schematic diagram of the staged hydraulic fracturing process in the present invention.

[0065] Figure 10 This is a cross-sectional view of the staged fracturing arrangement of a medium-long borehole according to the present invention.

[0066] Figure 11 This is a schematic diagram of the BZW series hydraulic fracturing equipment of the present invention.

[0067] Figure 12 This is a typical fracturing pressure-flow curve monitoring diagram in the present invention.

[0068] Figure 13 This is a schematic diagram of the DC resistivity detection arrangement scheme for the 1012006 working face in the present invention.

[0069] Figure 14 Schematic diagram of testing borehole leakage using the tracer gas method in the present invention.

[0070] Reference numerals: 1 water injection pump, 2 ultra-high pressure hydraulic hose, 3 special orifice device for fracturing, 4 fracturing sealing string, 5 special packer for fracturing. DETAILED DESCRIPTION

[0071] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0072] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0073] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0074] See also Figures 1 to 14 The purpose of the present invention can be achieved by the following technical solutions: a method for coordinating the prevention and control of multiple hazards in the coal seam advance exploration area under complex geological conditions, wherein the method adopts a drilling-exploration-pressure-extraction working procedure, and the specific steps are as follows:

[0075] S1 Geological Exploration: Conduct geological exploration through long hole drilling and in-hole geophysical exploration.

[0076] During the long hole drilling operation, a bed-level borehole is constructed along the working face strike direction in the drilling area of ​​the belt conveyor tunnel excavation working face.

[0077] During in-hole geophysical exploration, the transient electromagnetic measurement device, natural gamma ray logging device, and borehole radar device are connected and fixed to the drill pipe. The devices are pushed using a drilling rig. During the pushing process, the metal casing area is avoided to ensure that the measurement point is in the non-metallic casing area.

[0078] S2 staged hydraulic fracturing: After the in-hole geophysical survey, hydraulic fracturing is carried out using a hydraulic fracturing system;

[0079] In hydraulic fracturing operations, a backward fracturing method is used, with the initial fracturing located at the bottom of the hole along the bedding, and fracturing is carried out section by section according to the preset pressure range and designed spacing;

[0080] A three-dimensional comprehensive inspection of the fracturing effect in deep-hole areas of coal seams is conducted by combining water injection pressure, microseismic, ground sound, stress monitoring, and resistivity 3D imaging fracturing monitoring.

[0081] S3 Connected Hole Drainage: After the hydraulic fracturing operation is completed, a gas leakage test is conducted using the tracer gas test method and the borehole leakage attenuation test method. After the test is completed, the hole is sealed and the pipeline of the borehole and gas extraction system are connected. After the connection is successful, gas extraction operations are carried out;

[0082] In the sealing operation, the two-blocking and one-injection, pressure-sealing process is adopted;

[0083] In the multi-hazard coordinated prevention and control method, the settings for belt conveyor lanes are as follows: cross-sectional shape: the belt conveyor lane adopts a rectangular cross-section; support requirements: the support form is anchor mesh cable beam support; threaded steel anchor rods are used, and the threaded steel anchor rods are anchored with K2360 type resin rolls, the mesh is made of steel woven mesh, the anchor cable is made of steel strands, and the anchor cable is anchored with K2360 type resin rolls.

[0084] In step S1, the specific process of the in-hole geophysical exploration operation is as follows: during the pushing process, the in-hole radar detection is carried out, and after being pushed to the measuring point, it is fixed and the in-hole transient electromagnetic and natural gamma logging detection are carried out. The above process is repeated until the detection of the entire measuring range is completed.

[0085] In step S2, the hydraulic fracturing system consists of a water tank, a water injection pump 1, a fracturing sealing string 4, a multi-layer steel wire-wound ultra-high pressure hydraulic hose 2, a special fracturing orifice device 3 and a retrievable packer 5.

[0086] During hydraulic fracturing operations, a fracturing sealing string 4 is used to seal the well in stages. After the ultra-high-pressure hydraulic hose 2 with the recoverable packer 5 and the safety joint is delivered to the designed position, the recoverable packers 5 are all set at once. After the fracturing construction of the target fracturing section is completed, the water injection pump 1 is turned off and the water is drained and pressure is relieved, waiting for the recoverable packer 5 to shrink. The pump is then withdrawn and pushed to the next fracturing position to continue the fracturing construction. The above steps are repeated to perform staged fracturing step by step.

[0087] In step S2, in the resistivity three-dimensional imaging fracturing monitoring, the resistivity three-dimensional imaging monitoring system monitors the hydraulic fracturing effect of the belt conveyor lane roof.

[0088] In the leak test in step S3, the tracer gas testing method is specifically SF6. The equipment used includes an SF6 gas cylinder, a pressure reducing valve, a flow meter, a TD500-SH-SF6 portable SF6 detector, and a CFZ22(A) negative pressure sampler. The SF6 gas purity is ≥99.99%. In the sealing and control operation in step S3, the sealing device is a pouch, and the sealing tube is an antistatic sealing tube.

[0089] Both the anchor rod and anchor cable support plate are made of Q345 steel, and the anchor rod support plate is used in conjunction with the flat iron steel strip; the anchor cable support plate is used in conjunction with the pressure ring and anchor cable beam, and the installation direction of the anchor cable beam is perpendicular to the direction of the tunnel; each threaded steel anchor rod is anchored with 2 K2360 resin coils, and each anchor cable is anchored with 3 K2360 resin coils.

[0090] When connecting the borehole to the gas drainage system pipeline, the gas drainage system pipeline must not be laid on the same side of the roadway as the cable. The angle of the pipe bends in the gas drainage system pipeline should not exceed 50 degrees. The manifold in the gas drainage system pipeline must not be connected with a drainage hose.

[0091] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0092] According to the relevant requirements of mine gas, rock burst, water disaster and other disaster management work, various types of boreholes for gas extraction, anti-blowout pressure relief and geological structure exploration are arranged on each underground excavation working face. At present, various types of boreholes are constructed independently, interfere with each other, and occupy a large amount of manpower and equipment, which not only seriously restricts the level of single excavation, but also affects the disaster management effect. In order to achieve the coordinated prevention and control of multiple disasters and improve their management efficiency, in accordance with the principle of "one hole for multiple uses" and "overall consideration" of multiple disasters, on the basis of meeting the relevant national and industry standards, it is planned to use the advance exploration hole of the excavation working face to conduct coal seam hydraulic fracturing experiments in the 1012006 belt conveyor lane, so as to achieve the purpose of advance coal body pressure relief, reduce dust and improve extraction efficiency. In order to ensure the smooth implementation of various tasks, a method for coordinated prevention and control of multiple disasters by fracturing in the advance exploration hole area of ​​the coal seam of the excavation working face under complex geological conditions is specially formulated. Taking the belt conveyor lane of the 1012006 working face as an example, the specific contents are as follows:

[0093] I. General Principles

[0094] According to the principle of "drilling-exploration-pressure-extraction", ① a borehole is drilled along the direction of the working face in the drilling area of ​​the excavation working face; ② when the borehole is drilled to the designed position, geological conditions and geophysical exploration are carried out in front of the excavation; ③ after the geological exploration, high-pressure water is injected into the borehole to perform hydraulic fracturing and pressure relief; ④ after the hydraulic fracturing is completed, the hole is sealed and gas extraction is carried out. The specific process is shown in Figure 1 .

[0095] Implementation steps:

[0096] 1. Drilling construction

[0097] The gas extraction team was responsible for the drilling construction task. A borehole was arranged in the 1940m drilling site of the belt conveyor lane of the 1012006 working face. The borehole in the drilling site was 4m away from the laneway wall, the opening height was 1.7m above the laneway floor, the hole diameter was 94mm, the inclination angle was 0° (along the coal seam dip), the azimuth angle was 270°, and the plane projection was 200m (153m ahead of the head). The drilling construction parameters are shown in Table 1. The plan view of the drilling arrangement trajectory is shown in Figure 7 , drilling trajectory profile see Figure 8 After the drilling construction is completed, the gas extraction team will conduct drilling inclination measurement. Table 1 is the drilling design parameter table of 1012006 belt conveyor tunnel.

[0098]

[0099] Table 1

[0100] 2. In-hole geophysical exploration

[0101] The geological survey department is responsible for the in-hole geophysical exploration task, and the gas extraction team cooperates in the operation. The main parameters and steps of geophysical exploration are as follows:

[0102] 1. After the long borehole is completed, the drilling rig is used to push the geophysical exploration instrument to conduct geophysical exploration in the hole. The measurement point spacing is set to 3m. The design detection distance is 200m and the radial range is 30m.

[0103] 2. The specific process of geophysical exploration construction is as follows: During the actual measurement process, the in-hole transient, in-hole natural gamma logging and in-hole radar are connected, placed in the hole, and connected to the drill pipe. The equipment is pushed by the drilling rig (the first measuring point should completely avoid the metal casing). During the pushing process, in-hole radar detection is carried out. After being pushed to the measuring point, it is fixed and in-hole transient electromagnetic and natural gamma logging detection are carried out. This cycle is repeated until the measurement is completed.

[0104] The overview of the belt conveyor lane at the 1012006 working face is as follows:

[0105] (1) Working surface position and parameters

[0106] The 1012006 working face is located on the south side of the west wing of the 101 panel area. It is the fourth fully mechanized top coal caving working face of Yuanzigou Mine in the 101 panel area. The southern part of the 1012006 working face is the 1012007 goaf, and the width of the water-proof protection coal pillar is 35m; the northern part is the designed 1012005 working face, and the eastern part is adjacent to the safety coal pillar of the 101 panel area main tunnel; the western part is adjacent to the safety coal pillar of the south wing development main tunnel. The working face is 240m long, with a strike length of 2668m and a designed mineable length of 2120m. The working face is arranged with four tunnels: belt conveyor tunnel, return air tunnel, auxiliary transport tunnel and cutting eye. The schematic diagram of the working face plane position is as follows Figure 2 shown.

[0107] The belt conveyor lane at the 1012006 working face is designed to be 2,514 meters long and is arranged along the floor of the No. 2 coal seam. Both No. 2 coal seams are relatively stable, medium-hard coal seams with a thickness of 5.5 to 15 meters, averaging 11.5 meters. The working face coal seam floor elevation ranges from +485 to +620 meters, and the coal seam is buried at a depth of 630 to 780 meters, with an average depth of approximately 691 meters.

[0108] (2) Geological structure

[0109] The overall coal strata morphology within the working face is mainly controlled by the X1 and X2 synclines. Under the influence of folds, the coal seams within the working face are undulating. The eastern part of the working face is a monocline structure, while the western part is undulating. The structures that affect the construction of the tunneling working face are mainly the X1 and X2 synclines and the DF8 fault. The structural distribution and occurrence are shown in Figure 3 And Table 2, Table 2 is the main influencing structural occurrence table of the belt conveyor lane of the 1012006 working face.

[0110]

[0111] Wing Angle Table 2

[0112] (3) Hydrological conditions

[0113] During the excavation of the working face, the directly water-filled aquifer is the Jurassic Yan'an Formation, and the indirectly water-filled aquifer is the Zhiluo Formation sandstone fissure aquifer. Its water-richness is weak and the fissures are not well developed. During the excavation of the working face, water enters the mining space by top sprinkling.

[0114] (4) Gas

[0115] The gas content in the coal seam at Working Face 2 is generally less than 1 ml / g / daf, averaging 0.61 ml / g / daf. The gas content is generally uniform across the working face. The distribution of coal seam gas varies depending on the anticline, syncline, and faults. Within the syncline axis, gas migrates toward the flanks, resulting in lower gas content. Tensile normal faults facilitate gas escape, resulting in lower gas content near the faults.

[0116] (5) Impact ground pressure

[0117] According to the report "Evaluation of Impact Hazard and Anti-impact Design during Excavation of the 1012006 Working Face of Yuanzigou Coal Mine" compiled by Xi'an University of Science and Technology, the impact hazard level during the excavation of the 1012006 belt conveyor tunnel is a weak impact ground pressure hazard. During the excavation of the working face, due to factors such as coal seam impact tendency, deep mining, geological structure, coal thickness changes, bottom coal, goaf, and excavation disturbance, a total of 5 medium impact hazard areas and 6 weak impact hazard areas are divided. For details, see Figure 4 .

[0118] 3. Staged fracturing

[0119] China Coal Technology and Engineering Group Chongqing Research Institute Co., Ltd. is responsible for the fracturing construction, with the mine pressure prevention and control team and the gas extraction team cooperating in the operation, and the anti-bumping office tracking the fracturing implementation effect. After the completion of the in-hole geophysical exploration, segmented fracturing is carried out to weaken the coal body fracture and permeability, and reduce the original rock stress. The use of the packer 5 string system for segmented sealing can meet the requirements of rapid sealing and fracturing. After the high-pressure pipeline with the packer 5 and the safety joint is sent to the designed position, the packer 5 is sealed all at once. After the fracturing construction of the target fracturing section is completed, the fracturing pumping equipment is turned off and the water and pressure relief operation is carried out, waiting for the packer 5 to shrink; the fracturing tool string is exited, and then pushed to the next fracturing position to continue the fracturing construction, and this process is continuously repeated to perform fracturing step by step. The segmented hydraulic fracturing process along the long borehole of the coal seam is as follows Figure 9 shown.

[0120] The fracturing process is as follows: fracturing drilling and washing → fracturing area alert → fracturing equipment connection and trial operation → fracturing string, packer 5 and other tool strings are pushed into the hole → implementation of staged hydraulic fracturing → pressure and flow process monitoring → fracturing drilling and pump station video monitoring → reverse staged hydraulic fracturing → data monitoring → end of staged fracturing operation.

[0121] 1. Construction parameters

[0122] The backward staged fracturing is used, with the initial fracturing located at the bottom of the hole. According to the research results of the "Research Report on Staged Fracturing and Gas Extraction Technology of Long Boreholes Along the Layer in Yuanzigou Coal Mine", the fracturing radius can reach 30m when the pressure is 20-38MPa. The stage spacing of this fracturing design is 30m, with a total of 4 stages, and a safety distance of 30.5m from the head. The layout is shown in the figure. Figure 10 The staged fracturing time is not less than 30 minutes. Taking into account the 250m extraction drilling hole constructed on the mining side of the excavation face, the pressure is set to 15-30MPa.

[0123] 2. Construction equipment

[0124] The BZW series hydraulic fracturing equipment was selected as the fracturing test equipment for this long-hole segmented hydraulic fracturing test. The equipment mainly consists of a water tank, a water injection pump 1, a fracturing sealing pipe string 4, a multi-layer steel wire wrapped ultra-high pressure hydraulic hose 2 for harsh conditions, a special orifice device for fracturing 3, and a retrievable packer for fracturing 5. Its main working principle is to introduce the hydraulic fracturing theory and use the squeezing effect of high-pressure water in the coal seam or rock formation to cause damage or cracks in the structure. When a certain critical value is reached, the stress structure of the coal seam or rock formation changes and is destroyed, resulting in fragmentation and cracks, forming a fracture channel, and achieving the coal seam pressure relief effect. The schematic diagram of the BZW series hydraulic fracturing equipment is shown below. Figure 11 shown.

[0125] (1) BZW250 / 50 water injection pump 1

[0126] The BZW250 / 50 water injection pump 1 was used for this fracturing. The BZW250 / 50 water injection pump 1 is a pump unit specially designed for underground coal mine fracturing conditions. It is mainly used for underground coal mine fracturing and high-pressure water injection, auxiliary rock breaking and coal dropping, underground tunnel cleaning and other operations. Currently, the water injection pump 1 is placed in the 1700m drilling site in the tunnel behind the 1012006 excavation face.

[0127] (2) 73MFG1500 type fracturing sealing string 4

[0128] The fracturing seal string 4 serves as a flow channel for the fracturing fluid within the borehole of a hydraulic fracturing system, facilitating rapid injection of the fracturing fluid into coal or rock formations. The fracturing seal string 4 requires high flexibility, a large internal diameter, and excellent sealing performance. It should be 1500mm long, 73mm in outer diameter, and capable of maintaining pressure at 60MPa for half an hour without leakage.

[0129] (3) MKY70 type retrievable packer for fracturing 5

[0130] The structure of MKY70 type retrievable packer 5 for fracturing mainly consists of upper and lower joints, intermediate pipe and rubber sleeve, with a length of 2370mm and an outer diameter of 80mm.

[0131] 4. Continuous hole extraction

[0132] The gas extraction team is responsible for the construction, and the ventilation management department is responsible for tracking and implementation. After the hydraulic fracturing construction is completed, the drilling construction personnel on duty will seal the borehole and connect the pipe. When sealing the hole, a special bag "two blocking and one injection, pressure sealing" process is adopted. When the bag (sealer) + sealing agent is used to seal the hole, the grouting pressure shall not be less than 1.2MPa. The effective sealing length shall not be less than 12m (using 5 φ75mm×3m antistatic sealing pipes, with the end 1.5m as a screen pipe). The connection between the casing and the casing must be rotated into place to ensure a secure connection. The loose circle must be avoided (that is, the bag hole position is 1.5m away from the hole position). After sealing, it is connected to the extraction system for gas extraction and a single-hole metering device is installed.

[0133] 1. Extraction system and pipeline layout

[0134] According to the current pipeline layout of the 1012006 working face extraction system, the route of the advance pre-extraction drilling of the 1012006 excavation working face is: 4# system pump station (φ530mm, 78m long) ← outdoor pipeline area (φ630mm, 140m long) ← return air shaft (φ630mm, 591m long) ← west wing No. 2 return air tunnel and connecting tunnel (φ630mm, 750m long) ← 101 panel area No. 2 return air tunnel (φ450mm, 1700m long) ← 1012006 drift (φ450mm, 2512m long) ← extraction hose (φ159mm) ← seamless steel pipe (φ159mm) ← drilling extraction pipe (φ94mm).

[0135] 2. Requirements for sealing and connecting holes

[0136] (1) The extraction pipeline shall not be laid on the same side of the tunnel as the cables (including communication cables) and shall not come into contact with live objects. The extraction pipeline shall be as smooth as possible and the angle of the bend shall not exceed 50°.

[0137] (2) All pre-drilled confluence branch pipes shall be made of φ159mm seamless steel pipes, and the confluence pipes shall not be connected with any form of extraction hoses (except in special circumstances, but the gas extraction team must re-change the pipes as required after the drilling construction is completed).

[0138] (V) Comprehensive test of effects

[0139] The effectiveness test was conducted by Xi'an University of Science and Technology and the Office of Blowout Prevention. Using multiple methods, including water injection pressure, microseismic monitoring, ground sound, stress monitoring, and three-dimensional resistivity imaging fracturing monitoring, the three-dimensional comprehensive test of fracturing results in deep-hole areas of coal seams was conducted. The results analyzed the extent of fracturing cracks and comprehensively evaluated the regional fracturing multi-hazard prevention and control effects, providing support for optimizing parameters for fracturing weakening operations in coal seams in mines.

[0140] 1. Water injection pressure test

[0141] The analysis of the weakening effect of deep-hole fracturing in coal seams is mainly carried out by monitoring and analyzing the changes in water injection pressure data during the fracturing process. The analysis of the weakening effect of coal seams is as follows:

[0142] Utilize the downhole fracturing pump group to remotely and automatically monitor and record data, draw the dynamic changes of fracturing section pressure, flow and time, and analyze the fracturing effect through the pressure drop change characteristics, such as Figure 12 shown.

[0143] 2. Resistivity 3D imaging fracturing monitoring solution

[0144] (1) Layout plan

[0145] The CUMT mine DC resistivity 3D imaging monitoring system was used to monitor the hydraulic fracturing effect of the belt conveyor roadway roof at the 1012006 working face of Yuanzigou Coal Mine. The detection equipment installation plan is as follows:

[0146] Scope of construction: 1940m of the 1012006 working face belt conveyor lane and 1400m behind the drilling site, construction parameters: measuring electrode drilling interval 5m, drilling depth 20cm, hole size 1.8cm. The drilling is done at a height of 1.5m at the coal wall, with a total length of 400m, and the inclined lane side is drilled at 30°. It is estimated that 80 holes will need to be drilled. The B-pole drilling hole is located 1000m far from the end of the No. 80 electrode. The B-pole is composed of 5 copper poles bundled together, with a drilling depth of 20cm and a hole size of 1.8cm. 5 holes are required. A total of 85 holes need to be drilled. The design layout plan is as follows Figure 13 shown.

[0147] (2) Electrode and cable arrangement

[0148] Cables were laid in the 1012006 belt conveyor lane, and 80 measuring electrodes were installed in corresponding 5-meter-spaced boreholes. Five B electrodes were installed 1,000 meters from electrode 80. Finally, the electrodes for the CUMT mine DC resistivity 3D imaging monitoring system were installed, and all electrodes were connected to the cables in sequence.

[0149] (3) Equipment List

[0150] It is estimated that 85 copper electrodes, 8 cables with 5-meter spacing, and 1 long conductor will be required, with a total exploration length of 400m. Each borehole installation spacing is 5m, the hole diameter is 1.8cm, and the holes are drilled at a 30° angle on the side of the roadway. A total of 85 boreholes will be required. The monitoring equipment configuration list is shown in Table 3. Table 3 is the list of mine pressure monitoring equipment for the 1012006 working face.

[0151]

[0152]

[0153] Table 3

[0154] 3. Monitoring data verification

[0155] The pressure relief effect of fracturing on the coal body was evaluated by comparing and analyzing the microseismic, stress and ground sound monitoring data of the belt conveyor lane in the 1012006 working face before and after fracturing.

[0156] VI. Issues and measures to be addressed:

[0157] (1) Gas leakage problem

[0158] After the hydraulic fracturing construction is completed, the coal body around the borehole is crushed. When the tunnel is formed, the cracks in the tunnel wall form leakage channels, which may cause gas leakage during the later gas extraction of the coal seam. In order to solve this problem, the Ventilation Management Department is responsible for jointly conducting tests with Xi'an University of Science and Technology on extraction holes with different sealing lengths and different sealing materials within the fracturing range. After the construction of the gas extraction holes in the test section is completed, check for leakage according to the following method.

[0159] 1. Tracer gas testing method to detect drilling leakage

[0160] The SF6 tracer method is used to analyze the changes in SF6 concentration in the tunnel wall, and then determine the leakage situation of the tunnel wall, such as Figure 14 First, prepare an 8-liter SF6 gas cylinder (SF6 purity ≥ 99.99%), a pressure reducing valve, a flow meter, a TD500-SH-SF6 portable SF6 detector, and a CFZ22(A) negative pressure sampler (with a pumping rate of 22 L / min) for gas release, collection, and detection.

[0161] 2. Drilling Leakage Attenuation Test Method to Detect Drilling Leak Location

[0162] The borehole gas leakage attenuation test method is used to compare and analyze the gas concentration attenuation at different locations within the double-prevention borehole, thereby determining the location of the double-prevention borehole gas leakage. The coal seam borehole gas flow and concentration detection device is used to monitor the gas flow and concentration in the gas extraction borehole.

[0163] After the leakage test is completed, the ventilation management department compares and analyzes the gas extraction concentration and flow rate between the construction area and the normal section to obtain the optimal sealing process to solve the extraction leakage problem in the fracturing area.

[0164] risk assessment

[0165] Analysis of the drilling construction and hydraulic fracturing links shows the risks of gas accidents and object impacts. The corresponding control measures are shown in Table 4.

[0166]

[0167]

[0168]

[0169] Table 4

[0170] Support situation:

[0171] 1012006 belt conveyor tunnel adopts rectangular cross section, net cross section 20.9m2, excavation cross section 23.1m2 ( Figure 5 The support form is anchor mesh cable beam support, the anchor rod specification is φ22×2600mm threaded steel anchor rod, exposed 10-50mm, the anchor rod spacing is 800×900mm, each anchor rod is anchored by 2 K2360 resin coils, and the anchoring force is not less than 125KN; the mesh is φ6.5mm steel braided mesh, the mesh specification is 2×1m; the anchor cable is φ21.8×7300mm steel strand, the spacing is 1 600×1800mm, each anchor cable is anchored by 3 K2360 resin coils, with an anchoring force of not less than 250KN; the anchor rods and anchor cable support plates are made of Q345 steel, the anchor rod support plate specifications are 150×150×10mm, used in conjunction with flat iron steel strips; the anchor cable support plate specifications are 150×140×10mm, used in conjunction with the pressure ring and anchor cable beam, and the anchor cable beam is installed in a direction perpendicular to the direction of the roadway (see Figure 5 、 Figure 6 ).

[0172] Disaster avoidance principles and routes

[0173] 1. Disaster avoidance principle

[0174] (1) If an accident such as gas, coal dust, fire, flood, roof collapse, or rock burst occurs during drilling construction, the operator should quickly put on a self-rescue device and evacuate according to the disaster avoidance route.

[0175] (2) When an accident occurs and people cannot evacuate, the trapped people should take refuge in a nearby well-supported area with a compressed air self-rescue system and wait for rescue.

[0176] 2. Disaster evacuation routes

[0177] Work location → 1012006 belt conveyor lane → 101 panel area auxiliary transport lane → west wing No. 1 auxiliary transport lane → shaft bottom parking lot → auxiliary shaft → ground.

[0178] Emergency Response

[0179] In the following situations, evacuation measures must be taken.

[0180] 1. The methane concentration in the return air flow of all underground work sites exceeds 1.0%.

[0181] 2. There are obvious coal cannon sounds, blowholes, top drilling, bulging of coal walls, falling slag, gas outflow that continues to increase or fluctuates, and increased coal dust.

[0182] 3. There are signs of water seepage, water inrush, and water burst in the coal seam, such as wet coal seam, red coal seam, bottom bulging, increased water dripping (including sand), etc.

[0183] 4. The water level in the well field and surrounding puddles suddenly drops and bursts into the well.

[0184] 5. When the warning level for natural disasters such as heavy rain and floods is red (level 1) or orange (level 2).

[0185] 6. An open flame is discovered and cannot be extinguished immediately.

[0186] 7. Strong vibrations, loud noises, instantaneous bottom (side) drumming, coal and rock ejection and other dynamic phenomena occur at the underground mining operation site.

[0187] 8. The entire mine experiences an unplanned power outage that cannot be immediately and effectively restored.

[0188] 9. Other emergency situations such as signs of accidents where production should be stopped and people should be evacuated.

[0189] Support conditions

[0190] 1012006 belt conveyor tunnel adopts rectangular cross section, net cross section 20.9m2, excavation cross section 23.1m2 ( Figure 5 The support form is anchor mesh cable beam support, the anchor rod specification is φ22×2600mm threaded steel anchor rod, exposed 10-50mm, the anchor rod spacing is 800×900mm, each anchor rod is anchored by 2 K2360 resin coils, and the anchoring force is not less than 125KN; the mesh is φ6.5mm steel braided mesh, the mesh specification is 2×1m; the anchor cable is φ21.8×7300mm steel strand, the spacing is 1 600×1800mm, each anchor cable is anchored by 3 K2360 resin coils, with an anchoring force of not less than 250KN; the anchor rods and anchor cable support plates are made of Q345 steel, the anchor rod support plate specifications are 150×150×10mm, used in conjunction with flat iron steel strips; the anchor cable support plate specifications are 150×140×10mm, used in conjunction with the pressure ring and anchor cable beam, and the anchor cable beam is installed in a direction perpendicular to the direction of the roadway (see Figure 5 、 Figure 6 ).

[0191] 3. Implementation steps

[0192] (1) Drilling construction

[0193] The gas extraction team was responsible for the drilling construction task. A borehole was arranged in the 1940m drilling site of the belt conveyor lane of the 1012006 working face. The borehole in the drilling site was 4m away from the laneway wall, the opening height was 1.7m above the laneway floor, the hole diameter was 94mm, the inclination angle was 0° (along the coal seam dip), the azimuth angle was 270°, and the plane projection was 200m (153m ahead of the head). The drilling construction parameters are shown in Table 1. The plan view of the drilling arrangement trajectory is shown in Figure 7 , drilling trajectory profile see Figure 8 After the drilling construction is completed, the gas extraction team will conduct drilling inclination measurement.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for coordinating and preventing multiple disasters caused by fracturing in the advance drilling area of ​​a coal seam in a tunneling working face under complex geological conditions, characterized in that: The "drilling-probing-pressing-extraction" working procedure is adopted, which specifically includes the following steps: S1 Geological Exploration: Geological exploration is carried out through long-hole drilling operations and in-hole geophysical exploration operations; The long drilling operation includes drilling holes in the belt conveyor tunnel excavation working face along the working face strike direction in the drilling field; The in-hole geophysical exploration operation includes fixing a transient electromagnetic measurement device, a natural gamma logging device and a borehole radar device on a drill pipe, pushing them into the borehole by a drilling rig for detection, and avoiding the metal casing area during the detection process; S2 staged hydraulic fracturing: The hydraulic fracturing system is used to perform backward staged fracturing on the borehole. The initial fracturing position is the bottom of the bedding borehole, and the fracturing is carried out stage by stage according to the preset pressure range and spacing. During the fracturing process, the fracturing effect is comprehensively tested through water injection pressure, microseismicity, ground sound, stress monitoring and resistivity 3D imaging; S3 connected borehole drainage: After fracturing, gas leakage is detected by tracer gas testing and borehole leakage attenuation testing. The borehole is then sealed and connected to the gas drainage system for gas extraction. The sealing operation adopts the "two blocking and one injection, pressure sealing" process, the sealing device is a bag, and the sealing tube is an antistatic sealing tube; The belt conveyor tunnel adopts a rectangular cross-section and the support form is anchor mesh cable beam support.

2. The method according to claim 1, characterized in that The specific process of geophysical exploration in the S1 hole is as follows: During the pushing process, in-hole radar detection is carried out. After reaching the measuring point, the drill pipe is fixed and transient electromagnetic and natural gamma ray logging detection are carried out in sequence. The pushing and detection are repeated until the entire measuring range is completed.

3. The method according to claim 1, characterized in that The hydraulic fracturing system in S2 includes: a water tank connected to the inlet end of the water injection pump through a water inlet pipe, and used for storing and supplying fracturing fluid; The water injection pump, whose outlet end is connected to the fracturing sealing pipe string device through an ultra-high pressure hydraulic hose wrapped with multiple layers of steel wire, is used to pressurize the fracturing fluid to a preset pressure; The fracturing sealing string device includes a retrievable packer device, the front end of which is rigidly connected to the special fracturing orifice device through a threaded interface, and the rear end receives the high-pressure fracturing fluid delivered by the water injection pump through an ultra-high-pressure hydraulic hose; A special orifice device for fracturing, fixed at the borehole mouth, with a diversion channel inside, used to directionally inject fracturing fluid into the target fracturing section; The retrievable packer device is integrated into the fracturing sealing string device, and realizes the sealing and switching of staged fracturing through hydraulic control of setting and contraction.

4. The method according to claim 3, characterized in that The specific operations of the staged hydraulic fracturing are: Push the fracturing sealing string with a retrievable packer to the designed position and then set the packer; After completing the target section fracturing, shut down the water injection pump and release the pressure. After the packer shrinks, withdraw to the next fracturing section and repeat the fracturing.

5. The method according to claim 1, wherein The S2 medium resistivity three-dimensional imaging monitoring system is used to monitor the fracturing effect of the belt conveyor lane roof in real time.

6. The method according to claim 1, characterized in that The tracer gas test method in S3 uses SF6 tracer gas with a purity of ≥99.99%. The test equipment includes SF6 gas cylinder, pressure reducing valve, flow meter, TD500-SH-SF6 detector and CFZ22(A) negative pressure sampler.

7. The method according to claim 1, characterized in that The anchor mesh beam support includes threaded steel anchor rods, steel braided mesh, steel strand anchor cables and matching resin drug roll anchoring; The threaded steel anchor bolts are anchored to the coal wall through K2360 resin coils. Two coils are used to fill the drill hole and solidify to form the anchoring section for each bolt. The steel woven mesh is covered between adjacent anchor rods and fixed to the anchor rod support plate through flat iron strips to form a continuous support surface; The steel strand anchor cable is anchored deep in the coal wall through K2360 resin coils. Each anchor cable uses three coils, and the end of the anchor cable passes through the pressure ring and is connected to the anchor cable beam. The anchor cable beam is arranged transversely along the roadway and perpendicular to the roadway direction. The steel strands are fixed at both ends through anchor cable support plates and pressure rings to form a bidirectional bearing structure. The anchor rod support plate and the anchor cable support plate are both made of Q345 steel and are rigidly connected to the flat iron steel belt and the anchor cable beam by bolts to ensure the overall stability of the support system.

8. The method according to claim 1, characterized in that The gas drainage system pipeline laying requirements include: The pipeline shall not be laid on the same side as the cable, and the turning angle of the pipeline shall not exceed 50°; The manifolds are connected with seamless steel pipes and the use of extraction hoses is prohibited.

9. A fracturing system for use in the method according to any one of claims 1 to 8, characterized in that: include: The water tank is connected to the water injection pump through an ultra-high pressure hydraulic hose wrapped with multiple layers of steel wire; A water injection pump connected to the fracturing sealing string device is used to inject high-pressure fracturing fluid into the borehole; A fracturing sealing string device, including a retrievable packer, is connected to a dedicated fracturing orifice device via an ultra-high pressure hydraulic hose; A special orifice device for fracturing, fixed at the borehole, used to seal and guide the fracturing fluid; The resistivity 3D imaging monitoring system is integrated with the fracturing sealing string device to monitor the resistivity changes in the fracturing area in real time.

10. A supporting structure used in the method according to any one of claims 1 to 8, characterized in that: include: Threaded steel anchor rods are arranged at intervals along the roadway and anchored to the coal wall through resin coils; The steel strand anchor cable is installed in conjunction with the anchor beam and the pressure ring, with the direction perpendicular to the direction of the roadway; The steel woven mesh is covered between the anchor rods and anchor cables to form a continuous support surface.

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