Method for preventing harmful gas in fractures of driving working face for underground coal mining

Abstract

The invention relates to the technical field of mining engineering, and discloses a method for preventing harmful gas in fractures of a driving working face for underground coal mining, which comprises the following steps of: 1, determining fault and fracture trends, widths and influence ranges by geophysical exploration, drilling and drill rod exploration, and mastering distribution and occurrence states of gas and hydrogen sulfide; 2, according to the conditions of fracture gas and hydrogen sulfide, drilling treatment is conducted in a working moraine head or an ear tunnel drilling site; thirdly, an extraction system and an extraction pipeline are installed, and an extraction receiving and plugging material is prepared; fourthly, poisonous and harmful gas is extracted through moraine head drilling or ear way drilling; 5, comprehensive treatment is conducted through local ventilation, gas inspection, an extraction system, reinforcement supporting and long-distance blasting; the tunneling efficiency can be improved, the difficulty and safety risk of gas control are reduced, and the production cost of coal mining is reduced.

Description

Technical Field

[0001] This invention relates to the field of mining engineering technology, specifically to a method for preventing harmful gases from entering through cracks in underground coal mine working faces. Background Technology

[0002] Some coal mines have highly developed fault structures, resulting in severe fissure gas and hydrogen sulfide hazards. The main transport roadways, return air roadways, dedicated gas extraction roadways, and the upper and lower slopes of the mining area are all located in the Maokou limestone at the bottom of the K1 coal seam, at a normal distance of 20 to 30 meters from the bottom of the K1 coal seam. During the roadway excavation, fissure structures are frequently encountered. These fissures contain large amounts of high-concentration, high-pressure gas and hydrogen sulfide, posing a serious threat to the safe production of the mine.

[0003] Typically, water exploration holes and probe holes are used at the tunneling face to detect cracks and hazards such as hydrogen sulfide ahead of the tunnel. When encountering high concentrations of toxic and harmful gases such as methane or hydrogen sulfide, tunneling work must be stopped immediately, and the gas concentration must be diluted by strengthening the ventilation system until it reaches the safety standard.

[0004] Currently, the main problems in the treatment of toxic and harmful gases such as fissure gas and hydrogen sulfide are as follows: First, when toxic and harmful gases such as fissure gas and hydrogen sulfide emerge in a state of high concentration and high pressure, the concentration of gas such as gas and hydrogen sulfide in the roadway will exceed the safety limit, forcing the site to stop work immediately and evacuate all workers quickly. Secondly, when high concentrations and high pressures of fissure gas, hydrogen sulfide, and other toxic and harmful gases surge into the roadway, there is a high risk of suffocation and poisoning for workers. Third, although local ventilation fans are used to dilute the gas, the treatment is still difficult, the effect is limited, and there is still a high safety risk. Fourth, blasting is commonly used in rock tunnel excavation faces. If toxic and harmful gases such as methane and hydrogen sulfide are not properly controlled, they may cause explosions or other consequences. Fifth, the treatment time for ordinary fissure gas and hydrogen sulfide, which rely on local ventilation for dilution, is unpredictable and has a huge impact on safe production. It requires multiple backup tunneling faces, resulting in a great waste of production costs. Summary of the Invention

[0005] This invention provides a method for preventing harmful gases from fissures in underground coal mine tunneling faces. It employs a "probing, drilling, laying, extraction, and treatment" approach to manage fissure gas and hydrogen sulfide hazards. Combined with a "lay-in-drill" gas extraction system, this method enables the safe and rapid passage of gas through faults and fissures, facilitating the rapid extraction of gas and hydrogen sulfide. This not only improves tunneling efficiency and reduces the difficulty of gas management but also lowers safety risks during tunneling. It solves the problems of low tunneling efficiency, high safety risks, high management difficulty, and high production costs mentioned in the background art.

[0006] This invention provides the following technical solution: A method for preventing harmful gases from entering through cracks in underground coal mine working faces includes the following steps: Step 1: Use geophysical exploration, drilling and probing to determine the direction, width and range of influence of faults and fractures, and to understand the distribution and occurrence of gas and hydrogen sulfide; Step 2: Based on the situation of fracture gas and hydrogen sulfide, drill and treat the affected areas at the working head or "ear tunnel" drilling site; Step 3: Install the extraction system and extraction pipeline, and prepare the sealing materials for the extraction process; Step 4: Use a drill bit or a "side tunnel" drill to extract toxic and harmful gases; Step 5: Comprehensive treatment is carried out through local ventilation, gas inspection, extraction system, reinforcement support and remote blasting.

[0007] As a preferred technical solution of the present invention, geophysical exploration involves technicians detecting the occurrence of karst caves, faults and fissures within a specified range in front of the working face; Drilling involves using a fully hydraulic tunnel drilling rig to explore the fractures and faults in front of the working face, and to infer the occurrence of the structure and the accumulation of toxic and harmful gases. Probing involves using a pneumatic rock drill to determine the orientation of faults and fissures, as well as the presence of toxic and harmful gases, at a designated location before the working face is excavated to the point where the structure has been discovered.

[0008] As a preferred technical solution of the present invention, in step one, the fracture orientation detected by probing includes directional fractures and transverse fractures.

[0009] As a preferred technical solution of the present invention, in step one, the fractures are classified into Class I fractures, Class II fractures, and Class III fractures according to the situation of fracture gas and hydrogen sulfide.

[0010] As a preferred technical solution of the present invention, in step two, the drilling construction is carried out in an intermittent and staggered manner. Drilling sites are constructed on both sides of the roadway, and gas extraction boreholes are constructed within the drilling sites. The drilling site depth is 5m, the final borehole position is 3-5m outside the roadway outline, the distance between the borehole and the net rock column of the roadway wall is greater than or equal to 3m, the final borehole spacing is less than or equal to 3m, and the borehole length exceeds the expected fracture zone development position of the roadway by more than 20m.

[0011] As a preferred technical solution of the present invention, in step three, the sealing materials include glue, yellow mud, cement, and water glass.

[0012] As a preferred technical solution of the present invention, in steps four and five, when it is a type of fissure, the method of exploration and excavation is adopted, and ventilation is used to dilute the toxic and harmful gases such as methane and hydrogen sulfide. When the fissure is classified as Class II, the following measures should be taken: 1. Use local ventilation management to dilute the toxic and harmful gases such as methane and hydrogen sulfide; 2. Use compressed air pipes to introduce airflow into the fissure to dilute and disperse the toxic and harmful gases; 3. Use yellow mud sealing and shotcreting to inspect and manage the toxic and harmful gases and control the amount of toxic and harmful gases overflowing into the roadway. When the fracture is classified as Class III, and the concentrations of methane and hydrogen sulfide in the working face reach the threshold, the probe is sealed and connected to the extraction system. If the concentration of toxic and harmful gases continues to increase, methane extraction "ear tunnels" are constructed on both sides of the roadway. Drilling rigs are used to extract methane and hydrogen sulfide from the fracture. When the methane and hydrogen sulfide concentrations are within the safe range and the positive pressure methane flow from the probe stops, long-distance blasting is used for tunneling.

[0013] As a preferred technical solution of the present invention, in step five, for directional fractures, gas and hydrogen sulfide are extracted from the working face through probing; for transverse fractures, grouting is performed on the working face through probing.

[0014] As a preferred technical solution of the present invention, the grouting treatment includes drilling hole grouting, probe hole grouting and grouting hole grouting. The drilling hole grouting includes injecting cement into the drilling hole after the drill rod is withdrawn, and stopping grouting when the grouting pressure reaches a threshold.

[0015] As a preferred technical solution of the present invention, the grouting of the probe hole and the grouting hole include: when it is found that there is a fault or fissure or oblique to the excavation direction in front of the tunnel, and the gas and hydrogen sulfide in the fissure meet the grouting conditions, the tunneling is carried out while probing. When the distance between the working face and the fault or fissure reaches a threshold, the tunneling is stopped. After grouting, the probe is pulled out, the hole is sealed, and finally cement is injected into the hole. During grouting, grouting is carried out from the grouting hole at the bottom of the tunnel to the top. After the grouting back up, the grouting of the grouting hole is stopped. When the grouting pressure of the top grouting hole reaches a threshold, the grouting is stopped.

[0016] Compared with the prior art, the present invention provides a method for preventing harmful gases from entering through cracks in underground coal mine tunneling faces, which has the following beneficial effects: 1. The underground coal mine adopts a method for preventing harmful gases from fissures in the tunneling face. This method involves "exploration, drilling, application, extraction, and treatment" to control fissure gas and hydrogen sulfide disasters. Targeted treatment measures, corresponding support methods, and tunneling techniques are adopted according to the actual conditions of the tunneling face. Ultimately, this method aims to achieve safe and rapid passage through faults and fissure zones. It is applicable to fissure gas under various conditions, ensuring safe and efficient tunneling.

[0017] 2. In the method of preventing harmful gases from fissures in the tunneling face of the underground coal mine, the gas extraction system is laid and extracted using a "lay-as-you-go" gas extraction system. This ensures that the main gas extraction system is close to the rear of the tunneling face, and materials and tools for quick sealing and extraction are provided at each tunneling face. When encountering fissure gas and hydrogen sulfide, rapid extraction can be achieved.

[0018] 3. In the method of preventing harmful gases from cracks in the tunneling face of the underground coal mine, the risk assessment and comprehensive prevention and control plan can formulate appropriate treatment measures according to different geological conditions and gas concentrations. The use of high-strength support materials and advanced tunneling technology effectively reduces the safety risks during the tunneling process.

[0019] The parts of the device not covered herein are the same as or can be implemented using existing technologies. This invention can improve tunneling efficiency, reduce the difficulty and safety risks of gas control, and reduce the production cost of coal mining. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, the elements or parts are not necessarily drawn to actual scale.

[0021] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a cross-sectional view of the probe hole arrangement in this invention; Figure 3 This is a plan view of the probe hole arrangement in this invention; Figure 4 This is a cross-sectional view of the probe hole arrangement in this invention; Figure 5 This is a plan view of the directional fracture borehole layout in this invention; Figure 6 This is a diagram showing the final hole layout of the directional fracture drilling in this invention; Figure 7This is a cross-sectional view of the grouting hole arrangement in the transverse fracture of the present invention; Figure 8 This is a plan view of the grouting hole arrangement for the transverse fracture in this invention; Figure 9 This is a cross-sectional view of the arrangement of grouting holes in the transverse fracture in this invention; Figure 10 This is a schematic diagram of the gas control in the tunnel to be excavated in this invention. Figure 11 This is a schematic diagram of the crack gas control in the 313 return airway of this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0023] Reference Figures 1-11 A method for preventing harmful gases from cracks in the working face of underground coal mines includes the following steps: Step 1: Use geophysical exploration, drilling and probing to determine the direction, width and range of influence of faults and fractures, and to understand the distribution and occurrence of gas and hydrogen sulfide; Geophysical exploration involves technicians surveying a 150m radius in front of the working face to determine the presence of karst caves, faults, and fissures within that radius. Before each rock tunnel excavation face begins, geophysical exploration is conducted using ground-penetrating radar or transient electromagnetic instruments to detect the presence of karst caves, faults, and fissures within a 150m radius in front of the head. Excavation proceeds with a 20m geophysical advance distance. Before the excavation face reaches its final position, another geophysical exploration is conducted, and this process is repeated. During implementation, no missed explorations or over-excavation occurred. However, geophysical exploration cannot accurately predict small faults, fissures, or the accumulation of gas and hydrogen sulfide. Drilling will be conducted using a fully hydraulic tunnel drilling rig to directly drill 94mm geological boreholes. Three sets of boreholes will be laid out, with a designed length of 260m, extending 19m beyond the control tunnel outline. The aim is to investigate fractures and faults ahead of the working face, infer the geological structure's occurrence, and determine the accumulation of toxic and harmful gases. First, drilling sites will be set up on both sides of the rock tunnel excavation face. The site specifications are "length × height × depth = 5 × 3 × 5". Each site will have three exploratory boreholes along the tunnel excavation direction. The borehole design parameters are: azimuth consistent with the excavation direction; dip angles: -4° for downward boreholes, 1° for horizontal boreholes, and 4° for upward boreholes; depth 260m; and a 20m advance distance for the exploratory boreholes will be maintained during the excavation of the working face. When the exploratory boreholes reach faults or fractures, the width of the fault or fracture and its distance from the working face will be determined based on the drill rod's advance length. If gas or hydrogen sulfide is detected within the fault or fracture, the gate valve on the extraction pipe will be immediately opened for extraction. Probing was conducted using a pneumatic rock drill at a distance of 10 meters from the known structure during the excavation of the working face. The designed length of the probe holes was 5 meters, and 5 probe holes were arranged, located at the top, bottom, sides, and middle of the working face, respectively, to determine the orientation of faults and fissures ahead of the working face, as well as the accumulation of toxic and harmful gases. In order to further accurately explore the conditions of karst caves, faults and fissures ahead of the excavation head, as well as the occurrence of water, gas and hydrogen sulfide, the rock tunnel excavation face implemented "probing every time it is excavated". 4 to 5 probe holes were arranged in each excavation cycle. The probe holes were located in the middle of the tunnel, on both sides, and at the top and bottom. The probe holes in the middle of the tunnel were parallel to the tunnel excavation direction with an inclination angle of 0°. The other probe holes were located at an outward angle of 30° and were constructed within 3 meters of the tunnel outline. The depth of the probe holes was 4.8 meters, and a 3-meter advance distance for the probe holes was maintained during excavation. The fracture orientation detected by probing mainly includes two types: strike-type fractures, which are fractures that appear along the direction of excavation or on one side of the roadway; and cross-type fractures, which are fractures that cross the excavation face. Based on the presence of gas and hydrogen sulfide in the fractures, fractures are classified into three categories: Class I, Class II, and Class III. Class I fractures are ordinary fractures, Class II fractures are low-threat fractures, and Class III fractures are high-threat fractures. Ordinary fissures: No methane, hydrogen sulfide or other toxic or harmful gases are found after the fissures are exposed; Low-threat fractures: After the fracture is exposed, it releases a small amount of methane and hydrogen sulfide, which are toxic and harmful gases. There is no pressure inside the fracture, the methane concentration is less than 20%, and the hydrogen sulfide concentration is less than 50 ppm. High-threat fissures: After the fissures are exposed, they release high concentrations and high pressures of methane and hydrogen sulfide, which are toxic and harmful gases. The methane concentration is higher than 20% and the hydrogen sulfide concentration is higher than 50 ppm.

[0024] Step 2: Based on the situation of fracture gas and hydrogen sulfide, drill and treat the affected areas at the working head or "ear tunnel" drilling site; Drilling operations were carried out in a staggered, intermittent manner. Drilling sites were constructed on both sides of the roadway, and gas extraction boreholes were constructed within the drilling sites. The drilling depth was 5m, and the final borehole location was 3-5m outside the roadway outline. The distance between the borehole and the net rock pillar on the roadway perimeter was greater than or equal to 3m, the final borehole spacing was less than or equal to 3m, and the borehole length exceeded the expected fracture zone development location in the roadway by more than 20m.

[0025] Step 3: Install the extraction system and extraction pipeline, and prepare the sealing materials for the extraction process; The sealing materials include adhesive, yellow mud, cement, and water glass.

[0026] Step 4: Use a drill bit or a "side tunnel" drill to extract toxic and harmful gases; Step 5: Comprehensive treatment is carried out through local ventilation, gas inspection, extraction system, reinforced support and remote blasting; When it is a common fissure, we should explore and excavate at the same time, and dilute the toxic and harmful gases such as methane and hydrogen sulfide through ventilation. When the fracture is of low threat, the following measures can be taken: 1. Use local ventilation management to dilute the toxic and harmful gases such as methane and hydrogen sulfide; 2. Use compressed air pipes to introduce airflow into the fracture to dilute and disperse the toxic and harmful gases; 3. Use yellow mud to seal and spray grout to check and manage the toxic and harmful gases and control the amount of toxic and harmful gases overflowing into the roadway. When the fracture is a high-threat fracture, when the methane concentration in the airflow at the tunneling face reaches 0.8% and the hydrogen sulfide concentration reaches 5 ppm, the probe point is quickly sealed and connected to the extraction system. If the concentration of toxic and harmful gases continues to increase, methane extraction "ear tunnels" are constructed on both sides of the roadway, and drilling is carried out to extract methane and hydrogen sulfide from the fracture. When the methane and hydrogen sulfide concentrations are within the safe range and the positive pressure methane flow from the probe stops, long-distance blasting is adopted for tunneling. To prevent large-scale eruptions of methane and hydrogen sulfide when encountering fractured gas or hydrogen sulfide in the drilling borehole, thus avoiding gas accidents and hydrogen sulfide poisoning, a blowout preventer was installed at the outer end of the borehole pipe. Two 200mm long DN50mm steel pipes were welded 200mm from the outer end of the borehole pipe; one pipe faced the roadway floor for drainage, and the other faced the roadway roof for pumping out fractured gas and hydrogen sulfide. Simultaneously, a 200mm long 4-point steel pipe was welded to the side of the borehole pipe to measure the pressure, concentration, and flow rate of fractured gas. If methane or hydrogen sulfide erupts from the fault or fracture after the borehole is reached, immediate action is taken. The gate valve on the extraction pipe is opened for extraction. At the same time, the measuring hole on the orifice pipe is used to measure the pressure, concentration and flow rate of the fracture gas. When the probe hole hits the fracture and fracture gas and hydrogen sulfide gush out, the gas inspector immediately measures the concentration of gas and hydrogen sulfide in the hole. If the concentration is high and pressure is present, the grouting pipe is immediately installed. Then, the fracture gas pressure, concentration and other parameters are measured through the grouting pipe. The fracture gas pressure is generally 0 to 0.2 MPa, the gas concentration is 40% to 85%, the hydrogen sulfide concentration is 50 to 150 ppm, and the mixed gas flow rate during extraction is generally 1.3 to 1.7 m3 / min. For directional fractures, probe holes are used to extract methane and hydrogen sulfide from the working face in small amounts. For transverse fractures, grouting is performed on the working face using probe holes. When a fracture is encountered in the rock tunnel excavation face and fracture gas and hydrogen sulfide are gushing out, if the fracture gas shows no pressure and the gas concentration in the tunnel airflow is less than 0.5% and the hydrogen sulfide concentration is less than 10 ppm, then only shotcreting measures are needed to prevent the gushing out of fracture gas and hydrogen sulfide. When the fracture gas shows a certain pressure (can be felt by hand), and the gas and hydrogen sulfide concentrations gushing out from the drill hole or probe exceed the data in the first point, then grouting measures are required for treatment. Grouting treatment includes borehole grouting, probe hole grouting, and injection hole grouting. Borehole grouting involves installing a 10mm thick steel plate on the borehole pipe after the drill rod is withdrawn, matching the flange on the borehole pipe. A hole with a diameter of 19mm is drilled through the steel plate in the middle. A 100mm long steel pipe is welded to the borehole opening, and a direct head is welded to the other end of the steel pipe. The ball valve of the direct head is installed on the steel plate, and a steel braided pipe is connected to the ball valve and the grout outlet pipe of the grouting pump. Finally, cement is injected into the hole through the grouting pump. Grouting is stopped when the grouting pressure reaches 2MPa. The grouting of probe holes and grouting holes includes the following: when it is discovered that there is a fault or fissure or oblique to the direction of excavation in front of the tunnel, and the gas and hydrogen sulfide in the fissure meet the grouting conditions, the measures of exploration and excavation are adopted. When the working face is 4m away from the fault or fissure, the excavation is stopped, and grouting holes are constructed along the tunnel outline. The final position of the grouting hole is controlled to be 3m away from the tunnel outline. After grouting, the probe is pulled out, the grouting pipe is buried in the hole, and the hole is sealed. The grouting pipe and the steel braided pipe are connected to the grouting pump outlet pipe. Finally, cement is injected into the hole through the grouting pump. During grouting, grout is injected upwards from the grouting holes at the bottom of the tunnel. After the grout flows back up, grouting is stopped until the grouting pressure at the top grouting hole reaches 2 MPa. Example

[0027] The process is basically the same as in Example 1, and the specific steps are as follows: directional fracture extraction technology solution The method involves constructing drilling sites (ear tunnels) on both sides of the roadway, and drilling gas extraction boreholes within these sites. This ensures that the gas or hydrogen sulfide from the surrounding fracture zones enters the roadway extraction system under negative pressure, outside the roadway's perimeter outline. Drainage drilling sites are constructed at appropriate locations after the working face has retreated, with a drilling depth of approximately 5m. φ94mm extraction boreholes are drilled within these sites, with the final borehole location 3-5m outside the roadway outline. The borehole's distance from the roadway's surrounding rock column must be at least 3m, and the final borehole spacing must be at least 3m. The borehole length must exceed the expected fracture zone development location by more than 20m. When drilling extraction boreholes, an intermittent and staggered approach is adopted. If the continuous extraction after the completion of the intermittent drilling can effectively reduce the concentration of harmful gases in the roadway and achieve the treatment effect, then the drilling of other boreholes will be stopped. The main gas extraction system is connected to the transfer belt behind the scraper conveyor. In front of the transfer belt is a temporary extraction pipe with a diameter of 50mm or more, connected by a corrugated hose of the same diameter to ensure extraction negative pressure and extraction effect, thereby reducing the concentration of harmful gases in the roadway working environment and achieving the purpose of thoroughly controlling fissure gas and hydrogen sulfide.

[0028] Restore construction conditions To ensure that the drilling effectively controls the area around the roadway, after the extraction borehole at the drilling site was closed, the toxic and harmful gases at the head of the pit suddenly increased (proving that the extraction borehole effectively connected the fracture). After the extraction borehole is removed, the extraction borehole is under negative pressure. After continuous extraction from the drilling boreholes, the methane concentration at the mine head decreased to the normal range during construction.

[0029] Transverse fracture grouting sealing technology solution Grouting and sealing were carried out by probing grouting holes during the construction of the pit head. The tunneling was carried out by probing and excavating simultaneously. As soon as positive pressure fracture gas and hydrogen sulfide (H2S) were detected by a probing hole, the probing grouting hole was immediately constructed for grouting and sealing. Grouting holes are probed and drilled around the perimeter of the embankment. The hole depth is determined by penetrating the fracture. The grouting radius for single-component grout is designed to be 2.0m. The hole spacing is arranged to be less than or equal to 4m. The drilling is carried out at a 30° angle to ensure that there is a net rock column of more than or equal to 2.0m between the end of the borehole and the roadway wall. The grouting pipes are all 1m long and 20mm in diameter steel pipes with shut-off valves installed at the pipe ends. The water-cement ratio is 1:1 pure cement grout. The grouting pressure is gradually increased from 0 to 1MPa. When 1.5MPa is reached and injection cannot be continued, grouting can only be stopped after observing the grout return situation in other boreholes or the embankment. If the grouting volume reaches 10t of cement and still does not reach the design pressure, a double-component grout is injected in a water:cement:water glass ratio of 1:1:0.8 until the grouting pressure reaches the design pressure.

[0030] Restore construction conditions After the grouting was completed and the grout solidified for 24 hours, five inspection holes were constructed around and in front of the tunnel. No abnormalities were found in any of the inspection holes. The concentrations of methane and hydrogen sulfide in the tunnel have dropped to normal levels.

[0031] Tunnel-penetrating fracture gas control scheme Through-type fractures are mainly targeted at connecting roadways that are about to be penetrated. When it is discovered or inferred from the already excavated roadway that there is a high concentration of fracture gas or hydrogen sulfide in the middle, drainage boreholes are drilled through the through-roadway to allow the gas in the fracture to be pumped out through the drainage boreholes, thereby ensuring that the gas in the roadway is controllable and effective during normal excavation. Example

[0032] The process is basically the same as in Example 1, and the specific steps are as follows: 313 Return Air Main Roadway Fissure Gas Control Plan The drilling site is constructed approximately 5 meters behind the head of the tunnel. Drainage is then carried out to eliminate the positive pressure state of gas and hydrogen sulfide in the head fissure, reducing the amount of gas and hydrogen sulfide emanating from the fissure and ensuring that the gas concentration in the working environment remains within a safe range. Immediately after the fissure is exposed, the fissure points are sealed, shotcreted, and supported. Gas drainage pipes are pre-embedded to facilitate continuous monitoring of the gas situation within the fissure and to allow for drainage as needed, ensuring reliable gas management within the fissure. Based on the orientation of faults and fissures, we explored tunneling techniques and support methods for rapid passage through faults and fissures, eliminating safety threats and minimizing their impact on tunneling progress. First, based on drilling and probing data, we prepared the necessary equipment, materials, and personnel for drilling or grouting in advance, laying the foundation for rapid disaster mitigation. Second, during drilling or grouting, we ensured the rapid arrival of equipment and materials, guaranteeing a safe and fast construction process. Third, during tunneling through faults and fissures, we adopted shallow-circulation, weak-blasting, and multi-hole drilling with minimal explosive loading, controlling the circulation progress to within 1.0m. After excavation, we promptly sealed the working face with shotcrete to reduce the safety threats to workers from fissure gas and hydrogen sulfide during tunneling, achieving rapid construction. A hydrogen sulfide probe is set up 5m away from the pit head. The hydrogen sulfide sensor is calibrated every 15 days to ensure its sensitivity and reliability. The hydrogen sulfide concentration changes are monitored at any time, and any abnormalities are reported in a timely manner. Subsequently, the staff carry and hang portable hydrogen sulfide and gas detectors at appropriate locations in the drilling site to check the methane and hydrogen sulfide concentrations in the borehole at any time. If the methane concentration in the drilling site exceeds 1% or the hydrogen sulfide concentration exceeds 6.6 ppm, the operation must be stopped immediately. The local ventilation fans at the tunneling face shall be dual fans (2×30kW) with dual power supplies and automatic switching capability; the ventilation ducts shall be Ф600mm in diameter, and their installation and hanging shall be carried out in accordance with quality standards; the distance between the end of the ventilation duct and the head of the pit shall not exceed 6m; during blasting, the temporary ventilation duct at the end shall be a rigid ventilation duct or armored ventilation duct that is blast-resistant to impact, to ensure reliable ventilation and sufficient air volume at the head of the pit; ventilation at the advanced drilling site shall be strengthened by using the method of connecting the main ventilation duct to the air sleeve to dilute the concentration of toxic and harmful gases at the drilling site; For the 313 return air main roadway, the boreholes where gas outbursts have been detected are grouted and sealed using a sealing pump. During the gas drainage in the 313 return air main roadway, the concentration, negative pressure, and pressure difference of the single borehole at the gas drainage point are measured to facilitate timely monitoring of the gas drainage situation. At the same time, the gas in the boreholes at the junction of the 313 return air connecting roadway and the 313 return air main roadway, as well as the gas in the boreholes at the gas points in the 313 return air main roadway, are monitored. If the gas in the borehole is found to be under negative pressure and the gas concentration at the borehole opening is less than 1%, the tunneling can be resumed. During the tunneling of the 313 return air main roadway, if the cracks become fully visible, the cracks exposed on both sides of the roadway must be sealed in time and shotcreted to facilitate normal gas drainage from the cracks. After extraction operations were carried out at the fracture points in the 313 return air roadway, the extraction effect was investigated. The concentration extracted from a single well was generally between 50% and 80%. The branch pipe extraction situation is shown in the table below: 313 Return Air Main Roadway Fissure Gas Drainage Record Form

[0033] Example 4: Similar to Example 1, in order to further strengthen the prevention and control of fracture gas in rock tunnel excavation, a rock tunnel excavation fracture gas treatment plan is proposed, the specific steps of which are as follows: The gas concentration in the borehole is less than 10%, the hydrogen sulfide concentration is less than 30 ppm, and there is no positive pressure in the gas. The gas concentration in the airflow at the working face is less than 0.3%, and the hydrogen sulfide concentration is less than 6.6 ppm. If a new borehole is drilled near the original borehole and there are no cracks or harmful gases, the original borehole should be sealed with yellow mud after the harmful gases inside the borehole are diluted with compressed air and water is injected into the borehole. The length of the new borehole should be greater than 2m, and the operation should be carried out by blasting from a distance.

[0034] The gas concentration inside the borehole is greater than 10% and less than 50%, and the hydrogen sulfide concentration is greater than 30 ppm and less than 100 ppm. There is no positive pressure in the gas. The gas concentration in the airflow at the working face is less than 0.5%, and the hydrogen sulfide concentration is less than 6.6 ppm. First, the borehole is quickly sealed and pumped out. Then, a new borehole is drilled near the original borehole. The new borehole has no cracks or harmful gases. Long-distance blasting measures are adopted for the operation.

[0035] The gas concentration inside the borehole is greater than 50%, the hydrogen sulfide concentration is greater than 100 ppm, and there is no positive pressure in the gas. The gas concentration in the airflow at the working face is less than 0.5%, and the hydrogen sulfide concentration is less than 6.6 ppm. First, the borehole is quickly sealed and pumped out. Then, additional boreholes are drilled at 500 mm intervals above, below, left, and right of the original borehole. The additional boreholes are free of cracks and harmful gases. Long-distance blasting measures are adopted for the operation.

[0036] If the methane concentration in the borehole is greater than 50% and the hydrogen sulfide concentration is greater than 100 ppm, and the gas is under positive pressure, but the methane concentration in the working face airflow is less than 0.5% and the hydrogen sulfide concentration is less than 6.6 ppm, immediately seal the borehole and begin pumping. Then, drill additional boreholes at 500mm intervals around the original borehole. If no cracks or harmful gases are found in the additional boreholes, pump the original borehole again for one hour and then test it again. If the methane and hydrogen sulfide concentrations have significantly decreased, seal the borehole with yellow mud for a length greater than 2m and use long-distance blasting. If there are no signs of methane and hydrogen sulfide attenuation, continue pumping.

[0037] If gas and hydrogen sulfide are ejected under positive pressure from the probe hole, it is strictly forbidden to pull out the probe. Immediately and quickly connect or seal the probe hole, and connect the ventilation duct to the head of the pit. If the gas concentration in the airflow at the working face is greater than 0.8% and the hydrogen sulfide concentration is greater than 6.6ppm, the working face should be shut down.

[0038] Components not described in detail in this article are existing technologies.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preventing harmful gases from entering through cracks in the working face of an underground coal mine, characterized in that, Includes the following steps: Step 1: Use geophysical exploration, drilling and probing to determine the direction, width and range of influence of faults and fractures, and to understand the distribution and occurrence of gas and hydrogen sulfide; Step 2: Based on the situation of fracture gas and hydrogen sulfide, drill and treat the affected areas at the working head or "ear tunnel" drilling site; Step 3: Install the extraction system and extraction pipeline, and prepare the sealing materials for the extraction process; Step 4: Use a drill bit or "ear tunnel" drill to extract toxic and harmful gases; Step 5: Comprehensive treatment is carried out through local ventilation, gas inspection, extraction system, reinforcement support and remote blasting.

2. The method for preventing harmful gases from cracks in the working face of underground coal mines according to claim 1, characterized in that, In step one, geophysical exploration involves technicians detecting the occurrence of karst caves, faults, and fissures within a specified area in front of the work face. Drilling involves using a fully hydraulic tunnel drilling rig to investigate the fractures and faults ahead of the working face, and to infer the occurrence of the structure and the accumulation of toxic and harmful gases. Probing involves using a pneumatic rock drill to determine the orientation of faults and fissures, as well as the presence of toxic and harmful gases, at a designated location before the working face is excavated to the point where the structure has been discovered.

3. The method for preventing harmful gases from cracks in the working face of underground coal mines according to claim 2, characterized in that, In step one, the fracture orientation detected by probing includes strike-type fractures and transverse fractures.

4. A method for preventing harmful gases from entering through cracks in underground coal mine working faces according to claim 3, characterized in that, In step one, based on the condition of fissure gas and hydrogen sulfide, fissures are classified into Class I, Class II, and Class III fissures.

5. A method for preventing harmful gases from entering through cracks in underground coal mine working faces according to claim 1, characterized in that, In step two, drilling is carried out in an alternating manner with staggered drilling. Drilling sites are constructed on both sides of the roadway, and gas extraction boreholes are constructed within the drilling sites. The drilling depth is 5m, and the final borehole location is 3-5m outside the roadway outline. The distance between the borehole and the net rock column of the roadway wall is greater than or equal to 3m, the final borehole spacing is less than or equal to 3m, and the borehole length exceeds the expected fracture zone development location of the roadway by more than 20m.

6. A method for preventing harmful gases from cracks in the working face of an underground coal mine as described in claim 4, characterized in that, In step three, the sealing materials include glue, yellow mud, cement, and water glass.

7. A method for preventing harmful gases from entering through cracks in underground coal mine working faces according to claim 6, characterized in that, In steps four and five, when the fissure is of type I, the method of exploration and excavation is adopted, and ventilation is used to dilute the toxic and harmful gases such as methane and hydrogen sulfide. When the fissure is classified as Class II, the following measures should be taken:

1. Use local ventilation management to dilute the toxic and harmful gases such as methane and hydrogen sulfide; 2. Use compressed air pipes to introduce airflow into the fissure to dilute and disperse the toxic and harmful gases; 3. Use yellow mud sealing and shotcreting to inspect and manage the toxic and harmful gases and control the amount of toxic and harmful gases overflowing into the roadway. When the fracture is classified as Class III, and the concentrations of methane and hydrogen sulfide in the working face reach the threshold, the probe is sealed and connected to the extraction system. If the concentration of toxic and harmful gases continues to increase, methane extraction "ear tunnels" are constructed on both sides of the roadway. Drilling is carried out using a drilling rig to extract methane and hydrogen sulfide from the fracture. When the methane and hydrogen sulfide concentrations are within the safe range and the positive pressure methane flow from the probe stops, long-distance blasting is used for tunneling.

8. A method for preventing harmful gases from cracks in the working face of underground coal mines according to claim 6, characterized in that, In step five, for directional fractures, gas and hydrogen sulfide are drained from the working face through probing; for transverse fractures, grouting is performed on the working face through probing.

9. A method for preventing harmful gases from cracks in the working face of an underground coal mine as described in claim 8, characterized in that, The grouting process includes borehole grouting, probe hole grouting, and injection hole grouting. Borehole grouting includes injecting cement into the borehole after the drill rod is withdrawn, and stopping grouting when the grouting pressure reaches a threshold.

10. A method for preventing harmful gases from cracks in the working face of an underground coal mine as described in claim 9, characterized in that, The grouting of the probe hole and the grouting hole include the following: when it is found that there is a fault or fissure or oblique to the direction of excavation in front of the tunnel, and the gas and hydrogen sulfide in the fissure meet the grouting conditions, the tunneling is carried out while probing. When the working face reaches the threshold of the fault or fissure, the tunneling is stopped. After grouting, the probe is pulled out, the hole is sealed, and finally cement is injected into the hole. During grouting, grout is injected upwards from the grouting holes at the bottom of the tunnel. After the grout flows back up, grouting in the grouting holes is stopped. Grouting is stopped when the grouting pressure in the top grouting holes reaches the threshold.

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