Gas prevention and control method based on cascade progressive detection

Abstract

The invention discloses a gas prevention and control method based on stepped progressive detection, and relates to the technical field of coal mining and gas prevention and control. According to the method, gas prevention and control are conducted through a long-distance geophysical prospecting part and a short-distance prevention and control part, and the long-distance geophysical prospecting part comprises the steps that karst gas is detected in advance through geophysical prospecting, drilling, drill rod detection and other means, and drilling detection and release measures are conducted on abnormal areas. Meanwhile, geophysical prospecting data and geological condition comprehensive analysis need to be combined, and safety technical measures need to be formulated. In addition, the invention further relates to design and construction of a special roadway for gas extraction and construction and drilling in a specific area to detect the distance between the roadway and a coal seam. The short-distance prevention and control comprises drilling, drill rod detection, air exhaust, air exhaust, air blockage and winding avoidance; according to the method, through the two steps of long-distance geophysical prospecting and short-distance prevention and control, it is ensured that all links from detection to prevention and control are covered, and the problems that an existing karst fissure gas prevention and control management mechanism is poor in systematicness and low in safety are solved.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining and gas prevention and control, and in particular to a gas prevention and control method based on step-by-step detection. Background Art

[0002] There are a large number of coal mines with outbursts in southwest China, and the use of through-layer drilling to pre-extract coal seam gas is one of the key measures to prevent and control coal and gas outbursts. However, before pre-extracting coal seam gas through through-layer drilling, it is necessary to arrange special gas extraction tunnels in the underlying or overlying rock strata of the coal seam in advance. In the process of coal mine rock tunnel excavation, predicting and judging the engineering geological conditions of the area through which the coal mine rock tunnel excavation passes is a necessary condition for the construction of coal mine rock tunnel excavation. In the early stage of coal mine rock tunnel excavation, this issue was not given enough attention, and therefore some situations occurred that seriously affected the excavation of coal mine rock tunnels due to unclear geological conditions. With the gradual increase in the excavation of coal mine rock tunnels, especially the start of excavation of some deep horizontal coal mine rock tunnels, the application of advanced geological prediction technology has become more and more extensive, and the technical level has become more and more mature. However, for some complex geological problems, such as structural weak zones, karst, gas, etc., they are the key and difficult points in advanced geological prediction, especially when several geological problems occur at the same time and the groundwater content is rich, the prediction accuracy is easy to reduce. Secondly, the space in the rock tunnel of coal mines is limited, and the placement of construction equipment is disturbed, making it difficult to set up some instruments, resulting in inaccurate forecasts. In addition, the analysis of advanced geological forecast results requires a high level of technical skills from the staff. Reflecting specific geological conditions through graphics or data requires a lot of knowledge and experience, which is also a difficulty in advanced geological forecast technology.

[0003] Since the coal mine rock tunnel excavation often passes through areas with frequent geological activities, the geological conditions are very complex and there are many types of geological problems. Each advanced geological prediction method has its own advantages and disadvantages. It is not easy to achieve the expected effect by simply choosing a single method, and the prediction result is not accurate enough. Therefore, for most coal mine rock tunnel excavation, the comprehensive use of various advanced geological prediction methods is a relatively correct choice. For the comprehensive advanced geological prediction system for coal mine rock tunnel excavation, the guidance, operation and understanding of different mining areas and mines may be different.

[0004] In addition, geological structures such as fault zones, fissure fracture zones, and collapse columns destroy the continuity of the aquiclude, making them easy channels for karst fissure gas and water outbursts, and are the leading factors for karst fissure gas and water outbursts. Mining projects cause redistribution of ground stress, which causes certain damage to the aquiclude, exacerbating the possibility of karst fissure gas and water outbursts, and are the inducing factors for karst fissure gas and water outbursts.

[0005] As the depth of mines increases, abnormal outbursts of karst water or karst fissure gas become more frequent, and have even caused injuries in some areas. The southwest region has high-pressure, water-rich karst aquifers and karst fissure gas. Therefore, in the process of pre-extraction of special gas tunnels or other rock tunnel excavation, an improved gas detection and prevention method is needed, which is of great significance to improving the efficiency of rock tunnel excavation, ensuring the effect of gas prevention and control, and ensuring safe mine excavation. Summary of the invention

[0006] The purpose of the present invention is to provide a gas prevention and control method based on step-by-step detection, which can solve the problems of poor systematicity and low safety of the existing karst fissure gas prevention and control management mechanism.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A gas prevention and control method based on step-by-step detection, using a long-distance geophysical exploration part and a short-distance prevention and control part for gas prevention and control;

[0009] The long-range geophysical exploration comprises the following steps:

[0010] S1. When tunneling, karst gas must be detected and released in advance; the methods of advanced detection and release include geophysical exploration, drilling and drilling;

[0011] S2. If abnormal areas are still found after re-examination, drilling and exploration measures must be taken within 10 meters of the abnormal area;

[0012] S3. If the review shows that there is no geophysical anomaly area, no drilling and blasting measures will be taken, but the construction of the drill hole and the blasting requirements will still be carried out according to the original geophysical anomaly area;

[0013] S4. After drilling, the drilling results shall be obtained through comprehensive analysis based on geophysical data and geological conditions in adjacent areas, and safety and technical measures shall be formulated based on the drilling results notice;

[0014] S5. Set the vertical distance between the top of the dedicated gas extraction tunnel and the coal seam to 8 to 15 meters, except for the uphill and stone gate designed to penetrate the coal-bearing strata;

[0015] S6. When tunneling, if there is no measured or geological drilling stratigraphic control data within 150-200m around the moraine head in the normal area, at least one borehole shall be constructed to find out the distance between the tunnel and the coal seam and the thickness of the aluminous mudstone. In areas where the strike or dip of the fault or coal seam changes greatly, more geological drilling must be done. Both sides of the fault must have geological drilling control at the same time, and a stratigraphic control drilling table shall be established.

[0016] The close-range prevention and control methods include: drilling, probing, pumping, exhausting, blocking and avoiding;

[0017] The drilling is: when there is a certain deviation in the abnormal range of karst fissures determined by transient electromagnetic method or mine geological detector, in order to verify the accuracy of transient electromagnetic method determination, the verification method of the test adopts drilling method;

[0018] The drilling method is as follows: after the drilling method is used for verification in the first test, a larger number of drilling methods are used for final verification because the traditional drilling method is point contact and the number of holes drilled is small, and the control range is limited;

[0019] The gas extraction is: using the main extraction system that has been perfected in the study area, directly sealing and extracting the outside of the karst fissures to achieve the extraction of harmful gases;

[0020] The exhaust is: when the karst fissure gas enrichment is small, the harmful gas is safely discharged to the mine's total return air system by means of local ventilation measures;

[0021] The gas blocking is a shielding measure taken when the outflow of karst gas and water is large, there is a continuous gas and water supply, and it is not enough to reduce the safety threat to the allowable range in a short time;

[0022] The avoidance means avoiding cracks and structures that have a greater impact on safe production. For the more complex karst cracks and structures that have been discovered, an active avoidance method is adopted to reduce the complexity of construction and potential safety risks.

[0023] Optionally, in the long-distance geophysical exploration, if karst gas, water, bauxite or coal seam is detected during the drilling of the Maokou limestone tunnel in step S6, the operation must be stopped.

[0024] Optionally, the abnormal zone includes a geophysical abnormal zone and a drilling abnormal zone; wherein, the geophysical abnormal zone is the abnormal zone range delineated based on a comprehensive analysis of geophysical data and acquired geological information; the abnormal area actually exposed by drilling in the abnormal zone and the 5m before and after the area are all drilling abnormal zones.

[0025] Optionally, the requirements for the safety technical measures include: when geophysical exploration is abnormal but drilling is normal, the drill hole construction and blasting regulations are implemented according to the geophysical abnormality area; if both geophysical exploration and drilling are abnormal, specific measures are separately formulated according to the drilling abnormality.

[0026] Optionally, in the area where there are no geophysical anomalies, at least three drill holes are constructed in each cycle, two of which have their end points located 1.0m outside the tunnel, and one hole is located within the tunnel contour line. The opening and end positions of the drill holes in each cycle should be staggered and constructed alternately with those of the previous cycle.

[0027] Optionally, when the gas extraction is implemented, the gas extraction pipeline needs to be constructed while the gas extraction tunnel is being excavated, and the end thereof shall not be more than 200m away from the excavation working face, so as to facilitate the timely extraction of karst and fissure gas. The extraction pipe diameter is selected according to the following formula:

[0028]

[0029] Where D is the pipe diameter, m; Q is the flow rate, m 3 / s; V is the economic flow rate, which is taken as 10-15m / s; in addition, the water supply and air supply pipelines are temporarily and directly converted into karst fissure gas extraction pipelines to quickly and effectively reduce the threat of karst gas. Moreover, in the case of small outflow volume, low concentration and no pressure, temporary blocking and exploration eye extraction are directly adopted for treatment.

[0030] Optionally, when the exhaust is implemented, during the full-rock tunnel excavation construction process, when various detection boreholes obtain hidden disaster factors of karst gas risk, if the amount of water accumulated in the karst is small and the gas outburst characteristics are gentle, the safety threat to the workers on the mining face is small and the risk level is low, a drilling rig or rock drill is used to construct a borehole at a certain distance from the karst to pre-control the discharge of harmful substances such as gas and water; the required air volume of the excavation face is calculated according to the following formula:

[0031] Q j =100×q j ×K j

[0032] In the formula, Q j is the actual air volume required for the excavation working face m 3 / min;q j is the absolute gas outflow volume of the excavation working face m 3 / min; K j The absolute gas outburst imbalance coefficient of the excavation working face is taken as 1.3~1.5.

[0033] Optionally, when the gas blocking is implemented, it is divided into three categories according to the location of the karst blocking. The first category is mainly used inside the karst; the second category is to block the karst outside; and the third category is to block the karst exposed part.

[0034] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0035] The present invention discloses a gas prevention and control method based on step-by-step detection, the method comprising gas prevention and control using a long-distance geophysical exploration part and a short-distance prevention and control part, wherein the long-distance geophysical exploration includes the use of geophysical exploration, drilling, and brazing to advance the detection of karst gas, and drilling and exploration measures are carried out in abnormal areas. At the same time, it is also necessary to combine the geophysical data and the comprehensive analysis of geological conditions to formulate safety technical measures. In addition, it also involves the design and construction of special tunnels for gas extraction, as well as the construction of drilling holes in specific areas to find out the distance between the tunnel and the coal seam; short-distance prevention and control includes drilling, brazing, gas extraction, exhaust, gas blocking and bypassing. The present invention first forms a systematic gas prevention and control process through two major steps of long-distance geophysical exploration and short-distance prevention and control, ensuring that all links from detection to prevention and control are covered; secondly, karst gas is detected in advance through means of geophysical exploration, drilling, and probing, so that prevention can be carried out before gas disasters occur, reducing the risk of accidents; finally, a variety of prevention and control means are provided, such as drilling, probing, air extraction, exhaust, gas blocking, and avoidance, so that the most appropriate prevention and control method can be flexibly selected according to actual conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 This is a schematic plan view of the arrangement of the drilling holes in this embodiment;

[0038] Figure 2 This is a longitudinal cross-sectional schematic diagram of the arrangement of the drilling holes in this embodiment;

[0039] Figure 3 It is a schematic transverse cross-sectional view of the arrangement of the drilling holes in this embodiment.

[0040] Figure numerals: 1, first drill hole; 2, second drill hole; 3, third drill hole; 4, fourth drill hole; 5, fifth drill hole. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The purpose of the present invention is to provide a gas prevention and control method based on step-by-step detection, which can solve the problems of poor systematicity and low safety of the existing karst fissure gas prevention and control management mechanism.

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] like Figure 1-Figure 3 As shown, the present invention provides a gas prevention and control method based on step-by-step detection, including using a long-distance geophysical exploration part and a short-distance prevention and control part to carry out gas prevention and control. In the figure, the position arrangement of each drilling hole is marked, specifically including a first drilling hole 1, a second drilling hole 2, a third drilling hole 3, a fourth drilling hole 4 and a fifth drilling hole 5.

[0045] Long-range geophysical exploration includes the following steps:

[0046] S1. When tunneling, geophysical exploration, drilling, and drilling must be used to detect and release karst gas in advance. The advance distance for geophysical exploration is 10m, the advance distance for drilling is 5m, and the advance distance for drilling is 1.5m. Before the tunnel enters each geophysical anomaly area 10m, a geophysical recheck shall be carried out.

[0047] S2. For abnormal areas that still exist after re-examination, drilling and exploration measures must be taken 10 meters before the abnormal area. The mine geological technicians shall comprehensively determine the drilling hole parameters (the borehole diameter shall not exceed 65mm) based on the scope of the geophysical abnormal area in the tunnel, the excavated area, and the karst gas occurrence and structural development of the mining area or horizontal exposure.

[0048] S3. For areas that are verified to have no geophysical anomalies, no drilling and blasting measures will be taken, but the construction of drill holes and blasting requirements will still be carried out according to the original geophysical anomaly areas. During long-distance geophysical exploration, if karst gas, water, bauxite or coal seams are detected when drilling drill holes and blasting holes in Maokou limestone tunnel excavation, operations must be stopped.

[0049] The abnormal area is divided into geophysical anomaly area and drilling anomaly area, and the scope of the abnormal area is determined as follows: geophysical anomaly area, the scope of the abnormal area delineated based on comprehensive analysis of geophysical data and mastered geological information; drilling anomaly area, the abnormal area actually exposed by drilling, and the area 5m before and after the area are all drilling anomaly areas, and the safety technical measures are required as follows: When geophysical exploration is abnormal but drilling is normal, the drill hole construction and blasting regulations shall be implemented in the geophysical anomaly area; if there are abnormalities in both geophysical exploration and drilling, targeted measures shall be separately formulated according to the drilling anomaly situation.

[0050] S4. After drilling, the drilling results are obtained through comprehensive analysis combined with geophysical data and geological conditions in adjacent areas, and safety and technical measures are formulated based on the drilling results notification. At least three drill holes are constructed in each cycle in non-geophysical anomaly areas, two of which have their end points located 1.0m outside the tunnel and one hole located within the tunnel contour. The opening and end positions of the drill holes in each cycle should be staggered and constructed alternately with those of the previous cycle.

[0051] S5. The vertical distance between the top of the special tunnel for gas extraction and the coal seam is 8 to 15m (except for the uphill and stone gate designed to pass through the coal-bearing strata). If it exceeds this range, the tunnel layer should be adjusted in time or special measures should be formulated.

[0052] S6. During tunnel excavation, if there is no measured (or geological drilling) stratigraphic control data within 150 to 200 m around the head of the moraine in the normal area, at least one borehole shall be constructed to determine the distance between the tunnel and the coal seam and the thickness of the aluminous mudstone. In areas where the strike or dip of the fault or coal seam changes greatly, more geological drilling must be done. Both sides of the fault must have geological drilling control at the same time, and a stratigraphic control drilling table shall be established.

[0053] Close range control includes the following methods:

[0054] Method 1: Drilling. There may be some deviations in the determination of abnormal range of karst fissures using transient electromagnetic method or mine geological detector. In order to verify the accuracy of transient electromagnetic method, the verification method of this test adopts drilling method. The drilling uses ZYG-150 full hydraulic drilling rig, which is mainly used for drilling gas extraction (discharge) holes, grouting fire extinguishing holes, coal seam water injection holes, geological exploration holes and related engineering holes in coal mines. The drilling rig is suitable for various coal and rock formations with rock strength coefficient f≤8. It is suitable for tunnel section S≥4.5m 2 .

[0055] Method 2, drilling, there may be certain deviations in the use of transient electromagnetic method to determine the abnormal range of karst fissures. In order to verify the accuracy of transient electromagnetic method, the verification method of the first test adopted the drilling method. However, the drilling method is point contact and the number of boreholes is small, and the control range is limited. There may still be certain deviations. Therefore, it is planned to use a larger number of drilling methods for final verification.

[0056] Method 3: Extraction: Using the main extraction system that has been improved in the study area, the karst fissures are directly sealed and extracted to achieve the extraction of harmful gases. When the gas extraction prevention is implemented, the gas extraction pipeline should be constructed while the gas extraction tunnel is being excavated. The end should not be more than 200m away from the excavation working face, so as to facilitate the timely extraction of karst and fissure gas. The selection of the extraction pipe diameter can be calculated according to the following formula:

[0057]

[0058] Where: D is the pipe diameter (m), Q is the flow rate (m 3 / s), V is the economic flow rate, generally 10-15m / s. In addition, the water supply and air supply pipelines can be temporarily directly converted into karst fissure gas extraction pipelines, which can quickly and effectively reduce the threat of karst gas. In addition, when the outflow volume is small, the concentration is low, and there is no pressure, the temporary blocking of the exploration eye and extraction can be directly adopted for treatment.

[0059] Method 4: Exhaust. When the gas concentration in karst fissures is low, make full use of local ventilation measures to safely discharge harmful gases to the mine's total return air system. When exhaust prevention and control is implemented, during the construction of all-rock tunnels, when various detection boreholes are used to obtain hidden disaster factors of karst gas risks, if the amount of water accumulated in the karst is small and the gas outburst characteristics are gentle, the safety threat to the workers at the mining face is small and the risk level is low, a drilling rig or rock drill can be used to construct a borehole at a certain distance from the karst to pre-control the discharge of harmful substances such as gas and water. The required air volume for the excavation face is calculated according to the following formula:

[0060] Q j =100×q j ×K j

[0061] In the formula, Q j is the actual air volume required for the excavation working face m 3 / min;q j is the absolute gas outflow volume of the excavation working face m 3 / min; K j The absolute gas outburst imbalance coefficient of the excavation working face is taken as 1.3~1.5.

[0062] Method 5: Gas blocking. When the outflow of karst gas and water is large and there is continuous gas and water supply, it is not enough to reduce the safety threat to the allowable range in a short time. The shielding measures taken for gas blocking prevention and control can be divided into three categories according to the location of karst blocking: one is mainly applied to the inside of karst, such as grouting blocking measures for karst fissures. For example, when railways, bridge and tunnel projects, and main mine development shafts encounter karst, this type of engineering measure should be the first choice. The purpose is to ensure the stability of the surrounding rock and prevent the further expansion of karst cavities, which will endanger the safety of the project. The second type is to implement blocking outside the karst, such as the mine. For secondary shaft and tunnel projects used for gas extraction, the first option is to implement avoidance and detour, seal the exposed karst in a safer position, and take extraction measures in the sealed area. If necessary, the sealing facilities can be unsealed. A more typical approach is to construct a closed wall at a certain position behind the excavation working face, and reserve extraction boreholes for extraction. The third type is to seal the karst exposure. For areas with a small impact range of karst, in order to ensure the safety of support, measures such as anchor rods, anchor nets, shotcrete, and I-beam supports are used to seal and reinforce the karst. The purpose is to ensure the safety of support and prevent gas accumulation in karst cavities.

[0063] Method 6: Avoidance and detour: In order to avoid the greater impact of cracks and structures on safe production, the active method of avoidance and detour is mainly adopted for the more complex karst cracks and structures that have been explored to reduce the complexity of construction and potential safety risks.

[0064] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0065] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A gas prevention and control method based on step-by-step detection, characterized in that: Use the long-distance geophysical exploration part and the short-distance prevention and control part to carry out gas prevention and control; The long-range geophysical exploration comprises the following steps: S1. When tunneling, karst gas must be detected and released in advance; the methods of advanced detection and release include geophysical exploration, drilling and drilling; S2. If abnormal areas are still found after re-examination, drilling and exploration measures must be taken within 10 meters of the abnormal area; S3. If the review shows that there is no geophysical anomaly area, no drilling and blasting measures will be taken, but the construction of the drill hole and the blasting requirements will still be carried out according to the original geophysical anomaly area; S4. After drilling, the drilling results shall be obtained through comprehensive analysis based on geophysical data and geological conditions in adjacent areas, and safety and technical measures shall be formulated based on the drilling results notice; S5. Set the vertical distance between the top of the dedicated gas extraction tunnel and the coal seam to 8 to 15 meters, except for the uphill and stone gate designed to penetrate the coal-bearing strata; S6. When tunneling, if there is no measured or geological drilling stratigraphic control data within 150-200m around the moraine head in the normal area, at least one borehole shall be constructed to find out the distance between the tunnel and the coal seam and the thickness of the aluminous mudstone. In areas where the strike or dip of the fault or coal seam changes greatly, more geological drilling must be done. Both sides of the fault must have geological drilling control at the same time, and a stratigraphic control drilling table shall be established. The close-range prevention and control methods include: drilling, probing, pumping, exhausting, blocking and avoiding; The drilling is: when there is a certain deviation in the abnormal range of karst fissures determined by transient electromagnetic method or mine geological detector, in order to verify the accuracy of transient electromagnetic method determination, the verification method of the test adopts drilling method; The drilling method is as follows: after the drilling method is used for verification in the first test, a larger number of drilling methods are used for final verification because the traditional drilling method is point contact and the number of holes drilled is small, and the control range is limited; The gas extraction is: using the main extraction system that has been perfected in the study area, directly sealing and extracting the outside of the karst fissures to achieve the extraction of harmful gases; The exhaust is: when the karst fissure gas enrichment is small, the harmful gas is safely discharged to the mine's total return air system by means of local ventilation measures; The gas blocking is a shielding measure taken when the outflow of karst gas and water is large, there is a continuous gas and water supply, and it is not enough to reduce the safety threat to the allowable range in a short time; The avoidance means avoiding cracks and structures that have a greater impact on safe production. For the more complex karst cracks and structures that have been discovered, an active avoidance method is adopted to reduce the complexity of construction and potential safety risks.

2. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: In the long-distance geophysical exploration, if karst gas, water, bauxite or coal seam is detected during the drilling of the Maokou limestone tunnel in step S6, the operation must be stopped.

3. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: The abnormal area includes geophysical abnormal area and drilling abnormal area; wherein, the geophysical abnormal area is the abnormal area range delineated according to the comprehensive analysis of geophysical data and mastered geological information; the abnormal area actually exposed by drilling in the abnormal area and the area 5m before and after the area are all drilling abnormal areas.

4. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: The requirements for safety technical measures include: when geophysical exploration is abnormal but drilling is normal, the drill hole construction and blasting regulations shall be implemented according to the geophysical abnormality area; if both geophysical exploration and drilling are abnormal, specific measures shall be formulated separately according to the drilling abnormality.

5. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: In the area where there are no geophysical anomalies, at least three drill holes shall be constructed in each cycle, two of which have their end points located 1.0m outside the tunnel and one hole located within the tunnel contour line. The opening and end positions of the drill holes in each cycle shall be staggered and constructed alternately with those of the previous cycle.

6. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: When the above-mentioned gas extraction is implemented, the gas extraction pipeline needs to be constructed while the gas extraction tunnel is being excavated. The end of the gas extraction pipeline should not be more than 200m away from the excavation working face, so as to facilitate the timely extraction of karst and fissure gas. The extraction pipe diameter is selected according to the following formula: Where D is the pipe diameter, m; Q is the flow rate, m 3 / s; V is the economic flow rate, which is taken as 10-15m / s; in addition, the water supply and air supply pipelines are temporarily and directly converted into karst fissure gas extraction pipelines to quickly and effectively reduce the threat of karst gas. Moreover, in the case of small outflow volume, low concentration and no pressure, temporary blocking and exploration eye extraction are directly adopted for treatment.

7. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: When the exhaust is implemented, during the whole rock tunnel excavation construction, when various detection boreholes obtain hidden disaster factors of karst gas risk, if the amount of water accumulated in the karst is small, the gas outburst characteristics are gentle, and the safety threat to the workers at the mining face is small, and the risk level is low, a drilling rig or rock drill is used to construct a borehole at a certain distance from the karst to pre-control the discharge of gas, water and other harmful substances; the required air volume of the excavation face is calculated according to the following formula: Q j =100×q j ×K j In the formula, Q j is the actual air volume required for the excavation working face m 3 / min;q j is the absolute gas outflow volume of the excavation working face m 3 / min; K j The absolute gas outburst imbalance coefficient of the excavation working face is taken as 1.3~1.

5.

8. The gas prevention and control method based on step-by-step detection according to claim 1 is characterized in that: When the gas blocking is implemented, it is divided into three categories according to the location of the karst blocking. The first category mainly acts on the inside of the karst; the second category is to block the outside of the karst; and the third category is to block the karst at the exposed part.

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