Rapid calculation method for maximum gas gathering concentration in highway tunnel

Abstract

The invention belongs to the technical field of highway gas tunnel construction safety, and particularly relates to a rapid calculation method for the maximum gas gathering concentration in a highway tunnel, and the method comprises the steps: determining a gathering section of gas along the opposite side of a tunnel axial air duct based on field actual measurement and numerical simulation; defining a peak concentration expression, a stable stage average concentration expression and a maximum gas aggregation degree expression; the method comprises the following steps: dividing the cross section of a tunnel into nine areas, selecting an area 1 and an area 5 on the opposite side of an air duct as monitoring areas, and calculating and making a gas aggregation degree look-up table by monitoring the maximum gas concentration and stable concentration of each area at the initial stage of construction; detecting the gas concentration in the stable stage on site, abandoning the maximum value and the minimum value, and then taking arithmetic average; and querying the query table to obtain the maximum gas aggregation degree of the corresponding region, and substituting the maximum gas aggregation degree into a formula to quickly calculate the maximum gas aggregation concentration. According to the method, the maximum gas concentration peak value in the tunnel is rapidly and accurately obtained through a simple and convenient detection means, and an important basis is provided for gas disaster prevention and control.

Description

Technical Field

[0001] This invention relates to the field of safety technology for highway gas tunnel construction, and in particular to a rapid calculation method for the maximum gas accumulation concentration in a highway tunnel. Background Technology

[0002] Accurately controlling methane concentration is a core prerequisite for ensuring construction safety during highway tunnel construction. The explosive limits of methane (primarily composed of methane) are 5%-16%. If the concentration exceeds this limit and comes into contact with an ignition source, it can easily trigger an explosion, causing casualties and property damage. Precise methane monitoring provides a basis for the rational arrangement of construction plans and accurate assessment of safety risks, making it a low-cost, high-value safety assurance measure.

[0003] Currently, existing methods for monitoring methane concentration include fixed sensor monitoring, portable instrument detection, and bundled tube monitoring. However, these methods have many shortcomings in practical applications. First, the large cross-section of tunnels and the frequent vehicle traffic during construction affect the accuracy of methane concentration detection, leading to unstable measurement data. Second, it is difficult to place the detection instruments in a uniform, most unfavorable location, causing the measurement results to fail to accurately reflect the peak concentration in the most severely methane-accumulated areas. Furthermore, the maximum methane concentration changes dynamically; relying on manual monitoring in real time is not only cumbersome but also makes it difficult to capture the instantaneous maximum accumulation concentration. In particular, regarding the quantitative calculation of methane accumulation, there is currently no unified formula or method in existing technology for quickly calculating the maximum methane accumulation concentration, which poses a challenge to the prevention and control of tunnel methane disasters.

[0004] Therefore, there is an urgent need for a new method that can quickly and accurately calculate the maximum gas concentration in highway tunnels, in order to solve the shortcomings of existing technologies that cannot quickly quantify the degree of gas accumulation and are difficult to obtain peak concentrations, thereby providing more reliable technical support for tunnel construction safety. Summary of the Invention

[0005] This invention proposes a rapid calculation method for the maximum gas concentration in highway tunnels, aiming to solve the technical problem in the prior art that it is impossible to calculate the maximum gas concentration quickly and accurately.

[0006] This invention provides a rapid method for calculating the maximum gas accumulation concentration in highway tunnels, comprising: Based on field measurement data and numerical simulation data, it was determined that there is a gas accumulation zone on the opposite side of the ventilation duct along the tunnel axis; The maximum gas concentration occurring within the aforementioned accumulation zone is defined as the peak concentration. The gas concentration at a predetermined distance from the working face is defined as the average gas concentration during the steady-state phase. And define the maximum gas concentration. The expression is: ; The tunnel cross-section is divided into n regions. The first to the mth region on the opposite side of the ventilation duct are selected as the monitoring area, where m < n. The maximum gas concentration in each region is defined as follows: to The maximum gas concentration in each region is obtained as the peak concentration and the average gas concentration during the stable phase, and the maximum gas concentration is determined based on the maximum gas concentration. The expression is used to calculate the maximum gas concentration in each region, and a gas concentration lookup table is created. Obtain the methane concentration during the steady-state phase on the tunnel cross section. ; The maximum gas concentration in the corresponding monitoring area can be obtained by querying the gas concentration table. And according to the formula Calculate the maximum concentration of gas accumulation. .

[0007] The technical advantages of the rapid calculation method for the maximum methane concentration in highway tunnels disclosed in this invention are as follows: This method eliminates the need for long-term manual detection in hazardous areas. It only requires randomly measuring several sets of methane concentration data in a stable airflow area and combining this data with a lookup table to quickly and accurately calculate the potential peak methane concentration within the tunnel, providing a direct basis for determining whether the methane concentration exceeds the limit. This method combines simple detection with rapid calculation, reducing labor costs and detection blind spots. It can identify high-concentration methane accumulation areas in real time and trigger early warnings, buying crucial time for personnel evacuation and equipment shutdown. This effectively avoids explosions and fires caused by excessive methane concentrations, ensuring construction safety, improving construction efficiency, and providing important theoretical support and engineering application basis for tunnel methane disaster prevention and control.

[0008] Furthermore, the tunnel cross-section is divided into n regions, and the first to the mth regions on the opposite side of the ventilation duct are selected as the monitoring areas, specifically including: Based on the geometry of the tunnel cross section, it is divided into 9 sub-regions distributed along the tunnel arch to the invert and along both sides of the tunnel. The first to fifth areas on the opposite side of the ventilation duct were selected as the monitoring area, and the maximum gas concentration in each area was defined as follows: to .

[0009] Furthermore, the process of creating the gas concentration lookup table is as follows: By monitoring area 1 during a complete tunnel excavation cycle in the early stages of tunnel construction. The maximum and average gas concentrations of each of Region 5 were calculated, and the maximum gas concentration was determined. to ; A complete tunnel excavation cycle includes the entire process from blasting at the tunnel face to revealing the new coal seam to completing the muck removal operation after ventilation stabilization.

[0010] Furthermore, the gas concentration query table includes the range of maximum gas concentration corresponding to different monitoring time points.

[0011] Furthermore, the monitoring time points are 30 minutes and / or 60 minutes after tunnel ventilation.

[0012] Furthermore, the method of obtaining the stable stage gas concentration on the tunnel cross-section... Specifically, it includes: In the non-gas accumulation area of ​​the tunnel cross section, far from the influence zone of the ventilation duct jet, randomly test the gas concentration of more than m groups. Discarding the maximum and minimum values, the arithmetic mean of the remaining gas concentration is taken as the gas concentration in the steady-state phase. ; Among them, the number of random detection groups m is 5 groups, and the detection points are distributed in the non-clustered area on the tunnel cross section, avoiding the backflow area on the opposite side of the ventilation duct.

[0013] Furthermore, when creating the gas concentration lookup table, the step of obtaining the maximum gas concentration as the peak concentration and the average gas concentration during the stable phase in each region specifically includes: During several different tunneling cycles in the early stages of tunnel construction, the peak concentration and average gas concentration in each monitoring area after 30 minutes of ventilation were recorded, and the corresponding maximum gas concentration was calculated to form a statistical table containing the data range and error range.

[0014] Furthermore, the method of obtaining the stable stage gas concentration on the tunnel cross-section... Previously, it also included: During the coal seam exposure process in the tunnel, after the blasting at the working face reveals a new coal seam, a pre-set ventilation time is waited for, and a monitoring section is selected after the airflow stabilizes.

[0015] Furthermore, the preset ventilation waiting time is 30 minutes, and the monitoring section is selected at a tunnel cross section where the airflow is stable, smooth, straight, and unobstructed.

[0016] Furthermore, the maximum gas concentration in the corresponding monitoring area is obtained by querying the gas concentration lookup table. The steps specifically include: Based on the current monitoring time point and target monitoring area of ​​the tunnel construction, the corresponding maximum gas concentration range is retrieved from the gas concentration lookup table. Then, the maximum, minimum, or median value within this range is selected as the maximum gas concentration based on the project risk level. . Attached Figure Description

[0017] Figure 1 This is a diagram showing the distribution pattern of methane along the tunnel axis and a corresponding schematic diagram of the tunnel longitudinal section, as proposed in an embodiment of the present invention. Figure 2 A flowchart illustrating a rapid calculation method for the maximum gas accumulation concentration in a highway tunnel, provided by an embodiment of the present invention; Figure 3 This is a schematic diagram of the regional division of a highway tunnel cross section (AA section) provided in an embodiment of the present invention. Detailed Implementation

[0018] 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.

[0019] In view of the limitations mentioned in the background section regarding existing gas monitoring methods during highway tunnel construction—namely, the lack of a unified formula and the difficulty in quickly calculating the degree of gas accumulation—this embodiment uses a one-way three-lane highway tunnel under construction as an example to provide a detailed explanation of the calculation method provided by this invention.

[0020] This embodiment uses a one-way three-lane highway tunnel under construction as an engineering background to describe in detail the rapid calculation method for the maximum gas accumulation concentration in a highway tunnel provided by this invention. The tunnel design parameters are as follows: a clear height of 8m and a clear width of 13m, with a one-way three-lane cross-section; a length of 200m from the tunnel face is selected as the research object, including a 15m upper step; a flexible ventilation duct with a diameter of 2m is used, installed on the right side of the tunnel arch at a height of 6m from the tunnel bottom, and the distance from the duct outlet to the tunnel face is controlled within 15m to ensure ventilation effect. This tunnel traverses a coal seam group with a high gas content, classifying it as a high-gas tunnel; therefore, gas concentration monitoring is of paramount importance for safety management during construction.

[0021] Step 1: Identify gas accumulation zones and define basic parameters. During the tunnel construction preparation phase, on-site measurements are conducted first. During the first three tunneling cycles, multiple gas concentration monitoring sections are deployed along the tunnel axis. At each monitoring section, a high-precision gas sensor is placed near the arch opposite the ventilation duct to continuously monitor gas concentration changes. Simultaneously, a three-dimensional numerical model of the tunnel is established, and computational fluid dynamics is used to simulate the gas distribution along the tunnel axis under different ventilation conditions.

[0022] By comprehensively analyzing on-site measured data and numerical simulation results, it was found that during the axial movement of methane gas along the tunnel, due to the entrainment effect of the ventilation duct jet and the geometric constraints of the tunnel cross-section, a low-velocity backflow zone is formed on the opposite side of the ventilation duct (i.e., the side away from the ventilation duct). Methane accumulates in this area, resulting in a concentration increase. This section is defined as the "ventilation duct opposite side accumulation zone." This zone is typically located within a range of 20m to 80m from the tunnel face, with the specific location depending on the tunnel cross-section dimensions, ventilation duct location, and airflow volume.

[0023] Based on preliminary field measurement data and numerical simulation results, it was determined that there is a gas accumulation zone on the opposite side of the ventilation duct along the tunnel axis (e.g., Figure 1 (As shown). The maximum gas concentration within this section is defined as the peak concentration. The gas concentration more than 50m from the working face is defined as the average gas concentration during the steady-state phase. The criteria for determining the stable phase are: if the change in gas concentration at three consecutive monitoring points does not exceed 5%, it is considered to have entered the stable phase.

[0024] The maximum gas concentration degree D is defined as: .

[0025] This expression is used to quantify the degree of gas accumulation in a specific area. The larger the D value, the more severe the gas accumulation and the higher the risk.

[0026] Step 2: Divide the monitoring area and create a gas concentration query table.

[0027] Based on the geometric characteristics of the tunnel cross-section, the tunnel cross-section is divided into 9 sub-regions. Specifically, it is divided into three equal rows (upper, middle, and lower) along the direction from the tunnel arch to the invert, and into three equal columns (left, middle, and right) along both sides of the tunnel, forming a 3×3 grid, for a total of 9 regions.

[0028] Based on numerical simulation results and previous field measurements, gas accumulation mainly occurs in the area opposite the ventilation duct, while the area on the same side of the duct is affected by the jet flow, resulting in smaller gas concentration variations and limited reference value. Therefore, the first to fifth areas on the opposite side of the ventilation duct were selected as key monitoring areas, sequentially numbered as Area 1, Area 2, Area 3, Area 4, and Area 5. Figure 3 As shown, if the ventilation duct is located on the right side of the tunnel, then areas 1, 2, and 3 are the upper, middle, and lower zones on the left side, and areas 4 and 5 are the upper and middle zones in the middle.

[0029] During the initial stages of tunnel construction, gas concentration data were collected and statistically analyzed across multiple complete tunneling cycles. A complete tunneling cycle was defined as the entire process from the initial blasting at the tunnel face to the completion of muck removal after ventilation stabilized, typically lasting 4-6 hours. Within each tunneling cycle, peak concentrations and average concentrations during the stable phase were monitored in areas 1 through 5. Peak concentrations were monitored by continuously detecting the highest concentration in the accumulation zone using a portable gas detector at a frequency of once per minute. The average concentration during the stable phase was monitored by continuously collecting 10 sets of data at a cross-section 50m from the tunnel face under stable airflow conditions, and then taking the arithmetic mean.

[0030] In this embodiment, a total of 10 complete tunneling cycles were monitored, and the peak and stable concentration data of each area at two time points, 30 minutes and 60 minutes of ventilation, were recorded. Statistical analysis was performed on the 10 sets of data, and after removing outliers, the maximum gas concentration range of each area and time point was calculated, forming a gas concentration lookup table template as shown in Table 1.

[0031] Table 1 Gas Concentration Degree Query Table

[0032] In this embodiment, the actual query table 2 obtained after statistical analysis is as follows: Table 2 Actual Query Table

[0033] As shown in Table 2, the gas accumulation in each area after 30 minutes of ventilation is significantly higher than after 60 minutes, indicating that the gas accumulation gradually decreases with prolonged ventilation time. Meanwhile, Area 2 (the central area opposite the ventilation duct) has the highest accumulation rate, indicating that this area has the most severe gas accumulation and should be a key monitoring target. The data range in the table reflects the fluctuations between different tunneling cycles, providing a safety margin selection space for engineering applications.

[0034] In Table 1, ΔD1 represents the range of gas concentration in region 1, ΔD2 represents the range of gas concentration in region 2, ΔD3 represents the range of gas concentration in region 3, ΔD4 represents the range of gas concentration in region 4, and ΔD5 represents the range of gas concentration in region 5.

[0035] The lookup table of this invention is not limited to the tunnel dimensions and ventilation parameters in the embodiments. For any highway tunnel, it can be prepared according to the following general steps: (1) Based on the actual cross-sectional dimensions (width and height) of the tunnel, the diameter of the ventilation duct, the distance from the ventilation duct outlet to the working face, the installation position of the ventilation duct (height from the bottom plate and distance from the side wall) and the design air volume, a simplified two-dimensional or three-dimensional numerical model is established, and fluid simulation software is used to simulate the gas concentration distribution during ventilation for 30 minutes.

[0036] (2) Arrange the model cross-section according to Figure 3 Divided into 9 areas, extract the area opposite the air duct 1 Maximum concentration in region 5 Average concentration of cross section ,according to Calculate the clustering degree of each region.

[0037] (3) In the first two stages of tunnel construction During the three tunneling cycles, on-site measurements were taken in each area. and The simulation results are corrected using the measured values ​​(correction coefficient = measured D / simulated D), resulting in a lookup table applicable to this tunnel.

[0038] If numerical simulation is not available, empirical estimation can be used: for common two-lane and three-lane tunnels, the density of the central area (region 2) opposite the ventilation duct. Typically, the humidity should be between 40% and 70% (after 30 minutes of ventilation); other areas can be adjusted proportionally. ≈0.85 , , , Estimate.

[0039] It should be noted that after tunnel ventilation stabilizes, the methane concentration in the jet zone of the ventilation duct and at the bottom of the tunnel is less affected by local accumulation and can represent the background methane concentration at that ventilation time. In this method, multiple concentrations are randomly measured in nine regions across the entire cross-section and averaged because the accumulation zone (region 1 opposite the ventilation duct) is... Region 5, occupying approximately one-third of the cross-section, has a limited impact of its high concentration on raising the overall average concentration. Furthermore, by discarding the maximum and minimum values, the interference of high concentrations in the aggregation zone is further weakened. Actual measurements show that the deviation between the overall average concentration and the average concentration in the non-aggregate zone is less than 2%. Therefore, the overall average concentration is used as the baseline concentration for the stable phase. It has engineering-acceptable accuracy.

[0040] Step 3: Measure the gas concentration during the stable phase on site.

[0041] During subsequent coal seam exposure in the tunnel, after a new coal seam is exposed by blasting at the tunnel face, a 30-minute waiting period is required, as per regulations, to ensure that the ventilation system fully dilutes and removes the harmful gases generated by the blast. Subsequently, monitoring sections are selected to detect the gas concentration during the stable phase. The selection of monitoring sections must meet the following conditions: located in a stable airflow area, with a smooth and straight cross-section, and free from obstructions interfering with airflow; typically, they are chosen within a range of 50m to 100m from the tunnel face.

[0042] At the selected monitoring section, according to Figure 3 The nine zones shown are divided into several areas. One to two detection points are randomly selected within each zone, and a total of at least five sets of gas concentration data are collected. A calibrated portable gas detector is used during the detection process. The probe should be placed at the detection point and stabilized for at least 10 seconds before recording the reading.

[0043] In this embodiment, 30 minutes after a coal seam was exposed in the tunnel, a section 60m away from the tunnel face was selected as the monitoring section, and the following gas concentration data were obtained: Area 1: =0.0039; Region 2: =0.0038; Region 3: =0.0040; Area 4: =0.0048; Region 5: =0.0047; Region 6: =0.0028; Area 7: =0.0030; Region 8: =0.0032; Region 9: =0.0024.

[0044] To eliminate the influence of random errors on the calculation results, the above 9 sets of data were sorted by numerical value, and the maximum value of 0.0048 and the minimum value of 0.0024 were discarded. The arithmetic mean concentration of the remaining 7 data was calculated: ; The value of 0.00363 at this point is taken as the average gas concentration during the stable phase. .

[0045] Step 4: Calculate the maximum gas accumulation concentration .

[0046] Based on the current construction time being 30 minutes after ventilation, the maximum gas concentration range for each monitoring area can be obtained by referring to Table 2. In practical engineering applications, an appropriate concentration value can be selected according to the risk management strategy. Safety-oriented strategy: Take the upper limit of the range, suitable for high gas outburst risk areas or key control phases; Conventional strategy: Take the middle value of the range, which is suitable for daily monitoring in general gas work areas; Economical strategy: Take the lower limit of the range, applicable to low-gas areas or non-critical processes.

[0047] Based on the current construction time of 30 minutes of ventilation, Table 2 is consulted to obtain the maximum gas concentration range for each monitoring area. This embodiment adopts a safer approach, taking the upper limit of the concentration range for each area as the maximum gas concentration. Substitute into the formula Calculate the maximum concentration of gas accumulation: For region 1 (S=45%) =0.00363 (1+0.45)=0.00526; For region 2 (S=59%) =0.00363 (1+0.59)=0.00577; For region 3 (S=37%) =0.00363 (1+0.37)=0.00497; For region 4 (S=25%) =0.00363 (1+0.25)=0.00454; For region 5 (S=29%) =0.00363 (1+0.29)=0.00468.

[0048] Calculation results This represents the maximum possible methane concentration (peak concentration) in each monitored area at that ventilation time. Engineers can use this to assess the risk of methane exceeding limits and take appropriate safety measures.

[0049] Calculation results show that after 30 minutes of ventilation, the predicted maximum methane concentration in Area 2 is the highest, reaching 0.00577, which is close to but does not exceed the methane concentration limit specified in the regulations. This result can serve as an important basis for on-site safety management: it can be used to determine whether the current ventilation plan meets the requirements, whether the position of the ventilation duct needs to be adjusted or the air volume increased, and to focus on monitoring Area 2.

[0050] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1) This invention directly and quickly calculates the core safety indicator of “maximum gas concentration” that is of most concern in tunnel engineering, providing a direct and key basis for early warning of peak concentration for gas disaster prevention and control, and solving the problem that existing technologies cannot obtain this indicator in real time and accurately.

[0051] (2) It achieves rapid and convenient detection: On-site operators only need to measure several sets of gas concentrations on a stable and easily accessible cross-section and take the average value. Then, by consulting a pre-generated lookup table, they can quickly calculate the peak concentration that is difficult to measure directly. The whole process does not rely on complex equipment or long-term continuous monitoring. It is simple to operate and highly efficient.

[0052] (3) Improved monitoring accuracy and reliability: By dividing the tunnel cross-section into multiple areas and selecting the area with significant changes on the opposite side of the ventilation duct 1 Area 5 was designated as a key monitoring area, enhancing the representativeness of the data. When calculating the gas concentration during the stable phase, the method of "discarding the maximum and minimum values ​​and then calculating the arithmetic mean" was adopted, effectively reducing random errors and ensuring data reliability.

[0053] (4) Enhanced practicality and flexibility of the project: The gas concentration query table provides data in the form of range. Users can flexibly select the appropriate concentration value for calculation according to the actual risk level of the project (such as safety-oriented or economy-oriented), so that this method can better adapt to the risk control needs of different construction stages.

[0054] (5) Enhanced safety and economic value: By accurately predicting the peak concentration of gas, serious accidents such as gas explosions can be effectively avoided, ensuring the safety of personnel and equipment, and avoiding work stoppages, project delays and huge economic compensation caused by accidents. It has significant safety and economic benefits.

[0055] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A rapid calculation method for the maximum gas accumulation concentration in a highway tunnel, characterized in that, include: Based on field measurement data and numerical simulation data, it was determined that there is a gas accumulation zone on the opposite side of the ventilation duct along the tunnel axis; The maximum gas concentration occurring within the aforementioned accumulation zone is defined as the peak concentration. The gas concentration at a predetermined distance from the working face is defined as the average gas concentration during the steady-state phase. And define the maximum gas concentration. The expression is: ; The tunnel cross-section is divided into n regions. The first to the mth region on the opposite side of the ventilation duct are selected as the monitoring area, where m < n. The maximum gas concentration in each region is defined as follows: to The maximum gas concentration in each region is obtained as the peak concentration and the average gas concentration during the stable phase, and the maximum gas concentration is determined based on the maximum gas concentration. The expression is used to calculate the maximum gas concentration in each region, and a gas concentration lookup table is created. Obtain the methane concentration during the steady-state phase on the tunnel cross section. ; The maximum gas concentration in the corresponding monitoring area can be obtained by querying the gas concentration table. And according to the formula Calculate the maximum concentration of gas accumulation. .

2. The method according to claim 1, characterized in that, The process of dividing the tunnel cross-section into n regions and selecting the first to the mth regions on the opposite side of the ventilation duct as the monitoring area specifically includes: Based on the geometry of the tunnel cross section, it is divided into 9 sub-regions distributed along the tunnel arch to the invert and along both sides of the tunnel. The first to fifth areas on the opposite side of the ventilation duct were selected as the monitoring area, and the maximum gas concentration in each area was defined as follows: to .

3. The method according to claim 2, characterized in that, The process of creating the gas concentration lookup table is as follows: By monitoring area 1 during a complete tunnel excavation cycle in the early stages of tunnel construction. The maximum and average gas concentrations of each of Region 5 were calculated, and the maximum gas concentration was determined. to ; A complete tunnel excavation cycle includes the entire process from blasting at the tunnel face to revealing the new coal seam to completing the muck removal operation after ventilation stabilization.

4. The method according to claim 1, characterized in that, The gas concentration lookup table contains the range of maximum gas concentration corresponding to different monitoring time points.

5. The method according to claim 4, characterized in that, The monitoring time points are 30 minutes and / or 60 minutes after tunnel ventilation.

6. The method according to claim 1, characterized in that, The method for obtaining the stable stage gas concentration on the tunnel cross-section. Specifically, it includes: In the non-gas accumulation area of ​​the tunnel cross section, far from the influence zone of the ventilation duct jet, randomly test the gas concentration of more than m groups. Discarding the maximum and minimum values, the arithmetic mean of the remaining gas concentration is taken as the gas concentration in the steady-state phase. ; Among them, the number of random detection groups m is 5 groups, and the detection points are distributed in the non-clustered area on the tunnel cross section, avoiding the backflow area on the opposite side of the ventilation duct.

7. The method according to claim 1, characterized in that, When creating the gas concentration lookup table, the step of obtaining the maximum gas concentration as the peak concentration and the average gas concentration during the stable phase in each region specifically includes: During several different tunneling cycles in the early stages of tunnel construction, the peak concentration and average gas concentration in each monitoring area after 30 minutes of ventilation were recorded, and the corresponding maximum gas concentration was calculated to form a statistical table containing the data range and error range.

8. The method according to claim 1, characterized in that, The method for obtaining the stable stage gas concentration on the tunnel cross-section. Previously, it also included: During the coal seam exposure process in the tunnel, after the blasting at the working face reveals a new coal seam, a pre-set ventilation time is waited for, and a monitoring section is selected after the airflow stabilizes.

9. The method according to claim 8, characterized in that, The preset ventilation waiting time is 30 minutes, and the monitoring section is selected at a tunnel cross section where the airflow is stable, smooth and straight, and there are no obstructions.

10. The method according to claim 1, characterized in that, The maximum gas concentration in the corresponding monitoring area is obtained by querying the gas concentration table. The steps specifically include: Based on the current monitoring time point and target monitoring area of ​​the tunnel construction, the corresponding maximum gas concentration range is retrieved from the gas concentration lookup table. Then, the maximum, minimum, or median value within this range is selected as the maximum gas concentration based on the project risk level. .

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