Tunnel high gas grading method based on analytic hierarchy process

Abstract

The method comprises the following steps: step one, collecting data in the hole by using the advanced detection technology to form detection data; step two, combining the detection data and the stratum qualitative, marking and classifying the gas concentration influence factors, and assigning values to the classification results; step three, according to the classification results of step two, introducing the analytic hierarchy process to calculate the weight of each influence factor; step four, combining the assignment of the classification results of step two and the weight of the influence factors of step three, calculating the preliminary RLGT value, and preliminarily classifying the gas in the tunnel; step five, measuring other influence factors in the hole, and according to the marking and assignment results, calculating the weight of each influence factor by using the analytic hierarchy process; step six, combining the preliminary RLGT value of step four and the weight value of the other influence factors of step five, calculating the final risk grade RLGT' value of the tunnel gas, and dividing the gas risk grade, so as to meet the design, construction and use of the gas tunnel.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, specifically relating to a high-gas classification method for tunnels based on the analytic hierarchy process (AHP). Background Technology

[0002] Currently, the classification of railway gas tunnels is determined by the highest level of the gas-bearing zone within the tunnel. Low-gas and high-gas zones are distinguished by the absolute gas emission rate. A high-gas zone is defined as one where the total gas emission rate is less than 0.5 m³ / min. 3 A m³ / min is considered a low-gas work zone, greater than or equal to 0.5 m³ / min. 3 A gas concentration of 0.5 m³ / min indicates a high-gas work zone. However, this classification standard is too simplistic, leading to unnecessary equipment investment and engineering measures during construction, resulting in wasted costs.

[0003] In recent years, advanced horizontal drilling technology has been increasingly widely used in the field of tunnel engineering. Through advanced horizontal drilling, experienced technicians can observe and record the changes in slurry, drill cuttings, and gas concentration in the borehole throughout the entire process. This allows for accurate judgment of the geological information and gas conditions in the unworked areas ahead, which is beneficial for classifying the gas hazard level in advance, saving construction costs, and ensuring construction safety. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a high-gas classification method for tunnels based on the analytic hierarchy process (AHP). This invention is based on geological surveys and primarily uses advanced drilling, combined with geophysical exploration, tunnel geological description, and parameter testing for comprehensive prediction. Based on the exploration data, the AHP is used to comprehensively classify the gas hazard level according to the gas concentration in the advanced borehole, the surrounding rock grade, the groundwater conditions, the measured tunnel temperature, and the influence of other harmful gases, thereby meeting the design, construction, and use requirements of gas tunnels.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a tunnel high-gas classification method based on the analytic hierarchy process, characterized in that it includes:

[0006] Step 1: Collect data inside the tunnel using advanced tunnel gas detection technology to form detection data;

[0007] Step 2: Combining the data table and stratigraphic characterization of the detection data in the detection data, mark and classify the factors affecting gas concentration, and assign values ​​to the classification results;

[0008] Step 3: Based on the classification results of Step 2, use the analytic hierarchy process (AHP) to calculate the weights of the factors affecting gas concentration in Step 2.

[0009] Step 4: Combining the classification results from Step 2 with the weights of the factors influencing gas concentration from Step 3, calculate the preliminary RLGT value and perform preliminary classification of gas in the tunnel.

[0010] Step 5: Measure other influencing factors inside the cave, mark them, and calculate the weight of each influencing factor using the analytic hierarchy process (AHP).

[0011] Step 6: Combine the preliminary RLGT value from Step 4 with the weight values ​​of other influencing factors from Step 5 to calculate the final risk level RLGT' value of tunnel gas, and perform the final classification of gas in the tunnel.

[0012] Preferably, the classification of factors affecting gas concentration in step 2 includes: stratum lithology α1, geological structure α2, coal seam thickness α3, tunnel burial depth α4, hydrogeology α5, tunnel temperature α6, and other harmful gases α7, and other harmful gases include hydrogen sulfide, carbon monoxide, and carbon dioxide.

[0013] Preferred,

[0014] Assigning a value to the lithology α1 of the stratigraphy:

[0015] The surrounding rock lithology is grade III, with α1 assigned a value of 0 to 10;

[0016] The surrounding rock lithology is grade IV, with α1 assigned a value of 11–20;

[0017] The surrounding rock lithology is grade 5, with α1 assigned a value of 21–30;

[0018] Assigning a value to geological structure α2:

[0019] When the coal seam is open and exposed in the geological structure, α2 is assigned a value of 0 to 10;

[0020] When the coal seam is in a connected geological structure, α2 is assigned a value of 11 to 20;

[0021] When the coal seam is in a closed geological structure, α2 is assigned a value of 21 to 30;

[0022] Assign a value to the coal seam thickness α3:

[0023] When the coal seam thickness is <1m, α3 is assigned a value of 0 to 10;

[0024] When the coal seam thickness is 1-3m, α3 is assigned a value of 11-15;

[0025] When the coal seam thickness is >3m, α3 is assigned a value of 16 to 20;

[0026] Assign a value to the tunnel burial depth α4:

[0027] When the tunnel depth is less than 300m, α4 is assigned a value of 0 to 10;

[0028] When the tunnel depth is 300-500m, α4 is assigned a value of 10-15;

[0029] When the tunnel depth is >500m, α4 is assigned a value of 15 to 25;

[0030] Hydrogeological α5 value assignment:

[0031] When the groundwater volume is >3500m 3 When / d, α5 is assigned a value of 0 to 5;

[0032] When the groundwater volume is 150-3500 m³ 3 When / d, α5 is assigned a value of 5 to 15;

[0033] When the groundwater volume is <150m 3 When / d, α5 is assigned a value of 15 to 20;

[0034] Assign a value to the temperature α6 inside the cave:

[0035] When the temperature inside the cave is <20℃, α6 is assigned a value of 0 to 5;

[0036] When the temperature inside the cave is 20-30℃, α6 is assigned a value of 5-15;

[0037] When the temperature inside the cave is >30℃, α6 is assigned a value of 15 to 20;

[0038] Assigning values ​​to α7 for other harmful gases:

[0039] When the content of flammable and harmful gas components is not less than 0.0024%, α7 is assigned a value of 10 to 20;

[0040] When the content of flammable and harmful gas components is less than 0.0006%, α7 is assigned a value of 5 to 10;

[0041] When no flammable or harmful gases are found during advance drilling, α7 is assigned a value of 0 to 5.

[0042] Preferably, the weight calculation process for each influencing factor in step 3 includes:

[0043] (1) Construct a judgment matrix A that reflects the importance of each pair of influencing factors:

[0044]

[0045] Where n represents the number of influencing factors, α ij Indicating influencing factor C i and influencing factor C j The relative importance of the comparisons between them, when i = j, α ij =1; when i≠j, α ij =1 / α ji ;

[0046] (2) Calculate the consistency index CI and consistency ratio CR of matrix A:

[0047]

[0048]

[0049] Where, λ max The largest eigenvalue of the judgment matrix is ​​RI, and the average random consistency index of the judgment matrix is ​​RI.

[0050] (3) Calculate the eigenvector corresponding to the largest eigenvalue of matrix A:

[0051]

[0052]

[0053] in, φ represents the nth root of the product of each element in row j. j This represents the weight of the j-th influencing factor.

[0054] Preferably, the preliminary RLGT value calculation process in step 4 includes:

[0055] (1) When the gas concentration inside the hole is less than 5 g / m 3 The calculation formula is:

[0056] RLGT=0.95α1φ1+1.05α2φ2+1.1α3φ3+1.15α4φ4+0.75α5φ5+0.8α6φ6+1.2α7φ7;

[0057] (2) When the gas concentration inside the hole is greater than or equal to 5 g / m 3 And less than or equal to 16g / m 3 The calculation formula is:

[0058] RLGT=1.15α1φ1+1.05α2φ2+1.1α3φ3+1.35α4φ4+0.95α5φ5+0.85α6φ6+1.25α7φ7;

[0059] (3) When the gas concentration inside the hole is greater than 16 g / m 3 The calculation formula is:

[0060] RLGT=(1.15+x)α1φ1+(1.05+x)α2φ2+(1.1+x)α3φ3+(1.35+x)α4φ4+(0.95+x)α5φ5+(0.85+x)α6φ6+(1.25+x)α7φ7, where

[0061] Preferably, the process of determining the preliminary tunnel gas risk level in step 4 based on the RLGT value includes:

[0062] When RLGT is between 0 and 25, the tunnel is a gas-free tunnel;

[0063] When RLGT is between 26 and 75, the tunnel is a microgas tunnel;

[0064] When RLGT is between 76 and 125, the tunnel is a low-gas tunnel.

[0065] When RLGT is between 126 and 175, the tunnel is a high-gas tunnel.

[0066] Preferably, the other influencing factors in step 5 include carbon dioxide, carbon monoxide, hydrogen sulfide, and wind speed, and the weights of these other influencing factors are labeled as follows: The weights of each influencing factor are labeled as follows:

[0067] Preferably, the process of determining the final risk level of tunnel gas based on the RLGT' value in step 6 includes:

[0068] When RLGT' is 0 to 35, the tunnel is a gas-free tunnel;

[0069] When RLGT' is 36-85, the tunnel is a microgas tunnel;

[0070] When RLGT' is 86-135, the tunnel is a low-gas tunnel;

[0071] When RLGT' is 136-185, the tunnel is a high-gas tunnel;

[0072] When RLGT'>186, the tunnel is an ultra-high gas tunnel with a risk of gas outburst, and is therefore a gas outburst tunnel.

[0073] The beneficial effects of this invention are: This invention discloses a method for advanced detection of tunnel gas and high gas classification based on detection data. Compared with the prior art, the improvement of this invention lies in:

[0074] This invention is based on geological survey methods and primarily uses advanced drilling methods, combined with geophysical exploration, in-tunnel geological description, parameter testing, etc., to conduct comprehensive forecasting. Based on the exploration data, the gas hazard level is comprehensively classified according to the gas concentration in the advanced borehole, the surrounding rock grade, the groundwater conditions, the measured temperature in the tunnel, and the influence of whether other harmful gases are mixed in. Then, different levels of countermeasures are taken according to the risk level to reduce engineering costs and ensure construction safety. Attached Figure Description

[0075] Figure 1 This is a flowchart of the gas classification method of the present invention; Detailed Implementation

[0076] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0077] Example 1:

[0078] See attached document Figure 1 As shown, a high-gas classification method for tunnels based on the analytic hierarchy process (AHP) is characterized by: including...

[0079] Step 1: Collect borehole data using tunnel gas advance detection technology to form detection data. This borehole data acquisition is based on geological survey methods, mainly using advance drilling methods, combined with geophysical exploration, tunnel geological description, parameter testing, etc., to conduct comprehensive detection and prediction; see Table 2 for reference:

[0080] Table 2: Main Measures for Comprehensive Advanced Geological Forecasting

[0081]

[0082] Step 2: Combining the data table and stratigraphic characterization of the detection data, the factors affecting gas concentration are labeled and classified, and the classification results are assigned values. The factors affecting gas concentration are divided into 7 categories, and the weights of the 7 categories are labeled as follows: stratigraphic lithology α1, geological structure α2, coal seam thickness α3, tunnel burial depth α4, hydrogeology α5, tunnel temperature α6, and other flammable and harmful gases α7. Other harmful gases include hydrogen sulfide, carbon monoxide, and carbon dioxide. Values ​​are assigned to the 7 categories of factors.

[0083] (1) The stratigraphic lithology is denoted as α1:

[0084] When studying the geological characteristics of tunnels traversing coal-bearing strata, the focus is on the impact of coal seams on gas storage and dissipation. The influence of coal seams on gas occurrence and migration patterns is mainly determined by their permeability and gas-tightness. Generally, when the roof rock of a coal seam is relatively intact and forms a cohesive whole, such as shale, gas is easily stored in the coal. When the roof rock is porous or fractured, such as sandstone, gas is more easily dissipated. Furthermore, referring to the surrounding rock classification, overall integrity corresponds to level 5 surrounding rock, overall relative integrity corresponds to level 4 surrounding rock, and overall incompleteness corresponds to level 3 surrounding rock. In actual construction, most of the surrounding rock encountered is level 3, 4, or 5. The extremely unstable situation of level 1 and 2 surrounding rock is not discussed (this classification method is no longer applicable).

[0085] Assign a value to α1 based on the detection data:

[0086] The more intact and dense the surrounding rock, the easier it is for gas to be preserved in the surrounding rock. Therefore, α1 is assigned values ​​from low to high based on the lithology of the surrounding rock:

[0087] The surrounding rock lithology is grade III, with α1 assigned a value of 0 to 10;

[0088] The surrounding rock lithology is grade IV, with α1 assigned a value of 11–20;

[0089] The surrounding rock lithology is grade 5, with α1 assigned a value of 21–30;

[0090] (2) Geological structure α2:

[0091] Geological structures, such as anticlines, synclines, and faults, have a significant impact on gas escape. Anticlines tend to form oil and gas enrichment zones, while faults also have a prominent effect on gas escape. When classifying gas levels, the sealing properties of the geological structure are the primary consideration. The higher the sealing properties of the geological structure, the less likely gas is to escape, and the higher the corresponding risk level. Based on the exploration data, α2 is assigned the following value:

[0092] When the coal seam is open and exposed in a geological structure, α2 is assigned a value of 0 to 10; when the coal seam is in a connected geological structure, α2 is assigned a value of 11 to 20; when the coal seam is in a closed geological structure, α2 is assigned a value of 21 to 30.

[0093] (3) Coal seam thickness α3:

[0094] The thickness of the coal seam directly determines the amount of gas emitted. Based on the detection data, a value is assigned to α3:

[0095] When the coal seam thickness is <1m, α3 is assigned a value of 0 to 10; when the coal seam thickness is 1 to 3m, α3 is assigned a value of 11 to 15; when the coal seam thickness is >3m, α3 is assigned a value of 16 to 20.

[0096] (4) Tunnel depth α4:

[0097] In tunnel engineering, 300m is generally used as a dividing line. The deeper the tunnel, the greater the pressure, and the more dangerous the effects of gas escape and gas outburst. Based on the detection data, α4 is assigned a value:

[0098] When the tunnel depth is less than 300m, α4 is assigned a value of 0 to 10; when the tunnel depth is 300 to 500m, α4 is assigned a value of 10 to 15; when the tunnel depth is greater than 500m, α4 is assigned a value of 15 to 25.

[0099] (5) Hydrogeology α5:

[0100] Hydrogeology primarily considers the impact of groundwater. Generally speaking, the more groundwater there is, the lower the corresponding gas content. Based on the detection data, the value of α5 is assigned as follows:

[0101] When the groundwater volume is >3500m3 When / d, α5 is assigned a value of 0 to 5; when the groundwater volume is 150 to 3500 m³. 3 When the groundwater volume is less than 150m³, α5 is assigned a value of 5 to 15. 3 When / d, α5 is assigned a value of 15 to 20;

[0102] (6) Temperature inside the cave α6:

[0103] The tunnel temperature mainly considers the impact of temperature changes during tunnel construction on gas escape and consequently on gas concentration within the tunnel. Generally, for gas tunnels passing under oil and gas fields, higher tunnel temperatures result in higher gas content and concentration. The value of α6 is assigned based on the tunnel temperature feedback from monitoring data.

[0104] When the temperature inside the cave is <20℃, α6 is assigned a value of 0 to 5; when the temperature inside the cave is 20 to 30℃, α6 is assigned a value of 5 to 15; when the temperature inside the cave is >30℃, α6 is assigned a value of 15 to 20.

[0105] (7) Other flammable and harmful gases, etc. α7:

[0106] Other harmful gases mainly include hydrogen sulfide, carbon monoxide, and carbon dioxide. Gas disasters in high-gas tunnels passing under oil and gas fields are often unpredictable and complex, and the main reasons may involve more than one type of harmful gas. If other harmful gases such as hydrogen sulfide, carbon monoxide, and carbon dioxide are detected during advance drilling, this factor should also be taken into account when determining the tunnel's gas level. The value of α7 is assigned based on the advance drilling data.

[0107] When advanced drilling discovers hydrogen sulfide, carbon monoxide, and carbon dioxide with a component content of not less than 0.0024%, α7 is assigned a value of 10 to 20; when advanced drilling discovers hydrogen sulfide, carbon monoxide, and carbon dioxide with a component content of less than 0.0006%, α7 is assigned a value of 5 to 10; when advanced drilling does not discover flammable gases such as hydrogen sulfide and carbon monoxide, α7 is assigned a value of 0 to 5.

[0108] Step 3: Based on the classification results of Step 2, use the Analytic Hierarchy Process (AHP) to calculate the weights of each influencing factor in Step 2.

[0109] The weights of the above indicators are calculated using the analytic hierarchy process (AHP).

[0110] Based on past scholarly experience and practical engineering considerations, the Analytic Hierarchy Process (AHP) is used to quantify the relative importance of each indicator and determine the influence weights of relevant indicators, including:

[0111] (1) Construct a judgment matrix that reflects the importance of each pair of indicators:

[0112]

[0113] Where n represents the number of influencing indicators, α ij Indicator C i and index C j The comparison determines the relative importance of the values. i and j represent the indices of matrix A, where i represents the row and j represents the column. When i = j, α... ij =1; when i≠j. α ij =1 / α ji α ij The size was determined based on comparisons made from previous scholars' experience and practical engineering considerations.

[0114] (2) Check for consistency:

[0115] To determine the consistency index (CI) and consistency ratio (CR) of matrix A:

[0116]

[0117]

[0118] Where, λ max To determine the largest eigenvalue of a matrix, RI is used as the average random consistency index of the matrix. When CR < 0.1, the inconsistency of matrix A is within the acceptable range, and the normalized eigenvector of matrix A can be used as the weight vector. Otherwise, matrix A needs to be reconstructed and αij adjusted.

[0119] (3) Calculate the eigenvector corresponding to the largest eigenvalue of the judgment matrix, that is, the weight vector of the influencing factor at this level corresponds to the weight value of the influencing factor:

[0120]

[0121]

[0122] Where, φ j This represents the weight of the j-th influencing indicator. This represents the nth root of the product of each element in row j;

[0123] Step 4: Combining the values ​​assigned to the influencing factors in Step 2 and the weights assigned to the influencing factors in Step 3, calculate the preliminary RLGT value and perform a preliminary classification of the gas in the tunnel, as shown in Table 1.

[0124] Table 1: Gas Classification

[0125]

[0126]

[0127] Based on geological survey methods and primarily using advanced drilling methods, and considering the varying technical characteristics and field applicability, a comprehensive approach was adopted, employing geophysical exploration techniques such as seismic wave reflection, seismic wave refraction, and high-density electrical resistivity tomography. Referring to Table 3, preliminary RLGT values ​​were calculated based on the gas concentration within the advanced borehole and the influence weights of changes in surrounding rock, geological structure, and groundwater on gas emission. The calculation process for the preliminary RLGT values ​​includes:

[0128] (1) When the gas concentration inside the hole is less than 5 g / m 3 Here, the pore gas concentration refers to the pore gas concentration data collected in step one using advanced detection technology. The preliminary RLGT value calculation formula is:

[0129] RLGT=0.95α1φ1+1.05α2φ2+1.1α3φ3+1.15α4φ4+0.75α5φ5+0.8α6φ6+1.2α7φ7,

[0130] RLGT represents the preliminary classification of tunnel gas risk;

[0131] (2) When the gas concentration inside the hole is greater than or equal to 5 g / m 3 And less than or equal to 16g / m 3 Here, the pore gas concentration refers to the pore gas concentration data collected in step one using advanced detection technology. The preliminary RLGT value calculation formula is:

[0132] RLGT=1.15α1φ1+1.05α2φ2+1.1α3φ3+1.35α4φ4+0.95α5φ5+0.85α6φ6+1.25α7φ7;

[0133] (3) When the gas concentration inside the hole is greater than 16 g / m 3 Here, the pore gas concentration refers to the pore gas concentration data collected in step one using advanced detection technology. The preliminary RLGT value calculation formula is:

[0134] RLGT=(1.15+x)α1φ1+(1.05+x)α2φ2+(1.1+x)α3φ3+(1.35+x)α4φ4+(0.95+x)α5φ5+(0.85+x)α6φ6+(1.25+x)α7φ7, where

[0135] Table 3: Main Geophysical Exploration Techniques for Tunnels

[0136]

[0137]

[0138] Step 5: Measure other influencing factors inside the cave, and calculate the weight of each influencing factor based on its labeling and assignment results using the analytic hierarchy process (AHP). The AHP calculation process here is the same as that in Step 3 above.

[0139] Other influencing factors include on-site measured concentrations of carbon dioxide, hydrogen sulfide, and carbon monoxide, as well as wind speed data, with the weights of these other influencing factors labeled as follows: The weights of these four influencing factors are specifically marked as follows: Influencing factors can be added or removed here depending on the specific circumstances on site;

[0140] Step 6: Combine the preliminary RLGT value from Step 4 with the weight values ​​of other influencing factors from Step 5, calculate the final tunnel gas risk level RLGT' value, and determine the final tunnel gas level based on the RLGT' value.

[0141] The formula for calculating RLGT' is:

[0142]

[0143] When the value of RLGT' is 0-35, the tunnel is a gas-free tunnel; when the value of RLGT' is 36-85, the tunnel is a micro-gas tunnel; when the value of RLGT' is 86-135, the tunnel is a low-gas tunnel; when the value of RLGT' is 136-185, the tunnel is a high-gas tunnel; when RLGT'>186, the tunnel is an ultra-high-gas tunnel with a risk of gas outburst, and is a gas outburst tunnel.

[0144] Example 2:

[0145] This embodiment applies the method of Embodiment 1 to the construction of a high-gas tunnel in the Zigong-Yibin section. This tunnel is two kilometers long. Advanced geological exploration technology was used to detect the gas concentration within the boreholes, dividing this area into three levels:

[0146] Level 1, gas concentration inside the pore is less than 5 g / m³ 3 Level 2: Methane concentration inside the pore is greater than or equal to 5 g / m³ 3 And less than or equal to 16g / m 3 Level 3, methane concentration inside the pore is greater than 16 g / m³ 3 ;

[0147] Furthermore, advanced detection can also detect the groundwater situation and geological lithology ahead. The detected groundwater is divided into three situations: no groundwater, groundwater development, and groundwater underdevelopment; the lithology is mainly divided into three levels: level three, level four, and level five surrounding rocks, which is very obvious; if there is groundwater, some gas will dissolve in the water, so the gas concentration will decrease, while the surrounding rock is weak and broken, and the surrounding fissures and voids increase, making it easier for gas to diffuse. Therefore, based on this, different geological conditions are divided into seven influencing factors: (1) stratum lithology; (2) geological structure; (3) coal seam thickness; (4) tunnel burial depth; (5) hydrogeological conditions; (6) tunnel temperature; (7) other flammable and harmful gases;

[0148] Furthermore, these seven categories are denoted as α1, α2, α3, α4, α5, α6, and α7 based on their weighted impact on gas concentration; where:

[0149] (1) The stratigraphic lithology is denoted as α1:

[0150] When studying the geological characteristics of tunnels traversing coal-bearing strata, the focus is on the extent to which coal seams affect gas storage or dissipation. The influence of coal seams on gas occurrence and migration patterns is mainly determined by their permeability and gas-tightness. Generally speaking, when the roof rock of a coal seam is relatively intact and forms a self-contained whole, such as shale, gas in the coal is easily stored. When the roof rock is volcanic or fractured, such as sandstone, gas is more easily dissipated.

[0151] Assign a value to α1 based on the detection data:

[0152] The more intact and dense the surrounding rock, the easier it is for gas to be preserved in the surrounding rock. Therefore, based on the lithology of the surrounding rock from low to high, corresponding to lithology levels three, four, and five, the α1 values ​​are assigned to 0–10, 11–20, and 21–30 respectively.

[0153] (2) Geological structure α2:

[0154] Geological structures, such as anticlines, synclines, and faults, have a significant impact on gas escape. Anticlines are prone to forming oil and gas enrichment zones, and faults also have a prominent effect on gas escape. The sealing properties of geological structures are the primary consideration in gas classification.

[0155] The higher the sealing of a geological structure, the less likely gas is to escape, and the higher the corresponding risk level. Based on detection data, regarding α2 malfeasance:

[0156] When the coal seam is open and exposed in a geological structure, α2 is assigned a value of 0–10; when the coal seam is in a connected geological structure, α2 is assigned a value of 11–20; when the coal seam is in a closed geological structure, α2 is assigned a value of 21–30.

[0157] (3) Coal seam thickness α3:

[0158] The thickness of the coal seam directly determines the amount of gas emitted. Based on the detection data, a value is assigned to α3:

[0159] When the coal seam thickness is <1m, α3 is assigned a value of 0-10; when the coal seam thickness is 1-3m, α3 is assigned a value of 11-15; when the coal seam thickness is >3m, α3 is assigned a value of 16-20.

[0160] (4) Tunnel depth α4:

[0161] In tunnel engineering, 300m is generally used as a dividing line. The deeper the tunnel is buried, the greater the pressure, and the more dangerous the effects of gas escape and gas outburst.

[0162] Assign a value to α4 based on the detection data:

[0163] When the tunnel depth is less than 300m, α4 is assigned a value of 0 to 10; when the tunnel depth is 300 to 500m, α4 is assigned a value of 10 to 15; when the tunnel depth is greater than 500m, α4 is assigned a value of 15 to 25.

[0164] (5) Hydrogeology α5:

[0165] Hydrogeology mainly considers the impact of groundwater. Generally speaking, the more groundwater there is, the lower the corresponding gas content.

[0166] Assign a value to α5 based on the detection data:

[0167] When the groundwater volume is >3500m 3 When / d, α5 is assigned a value of 0 to 5; when the groundwater volume is 150 to 3500 m³. 3 When the groundwater volume is less than 150m³, α5 is assigned a value of 5 to 15. 3 When / d, α5 is assigned a value of 15 to 20;

[0168] (6) Temperature inside the cave α6:

[0169] The temperature inside the tunnel mainly considers the impact of temperature changes during tunnel construction on gas escape and consequently on gas concentration within the tunnel. Generally speaking, for gas tunnels passing under oil and gas fields, the higher the temperature inside the tunnel, the higher the corresponding gas content and concentration.

[0170] The value of α6 is assigned based on the temperature inside the cave as reported by monitoring data:

[0171] When the temperature inside the cave is <20℃, α6 is assigned a value of 0 to 5; when the temperature inside the cave is 20 to 30℃, α6 is assigned a value of 5 to 15; when the temperature inside the cave is >30℃, α6 is assigned a value of 15 to 20.

[0172] (7) Other flammable and harmful gases, etc. α7:

[0173] Other flammable and harmful gases mainly include hydrogen sulfide, carbon monoxide and other flammable and harmful gases. The occurrence of gas disasters in high-gas tunnels passing under oil and gas fields is often unpredictable and complex. One of the main reasons is that there may be more than one flammable gas. If other flammable and harmful gases such as hydrogen sulfide and carbon monoxide are found during the advance detection process, this factor should also be taken into account when determining the gas level of the tunnel.

[0174] The value of α7 is assigned based on the advanced drilling:

[0175] When advanced drilling discovers harmful gases such as hydrogen sulfide, carbon monoxide, and carbon dioxide, and the content of these components is not less than 0.0024%, α7 is assigned a value of 10–20; when advanced drilling discovers harmful gases such as hydrogen sulfide, carbon monoxide, and carbon dioxide, but the content of these components is less than 0.0006%, α7 is assigned a value of 5–10; when advanced drilling does not discover harmful gases such as hydrogen sulfide, carbon monoxide, and carbon dioxide, α7 is assigned a value of 0–5.

[0176] Furthermore, the weights of the above indicators are calculated using the analytic hierarchy process (AHP).

[0177] Based on past scholarly experience and practical engineering considerations, the Analytic Hierarchy Process (AHP) is used to quantify the relative importance of each indicator and determine the influence weights of relevant indicators, including:

[0178] (1) Construct a judgment matrix that reflects the importance of each pair of indicators:

[0179] (2) Check for consistency:

[0180] Determine the consistency index (CI) and consistency ratio (CR) of matrix A;

[0181] (3) Calculate the eigenvector corresponding to the largest eigenvalue of the judgment matrix, that is, the weight vector of the corresponding indicator at this level corresponds to the weight value of each indicator;

[0182] Based on geological survey methods and primarily using advanced drilling methods, and taking into account the varying technical characteristics and on-site applicability, a comprehensive approach is adopted, including geophysical exploration techniques such as seismic wave reflection, seismic wave refraction, and high-density electrical resistivity tomography (Table 3). Based on the weighted impact of gas concentration within the advanced borehole and changes in surrounding rock, geological structure, and groundwater on gas emission, the tunnel gas risk level is calculated independently in the following scenarios:

[0183] (1) The gas concentration inside the hole is less than 5 g / m³ 3 The formula used is:

[0184] RLGT=0.95α1φ1+1.05α2φ2+1.1α3φ3+1.15α4φ4+0.75α5φ5+0.8α6φ6+1.2α7φ7, where RLGT represents the tunnel gas risk classification;

[0185] (2) The gas concentration inside the hole is greater than or equal to 5 g / m³ 3 And less than or equal to 16g / m 3 The formula used is:

[0186] RLGT=1.15α1φ1+1.05α2φ2+1.1α3φ3+1.35α4φ4+0.95α5φ5+0.85α6φ6+1.25α7φ7;

[0187] (2) The gas concentration inside the hole is greater than 16 g / m³ 3 The formula used is:

[0188] RLGT=(1.15+x)α1φ1+(1.05+x)α2φ2+(1.1+x)α3φ3+(1.35+x)α4φ4+(0.95+x)α5φ5+(0.85+x)α6φ6+(1.25+x)α7φ7, where

[0189] Furthermore, based on the RLGT value, a preliminary assessment of the tunnel's gas risk level is made:

[0190] When RLGT is 0-25, the tunnel is a gas-free tunnel; when RLGT is 26-75, the tunnel is a micro-gas tunnel; when RLGT is 76-125, the tunnel is a low-gas tunnel; when RLGT is 126-175, the tunnel is a high-gas tunnel.

[0191] Furthermore, based on the analytic hierarchy process (AHP) in section 4), the weights of factors affecting the gas tunnel level after tunnel excavation were calculated. Since the existence of objectively variable factors such as on-site measured data, including carbon dioxide concentration, hydrogen sulfide concentration, carbon monoxide concentration, and wind speed, also affects the gas risk, the AHP was used to calculate and assign weights to these factors.

[0192] This section only considers four influencing factors: carbon dioxide concentration, carbon monoxide concentration, hydrogen sulfide concentration, and wind speed. Influencing factors can be added or removed here depending on the specific circumstances on site;

[0193] Further, the RLGT calculated in 5) is compared with... Calculation yields

[0194] Where Y represents the maximum measured values ​​of carbon dioxide concentration, carbon monoxide concentration, hydrogen sulfide concentration, and wind speed on that day;

[0195] Furthermore, based on the gas concentration in the advanced detection borehole, a gas classification system for gas tunnels is established according to the calculation results of RLGT under different classifications:

[0196] When the value of RLGT' is 0-35, the tunnel is a gas-free tunnel; when the value of RLGT' is 36-85, the tunnel is a micro-gas tunnel; when the value of RLGT' is 86-135, the tunnel is a low-gas tunnel; when the value of RLGT' is 136-185, the tunnel is a high-gas tunnel; when RLGT'>186, the tunnel is an ultra-high-gas tunnel with a risk of gas outburst, and is classified as a gas outburst tunnel.

[0197] According to Appendix 1, the hazard levels of gas tunnels are refined. Different gas risk levels are determined based on different advanced detection data, and different countermeasures are taken. This ensures construction safety while significantly reducing construction costs, providing a reference for gas tunnel engineering. The above describes the basic principles, main features, and advantages of this invention. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for classifying high-gas levels in tunnels based on the analytic hierarchy process (AHP), characterized in that: include Step 1: Collect data inside the tunnel using advanced tunnel gas detection technology to form detection data; Step 2: Combining the data table and stratigraphic characterization of the detection data in the detection data, mark and classify the factors affecting gas concentration, and assign values ​​to the classification results; The classification of factors affecting gas concentration in step 2 includes: stratigraphy and lithology. Geological structure Coal seam thickness Tunnel depth Hydrogeology Temperature inside the cave Other harmful gases Other harmful gases include hydrogen sulfide, carbon monoxide, and carbon dioxide; Step 3: Based on the classification results of Step 2, use the analytic hierarchy process (AHP) to calculate the weights of the factors affecting gas concentration in Step 2. Step 4: Combining the classification results from Step 2 with the weights of the factors influencing gas concentration from Step 3, calculate the preliminary RLGT value and perform preliminary classification of gas in the tunnel. Step 5: Measure other influencing factors inside the cave, mark them, and calculate the weight of each influencing factor using the analytic hierarchy process (AHP). Step 6: Combining the preliminary RLGT value from Step 4 and the weight values ​​of other influencing factors from Step 5, calculate the final risk level RLGT' value for tunnel gas and perform the final classification of gas in the tunnel. Other influencing factors in step 5 include carbon dioxide, carbon monoxide, hydrogen sulfide, and wind speed. The weights of these other influencing factors are labeled as follows: The weights of each influencing factor are labeled as follows: , , , ; The value is calculated as follows: ； In the above formula, This indicates the measured maximum values ​​of carbon dioxide, carbon monoxide, hydrogen sulfide, and wind speed. Step 4, the preliminary RLGT value calculation process, includes: (1) When the gas concentration inside the hole is less than 5 The calculation formula is: RLGT=0.95 +1.05 +1.1 +1.15 +0.75 +0.8 +1.2 ; (2) When the gas concentration inside the orifice is greater than or equal to 5 And less than or equal to 16 The calculation formula is: RLGT=1.15 +1.05 +1.1 +1.35 +0.95 +0.85 +1.25 ; (3) When the gas concentration inside the hole is greater than 16 The calculation formula is: RLGT = (1.15 + x) +(1.05+x) +(1.1+x) +(1.35+x) +(0.95+x) +(0.85+x) +(1.25+x) , where x (0, 0.5); The process of determining the final risk level of tunnel gas based on the RLGT' value in step 6 includes: When RLGT' is 0~35, the tunnel is a gas-free tunnel; When RLGT' is 36~85, the tunnel is a microgas tunnel; When RLGT' is 86~135, the tunnel is a low-gas tunnel; When RLGT' is 136~185, the tunnel is a high-gas tunnel; When RLGT'>186, the tunnel is an ultra-high gas tunnel with a risk of gas outburst, and is therefore a gas outburst tunnel.

2. The tunnel high-gas classification method based on the analytic hierarchy process according to claim 1, characterized in that: lithology of stratigraphy Assignment: The surrounding rock lithology is classified as level three. Assign a value between 0 and 10; The surrounding rock lithology is classified as level four. Assign values ​​from 11 to 20; The surrounding rock lithology is grade five. Assign values ​​between 21 and 30; Geological structure Assignment: When coal seams are exposed and open within geological structures Assign a value between 0 and 10; When the coal seam is in a connected geological structure Assign values ​​from 11 to 20; When the coal seam is in a closed geological structure Assign values ​​from 21 to 30; Regarding coal seam thickness Assignment: When the coal seam thickness is <1m Assign a value between 0 and 10; When the coal seam thickness is 1~3m Assign values ​​from 11 to 15; When the coal seam thickness is >3m Assign values ​​from 16 to 20; tunnel burial depth Assignment: When the tunnel depth is less than 300m, Assign a value between 0 and 10; When the tunnel depth is 300~500m, Assign a value of 10~15; When the tunnel depth is >500m Assign values ​​from 15 to 25; Hydrogeology Assignment: When groundwater volume > 3500 hour, Assign a value between 0 and 5; When the groundwater volume is 150~3500 At that time, Assign values ​​from 5 to 15; When groundwater volume <150 hour, Assign values ​​of 15 to 20; Temperature inside the cave Assignment: When the temperature inside the cave is <20℃ Assign a value between 0 and 5; When the temperature inside the cave is 20~30℃ Assign values ​​from 5 to 15; When the temperature inside the cave is >30℃ Assign values ​​of 15 to 20; For other harmful gases Assignment: When the content of flammable and harmful gas components is not less than 0.0024%, Assign a value of 10~20; When the content of flammable and harmful gas components is less than 0.0006%, Assign values ​​from 5 to 10; When advanced drilling fails to detect flammable or harmful gases Assign a value between 0 and 5.

3. The tunnel high-gas classification method based on the analytic hierarchy process according to claim 1, characterized in that: The weight calculation process for each influencing factor in step 3 includes: (1) Construct a judgment matrix A that reflects the importance of each pair of influencing factors: ； Where n represents the number of influencing factors, Indicating influencing factors and influencing factors The relative importance of the comparisons between them, when i=j, When i ≠ j, ; (2) Calculate the consistency index CI and consistency ratio CR of matrix A: ； ； in, The largest eigenvalue of the judgment matrix is ​​RI, and the average random consistency index of the judgment matrix is ​​RI. (3) Calculate the eigenvector corresponding to the largest eigenvalue of matrix A: ； ； in, This represents the nth root of the product of each element in row j. This represents the weight of the j-th influencing factor.

4. The tunnel high-gas classification method based on the analytic hierarchy process according to claim 1, characterized in that: The process of determining the preliminary risk level of tunnel gas in step 4 based on the RLGT value includes: When RLGT is between 0 and 25, the tunnel is a gas-free tunnel; When RLGT is between 26 and 75, the tunnel is a microgas tunnel; When RLGT is between 76 and 125, the tunnel is a low-gas tunnel. When RLGT is between 126 and 175, the tunnel is a high-gas tunnel.

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