Coal measure stratum tunnel gas section grading evaluation method

Abstract

A method for segmented and graded evaluation of gas in coal-bearing strata tunnels includes the following steps: Based on the regional coal and petrological background and regional geological conditions, the tunnel body is divided into engineering geological segments; test boreholes are arranged to measure the resistivity of the coal-bearing strata and the gas content per ton of coal; the relationship between the gas content per ton of coal and the resistivity is fitted as Q0 = 6.07 × e (‑p / 199.46) +0.33; Exploration boreholes were arranged in engineering geological sections. The coal-bearing strata sections of the tunnel were calculated based on their occurrence. The resistivity inside the boreholes was measured through comprehensive borehole logging tests. Based on the measured resistivity inside the boreholes, the gas content per ton of coal in each test borehole was calculated, and the variation curve of gas content per ton of coal in the coal-bearing tunnel was plotted. A comprehensive gas evaluation was conducted for each tunnel section. By dividing the tunnel into engineering geological sections and fitting the relationship between gas content per ton of coal and resistivity, the gas concentration detection and emission calculation are reduced while ensuring continuous exploration, shortening the exploration cycle and saving exploration costs.

Description

Technical Field

[0001] This invention relates to tunnel engineering, and in particular to a method for segmented and graded evaluation of gas in coal-bearing strata tunnels. Background Technology

[0002] The geological conditions along railway and highway lines in the southwestern mountainous region are complex, with diverse geological structures, well-developed faults, and a complete range of rock types, including igneous, metamorphic, and sedimentary rocks. A large number of coal-bearing strata tunnels have emerged during the planning and construction of railways and highways. For a long time, encountering harmful gases during tunnel construction has been a major challenge to safe tunnel construction and one of the main types of common tunnel engineering defects. From the first gas explosion on the Yunnan-Guizhou Railway's Yanjiaozhai Tunnel to the gas explosion at the Dongjiashan Tunnel site on the Dujiangyan-Wenchuan Expressway in Sichuan, both have resulted in enormous loss of life and property. Therefore, strengthening research on harmful gases during the tunnel survey and design phase is essential.

[0003] Currently, the investigation of methane and hazardous gases in tunnels mainly relies on independent data collection, geological mapping, and exploration testing. The data collection phase primarily gathers regional geological, mineral geological, hydrogeological, and hazardous gas area survey data. Geological mapping focuses on the lithology of gas-bearing strata, the structural location and closed-loop structures of coal-bearing strata, oil and gas layers, and oil shale layers. These methods are mostly qualitative or semi-qualitative / semi-quantitative studies, requiring significant manpower and resources, and have limited accuracy. Exploration testing mainly relies on drilling, combined with geophysical well drilling and field testing. Its primary purpose is to identify the characteristics of coal, oil shale, oil and gas bodies, and hazardous gases. This method offers high accuracy, but requires numerous boreholes and methane concentration and emission rate tests, resulting in long investigation cycles and significantly increased costs. Therefore, there is an urgent need for a high-accuracy, low-cost method for segmented and graded evaluation of methane in coal-bearing strata tunnels. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for segmented and graded evaluation of gas in coal-bearing strata tunnels, so as to effectively reduce the exploration cycle, save exploration costs and improve exploration accuracy.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] This invention discloses a method for segmented and graded evaluation of gas in coal-bearing strata tunnels, comprising the following steps:

[0007] ①Based on the regional coal and rock geological background and tunnel geological conditions, the tunnel body is divided into engineering geological sections;

[0008] ② Test boreholes were arranged on the engineering geological sections to measure the resistivity of the coal-bearing strata, and the content of methane and harmful gases was detected in the same test borehole. The relationship between the methane content and resistivity per ton of coal was obtained by fitting analysis as shown in equation (1):

[0009] Q0 = 6.07 × e (-p / 199.46) +0.33 (1)

[0010] In the formula, Q0 represents the gas content per ton of coal in the coal-bearing strata, in m³. 3 / t; p is the resistivity of the coal-bearing strata;

[0011] ③ Arrange several drilling exploration holes on the engineering geological section, infer the coal-bearing strata section of the tunnel body based on the occurrence, and measure the resistivity in the exploration hole through comprehensive logging test in the hole;

[0012] ④ Based on the measured magnetic resistivity in the exploration boreholes, calculate the gas content per ton of coal in each test borehole of the tunnel, plot the variation curve of gas content per ton of coal in coal-bearing tunnels, and conduct a comprehensive gas evaluation of the tunnel sections according to the following table of hazard level judgment for gas sections in coal-bearing strata tunnels:

[0013]

[0014] The basis for the engineering geological segmentation in step ① includes coal-bearing strata such as coal seams, carbonaceous layers, oil-bearing layers, and asphaltite layers in coal-bearing strata tunnels, as well as low-resistivity anomaly zones / resistivity variation zones in areas affected by tectonic activity, such as anticlines, fault zones, densely jointed zones, and areas of intense crustal activity.

[0015] Step ③ involves inferring the coal-bearing strata section of the tunnel body based on its occurrence, and revealing the occurrence, location, and thickness of the coal-bearing strata through drilling exploration boreholes, wherein:

[0016] Apparent dip angle of coal-bearing strata Calculate according to equation (2):

[0017]

[0018] In the formula, α is the true dip angle of the coal-bearing strata, in °; ω is the angle between the true dip and apparent dip of the coal-bearing strata, in °; β is the angle between the strike of the coal-bearing strata and the tunnel axis, in °.

[0019] The relationship between the angle ω between the true dip and apparent dip of the coal-bearing strata and the angle β between the strike of the coal-bearing strata and the tunnel axis is shown in equation (3):

[0020] ω+β=90°(3)

[0021] The true thickness H of the coal-bearing strata revealed by drilling exploration boreholes is calculated according to formula (4):

[0022]

[0023] In the formula, M is the thickness of the coal-bearing strata revealed by the drilling exploration borehole, in meters;

[0024] Based on the true thickness, apparent dip angle, and strike of the coal-bearing strata revealed by the drilling exploration boreholes, the mileage range and length of the coal-bearing strata in the tunnel body are calculated. The length L of the coal-bearing strata in the tunnel body section is calculated according to formula (5):

[0025]

[0026] The beneficial effects of this invention are that it divides the tunnel section into several engineering geological segments, and drills in each segment to reduce the number of boreholes; it obtains the relationship between the resistivity of coal-bearing strata and the gas content per ton of coal through fitting analysis, which reduces gas concentration and emission tests while ensuring continuous exploration; this exploration and evaluation method can effectively shorten the exploration cycle, save exploration costs, and improve exploration accuracy. Attached Figure Description

[0027] Figure 1 This is a flowchart of a method for segmented and graded evaluation of gas in coal-bearing strata tunnels according to the present invention;

[0028] Figure 2 This is a schematic diagram of the tunnel body section in a coal-bearing stratum based on engineering geological segmentation;

[0029] Figure 3 It is the relationship between the resistivity of coal-bearing strata and the gas content per ton of coal;

[0030] Figure 4 This is a structural schematic diagram of the apparent dip angle and the true dip angle of the coal-bearing strata tunnel;

[0031] Figure 5 This is a structural diagram of the coal-bearing strata section in the tunnel body, calculated based on the thickness and occurrence of the coal-bearing strata revealed by drilling exploration boreholes.

[0032] Figure 6 This is a diagram showing the results of the gas content per ton of coal and the work area level in the tunnel section of the coal-bearing strata based on the gas segmentation and grading evaluation in Example 1.

[0033] The markings in the diagram and their meanings are as follows: 1 - Tunnel, 2 - Tunnel body, 3 - Engineering geological section, 4 - Engineering geological section interface, 5 - Coal-bearing strata, 6 - Drilling exploration hole, 7 - Fault. Detailed Implementation

[0034] 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 a part of the embodiments of the present invention, and not all of them. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] The technical flowchart of the method for segmented and graded evaluation of gas in coal-bearing strata tunnels of this invention is as follows: Figure 1 As shown, the method includes steps ① to ④.

[0036] In step ①, the tunnel body is divided into engineering geological sections based on the regional coal and rock geological background and tunnel geological conditions;

[0037] The engineering geological segmentation is based on strata including coal-bearing, carbonaceous, oil-bearing, and asphaltite rock layers in coal-bearing strata tunnels, as well as low-resistivity anomaly zones / resistivity variation zones in areas affected by tectonic activity such as anticlines, fault zones, densely jointed zones, and areas of intense crustal activity.

[0038] Figure 2 This is a schematic diagram of the tunnel section in coal-bearing strata based on engineering geological segmentation, according to the present invention. See also... Figure 2 Based on the coal seam, carbonaceous layer, oil layer, asphalt rock layer, etc., and the areas affected by tectonic activities such as anticline structure, fault zone, dense joint zone, and strong crustal activity zone, the tunnel is divided into several engineering geological segments according to the engineering geological segmentation interface.

[0039] In step ②, test boreholes are arranged on the engineering geological section to measure the resistivity of the coal-bearing strata, as shown in Table 1:

[0040] Table 1

[0041]

[0042] Gas content measurements were conducted per ton of coal in the same test well. Figure 3 The present invention relates the resistivity of coal-bearing strata to the gas content per ton of coal. The fitting analysis yields the relationship between the gas content per ton of coal and the resistivity as shown in equation (1):

[0043] Q0 = 6.07 * e (-p / 199.46) +0.33 (1)

[0044] In the formula, Q0 represents the gas content per ton of coal in the coal-bearing strata, in m³. 3 / t; p—resistivity of coal-bearing strata.

[0045] In step ③, several exploration boreholes are arranged on the engineering geological section, and the coal-bearing strata section of the tunnel body is inferred based on the occurrence. The resistivity inside the exploration borehole is measured by comprehensive logging tests inside the borehole.

[0046] Among them, several exploration holes are arranged on the engineering geological section. The spacing between the exploration holes should be 2 to 3 times the hole depth, and the hole depth of each exploration hole should exceed the tunnel foundation by 10 to 50m.

[0047] Figure 4 This is a structural schematic diagram showing the apparent dip angle of a tunnel in a coal-bearing stratum and the true dip angle of the coal-bearing strata. (See also...) Figure 4 The section of coal-bearing strata in the tunnel body, inferred from its occurrence, is revealed through drilling exploration boreholes, which show the occurrence, location, and thickness of the coal-bearing strata. The apparent dip angle of the coal-bearing strata is also mentioned. Calculate according to formula (2):

[0048]

[0049] In the formula, α—true dip angle of the coal-bearing strata, in °; ω—angle between the true dip and apparent dip of the coal-bearing strata, in °; β—angle between the strike of the coal-bearing strata and the tunnel axis, in °;

[0050] The relationship between the angle ω between the true dip and apparent dip of the coal-bearing strata and the angle β between the strike of the coal-bearing strata and the tunnel axis is as shown in equation (3):

[0051] ω+β=90° (3)

[0052] Figure 6 This is a structural diagram illustrating the coal-bearing strata sections within the tunnel body, calculated based on the thickness and occurrence of the coal-bearing strata revealed by drilling exploration boreholes. (See also...) Figure 6 The true thickness H of the coal-bearing strata revealed by the drilling exploration boreholes is calculated according to formula (4):

[0053]

[0054] In the formula, M represents the thickness of the coal-bearing strata revealed by the drilling borehole, in meters (m).

[0055] Based on the true thickness, apparent dip angle, and strike of the coal-bearing strata revealed by the drilling exploration boreholes, the mileage range and length of the coal-bearing strata in the tunnel body are calculated. The length L of the coal-bearing strata in the tunnel body section is calculated according to formula (5):

[0056]

[0057] In step ④4, based on the measured resistivity in the exploration boreholes, the gas content per ton of coal in each test borehole of the tunnel is calculated, and a comprehensive gas evaluation is performed on the tunnel sections. Table 3 is a table for judging the hazard level of gas sections in coal-bearing strata tunnels. A comprehensive gas evaluation is performed on the tunnel sections.

[0058] Table 3

[0059]

[0060] The drilling exploration holes include vertical exploration holes, horizontal exploration holes, upward-sloping exploration holes, and downward-sloping exploration holes.

[0061] Example 1

[0062] See Figure 6 A railway tunnel in a mountainous area of ​​southwestern China is approximately 24,069 meters long, with a maximum burial depth of about 1,350 meters. By combining regional geological data collection, on-site geological mapping, and geophysical exploration, the geological conditions of the tunnel site were determined, and a geological longitudinal profile map of the tunnel was drawn. Based on the engineering geological segmentation criteria, the tunnel is divided into six engineering geological segments, primarily using major engineering geological segment interfaces such as coal-bearing strata and faults as boundaries.

[0063] Six exploration boreholes are arranged on the engineering geological section, and the depth of each exploration borehole must exceed the tunnel base by 10-50m. The resistivity value inside the exploration borehole is obtained by testing inside the borehole. Substituting into formula (1), the gas content value per ton of coal in the six exploration boreholes can be calculated. According to Table 3, the gas hazard of the tunnel exploration boreholes is evaluated. Table 4 shows the test data and gas hazard level of the exploration boreholes in the coal-bearing strata tunnel.

[0064] Table 4

[0065]

[0066] Based on the thickness and occurrence of the coal-bearing strata revealed by the drilling exploration boreholes, the coal-bearing strata sections of the tunnel body can be calculated according to formulas (2) to (5). According to Tables 4 and 5, the specific gas sections and hazard levels of the coal-bearing strata tunnel can be identified. A total of 7 gas sections are divided, including 1 high-gas section with a total length of 3500m; 3 low-gas sections with a total length of 11700m; and 3 micro-gas sections with a total length of 8869m.

[0067] Table 5

[0068]

[0069] Based on Tables 4 and 5, the specific gas sections and hazard levels of the coal-bearing strata tunnel can be identified. This method reduces the number of boreholes by dividing the tunnel section into several engineering geological sections and drilling in each section. By fitting analysis, the relationship between the resistivity of the coal-bearing strata and the gas content per ton of coal is obtained, reducing gas concentration and emission tests while ensuring continuous exploration. This exploration and evaluation method can effectively shorten the exploration cycle, save exploration costs, and improve exploration accuracy.

[0070] This method can also be used for gas segmentation exploration and evaluation in coal-bearing strata tunnels such as hydropower stations, water diversion tunnels, underground caverns, and coal mines, as well as for gas segmentation exploration and evaluation in strata such as carbonaceous layers, oil-bearing layers, and bituminous rock layers.

[0071] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Elements and features described in one drawing or embodiment of the present invention may be combined with elements and features shown in one or more other drawings or embodiments. It should be noted that, for clarity, representations and descriptions of components and processes unrelated to the present invention and known to those skilled in the art have been omitted from the drawings and descriptions. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0072] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment includes only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for segmented and graded evaluation of gas in coal-bearing strata tunnels, comprising the following steps: ①Based on the regional coal and rock geological background and tunnel geological conditions, the tunnel body is divided into engineering geological sections; ② Test boreholes were arranged on the engineering geological sections to measure the resistivity of the coal-bearing strata, and the content of methane and harmful gases was detected in the same test borehole. The relationship between the methane content and resistivity per ton of coal was obtained by fitting analysis as shown in equation (1): 　　　　　　　　（1） In the formula, Q0 represents the gas content per ton of coal in the coal-bearing strata, in m³. 3 / t; p Resistivity of coal-bearing strata; ③ Arrange several drilling exploration holes on the engineering geological section, infer the coal-bearing strata section of the tunnel body based on the occurrence, and measure the resistivity in the exploration hole through comprehensive logging test in the hole; ④ Based on the measured magnetic resistivity in the exploration boreholes, calculate the gas content per ton of coal in each test borehole of the tunnel, plot the variation curve of gas content per ton of coal in coal-bearing tunnels, and conduct a comprehensive gas evaluation of the tunnel sections according to the following table of hazard level judgment for gas sections in coal-bearing strata tunnels: In step ③, the spacing between the exploration holes is 1.5 to 3 times the hole depth, and the hole depth of each exploration hole must exceed the tunnel foundation by 10 to 50 m.

2. The method for segmented and graded evaluation of gas in coal-bearing strata tunnels as described in claim 1, characterized in that: Step ③ involves inferring the coal-bearing strata section of the tunnel body based on its occurrence, and revealing the occurrence, location, and thickness of the coal-bearing strata through drilling exploration boreholes, wherein: The apparent dip angle φ of the coal-bearing strata is calculated according to equation (2): （2） In the formula, α This represents the true dip angle of the coal-bearing strata, in degrees. ω The angle between the true dip and apparent dip of the coal-bearing strata is expressed in degrees. β The angle between the strike of the coal-bearing strata and the tunnel axis is expressed in degrees. The angle between the true dip and apparent dip of coal-bearing strata ω The angle between the strike of the coal-bearing strata and the tunnel axis β The relationship is as shown in equation (3): 　　　　　　　　　　（3） Drilling exploration boreholes reveal the true thickness of coal-bearing strata H Calculate according to formula (4): 　　　　　　　　　　（4） In the formula, M Thickness of coal-bearing strata revealed by drilling exploration boreholes, in meters; Based on the true thickness, apparent dip angle, and strike of the coal-bearing strata revealed by drilling exploration boreholes, the mileage range and length of the coal-bearing strata within the tunnel body are calculated, including the length of the coal-bearing strata within the tunnel body section. L Calculate according to formula (5): 　　　　　　　　　　（5）。 3. The method for segmented and graded evaluation of gas in coal-bearing strata tunnels as described in claim 1, characterized in that: The drilling exploration holes include vertical exploration holes, horizontal exploration holes, upward-sloping exploration holes, and downward-sloping exploration holes.

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