A combustible gas detection method and module for tunnel engineering

Abstract

The present invention belongs to the field of tunnel engineering, and relates to a combustible gas detection method and module for tunnel engineering. By extracting the grayscale value and contrast of each pixel point in a three-dimensional geological structure map, a first data sample and a second data sample are established respectively; the normal distribution map of the first data sample and the second data sample are obtained respectively; the data outside the confidence interval of the normal distribution map are extracted from the first data sample and the second data sample to establish a first data set and a second data set; according to the coordinates of the pixel points, the grayscale value of the first data set and the contrast of the second data set are coordinate matched; if the match is successful, it is determined whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval; if it falls within the numerical simulation interval, the first detection result is output; if it does not fall within the numerical simulation interval, the second detection result is output. The present invention can detect whether there is combustible gas in the surrounding rock structure in front of the tunnel excavation face.

Description

Technical Field

[0001] The present invention relates to the field of tunnel engineering, and in particular to a combustible gas detection method and module for tunnel engineering. Background Art

[0002] In tunnel engineering, the elastic wave advanced geological prediction instrument is used to detect the surrounding rock structure and geological conditions in front of the tunnel excavation face. The elastic wave advanced geological prediction instrument consists of a vibration source, a detector and an analyzer. Among them, the vibration source excites elastic waves near the tunnel side wall or the face, and the elastic waves propagate in the three-dimensional space in the form of spherical waves; when the elastic waves encounter the interface with wave impedance difference, reflection occurs; the reflected wave signal is received by the detector arranged in the tunnel; the detector converts the received reflected wave signal, amplifies the signal, filters the signal, digitizes the signal, adds a time mark, extracts the characteristic information such as the amplitude, frequency and phase of the reflected wave signal, and sends the processed signal to the analyzer; the analyzer amplifies the received signal, filters the signal, analyzes the time domain, analyzes the frequency domain, performs interference processing and inversion imaging, and finally presents the geological structure in front of the tunnel excavation face in the form of three-dimensional imaging. The three-dimensional geological structure map is professionally analyzed by professionals to obtain the geological conditions in front of the tunnel excavation face.

[0003] However, some rock masses (such as shale) may store a large amount of combustible gas in their pore structures. Three-dimensional imaging can only reflect the surrounding rock structure in front of the tunnel excavation face, but cannot reflect whether there is combustible gas stored in the surrounding rock. In actual tunnel engineering, when it is detected that there are rock structures such as shale, sandstone, carbonate, etc. that may store combustible gas in front of the tunnel excavation face, in order to prevent danger caused by combustible gas leakage during excavation, gas detectors are usually used in advance to monitor the concentration of combustible gas in the tunnel in real time. As we all know, gas detectors can only obtain effective detection results when the concentration of a certain gas in the air reaches a detectable value, and there is a lag. That is, when the gas detector detects the presence of a certain combustible gas in the tunnel, the combustible gas has already leaked and reached a certain concentration within the detection space. Therefore, in actual tunnel engineering, even if a gas detector is used in advance to detect whether there is combustible gas in the tunnel space in real time, there is still the possibility of danger caused by combustible gas leakage.

[0004] In view of this, this application is hereby filed. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing elastic wave advanced geological prediction instrument can only detect the geological structure in front of the tunnel excavation face in the form of three-dimensional imaging, but cannot detect whether there is combustible gas in the surrounding rock structure in front of the tunnel excavation face.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, a combustible gas detection method for tunnel engineering is proposed, comprising the following steps: extracting the grayscale value of each pixel point in a three-dimensional geological structure map to establish a first data sample; extracting the contrast of each pixel point in the three-dimensional geological structure map to establish a second data sample; obtaining a first normal distribution map of the first data sample; obtaining a second normal distribution map of the second data sample; extracting all grayscale values ​​outside the confidence interval of the first normal distribution map from the first data sample to establish a first data set; extracting all contrasts outside the confidence interval of the second normal distribution map from the second data sample to establish a second data set. two data sets; according to the pixel coordinates, coordinate matching is performed on the grayscale value of the first data set and the contrast of the second data set; if the match is successful, it is determined whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval; if it falls within the numerical simulation interval, a first detection result is output; if it does not fall within the numerical simulation interval, a second detection result is output; the numerical simulation interval is composed of simulation values ​​of the amplitude attenuation rate of the elastic wave when propagating in a variety of combustible gases; the first detection result is used to indicate that the surrounding rock in front of the tunnel excavation face contains combustible gas, and the second detection result is used to indicate that the surrounding rock in front of the tunnel excavation face does not contain combustible gas.

[0008] In the second aspect, a combustible gas detection module for tunnel engineering is proposed, and the combustible gas detection module is located in the analyzer of the elastic wave advanced geological forecaster; the combustible gas detection module includes: a sample establishment unit, which is used to extract the gray value of each pixel point in the three-dimensional geological structure map to establish a first data sample, and to extract the contrast of each pixel point in the three-dimensional geological structure map to establish a second data sample; a first analysis unit, which is used to obtain a first normal distribution map of the first data sample, and to obtain a second normal distribution map of the second data sample; a data extraction unit, which is used to extract all gray values ​​outside the confidence interval of the first normal distribution map from the first data sample to establish a first data set, and to extract all gray values ​​outside the confidence interval of the second normal distribution map from the second data sample A second data set is established with contrast; a coordinate matching unit is used to coordinate match the grayscale value of the first data set with the contrast of the second data set according to the pixel coordinates; a second analysis unit is used to determine whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval when the coordinate matching is successful; a result output unit is used to output a first detection result when the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval, and output a second detection result when the amplitude attenuation rate of the elastic wave does not fall within the numerical simulation interval, and the numerical simulation interval is composed of simulation values ​​of the amplitude attenuation rate of the elastic wave when propagating in multiple combustible gases; the first detection result is used to indicate that the surrounding rock in front of the tunnel excavation face contains combustible gas, and the second detection result is used to indicate that the surrounding rock in front of the tunnel excavation face does not contain combustible gas.

[0009] Compared with the prior art, the present invention has the following advantages and beneficial effects: by analyzing the propagation characteristics of elastic waves in the rock mass, it is possible to detect whether there is combustible gas in the surrounding rock in front of the tunnel excavation face. The existing elastic wave advanced geological prediction instrument can only detect the geological structure in front of the tunnel excavation face in the form of three-dimensional imaging, thereby ensuring the safety of the tunnel project. Specifically, firstly, based on image analysis and numerical analysis, a preliminary judgment is made on whether the surrounding rock in front of the tunnel excavation face contains heterogeneous media - according to the obvious attenuation characteristics of elastic waves when propagating in the rock mass containing heterogeneous media, the wave velocity and amplitude have low wave velocity areas and low amplitude areas at the wave impedance difference interface, and the numerical distribution of grayscale values ​​and contrast in the three-dimensional geological image is specifically analyzed, and the area associated with the low wave velocity area and the low amplitude area is determined to be the area where the heterogeneous medium is located according to the numerical distribution characteristics. Then, the type of heterogeneous medium in the rock mass was determined through numerical simulation. The actual attenuation rate of the elastic wave was compared with the simulation results of the attenuation rate of the elastic wave propagating in various combustible gases. Based on the positional relationship between the actual attenuation rate and the numerical simulation interval, it was determined whether the heterogeneous medium in the rock mass was a combustible gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 A schematic flow chart of a combustible gas detection method for tunnel engineering provided in an embodiment of the present invention.

[0012] Figure 2 A schematic flow chart of a method for obtaining the amplitude attenuation rate of elastic waves provided in an embodiment of the present invention.

[0013] Figure 3 A schematic flow chart of a numerical simulation method for establishing an amplitude attenuation rate fluctuation range provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0015] Example:

[0016] Firstly, a combustible gas detection method for tunnel engineering is proposed, comprising: Figure 1 The following steps are shown:

[0017] Step 1: extract the gray value of each pixel in the three-dimensional geological structure map to establish a first data sample; extract the contrast of each pixel in the three-dimensional geological structure map to establish a second data sample.

[0018] The purpose of this step is to use grayscale values ​​to characterize different wave velocity areas in the three-dimensional geological structure map, and to use contrast to characterize different amplitude areas in the three-dimensional geological structure map. The specific description is as follows:

[0019] On the one hand, the presence of heterogeneous media in the rock mass will affect the propagation speed of elastic waves. Specifically, the speed of elastic waves will be reduced by the presence of fluids (liquid or gaseous) in rock pores and rock fractures, resulting in low-beam areas in the rock mass containing heterogeneous media in three-dimensional imaging, while these low-beam areas do not exist in the rock mass without heterogeneous media. Furthermore, low-beam areas are displayed as low gray values ​​in the three-dimensional geological structure map or appear as discontinuous boundaries of wave impedance differences. Therefore, by extracting the gray value of each pixel, low-velocity areas and high-velocity areas in the three-dimensional geological image can be divided.

[0020] On the other hand, the presence of heterogeneous media (liquid or gaseous) in the rock mass increases the attenuation of elastic waves. Specifically, heterogeneous media in rock pores and rock fractures cause the energy of elastic waves to dissipate. In three-dimensional imaging, the attenuation of elastic waves causes the signal intensity to weaken, which appears as low-amplitude areas in three-dimensional imaging. Furthermore, low-amplitude areas are displayed as low contrast in three-dimensional geological structure maps or as discontinuous boundaries with wave impedance differences. Therefore, extracting the contrast of each pixel can divide low-amplitude areas and high-amplitude areas in three-dimensional geological images.

[0021] About the extraction method of grayscale value and contrast:

[0022] The grayscale value of an image reflects the brightness information of each pixel in the image; by analyzing the change in grayscale value, the edges and contours in the image can be detected. For a grayscale image, the grayscale value of each pixel can be read directly from the image data; for a color image, it needs to be converted into a grayscale image first. In this embodiment, the color three-dimensional geological structure map is first converted into a corresponding grayscale image, and then the grayscale value of each pixel is calculated one by one by weighted averaging the values ​​of the RGB channels. The first data sample is established using the calculated grayscale values ​​of all pixels.

[0023] The contrast of an image is used to describe the brightness or color difference between different areas in the image. A high contrast can clearly highlight the boundary of the image, while a low contrast makes the boundary discontinuous. This embodiment uses the Michel contrast calculation formula to calculate the contrast of each pixel. The calculated contrast of all pixels is used to establish a second data sample.

[0024] Step 2: Obtain a first normal distribution graph of the first data sample and a second normal distribution graph of the second data sample. According to the first normal distribution graph, extract all grayscale values ​​outside the confidence interval of the first normal distribution graph from the first data sample to establish a first data set; according to the second normal distribution graph, extract all contrasts outside the confidence interval of the second normal distribution graph from the second data sample to establish a second data set.

[0025] In step 1, the extracted grayscale values ​​are used to create a first data sample (including low grayscale values), and the extracted contrast is used to create a second data sample (including low contrast). The purpose of this step is to extract all low grayscale values ​​from the first data sample to characterize the low wave velocity area; and to extract all low contrast from the second data sample to characterize the low amplitude area. The specific description is as follows:

[0026] In many fields such as statistics and engineering, the normal distribution is often used to describe the data distribution. By obtaining the normal distribution of the data, abnormal data can be screened out. According to the 3σ principle: about 68% of the data fall within the range of μ±σ, about 95% of the data fall within the range of μ±2σ, and about 99.7% of the data fall within the range of μ±3σ. Among them, μ represents the mean and σ represents the standard deviation. If the data obeys the normal distribution, then the data points outside the interval (μ-3σ, μ+3σ) can be considered as outliers. Furthermore, since the grayscale value of the low wave velocity area is significantly lower than the grayscale value of other beam areas in the three-dimensional geological structure map, it can be regarded as an "outlier". Combined with the data distribution characteristics in the normal distribution map, the grayscale value distribution of the low beam area is outside the specified interval of the first normal distribution map. The preset specified interval in this embodiment is (μ-3σ, μ+3σ). Of course, due to the error in data collection, (μ-σ, μ+σ), (μ-2σ, μ+2σ) or (μ-3σ, μ+3σ) can be flexibly selected when presetting the specified interval. Similarly, in the normal distribution diagram corresponding to the second data sample, the grayscale value of the low amplitude area is also distributed outside the specified interval.

[0027] This step extracts all grayscale values ​​distributed outside the specified interval (μ-3σ, μ+3σ) from the first data sample to establish the first data set, and extracts all contrasts distributed outside the specified interval (μ-3σ, μ+3σ) from the second data sample to establish the second data set. Among them, the pixel points corresponding to all grayscale values ​​in the first data set constitute the low wave velocity area, and the pixel points corresponding to all contrasts in the second data set constitute the low amplitude area.

[0028] Step 3: According to the pixel coordinates, coordinate matching is performed between the data of the first data set and the data of the second data set.

[0029] The purpose of this step is to use the correspondence between low wave velocity areas and low amplitude areas in the three-dimensional geological image to determine whether the surrounding rock in front of the tunnel excavation face contains heterogeneous media. The specific description is as follows:

[0030] Since the area where the heterogeneous medium in the rock mass is located can be characterized by both the low beam area and the low amplitude area, then in the three-dimensional geological structure map, if a certain area is both a low beam area and a low amplitude area, it can be determined that the area contains heterogeneous media. In other words, in the three-dimensional geological structure map, if the low beam area and the low amplitude area "simultaneously" point to the same area, then it can be considered that the rock mass in the area contains heterogeneous media.

[0031] Based on the above analysis, this embodiment uses pixel point coordinates to characterize the correspondence between low wave velocity areas and low amplitude areas in three-dimensional geological images. Specifically, in the three-dimensional geological structure map, each pixel point in the heterogeneous medium area has a corresponding point coordinate. When the low beam area is used to characterize the area where the heterogeneous medium in the rock mass is located, each gray value in the first data set is also correspondingly associated with a corresponding point coordinate; when the low amplitude area is used to characterize the area where the heterogeneous medium in the rock mass is located, each contrast in the second data set is also correspondingly associated with a corresponding point coordinate. Therefore, if the gray value in the first data set and the contrast in the second data set have the same point coordinates, it means that the low beam area and the low amplitude area point to the same area, which can further prove that the same area is the area where the heterogeneous medium is located.

[0032] Step 4: If the match is successful, determine whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval; if it falls within the numerical simulation interval, output the first detection result; if it does not fall within the numerical simulation interval, output the second detection result.

[0033] After steps 1 to 3, it can only be determined that the surrounding rock in front of the tunnel excavation face contains heterogeneous media, but it cannot be determined that the heterogeneous media is combustible gas. This is because the heterogeneous media in the rock pores or rock cracks may be liquid media in addition to gaseous media. When elastic waves encounter the wave impedance difference interface formed by rock and liquid media during propagation in the rock mass, beam reduction and beam attenuation will also occur. Therefore, it is necessary to further identify whether the heterogeneous medium is a combustible gas.

[0034] Before elaborating on the identification method, we first compare and analyze the amplitude attenuation rate of elastic waves propagating in gaseous media and in liquid media. From the perspective of attenuation mechanism, the distance between gas molecules is large. When elastic waves propagate in gas, the energy is mainly dissipated through molecular collision and diffusion processes, and the attenuation is fast. The distance between liquid molecules is close, and the intermolecular force is strong. When elastic waves propagate in liquid, the energy loss is mainly through the viscosity and interface effect between molecules. Therefore, the amplitude attenuation rate of elastic waves propagating in gaseous media is significantly different from that in liquid media, that is, the amplitude attenuation rate is larger. Therefore, the gaseous medium is distinguished from the liquid medium by analyzing the attenuation degree.

[0035] In addition, the common combustible gas components in rock mass include natural gas, coalbed methane, shale gas, etc., the main component is methane (also mixed with different concentrations of hydrogen, carbon monoxide, etc.). Affected by the density, viscosity, thermal conductivity, etc. of the gaseous medium, there are obvious differences in the amplitude attenuation rate of elastic waves when they propagate in combustible gases of different components. By calculating the amplitude attenuation rate of elastic waves when they propagate in different combustible gases, the corresponding amplitude attenuation rate fluctuation range can be obtained. If the amplitude attenuation rate detected when the elastic wave propagates in a rock mass containing a heterogeneous medium falls within the amplitude attenuation rate fluctuation range, it can be judged that the heterogeneous medium is a combustible gas (i.e., the first detection result); if it does not fall within the amplitude attenuation rate fluctuation range, it can be judged that the heterogeneous medium is not a combustible gas (i.e., the second detection result).

[0036] It should be noted that when determining the fluctuation range of the amplitude attenuation rate, the range should be expanded as much as possible to avoid false detection or missed detection.

[0037] Since step 4 needs to determine whether the amplitude attenuation rate of the elastic wave falls within the amplitude attenuation rate fluctuation range, on the one hand, it is necessary to obtain the actual amplitude attenuation rate of the elastic wave when it propagates in the rock mass containing heterogeneous media, and on the other hand, it is necessary to establish the amplitude attenuation rate fluctuation range in advance. Next, the calculation method of the amplitude attenuation rate of the elastic wave and the method of establishing the amplitude attenuation rate fluctuation range are described in detail.

[0038] 1. Obtain the amplitude attenuation rate of elastic waves when propagating in the surrounding rock in front of the tunnel excavation face

[0039] The amplitude attenuation rate refers to the degree to which the amplitude attenuates with the propagation distance during the propagation of elastic waves in the medium. The amplitude attenuation rate of elastic waves in the rock mass can be obtained by analyzing the reflected signal collected by the detector. Figure 2 The following steps are shown:

[0040] Step A1: Select two reference signals from all reflected signals collected by the detector.

[0041] Step A2: Obtain the peak amplitude of each reference signal.

[0042] Step A3: Obtain the propagation distance of each reference signal from the vibration source according to the acquisition time and wave speed.

[0043] Step A4: Substitute the two peak amplitudes and the two propagation distances into the calculation model to obtain the amplitude attenuation rate of the elastic wave.

[0044] The expression of the calculation model is: .in, represents the amplitude decay rate, x1 represents the propagation distance of the first reference signal, x 2 represents the propagation distance of the second reference signal, A 1 represents the peak amplitude of the first reference signal, A 2 represents the peak amplitude of the second reference signal.

[0045] 2. Establish the amplitude attenuation rate fluctuation range

[0046] The amplitude attenuation rate fluctuation range represents the numerical range of the maximum and minimum values ​​of the amplitude attenuation rate when the elastic wave propagates in different combustible gases, which can be realized through numerical simulation. Figure 3 The following steps are shown:

[0047] Step B1: Convert the 3D geological structure map into a 3D geological model.

[0048] Step B2: Obtain material mechanical parameters of the rock mass through rock mass mechanics tests.

[0049] Step B3: Set the boundary conditions for numerical simulation, including the composition of the gaseous medium, the concentration of each component, etc.

[0050] Step B4: Perform simulation calculations in numerical simulation software to obtain the amplitude attenuation rate of the elastic wave.

[0051] Step 5: Issue an early warning based on the first detection result.

[0052] In summary, the present embodiment proposes a combustible gas detection method for tunnel engineering, which can detect whether there is combustible gas in the surrounding rock in front of the tunnel excavation face by analyzing the propagation characteristics of elastic waves in the rock mass.

[0053] The second aspect of this embodiment proposes a combustible gas detection module for tunnel engineering. The combustible gas detection module is located in the analyzer of the elastic wave advanced geological prediction instrument. The combustible gas detection module includes:

[0054] A sample creation unit is used to extract the gray value of each pixel in the three-dimensional geological structure map to create a first data sample, and to extract the contrast of each pixel in the three-dimensional geological structure map to create a second data sample;

[0055] A first analysis unit, configured to obtain a first normal distribution graph of the first data sample, and to obtain a second normal distribution graph of the second data sample;

[0056] a data extraction unit, configured to extract all grayscale values ​​outside the confidence interval of the first normal distribution graph from the first data sample to establish a first data set, and to extract all contrast values ​​outside the confidence interval of the second normal distribution graph from the second data sample to establish a second data set;

[0057] A coordinate matching unit, used for matching the grayscale value of the first data set with the contrast of the second data set according to the pixel coordinates;

[0058] A second analysis unit is used to determine whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation range when the coordinate matching is successful;

[0059] The result output unit is used to output a first detection result when the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval, and to output a second detection result when the amplitude attenuation rate of the elastic wave does not fall within the numerical simulation interval, wherein the numerical simulation interval is composed of simulation values ​​of the amplitude attenuation rate of the elastic wave when propagating in a plurality of combustible gases; the first detection result is used to indicate that the surrounding rock in front of the tunnel excavation face contains combustible gas, and the second detection result is used to indicate that the surrounding rock in front of the tunnel excavation face does not contain combustible gas.

[0060] Furthermore, the coordinate matching unit includes:

[0061] A first coordinate acquisition unit, used to acquire pixel coordinates corresponding to grayscale values;

[0062] A data access control unit, used for traversing the second data set, and controlling the second coordinate acquisition unit and the coordinate comparison unit to work each time a contrast is accessed;

[0063] A second coordinate acquisition unit, used to acquire pixel coordinates corresponding to the contrast;

[0064] The mapping relationship establishing unit is used to compare the pixel coordinates corresponding to the grayscale value with the pixel coordinates corresponding to the contrast, and if the pixel coordinates of the two are the same, establish a mapping relationship between the grayscale value and the contrast.

[0065] Furthermore, the second analysis unit includes:

[0066] A reference signal selection unit, used to select a first reference signal and a second reference signal from all reflected signals collected by the detector;

[0067] a peak amplitude acquisition unit, configured to acquire a peak amplitude of the first reference signal and a peak amplitude of the second reference signal;

[0068] a propagation distance acquisition unit, configured to acquire the propagation distance of the first reference signal and the propagation distance of the second reference signal according to the wave velocity data and the acquisition time sent by the detector;

[0069] an amplitude attenuation rate calculation unit, configured to calculate the amplitude attenuation rate of the elastic wave according to the peak amplitude of the first reference signal, the propagation distance of the first reference signal, the peak amplitude of the second reference signal, and the propagation distance of the second reference signal;

[0070] The calculation model expression of the amplitude decay rate is: .in, represents the amplitude decay rate, x 1 represents the propagation distance of the first reference signal, x 2 represents the propagation distance of the second reference signal, A 1 represents the peak amplitude of the first reference signal, A 2 represents the peak amplitude of the second reference signal.

[0071] Furthermore, the combustible gas detection module further includes:

[0072] A model conversion unit, used for converting the three-dimensional geological structure map into a three-dimensional geological structure model;

[0073] A parameter acquisition unit, used to acquire material mechanical parameters of the rock mass; the material mechanical parameters include: Poisson's ratio, elastic modulus and density;

[0074] A data configuration unit is used to set the combustible gas ratio; the combustible gas ratio includes: gas components and the concentration of each gas component;

[0075] A numerical simulation unit, used for performing finite element simulation on the three-dimensional geological structure model, the material mechanical parameters and the combustible gas ratio, and outputting simulation results;

[0076] An interval establishing unit, used for establishing a numerical simulation interval; the upper limit of the numerical simulation interval is the maximum value of a plurality of amplitude attenuation rates, and the minimum value of the numerical simulation interval is the minimum value of the plurality of amplitude attenuation rates;

[0077] An early warning unit is used to issue an early warning according to the first detection result.

[0078] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A combustible gas detection method for tunnel engineering, characterized in that: The following steps are involved: Extracting the gray value of each pixel in the three-dimensional geological structure map to establish a first data sample; extracting the contrast of each pixel in the three-dimensional geological structure map to establish a second data sample; Obtaining a first normal distribution graph of the first data sample; Obtaining a second normal distribution graph of the second data sample; Extracting all grayscale values ​​outside the confidence interval of the first normal distribution graph from the first data sample to establish a first data set; Extracting all contrasts outside the confidence interval of the second normal distribution graph from the second data sample to establish a second data set; Converting the three-dimensional geological structure map into a three-dimensional geological structure model; Obtain material mechanical parameters of rock mass; The material mechanical parameters include: Poisson's ratio, elastic modulus and density; For each combustible gas, steps B1 to B2 are executed to obtain multiple amplitude attenuation rates; wherein step B1: setting the combustible gas ratio; the combustible gas ratio includes: gas components and the concentration of each gas component; step B2: performing finite element simulation on the three-dimensional geological structure model, the material mechanical parameters and the combustible gas ratio, and outputting the simulation results; Establishing a numerical simulation interval; the upper limit of the numerical simulation interval is the maximum value of the multiple amplitude attenuation rates, and the minimum value of the numerical simulation interval is the minimum value of the multiple amplitude attenuation rates; According to the pixel coordinates, coordinate matching is performed between the grayscale value of the first data set and the contrast of the second data set; If the match is successful, it is determined whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval; if it falls within the numerical simulation interval, a first detection result is output; if it does not fall within the numerical simulation interval, a second detection result is output; the numerical simulation interval is composed of simulation values ​​of the amplitude attenuation rate of the elastic wave when propagating in a variety of combustible gases; the first detection result is used to indicate that the surrounding rock in front of the tunnel excavation face contains combustible gas, and the second detection result is used to indicate that the surrounding rock in front of the tunnel excavation face does not contain combustible gas; The method for obtaining the amplitude decay rate of elastic waves is: Selecting a first reference signal and a second reference signal from all reflected signals collected by the detector; Acquire a peak amplitude of the first reference signal and a peak amplitude of the second reference signal; Acquire the propagation distance of the first reference signal and the propagation distance of the second reference signal according to the wave velocity data and the acquisition time sent by the detector; Calculating the amplitude attenuation rate of the elastic wave according to the peak amplitude of the first reference signal, the propagation distance of the first reference signal, the peak amplitude of the second reference signal, and the propagation distance of the second reference signal; The calculation model expression of the amplitude decay rate is: ,in, represents the amplitude decay rate, x 1 represents the propagation distance of the first reference signal, x 2 represents the propagation distance of the second reference signal, A 1 represents the peak amplitude of the first reference signal, A 2 represents the peak amplitude of the second reference signal.

2. A combustible gas detection method for tunnel engineering according to claim 1, characterized in that: The coordinate matching method is: performing S1 and S2 on each gray value in the first data set; S1: Get the pixel coordinates corresponding to the gray value; S2: traverse the second data set, and execute S21-S22 each time a contrast is accessed; S21: Obtaining pixel coordinates corresponding to the contrast; S22: Compare the pixel coordinates corresponding to the grayscale value with the pixel coordinates corresponding to the contrast, and if the pixel coordinates of the two are the same, establish a mapping relationship between the grayscale value and the contrast; The successful matching means that for each grayscale value in the first data set, a unique contrast with a mapping relationship can be found in the second data set.

3. A combustible gas detection method for tunnel engineering according to claim 1 or 2, characterized in that: The following steps are also included: An early warning is issued according to the first detection result.

4. A combustible gas detection module for tunnel engineering, characterized in that: The combustible gas detection module is located in the analyzer of the elastic wave advanced geological prediction instrument; The combustible gas detection module comprises: A sample creation unit is used to extract the gray value of each pixel in the three-dimensional geological structure map to create a first data sample, and to extract the contrast of each pixel in the three-dimensional geological structure map to create a second data sample; A first analysis unit, configured to obtain a first normal distribution graph of the first data sample, and to obtain a second normal distribution graph of the second data sample; a data extraction unit, configured to extract all grayscale values ​​outside the confidence interval of the first normal distribution graph from the first data sample to establish a first data set, and to extract all contrast values ​​outside the confidence interval of the second normal distribution graph from the second data sample to establish a second data set; A model conversion unit, used for converting the three-dimensional geological structure map into a three-dimensional geological structure model; A parameter acquisition unit, used to acquire material mechanical parameters of the rock mass; the material mechanical parameters include: Poisson's ratio, elastic modulus and density; A data configuration unit is used to set the combustible gas ratio; the combustible gas ratio includes: gas components and the concentration of each gas component; A numerical simulation unit, used for performing finite element simulation on the three-dimensional geological structure model, the material mechanical parameters and the combustible gas ratio, and outputting simulation results; An interval establishing unit, used for establishing a numerical simulation interval; the upper limit of the numerical simulation interval is the maximum value of a plurality of amplitude attenuation rates, and the minimum value of the numerical simulation interval is the minimum value of the plurality of amplitude attenuation rates; A coordinate matching unit, used for matching the grayscale value of the first data set with the contrast of the second data set according to the pixel coordinates; A second analysis unit is used to determine whether the amplitude attenuation rate of the elastic wave falls within the numerical simulation range when the coordinate matching is successful; A result output unit, used for outputting a first detection result when the amplitude attenuation rate of the elastic wave falls within the numerical simulation interval, and outputting a second detection result when the amplitude attenuation rate of the elastic wave does not fall within the numerical simulation interval, wherein the numerical simulation interval is composed of simulation values ​​of the amplitude attenuation rate of the elastic wave when propagating in a plurality of combustible gases; the first detection result is used to indicate that the surrounding rock in front of the tunnel excavation face contains combustible gas, and the second detection result is used to indicate that the surrounding rock in front of the tunnel excavation face does not contain combustible gas; The second analysis unit comprises: A reference signal selection unit, used to select a first reference signal and a second reference signal from all reflected signals collected by the detector; a peak amplitude acquisition unit, configured to acquire a peak amplitude of the first reference signal and a peak amplitude of the second reference signal; a propagation distance acquisition unit, configured to acquire the propagation distance of the first reference signal and the propagation distance of the second reference signal according to the wave velocity data and the acquisition time sent by the detector; an amplitude attenuation rate calculation unit, configured to calculate the amplitude attenuation rate of the elastic wave according to the peak amplitude of the first reference signal, the propagation distance of the first reference signal, the peak amplitude of the second reference signal, and the propagation distance of the second reference signal; The calculation model expression of the amplitude decay rate is: ,in, represents the amplitude decay rate, x 1 represents the propagation distance of the first reference signal, x 2 represents the propagation distance of the second reference signal, A 1 represents the peak amplitude of the first reference signal, A 2 represents the peak amplitude of the second reference signal.

5. A combustible gas detection module for tunnel engineering according to claim 4, characterized in that: The coordinate matching unit comprises: A first coordinate acquisition unit, used to acquire pixel coordinates corresponding to grayscale values; A data access control unit, used for traversing the second data set, and controlling the second coordinate acquisition unit and the coordinate comparison unit to work each time a contrast is accessed; A second coordinate acquisition unit, used to acquire pixel coordinates corresponding to the contrast; The mapping relationship establishing unit is used to compare the pixel coordinates corresponding to the grayscale value with the pixel coordinates corresponding to the contrast, and if the pixel coordinates of the two are the same, establish a mapping relationship between the grayscale value and the contrast.

6. A combustible gas detection module for tunnel engineering according to claim 4 or 5, characterized in that: Also includes: An early warning unit is used to issue an early warning according to the first detection result.

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