Tunnel ground disaster exploration method based on swept-frequency scattered radio waves

Abstract

The application discloses a tunnel ground disaster exploration method based on frequency sweeping scattered radio waves, which comprises the following steps: step 1, a plurality of equidistant detection points are arranged along the tunnel trend in the tunnel, and a plurality of rounds of measurement are carried out in the tunnel by using frequency sweeping radio waves, and the frequency sweeping radio wave scattering field intensity signals of each detection point are obtained in each round of measurement; step 2, the no-anomaly theoretical field intensity value when the corresponding source detection distance d in each round of measurement is calculated, and the measured field intensity value of each detection point in each round of measurement obtained in step 1 is compared to determine whether a geological anomaly body exists in the tunnel, and the conductivity and the buried depth of the geological anomaly body are calculated. The application solves the problem that the radio wave exploration method cannot be used in the underground tunnel.

Description

Technical Field

[0001] This invention relates to the field of tunnel geological exploration methods, specifically a tunnel geological disaster exploration method based on swept-frequency scattering radio waves. Background Technology

[0002] Transportation, as a form of infrastructure, is a pioneer in national economic development. my country has vast mountainous areas and a large number of low-grade roads, making a fast and efficient high-level transportation network an urgent need for national development. The spirit of "opening roads through mountains" represents not only a spirit but also advanced technology. Tunnels are underground engineering structures built into the earth's strata, offering advantages such as shortening travel distances, improving driving efficiency, and increasing the utilization rate of underground space. Currently, my country's comprehensive transportation industry is extending from the eastern coastal areas to the western mountainous regions, resulting in an increasing number of tunnels and a larger scale of investment. However, tunnels may face various complex geological problems during construction and operation, such as water inrush, ground subsidence, landslides, and karst anomalies. Therefore, geological exploration is necessary both before and after tunnel construction.

[0003] Radio wave imaging technology is mainly used to explore underground coal resources and geological anomalies. It boasts advantages such as low cost, lightweight instruments, high precision, high efficiency, and long imaging distance, and is widely used in the pre-mining stage of mine working faces. During operation, radio waves are transmitted and received into the detection medium through two tunnels. The acquired field strength values ​​are used to invert imaging to analyze potential anomalies within the working face. Tunnels are underground engineering projects buried in strata, possessing the environmental elements for radio wave exploration. Theoretically, this technology can be used to explore the geological conditions near tunnels after construction and to investigate safety issues of the surrounding mountains. However, due to the lack of the dual-tunnel observation conditions required for conventional mine radio wave imaging methods, this method is difficult to apply.

[0004] Currently, the commonly used electromagnetic exploration methods in underground tunnels after completion include high-density resistivity and ground-penetrating radar, but these methods have limitations in terms of detection range and depth. Given the complex and varied geological characteristics and safety control requirements of underground tunnels after completion, a combination of diverse geophysical exploration methods is needed for detection and prevention. Summary of the Invention

[0005] This invention provides a tunnel geological disaster exploration method based on frequency sweeping scattering radio waves, to solve the problem that the existing technology—radio wave exploration method—cannot be used for underground tunnel geological disaster exploration.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A tunnel geological disaster exploration method based on swept-frequency scattering radio waves includes the following steps:

[0008] Step 1: Arrange multiple equally spaced detection points along the tunnel's direction within the tunnel. Perform multiple rounds of measurements using swept-frequency radio waves within the tunnel. In each round of measurements, obtain the swept-frequency radio wave scattered field strength signal for each detection point. The process is as follows:

[0009] In each round of measurement, a radio wave transmitter used to generate a swept radio wave is placed inside the tunnel at the location of the first detection point. A radio wave receiver is positioned at a distance *d* from the transmitter, where *d* is an integer multiple of *L*. The transmitter emits a swept radio wave into the tunnel, and the receiver receives the scattered field strength signal of the swept radio wave at the detection point at the distance *d* from the transmitter, completing the first detection of the current round. Then, the transmitter and receiver are moved a distance *L* along the tunnel's direction, and the process is repeated to complete the second detection. This process continues until the transmitter receives the scattered field strength signal of the swept radio wave at the last detection point, completing the current round of measurement.

[0010] After each round of measurement, the radio wave transmitter is placed back at the first detection point, and the above process is repeated multiple times after setting different source-detector distances d to obtain the swept radio wave scattered field strength signal at each detection point, thereby completing multiple rounds of measurement.

[0011] Step 2: Calculate the theoretical field strength H without anomalies at the corresponding source-detector distance d in each round of measurement. Aj And the measured field strength H at each detection point in the wheel measurement corresponding to the source-detector distance d obtained in step 1. Cj The calculated theoretical field strength value H of the corresponding wheel measurement without anomalies was compared with that of the wheel measurement. Aj Comparison, when H Aj =H Cj When H is present, it is determined that there are no geological anomalies inside the tunnel; when H Aj Not equal to H Cj If the location is determined to be a geological anomaly within the tunnel, the location of the corresponding detection point is taken as the location of the geological anomaly.

[0012] In further step 1, the radio wave transmitter operates in the frequency range of 0.05MHz-10MHz.

[0013] In the further step 2, the theoretical field strength H without anomalies at the corresponding source-detector distance d in each round of measurement is... Aj The calculation formula is as follows:

[0014]

[0015] Where H0 is the initial field strength value of the swept radio wave emitted by the radio wave transmitter; β Aj It is the radio wave energy attenuation coefficient for swept-frequency radio waves propagating in the tunnel cavity and on the tunnel surface.

[0016] In the further step 2, when a geological anomaly is determined to exist within the tunnel, the conductivity at the corresponding detection point location, i.e., the location of the geological anomaly, is calculated using the following formula:

[0017]

[0018]

[0019] Where ε is the dielectric constant of the geological anomaly; μ is the relative magnetic permeability of the geological anomaly; f j H is the operating frequency for the j-th radio wave detection; Bj To store anomalous theoretical field strength values;

[0020] r is the propagation path length of the swept-frequency radio wave from the radio wave transmitter to the geological anomaly and then to the radio wave receiver, and we have:

[0021]

[0022] Where c is the speed of light; t is the time it takes for the swept radio wave to travel from the radio wave source to the geological anomaly and then to the radio wave receiver; and ε0 is the absolute permittivity.

[0023] In the further step 2, when it is determined that a geological anomaly exists within the tunnel, the location of the corresponding detection point, i.e., the burial depth d1 of the geological anomaly from the tunnel, is calculated using the following formula:

[0024]

[0025] The commonly used tunnel detection instrument in the current technology is ground penetrating radar, which uses high-frequency broadband electromagnetic waves to conduct scattering measurements and has a good effect on detecting geological anomalies at close range. It is often used in tunnel construction, but it has shortcomings such as shallow detection depth and limited data from single transmission and reception.

[0026] Compared to ground-penetrating radar, this invention utilizes low-frequency electromagnetic wave detection technology, offering a long detection range. Using a single-tunnel after completion as the observation channel, it employs frequency-sweeping radio wave scattering exploration technology to transmit radio wave signals to the detection area. A single detection acquires scattering data from multiple operating frequencies. Combined with a full-coverage, same-source ranging scattering radio wave measurement method, it can obtain massive amounts of detection data. Existing instruments can be used to detect geological anomalies at considerable distances around the tunnel. Subsequent data processing primarily focuses on the observed field strength values, supplemented by resistivity parameters (obtained from conductivity). This allows for the acquisition of both scattered radio wave field strength curves and corresponding tomographic inversion maps. With sufficient geological data, the acquired resistivity values ​​can also be compared with actual resistivity.

[0027] Therefore, compared with the prior art, the advantages of the present invention are:

[0028] 1. It can detect the geological environment around a single tunnel under existing conditions, breaking the status quo that radio wave exploration methods cannot be used in tunnels. It not only enriches the geophysical exploration methods for tunnel detection, but can also be used in combination with ground penetrating radar instruments to improve the inspection and monitoring of the geological environment around the tunnel after its completion.

[0029] 2. It can obtain the depth and range of geological anomaly zones within the detection area. It not only has good anti-interference ability, high resolution, and long detection distance, but also is simple to operate, lightweight, fast detection speed, and easy to promote.

[0030] 3. In addition to using frequency sweeping radio wave detection, which can obtain accurate and reliable high-frequency results and low-frequency results with a wider detection range with a single transmission, the data processing of this invention is not limited to the traditional inversion imaging using the received field strength signal. A new data processing method is used to assist it, namely the resistivity parameter method to reflect the distribution of geological anomalies. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the observation system for implementing the present invention (source-detector distance 50m).

[0032] Figure 2 This is a schematic diagram illustrating the "transmit-receive" principle of tunnel scattering radio waves according to the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] This embodiment discloses a tunnel geological disaster exploration method based on swept-frequency scattering radio waves, including the following steps:

[0035] Step 1: Arrange multiple equally spaced detection points along the tunnel direction inside the tunnel. Use swept-frequency radio waves to conduct multiple rounds of measurements inside the tunnel. In each round of measurements, obtain the swept-frequency radio wave scattered field strength signal of each detection point.

[0036] Specifically, based on the geological survey data of the tunnel project, several detection points are arranged at equal intervals along the tunnel direction and numbered sequentially according to the detection direction, with the starting point designated as point 0. The distance between adjacent detection points is set to L, and the range of L between two adjacent detection points is 5m to 10m. To more comprehensively test the surrounding geological conditions, this embodiment primarily uses full-coverage co-source ranging scattered radio waves for detection, meaning the transmission-reception interval will pass through all points on the designed survey line during the detection process. This embodiment uses a radio wave transmitter as the radio wave source and a radio wave receiver as the radio wave receiving end. The operating frequency range of the radio transmitter in this embodiment is 0.01MHz-10MHz.

[0037] like Figure 1 As shown, Figure 1 ● indicates a detection point, numbered from point 0 to point n according to the tunnel's orientation; ★ indicates the location of the radio transmitter; ▲ indicates the location of the radio receiver. The first round of measurement process is as follows:

[0038] (S1) During the first detection in the first round of measurement, a radio wave transmitter is first placed at the location corresponding to detection point 0 inside the tunnel to transmit frequency-sweeping radio waves. A source-receiver distance d is set, which must be a positive integer multiple of the distance L between adjacent detection points. A radio wave receiver is placed at the corresponding location of the detection point at a source-receiver distance d from detection point 0. The radio wave receiver is used to receive radio wave signals of multiple frequency bands, and the detection work is carried out in combination with the full-coverage same-source-distance detection method.

[0039] For ease of explanation, this embodiment assumes an adjacent detection point spacing L of 10m and a source-detector distance d of 50m as an example. Figure 1 As shown, Figure 1 In the diagram, ① represents the detection segment of the first detection (detection points 0-5), where the radio wave transmitter is positioned at detection point 0 and the radio wave receiver is positioned at detection point 5. The required frequency and number of frequencies are set on the radio wave transmitter, and the transmitter is turned on to emit multiple continuous sweeping radio waves with equal intervals between different frequencies. The radio wave receiver receives and stores the scattered field strength signal of the sweeping radio waves at the detection point located at a distance d from the radio wave transmitter (i.e., the scattered field strength signal of the sweeping radio waves at detection point 5), thus completing the first detection in the first round of measurements.

[0040] (S2) After the first detection in the first round of measurement, keep the radio wave transmitter in working order and move the radio wave transmitter and receiver synchronously along the tunnel direction a distance L, i.e., 10m. Figure 1 As shown, Figure 1 ② represents the detection segment of the second detection (detection points 1 to 6). At this time, the radio wave transmitter is located at detection point 1, and the radio wave receiver is located at detection point 6. The radio wave receiver receives and stores the swept radio wave scattering field strength signal at the detection point located at a distance d from the radio wave transmitter pole (i.e., the swept radio wave scattering field strength signal at detection point 6), thus completing the second detection in the first round of measurement.

[0041] (S3) Similarly, after each detection in the first round of measurements, the source-detector distance d is kept constant at 50m, and the radio wave transmitter and receiver are moved at a distance L = 10m. Figure 1 As shown, Figure 1 In the diagram, ③ represents the detection segment for the 3rd detection (detection points 2-7), ④ represents the detection segment for the (n-7)th detection (detection points n-7-n-3), ⑤ represents the detection segment for the (n-6)th detection (detection points n-6-n-2), and ⑥ represents the detection segment for the (n-5)th detection (detection points n-6-n-1). This allows the radio wave transmitter and receiver to sequentially pass through each detection point on the side line until the radio wave receiver receives and stores the swept radio wave scattering field strength signal at the last detection point, thus completing the first round of measurement with a source-detector distance d of 50m.

[0042] After the first round of measurement is completed, the radio wave transmitter is paused and moved back to the 0 point detection point. A new source-detection distance d is selected (i.e., d is no longer 50m). Then, the steps (S1)-(S3) of the first round of measurement are repeated to obtain all the swept-frequency radio wave scattered field strength signals of the corresponding detection points along the tunnel side line under the source-detection distance condition, thus completing the second round of data acquisition.

[0043] By repeatedly selecting new source-detector distances d and conducting multiple rounds of measurements, the sweep radio wave scattering field strength signals under all source-detector distance conditions are obtained, thereby completing the measurement inside the tunnel.

[0044] Step 2: By analyzing and processing all the frequency-sweeping radio wave scattered field strength signals collected on-site, multiple radio wave field strength curves corresponding to multiple source-detector distances and multiple frequencies are obtained. If the field strength curve is linear, there is no geological anomaly in the detection area. If the field strength curve is non-linear, the geological anomaly zone and depth of the tunnel can be determined according to the corresponding formula (the principle is that the radio wave signal energy emitted by the transmitter propagates in the tunnel, and the signal received by the receiver is mainly the result of direct energy and fixed scattered energy from the wall. When encountering a geological anomaly zone in the strata surrounding the tunnel, it will cause changes in the scattered waves. By processing the collected scattered radio wave field strength values, the anomalous medium, location, range, distance, etc. can be inferred). Regularly conducting scattered radio wave exploration can monitor the development of the anomaly zone.

[0045] Specifically, such as Figure 2 As shown, let d1 be the vertical distance between the tunnel surface and the anomaly zone. Let i be the number of different field strength values, and i = A, B, C, where A represents the number of the theoretical field strength value without anomalies, B represents the number of the theoretical field strength value with anomalies, and C represents the number of the measured field strength value (i.e., the swept radio wave scattered field strength value obtained in step 1) at each detection point. And let H... Aj Let H be the theoretical field strength value without anomalies at the corresponding source-detector distance d in each round of measurement. Bj Let H be the theoretical field strength value of the stored anomaly at the corresponding source-detector distance d in each round of measurement. Cj The measured field strength value at each detection point at the corresponding source-detector distance d in each round of measurement is expressed in dB.

[0046] At this point, the following quantities are known: the initial field strength of the radio wave emitted by the radio wave transmitter during the current round of measurement is H0; the radio wave energy attenuation coefficient β during propagation in the tunnel cavity and on the tunnel surface is... Aj The source-detector distance d during the current wheel measurement. Then the theoretical field strength H without anomalies measured by the current wheel. Aj As calculated by formula (1):

[0047]

[0048] If there are no geological anomalies within the tunnel area during the current round of measurement, then formula (2) applies:

[0049] H Aj =H Cj (2),

[0050] Where, β Aj The value is in dB / m, and the d value is in m.

[0051] Therefore, based on formula (2), it is possible to determine whether there are geological anomalies inside the tunnel based on the data from each round of measurements. That is, when formula (2) is satisfied, it can be determined that there are geological anomalies inside the tunnel.

[0052] When one round of measurement data does not satisfy formula (2), i.e. H Aj Not equal to H Cj If a geological anomaly is detected, it is determined that a geological anomaly exists within the tunnel. The location of the geological anomaly can be determined based on the location of the detection point that does not satisfy formula (2) during the measurement round. Furthermore, the conductivity σ of the geological anomaly corresponding to the detection point that does not satisfy formula (2) during the measurement round and the burial depth d1 of the geological anomaly from the tunnel can be calculated. The process is as follows:

[0053] (a) Let j be the number of different operating frequencies set on the instrument, j = 1, 2, 3...n (n ≥ 2), β Bj β is the energy attenuation coefficient of radio waves propagating within the strata. Bj The general formula is:

[0054]

[0055] In formula (3), ε is the dielectric constant of the geological anomaly, in units of F / m, and is a known quantity; μ is the relative magnetic permeability of the geological anomaly, in units of H / m, and is a known quantity; f j σ is the operating frequency of the j-th radio wave detection, in MHz, and is a known quantity; σ is the electrical conductivity of the geological anomaly, in S / m, and is an unknown quantity.

[0056] When radio waves encounter geological anomalies during detection, they will be scattered, as shown by the following formula;

[0057] H Bj -H Aj =H0-8.69lnr-8.69β Bj r (4),

[0058] Combining formulas (3) and (4), we can obtain the formula for calculating the electrical conductivity σ of geological anomalies:

[0059]

[0060] In order to facilitate observation and writing, the complex formula in formula (5) is simplified to y, and the specific y is shown in formula (6):

[0061]

[0062] Where r is the propagation path length of the swept-frequency radio wave from the radio wave transmitter to the geological anomaly and then to the radio wave receiver, in meters, and we have:

[0063]

[0064] In formula (7), c is the speed of light, which is generally 3 × 10⁻⁶. 8 m / s; t is the time taken for the swept radio wave to travel from the radio wave source to the geological anomaly and then to the radio wave receiver, in seconds; ε0 is the absolute permittivity, typically 8.85 × 10⁻⁶. -12 F / m.

[0065] H Bj Available actual field strength value H Cj By approximating and combining (5), (6), and (7), the electrical conductivity σ of the geological anomaly can be obtained, and then the resistivity of the geological anomaly can be obtained.

[0066] (b) The burial depth d1 of the geological anomaly from the tunnel can be obtained by formula (8):

[0067]

[0068] If multiple sets of scattered field intensity curves show a non-linear pattern and the resistivity parameter fluctuates significantly, it indicates the presence of an anomaly in the tunnel strata. If possible, the resistivity at this location can be compared with geological borehole data to determine the error between the observed and actual resistivity values.

[0069] Finally, by combining the geological data from the tunnel excavation plan and profile, the geological structural characteristics around the tunnel can be further determined, a geological anomaly interpretation map can be submitted, and hidden safety hazards in the tunnel can be eliminated.

[0070] The principle of this embodiment is as follows:

[0071] 1. Single-tunnel sweeping scattering radio wave detection technology after completion

[0072] Current scattered radio wave detection technology is only used within coal mining faces, limiting its application and often employing single-frequency detection, meaning it uses only one frequency to detect geological features in the coal seam and obtain the received field strength value. This invention, however, pioneers the application of scattered radio wave detection technology in completed tunnels, breaking the current limitation of radio wave exploration in tunnels. This expands the application scope of scattered radio wave exploration and enriches the geophysical exploration methods usable underground. Furthermore, this invention uses a frequency-sweeping detection method, saving experimental time, reducing labor intensity, and simultaneously acquiring multiple sets of detection results at different frequencies. Compared to single-frequency detection, this method is more conducive to improving and correcting the resolution of inversion images, significantly increasing the accuracy of geological anomaly interpretation.

[0073] 2. Data Collection and Processing for Tunnel Frequency Scanning Radio Wave Detection

[0074] Theoretically, radio waves are usually considered as rays propagating directionally along a certain path in a medium. Tunnels without longitudinal conductors often serve as hollow medium waveguides. During propagation, the receivable signal detected by frequency-sweeping radio waves is often the result of the superposition of direct waves and scattered waves. This invention eliminates the need for repeated measurements during data acquisition. It can acquire and store the received scattered field strength values ​​at different operating frequencies at a single receiving point and automatically record the detection time when radio waves encounter anomalies near the tunnel and are scattered to the receiver. Subsequent data processing involves tomographic inversion using the scattered field strength signal values ​​and resistivity parameters. If there are no geological anomalies within the receiver's receivable range, multiple scattered field strength curves will appear as straight lines, the resistivity parameter will remain stable, and the resistivity inversion diagram will show no anomalies. Conversely, if one or more geological anomalies of different depths exist within the receiver's receivable range, multiple scattered field strength values ​​will show a significant response, the resistivity parameter will fluctuate considerably, and the resistivity inversion diagram will show anomalies. The depth and geoelectric property detection formulas based on swept-frequency scattering radio waves for single-tunnel exploration designed in this embodiment can be used to detect and monitor the approximate location, burial depth, and development of geological anomalies around the tunnel. Combining the principles of radio wave energy propagation and attenuation, the collected swept-frequency scattering radio wave field strength values ​​are analyzed and processed, and inversion imaging is performed using the received signal and resistivity parameters. By utilizing multiple parameters for inversion imaging, a more accurate range of anomalous structures and geoelectrical changes around the completed tunnel can be obtained.

[0075] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0076] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of ​​this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A tunnel geological disaster exploration method based on swept-frequency scattering radio waves, characterized in that, Includes the following steps: Step 1: Arrange multiple equally spaced detection points along the tunnel's direction within the tunnel. Perform multiple rounds of measurements using swept-frequency radio waves within the tunnel. In each round of measurements, obtain the swept-frequency radio wave scattered field strength signal for each detection point. The process is as follows: In each round of measurement, a radio wave transmitter used to generate a swept radio wave is placed inside the tunnel at the location of the first detection point. A radio wave receiver is positioned at a distance *d* from the transmitter, where *d* is an integer multiple of *L*. The transmitter emits a swept radio wave into the tunnel, and the receiver receives the scattered field strength signal of the swept radio wave at the detection point at the distance *d* from the transmitter, completing the first detection of the current round. Then, the transmitter and receiver are moved a distance *L* along the tunnel's direction, and the process is repeated to complete the second detection. This process continues until the transmitter receives the scattered field strength signal of the swept radio wave at the last detection point, completing the current round of measurement. After each round of measurement, the radio wave transmitter is placed back at the first detection point, and the above process is repeated multiple times after setting different source-detector distances d to obtain the swept radio wave scattered field strength signal at each detection point, thereby completing multiple rounds of measurement. The radio wave transmitter operates in the frequency range of 0.05MHz-10MHz; the distance L between adjacent detection points is assumed to be 5m~10m. Step 2: By analyzing and processing all the frequency-sweeping radio wave scattered field strength signals collected on site, multiple radio wave field strength curves corresponding to multiple source-detector distances and multiple frequencies are obtained. The signals received by the receiver are mainly the results of direct energy and fixed scattered energy from the tunnel walls. If the field strength curve is linear, there is no geological anomaly in the detection area. If the field strength curve is non-linear, the geological anomaly zone and depth of the tunnel are obtained according to the corresponding formula. The collected scattered radio wave field strength values ​​are processed to infer the anomalous medium, location, range, and distance. Scattered radio wave exploration is carried out regularly to monitor the development of the anomalous zone. Calculate the theoretical field strength value without anomalies at the corresponding source-detector distance d in each round of measurement. The measured field strength values ​​at each detection point in the wheel measurement corresponding to the source-detector distance d obtained in step 1 will be used. The calculated theoretical field strength values ​​without anomalies were compared with those obtained from the corresponding wheel measurements. When comparing, If at that time, it is determined that there are no geological anomalies inside the tunnel; when H Aj Not equal to H Cj If so, it is determined that there is a geological anomaly inside the tunnel, and the location of the corresponding detection point is taken as the location of the geological anomaly; Among them, the theoretical field strength value without anomalies at the corresponding source-detector distance d in each round of measurement. The calculation formula is as follows: ， in, This represents the initial field strength value of the swept radio waves emitted by the radio wave transmitter. The radio wave energy attenuation coefficient is the frequency sweep radio wave propagating in the tunnel cavity and on the tunnel surface. In step 2, when a geological anomaly is determined to exist within the tunnel, the conductivity at the corresponding detection point location, i.e., the location of the geological anomaly, is calculated using the following formula: ， ， in, The dielectric constant of the geological anomaly; The relative magnetic permeability of the geological anomaly; Let j be the operating frequency for radio wave detection; H Bj To store anomalous theoretical field strength values; r Let be the propagation path length of the swept-frequency radio wave from the radio wave transmitter to the geological anomaly and then to the radio wave receiver, and we have: ， in, c The speed of light; t The time it takes for a swept-frequency radio wave to travel from the radio wave source to the geological anomaly and then to the radio wave receiver. It is the absolute dielectric constant; In step 2, when a geological anomaly is detected within the tunnel, the location of the corresponding detection point, i.e., the depth of the geological anomaly from the tunnel, is calculated using the following formula. : 。

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