A tunnel sidewall-based transient electromagnetic detection method based on electrical source

Abstract

The application relates to a tunnel sidewall-based electrical source transient electromagnetic detection method, which comprises the following steps: arranging electrical source transient electromagnetic transmitting and receiving devices based on tunnel sidewalls, obtaining transient electromagnetic data, processing the transient electromagnetic data, and acquiring conductivity information perpendicular to the tunnel sidewall direction; according to the arrangement mode of the electrical source transient electromagnetic transmitting and receiving devices, recording the attenuation characteristics of the electric field with time, and deriving the electric field with time, extracting the electric field response excited by the pulse source, constructing a relative pulse time variable based on the peak time of the electric field response excited by the pulse source; using the relative pulse time variable, establishing an explicit relationship between the electromagnetic pulse response and the conductivity information, converting the electric field data with time into conductivity, and obtaining the conductivity distribution perpendicular to the tunnel sidewall direction. The application can increase the detection depth of the existing loop source transient electromagnetic device based on the tunnel space, and widen the application range of the tunnel transient electromagnetic detection.

Description

Technical Field

[0001] This invention relates to the field of detection technology for mines or tunnels, and in particular to a transient electromagnetic detection method based on an electrical source on the tunnel sidewall. Background Technology

[0002] Transient electromagnetic methods (TEM) are based on the propagation characteristics of diffused electromagnetic fields in underground media to obtain electrical information about the underground medium. Depending on the nature of the emission source, TEM can be divided into electrical source devices and magnetic source devices. Electrical source devices use a grounded wire to transmit the signal, while magnetic source devices use an ungrounded return wire. Because electrical source devices directly inject a high-power electromagnetic field into the underground, their detection depth is typically greater than that of magnetic source TEM, allowing them to detect targets at greater depths.

[0003] Depending on the arrangement of the source and receiver, transient electromagnetic methods can be categorized into ground-based, ground-to-air, airborne, underground, and tunnel-based devices. For tunnel detection devices, transient electromagnetic methods place the source and receiving antenna at the tunnel face during excavation, primarily to acquire information about the electrical structure ahead of the tunnel face. Due to the limited area of ​​the tunnel face, current transient electromagnetic detection in tunnels primarily uses magnetic sources, collecting magnetic field signals within a transmitting loop frame, thus limiting the detection depth. Although similar loop source devices can be used on tunnel sidewalls, the detection depth is smaller, limiting their application scope.

[0004] For the transient electromagnetic method using electric sources, existing devices all place the grounded conductor source on the ground and collect the electric or magnetic field response on the ground, underground, or in the air. Because existing devices require the source to be deployed on the ground, the distance between the source and the deep target is large, and the coupling strength is limited, resulting in insufficient detection accuracy over large depths. Since tunnels or roadways are often very deep, transient electromagnetic devices based on ground-based electric sources have poor detection performance. Furthermore, the complex terrain above tunnels makes it difficult to lay ground-based conductor sources, further complicating the application of the transient electromagnetic method near tunnels. Summary of the Invention

[0005] Existing transient electromagnetic detection methods in tunnels or mines are based on ungrounded loop transient electromagnetic devices, which limit the detection depth. Therefore, this invention proposes a transient electromagnetic detection method based on an electrical source on the tunnel sidewall to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A transient electromagnetic detection method based on an electrical source in a tunnel sidewall includes:

[0008] Transient electromagnetic transmitting and receiving devices based on electrical sources are installed on the tunnel sidewall to obtain transient electromagnetic data. The transient electromagnetic data is then processed to obtain conductivity information perpendicular to the tunnel sidewall.

[0009] Based on the arrangement of the transient electromagnetic transmitting and receiving device of the electric source, the decay characteristics of the electric field over time are recorded, and the derivative of the electric field decaying over time is calculated to extract the electric field response excited by the pulse source. Based on the peak time of the electric field response excited by the pulse source, a relative pulse time variable is constructed.

[0010] By utilizing the relative pulse time variable, an explicit relationship between the electromagnetic pulse response and the conductivity information is established, and the electric field data that decays over time is converted into conductivity to obtain the conductivity distribution perpendicular to the tunnel sidewall.

[0011] Preferably, recording the decay characteristics of the electric field over time includes:

[0012] By installing a pair of grounding electrodes on the tunnel sidewall, a bipolar rectangular wave electromagnetic signal containing a turn-off time is injected into the ground. The electromagnetic signal collected during the turn-off time after the positive amplitude is superimposed with the electromagnetic signal collected during the turn-off time after the negative amplitude to eliminate unrelated electromagnetic noise.

[0013] In the axial direction of the transmitting electrode pair, the decay characteristics of the electric field of the grounding electrode pair over time are recorded during the off-time period of the transmitting source.

[0014] The bipolar rectangular wave electromagnetic signal contains a positive amplitude rectangular wave and a negative amplitude rectangular wave in each cycle; the off-time period is used to record the decay characteristics of the electromagnetic field over time.

[0015] Preferably, extracting the electric field response excited by the pulse source includes:

[0016] Based on the electromagnetic field equations defined by Maxwell's equations, the axial electric field response of the grounding electrode to the observed axial electric field during the turn-off time of the falling edge of a bipolar rectangular wave emitted by a grounded wire source is derived, and the derivative of the axial electric field response is obtained to extract the electric field response excited by the pulse source.

[0017] Preferably, the grounding electrode responds to the observed axial electric field as follows:

[0018]

[0019] Where σ is the electrical conductivity, μ is the magnetic permeability, r is the distance between the center points of the source electrode pair and the center points of the receiving electrode pair, t is time, E is the observed axial electric field response of the ground electrode pair, and φ is the error function.

[0020] Preferably, constructing the relative pulse time variable includes:

[0021] Based on the transient electromagnetic transmitting and receiving device of the electric source, the implicit functional relationship between conductivity and electric field response perpendicular to the tunnel direction is derived. Based on the implicit functional relationship, the electric field response formula is differentiated to obtain the electric field response under pulse excitation. The relative pulse time variable is constructed through the electric field response under pulse excitation.

[0022] Preferably, the derivative of the electric field response formula is as follows:

[0023]

[0024] Where g is the electric field impulse response, σ is the conductivity, r is the distance between the center points of the source electrode pair and the center points of the receiving electrode pair, and t is the time.

[0025] Preferably, the expression for the relative pulse time variable is:

[0026] η = t / t peak

[0027] Where η is the relative pulse time, t peak This represents the moment corresponding to the maximum value of the impulse response.

[0028] Preferably, the explicit relationship between the electromagnetic pulse response and the conductivity information is as follows:

[0029]

[0030] Where η is the relative pulse time, σ is the conductivity, and r is the distance between the center point of the source electrode pair and the center point of the receiving electrode pair.

[0031] The beneficial effects of this invention are as follows:

[0032] The electric transient electromagnetic transmitter and receiver device of this invention can inject high-power transmission current into the ground, and the tunnel sidewalls have ample space for arranging the transmitter. Therefore, the transmission energy is far greater than that of existing small-loop transient electromagnetic devices deployed at the tunnel face, which can increase the detection depth of existing loop-source transient electromagnetic devices based on tunnel space and broaden the application range of tunnel transient electromagnetic detection. It can be used for detection in tunnels or mines under construction, as well as in completed tunnels or mines, and has promising applications in locating water-rich structures and detecting lateral holes in tunnels. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the layout of the transient electromagnetic detection device based on the tunnel sidewall according to an embodiment of the present invention, wherein 1, tunnel sidewall; 2, tunnel floor; 3, transmitting electrode; 4, electromagnetic transmitter; 5, receiving electrode; 6, electromagnetic signal receiver;

[0035] Figure 2 This is a schematic diagram of the emission waveform and response data of the transient electromagnetic method of the electric source according to an embodiment of the present invention, wherein 7 is the waveform of an electromagnetic emission source in one cycle; and 8 is the transient electromagnetic response curve.

[0036] Figure 3 The graphs show the transient electromagnetic attenuation curves at different offset distances in the embodiments of the present invention; where (a) is an offset distance of 10 meters; (b) is an offset distance of 100 meters; and (c) is an offset distance of 700 meters.

[0037] Figure 4 The apparent resistivity calculation results of the transient electromagnetic complete attenuation curve in this embodiment of the invention, with the dashed line representing the actual model. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] This invention proposes a transient electromagnetic detection method based on an electrical source on the tunnel sidewall for deep-penetration detection near tunnels. The method consists of two parts: device type and data processing.

[0041] The first part involves deploying a transient electromagnetic grounding source and receiving antenna within the tunnel to acquire the transient electromagnetic response that decays over time. Due to the long distance along the tunnel direction, the tunnel sidewalls provide sufficient space to deploy long grounding wires. Therefore, this embodiment proposes deploying grounding wires on the tunnel sidewalls, and then using grounding electrodes in the axial direction of the grounding wire source to record the change in the electric field response over time.

[0042] The second part involves extracting resistivity variation information with depth from the recorded transient electromagnetic field data. Based on the electromagnetic field response derived from the electromagnetic field equations, the time-varying voltage response of the transient electromagnetic attenuation curves acquired in the tunnel space is converted into resistivity information varying with depth.

[0043] Specifically, it includes:

[0044] First, transient electromagnetic emission and reception devices are deployed on the tunnel sidewall to acquire transient electromagnetic data containing electrical information of the underground medium. Second, the acquired transient electromagnetic data is processed and imaged to obtain conductivity information perpendicular to the tunnel sidewall.

[0045] The deployment method of the transient electromagnetic device based on the electrical source on the tunnel sidewall is as follows: Figure 1 As shown. A pair of grounding electrodes are installed on the tunnel sidewall. An electromagnetic transmitter injects a bipolar rectangular wave electromagnetic signal containing a turn-off time into the tunnel sidewall through the grounding electrodes, such as... Figure 2 As shown by the solid line. Along the extension of the transmitting electrode pair, grounding electrode pairs or receiving electrode arrays are arranged. The electromagnetic signal receiver records the change in the electromagnetic field collected by each pair of grounding electrodes over time, which is the transient electromagnetic axial electric field data.

[0046] Each cycle of the source signal contains two off-time periods: a positive-amplitude rectangular wave and a negative-amplitude rectangular wave. The off-time periods are used to record the decay characteristics of the electromagnetic field over time. Uncorrelated electromagnetic noise can be eliminated by superimposing the electromagnetic signals from the positive and negative amplitude off-time periods. Along the axial direction of the transmitting electrode pair, during the off-time periods of the transmitting source, a grounding electrode pair is deployed to record the decay characteristics of the electric field over time, such as... Figure 2 As shown by the dashed line.

[0047] based on Figure 1 The propagation law of electromagnetic field under the device type was studied, and electrical information perpendicular to the tunnel sidewall was extracted from the recorded transient electromagnetic data that decayed over time. Specifically:

[0048] (1) Based on the electromagnetic field equations defined by Maxwell's equations, the derived expression for the axial electric field response E of the grounded electrode to the observed electric field during the turn-off time of the falling edge of a bipolar rectangular wave emitted by a grounded conductor source is as follows:

[0049]

[0050] Where σ is the electrical conductivity, μ is the magnetic permeability, r is the distance between the center points of the source electrode pair and the receiver electrode pair, t is time, E is the observed axial electric field response of the ground electrode, and φ is the error function.

[0051] (2) Since the derived conductivity and electric field response have an implicit functional relationship, this functional relationship needs to be simplified to further develop the definition of apparent conductivity. Taking the derivative of both sides of equation (1) yields the expression for the electromagnetic field response under pulse source excitation:

[0052]

[0053] (3) Since the impulse response has a maximum value, a relative impulse time variable is constructed.

[0054] η = t / t peak (3)

[0055] Among them, t peak This represents the moment corresponding to the maximum value of the impulse response.

[0056] Using the constructed relative pulse moments, an explicit relationship between electromagnetic pulse response and conductivity can be established:

[0057]

[0058] (4) From equation (4), we can obtain the definition of apparent conductivity:

[0059]

[0060] According to equation (5), the electric field data recorded by the transient electromagnetic detection device based on the electric source of the tunnel sidewall can be converted into conductivity, thereby obtaining the conductivity distribution perpendicular to the tunnel sidewall, providing a basis for the location of water-rich structures.

[0061] Based on the proposed transient electromagnetic detection device based on the tunnel sidewall, a grounded source device with a source length of 5 meters and a receiving electrode pair with a length of 5 meters were set up. A model was constructed to show a low-resistivity layer of 10 ohm-meters at a distance of 80 meters in front of the sidewall, with a layer thickness of 40 meters and a surrounding rock resistivity of 100 ohm-meters. An electromagnetic field simulation program was used to calculate the observable electric field data under the device and model parameters, with and without the low-resistivity layer. The calculation results show that the proposed detection device is highly sensitive to the designed target layer, and the response with the target layer differs significantly from the background model. Especially when the offset between the transmitter and receiver increases, the anomalous response amplitude is extremely large. Figure 4 The apparent resistivity calculation results are shown for the complete transient electromagnetic attenuation curve. The dashed line represents the actual model.

[0062] The transient electromagnetic observation device based on an electrical source on the tunnel sidewall proposed in this invention has a large detection depth. Numerical simulation results show that when the target body is buried at a depth of 80 meters, the response generated by this device will produce identifiable anomalies (relative error greater than 5%), such as... Figure 3 As shown, this demonstrates that the target at this depth is detectable. Currently, tunnel transient electromagnetic detection devices based on loop sources struggle to achieve a detection depth of 80 meters, indicating that the proposed device outperforms existing tunnel-based transient electromagnetic detection methods in terms of detection depth.

[0063] The apparent resistivity imaging method for transient electromagnetic data of electrical sources in tunnel sidewalls proposed in this invention can directly extract the apparent resistivity of the data throughout its entire lifecycle. Figure 4 It can be seen that the apparent resistivity imaging results are in good agreement with the actual model results, and can be used for rapid data interpretation and real-time quality control judgment in actual detection.

[0064] Furthermore, compared to traditional loop-source transient electromagnetic detection devices, the transient electromagnetic anomalies of the proposed device mainly occur in the early stage with larger amplitudes, making them less likely to be submerged in background electromagnetic noise and exhibiting stronger anti-interference capabilities.

[0065] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A transient electromagnetic detection method for electrical sources based on tunnel sidewalls, characterized in that, include: Transient electromagnetic transmitting and receiving devices based on electrical sources are installed on the tunnel sidewall to obtain transient electromagnetic data. The transient electromagnetic data is then processed to obtain conductivity information perpendicular to the tunnel sidewall. Based on the arrangement of the transient electromagnetic transmitting and receiving device of the electric source, the decay characteristics of the electric field over time are recorded, and the derivative of the electric field decaying over time is calculated to extract the electric field response excited by the pulse source. Based on the peak time of the electric field response excited by the pulse source, a relative pulse time variable is constructed. By utilizing the relative pulse time variable, an explicit relationship between the electromagnetic pulse response and the conductivity information is established, and the electric field data that decays over time is converted into conductivity to obtain the conductivity distribution perpendicular to the tunnel sidewall.

2. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 1, characterized in that, Record the decay characteristics of the electric field over time, including: By installing a pair of grounding electrodes on the tunnel sidewall, a bipolar rectangular wave electromagnetic signal containing a turn-off time is injected into the ground. The electromagnetic signal collected during the turn-off time after the positive amplitude is superimposed with the electromagnetic signal collected during the turn-off time after the negative amplitude to eliminate unrelated electromagnetic noise. In the axial direction of the transmitting electrode pair, the decay characteristics of the electric field of the grounding electrode pair over time are recorded during the off-time period of the transmitting source. The bipolar rectangular wave electromagnetic signal contains a positive amplitude rectangular wave and a negative amplitude rectangular wave in each cycle; the off-time period is used to record the decay characteristics of the electromagnetic field over time.

3. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 2, characterized in that, Extracting the electric field response excited by the pulse source includes: Based on the electromagnetic field equations defined by Maxwell's equations, the axial electric field response of the grounding electrode to the observed axial electric field during the turn-off time of the falling edge of a bipolar rectangular wave emitted by a grounded wire source is derived, and the derivative of the axial electric field response is obtained to extract the electric field response excited by the pulse source.

4. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 2, characterized in that, The grounding electrode's response to the observed axial electric field is as follows: Where σ is the electrical conductivity, μ is the magnetic permeability, r is the distance between the center points of the source electrode pair and the center points of the receiving electrode pair, t is time, E is the observed axial electric field response of the ground electrode pair, and φ is the error function.

5. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 1, characterized in that, The construction of the relative pulse time variable includes: Based on the transient electromagnetic transmitting and receiving device of the electric source, the implicit functional relationship between conductivity and electric field response perpendicular to the tunnel direction is derived. Based on the implicit functional relationship, the electric field response formula is differentiated to obtain the electric field response under pulse excitation. The relative pulse time variable is constructed through the electric field response under pulse excitation.

6. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 5, characterized in that, The derivative of the electric field response formula is as follows: Where g is the electric field impulse response, σ is the conductivity, r is the distance between the center points of the source electrode pair and the center points of the receiving electrode pair, and t is the time.

7. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 5, characterized in that, The expression for the relative pulse time variable is: n = t / t peak Where η is the relative pulse time, t peak This represents the moment corresponding to the maximum value of the impulse response.

8. The transient electromagnetic detection method for electrical sources based on tunnel sidewalls according to claim 1, characterized in that, The explicit relationship between the electromagnetic pulse response and the conductivity information is as follows: Where η is the relative pulse time, σ is the conductivity, and r is the distance between the center point of the source electrode pair and the center point of the receiving electrode pair.

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