A method for three-dimensional imaging of advanced detection of shield tunnel ground penetrating radar circular line

Abstract

The application relates to a kind of shield tunnel ground penetrating radar circular line advanced detection three-dimensional imaging methods, comprising: according to the region to be measured in front of shield tunnel, the position and size of circular line are determined;Ground penetrating radar transceiver antenna is arranged on the shield cutterhead, the cutterhead rotates and drives the antenna to move along the circular line for a circle, and echo data is acquired;Determine the three-dimensional space to be imaged, select the imaging point, calculate the electromagnetic wave propagation two-way travel time between the point and ground penetrating radar transceiver antenna;The amplitude intensity corresponding to the electromagnetic wave propagation two-way travel time in the echo signal of all angle positions is acquired to obtain the imaging result of the imaging point;Along the angle direction, the polar coordinate radius direction and the depth direction are traversed to select the imaging point, and the imaging result of the entire three-dimensional space to be imaged is obtained.Compared with the prior art, the application can reconstruct the three-dimensional space only by using two-dimensional circular line ground penetrating radar data, and the detection efficiency and accuracy of the three-dimensional space are improved.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional imaging technology for shield tunnels, and in particular to a three-dimensional imaging method for advanced detection of circular survey lines by ground-penetrating radar in shield tunnels. Background Technology

[0002] With the increasing number and mileage of underground shield tunnels for highways, railways, and subways, the construction depth of newly built underground shield tunnels has increased to 20m-50m, and the geological environment they traverse is becoming increasingly complex, gradually transitioning from homogeneous strata to composite strata, frequently encountering adverse geological conditions such as isolated boulders and bedrock uplifts. Traditional surface geophysical exploration and geophysical methods are unable to achieve detailed geological detection along the tunnel excavation route when facing deep-buried tunnels and underwater tunnel scenarios. Therefore, it is necessary to conduct advanced geological prediction inside the shield machine.

[0003] Ground penetrating radar (GPR) technology, as a highly efficient and precise geophysical exploration method, radiates high-frequency electromagnetic waves into the underground medium through a transmitting antenna. The electromagnetic waves propagate in three dimensions as they enter the geology. When they encounter media with different dielectric parameters, they are reflected and refracted. The electromagnetic waves reflected upward to the surface are recorded by the receiving antenna. By analyzing the amplitude, intensity, and travel time of the echo signal, the presence of anomalies can be inferred.

[0004] By fixing the ground-penetrating radar (GPR) transceiver antenna to the tunnel boring machine (TBM) cutterhead, real-time advance prediction of the geological strata ahead can be achieved while the TBM is excavating. Although the GPR echo signal recorded at a single measuring point contains information about certain three-dimensional objects in the surrounding space, the related echo signals are fused together, making them difficult to identify. To improve the detection effect, while the TBM cutterhead rotates, the GPR transceiver antenna radiates electromagnetic waves forward at certain intervals, forming a circular detection profile. This can acquire information about target objects in the three-dimensional space ahead, but how to reconstruct the three-dimensional space is a problem that needs to be solved.

[0005] Currently, accurate detection and imaging in three-dimensional space requires the acquisition of dense three-dimensional data, which is then processed through three-dimensional offset. This process is computationally intensive and time-consuming, making real-time imaging difficult. For example, the invention application with publication number CN118859339A discloses a fan-shaped scanning three-dimensional ground penetrating radar underground advanced detection method and advanced detection support device. This method uses a fan-shaped scanning three-dimensional ground penetrating radar method and an advanced detection support device. By setting horizontal and vertical fan-shaped scanning modes, it uses a three-dimensional coordinate algorithm to construct a fan-shaped profile image of single-channel or channel group data. Combined with a rotating disk and a triangular support device, it realizes the rotation positioning of the antenna and data fusion.

[0006] The shield tunneling cutterhead consists of spokes and a panel, and is designed with a certain opening ratio to ensure the discharge of excavated soil in front. For example, using the integrated ground-penetrating radar antenna device for the shield tunneling cutterhead disclosed in invention application CN120065132A, the antenna cannot be moved after being fixed on the cutterhead. The space on the cutterhead that allows for the placement of ground-penetrating radar antennas is limited, and densely arranged ground-penetrating radar antennas will adversely affect the mechanical strength and tunneling performance of the cutterhead. Therefore, in the absence of three-dimensional ground-penetrating radar data, how to utilize the two-dimensional data collected along a circular survey line by a set of transceiver antennas to achieve accurate three-dimensional imaging of the three-dimensional space ahead is the key problem addressed by this invention. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for advanced detection and three-dimensional imaging of shield tunnel ground-penetrating radar circular survey lines by using a set of transceiver antennas to collect two-dimensional data along a circular survey line to achieve accurate three-dimensional imaging of the three-dimensional space in front.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for advanced detection and three-dimensional imaging of circular ground-penetrating radar lines in shield tunnels includes the following steps: S1: Based on the area to be measured in front of the shield tunnel, determine the position and size of the circular measuring line on the shield cutterhead of the shield machine; S2: A ground-penetrating radar transceiver antenna is set on the shield cutterhead for detection. The shield cutterhead rotates and drives the ground-penetrating radar transceiver antenna to rotate and move one circle along the circular survey line according to the preset track spacing to obtain the ground-penetrating radar echo data of the circular survey line. S3: Determine the three-dimensional imaging space in the cylindrical coordinate system based on the depth of the area to be measured and the size of the circular survey line; S4: Select any point in the three-dimensional imaging space as the imaging point, and calculate the two-way travel time of electromagnetic wave propagation between the imaging point and the ground-penetrating radar transceiver antenna. S5: In the ground-penetrating radar echo data of the circular survey line, select the echo signal of the ground-penetrating radar transceiver antenna at any angle position of the circular survey line, and extract the amplitude intensity corresponding to the electromagnetic wave propagation two-way travel time determined in step S4 from the echo signal. S6: Repeat step S5 until the amplitude intensity of the corresponding electromagnetic wave propagation two-way travel time in the echo signals of all angular positions is obtained, so as to obtain the imaging result of the current imaging point. S7: Sequentially select imaging points along the angular direction, polar coordinate radius direction, and depth direction of the three-dimensional imaging space, and repeat steps S4-S6 to obtain the imaging result of the entire three-dimensional imaging space.

[0009] Furthermore, the ground-penetrating radar transceiver antenna includes a transmitting antenna and a receiving antenna, wherein the transmitting antenna is used to radiate electromagnetic waves into the ground, and the receiving antenna is used to receive echo signals; During the rotation and movement of the ground-penetrating radar transceiver antenna, the distance between the transmitting antenna and the receiving antenna remains unchanged.

[0010] Furthermore, the center of the circular measuring line is located at the center of the shield cutterhead, the radius of the circular measuring line is smaller than the radius of the shield cutterhead, and the circular measuring line is close to the edge of the shield cutterhead.

[0011] Furthermore, the three-dimensional imaging space is divided into sampling intervals for imaging points using angle, polar coordinate radius, and depth as variables; the angular direction sampling interval is consistent with the track spacing corresponding to the circular survey line.

[0012] Furthermore, the maximum value of the polar coordinate radius of the three-dimensional imaging space is not less than the radius of the circular survey line.

[0013] Furthermore, for the imaging points selected within the three-dimensional imaging space ( , , ), which is relative to the center position of the ground-penetrating radar transceiver antenna ( , The expression for calculating the two-way travel time of electromagnetic wave propagation between (0, 0) is: In the formula, For imaging points ( , , The two-way travel time of electromagnetic wave propagation between the center position of the ground-penetrating radar transceiver antenna and the center position of the ground-penetrating radar transceiver antenna. The distance between the imaging point and the center of the ground-penetrating radar transceiver antenna. This represents the propagation speed of electromagnetic waves in underground media.

[0014] Furthermore, in step S6, the amplitude intensity of the corresponding electromagnetic wave propagation two-way travel time in the echo signals at all angular positions is summed or the root mean square is calculated to obtain the imaging result of the current imaging point.

[0015] Furthermore, step S7 specifically includes: S701: Select the initial value of the imaging point in the three-dimensional imaging space, and execute steps S4-S6; S702: Change the position of the imaging point along the angular direction and execute steps S4-S6 to obtain the imaging results of the imaging points in all angular directions under the current polar coordinate radius and depth; S703: Change the position of the imaging point along the radial direction and return to step S702 until the imaging results of all imaging points in the radial and angular directions at the current depth are obtained; S704: Change the position of the imaging point along the depth direction and return to step S702 until the imaging result of the entire three-dimensional imaging space is obtained.

[0016] Furthermore, the method also includes converting the imaging results of the entire three-dimensional imaging space in the cylindrical coordinate system to a rectangular coordinate system for three-dimensional slice display.

[0017] Furthermore, the method also includes searching for the region with the strongest imaging energy based on the imaging results of the entire three-dimensional imaging space, as the detection result of the target object.

[0018] Compared with the prior art, the present invention has the following advantages: (1) Based on the shield tunnel scenario and the principle of back projection, the present invention adjusts the three-dimensional imaging space to a cylindrical coordinate system that is more in line with the circular survey line. By calculating the two-way travel time of the target body and the antenna, the corresponding amplitude intensity is extracted, and the amplitude intensity at different positions of the antenna is superimposed as the imaging result. Only one two-dimensional circular survey line ground-penetrating radar data is needed to realize the reconstruction of the three-dimensional space. It is not necessary to deploy multiple antennas on the shield cutterhead to collect three-dimensional data, which greatly reduces the detection workload and improves the detection efficiency and accuracy of the three-dimensional space.

[0019] (2) Based on the ray theory of electromagnetic wave propagation, the present invention performs three-dimensional imaging based on circular survey line data. It does not require solving the three-dimensional wave equation, has a fast calculation speed, and requires a short time for three-dimensional imaging. In practical engineering applications, it can realize real-time imaging.

[0020] (3) The imaging results of the present invention have high reliability and can achieve high-precision three-dimensional imaging, accurately reflecting the planar position coordinates and depth of the target. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a three-dimensional imaging method for advanced detection of circular survey lines in a shield tunnel using ground-penetrating radar, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the state of the detection area and the target position provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the effect of three-dimensional slicing along the depth direction after imaging, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating a two-dimensional slice along a depth of 5m provided in an embodiment of the present invention; Figure 5This is a schematic diagram illustrating a three-dimensional slice display effect along three directions provided in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] Example 1 like Figure 1 As shown in the figure, this embodiment provides a method for advanced detection and three-dimensional imaging of circular ground-penetrating radar lines in shield tunnels, including the following steps: S1: Based on the area to be measured in front of the shield tunnel, determine the position and size of the circular measuring line on the shield cutterhead of the shield machine; S2: A ground-penetrating radar transceiver antenna is set on the shield cutterhead for detection. The shield cutterhead rotates and drives the ground-penetrating radar transceiver antenna to rotate and move one circle along the circular survey line according to the preset track spacing to obtain the ground-penetrating radar echo data of the circular survey line. S3: Determine the three-dimensional imaging space in the cylindrical coordinate system based on the depth of the area to be measured and the size of the circular survey line; S4: Select any point in the three-dimensional imaging space as the imaging point, and calculate the two-way travel time of electromagnetic wave propagation between the imaging point and the ground-penetrating radar transceiver antenna. S5: In the ground-penetrating radar echo data of the circular survey line, select the echo signal of the ground-penetrating radar transceiver antenna at any angle position of the circular survey line, and extract the amplitude intensity corresponding to the electromagnetic wave propagation two-way travel time determined in step S4 from the echo signal. S6: Repeat step S5 until the amplitude intensity of the corresponding electromagnetic wave propagation two-way travel time in the echo signals of all angular positions is obtained, so as to obtain the imaging result of the current imaging point. S7: Sequentially select imaging points along the angular direction, polar coordinate radius direction, and depth direction of the three-dimensional imaging space, and repeat steps S4-S6 to obtain the imaging result of the entire three-dimensional imaging space.

[0026] Specifically, in step S1, the area to be measured is often the area directly in front of the tunnel boring machine. The center of the circular measuring line is set at the center of the shield cutterhead, and the radius of the circular measuring line is slightly smaller than the radius of the shield tunnel, so that the ground penetrating radar transceiver antenna subsequently set on the circular measuring line is close to the edge of the area to be measured.

[0027] In step S2, the spacing between the circular survey lines is set in the same way as that of the straight survey lines. The smaller the spacing, the more data is collected and the better the imaging quality. For a 100MHz frequency antenna, the spacing between the measurement points should not exceed 0.1m.

[0028] Ground penetrating radar transceiver antennas include a transmitting antenna and a receiving antenna. The transmitting antenna is used to radiate electromagnetic waves into the ground, and the receiving antenna is used to receive echo signals. The transmitting and receiving antennas rotate and move one full circle along the circular survey line according to the set track spacing, keeping the spacing between the transmitting and receiving antennas constant during the movement, to acquire the circular survey line ground-penetrating radar B-scan data; The B-scan data of the circular ground-penetrating radar is a two-dimensional matrix DATA[nt,nθ] of size nt*nθ, where nt is the number of sampling points in a single-channel A-scan data and nθ is the number of A-scans collected during one rotation of the antenna.

[0029] In step S3, the three-dimensional imaging space is divided into sampling intervals for imaging points using angle θ, polar coordinate radius r, and depth z as variables; the depth dimension is equal to the depth of the area to be detected, and the polar coordinate radius dimension is equal to or slightly larger than the radius of the circular survey line.

[0030] The resolution in the depth and radius directions can be set according to the imaging accuracy. The resolution in the angular direction is consistent with the trace spacing of the circular survey line, thus defining the three-dimensional space as I[nθ,nr,nz].

[0031] In step S4, the specific calculation process for the two-way travel time of electromagnetic wave propagation is as follows: For the imaging points selected within the three-dimensional imaging space ( , , In a three-dimensional space represented by a cylindrical coordinate system, assuming that the ground-penetrating radar transceiver antenna is integrated and located at its center ( , The three-dimensional spatial distance between this point and the antenna is: The two-way travel time of the electromagnetic wave from the ground-penetrating radar transceiver antenna to the imaging point is: In the formula, For imaging points ( , , Two-way travel time of electromagnetic wave propagation between the center position of the ground-penetrating radar transceiver antenna and the center position of the radar. The distance between the imaging point and the center of the ground-penetrating radar transceiver antenna. This represents the propagation speed of electromagnetic waves in underground media.

[0032] In step S5, the A-scan data DATA[:,θj] corresponding to the ground penetrating radar transceiver antenna being located at angle θj is extracted from the ground penetrating radar data matrix DATA. Based on the two-way travel time ti calculated in step S4, the corresponding amplitude intensity DATA[ti,θj] is obtained using a one-dimensional interpolation method, which is used as the signal intensity SAD[θj] at that point when the ground penetrating radar transceiver antenna is located at angle θj. The corresponding calculation expression is: In step S6, by keeping the position of the imaging point unchanged, the antenna angle θj changes from 0° to 360°, and step S5 is repeated to extract the amplitude intensity at the corresponding travel time from the A-scan echo signals of all angles, thus obtaining a signal intensity vector SAD[nθ] related to the antenna angle.

[0033] For the echo signals at all angular positions, the amplitude intensity corresponding to the two-way travel time of electromagnetic wave propagation is summed or the root mean square is calculated to obtain the imaging result of the current imaging point.

[0034] Specifically, for the elements in the signal intensity vector SAD[nθ], the expression for the imaging result of the imaging point obtained by accumulating and summing is as follows: The expression for the imaging result of the imaging point obtained by calculating its root mean square for the elements in the signal intensity vector SAD[nθ] is as follows: Step S7 specifically includes: S701: Select the initial value of the imaging point in the three-dimensional imaging space and execute steps S4-S6; S702: Change the position of the imaging point along the angular direction and execute steps S4-S6 to obtain the imaging results of the imaging points in all angular directions under the current polar coordinate radius and depth; That is, first, loop along the angular direction, where the angle θi of the point changes from 0° to 360°, and a row vector I (:,ri,zi) of size nθ can be obtained. S703: Change the position of the imaging point along the radial direction and return to step S702 until the imaging results of all imaging points in the radial and angular directions at the current depth are obtained; That is, based on step S702, the position of the imaging point is changed along the radial direction, ri from 0 to the imaging space r, and step S702 is repeated to obtain two-dimensional data I (:,:,zi) in all radii and all directions. S704: Change the position of the imaging point along the depth direction and return to step S702 until the imaging result of the entire three-dimensional imaging space is obtained. That is, finally change the position of the point along the depth z direction, starting from the depth of 0, repeat step S703, and loop until the nz-th point, thereby obtaining the entire three-dimensional space data I.

[0035] Furthermore, the methods also include: S8: Convert the imaging results of the entire three-dimensional imaging space in the cylindrical coordinate system to the rectangular coordinate system for three-dimensional slice display; The specific process includes the following sub-steps: S801: Extract a one-dimensional vector I(θi,ri,:) from the three-dimensional spatial data I in cylindrical coordinates according to the angular and radial directions, and perform polar coordinate to rectangular coordinate conversion according to the following formula: in,( , ( ) are the rectangular coordinates of the center of the circular survey line. , () are coordinates in a rectangular coordinate system. , () represents the coordinates in the polar coordinate system.

[0036] S802: Assign the one-dimensional vector I(θi,ri,:) in cylindrical coordinates to the one-dimensional vector I(xi,yi,:) in rectangular coordinates according to the calculation result in step S801. S803: Change the angle and radius, repeat steps S801 and S802 to obtain the three-dimensional spatial imaging results in the rectangular coordinate system, which can be sliced ​​and displayed along the x, y, and z directions.

[0037] Optionally, the method also includes searching for the region with the strongest imaging energy based on the imaging results of the entire three-dimensional imaging space, and using this as the detection result of the target body to achieve target detection.

[0038] Taking a 100MHz frequency antenna and ground-penetrating radar (GPR) applied to an 8m diameter shield tunnel as an example, a 1m diameter spherical target exists 5-6m away from the detection face within the detection area 7 meters ahead of the excavation face. The GPR transceiver antenna moves along an 8m diameter circular survey line, moving at 0.1m intervals, collecting 251 data points in one rotation. The antenna's starting position and the target's position are shown below. Figure 2 As shown in the figure. The relative permittivity of the stratum is taken as 9, and the electromagnetic wave propagation speed is 0.1 m / ns.

[0039] Two-dimensional circular survey line data acquired by ground penetrating radar is preprocessed through Carlow filtering, time gain adjustment, and other methods to obtain a two-dimensional data image. The reflected wave of the target object exhibits a wavy shape, rather than the hyperbolic shape seen in straight survey lines. In this case, it is difficult to determine the three-dimensional spatial position of the target object from this two-dimensional data image.

[0040] After processing using the aforementioned three-dimensional imaging method for advanced detection of circular ground-penetrating radar in shield tunnels, the imaging area is a cylinder with a diameter of 10m and a depth of 7m. The results are displayed as slices along the depth from 0m to 7m at 1m intervals. Figure 3 As shown, the 3D imaging time is less than 20 seconds. From Figure 3 The image shows that the region with the strongest imaging energy is concentrated in a 5m depth slice. This is consistent with the upper surface of the target object at a depth of 5m. The two-dimensional slice results along the 5m depth are shown below. Figure 4 As shown. The center coordinates are (0, 0, 0), and the plane coordinates of the point with the strongest energy are (3, 0), which is consistent with the actual target body's center plane coordinates (3, 0). The 3D slice effect along the three directions x=3m, y=0m, and z=5m is shown below. Figure 5 As shown, the region with the strongest energy in the entire imaging three-dimensional space is concentrated at the coordinates (3, 0, 5), which is the position of the top surface of the spherical target.

[0041] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for advanced detection and three-dimensional imaging of circular ground-penetrating radar lines in shield tunnels, characterized in that, Includes the following steps: S1: Based on the area to be measured in front of the shield tunnel, determine the position and size of the circular measuring line on the shield cutterhead of the shield machine; S2: A ground-penetrating radar transceiver antenna is set on the shield cutterhead for detection. The shield cutterhead rotates and drives the ground-penetrating radar transceiver antenna to rotate and move one circle along the circular survey line according to the preset track spacing to obtain the ground-penetrating radar echo data of the circular survey line. S3: Determine the three-dimensional imaging space in the cylindrical coordinate system based on the depth of the area to be measured and the size of the circular survey line; S4: Select any point in the three-dimensional imaging space as the imaging point, and calculate the two-way travel time of electromagnetic wave propagation between the imaging point and the ground-penetrating radar transceiver antenna. For the imaging points selected within the three-dimensional imaging space ( , , ), which is relative to the center position of the ground-penetrating radar transceiver antenna ( , The expression for calculating the two-way travel time of electromagnetic wave propagation between (0, 0) is: In the formula, For imaging points ( , , The two-way travel time of electromagnetic wave propagation between the center position of the ground-penetrating radar transceiver antenna and the center position of the ground-penetrating radar transceiver antenna. The distance between the imaging point and the center of the ground-penetrating radar transceiver antenna. The speed at which electromagnetic waves propagate in underground media; S5: In the ground-penetrating radar echo data of the circular survey line, select the echo signal of the ground-penetrating radar transceiver antenna at any angle position of the circular survey line, and extract the amplitude intensity corresponding to the electromagnetic wave propagation two-way travel time determined in step S4 from the echo signal. S6: Repeat step S5 until the amplitude intensity of the corresponding electromagnetic wave propagation two-way travel time in the echo signals of all angular positions is obtained, so as to obtain the imaging result of the current imaging point. S7: Sequentially select imaging points along the angular direction, polar coordinate radius direction and depth direction of the three-dimensional imaging space, and repeat steps S4-S6 to obtain the imaging result of the entire three-dimensional imaging space. In step S6, the imaging result of the current imaging point is obtained by summing or taking the root mean square of the amplitude intensity of the corresponding electromagnetic wave propagation two-way travel time in the echo signals at all angular positions.

2. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, The ground-penetrating radar transceiver antenna includes a transmitting antenna and a receiving antenna. The transmitting antenna is used to radiate electromagnetic waves into the ground, and the receiving antenna is used to receive echo signals. During the rotation and movement of the ground-penetrating radar transceiver antenna, the distance between the transmitting antenna and the receiving antenna remains unchanged.

3. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, The center of the circular measuring line is located at the center of the shield cutterhead, the radius of the circular measuring line is smaller than the radius of the shield cutterhead, and the circular measuring line is close to the edge of the shield cutterhead.

4. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, The three-dimensional imaging space is divided into sampling intervals for imaging points using angle, polar coordinate radius, and depth as variables; the angular direction sampling interval is consistent with the track spacing corresponding to the circular survey line.

5. A three-dimensional imaging method for advanced detection of circular ground-penetrating radar lines in shield tunnels according to claim 1, characterized in that, The maximum value of the polar coordinate radius of the three-dimensional imaging space is not less than the radius of the circular survey line.

6. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, Step S7 specifically includes: S701: Select the initial value of the imaging point in the three-dimensional imaging space, and execute steps S4-S6; S702: Change the position of the imaging point along the angular direction and execute steps S4-S6 to obtain the imaging results of the imaging points in all angular directions under the current polar coordinate radius and depth; S703: Change the position of the imaging point along the radial direction and return to step S702 until the imaging results of all imaging points in the radial and angular directions at the current depth are obtained; S704: Change the position of the imaging point along the depth direction and return to step S702 until the imaging result of the entire three-dimensional imaging space is obtained.

7. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, The method also includes converting the imaging results of the entire three-dimensional imaging space in the cylindrical coordinate system to the rectangular coordinate system for three-dimensional slice display.

8. The method for three-dimensional imaging of a circular ground-penetrating radar survey line for advanced detection in a shield tunnel according to claim 1, characterized in that, The method also includes searching for the region with the strongest imaging energy based on the imaging results of the entire three-dimensional imaging space, as the detection result of the target object.

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