Advanced Detection Method for Tunnel Geological Anomalies Based on Omnidirectional Toroidal Electrode Arrangement

Abstract

The present invention discloses a method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement. First, an omnidirectional toroidal electrode observation system is arranged in the tunnel behind the shield machine, and an advanced detection observation coordinate system is established. Advanced detection is carried out through the omnidirectional toroidal electrode observation system to obtain corresponding excitation current and potential data. Then, through multi-directional toroidal electrode synchronous coupling measurement and enhanced superposition processing, a virtual electrode coordinate is formed, and the electrode arrangements generated by the virtual electrodes are screened. The electrode arrangements that meet the requirements are selected to obtain their corresponding data for subsequent calculation of apparent resistivity, so as to realize the detection of geological anomaly bodies in front of the subway tunnel excavation. Compared with the existing conventional resistivity advanced detection, the present invention effectively improves the accuracy and coverage of advanced detection.

Description

Technical Field

[0001] The present invention relates to a method for advanced detection of tunnel geological anomalies, specifically a method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement, and belongs to the technical field of advanced detection for tunnel excavation. Background Art

[0002] The advanced detection method for subway tunnels is an effective means to understand the geological anomalies in front of the tunnel face during tunnel construction, reduce or eliminate geological disasters during construction, and ensure production safety, and has important practical significance for promoting the development and utilization of urban underground space in China.

[0003] The advanced detection methods for subway tunnels mainly include the transient electromagnetic method, the seismic wave method, and the direct current method. Among them, the transient electromagnetic method is greatly affected by the metal shield head in front of the excavation, and it is necessary to determine the optimal layout position of the detection equipment to minimize the influence of the shield head on its detection as much as possible, which results in a complex implementation process; the seismic wave method can effectively detect the geological structure in front of the tunnel but cannot predict whether the anomalies in front contain water, while the direct current method can effectively detect the water-bearing property of the geological anomaly body in front of the tunnel, effectively making up for the deficiency of the seismic wave method. However, the existing direct current method for advanced detection mainly uses a single survey line for data measurement and cannot cover the geological anomaly information of the entire tunnel torus. Therefore, how to provide a new method that can obtain the geological anomaly information of the entire tunnel torus in front of the tunnel excavation is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the present invention provides a method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement. By arranging an omnidirectional toroidal electrode observation system and using the method of virtual electrode calculation, the geological anomaly information of the entire tunnel torus in front of the tunnel excavation can be obtained, effectively ensuring the accuracy and scope of the advanced detection.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement, and the specific steps are as follows:

[0006] Step 1. Arrange the omnidirectional toroidal electrode observation system: According to the previous geological exploration situation, first use a shield machine to construct a certain distance along the tunneling direction and then stop. In the excavated tunnel behind the shield machine, s omnidirectional toroidal electrode groups are arranged at equal intervals starting from the tail end of the shield machine. Each omnidirectional toroidal electrode group consists of 6 toroidal electrodes. The 6 toroidal electrodes are fixed on the inner wall of the excavated tunnel, and are located on the circumference of the same cross-section of the excavated tunnel and evenly divide the circumference. The horizontal distance between adjacent two omnidirectional toroidal electrode groups is d. And starting from the tail end of the shield machine, each toroidal electrode in each omnidirectional toroidal electrode group is numbered in sequence. And place a measuring electrode in the unexcavated formation in front of the shield machine through a ground borehole as an infinite far electrode.

[0007] Step 2. Establish an advanced detection observation coordinate system: Take the center of the circle where the omnidirectional toroidal electrode group closest to the tail end of the shield machine in Step 1 is located as the origin O, the opposite direction of tunneling as the X-axis, the direction perpendicular to the X-axis and towards the top of the tunnel as the Z-axis, and the direction perpendicular to the X-axis and towards the horizontal side of the tunnel as the Y-axis to establish an advanced detection observation coordinate system. And according to this coordinate system, the spatial coordinates of each toroidal electrode in s omnidirectional toroidal electrode groups are obtained in sequence.

[0008] Step 3. Conduct advanced detection with the omnidirectional toroidal electrode observation system: Connect each toroidal electrode in each omnidirectional toroidal electrode group to a parallel electrical method instrument, and supply power to each toroidal electrode in the 1st group to the mth group in sequence according to the numbering order starting from the tail end of the shield machine. When each toroidal electrode is powered, record the excitation current at this time. Potential data acquisition is carried out for the remaining toroidal electrodes in s omnidirectional toroidal electrode groups. Finally, 6*m power supplies are carried out, so as to obtain the excitation current and potential data acquisition corresponding to each power supply.

[0009] Step 4. Calculate the excitation current of each omnidirectional toroidal electrode group: According to the excitation current data recorded in Step 3, average the excitation currents recorded when each of the 6 toroidal electrodes in the 1st group is powered to obtain the excitation current value of the 1st group. Subsequently, repeat the above process to calculate the excitation current values of each group in sequence, so as to obtain the excitation current values of the 1st group to the mth group respectively.

[0010] Step 5. Calculate the primary field potential data of each omnidirectional toroidal electrode group: According to the potential data collected in Step 3, when the 1st toroidal electrode in the 1st group is powered, obtain the primary field potential data collected by all toroidal electrodes in the 2nd group and average them to get U 1,2,1,avg ; when the 2nd toroidal electrode in the 1st group is powered, obtain the primary field potential data collected by all toroidal electrodes in the 2nd group and average them to get U 1,2,2,avg ; and so on. After the 6 toroidal electrodes in the 1st group are powered in sequence, the primary field potential data collected corresponding to different electrode power supplies in the 2nd group are obtained as U 1,2,1,avg ,U1,2,2,avgr , U 1,2,3,avgr , U 1,2,4,avg , U 1,2,5,avg , U 1,2,6,avg , then calculate the average of these 6 data as the primary field potential data U collected by all toroidal electrodes in the second group during the power supply of the first group 1,2,avg ; Repeat the above process. When the toroidal electrodes numbered 1-6 in the first group are powered on in sequence, the primary field potential data collected by all toroidal electrodes in the third group to the s-th group are obtained in sequence, which are U 1,3,avg , U 1,4,avg ... U 1,s，avg ;

[0011] After completing the calculation of the potential data of each group during the power supply of the first group, repeat the above steps to calculate the primary field potential data collected by all toroidal electrodes in the third group to the s-th group during the power supply of the second group, which are U 2,3,avg , U 2,4,avg ... U 2,s,avg ;

[0012] Repeat in this way until calculating the primary field potential data collected by all toroidal electrodes in the (m + 1)-th group to the s-th group during the power supply of the m-th group, which are U m,m+1,avg , U m,m+2,avg ... U m,s,avg ;

[0013] Step Six: Establish virtual electrodes: Based on the data obtained in Step Four and Step Five respectively, take the center of each omnidirectional toroidal electrode group as the virtual electrode of this group. Then, a total of s virtual electrodes are formed on the central axis of the tunnel, and each virtual electrode corresponds to the excitation current I iavg and the primary field potential data U ijavg ; And the coordinates of each virtual electrode can be obtained;

[0014] Step Seven: Screen the virtual electrode arrangement that meets the requirements: According to the virtual electrode coordinates and data established in Step Six, screen out the virtual electrode arrangement that meets the requirements;

[0015] Step Eight: Calculate the apparent resistivity for the virtual electrode arrangement: According to the virtual electrode arrangement screened in Step Seven and its corresponding potential data, calculate the apparent resistivity;

[0016] Step Nine: Judge the geological conditions in front of the shield machine: According to the apparent resistivity data obtained in Step Eight, use the spherical shell theory for forward offset imaging to obtain the position of abnormal geological development in front.

[0017] Furthermore, in the above Step One, the numbers are E ij ~E ij, where \(i = 1\sim s\) and \(j = 1\sim6\), where \(i\) represents the group number and \(j\) represents the serial number of each toroidal electrode in each group.

[0018] Furthermore, in the first step, the toroidal electrodes are coupled with the annular concrete segments on the inner wall of the tunnel by conductive adhesive. This can ensure the electrode coupling effect, reduce the grounding resistance, and achieve lossless installation.

[0019] Furthermore, in the third step, the supply voltage during each power supply is 96V, the constant current time is 0.5s, and the sampling interval is 50ms. Using these parameters for power supply can better ensure the accuracy of the acquired data.

[0020] Furthermore, in the fourth step, when calculating the average of the excitation currents recorded when each of the 6 toroidal electrodes in the first group is powered, the specific process is as follows: The excitation currents collected by the 6 toroidal electrodes in the first group are \(I\) ij , where \(i = 1\) and \(j = 1\sim6\), then the average value \(I\) of the excitation currents in the first group 1avg is calculated by the following formula:

[0021]

[0022] Furthermore, the specific screening process in the seventh step is as follows:

[0023] When a certain virtual electrode is used as the power supply electrode, it is represented by \(A\), the potential measurement electrodes are represented by \(M\) and \(N\), and the midpoint of \(M\) and \(N\) is \(O'\). The specific screening conditions are as follows:

[0024] (1) When , since \(MN\) is too large, indicating that the underground range reflected is too large, this electrode arrangement is excluded;

[0025] (2) When \(OA>AO'\), this electrode arrangement is excluded.

[0026] Furthermore, the specific process of calculating the apparent resistivity in the eighth step is as follows:

[0027] (1) The formula for calculating the apparent resistivity of a single virtual electrode arrangement is:

[0028]

[0029] In the formula, \(\rho\) s represents the apparent resistivity, \(AM\) represents the distance between the power supply electrode \(A\) and the measurement electrode \(M\), \(AN\) represents the distance between the power supply electrode \(A\) and the measurement electrode \(N\), \(U\) M represents the measured potential at the electrode \(M\) point, and \(U\) N represents the measured potential at the electrode \(N\) point;

[0030] (2) For the same power supply electrode A, assuming that there are n pairs of MN corresponding to the same O', the apparent resistivity value at point O' is calculated using the weighted average method, and the calculation formula is as follows:

[0031]

[0032] Where ρ so' represents the apparent resistivity value at point O' calculated by the weighted average method, and ρ sp represents the apparent resistivity value calculated for the Pth pair of MN corresponding to the same power supply electrode A, AN p represents the distance between the power supply electrode A and the measuring electrode N p between them, AN q represents the distance between the power supply electrode A and the measuring electrode N q between them.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The present invention first proposes a subway tunnel advanced detection technology based on an omnidirectional toroidal electrode arrangement. First, an omnidirectional toroidal electrode observation system is arranged in the tunnel behind the shield machine, and an advanced detection observation coordinate system is established. Through the omnidirectional toroidal electrode observation system, advanced detection is carried out to obtain the corresponding excitation current and potential data. Then, through multi-directional toroidal electrode synchronous coupling measurement and enhanced superposition processing, a virtual electrode coordinate is formed, and the electrode arrangements generated by the virtual electrodes are screened. The electrode arrangements that meet the requirements are selected to obtain the corresponding data for subsequent calculation of the apparent resistivity, so as to realize the detection of geological anomalies in front of the subway tunnel excavation. Compared with the existing conventional resistivity advanced detection, the present invention effectively improves the accuracy and scope of the advanced detection.

[0035] (2) The present invention forms a subway tunnel advanced detection observation system based on an omnidirectional toroidal electrode arrangement with geoelectric information acquisition, processing and imaging. This system can realize the advanced detection of geological anomalies in front of the tunnel, serve the advanced prediction of geological disasters in front of the subway shield machine excavation, and provide technical support for the construction of deep space in China. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a layout schematic diagram of the omnidirectional toroidal electrode observation system of the present invention;

[0037] Figure 2 is a coordinate diagram of each toroidal electrode in the first group after the advanced detection observation coordinate system of the present invention is established;

[0038] Figure 3 is a schematic diagram of establishing a virtual electrode of the present invention;

[0039] Figure 4It is a schematic diagram showing that there are n pairs of MN measurement electrodes at the same O point in the present invention. Detailed implementation manners

[0040] The present invention will be further described below.

[0041] As Figure 1 shown, in a certain area, subway tunnel boring is required. The method of the present invention is used to conduct advanced detection on the front of the boring. The specific steps are as follows:

[0042] Step 1: Arrange an all-round toroidal electrode observation system: According to the previous geological exploration situation, first use a shield machine to construct a certain distance along the boring direction and then stop. In the excavated tunnel behind the shield machine, 16 all-round toroidal electrode groups are arranged at equal intervals starting from the tail end of the shield machine. Each all-round toroidal electrode group consists of 6 toroidal electrodes. The 6 toroidal electrodes are fixed on the inner wall of the excavated tunnel and are on the circumference of the same cross-section of the excavated tunnel and equally divide the circumference; the horizontal distance between adjacent two all-round toroidal electrode groups is 6 m; and starting from the tail end of the shield machine, each toroidal electrode in each all-round toroidal electrode group is numbered in sequence, which are E ij ~E ij , where i = 1 to s, j = 1 to 6, i represents the group number, and j represents the serial number of each toroidal electrode in each group; and a measurement electrode is placed through a ground borehole in the unexcavated formation in front of the shield machine as an infinite far electrode; in addition, the toroidal electrodes are coupled with the annular concrete segments on the inner wall of the tunnel by conductive adhesive. This can ensure the electrode coupling effect, reduce the grounding resistance, and achieve non-destructive installation.

[0043] Step 2: Establish an advanced detection observation coordinate system: Take the center of the circle of the circumference where the all-round toroidal electrode group closest to the tail end of the shield machine is located in Step 1 as the origin O, the opposite direction of the boring as the X-axis, the direction perpendicular to the X-axis and towards the top of the tunnel as the Z-axis, and the direction perpendicular to the X-axis and towards the horizontal side of the tunnel as the Y-axis to establish an advanced detection observation coordinate system; and according to this coordinate system, the spatial coordinates of each toroidal electrode in the 16 all-round toroidal electrode groups are obtained in sequence, which are the first group (X 1 ,R,0), (X 1 ,0.5R,Rsin60°), (X 1 ,-0.5R,Rsin60°), (X 1 ,-R,0), (X 1 ,-0.5R,-Rsin60°), (X 1 ,0.5R,-Rsin60°) as Figure 2 shown; the second group (X 2 ,R,0), (X 2 ,0.5R,Rsin60°), (X 2, -0.5R, Rsin60°), (X 2 , -R, 0), (X 2 , -0.5R, -Rsin60°), (X 2 , 0.5R, -Rsin60°) …… The 16th group (X 16 , R, 0), (X 16 , 0.5R, Rsin60°), (X 16 , -0.5R, Rsin60°), (X 16 , -R, 0), (X 16 , -0.5R, -Rsin60°), (X 16 , 0.5R, -Rsin60°), where X 1 , X 2 , X 3 ~X 15 , X 16 are the horizontal distances from the origin O, which are 0, 6, 12, ……, 84, 90 in sequence.

[0044] Step 3: The omnidirectional toroidal electrode observation system conducts advanced detection: Connect each toroidal electrode in each omnidirectional toroidal electrode group to a parallel electrical resistivity instrument, and supply power to each toroidal electrode in the 1st to 7th groups in sequence according to the numbering order starting from the tail end of the shield machine. When power is supplied to each toroidal electrode, record the excitation current at this time. Potential data is collected for the remaining 95 toroidal electrodes in the 16 omnidirectional toroidal electrode groups. The supply voltage for each power supply is 96V, the constant current time is 0.5s, and the sampling interval is 50ms. Using these parameters for power supply can better ensure the accuracy of the acquired data. Finally, 42 power supplies are performed to obtain the excitation current and potential data acquisition corresponding to each power supply;

[0045] Step 4: Calculate the excitation current of each omnidirectional toroidal electrode group: According to the excitation current data recorded in Step 3, average the excitation currents recorded when each of the 6 toroidal electrodes in the 1st group is powered, as the excitation current value of the 1st group; The specific process is as follows: The excitation currents collected by the 6 toroidal electrodes in the 1st group are I ij , where i = 1, j = 1~6, then the average value I 1avg of the excitation current of the 1st group is calculated by the following formula:

[0046]

[0047] Subsequently, repeat the above process to calculate the excitation current values of each group in sequence, so as to obtain the excitation current values of the 1st to 7th groups respectively;

[0048] Step 5. Calculate the primary field potential data of each omnidirectional toroidal electrode group: According to the potential data collected in Step 3, when the No. 1 toroidal electrode in Group 1 is powered, obtain the primary field potential data collected by all toroidal electrodes in Group 2 and calculate the average to get U 1,2,1,avg ; when the No. 2 toroidal electrode in Group 1 is powered, obtain the primary field potential data collected by all toroidal electrodes in Group 2 and calculate the average to get U 1,2,2,avg ; and so on. After the 6 toroidal electrodes in Group 1 are powered in sequence, the primary field potential data collected corresponding to different electrode power supplies in Group 2 are U 1,2,1,avg , U 1,2,2,avgr , U 1,2,3,avgr , U 1,2,4,avg , U 1,2,5,avg , U 1,2,6,avg respectively. Then, average these 6 data as the primary field potential data U 1,2,avg collected by all toroidal electrodes in Group 2 when Group 1 is powered; repeat the above process. When the No. 1-6 toroidal electrodes in Group 1 are powered in sequence, the primary field potential data collected by all toroidal electrodes in Groups 3 to 16 are obtained in sequence, which are U 1,3,avg , U 1,4,avg ... U 1,16，avg ;

[0049] After calculating the potential data of each group when Group 1 is powered, repeat the above steps to calculate the primary field potential data collected by all toroidal electrodes in Groups 3 to 16 when Group 2 is powered, which are U 2,3,avg , U 2,4,avg ... U 2,16,avg ;

[0050] Repeat in this way until calculating the primary field potential data collected by all toroidal electrodes in Groups 8 to 16 when Group 7 is powered, which are U 7,8,avg , U 7,9,avg ... U 7,16,avg ;

[0051] Step 6. Establish virtual electrodes: According to the data obtained in Step 4 and Step 5 respectively, take the center of each omnidirectional toroidal electrode group as the virtual electrode of this group. Then, a total of 16 virtual electrodes are formed on the central axis of the tunnel as shown in Figure 3 . And each virtual electrode corresponds to the excitation current I iavg (i represents the serial number of the power supply electrode of the virtual electrode, i = 1-7) and the primary field potential data U ijavg (i represents the serial number of the power supply electrode of the virtual electrode, and j represents the serial number of the measurement electrode of the virtual electrode); and the coordinates of the 16 virtual electrodes can be obtained as (0, 0, 0), (6, 0, 0), (12, 0, 0)... (90, 0, 0) in sequence;

[0052] Step 7. Screen the virtual electrode arrangements that meet the requirements: Based on the virtual electrode coordinates and data established in Step 6, screen out the virtual electrode arrangements that meet the requirements. The specific screening process is as follows:

[0053] When a certain virtual electrode is used as the power supply electrode, it is represented by A, the potential measurement electrodes are represented by M and N, and the midpoint of M and N is O'. The specific screening conditions are as follows:

[0054] (1) When , since MN is too large, the reflected underground range is too large, and this electrode arrangement is excluded;

[0055] (2) When OA > AO', this electrode arrangement is excluded.

[0056] Step 8. Calculate the apparent resistivity of the virtual electrode arrangement: Based on the virtual electrode arrangement screened in Step 7 and its corresponding potential data, calculate the apparent resistivity. The specific process is as follows:

[0057] (1) The formula for calculating the apparent resistivity of a single virtual electrode arrangement is:

[0058]

[0059] In the formula, ρ s represents the apparent resistivity, AM represents the distance between the power supply electrode A and the measurement electrode M, AN represents the distance between the power supply electrode A and the measurement electrode N, U M represents the measured potential at the M point of the electrode, U N represents the measured potential at the N point of the electrode;

[0060] (2) For the same power supply electrode A, assuming there are n pairs of MN corresponding to the same O', the weighted average method is used to calculate the apparent resistivity value at the O' point. The calculation formula is as follows:

[0061]

[0062] In the formula, ρ so ' represents the apparent resistivity value calculated by the weighted average method at the O' point, ρ sp represents the apparent resistivity value calculated for the Pth pair of MN corresponding to the same power supply electrode A, AN p represents the distance between the power supply electrode A and the measurement electrode N p , AN q represents the distance between the power supply electrode A and the measurement electrode N q .

[0063] Step 9. Determine the geological conditions in front of the shield machine: According to the apparent resistivity data obtained in Step 8, use the spherical shell theory for forward migration imaging to obtain the positions where geological anomalies develop in the front. If there are geological anomalies, adjust the tunneling direction or take corresponding protective measures. If there are no geological anomalies, the shield machine stops working again after tunneling a certain distance along the pre-set tunneling direction, and repeat the above process to conduct forward detection at the current position again.

[0064] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement, characterized in that, the specific steps are as follows: Step 1: Arrange an omnidirectional toroidal electrode observation system: According to the previous geological exploration situation, first use a shield machine to construct a certain distance along the tunneling direction and then stop. In the excavated tunnel behind the shield machine, s omnidirectional toroidal electrode groups are equally spaced from the end of the shield machine. Each omnidirectional toroidal electrode group consists of 6 toroidal electrodes. The 6 toroidal electrodes are fixed on the inner wall of the excavated tunnel and are on the circumference of the same cross-section of the excavated tunnel and evenly divide the circumference; the horizontal distance between adjacent omnidirectional toroidal electrode groups is d; and starting from the end of the shield machine, each toroidal electrode in each omnidirectional toroidal electrode group is numbered in sequence; and a measuring electrode is placed through a ground borehole in the unexcavated formation in front of the shield machine as an infinite far electrode; Step 2: Establish an advanced detection observation coordinate system: Take the center of the circle of the omnidirectional toroidal electrode group closest to the end of the shield machine in Step 1 as the origin O, the opposite direction of tunneling as the X-axis, the direction perpendicular to the X-axis and towards the top of the tunnel as the Z-axis, and the direction perpendicular to the X-axis and towards the horizontal side of the tunnel as the Y-axis to establish an advanced detection observation coordinate system; And according to this coordinate system, the spatial coordinates of each toroidal electrode in the s omnidirectional toroidal electrode groups are obtained in sequence; Step 3: Conduct advanced detection with the omnidirectional toroidal electrode observation system: Connect each toroidal electrode in each omnidirectional toroidal electrode group to a parallel electrical method instrument, and supply power to each toroidal electrode in the 1st to mth groups in sequence according to the numbering order starting from the end of the shield machine. When each toroidal electrode is powered, record the excitation current at this time, and collect potential data for the remaining toroidal electrodes in the s omnidirectional toroidal electrode groups. Finally, 6*m power supplies are carried out to obtain the excitation current and potential data collection corresponding to each power supply; Step 4: Calculate the excitation current of each omnidirectional toroidal electrode group: According to the excitation current data recorded in Step 3, average the excitation currents recorded when each of the 6 toroidal electrodes in the 1st group is powered to obtain the excitation current value of the 1st group; subsequently, repeat the above process to calculate the excitation current values of each group in sequence, so as to obtain the excitation current values of the 1st to mth groups respectively; Step 5. Calculate the primary field potential data of each omnidirectional toroidal electrode group: According to the potential data collected in Step 3, when the 1st toroidal electrode in the 1st group supplies power, obtain the primary field potential data collected by all toroidal electrodes in the 2nd group and calculate the average to get U 1,2,1,avg ; when the 2nd toroidal electrode in the 1st group supplies power, obtain the primary field potential data collected by all toroidal electrodes in the 2nd group and calculate the average to get U 1,2,2,avg ; and so on. After the 6 toroidal electrodes in the 1st group supply power in sequence, the primary field potential data collected correspondingly when different electrodes in the 2nd group supply power are U 1,2,1,avg , U 1,2,2,avgr , U 1,2,3,avgr , U 1,2,4,avg , U 1,2,5,avg , U 1,2,6,avg . Then calculate the average of these 6 data as the primary field potential data U 1,2,avg collected by all toroidal electrodes in the 2nd group when the 1st group supplies power; Repeat the above process. When the 1st to 6th toroidal electrodes in the 1st group supply power in sequence, the primary field potential data collected by all toroidal electrodes in the 3rd group to the s-th group are obtained in sequence, which are U 1,3,avg , U 1,4,avg ... U 1,s，avg ; After calculating the potential data of each group when the first power supply is completed, repeat the above steps. When calculating the second power supply, the primary field potential data collected by all toroidal electrodes in the third group to the s-th group are U 2,3,avg 、U 2,4,avg ……U 2,s,avg ; Repeat the above process until when calculating the power supply for the m-th group, the on-site potential data are collected once for all toroidal electrodes in the (m + 1)-th group to the s-th group, which are U m,m+1,avg , U m,m+2,avg ... U m,s,avg ; Step 6. Establish virtual electrodes: Based on the data obtained in Step 4 and Step 5 respectively, take the center of each omnidirectional toroidal electrode group as the virtual electrode of this group. Then, s virtual electrodes are formed on the central axis of the tunnel, and each virtual electrode corresponds to the excitation current I iavg and the primary field potential data U ijavg ; and the coordinates of each virtual electrode can be obtained; Step 7: Screen the virtual electrode arrangements that meet the requirements: According to the virtual electrode coordinates and data established in Step 6, screen out the virtual electrode arrangements that meet the requirements; Step 8: Calculate the apparent resistivity of the virtual electrode arrangements: According to the virtual electrode arrangements screened in Step 7 and their corresponding potential data, calculate the apparent resistivity; Step 9: Judge the geological conditions in front of the shield machine: According to the apparent resistivity data obtained in Step 8, use the spherical shell theory for advanced offset imaging to obtain the positions of geological anomalies in front.

2. The method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement according to claim 1, characterized in that, In the first step, those numbered E ij ~E ij , where i = 1 to s and j = 1 to 6, with i representing the number of groups and j representing the serial number of each toroidal electrode in each group.

3. The method for advanced detection of tunnel geological anomalies based on an omnidirectional toroidal electrode arrangement according to claim 1, characterized in that, In Step 1, the toroidal electrodes are coupled with the annular cement segments on the inner wall of the tunnel by conductive glue.

4. The tunnel geological anomaly advanced detection method based on the omnidirectional toroidal electrode arrangement according to claim 1, characterized in that, the power supply voltage during each power supply in step 3 is 96V, the constant current time is 0.5s, and the sampling interval is 50ms.

5. The tunnel geological anomaly advanced detection method based on the omnidirectional toroidal electrode arrangement according to claim 1, characterized in that, The average of the excitation currents recorded when each of the 6 toroidal electrodes in the first group is powered in the fourth step is calculated as follows: The excitation currents collected by the 6 toroidal electrodes in the first group are successively I ij , where i = 1, j = 1 to 6. Then the average value I 1avg of the excitation currents in the first group is calculated by the following formula:

6. The tunnel geological anomaly advanced detection method based on the omnidirectional toroidal electrode arrangement according to claim 1, characterized in that, the specific screening process in step 7 is as follows: When a certain virtual electrode is used as the power supply electrode, it is represented by A, the potential measurement electrodes are represented by M and N, and the midpoint of M and N is O'. The specific screening conditions are as follows: (1)When the time comes, since MN is too large, reflecting too large a subsurface area, this electrode array is excluded; (2) When OA > AO', this electrode arrangement is excluded.

7. The tunnel geological anomaly advanced detection method based on the omnidirectional toroidal electrode arrangement according to claim 6, characterized in that, the specific process of calculating the apparent resistivity in step 8 is as follows: (1) The formula for calculating the apparent resistivity of a single virtual electrode arrangement is where ρ s represents apparent resistivity, AM represents the distance between the power supply electrode A and the measuring electrode M, AN represents the distance between the power supply electrode A and the measuring electrode N, U M represents the measured potential at electrode M, U N represents the measured potential at electrode N; (2) For the same power supply electrode A, assuming that there are n pairs of MN corresponding to the same O', the weighted average method is used to calculate the apparent resistivity value at the O' point. The calculation formula is as follows: where ρ so' represents the apparent resistivity value at point O calculated by the weighted average method, ρ sp represents the apparent resistivity value calculated for the Pth pair of MN for the same power supply electrode A, AN p represents the distance between the power supply electrode A and the measuring electrode N p AN q represents the distance between the power supply electrode A and the measuring electrode N q and the distance therebetween.

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