Shield tunnel prestress monitoring system and method

Abstract

The invention discloses a shield tunnel pre-stress monitoring system and method, belongs to the technical field of pre-stress monitoring, and solves the technical problem of reliability monitoring of states such as annular pre-stress distribution and pre-stress loss in a shield tunnel structure. The method comprises: selecting a measuring point position; arranging a first type of tension sensor at the measuring point position; selecting a plurality of measuring point positions from the measuring point positions for arranging a second type of tension sensor; monitoring the cable force value of the prestressed tendon at each measuring point position in real time through a first type of tension sensor and a second type of tension sensor; comparing and analyzing the cable force value monitored by the first type of tension sensor and the cable force value monitored by the second type of tension sensor, and backing up the cable force value at the important measuring point position; calculating a prestress loss actual value of each measuring point position according to the cable force value of each measuring point position; and comparing the actual value of the prestress loss of each measuring point position with the theoretical value of the prestress loss to verify the reliability of the project.

Description

Technical Field

[0001] The present invention relates to the technical field of prestress monitoring, and more particularly to a shield tunnel prestress monitoring system and method. Background Art

[0002] Currently, the segmental lining structure serves as the initial support component of shield tunnels and is also the permanent structure of the tunnel, bearing the effects of the reaction force of the shield support shoe, soil pressure, groundwater pressure, and some special loads. In fact, the segmental structure is a discontinuous structure connected by bolts, tongues and grooves, and pins, with poor overall rigidity and weak deformation resistance. With the development of underground space construction, the burial depth and diameter of shield tunnel projects have gradually increased, and the conditions of the strata they pass through are complex and changeable. This has caused the load on the segment structure to increase, and the force is uneven and the force pattern is complex. At the same time, it has also put higher requirements on the mechanical properties of the segment structure.

[0003] As shield tunnel structures are closely related to engineering safety, an invention currently published in China with the publication number CN105422177A has disclosed a shield tunnel structure health monitoring and safety early warning system, which effectively monitors tunnel deformation, settlement, cracking, segment damage, water leakage, and the environment. However, it lacks reliable monitoring of the circumferential prestress distribution and prestress loss within the shield tunnel structure. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art. One purpose of the present invention is to provide a method for monitoring prestress in a shield tunnel.

[0005] The second purpose of the present invention is to provide a shield tunnel prestress monitoring system.

[0006] In order to achieve the above-mentioned first object, the present invention provides a shield tunnel prestressing monitoring method, comprising the following steps:

[0007] Step 1. Construct a prestressed tendon model for a shield segment tunnel, simulate the stress distribution of the prestressed tendons after tensioning under the condition of bonding and no slip, and select the measurement point locations based on theoretical calculations of prestress loss and finite element simulation analysis results;

[0008] Step 2. Arrange a first type of tension sensor at the measuring point;

[0009] Step 3. Selecting a plurality of measuring point locations from the measuring point locations for arranging the second type of tension sensor;

[0010] Step 4. Using the first type tension sensor and the second type tension sensor, the tension value of the prestressed tendons at each of the measuring points is monitored in real time;

[0011] Step 5. Compare and analyze the cable force values ​​monitored by the first type of tension sensor with the cable force values ​​monitored by the second type of tension sensor, and back up the cable force values ​​at important measuring points;

[0012] Step 6. Calculating the actual value of prestress loss at each measuring point based on the cable force value at each measuring point;

[0013] Step 7. Compare the actual value of prestress loss at each of the measuring points with the theoretical value of prestress loss to verify the reliability of the project.

[0014] As a further improvement, the measuring point locations include the anchorage end corner transition point of the prestressed tendon (1#, 7#), vertical direction (3#, 4#), the horizontal angle of 37.5° above the anchorage end (5#), horizontal direction (6#), and circumferential midpoint (2#), a total of 7 measuring points.

[0015] Furthermore, the measuring point positions for arranging the second type of tension sensor include three measuring points, namely the anchor end corner transition points (1#, 7#) and the circumferential midpoint (2#).

[0016] Furthermore, the prestress loss includes the prestress loss caused by the friction between the prestressing tendons and the pipe wall, and the calculation process is:

[0017] The cable force value F at the measuring point i The sensor calibration curve is used to calculate the stress σ of the prestressed tendon at each measuring point. i , the friction coefficient μ between the prestressed tendons and the pipe wall is calculated according to the following formula:

[0018]

[0019] Where: σ1 is the stress value of the prestressed tendon at the transition point (1#) of the anchor end after tensioning; σ2 is the stress value of the circumferential midpoint (2#) after tensioning; k is the coefficient of influence of local deviation per meter of pipeline on friction; θ is the sum of the angles of the tangent lines of the pipeline section from the tensioning end to the calculated section curve; x is the length of the pipeline from the tensioning end to the calculated section;

[0020] Prestress loss σ caused by friction between the prestressing tendons and the pipe wall l1 for:

[0021] σ l1 =σ con [1-e -(μθ+kx) ],x≤L / 2

[0022] Where: σ con is the tension control stress value under the prestressed tendon anchor; L is the total length of the prestressed tendon.

[0023] Furthermore, the prestress loss also includes the prestress loss caused by the deformation of the tensioning end anchor and the shrinkage of the prestressed tendons. The calculation process is:

[0024]

[0025] Where: σ l2 is the prestress loss caused by the deformation of the tensioning end anchor and the shrinkage of the prestressed tendons, and Ep is the elastic modulus of the steel strand.

[0026] Furthermore, the following warnings are issued based on the deviation between the actual value of prestress loss and the theoretical value of prestress loss:

[0027] Warning of excessive prestress loss. When the deviation exceeds the allowable range, it will lead to insufficient structural stiffness, reduced ultimate bearing capacity reserve, and reduced safety margin. It is necessary to quickly investigate the cause and evaluate the impact on structural safety and performance;

[0028] Early warning of rapid prestress loss development: Through continuous monitoring data comparison, when the rate of change of deviation is higher than the theoretically predicted rate or the range of the historical average rate of change, it indicates that some damage or deterioration may be occurring or aggravated. It is necessary to closely monitor the development trend, find the cause, and consider whether intervention is needed;

[0029] Prestress loss distribution abnormality warning: When the actual distribution of prestress loss at each measuring point is inconsistent with the theoretical prediction or structural symmetry, it indicates that there may be a problem in the local area and the abnormal area needs to be located and inspected immediately;

[0030] Prestress sudden loss warning: monitoring data shows that the stress value has dropped significantly in a short period of time, and the prestress loss increment is much greater than the normal time-varying loss rate, indicating that some kind of sudden damage or failure event is very likely to have occurred, and emergency inspection and structural safety assessment are required.

[0031] Furthermore, shield segments for monitoring prestress are evenly spaced within the tunnel route section, and additional shield segments for monitoring prestress are provided in areas with sudden line changes, complex geology, and irregular loads.

[0032] In order to achieve the above-mentioned second purpose, the present invention provides a shield tunnel prestressed force monitoring system, including a remote operation workbench, and a first type of tension sensor and a second type of tension sensor installed at a measuring point. The remote operation workbench is provided with a data acquisition edge module, the first type of tension sensor is electrically connected to a first data acquisition station, and the second type of tension sensor is electrically connected to a second data acquisition station. The first data acquisition station and the second data acquisition station are wirelessly connected to the data acquisition edge module.

[0033] As a further improvement, the first type of tension sensor is a magnetic flux sensor, and accordingly, the first data acquisition station is a magnetic flux data acquisition station, which is provided with a multiplexing module and a magnetoelastic instrument;

[0034] The second type of tension sensor is a fiber Bragg grating strain gauge. Correspondingly, the second data acquisition station is a fiber Bragg grating data acquisition station, and a fiber Bragg grating demodulator is provided in the fiber Bragg grating data acquisition station.

[0035] Furthermore, the magnetic flux sensor includes a curved bobbin and a data line. The curvature of the curved bobbin is adapted to the curvature of the prestressed channel in the shield segment. A coil is wound around the outer wall of the curved bobbin. The outer periphery of the curved bobbin is provided with a curved outer sleeve covering the coil. A baffle is provided between the two ends of the curved bobbin and the curved outer sleeve. The data line passes through the baffle and is electrically connected to the coil. The gap between the coil and the curved outer sleeve is poured with epoxy resin, and the outer wall of the curved outer sleeve is provided with a polyurea layer.

[0036] Beneficial effects

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. The present invention uses a magnetic flux sensor and intelligent prestressed tendons to construct a prestress monitoring system to monitor the cable tension in the shield tunnel segment, calculate the actual value of prestress loss at each measuring point, and compare it with the theoretical value of prestress loss. The reliability of the project is verified based on the comparison results, and reliability monitoring of the circumferential prestress distribution, prestress loss and other conditions in the shield tunnel structure is achieved.

[0039] 2. The present invention combines magnetic flux sensors and intelligent prestressed tendons to monitor cable tension, which can achieve complementary advantages in measurement methods, comparative analysis of monitoring data, and backup of important monitoring points.

[0040] 3. Compared with conventional linear magnetic flux sensors, the curved magnetic flux sensor of the present invention can be suitable for prestress monitoring of tunnel structures with different prestressed channel curvature radii, greatly increasing the applicability and practicality of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the layout diagram of the magnetic flux sensor measurement points;

[0042] Figure 2 Layout diagram of intelligent prestressed reinforcement measurement points for shield tunnel structures;

[0043] Figure 3 This is the framework diagram of the magnetic flux sensor prestress monitoring;

[0044] Figure 4This is a diagram of the intelligent prestressing reinforcement prestressing monitoring framework for shield tunnel structures;

[0045] Figure 5 Schematic diagram of the magnetic flux sensor structure.

[0046] Among them: 1-first type tension sensor, 2-second type tension sensor, 3-prestressed tendon, 4-pipe wall, 5-remote operation workbench, 6-data acquisition edge module, 7-first data acquisition station, 8-second data acquisition station, 9-multiplexing module, 10-magnetoelastic instrument, 11-fiber Bragg grating demodulator, 12-bending spool, 13-data line, 14-coil, 15-bending outer sleeve, 16-baffle, 17-epoxy resin, 18-polyurea layer, 19-vent. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the specific embodiments in the accompanying drawings.

[0048] See Figures 1 to 5 , a shield tunnel prestressing monitoring method, comprising the following steps:

[0049] Step 1. Construct a prestressed tendon model for a shield segment tunnel, simulate the stress distribution of the prestressed tendons after tensioning under the condition of bonding and no slip, and select the measurement point locations based on theoretical calculations of prestress loss and finite element simulation analysis results;

[0050] Step 2. Arrange the first type of tension sensor 1 at the measuring point;

[0051] Step 3. Select several measuring point locations from the measuring point locations for arranging the second type tension sensor 2;

[0052] Step 4. Using the first type tension sensor 1 and the second type tension sensor 2 to monitor the cable tension value of the prestressed tendons at each measuring point in real time;

[0053] Step 5. Compare and analyze the cable force values ​​monitored by the first type tension sensor 1 and the cable force values ​​monitored by the second type tension sensor 2, and back up the cable force values ​​at important measuring points;

[0054] Step 6. Calculate the actual value of prestress loss at each measuring point based on the cable force value at each measuring point;

[0055] Step 7. Compare the actual value of prestress loss at each measuring point with the theoretical value of prestress loss to verify the reliability of the project.

[0056] Specifically, the measuring points include the anchorage end corner transition point of the prestressed tendon 3 (1#, 7#), the vertical direction (3#, 4#), the horizontal angle of 37.5° above the anchorage end (5#), the horizontal direction (6#), and the circumferential midpoint (2#), a total of 7 measuring points.

[0057] The locations of the 7 measuring points are described as follows:

[0058] ① Anchorage end corner transition point (1#, 7#): monitor prestress loss caused by prestressed tendon shrinkage;

[0059] ② The midpoint of the circumferential prestressed tendons (2#): the point where the prestress loss is the largest;

[0060] ③ The direction with a horizontal angle of 37.5° above the anchor end (5#): the point of maximum stress;

[0061] ④Vertical direction (3#, 4#): monitor the vertical stress of the hoop prestressed tendons;

[0062] ⑤Horizontal direction (6#): monitor the horizontal stress of the circumferential prestressed tendons.

[0063] The measuring point positions for arranging the second type tension sensor 2 include three measuring points, namely the anchor end corner transition points (1#, 7#) and the circumferential midpoint (2#).

[0064] The first type of tension sensor 1 and the second type of tension sensor 2 are two different types of tension sensors, which are used to perform multiple monitoring and comparative analysis of monitoring data on important prestressed parts of the structure, judge the reliability of each sensor data in combination with the theoretical calculation results of prestress loss, and calibrate the data of another sensor.

[0065] The prestress loss includes the prestress loss caused by the friction between the prestressing tendons 3 and the pipe wall 4. The calculation process is:

[0066] The cable force value F at the measuring point i Bring in the sensor calibration curve (the sensor calibration curve is pre-calibrated and produced) to calculate the stress σ of the prestressed tendon 3 at each measuring point i The friction coefficient μ between the prestressed tendon 3 and the pipe wall 4 is calculated according to the following formula:

[0067]

[0068] Where: σ1 is the stress value of the prestressed tendon 3 at the transition point (1#) of the anchor end after tensioning; σ2 is the stress value of the circumferential midpoint (2#) after tensioning; k is the influence coefficient of the local deviation of the pipeline per meter on friction; θ is the sum of the angles of the tangent lines of the pipeline section from the tensioning end to the calculated section curve; and x is the length of the pipeline from the tensioning end to the calculated section.

[0069] Prestress loss σ caused by friction between the prestressing tendon 3 and the pipe wall 4 l1 for:

[0070] σ l1 =σ con [1-e -(μθ+kx) ],x≤L / 2

[0071] Where: σ con is the tension control stress value under the anchor of prestressed tendon 3; L is the total length of prestressed tendon 3.

[0072] The prestress loss also includes the prestress loss caused by the deformation of the tensioning end anchor and the shrinkage of the prestressed tendon 3. The calculation process is as follows:

[0073]

[0074] Where: σ l2 is the prestress loss caused by the deformation of the tensioning end anchorage and the shrinkage of the prestressed tendon 3, and Ep is the elastic modulus of the steel strand.

[0075] Since two different tension sensors, the first type tension sensor 1 and the second type tension sensor 2, are used to monitor data, at the anchor end corner transition point (1#, 7#) and the circumferential midpoint (2#), when the difference between the data monitored by the first type tension sensor 1 and the second type tension sensor 2 is within the set range, the average value of the first type tension sensor 1 and the second type tension sensor 2 is taken as the cable force value F at the measuring point. i When the data monitored by the first type tension sensor 1 and the second type tension sensor 2 differ too much, it is necessary to check or calibrate the tension sensor whose data changes too much, and take the data of the normal tension sensor as the cable force value F at the measuring point. i .

[0076] That is, the first type of tension sensor 1 and the second type of tension sensor 2 can be used for data comparison and analysis, important detection point backup, sensor calibration, etc.; if there are differences, it is necessary to conduct working condition analysis, and judge the reliability of the data in combination with theoretical values, and recalibrate the sensor with large data errors.

[0077] The following warnings are issued based on the deviation between the actual value of prestress loss and the theoretical value of prestress loss (the theoretical value of prestress loss is the value obtained by theoretical calculation based on the set parameters):

[0078] 1. Warning of excessive prestress loss. When the deviation exceeds the allowable range, it will lead to insufficient structural stiffness, reduced ultimate bearing capacity reserve, and reduced safety margin. It is necessary to quickly investigate the cause and evaluate the impact on structural safety and performance;

[0079] 2. Early warning of rapid development of prestress loss. By comparing continuous monitoring data, when the rate of change of deviation is higher than the theoretically predicted rate or the range of the historical average rate, it indicates that some damage or deterioration may be occurring or aggravating. It is necessary to closely monitor the development trend, find the cause, and consider whether intervention is needed;

[0080] 3. Prestress loss distribution abnormality warning: When the actual distribution of prestress loss at each measuring point is inconsistent with the theoretical prediction or structural symmetry (such as in the vertical direction (3#, 4#)), it indicates that there may be a problem in the local area and the abnormal area needs to be located and inspected immediately;

[0081] 4. Prestress sudden loss warning: Monitoring data shows that the stress value drops significantly in a short period of time, and the prestress loss increment is much greater than the normal time-varying loss rate, indicating that some sudden damage or failure event is very likely to have occurred, and emergency inspection and structural safety assessment are required.

[0082] Furthermore, shield segments for monitoring prestress are evenly spaced throughout the tunnel route, and additional shield segments for monitoring prestress are added in areas with sudden changes in line shape, complex geology, and irregular loads. This eliminates the need to deploy both the first-type tension sensor 1 and the second-type tension sensor 2 on every ring of shield segments for monitoring, saving costs.

[0083] A shield tunnel prestress monitoring system includes a remote operation workbench 5, and a first-type tension sensor 1 and a second-type tension sensor 2 installed at a measuring point. The remote operation workbench 5 is provided with a data acquisition edge module 6. The first-type tension sensor 1 is electrically connected to a first data acquisition station 7, and the second-type tension sensor 2 is electrically connected to a second data acquisition station 8. The first data acquisition station 7 and the second data acquisition station 8 are wirelessly connected to the data acquisition edge module 6.

[0084] In this embodiment, the first type of tension sensor 1 is a magnetic flux sensor. Accordingly, the first data acquisition station 7 is a magnetic flux data acquisition station, which includes a multiplexing module 9 and a magnetoelastic instrument 10. Data from each magnetic flux sensor is transmitted to the magnetoelastic instrument 10 via the multiplexing module 9. After obtaining the monitoring data, the magnetic flux data acquisition station uploads it to the data acquisition edge module 6 via a 4G / 5G network. The data acquisition edge module 6 then transmits the data to the remote operation workstation 5 for analysis.

[0085] The magnetic flux sensor needs to be embedded in advance, that is, when casting the shield segment, the magnetic flux sensor is installed in a through-hole type outside the corrugated pipe / steel sheath pipe. The corrugated pipe / steel sheath pipe constitutes a prestressed channel. The magnetic flux sensor is fixed with a positioning block. The data line of the magnetic flux sensor is led out along the steel bar through the wire protection pipe and the exhaust hole 19.

[0086] The second-type tension sensor 2 is a fiber Bragg grating strain gauge. Accordingly, the second data acquisition station 8 is a fiber Bragg grating data acquisition station, which is equipped with a fiber Bragg grating demodulator 11. After the data from each fiber Bragg grating strain gauge is input into the fiber Bragg grating demodulator 11 and obtained, the fiber Bragg grating data acquisition station uploads the data to the data acquisition edge module 6 via the 4 / 5G network. The data acquisition edge module 6 then transmits the data to the remote operation workstation 5 for analysis.

[0087] Three fiber Bragg grating (FBG) measurement points (i.e., three fiber Bragg grating (FBG) strain gauges) are arranged through the intelligent prestressed tendons used in shield tunnel structures. These are located at the transition point of the anchor end corner and the midpoint of the circumferential prestressed tendons. This allows for multiple monitoring of important structural stress-bearing locations and comparative analysis of monitoring data. The intelligent prestressed tendons used in shield tunnel structures are directly inserted into the steel pipe sheath / corrugated tube, and the outgoing wires are led out from the end of the steel strand.

[0088] The intelligent prestressed tendons used in shield tunnel structures are made by coupling the optical fiber of the sensor grating with the central wire of the steel strand before leaving the factory, thereby manufacturing intelligent prestressed tendons with the function of sensing force. Their technical parameters are as follows: ① Measurement range: ≥8000με; ② Adaptable ambient temperature: -40~80℃; ③ Accuracy: ≤1%FS; ④ Measurement resolution: 0.1%FS; ⑤ Wavelength range: 1528~1568nm.

[0089] The communication cables and optical fibers of the magnetic flux sensor are protected by conduit.

[0090] In this embodiment, the magnetic flux sensor includes a curved spool 12 and a data line 13. The curvature of the curved spool 12 is adapted to the curvature of the prestressed channel in the shield segment. A coil 14 is wound around the outer wall of the curved spool 12. The outer periphery of the curved spool 12 is provided with a curved outer sleeve 15 covering the coil 14. A baffle 16 is provided between the two ends of the curved spool 12 and the curved outer sleeve 15. The data line 13 passes through the baffle 16 and is electrically connected to the coil 14. The gap between the coil 14 and the curved outer sleeve 15 is poured with epoxy resin 17, and the outer wall of the curved outer sleeve 15 is provided with a polyurea layer 18.

[0091] The inner diameter of the magnetic flux sensor (i.e., the inner diameter of the curved bobbin 12) is the outer diameter of the mounting component (i.e., the bellows / steel sheath tube) + (3mm~10mm), and its technical parameters are: ① Measuring range: 0~yield stress; ② Adaptable ambient temperature: -40~80℃; ③ Accuracy: ≤3%FS; ④ Measurement resolution: 0.2%FS.

[0092] Compared with conventional linear magnetic flux sensors, curved magnetic flux sensors can be suitable for prestress monitoring of tunnel structures with different prestressed channel curvature radii, greatly increasing the applicability and practicality of the sensor.

[0093] Of course, in other embodiments, the first type tension sensor 1 and the second type tension sensor 2 may also be tension sensors of other forms.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A shield tunnel prestressing monitoring method, characterized in that: The following steps are involved: Step 1. Construct a prestressed tendon model for a shield segment tunnel, simulate the stress distribution of the prestressed tendons after tensioning under the condition of bonding and no slip, and select the measurement point locations based on theoretical calculations of prestress loss and finite element simulation analysis results; Step 2. Arranging a first type of tension sensor (1) at the measuring point; Step 3. Selecting a plurality of measuring point locations from the measuring point locations for arranging the second type tension sensor (2); Step 4. Real-time monitoring of the cable tension value of the prestressed tendons at each of the measuring points using the first type tension sensor (1) and the second type tension sensor (2); Step 5. Compare and analyze the cable force value monitored by the first type tension sensor (1) and the cable force value monitored by the second type tension sensor (2), and back up the cable force values ​​at important measuring points; Step 6. Calculating the actual value of prestress loss at each measuring point based on the cable force value at each measuring point; Step 7. Compare the actual value of prestress loss at each of the measuring points with the theoretical value of prestress loss to verify the reliability of the project.

2. A shield tunnel prestressing monitoring method according to claim 1, characterized in that: The measuring point positions include seven measuring points in total, namely, the anchorage end corner transition point (1#, 7#) of the prestressed tendon (3), the vertical direction (3#, 4#), the horizontal angle 37.5° direction above the anchorage end (5#), the horizontal direction (6#), and the circumferential midpoint (2#).

3. A shield tunnel prestressing monitoring method according to claim 2, characterized in that: The measuring point positions for arranging the second type tension sensor (2) include three measuring points, namely, the anchor end corner transition points (1#, 7#) and the circumferential midpoint (2#).

4. A shield tunnel prestress monitoring system according to claim 1, characterized in that: The prestress loss includes the prestress loss caused by the friction between the prestressing tendons (3) and the pipe wall (4). The calculation process is: The cable force value F at the measuring point i Substitute the sensor calibration curve to calculate the stress σ of the prestressed tendon (3) at each measuring point i The friction coefficient μ between the prestressed tendon (3) and the pipe wall (4) is calculated according to the following formula: Where: σ1 is the stress value of the prestressed tendon (3) at the transition point (1#) of the anchor end after tensioning; σ2 is the stress value of the circumferential midpoint (2#) after tensioning; k is the coefficient of influence of local deviation per meter of pipeline on friction; θ is the sum of the angles of the tangent lines of the pipeline section from the tensioning end to the calculated section curve; x is the length of the pipeline from the tensioning end to the calculated section; Prestress loss σ caused by friction between the prestressing tendons (3) and the pipe wall (4) l1 for: s l1 =s con [1-e -(μθ+kx) ],x≤L / 2 Where: σ con is the tension control stress value under the anchor of the prestressed tendon (3); L is the total length of the prestressed tendon (3).

5. A shield tunnel prestressing monitoring method according to claim 4, characterized in that: The prestress loss also includes the prestress loss caused by the deformation of the tensioning end anchor and the shrinkage of the prestressed tendon (3). The calculation process is: Where: σ l2 is the prestress loss caused by the deformation of the anchorage at the tensioning end and the shrinkage of the prestressed tendon (3), and Ep is the elastic modulus of the steel strand.

6. A shield tunnel prestressing monitoring method according to claim 1, characterized in that: The following warnings are issued based on the deviation between the actual value of prestress loss and the theoretical value of prestress loss: Warning of excessive prestress loss. When the deviation exceeds the allowable range, it will lead to insufficient structural stiffness, reduced ultimate bearing capacity reserve, and reduced safety margin. It is necessary to quickly investigate the cause and evaluate the impact on structural safety and performance; Early warning of rapid prestress loss development: Through continuous monitoring data comparison, when the rate of change of deviation is higher than the theoretically predicted rate or the range of the historical average rate of change, it indicates that some damage or deterioration may be occurring or aggravated. It is necessary to closely monitor the development trend, find the cause, and consider whether intervention is needed; Prestress loss distribution abnormality warning: When the actual distribution of prestress loss at each measuring point is inconsistent with the theoretical prediction or structural symmetry, it indicates that there may be a problem in the local area and the abnormal area needs to be located and inspected immediately; Prestress sudden loss warning: monitoring data shows that the stress value has dropped significantly in a short period of time, and the prestress loss increment is much greater than the normal time-varying loss rate, indicating that some kind of sudden damage or failure event is very likely to have occurred, and emergency inspection and structural safety assessment are required.

7. A shield tunnel prestressing monitoring method according to any one of claims 1 to 6, characterized in that: The shield segments for monitoring prestress are evenly spaced within the tunnel route section, and additional shield segments for monitoring prestress are provided in areas with sudden linear changes, complex geology, and irregular loads.

8. A system for implementing the shield tunnel prestressing monitoring method according to any one of claims 1 to 7, characterized in that: The invention comprises a remote operation workbench (5), and a first type tension sensor (1) and a second type tension sensor (2) installed at a measuring point. The remote operation workbench (5) is provided with a data acquisition edge module (6). The first type tension sensor (1) is electrically connected to a first data acquisition station (7), and the second type tension sensor (2) is electrically connected to a second data acquisition station (8). The first data acquisition station (7) and the second data acquisition station (8) are wirelessly connected to the data acquisition edge module (6).

9. A shield tunnel prestress monitoring system according to claim 8, characterized in that: The first type of tension sensor (1) is a magnetic flux sensor, and correspondingly, the first data acquisition station (7) is a magnetic flux data acquisition station, wherein a multiplexing module (9) and a magnetic elastic instrument (10) are provided in the magnetic flux data acquisition station; The second type of tension sensor (2) is a fiber Bragg grating strain gauge, and correspondingly, the second data acquisition station (8) is a fiber Bragg grating data acquisition station, wherein a fiber Bragg grating demodulator (11) is provided in the fiber Bragg grating data acquisition station.

10. A shield tunnel prestress monitoring system according to claim 9, characterized in that: The magnetic flux sensor comprises a curved bobbin (12) and a data line (13). The curvature of the curved bobbin (12) is adapted to the curvature of a prestressed channel in a shield segment. A coil (14) is wound around the outer wall of the curved bobbin (12). A curved outer sleeve (15) covering the coil (14) is provided on the outer periphery of the curved bobbin (12). Baffles (16) are provided between the two ends of the curved bobbin (12) and the curved outer sleeve (15). The data line (13) passes through the baffles (16) and is electrically connected to the coil (14). The gap between the coil (14) and the curved outer sleeve (15) is filled with epoxy resin (17). The outer wall of the curved outer sleeve (15) is provided with a polyurea layer (18).

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