Distributed wide-area high-density stress sensing method for shield tunnel segment service status

Abstract

This invention discloses a distributed wide-area high-density stress sensing method for shield tunnel segments in service, belonging to the field of geotechnical engineering monitoring technology. It is implemented using an FBG sensor equipped with a fiber Bragg grating, a spectrometer, a temperature chamber, and a universal testing machine, and includes the following steps: S1, calibrating the strain sensitivity coefficient of the fiber Bragg grating; S2, calibrating the temperature sensitivity coefficient; S3, deriving the center wavelength-stress relationship under the influence of strain and temperature; S4, embedding the FBG sensor inside the shield tunnel segment and performing targeted compensation correction; S5, obtaining the multiaxial strain and stress of the shield tunnel segment based on the optimal center wavelength-stress relationship. This invention combines the strain and temperature sensitivity coefficients of the FBG sensor with the temperature compensation formula to construct a high-density FBG sensor network, significantly improving measurement accuracy, realizing three-dimensional monitoring of the tunnel, and possessing anti-electromagnetic interference and long-term creep compensation characteristics, providing a reliable basis for tunnel safety assessment.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering monitoring technology, and in particular to a distributed wide-area high-density stress sensing method for the service status of shield tunnel segments. Background Technology

[0002] Stress measurement of shield tunnel segments is a crucial step in assessing their service condition. Currently, this field mainly relies on traditional mechanical testing methods and sensing technologies, such as directly deploying strain gauges and pressure sensors at key locations on the segments for localized stress monitoring.

[0003] However, existing technologies have significant drawbacks: ① Most measuring devices are prone to failure in humid, high-temperature, or corrosive environments. ② Strain gauges typically only monitor stress changes in localized areas, making it difficult to cover the large-scale stress distribution of tunnel structures. ③ Resistance strain gauges and wire-type sensors are susceptible to electromagnetic interference, especially in high-voltage or strong electromagnetic field environments, leading to unstable sensor signals. ④ Cable sensors suffer from instability over long-term use due to cable aging, breakage, and other issues, requiring frequent inspection and maintenance.

[0004] Fiber Bragg grating (FBG) sensors are particularly suitable for wide-area, high-density stress sensing in complex tunnel conditions due to their advantages such as high precision, resistance to electromagnetic interference, distributed measurement, and strong environmental adaptability, providing a breakthrough direction for the above problems.

[0005] Based on this, a distributed wide-area high-density stress sensing method for the service status of shield tunnel segments is provided. Summary of the Invention

[0006] The purpose of this invention is to provide a distributed wide-area high-density stress sensing method for the service status of shield tunnel segments, so as to solve the problems in the background art.

[0007] To achieve the above objectives, this invention provides a distributed wide-area high-density stress sensing method for shield tunnel segments in service status. This method utilizes an FBG sensor equipped with a fiber Bragg grating, a spectrometer, a temperature chamber, and a universal testing machine, and includes the following steps:

[0008] S1, Calibrate the sensitivity coefficient of the center wavelength of the fiber Bragg grating to strain;

[0009] S2. Calibrate the temperature sensitivity coefficient of the center wavelength of the fiber Bragg grating;

[0010] S3. Based on the results of S1 and S2, the center wavelength-stress relationship of the fiber Bragg grating under the combined influence of strain and temperature is derived.

[0011] S4. Multiple FBG sensors equipped with fiber Bragg gratings are embedded inside the shield tunnel segments. Based on the different locations of the FBG sensors, targeted compensation and correction are performed on each FBG sensor to obtain the optimal center wavelength-stress relationship for each FBG sensor.

[0012] The compensation and correction include: multiaxial stress correction, joint effect compensation, and long-term creep compensation.

[0013] S5. Obtain the multiaxial strain and stress of the shield tunnel segment based on the optimal center wavelength-stress relationship.

[0014] Preferably, the specific process of S1 is as follows:

[0015] S11. Reference wavelength measurement: The reference center wavelength of the fiber Bragg grating is measured using a spectrometer at room temperature without any external force applied; the spectrometer is either a fiber optic spectrometer or a spectral analyzer.

[0016] S12. Apply known strain: Use a universal testing machine to gradually increase different known strains to the fiber Bragg grating and record the center wavelength corresponding to each strain value;

[0017] S13. Repeated measurement: Repeat the measurement multiple times under the same strain conditions and take the average value;

[0018] S14. Establish the relationship between the center wavelength and strain to obtain the strain sensitivity coefficient.

[0019] Preferably, in step S14, the relationship between wavelength and strain is expressed as follows:

[0020] Δλ strain =λ B0 ·p·Δ∈;

[0021] In the formula, Δλ strain λ represents the change in center wavelength caused by strain. B0 λ is the reference center wavelength, p is the strain sensitivity coefficient, and Δ∈ is the change in strain.

[0022] Preferably, the specific process of S2 is as follows:

[0023] S21. Reference wavelength measurement: The reference reflection center wavelength of the fiber Bragg grating is measured using a spectrometer at room temperature without any external force applied.

[0024] S22. Temperature control: The temperature of the fiber Bragg grating is adjusted using a temperature chamber, and the value of each temperature point and the corresponding wavelength data are recorded.

[0025] S23. Repeated measurement: Repeat the measurement multiple times under the same temperature conditions and take the average value;

[0026] S24. Establish the relationship between the center wavelength and temperature to obtain the temperature sensitivity coefficient.

[0027] Preferably, in step S22, the temperature chamber has an adjustment range of -5 to 30°C.

[0028] Preferably, in step S24, the relationship between wavelength and temperature is expressed as follows:

[0029] Δλ temperature =λ B0 ·q·ΔT;

[0030] In the formula, Δλ temperature This represents the change in the center wavelength of reflection caused by temperature, where q is the temperature sensitivity coefficient and ΔT is the change in temperature.

[0031] Preferably, in step S3, the specific derivation process of the center wavelength-stress relationship of the fiber Bragg grating is as follows:

[0032] 1) Establish the relationship between the total wavelength change of the FBG sensor and the strain, expressed as:

[0033] Δλ B =λ B0 ·(p·Δ∈+q·ΔT);

[0034] In the formula, Δλ B This represents the total change in center wavelength caused by the combined effects of strain and temperature changes.

[0035] 2) Combine the stress-strain relationship and the wavelength-strain relationship into a single equation. The resulting formula is as follows:

[0036]

[0037] In the formula, σ is the stress, and E is the Young's modulus of the material of the tested pipe segment;

[0038] 3) Perform temperature compensation to obtain the center wavelength-stress relationship of the fiber Bragg grating;

[0039] The center wavelength-stress relationship of a fiber Bragg grating is expressed as:

[0040]

[0041] Preferably, in S4, the multiaxial stress correction is expressed as:

[0042] Δλ B =λ B0 ·[(1-v)ε x -v(ε y +ε z)]·p+λ B0 ·ΔT·q;

[0043] In the formula, v is Poisson's ratio, ε x For axial strain, ε y For circumferential strain, ε z For radial strain.

[0044] Preferably, in S4, the seam effect compensation is expressed as:

[0045]

[0046] In the formula, K ε β is the strain transfer coefficient, β is the joint effect compensation coefficient, and ΔF is the change in bolt preload.

[0047] Preferably, in S4, long-term creep compensation is expressed as:

[0048] σ actual =σ measured ·[1-0.05ln(t+1)];

[0049] In the formula, σ actual The corrected actual stress value, σ measured The stress value is measured by the FBG sensor, t is time, and [1-0.05 ln(t+1)] represents the time decay factor.

[0050] Therefore, the distributed wide-area high-density stress sensing method for the service status of shield tunnel segments of the present invention has the following beneficial effects:

[0051] (1) Through laboratory calibration of the FBG sensor, the strain sensitivity coefficient and temperature sensitivity coefficient are accurately obtained. Combined with the temperature compensation formula, environmental interference is eliminated, which is superior to traditional strain gauges and pressure sensors and significantly improves measurement accuracy.

[0052] (2) By embedding multiple FBG sensors inside the tunnel segments to form a high-density sensing network, and combining it with the multi-axis stress correction formula, the stress distribution in the circumferential, longitudinal and radial directions of the shield tunnel is covered, breaking through the limitations of traditional single-point monitoring and realizing three-dimensional monitoring of stress state.

[0053] (3) The use of fiber optic sensing technology is immune to electromagnetic interference; it replaces easily aging cables and metal parts, has excellent corrosion resistance and mechanical durability, and effectively avoids problems such as cable aging and breakage; at the same time, through the long-term creep compensation formula, it dynamically corrects the influence of concrete creep, adapts to the harsh environment of the tunnel, improves the stability of long-term detection data, reduces maintenance costs, and provides a direct basis for tunnel safety assessment.

[0054] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0055] Figure 1 This is an overall flowchart of an embodiment of the present invention. Detailed Implementation

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] 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 some embodiments of the present invention, but not all embodiments.

[0058] Example

[0059] like Figure 1 As shown, the present invention provides a distributed wide-area high-density stress sensing method for shield tunnel segments in service status. This method utilizes an FBG sensor equipped with a fiber Bragg grating, a spectrometer (fiber optic spectrometer (OSL) or spectrometer), a temperature chamber, and a universal testing machine, and includes the following steps:

[0060] S1. In the laboratory, calibrate the sensitivity coefficient p of the center wavelength of the fiber Bragg grating to strain, specifically as follows:

[0061] S11. Reference Wavelength Measurement: Under room temperature conditions without any external strain, the reference center wavelength λ of the fiber Bragg grating is accurately measured using a spectrometer. B0 ;

[0062] S12. Apply known strain: Using a universal testing machine, gradually increase different known strains ∈ to the fiber Bragg grating, and record the corresponding reflection center wavelength λ for each strain value. B1 .

[0063] S13. Repeated measurement: Repeat the measurement multiple times under the same strain and take the average value to reduce error;

[0064] S14. Establish the relationship between the center wavelength and strain, expressed as:

[0065] Δλ strain =λ B1 -λ B0 ;

[0066] Δλ strain =λ B0 ·p·Δ∈;

[0067] In the formula, Δλ straindenoted by p, where p is the strain sensitivity coefficient and Δ∈ represents the change in center wavelength caused by strain.

[0068] The strain sensitivity coefficient can be obtained by performing a linear fit, which is typically 1.2 με. -1 , is represented as:

[0069]

[0070] S2. Based on the S1 experiment, a temperature chamber was added (the temperature range was set to -5℃ to 30℃ considering the actual conditions of the shield tunnel) for temperature compensation. The temperature sensitivity coefficient q of the center wavelength of the fiber Bragg grating was calibrated, specifically as follows:

[0071] S21. Reference Wavelength Measurement: Under room temperature conditions without any external force applied, the reference reflection center wavelength λ of the fiber Bragg grating is measured using a spectrometer. B0 ;

[0072] S22. Temperature Control: Place the FBG sensor inside a temperature chamber and precisely control the temperature of the fiber Bragg grating from -5℃ to 30℃. At each temperature value, use a spectrometer to measure the center wavelength λ reflected by the FBG. B2 Record the value of T and the corresponding center wavelength data λ at each temperature point. B2 ;

[0073] S23. Repeated measurement: Repeat the measurement multiple times under the same temperature conditions and take the average value to reduce error;

[0074] S24. Establish the relationship between the center wavelength and temperature, expressed as:

[0075] Δλ temperature =λ B2 -λ B0 ;

[0076] Δλ temperature =λ B0 ·q·ΔT;

[0077] In the formula, Δλ temperature The change in the center wavelength of reflection caused by temperature is represented by q, where q is the temperature sensitivity coefficient and ΔT is the change in temperature.

[0078] The temperature sensitivity coefficient is obtained by performing linear fitting, typically 12℃. -1 , is represented as:

[0079]

[0080] S3. Based on the results of S1 and S2, the center wavelength-stress relationship of the fiber Bragg grating under the combined influence of strain and temperature is derived. The specific derivation process is as follows:

[0081] 1) Establish the relationship between the total wavelength change of the FBG sensor and strain:

[0082] Δλ B =λB0·(p·Δ∈+q·ΔT);

[0083] In the formula, Δλ B This represents the total change in center wavelength caused by the combined effects of strain and temperature changes.

[0084] 2) Stress-strain relationship:

[0085] σ=E·∈;

[0086] In the formula, σ is the stress applied to the structure, and E is the Young's modulus of the material of the tested segment;

[0087] 3) Relationship between center wavelength and stress:

[0088] ① First, let's start with the formula for the change in FBG wavelength caused by strain:

[0089] Δλ strain =λ B0 ·p·Δ∈;

[0090] ② Combining the formulas in 2), we get:

[0091]

[0092] ③The stress calculation formula is expressed as:

[0093]

[0094] ④ The stress calculation formula after temperature compensation, i.e., the center wavelength-stress relationship of the fiber Bragg grating, is expressed as:

[0095]

[0096] S4. Multiple FBG sensors equipped with fiber Bragg gratings are embedded inside the shield tunnel segments to form a high-density sensor network, ensuring wide-area monitoring of the tunnel's stress state. Due to the arc-shaped splicing structure of the segments, their stress distribution has the following unique characteristics: ① The segments are subjected to earth pressure, water pressure, and dynamic construction loads, resulting in uneven circumferential and longitudinal stress distribution; ② Stress peaks easily form at bolt connections, joint areas, and the inner surface of the segments; ③ The creep characteristics of concrete cause stress to redistribute over time, requiring dynamic correction of measurement data.

[0097] Therefore, considering the stress characteristics of the tunnel lining segments and environmental factors, targeted compensation and corrections (including multiaxial stress correction, joint effect compensation, and long-term creep compensation) are performed on the FBG sensors at each location to obtain the optimal center wavelength-stress relationship for each FBG sensor. The correction formula is as follows:

[0098] 1) Multiaxial stress correction: The segments are in a three-dimensional stress state, and the uniaxial strain formula is extended to:

[0099] Δλ B =λ B0 ·[(1-ν)ε x -v(ε y +ε z )]·p+λ B0 ·ΔT·q;

[0100] In the formula, v is Poisson's ratio, ε x For axial strain, ε y For circumferential strain, ε z For radial strain.

[0101] 2) Joint effect compensation: The local strain deviation caused by bolt preload is compensated by experimentally calibrated compensation coefficient β, and the strain deviation caused by the joint is compensated by experimentally calibrated transfer coefficient K. ε The corrected formula is:

[0102]

[0103] In the formula, ΔF is the change in bolt preload;

[0104] Among them, K ε The calibration method is as follows:

[0105] ① Prepare tunnel segment specimens with joints, fill the joints with actual engineering materials, and apply uniaxial loads to the segments;

[0106] ② Install FBG sensors at the joint and in the homogeneous area away from the joint to measure strain simultaneously;

[0107] ③ Calculate the strain transfer coefficient:

[0108]

[0109] In the formula, Δλ B ,homogeneous represents the change in center wavelength corresponding to a homogeneous region, Δλ B,seam This represents the change in center wavelength corresponding to the seam area.

[0110] The calibration method for β is as follows:

[0111] ① In the same joint specimen, under fixed temperature conditions, the bolt preload is gradually changed, and the total wavelength change Δλ of the FBG sensor at the joint is recorded. B ;

[0112] ② By fitting the relationship between bolt preload and wavelength variation through linear regression, the joint effect compensation coefficient β is extracted:

[0113] Δλ B =β·F+b;

[0114] In the formula, F is the bolt preload, and b is a constant.

[0115] 3) Long-term creep compensation: Introducing a time decay factor γ(t) to correct long-term monitoring values:

[0116] σ actual =σ measured ·γ(t);

[0117] γ(t) = 1 - 0.05n(t+1);

[0118] In the formula, σ actual The corrected actual stress value, σ measured The stress value is measured by the FBG sensor, and t is time.

[0119] S5. Based on the optimal center wavelength-stress relationship of the FBG sensor network, the stress distribution of the tunnel segments in complex environments is monitored in real time, and the multiaxial strain and stress of the shield tunnel segments are obtained, providing high-precision data support for tunnel structural health assessment.

[0120] Therefore, this invention provides a distributed wide-area high-density stress sensing method for shield tunnel segments in service. Through laboratory calibration, the strain sensitivity coefficient and temperature sensitivity coefficient of the FBG sensor are obtained. Combined with a temperature compensation formula, environmental interference is effectively eliminated, significantly improving measurement accuracy, which is superior to traditional strain gauges and pressure sensors. Simultaneously, multiple sets of FBG sensors are embedded inside the segments to construct a high-density sensing network. A multi-axis stress correction formula is used to achieve three-dimensional monitoring of the circumferential, longitudinal, and radial stress distribution of the shield tunnel, overcoming the limitations of traditional single-point monitoring. Furthermore, utilizing the anti-electromagnetic interference characteristics of fiber optic sensing technology and combining it with a long-term creep compensation formula to dynamically correct for the effects of concrete creep, it effectively adapts to the harsh tunnel environment, improves the stability of long-term monitoring data, reduces maintenance costs, and provides direct evidence for tunnel safety assessment.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A distributed wide-area high-density stress sensing method for shield tunnel segment service status, implemented using an FBG sensor equipped with a fiber Bragg grating, a spectrometer, a temperature chamber, and a universal testing machine, characterized in that... Includes the following steps: S1, Calibrate the sensitivity coefficient of the center wavelength of the fiber Bragg grating to strain; S2. Calibrate the temperature sensitivity coefficient of the center wavelength of the fiber Bragg grating; S3. Based on the results of S1 and S2, the center wavelength-stress relationship of the fiber Bragg grating under the combined influence of strain and temperature is derived. S4. Multiple FBG sensors equipped with fiber Bragg gratings are embedded inside the shield tunnel segments. Based on the different locations of the FBG sensors, targeted compensation and correction are performed on each FBG sensor to obtain the optimal center wavelength-stress relationship for each FBG sensor. The compensation and correction include: multiaxial stress correction, joint effect compensation, and long-term creep compensation. S5. Obtain the multiaxial strain and stress of the shield tunnel segment based on the optimal center wavelength-stress relationship of each FBG sensor; In S3, the center wavelength-stress relationship of the fiber Bragg grating is expressed as: ； In the formula, For stress, This represents the total change in center wavelength caused by the combined effects of strain and temperature changes. The Young's modulus of the tested pipe segment material is given. As the reference center wavelength, The strain sensitivity coefficient, This is the temperature sensitivity coefficient. The change in temperature; In S4, the multiaxial stress correction is expressed as: ； In the formula, Poisson's ratio, For axial strain, For circumferential strain, Radial strain; In S4, the seam effect compensation is expressed as: ； In the formula, The strain transfer coefficient is... This is the seam effect compensation coefficient. This represents the change in bolt preload. In S4, long-term creep compensation is expressed as: ； In the formula, This is the corrected actual stress value. The stress value was measured by the FBG sensor. For time, This represents the time decay factor.

2. The distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that, The specific process of S1 is as follows: S11. Reference wavelength measurement: The reference center wavelength of the fiber Bragg grating is measured using a spectrometer at room temperature without any external force applied. S12. Apply known strain: Use a universal testing machine to gradually increase different known strains to the fiber Bragg grating and record the center wavelength corresponding to each strain value. S13. Repeated measurement: Repeat the measurement multiple times under the same strain conditions and take the average value; S14. Establish the relationship between the center wavelength and strain to obtain the strain sensitivity coefficient.

3. The distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 2, characterized in that, In S14, the relationship between wavelength and strain is expressed as follows: ； In the formula, This represents the change in center wavelength caused by strain. As the reference center wavelength, The strain sensitivity coefficient, The change in strain.

4. The distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that, The specific process of S2 is as follows: S21. Reference wavelength measurement: The reference reflection center wavelength of the fiber Bragg grating is measured using a spectrometer at room temperature without any external force applied. S22. Temperature control: The temperature of the fiber Bragg grating is adjusted using a temperature chamber, and the value of each temperature point and the corresponding wavelength data are recorded. S23. Repeated measurement: Repeat the measurement multiple times under the same temperature conditions and take the average value; S24. Establish the relationship between the center wavelength and temperature to obtain the temperature sensitivity coefficient.

5. The distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 4, characterized in that: In step S22, the temperature chamber's adjustment range is: .

6. The distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 4, characterized in that, In step S24, the relationship between wavelength and temperature is expressed as follows: ； In the formula, This represents the amount of change in the center wavelength of reflection caused by temperature. This is the temperature sensitivity coefficient. This represents the change in temperature.

Images