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

Abstract

The invention discloses a distributed wide-area high-density stress sensing method for a shield tunnel segment service state, and belongs to the technical field of geotechnical engineering monitoring, the method is realized through an FBG sensor carrying a fiber bragg grating, a spectrometer, a temperature box and a universal testing machine, and the method comprises the following steps: S1, calibrating a strain sensitivity coefficient of the fiber bragg grating; s2, calibrating a temperature sensitivity coefficient; s3, deriving a central wavelength-stress relation under the influence of strain and temperature; s4, an FBG sensor is embedded in the shield tunnel segment, and targeted compensation and correction are carried out; and S5, obtaining the multi-axis strain and stress of the shield tunnel segment according to the optimal central wavelength-stress relationship. The high-density FBG sensing network is constructed by combining the strain and temperature sensitivity coefficients of the FBG sensors and the temperature compensation formula, so that the measurement precision is remarkably improved, three-dimensional monitoring of the tunnel is realized, the system has the characteristics of electromagnetic interference resistance and long-term creep compensation, and a reliable basis is provided for safety assessment of the tunnel.

Description

Technical Field

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

[0002] Stress measurement of shield tunnel segments is an important part of evaluating their service status. Currently, this field mainly relies on traditional mechanical testing methods and sensing technologies, such as strain gauges, pressure sensors and other equipment directly deployed at key parts of the segments for local stress monitoring.

[0003] However, the existing technology has significant defects: ① Most measuring devices are prone to failure in humid, high temperature or corrosive environments. ② Strain gauges can usually only monitor stress changes in local areas and it is 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, resulting in unstable sensor signals. ④ Cable sensors are unstable in long-term use due to cable aging, breakage and other problems, and require frequent inspection and maintenance.

[0004] Fiber Bragg grating (FBG) sensors are particularly suitable for wide-area, high-density stress perception under complex tunnel conditions due to their advantages such as high precision, anti-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 perception method for the service status of shield tunnel segments is provided. Summary of the invention

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

[0007] To achieve the above object, the present invention provides a distributed wide-area high-density stress sensing method for the service status of shield tunnel segments, which is implemented by 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, the sensitivity coefficient of the central wavelength of the calibrated fiber Bragg grating to strain;

[0009] S2, calibrate the sensitivity coefficient of the central wavelength of the fiber Bragg grating to temperature;

[0010] S3. Based on the results of S1 and S2, the central 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. According to the different positions of the FBG sensors, targeted compensation corrections are performed on each FBG sensor to obtain the optimal central wavelength-stress relationship corresponding to each FBG sensor;

[0012] Among them, compensation correction includes: multi-axial 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 central wavelength-stress relationship.

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

[0015] S11. Reference wavelength measurement: Under room temperature without any external force, a spectrometer is used to measure the reference center wavelength of the fiber Bragg grating; the spectrometer is a fiber spectrometer or a spectrum analyzer;

[0016] S12, applying known strain: using a universal testing machine to gradually add different known strains to the fiber Bragg grating, and recording the corresponding central wavelength under 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 central wavelength and the strain, and obtain the strain sensitivity coefficient.

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

[0020] Δλ strain =λ B0 ·p·Δ∈;

[0021] In the formula, Δλ strain represents the change in central wavelength caused by strain, λ B0 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:

[0023] S21. Reference wavelength measurement: Under room temperature without any external force, a spectrometer is used to measure the reference reflection center wavelength of the fiber Bragg grating;

[0024] S22, controlling temperature changes: using a temperature box to adjust the temperature of the fiber Bragg grating, and recording the value of each temperature point and the corresponding wavelength data;

[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 central wavelength and temperature and obtain the temperature sensitivity coefficient.

[0027] Preferably, in S22, the adjustment range of the temperature box is -5 to 30°C.

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

[0029] Δλ temperature =λ B0 ·q·ΔT;

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

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

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

[0033] Δλ B =λ B0 ·(p·Δ∈+q·ΔT);

[0034] In the formula, Δλ B It represents the total change of the central wavelength caused by the combined effect of strain change and temperature change;

[0035] 2) The stress-strain relationship and the relationship between wavelength and strain are combined, and the combined formula is expressed as:

[0036]

[0037] Where σ is stress, and E is the Young's modulus of the measured segment material;

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

[0039] The central wavelength-stress relationship of the 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] Where v is Poisson's ratio, ε x is the axial strain, ε y is the hoop strain, ε z is the radial strain.

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

[0045]

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

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

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

[0049] In the formula, σ actual is the actual stress value after correction, σ measured is the stress value measured by the FBG sensor, t is the time, and [1-0.05 ln(t+1)] represents the time attenuation 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 FBG sensors, 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 groups of FBG sensors inside the segments, a high-density sensing network is formed. Combined with the multi-axis stress correction formula, it covers the circumferential, longitudinal, and radial stress distribution of the shield tunnel, breaks through the limitations of traditional single-point monitoring, and realizes three-dimensional monitoring of the stress state.

[0053] (3) Fiber optic sensing technology is used, which is immune to electromagnetic interference. It replaces easily aged cables and metal parts, has excellent corrosion resistance and mechanical durability, and effectively avoids cable aging, breakage and other problems. 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 is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is an overall flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0058] Example

[0059] like Figure 1 As shown, the present invention provides a distributed wide-area high-density stress sensing method for the service status of a shield tunnel segment, which is implemented by a FBG sensor equipped with a fiber Bragg grating, a spectrometer (fiber spectrometer (OSL) or spectrum analyzer), a temperature chamber, and a universal testing machine, and includes the following steps:

[0060] S1. Calibrate the sensitivity coefficient p of the central wavelength of the fiber Bragg grating to strain in the laboratory, specifically:

[0061] S11. Reference wavelength measurement: Under room temperature without any external strain, use a spectrometer to accurately measure the reference center wavelength λ of the fiber Bragg grating B0 ;

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

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

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

[0065] Δλ strain =λ B1 -λ B0 ;

[0066] Δλ strain =λ B0 ·p·Δ∈;

[0067] In the formula, Δλ strainIt represents the change of the central wavelength caused by strain, p is the strain sensitivity coefficient, and Δ∈ is the change of strain;

[0068] The strain sensitivity coefficient can be obtained by linear fitting, which is usually 1.2με -1 , expressed as:

[0069]

[0070] S2. Based on the S1 experiment, a temperature box is added (the temperature change is set to -5℃-30℃ considering the actual situation of the shield tunnel), temperature compensation is performed, and the sensitivity coefficient q of the central wavelength of the fiber Bragg grating to temperature is calibrated, which is:

[0071] S21. Reference wavelength measurement: Under room temperature without any external force, use a spectrometer to measure the reference reflection center wavelength λ of the fiber Bragg grating. B0 ;

[0072] S22. Control temperature change: Place the FBG sensor in a temperature box and accurately control the temperature of the fiber Bragg grating from -5℃ to 30℃. At each temperature value, use a spectrometer to measure the central wavelength λ reflected by the FBG. B2 , record the value of each temperature point T and the corresponding central wavelength data λ B2 ;

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

[0074] S24. Establish the relationship between the central 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 It represents the change of the reflection center wavelength caused by temperature, q is the temperature sensitivity coefficient, and ΔT is the change of temperature;

[0078] The temperature sensitivity coefficient is obtained by linear fitting, usually 12℃ -1 , expressed as:

[0079]

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

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

[0082] Δλ B =λB 0 ·(p·Δ∈+q·ΔT);

[0083] In the formula, Δλ B It represents the total change of the central wavelength caused by the combined effect of strain change and temperature change;

[0084] 2) Relationship between stress and strain:

[0085] σ=E·∈;

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

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

[0088] ①First, start from the formula of FBG wavelength change caused by strain:

[0089] Δλ strain =λ B0 ·p·Δ∈;

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

[0091]

[0092] ③Then the stress calculation formula is expressed as:

[0093]

[0094] ④ The stress calculation formula after temperature compensation, that is, the central 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 sensing network to ensure wide-area monitoring of the stress state of the tunnel. Since the segments are arc-shaped spliced ​​structures, their stress distribution has the following particularities: ① The segments are subjected to soil pressure, water pressure and construction dynamic loads, resulting in uneven distribution of circumferential and longitudinal stresses; ② Stress peaks are easily formed at bolted joints, joint areas and the inner surface of the segments; ③ The creep characteristics of concrete cause stress to be redistributed over time, requiring dynamic correction of measurement data.

[0097] Therefore, combined with the stress characteristics of the segment and environmental factors, targeted compensation corrections are made to the FBG sensors at each position (including multi-axis stress correction, joint effect compensation, and long-term creep compensation), and the optimal central wavelength-stress relationship corresponding to each FBG sensor is obtained. The correction formula is as follows:

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

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

[0100] Where v is Poisson's ratio, ε x is the axial strain, ε y is the hoop strain, ε z is the radial strain.

[0101] 2) Joint effect compensation: The local strain deviation caused by the bolt preload is calibrated by the compensation coefficient β through experiments, and the strain deviation caused by the joint is calibrated by the transmission coefficient K through experiments ε , the correction formula is:

[0102]

[0103] Where ΔF is the change in bolt preload;

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

[0105] ①Prepare 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 synchronously;

[0107] ③Calculate the strain transfer coefficient:

[0108]

[0109] In the formula, Δλ B , homogeneous is the change in the central wavelength corresponding to the homogeneous area, Δλ B,seam is the change in central wavelength corresponding to the seam area.

[0110] The calibration method of β is:

[0111] ① In the same joint specimen, fix the temperature condition, gradually change the bolt preload, and record the total wavelength change Δλ of the FBG sensor at the joint B ;

[0112] ② The relationship between bolt preload and wavelength change is fitted by linear regression, and the joint effect compensation coefficient β is extracted:

[0113] Δλ B =β·F+b;

[0114] Where F is the bolt preload and b is a constant.

[0115] 3) Long-term creep compensation: Introduce the time decay factor γ(t) to correct the long-term monitoring value:

[0116] σ actual =σ measured γ(t);

[0117] γ(t)=1-0.05n(t+1);

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

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

[0120] Therefore, the present invention provides a distributed wide-area high-density stress sensing method for the service status of shield tunnel segments. The strain sensitivity coefficient and temperature sensitivity coefficient of the FBG sensor are obtained through laboratory calibration, and combined with the temperature compensation formula, the environmental interference is effectively eliminated, and the measurement accuracy is significantly improved, which is better than traditional strain gauges and pressure sensors. At the same time, multiple groups of FBG sensors are embedded inside the segments to construct a high-density sensing network, and 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, breaking through the limitations of traditional single-point monitoring. In addition, the anti-electromagnetic interference characteristics of the optical fiber sensing technology are utilized, and the influence of concrete creep is dynamically corrected in combination with the long-term creep compensation formula, which effectively 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 the safety assessment of the tunnel.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments, which is realized by using a fiber Bragg grating (FBG) sensor, a spectrometer, a temperature chamber, and a universal testing machine, and is characterized in that: The following steps are involved: S1, the sensitivity coefficient of the central wavelength of the calibrated fiber Bragg grating to strain; S2, calibrate the sensitivity coefficient of the central wavelength of the fiber Bragg grating to temperature; S3. Based on the results of S1 and S2, the central 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. According to the different positions of the FBG sensors, targeted compensation corrections are performed on each FBG sensor to obtain the optimal central wavelength-stress relationship corresponding to each FBG sensor; Among them, compensation correction includes: multi-axial stress correction, joint effect compensation, and long-term creep compensation; S5. Obtain the multi-axial strain and stress of the shield tunnel segment based on the optimal central wavelength-stress relationship of each FBG sensor.

2. A 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: Under room temperature without any external force, measure the reference center wavelength of the fiber Bragg grating using a spectrometer; S12, applying known strain: using a universal testing machine to gradually add different known strains to the fiber Bragg grating, and recording the corresponding central wavelength under 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 central wavelength and the strain, and obtain the strain sensitivity coefficient.

3. A 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: Dl strain =λ B0 ·p·Δ∈; In the formula, Δλ strain represents the change in central wavelength caused by strain, λ B0 is the reference center wavelength, p is the strain sensitivity coefficient, and Δ∈ is the change in strain.

4. A 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: S21. Reference wavelength measurement: Under room temperature without any external force, a spectrometer is used to measure the reference reflection center wavelength of the fiber Bragg grating; S22, controlling temperature changes: using a temperature box to adjust the temperature of the fiber Bragg grating, and recording the value of each temperature point and the corresponding wavelength data; S23, repeated measurement: repeat the measurement multiple times under the same temperature conditions and take the average value; S24. Establish the relationship between the central wavelength and temperature and obtain the temperature sensitivity coefficient.

5. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 4, characterized in that: In S22, the adjustment range of the temperature box is -5 to 30°C.

6. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 4, characterized in that: In S24, the relationship between wavelength and temperature is expressed as: Dl temperature =λ B0 ·q·ΔT; In the formula, Δλ temperature It represents the change in the reflection center wavelength caused by temperature, q is the temperature sensitivity coefficient, and ΔT is the change in temperature.

7. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that: In S3, the central wavelength-stress relationship of the fiber Bragg grating is expressed as: Where σ is stress, Δλ is B It represents the total change of the central wavelength caused by the combined effect of strain change and temperature change, and E is the Young's modulus of the measured segment material.

8. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that: In S4, the multiaxial stress correction is expressed as: Dl B =λ B0 ·[(1-v)ε x -v(e y +e z )]·p+λ B0 ·ΔT·q; Where v is Poisson's ratio, ε x is the axial strain, ε y is the hoop strain, ε z is the radial strain.

9. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that: In S4, the seam effect compensation is expressed as: In the formula, K ε is the strain transfer coefficient, β is the joint effect compensation coefficient, and ΔF is the change in bolt preload.

10. A distributed wide-area high-density stress sensing method for the service status of shield tunnel segments according to claim 1, characterized in that: In S4, long-term creep compensation is expressed as: s actual =s measured ·[1-0.05ln(t+1)]; In the formula, σ actual is the actual stress value after correction, σ measured is the stress value measured by the FBG sensor, t is the time, and [1-0.05ln(t+1)] represents the time attenuation factor.

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