A method for detecting the sealing performance of a shield tail by using an FBG optical fiber composite sensor and a pre-warning method

Abstract

The present application relates to a kind of methods for detecting shield tail sealing property and early warning method using FBG optical fiber composite sensor, belong to temperature measuring fiber related technical field.The present application introduces the principle that FBG self-heating optical fiber reflects environmental temperature rise and fall through wavelength change of grating measuring point into the detection of shield tail grease seal cavity leakage, proposes to use self-heating optical fiber composite sensor to actively change the temperature of cavity, because there is difference in specific heat capacity of different substances, wavelength difference of each grating measuring point obtained by measuring shield propulsion gap each time is compared with wavelength difference of the grating measuring point obtained by measuring last time, to determine the leakage of shield tail grease seal cavity.The present application is based on a kind of active heating FBG optical fiber composite sensor, publishes the judgment standard of shield tail grease seal abnormal state on the basis of test, and gives corresponding management measures, effectively reduces the construction risk caused by shield tail grease seal abnormality, significantly improves shield construction safety.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field related to temperature measurement optical fibers, and more particularly, to a method for detecting the sealing performance of a shield tail and a warning method using an FBG optical fiber composite sensor. BACKGROUND

[0002] With the acceleration of urbanization, tunnel transportation such as subway has become increasingly mainstream. As of December 31, 2024, there are 54 cities in China that have opened and operated urban rail transit lines, with a total operating mileage of 10945.6 kilometers. In 2024, 18 new urban rail transit operating lines were added nationwide, with 27 new operating sections and 748 kilometers of new operating mileage. It is estimated that by 2030, the total mileage of urban rail transit operating lines in the country will exceed 15,000 kilometers, and the investment scale of urban subway construction will continue to expand, with huge future development space. However, due to the complex hydrological conditions that shield equipment must face during its journey, shield tail sealing leakage problems often occur during subway shield construction, leading to road collapse, construction personnel injury and damage to the shield machine, which has been reported in the media. In addition, shield tail sealing leakage can also cause a series of problems such as shield construction interruption, ground traffic congestion, underground pipeline rupture, and house deformation and collapse, seriously affecting social safety and causing personnel and property losses. Therefore, real-time detection of the sealing performance of shield tail grease during shield construction and the implementation of targeted control measures are important means to prevent shield accidents and reduce personnel casualties.

[0003] In existing shield tail sealing detection technologies, methods based on pressure monitoring or electromagnetic induction have significant limitations. Active heating fiber Bragg grating (FBG) temperature measurement technology, with its high sensitivity and electromagnetic interference resistance, has become a new direction for shield tail sealing monitoring. Our team previously disclosed an active heating FBG optical fiber shield tail sealing detection composite sensor that changes the temperature field of the medium around the sensor using active heating, and determines the sealing performance of the shield tail sealing grease cavity based on abnormal temperature data at the grating measurement points. However, there is still a gap in the layout and use method of the sensor in the shield tail sealing environment, and the criteria for determining abnormal medium in the cavity based on wavelength data have not been determined. The warning method and management measures to be taken in response to abnormal wavelength data have also not been disclosed. SUMMARY

[0004] Based on the active heating FBG optical fiber shield tail sealing detection composite sensor designed by our team, the present application provides a method for detecting the sealing performance of a shield tail and a warning method using an FBG optical fiber composite sensor. The composite sensor is used to actively change the environmental temperature in the shield tail sealing cavity, and the sealing condition in the shield tail grease sealing cavity is detected in real time based on the abnormal changes in wavelength data at the grating measurement points.

[0005] To achieve the above object, according to one aspect of the present application, a method for detecting the sealing performance of a shield tail by using a FBG optical fiber composite sensor is provided, comprising the following steps:

[0006] S1: after the shield is assembled, before the grease is filled in the grease sealing cavity of the shield tail, a FBG optical fiber composite sensor is arranged in the form of a ring in the grease sealing cavity of the shield tail and closely attached to the inner surface of the shield shell, and fixed on the brush pressure plate of the shield tail, the FBG optical fiber composite sensor can be connected with an external power supply and a FBG optical fiber demodulator through the internal channel of the shield shell;

[0007] S2: during the period from the start of the shield to the reinforcement of the tail end, the wavelength data under the ambient temperature are measured and recorded, then the composite sensor is heated by using the external power supply, the FBG optical fiber demodulator measures and records the wavelength data along the path of each grating measuring point in each sealing cavity under the heated environment; the maximum value of the wavelength of each grating measuring point in each sealing cavity after heating is subtracted from the minimum value of the wavelength of the corresponding measuring point without heating, to obtain the wavelength difference value of the corresponding grating measuring point;

[0008] S3: during the gap between the stop of the shield and the advance of the shield by 50-100 rings, the sensor is connected with the external power supply and the FBG optical fiber demodulator, and the wavelength data under the ambient temperature without heating are recorded; the composite sensor is heated by using the external power supply, the heating time after each advance of the shield is the same as the heating time in step S2, and the FBG optical fiber demodulator is used to obtain the wavelength data along the path of each grating measuring point in each sealing cavity after each advance of the shield; the maximum value of the wavelength measured by heating each grating measuring point in each sealing cavity after each advance of the shield is subtracted from the minimum value of the wavelength of the corresponding measuring point without heating after the advance, to obtain the wavelength difference value of the corresponding grating measuring point;

[0009] S4: the wavelength difference value of each grating measuring point obtained by each measurement is compared with the wavelength difference value of the grating measuring point obtained by the previous measurement, when the wavelength difference value decreases by more than 50%, it is judged that leakage occurs in the corresponding measuring point area in the grease cavity, and slurry enters the sealing cavity; when the wavelength difference value increases by more than 50%, it is judged that there is air at the measuring point position in the cavity, and the grease in the grease cavity is not fully filled; when the wavelength difference value decreases or increases by less than or equal to 50%, it is judged that no leakage occurs in the corresponding measuring point area in the grease cavity.

[0010] Preferably, the heating in steps S2 and S3 comprises multiple stages, and the heating time of each stage is the same;

[0011] Step S4 specifically involves comparing the wavelength difference of each grating measuring point in each heating stage obtained from each measurement with the wavelength difference of the corresponding heating stage obtained from the previous measurement. If the wavelength difference of at least one heating stage decreases by more than 50%, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease chamber, and mud and water have entered the sealing chamber. If the wavelength difference of at least one heating stage increases by more than 50%, it is determined that air exists at the measuring point location in the chamber, and the grease injection in the grease chamber is not full. If the wavelength difference decreases or increases by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease chamber.

[0012] Preferably, the multiple heating stages in steps S2 and S3 are as follows: first heating for time T1, then naturally cooling to ambient temperature and then heating for time T2, then naturally cooling to ambient temperature and then heating for time T3; wherein 40 s≤T1≤60s, 100 s≤T2≤120 s, 160 s≤T3≤180 s.

[0013] Preferably, the grating measurement points of the FBG fiber composite sensor arranged in the same sealed cavity are spaced 5°-10° apart.

[0014] Preferably, the grating measurement points in adjacent sealed cavities are staggered to ensure uniform distribution of the measurement points.

[0015] According to another aspect of the present invention, a method for early warning of shield tail sealing is provided, wherein a range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity is defined as a risk-sensitive area, and other areas are defined as general risk areas; the front cavity is defined as the sealing cavity close to the shield tail, and the rear cavity is defined as the sealing cavity far from the shield tail; and the corresponding early warning level is determined according to the number of leakage points in different risk areas of different cavities.

[0016] When the grease sealing cavity has two layers: if there are ≥2 leakage points in the risk-sensitive area of ​​the front cavity, or ≥5 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0017] When the grease-sealed cavity has two layers: an orange warning will be activated in the following two situations: the first situation is when there are ≥5 leakage points in the risk-sensitive area of ​​the front cavity; the second situation is when there are ≥1 leakage point in the general risk area of ​​the rear cavity and ≥3 leakage points in the entire front cavity.

[0018] When the grease sealing cavity has two layers: when there are ≥2 leakage points in the risk-sensitive area of ​​the rear cavity, or ≥4 leakage points in the general risk area of ​​the rear cavity, or ≥10 leakage points in the risk-sensitive area of ​​the front cavity, or ≥20 leakage points in the general risk area of ​​the front cavity, a red warning is activated.

[0019] Preferably, the risk-sensitive area is defined as the range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity, and the other areas are general risk areas; the front cavity is defined as the sealing cavity close to the shield tail, the rear cavity is defined as the sealing cavity far from the shield tail, and the middle cavity is defined as the cavity between the sealing cavities closest to the shield tail and the sealing cavities farthest from the shield tail; the corresponding warning level is determined according to the number of leakage points in different risk areas of different cavities.

[0020] When the grease sealing cavity has 3 layers: if there are ≥3 leakage points in the risk-sensitive area of ​​the front cavity, or ≥8 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0021] When the grease sealing cavity has 3 layers: an orange warning will be activated in the following two cases: the first case is when there are ≥2 leakage points in the risk-sensitive area of ​​the middle cavity, and the radial angle difference between any leakage point in the risk-sensitive area of ​​the middle cavity and any leakage point in the risk-sensitive area of ​​the front cavity is ≤5°; the second case is when there are ≥4 leakage points in the general risk area of ​​the middle cavity.

[0022] When the grease-sealed cavity has 3 channels: when there is ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, or ≥2 leakage points in the general risk area of ​​the rear cavity, or ≥8 leakage points in the risk-sensitive area of ​​the middle cavity, or ≥16 leakage points in the general risk area of ​​the middle cavity, a red warning is activated.

[0023] Preferably, the risk-sensitive area is defined as the range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity, and the other areas are general risk areas; the front cavity is defined as the sealing cavity close to the shield tail, the rear cavity is defined as the sealing cavity far from the shield tail, and the middle cavity is defined as the cavity between the sealing cavities closest to the shield tail and the sealing cavities farthest from the shield tail; the corresponding warning level is determined according to the number of leakage points in different risk areas of different cavities.

[0024] When the grease sealing cavity has 4 layers: if there are ≥4 leakage points in the risk-sensitive area of ​​the front cavity, or ≥10 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0025] When the grease sealing cavity has 4 layers: an orange warning will be activated in the following two situations: the first situation is that there are ≥3 leakage points in the risk-sensitive areas of both layers, and there are at least 2 adjacent leakage points in the risk-sensitive area of ​​any layer; the second situation is that there are ≥12 leakage points in the general risk areas of both layers.

[0026] When the grease sealing cavity has 4 layers: when there is ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, or ≥2 leakage points in the general risk area of ​​the rear cavity, or ≥6 leakage points in the risk-sensitive areas of both middle cavities, or a total of ≥24 leakage points in the general risk areas of the two middle cavities, a red warning is activated.

[0027] In summary, compared with the prior art, the method and early warning method for detecting shield tail seals using an FBG fiber optic composite sensor provided by the present invention have the following advantages:

[0028] (1) This invention introduces the principle of FBG self-heating optical fiber reflecting the rise and fall of ambient temperature through the wavelength change of grating measurement point to detect leakage in the shield tail grease sealing cavity. It proposes to use a self-heating optical fiber composite sensor to actively change the ambient temperature inside the cavity. Since different materials have different specific heat capacities, the leakage situation of the shield tail grease sealing cavity is judged by comparing the wavelength difference of each grating measurement point obtained by each measurement of the shield advancement gap with the wavelength difference of the grating measurement point obtained by the previous measurement.

[0029] (2) To address the limitations of existing pressure monitoring or electromagnetic induction detection methods, an endoscopic composite sensor is preferred to achieve real-time monitoring of the grease sealing cavity at the tail of the shield throughout the entire shield tunneling process using a non-destructive testing method. Based on this, the construction and management teams can accurately determine the sealing status of each grease cavity at the tail of the shield, thereby selecting a more reasonable management strategy.

[0030] (3) In this invention, the composite sensor is fixed on the pressure plate of the shield tail brush, which can effectively reduce the damage of the optical fiber to the high-pressure grease in the cavity, and also ensure the identification of abnormal media in the cavity at the first time when the shield tail brush wears or external mud and water leaks. The grating measurement points in adjacent cavities are staggered to achieve uniform distribution of measurement points and improve the accuracy of detection.

[0031] (4) Based on an active heating FBG fiber optic composite sensor, this invention publishes the judgment criteria for abnormal shield tail grease sealing state on the basis of experiments, and gives corresponding management measures, which effectively reduces the construction risk caused by abnormal shield tail grease sealing and significantly improves shield construction safety. Attached Figure Description

[0032] Figure 1 This is a diagram illustrating the implementation steps of a method for detecting shield tail seals using an FBG fiber optic composite sensor proposed in this invention.

[0033] Figure 2 This is a cross-sectional view of the shield tunnel where the composite sensor described in this invention is deployed in the shield tunneling environment.

[0034] Figure 3 This is a schematic diagram of the staggered arrangement of the composite sensor grating measurement points and its connection with external instruments as described in this invention.

[0035] Figure 4 This is a schematic diagram of the risk-sensitive area and the general risk area within the grease-sealed cavity described in this invention.

[0036] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0037] 1-Internal channel of shield shell; 2-Pressure plate of shield tail brush; 3-Shield shell; 4-FBG fiber optic composite sensor; 5-Grease sealing cavity of shield tail; 6-Shield tail brush; 7-Tube segment; 8-Grate measuring point; 9-Risk sensitive area; 10-General risk area. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] This invention proposes a method for detecting shield tail seals using an FBG fiber optic composite sensor. Please refer to [link to relevant documentation]. Figure 1 It mainly includes the following steps:

[0040] S1: After the shield is assembled, before filling the shield tail grease sealing cavity with grease, the FBG fiber composite sensor is arranged in a ring inside the shield tail grease sealing cavity, close to the inner surface of the shield shell, and fixed to the shield tail brush pressure plate. The FBG fiber composite sensor can be connected to the external power supply and FBG fiber demodulator through the internal channel of the shield shell.

[0041] S2: During the period when the shield tunneling starts but the tail of the shield has not yet exited the end reinforcement zone, the wavelength data under ambient temperature is measured and recorded. Then, the composite sensor is heated by an external power supply. The FBG fiber demodulator measures and records the wavelength along the path of each grating measuring point in each sealed cavity under the heating environment. The wavelength difference is obtained by subtracting the minimum wavelength of the corresponding measuring point when it is not heated from the maximum wavelength of each grating measuring point after heating.

[0042] S3: During the 50-100 ring advance interval of the tunnel boring machine (TBM), connect the sensor to an external power supply and an FBG fiber optic demodulator to record the wavelength data under unheated conditions. Heat the composite sensor using the external power supply. The heating time after each TBM advance is the same as the heating time in step S2. Use the FBG fiber optic demodulator to obtain the wavelength data along the path of each grating measuring point in each sealed cavity after each TBM advance. Subtract the minimum wavelength of the corresponding measuring point when it was not heated from the maximum wavelength measured by heating at each grating measuring point in each sealed cavity after each TBM advance to obtain the wavelength difference.

[0043] S4: Compare the wavelength difference of each grating measuring point obtained in each measurement with the wavelength difference of the same grating measuring point obtained in the previous measurement. When the wavelength difference decreases by more than 50%, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease cavity, and mud and water have entered the sealing cavity. When the wavelength difference increases by more than 50%, it is determined that there is air (cavity) at the measuring point location in the cavity, and the grease injection in the grease cavity is not full. When the wavelength difference decreases or increases by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease cavity.

[0044] Based on this, the leakage situation in the shield tail grease sealing cavity is determined according to the abnormality of fiber optic data, and corresponding emergency management measures are taken according to the number of leakage points in different risk areas of the inner and outer cavities.

[0045] In some embodiments, the FBG fiber composite sensor can be an active heating FBG fiber optic shield tail seal detection composite sensor independently designed by our team (patent publication number CN 120063521A). The grating measurement points engraved on this sensor are spaced approximately 5° apart. Depending on engineering needs, the density of measurement points can be increased within a 30° range (5-7 o'clock direction) to the left and right of the line connecting the center point and the lowest point of the shield tunnel grease sealing cavity. Furthermore, the ambient temperature can be presented as wavelength data on the fiber optic demodulator. That is, the density of grating measurement points within each sealing cavity is greater within a 30° range to the left and right of the line connecting the center point and the lowest point of the sealing cavity than in other areas.

[0046] The FBG fiber optic composite sensor includes a temperature-sensing fiber, a reinforcing component, a heating component, a high-temperature resistant silicone gel filler, and an external protective device. The temperature-sensing fiber, the reinforcing component, and the heating component are arranged in a row adjacent to each other, forming the central component of the sensor. The external protective device includes an inner layer and an outer layer. The inner layer is used to wrap the high-temperature resistant silicone gel filler, and the outer layer is a high thermal conductivity sheath. The high-temperature resistant silicone gel filler is filled between the inner layer and the central component.

[0047] Preferably, the temperature-sensing optical fiber is an FBG optical fiber, and multiple grating measurement points are uniformly etched at equal intervals on the temperature-sensing optical fiber.

[0048] The spacing of the grating measurement points is set as follows: one grating measurement point is arranged every 5° along the cross-section of the shield tail grease sealing cavity; each grating measurement point can measure the ambient temperature and present it in the form of wavelength data on the FBG fiber demodulator.

[0049] The reinforcing component is a high-strength metal reinforcing wire with a diameter of 1mm.

[0050] The heating element is a self-insulating resistance wire heating strip with a circular cross-section and a diameter of 1mm.

[0051] The heating element heats up by connecting to an external power source. A self-heating temperature control switch is installed at the external power source to adjust the heating power and temperature. The heating power is set to 25W per meter. 40W, heating temperature set not exceeding 40℃ to avoid melting the grease.

[0052] The high-temperature resistant silicone gel filler uniformly wraps the temperature-sensing optical fiber, the reinforcing component, and the heating component, and is used to separate and fix the temperature-sensing optical fiber, the reinforcing component, and the heating component.

[0053] The inner layer is an aluminum-plastic armor layer, made of aluminum alloy material, with a thickness of 1mm.

[0054] The outer layer is a high thermal conductivity XLPE sheath with a thickness of 1mm. It is made of cross-linked polyethylene and can be used to protect the central component.

[0055] The composite sensor is arranged in a ring inside the shield tail grease sealing cavity, closely attached to the inner surface of the shield shell, and fixed to the shield tail brush pressure plate.

[0056] The composite sensor of this invention is arranged in a ring inside the grease-sealed cavity of the shield tail, closely attached to the inner surface of the shield shell, and fixed to the pressure plate of the shield tail brush. It is connected to an external power supply and FBG fiber optic demodulator through an internal channel of the shield shell. This arrangement can effectively reduce the damage of high-pressure grease in the cavity to the optical fiber and improve the service life of the optical fiber.

[0057] In this invention, the FBG fiber optic composite sensor is independently deployed within each shield tail grease-sealed cavity and connected to an external power supply and fiber optic demodulator, respectively. This ensures that the detection results of each grease-sealed cavity are independent, allowing for the determination of changes in the medium within different cavities and thus the assessment of leakage. The grating measurement points in adjacent grease-sealed cavities are staggered, resulting in a uniform grating distribution across different cavities and improving detection accuracy.

[0058] The relationship between wavelength data anomalies at various grating measurement points of the actively heated FBG fiber optic composite sensor and leakage points in the shield tail grease sealing cavity was determined by comparing the wavelength differences under heated and normal temperature conditions. Based on the shield tail sealing working mechanism and leakage mechanism, under the condition of decreased shield tail sealing performance, the medium in the grease cavity may be one of four types: pure grease, cavity, a mixture of grease and mud-water, or pure mud-water. Among them, the specific heat capacity of air is approximately 1.004 × 10⁻⁶. 3 J / (kg·℃), the specific heat capacity of oils is usually between 1.8 and 2.4 × 10⁻⁶. 3 The specific heat capacity of low-concentration mud slurry is approximately 4 × 10⁻⁶ J / (kg·℃). 3J / (kg·℃), the specific heat capacity of the mixture of grease and mud-water falls between the two. Substances with higher specific heat capacity heat up and cool down more slowly per unit time, while substances with lower specific heat capacity heat up and cool down more significantly per unit time. Therefore, if leakage occurs inside the cavity and the medium inside the cavity is heated under the same conditions, the fiber optic wavelength data will show obvious anomalies.

[0059] This invention measures and records wavelength data under ambient temperature during the period when the shield tunneling begins but before the tail of the shield has exited the end reinforcement zone. Then, an external power supply is used to heat the composite sensor, and an FBG fiber optic demodulator measures and records the wavelength along the path data of each grating measuring point in each sealed cavity during multiple heating stages. The wavelength difference is obtained by subtracting the minimum wavelength of the corresponding measuring point when it is not heated from the maximum wavelength of each grating measuring point after heating.

[0060] The subsequent wavelength data of this invention are obtained by selecting the advancement gap between 50 and 100 rings of the shield tunneling. The changes in wavelength data under unheated conditions and multiple heating stages are measured and saved respectively. The wavelength difference is obtained by subtracting the minimum wavelength of the corresponding measuring point when it is not heated after each advancement from the maximum wavelength measured by heating at each grating measuring point in each sealed cavity after each advancement.

[0061] This invention compares the wavelength difference of each grating measuring point obtained in each measurement with the wavelength difference of the same grating measuring point obtained in the previous measurement. When the wavelength difference decreases by more than 50% in at least one heating stage, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease chamber, and mud and water have entered the sealed chamber. When the wavelength difference increases by more than 50% in at least one heating stage, it is determined that there is air (cavity) at the measuring point location in the chamber, and the grease injection in the grease chamber is not full. When the wavelength difference decreases or increases by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease chamber.

[0062] Based on engineering practice, this invention designates a 30° radius (5-7 o'clock direction) to the left and right of the line connecting the center point and the lowest point of the annular shield tail grease sealing cavity as a risk-sensitive zone, and other areas as general risk zones. Referring to the "Metro Engineering Construction Safety Evaluation Standard," the early warning response levels are divided into three levels: yellow, orange, and red, with normal sealing conditions designated as green. Based on the number of leakage points in different risk zones of the inner and outer cavities, corresponding early warning levels and management measures are selected. Specific management recommendations are provided in the shield tail leakage early warning classification response table. Following engineering practice, shield tail sealing cavities typically have 2-4 layers. This invention discusses a shield tail leakage early warning response method for cavities containing 2-4 sealing cavities. The front cavity refers to the sealing cavity closest to the shield tail, the rear cavity refers to the sealing cavity furthest from the shield tail, and the middle cavity refers to the cavity between the sealing cavities closest to and furthest from the shield tail.

[0063] Table 1. Shield Tail Leakage Early Warning Classification Response Table

[0064]

[0065] For the deployment location of an actively heated FBG fiber optic composite sensor in a tunnel boring machine environment, please refer to [link to relevant documentation]. Figure 2 The system includes an internal shield channel 1, a tail brush pressure plate 2, a shield 3, an FBG fiber optic composite sensor 4, a tail grease sealing cavity 5, a tail brush 6, and tubular segments 7. The tail brush pressure plate 2 is located at the root of the tail brush 6, tightly attached to the inner surface of the shield 3, thus securing the tail brush 6. The FBG fiber optic composite sensor 4 is arranged on the surface of the tail brush pressure plate 2, forming a ring along the inner surface of the shield 3. It connects to a handheld FBG fiber optic demodulator and an external power supply through the internal shield channel 1. Each FBG fiber optic demodulator has 8-12 demodulation channels, and engineers can select the demodulation interface according to their needs and the number of sensors.

[0066] The staggered arrangement of grating measurement points between adjacent cavities described in this invention can be found in the following reference: Figure 3 The system includes an FBG fiber composite sensor 4, a tail shield brush 6, and grating measurement points 8. The grating measurement points 8 on a single FBG fiber composite sensor are spaced approximately 5° apart. Within the risk-sensitive area 9 of the sealed cavity, the grating marking density can be appropriately increased according to engineering requirements. The grating measurement points 8 in adjacent cavities are staggered to achieve a uniform distribution of grating measurement points 8 within the multi-layered tail shield grease sealing cavity, thereby improving the accuracy of tail shield sealing detection.

[0067] The following are specific examples.

[0068] Example 1

[0069] This invention discloses a shield tail seal detection method using an FBG fiber optic composite sensor. The correlation between abnormal changes in wavelength data at the grating measurement points and leakage points in the sealing cavity is established through the following experimental method:

[0070] a: The active heating fiber optic composite sensor is arranged in a ring inside the sealed cavity shield shell. When the shield starts and the tail of the shield has not yet left the end reinforcement area, the wavelength data of each grating measurement point on each fiber optic cable is measured and recorded in advance under normal temperature conditions.

[0071] b: Turn on the heating switch, set the heating time to 60s, disconnect the heating power and wait for at least 20 minutes to allow the sensor and surrounding medium to return to the tunnel ambient temperature; under the same conditions, set the heating time to 120s and 180s respectively, and repeat the above operation; measure and record the wavelength data changes of each measuring point of the sensor during the entire heating and cooling process at heating times of 60s, 120s, and 180s; subtract the minimum wavelength of the corresponding measuring point when it is not heated from the maximum wavelength after heating at each grating measuring point in each sealed cavity under different heating time conditions to obtain the wavelength difference;

[0072] c: After the shield tunneling machine exits the reinforced end area, after advancing 100 rings, select a pause interval for the shield tunneling machine to connect the sensor to the FBG fiber optic demodulator, measure and record the wavelength data under the tunnel ambient temperature; set the heating time to 60s, 120s and 180s respectively, disconnect the heating power and allow it to cool naturally for at least 20 minutes, measure and record the wavelength data changes of each measuring point of the fiber optic cable during the entire heating and cooling process under heating time of 60s, 120s and 180s respectively; subtract the minimum wavelength of the corresponding measuring point when it is not heated from the maximum wavelength after heating under different heating time conditions at each grating measuring point in each sealed cavity to obtain the wavelength difference;

[0073] d: Compare the wavelength difference values ​​of each grating measuring point obtained in each measurement with the wavelength difference values ​​of the same grating measuring point obtained in the previous measurement to determine whether there are abnormal wavelength data in the subsequent construction process in c, and to determine the sealing status of the shield tail grease sealing cavity; when the wavelength difference value of at least one heating stage decreases by more than 50%, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease cavity, and mud and water have entered the sealing cavity; when the wavelength difference value of at least one heating stage increases by more than 50%, it is determined that there is air (cavity) at the measuring point location in the cavity, and the grease injection in the grease cavity is not full; when the wavelength difference values ​​all decrease or increase by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease cavity.

[0074] e: Based on engineering practice experience, the annular shield tail grease sealing cavity is located at the 5-7 o'clock position (bottom 60). 0 The area within the specified range is designated as a risk-sensitive zone, while other areas are designated as general risk zones. Based on the number of leakage points in different risk zones of the inner and outer cavities, the corresponding early warning level is determined, and appropriate emergency management measures are selected.

[0075] Set the lower 60° range (5-7 o'clock direction) of each grease sealing cavity (e.g.) Figure 4 The area shown is designated as a risk-sensitive area, and other areas are designated as general risk areas; the front cavity is designated as the sealed cavity near the shield tail, the rear cavity is designated as the sealed cavity far from the shield tail, and the middle cavity is designated as the cavity between the sealed cavities closest to and furthest from the shield tail; the corresponding early warning level is determined according to the number of leakage points in different risk areas of different cavities.

[0076] When the grease sealing cavity has two layers: if there are ≥2 leakage points in the risk-sensitive area of ​​the front cavity, or ≥5 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0077] If there are ≥5 leakage points in the current cavity's risk-sensitive area, or ≥1 leakage point in the rear cavity's general risk area while there are ≥3 leakage points throughout the entire front cavity, an orange alert will be activated.

[0078] A red alert is activated when there are ≥2 leak points in the risk-sensitive area of ​​the rear cavity, ≥4 leak points in the general risk area of ​​the rear cavity, ≥10 leak points in the risk-sensitive area of ​​the front cavity, or ≥20 leak points in the general risk area of ​​the front cavity.

[0079] When the grease sealing cavity has 3 layers: if there are ≥3 leakage points in the risk-sensitive area of ​​the front cavity, or ≥8 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0080] If there are ≥2 leakage points in the risk-sensitive area of ​​the central cavity, and the radial angle difference between any one of the leakage points in the risk-sensitive area of ​​the central cavity and any one of the leakage points in the risk-sensitive area of ​​the front cavity is ≤5°, or if there are ≥4 leakage points in the general risk area of ​​the central cavity, an orange alert will be activated.

[0081] A red alert is activated when there are ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, ≥2 leakage points in the general risk area of ​​the rear cavity, ≥8 leakage points in the risk-sensitive area of ​​the middle cavity, or ≥16 leakage points in the general risk area of ​​the middle cavity.

[0082] When the grease sealing cavity has 4 layers: if there are ≥4 leakage points in the risk-sensitive area of ​​the front cavity, or ≥10 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated;

[0083] An orange alert is activated when there are ≥3 leakage points in the risk-sensitive areas of both central cavities, and at least 2 adjacent leakage points in the risk-sensitive area of ​​either central cavity, or a total of ≥12 leakage points in the general risk areas of both central cavities.

[0084] A red alert is activated when there is ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, ≥2 leakage points in the general risk area of ​​the rear cavity, ≥6 leakage points in the risk-sensitive areas of both middle cavities, or a cumulative total of ≥24 leakage points in the general risk areas of both middle cavities.

[0085] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting shield tail sealing performance using an FBG fiber optic composite sensor, characterized in that, Includes the following steps: S1: After the shield is assembled, before filling the grease sealing cavity at the tail of the shield with grease, the FBG fiber composite sensor is arranged in a ring inside the grease sealing cavity at the tail of the shield and is closely attached to the inner surface of the shield shell and fixed to the pressure plate of the tail of the shield. The FBG fiber composite sensor can be connected to an external power supply and an FBG fiber demodulator through the internal channel of the shield shell. S2: During the period when the shield tunneling machine starts but the tail of the shield has not yet exited the end reinforcement zone, the wavelength data under ambient temperature is measured and recorded. Then, the composite sensor is heated by an external power supply. The FBG fiber demodulator measures and records the wavelength along the path of each grating measuring point in each sealed cavity under the heating environment. The maximum wavelength of each grating measuring point after heating is subtracted from the minimum wavelength of the corresponding measuring point when it is not heated to obtain the wavelength difference of the corresponding grating measuring point. S3: During the advance stop interval after every 50-100 rings of the tunnel boring machine (TBM), connect the sensor to an external power supply and an FBG fiber optic demodulator to record the wavelength data under unheated conditions. Heat the composite sensor using the external power supply. The heating time after each TBM advance is the same as the heating time in step S2. Use the FBG fiber optic demodulator to obtain the wavelength data along the path of each grating measuring point in each sealed cavity after each TBM advance. Subtract the minimum wavelength of the corresponding measuring point when it was not heated from the maximum wavelength measured by heating at each grating measuring point in each sealed cavity after each TBM advance to obtain the wavelength difference of the corresponding grating measuring point. S4: Compare the wavelength difference of each grating measuring point obtained in each measurement with the wavelength difference of the same grating measuring point obtained in the previous measurement. If the wavelength difference decreases by more than 50%, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease sealing cavity, and mud and water have entered the sealing cavity. If the wavelength difference increases by more than 50%, it is determined that there is air at the corresponding measuring point position in the grease sealing cavity, and the grease injection in the grease sealing cavity is not full. If the wavelength difference decreases or increases by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease sealing cavity.

2. The method for detecting shield tail sealing using an FBG fiber optic composite sensor as described in claim 1, characterized in that, The heating described in steps S2 and S3 both include multiple stages, and the heating time for each stage is the same; Step S4 specifically involves comparing the wavelength difference of each grating measuring point in each heating stage obtained from each measurement with the wavelength difference of the corresponding heating stage obtained from the previous measurement. If the wavelength difference of at least one heating stage decreases by more than 50%, it is determined that leakage has occurred in the corresponding measuring point area of ​​the grease sealing cavity, and mud and water have entered the grease sealing cavity. If the wavelength difference of at least one heating stage increases by more than 50%, it is determined that air exists at the corresponding measuring point position in the cavity, and the grease injection in the grease sealing cavity is not full. If the wavelength difference decreases or increases by less than or equal to 50%, it is determined that no leakage has occurred in the corresponding measuring point area of ​​the grease sealing cavity.

3. The method for detecting shield tail sealing using an FBG fiber optic composite sensor as described in claim 2, characterized in that, The multiple heating stages described in steps S2 and S3 are as follows: first heat for time T1, then allow to cool naturally to ambient temperature, then heat for time T2, then allow to cool naturally to ambient temperature, and then heat for time T3. Where 40 s≤T1≤60 s, 100 s≤T2≤120 s, and 160 s≤T3≤180 s.

4. The method for detecting shield tail sealing using an FBG fiber optic composite sensor as described in claim 1, characterized in that, The grating measurement points of the FBG fiber composite sensor arranged in the same sealed cavity are spaced 5°-10° apart.

5. The method for detecting shield tail sealing using an FBG fiber optic composite sensor as described in claim 1, characterized in that, The grating measurement points are staggered between adjacent sealed cavities to ensure uniform distribution of the measurement points.

6. The method for early warning of shield tail sealing according to any one of claims 1-5, characterized in that, The risk-sensitive area is defined as the range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity, and the other areas are defined as general risk areas; the front cavity is defined as the sealing cavity close to the shield tail, and the rear cavity is defined as the sealing cavity far away from the shield tail; the corresponding warning level is determined according to the number of leakage points in different risk areas of different cavities. When the grease sealing cavity has two layers: if there are ≥2 leakage points in the risk-sensitive area of ​​the front cavity, or ≥5 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated; When the grease-sealed cavity has two layers: an orange warning will be activated in the following two situations: the first situation is when there are ≥5 leakage points in the risk-sensitive area of ​​the front cavity; the second situation is when there are ≥1 leakage point in the general risk area of ​​the rear cavity and ≥3 leakage points in the entire front cavity. When the grease sealing cavity has two layers: when there are ≥2 leakage points in the risk-sensitive area of ​​the rear cavity, or ≥4 leakage points in the general risk area of ​​the rear cavity, or ≥10 leakage points in the risk-sensitive area of ​​the front cavity, or ≥20 leakage points in the general risk area of ​​the front cavity, a red warning is activated.

7. The method for early warning of shield tail sealing according to any one of claims 1-5, characterized in that, The risk-sensitive area is defined as the range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity, and the other areas are defined as general risk areas. The front cavity is defined as the sealing cavity close to the shield tail, the rear cavity is defined as the sealing cavity far from the shield tail, and the middle cavity is defined as the cavity between the sealing cavities closest to the shield tail and the sealing cavities farthest from the shield tail. The corresponding warning level is determined according to the number of leakage points in different risk areas of different cavities. When the grease sealing cavity has 3 layers: if there are ≥3 leakage points in the risk-sensitive area of ​​the front cavity, or ≥8 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated; When the grease sealing cavity has 3 layers: an orange warning will be activated in the following two situations: the first situation is that there are ≥2 leakage points in the risk-sensitive area of ​​the middle cavity, and the radial angle difference between any leakage point in the risk-sensitive area of ​​the middle cavity and any leakage point in the risk-sensitive area of ​​the front cavity is ≤5°; the second situation is that there are ≥4 leakage points in the general risk area of ​​the middle cavity. When the grease-sealed cavity has 3 channels: when there is ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, or ≥2 leakage points in the general risk area of ​​the rear cavity, or ≥8 leakage points in the risk-sensitive area of ​​the middle cavity, or ≥16 leakage points in the general risk area of ​​the middle cavity, a red warning is activated.

8. The method for early warning of shield tail sealing according to any one of claims 1-5, characterized in that, The risk-sensitive area is defined as the range of 30° to the left and right of the line connecting the center point and the lowest point of each grease sealing cavity, and the other areas are defined as general risk areas. The front cavity is defined as the sealing cavity close to the shield tail, the rear cavity is defined as the sealing cavity far from the shield tail, and the middle cavity is defined as the cavity between the sealing cavities closest to the shield tail and the sealing cavities farthest from the shield tail. The corresponding warning level is determined according to the number of leakage points in different risk areas of different cavities. When the grease sealing cavity has 4 layers: if there are ≥4 leakage points in the risk-sensitive area of ​​the front cavity, or ≥10 leakage points in the general risk area of ​​the front cavity, a yellow warning will be activated; When the grease sealing cavity has 4 layers: an orange warning will be activated in the following two situations: the first situation is that there are ≥3 leakage points in the risk-sensitive areas of both layers, and there are at least 2 adjacent leakage points in the risk-sensitive area of ​​any layer; the second situation is that there are ≥12 leakage points in the general risk areas of both layers. When the grease sealing cavity has 4 layers: when there is ≥1 leakage point in the risk-sensitive area of ​​the rear cavity, or ≥2 leakage points in the general risk area of ​​the rear cavity, or ≥6 leakage points in the risk-sensitive areas of both middle cavities, or a total of ≥24 leakage points in the general risk areas of the two middle cavities, a red warning is activated.

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