Shield tunnel optical fiber earthquake forecasting method and system

Abstract

The invention belongs to the technical field of advanced detection, and provides a shield tunnel optical fiber earthquake forecasting method and system, and the method comprises the steps: obtaining the carrying position and number of seismic wave excitation seismic source equipment based on a shield tunneling machine structure type, installing a pneumatic hammering seismic source, calculating the dynamic correlation between the air pressure and the hammering force, and determining the shield air pressure range. Determining the relative spatial position of the seismic source and the optical fiber sensor, and establishing an observation mode; according to the relative spatial position and the observation mode, arranging an optical fiber sensor in a spatial range behind the shield tail of the shield tunnel, controlling a pneumatic hammering seismic source to hammer surrounding rock to generate seismic waves to obtain geological forecast data, preprocessing the obtained geological forecast data to obtain geological wave field data, and calculating the geological wave field data according to the geological wave field data. And calculating rock mass mechanical parameters, a reflection coefficient and a stress gradient of the shield excavation surface, obtaining a three-dimensional image, carrying out feature analysis, obtaining a disaster-causing structure position, a disaster-causing structure scale and an underground water occurrence condition, and completing prediction of the shield tunnel optical fiber earthquake.

Description

Technical Field

[0001] The invention belongs to the technical field of advanced detection, and particularly relates to a fiber optic seismic prediction method and system for shield tunnels. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] It is crucial to detect major geological disaster sources in front of the excavation face in advance to ensure the safe construction of shield tunnels. Geophysical exploration methods are the key to geological detection. Currently, it mainly relies on surface detection methods, but there are still many difficulties: (1) The urban environment is complex and various interference noises are strong, which easily leads to a low signal-to-noise ratio of the observed data. For example, vehicles / pedestrians, etc. will generate random vibration noises, and the intertwined power grids and radio signals will generate strong electromagnetic interference, while buildings will hinder the layout of survey lines and survey points; (2) The particularity of the urban environment has led to strict restrictions on the use of some geophysical methods. Traditional geological drilling has the drawback of seeing only one hole and it is difficult to effectively obtain continuous geological information.

[0004] Currently, there are also many problems in the advanced geological prediction in shield tunnels. There is no exposed surrounding rock mass in the tunnel, and the huge metal body of the shield machine leads to a narrow observation space, which in turn leads to a complex prediction environment. The existing seismic prediction methods for shield tunnels cannot adapt to the complex environment of shield tunnels; at the same time, the normal pressure maintenance of the excavation face in shield tunnels causes the shield machine to be unable to retreat, which in turn compresses the layout space of the observation. Therefore, the location and scale information of the occurrence of bad geology cannot be obtained in advance, resulting in the shield machine often being in a "blind push" state during tunneling, and the safe tunneling faces a major challenge. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a fiber optic seismic prediction method and system for shield tunnels. Through the pneumatic source shield loading and the two-way minimum offset observation mode, based on the collaborative imaging of multi-parameters such as geotechnical mechanical parameters, reflection coefficients, and stress gradients, it overcomes the deficiency that the existing geological prediction technology is not applicable to the complex environment of shield tunnels, realizes zero-interference continuous advanced detection under the condition of rapid shield tunneling, enables geological prediction to truly integrate into the shield construction process, and provides an effective geological basis for shield construction.

[0006] According to some embodiments, the first solution of the present invention provides a fiber optic seismic prediction method for shield tunnels, and adopts the following technical solutions: A fiber optic seismic prediction method for shield tunnels, comprising: Based on the structural type of the shield machine, obtain the loading position and quantity of the seismic wave excitation source equipment; Install a pneumatic hammering seismic source according to the obtained mounting positions and quantities, calculate the dynamic correlation between the air pressure magnitude and the hammering force, and determine the shield air pressure range; Determine the relative spatial positions of the seismic source and the fiber optic sensor according to the shield air pressure range, and establish an observation mode; Lay fiber optic sensors within the spatial range behind the shield tail of the shield tunnel according to the relative spatial positions and the observation mode, control the pneumatic hammering seismic source to hammer the surrounding rock to generate seismic waves, and obtain geological prediction data; Combine the determined relative spatial positions of the seismic source and the fiber optic sensor, preprocess the obtained geological prediction data, and obtain geological wave field data; Calculate the rock mass mechanical parameters, reflection coefficient, and stress gradient of the shield excavation face according to the obtained geological wave field data; Convert the obtained rock mass mechanical parameters, reflection coefficient, and stress gradient into three-dimensional imaging, analyze the obtained three-dimensional imaging characteristics, obtain the location, scale of disaster-causing structures, and the occurrence situation of groundwater, and complete the prediction of fiber optic seismic in the shield tunnel.

[0007] As a further technical limitation, according to the obtained geological wave field data, construct a seismic wave travel time equation, combine tomography to solve the seismic wave velocity model, iteratively optimize the seismic wave velocity model through the seismic wave travel time objective function, obtain the optimal seismic wave velocity, and calculate the rock mass mechanical parameters including shear modulus, elastic modulus, and Poisson's ratio; calculate the reflection coefficient in combination with wave impedance; according to the acoustoelastic theory, obtain the relationship between stress and wave velocity, perform gradient inversion on the obtained stress, and obtain the stress gradient.

[0008] As a further technical limitation, the fiber optic sensors are arranged behind the shield tail, in the bottom area of the cross-section of the shield tunnel, or on the inner surface of the shield tunnel segment structure; the coupling method of the fiber optic sensor with the shield tunnel segment structure is to fix the fiber optic sensor with a coupling agent or through a secondary grouting hole; after the fiber optic sensor is fixedly connected, the seismic source needs to act on the surrounding rock mass, and the pneumatic hammering seismic source is controlled by a remote control system to generate seismic waves. The seismic waves propagate in all directions, and when they encounter an interface with different wave impedances, reflected echoes are received by the fiber optic sensors; the data of the same mileage section obtained by the action of the pneumatic hammering seismic source on the surrounding rock N times are used to obtain the geological prediction data.

[0009] As a further technical limitation, the preprocessing at least includes spectral analysis, time-frequency filtering, seismic time base correction, energy balance, inverse Q filtering, reflected wave extraction, and P-S wave separation.

[0010] As a further technical limitation, the obtained rock mass mechanical parameters, reflection coefficients, and stress gradients are unified into the tunnel three-dimensional coordinate system. The rock mass mechanical parameters, reflection coefficients, and stress gradients are normalized respectively using Min-Max normalization to eliminate the dimensional differences. The Kriging interpolation method is used to interpolate the parameters of discrete measuring points into a three-dimensional continuous field. Then, the detection area is divided into regular voxel grids, and each voxel is associated with mechanical parameters, reflection coefficients, and stress gradients to obtain a three-dimensional imaging.

[0011] As a further technical limitation, by differentiating and extracting the features of the obtained three-dimensional imaging, analyzing the extracted features, the three-dimensional imaging of full-space parameters is transformed into the results of bad geological interpretation to obtain the location, scale of disaster-causing structures, and the occurrence situation of groundwater.

[0012] As a further technical limitation, the relative spatial positions of the seismic source and the fiber optic sensor include the fiber optic sensor in front and the seismic source behind, the fiber optic sensor behind and the seismic source in front, as well as the distance between the fiber optic sensor and the seismic source, and the distance between fiber optic sensors; the established observation modes are the front-source and rear-receive observation mode and the two-way minimum offset spatial observation mode, where a set of minimum offset observation modes is set for both the left and right sidewalls of the shield tunnel for the two-way minimum offset.

[0013] As a further technical limitation, the gas source used by the pneumatic hammering seismic source is provided by the shield machine air pump. The air pressure of the shield machine air pump determines the hammering force, and the hammering force has a linear relationship with the magnitude of the air pressure.

[0014] As a further technical limitation, the mounting position of the seismic wave excitation seismic source equipment is set as the gap between the shield hydraulic cylinders. A pneumatic seismic source is symmetrically arranged on both sides of the shield hydraulic cylinders according to the differences in the shield machine structure type.

[0015] According to some embodiments, the second solution of the present invention provides a fiber optic seismic prediction system for shield tunnels, adopting the following technical solutions: A fiber optic seismic prediction system for shield tunnels, comprising: An acquisition module configured to acquire the mounting position and quantity of the seismic wave excitation seismic source equipment based on the shield machine structure type; A calculation module configured to install a pneumatic hammering seismic source according to the acquired mounting position and quantity, calculate the dynamic correlation relationship between the air pressure magnitude and the hammering force, and determine the shield air pressure range; A determination module configured to determine the relative spatial positions of the seismic source and the fiber optic sensor according to the shield air pressure range and establish an observation mode; A control module, configured to deploy fiber optic sensors within the space range behind the tail of a shield tunnel according to the relative spatial position and observation mode, control a pneumatic hammering seismic source to hammer the surrounding rock to generate seismic waves, and obtain geological prediction data; A preprocessing module, configured to preprocess the obtained geological prediction data in combination with the determined relative spatial position of the seismic source and the fiber optic sensors to obtain geological wave field data; A prediction module, configured to calculate the rock mass mechanical parameters, reflection coefficient, and stress gradient of the shield excavation face according to the obtained geological wave field data; convert the obtained rock mass mechanical parameters, reflection coefficient, and stress gradient into three-dimensional imaging, analyze the obtained three-dimensional imaging characteristics, obtain the location, scale of disaster-causing structures, and the occurrence situation of groundwater, and complete the prediction of fiber optic seismic in shield tunnels.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Through the pneumatic seismic source shield carried with the two-way minimum offset observation mode, the present invention overcomes the deficiency that the existing geological prediction technology is not applicable to the complex environment of shield tunnels due to the narrow observation space, realizes zero-interference continuous forward detection under the condition of rapid shield tunneling, enables geological prediction to be truly integrated into the shield construction process, and provides an effective geological basis for shield construction.

[0017] Through the collaborative imaging of multiple parameters such as rock mass mechanical parameters, reflection coefficient, and stress gradient, the present invention breaks through the industry common problem that traditional seismic wave methods cannot detect underground water bodies, solves the state problem of blind tunneling of shield machines caused by the inability to obtain information on the occurrence and scale of bad geology in advance, and reverses the situation where only electromagnetic methods can be used for water detection. Description of the Drawings

[0018] The schematic diagrams of the specification drawings forming a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments and descriptions of this embodiment are used to explain this embodiment and do not constitute an improper limitation to this embodiment.

[0019] Figure 1 It is a flowchart of a fiber optic seismic prediction method for shield tunnels in Embodiment 1 of the present invention; Figure 2 It is a schematic diagram of the application scenario of the fiber optic seismic prediction method for shield tunnels in Embodiment 1 of the present invention in a shield tunnel; Figure 3 It is a flowchart of data preprocessing in Embodiment 1 of the present invention; Figure 4 It is a structural block diagram of a fiber optic seismic prediction system for shield tunnels in Embodiment 2 of the present invention; Among them, 1. the structural type of the shield machine; 2. the seismic wave hammering seismic source equipment; 3. the three-component fiber optic sensor; 4. the signal transmission center; 5. the fiber optic demodulator; 6. the remote control system. Detailed implementation mode

[0020] The present invention will be further described below in conjunction with the drawings and embodiments.

[0021] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0022] It should be noted that the terms used herein are only for describing specific implementation modes and are not intended to limit the exemplary implementation modes according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] In the present invention, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only relationship terms determined for the convenience of describing the structural relationship of each component or element of the present invention and do not specifically refer to any component or element of the present invention and should not be construed as a limitation of the present invention.

[0024] In the present invention, terms such as "fixed connection", "connected", "connected" should be understood in a broad sense, which may mean a fixed connection, an integral connection or a detachable connection; it may be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances and should not be construed as a limitation of the present invention.

[0025] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0026] Embodiment 1 Embodiment 1 of the present invention introduces a fiber optic seismic prediction method for shield tunnels.

[0027] As Figure 1 shown, a fiber optic seismic prediction method for shield tunnels includes: Based on the structural type of the shield machine, obtain the mounting positions and quantities of the seismic wave excitation seismic source equipment; Install a pneumatic hammering vibration source according to the obtained mounting positions and quantities, calculate the dynamic correlation between the air pressure and the hammering force, and determine the shield air pressure range; Determine the relative spatial positions of the vibration source and the fiber optic sensor according to the shield air pressure range, and establish an observation mode; According to the relative spatial positions and the observation mode, arrange fiber optic sensors within the spatial range behind the shield tail of the shield tunnel, control the pneumatic hammering vibration source to hammer the surrounding rock to generate seismic waves, and obtain geological prediction data; Combined with the determined relative spatial positions of the vibration source and the fiber optic sensor, preprocess the obtained geological prediction data to obtain geological wave field data; Calculate the rock mass mechanical parameters, reflection coefficient, and stress gradient of the shield excavation face according to the obtained geological wave field data; Convert the obtained rock mass mechanical parameters, reflection coefficient, and stress gradient into three-dimensional imaging, analyze the obtained three-dimensional imaging characteristics, and obtain the location, scale of the disaster-causing structure, and the occurrence situation of groundwater, thus completing the prediction of fiber optic earthquake in the shield tunnel.

[0028] Next, this embodiment combines Figure 2 and Figure 3 to introduce in detail the method for predicting fiber optic earthquake in the shield tunnel: First of all, based on the shield machine structure type 1, design the mounting positions and quantities of the seismic wave hammering vibration source equipment 2; that is, the mounting position of the seismic wave excitation vibration source equipment is generally selected in the gap of the middle shield hydraulic cylinder, and one pneumatic vibration source is mounted symmetrically on both sides. According to the differences in the shield machine structure type, the mounting positions and quantities can be flexibly selected, but at least one vibration source should be guaranteed, and the vibration source position should be as close as possible to the shield tail position; the vibration source mounting position needs to drill holes on the shield body, and the hole size needs to be calculated through relevant force calculations, and the stability and safety of the shield structure should be ensured first.

[0029] Secondly, based on the targeted transformation of the shield machine, install the hammering vibration source equipment 2 driven by the air pressure of the shield air pump, calculate the dynamic correlation between the air pressure and the hammering force, and determine the shield air pressure range; the installation of the pneumatic hammering vibration source should meet the sealing requirements, and the inner and outer surfaces of the shield body are strengthened by welding; the air source used by the pneumatic hammering vibration source is provided by the self-owned air pump of the shield machine, and the air pressure supplied by the air pump determines the hammering force, and the hammering force has a linear relationship with the air pressure; in this embodiment, when the air pressure reaches 0.6 Mpa, the hammering force is 4000 N.

[0030] This embodiment establishes a geological model of the shield tunnel and a typical bad geological model, and determines the relative spatial positions of the fiber optic sensor and the vibration source through the analysis of the wave field snapshot and the seismic record characteristics, and establishes an observation mode; specifically: In the shield tunnel geological model, the tunnel burial depth, diameter, cross-section form, and surrounding rock wave impedance parameters (longitudinal wave velocity, transverse wave velocity, density, etc.) are selected according to the relevant parameters of the actual shield tunnel; the relative spatial position relationship between the fiber optic sensor and the seismic source mainly includes: the fiber optic sensor is in front and the seismic source is behind, the fiber optic sensor is behind and the seismic source is in front, the distance between the fiber optic sensor and the seismic source, and the distance between fiber optic sensors; the observation modes include the front-source and rear-receiving observation method and the two-way minimum offset spatial observation mode. Among them, a set of minimum offset observation modes is set for both the left and right sidewalls of the shield tunnel, which not only satisfies three-dimensional observation, but also realizes effective application in the narrow space of the shield tunnel, and effectively suppresses the cross-talk between longitudinal and transverse waves, which is beneficial to the subsequent separation and processing of longitudinal and transverse wave data.

[0031] Then, in this embodiment, a three-component fiber optic sensor array 3 is arranged within a certain space range behind the shield tail of the shield tunnel according to the designed observation mode. The fiber optic sensor is connected to the signal transmission center 4, and then connected to the fiber optic demodulator 5 through a fiber optic cable. The pneumatic hammering seismic source is controlled by the remote control system 6 to hammer the surrounding rock to generate seismic waves, and N groups of geological prediction data for the current mileage are obtained.

[0032] In this embodiment, the fiber optic sensors are arranged within a range of 10 - 15 m behind the shield tail. The fiber optic sensors are generally located in the bottom area (within 90°) of the cross-section of the shield tunnel, and the distance between the fiber optic sensors is 1.5 m; the fiber optic sensors are attached to the inner surface of the segment structure of the shield tunnel, and the coupling scheme between the fiber optic sensors and the segment structure is: using a coupling agent to fix the fiber optic sensors or ensuring the coupling effect of the fiber optic sensors through secondary grouting holes; after the fiber optic sensors are fixed and connected, the pneumatic hammering seismic source is controlled by the remote control system to generate seismic waves. The seismic waves propagate in all directions and generate reflected echoes when encountering the wave impedance difference interface, which are received by the fiber optic sensors; the length of the pneumatic hammering seismic source extending out of the shield body is 15 cm, and the seismic source needs to act on the surrounding rock mass to generate seismic waves; the N groups of geological predictions are the data of the same mileage section obtained by the pneumatic hammering seismic source acting on the surrounding rock N times, and the signal-to-noise ratio of the prediction data is improved through signal processing means such as stacking.

[0033] Define the actual observation system parameters of the shield tunnel, that is, the three-dimensional spatial coordinates of the fiber optic sensor and the seismic source and the stacking times, and set the spatial position relationship of each group of data, such as Figure 3 shown in the refined preprocessing (at least including spectral analysis, time-frequency filtering, seismic time base correction, energy balance, inverse Q filtering, reflection wave extraction, longitudinal and transverse wave separation, etc.), to obtain high-quality wave field data with a low noise level.

[0034] According to the geological prediction data, calculate the rock mass mechanical parameters, reflection coefficient, and stress gradient within a certain space range in front of the shield excavation face to obtain an imaging result of three-dimensional spatial distribution; specifically: ① Using the travel time data of direct waves and reflected waves that have been obtained through on-site monitoring, construct a seismic wave travel time equation system, that is ; where is the P-wave velocity, is the travel time of the seismic wave in the i-th channel, is the path differential; ② Adopt tomography to solve the velocity model , and the objective function is ; By iteratively optimizing the wave velocity model, the calculated travel time approaches the observed value ; ③ In the calculation of rock mass mechanical parameters, use the P-wave velocity , the S-wave velocity and the geological density to calculate the shear modulus , the elastic modulus and the Poisson's ratio , that is ; ④ In the calculation of the reflection coefficient R, it can be calculated according to the formula of wave impedance and reflection coefficient ; where , are the wave impedances on both sides of the interface respectively; then, according to the travel time of the reflected wave and the velocity model, calculate the position of the reflection interface ; where is the distance of the reflection interface in front of the excavation face, is the two-way travel time of the reflected wave; ⑤ In the calculation of the stress gradient, based on the acoustoelastic theory, the wave velocity changes with stress as ; where , is the acoustoelastic coefficient of the rock; then perform stress gradient inversion, that is, deduce the stress gradient through the wave velocity gradient, and construct a three-dimensional stress gradient tensor by combining multi-directional wave velocity data; ; where is the wave velocity gradient.

[0035] In this embodiment, the rock mass mechanical parameters, reflection coefficient and stress gradient are unified into the tunnel three-dimensional coordinate system. The parameters are normalized by using Min-Max normalization to eliminate the dimension difference. The Kriging interpolation method is used to interpolate the parameters of discrete measuring points into a three-dimensional continuous field. Subsequently, the detection area is divided into regular voxel grids, and each voxel is associated with mechanical parameters, reflection coefficient and stress gradient. Finally, a three-dimensional imaging result is obtained. The three-dimensional imaging of the full-space parameters is transformed into a more intuitive bad geological interpretation result through a differential extraction method, and the location, scale and groundwater occurrence of the disaster-causing structure are obtained through imaging feature analysis.

[0036] In this embodiment, through the pneumatic source shield carried with the bidirectional minimum offset observation mode, and based on the collaborative imaging of multi-parameters such as geomechanical parameters, reflection coefficients, and stress gradients, it overcomes the deficiencies of existing geological prediction technologies that are not applicable to the complex environment of shield tunnels, realizes zero-interference continuous forward detection under the condition of rapid shield tunneling, enables geological prediction to truly integrate into the shield construction process, and provides an effective geological basis for shield construction; the use of a three-component fiber optic seismic prediction equipment not only realizes the effective perception of multi-component seismic wave data, can effectively avoid strong electromagnetic interference in shield tunnels, and ensures the authenticity and accuracy of prediction data; through the collaborative imaging of multi-parameters such as rock mass mechanical parameters, reflection coefficients, and stress gradients, it breaks through the industry common problem that traditional seismic wave methods cannot detect underground water bodies, and reverses the situation where only electromagnetic methods can be used for water exploration.

[0037] Embodiment 2 Embodiment 2 of the present invention introduces a fiber optic seismic prediction system for shield tunnels.

[0038] As Figure 4 shown, a fiber optic seismic prediction system for shield tunnels includes: An acquisition module, which is configured to obtain the installation positions and quantities of seismic wave excitation source equipment based on the structural type of the shield machine; A calculation module, which is configured to install a pneumatic hammering source according to the obtained installation positions and quantities, calculate the dynamic correlation between the air pressure magnitude and the hammering force, and determine the shield air pressure range; A determination module, which is configured to determine the relative spatial positions of the source and the fiber optic sensor according to the shield air pressure range, and establish an observation mode; A control module, which is configured to deploy fiber optic sensors within the space range behind the shield tail of the shield tunnel according to the relative spatial positions and the observation mode, control the pneumatic hammering source to hammer the surrounding rock to generate seismic waves, and obtain geological prediction data; A preprocessing module, which is configured to preprocess the obtained geological prediction data in combination with the determined relative spatial positions of the source and the fiber optic sensor to obtain geological wave field data; A prediction module, which is configured to calculate the rock mass mechanical parameters, reflection coefficients, and stress gradients of the shield excavation face according to the obtained geological wave field data; convert the obtained rock mass mechanical parameters, reflection coefficients, and stress gradients into three-dimensional imaging, analyze the obtained three-dimensional imaging characteristics, and obtain the location, scale of disaster-causing structures, and the occurrence situation of groundwater, thereby completing the prediction of fiber optic seismic in shield tunnels.

[0039] The detailed steps are the same as those of a fiber optic seismic prediction method provided in Embodiment 1, and will not be elaborated here.

[0040] The above are only the preferred embodiments of this embodiment and are not intended to limit this embodiment. For those skilled in the art, various changes and modifications can be made to this embodiment. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this embodiment shall be included within the protection scope of this embodiment.

Claims

1. A shield tunnel optical fiber earthquake prediction method, characterized in that: include: Based on the structure type of the shield machine, obtain the location and quantity of the seismic wave excitation source equipment; According to the acquired loading positions and quantities, install the pneumatic hammer source, calculate the dynamic correlation between the air pressure and the hammer force, and determine the air pressure range of the shield machine; According to the shield air pressure range, determine the relative spatial position of the seismic source and the optical fiber sensor, and establish the observation mode; According to the relative spatial position and observation mode, optical fiber sensors are arranged in the space behind the shield tail of the shield tunnel, and the pneumatic hammer source is controlled to hammer the surrounding rock to generate seismic waves, thereby obtaining geological prediction data; Combined with the determined relative spatial position of the earthquake source and the optical fiber sensor, the obtained geological prediction data is preprocessed to obtain geological wave field data; According to the obtained geological wave field data, the rock mechanical parameters, reflection coefficient and stress gradient of the shield excavation face are calculated; The obtained rock mechanical parameters, reflection coefficient and stress gradient are converted into three-dimensional images. The obtained three-dimensional imaging characteristics are analyzed to obtain the location, scale and groundwater storage conditions of the disaster-causing structure, and complete the prediction of fiber-optic earthquakes in shield tunnels.

2. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: Based on the obtained geological wave field data, the seismic wave travel time equation is constructed, and the seismic wave velocity model is solved in combination with tomography. The seismic wave velocity model is iteratively optimized through the seismic wave travel time objective function to obtain the optimal seismic wave velocity, and the rock mechanical parameters including shear modulus, elastic modulus and Poisson's ratio are calculated; the reflection coefficient is calculated in combination with the wave impedance; according to the acoustic elasticity theory, the relationship between stress and wave velocity is obtained, and the obtained stress is gradient inverted to obtain the stress gradient.

3. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The optical fiber sensor is arranged behind the shield tail, at the bottom area of ​​the shield tunnel cross section or on the inner surface of the shield tunnel segment structure; the optical fiber sensor is coupled to the shield tunnel segment structure by using a coupling agent to fix the optical fiber sensor or through a secondary grouting hole; after the optical fiber sensor is fixedly connected, the seismic source is applied to the surrounding rock mass, and the pneumatic hammer seismic source is controlled by a remote control system to excite seismic waves. The seismic waves propagate in all directions and encounter a wave impedance difference interface to generate a reflected echo that is received by the optical fiber sensor; the data of the same mileage section obtained by applying the pneumatic hammer seismic source to the surrounding rock N times is used to obtain geological prediction data.

4. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The preprocessing includes at least spectrum analysis, time-frequency filtering, seismic time base correction, energy balance, inverse Q filtering, reflection wave extraction and longitudinal and transverse wave separation.

5. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The obtained rock mechanical parameters, reflection coefficient and stress gradient are unified into the three-dimensional coordinate system of the tunnel. The rock mechanical parameters, reflection coefficient and stress gradient are normalized by Min-Max normalization to eliminate the dimensional difference. The parameters of discrete measuring points are interpolated into a three-dimensional continuous field by the Kriging interpolation method. The detection area is then divided into a regular voxel grid. Each voxel is associated with mechanical parameters, reflection coefficient and stress gradient to obtain a three-dimensional image.

6. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: By differentially extracting the features of the obtained three-dimensional imaging and analyzing the extracted features, the full-space parameter three-dimensional imaging is converted into adverse geological interpretation results to obtain the location, scale and groundwater storage conditions of the disaster-causing structure.

7. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The relative spatial position of the seismic source and the optical fiber sensor includes the optical fiber sensor in front and the seismic source behind, the optical fiber sensor in the back and the seismic source in front, the distance between the optical fiber sensor and the seismic source, and the distance between the optical fiber sensors; the established observation modes are the front source and the back receiver observation mode and the two-way minimum offset distance space observation mode, among which the two-way minimum offset distance is a set of minimum offset distance observation modes for both the left and right side walls of the shield tunnel.

8. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The air source used by the pneumatic hammering source is provided by the shield machine air pump. The air pressure of the shield machine air pump determines the hammering force, and the hammering force is linearly related to the air pressure.

9. A shield tunnel optical fiber earthquake prediction method as claimed in claim 1, characterized in that: The mounting position of the seismic wave excitation source equipment is set as the gap between the shield hydraulic cylinders, and a pneumatic source is symmetrically arranged on both sides of the shield hydraulic cylinders, according to the differences in the structural types of the shield machine.

10. A shield tunnel optical fiber earthquake prediction system, using a shield tunnel optical fiber earthquake prediction method as claimed in any one of claims 1 to 9, characterized in that: include: An acquisition module, which is configured to acquire the mounting position and quantity of seismic wave excitation source equipment based on the structure type of the shield machine; A calculation module is configured to install a pneumatic hammer source according to the acquired carrying position and quantity, calculate the dynamic correlation between the air pressure and the hammer force, and determine the air pressure range of the shield machine; A determination module, which is configured to determine the relative spatial position of the seismic source and the optical fiber sensor according to the shield pressure range and establish an observation mode; A control module is configured to arrange optical fiber sensors in the space behind the shield tail of the shield tunnel according to the relative spatial position and the observation mode, control the pneumatic hammer source to hammer the surrounding rock to generate seismic waves, and obtain geological prediction data; A preprocessing module is configured to preprocess the obtained geological prediction data in combination with the determined relative spatial position of the earthquake source and the optical fiber sensor to obtain geological wave field data; The prediction module is configured to calculate the rock mechanical parameters, reflection coefficient and stress gradient of the shield excavation surface according to the obtained geological wave field data; convert the obtained rock mechanical parameters, reflection coefficient and stress gradient into three-dimensional images, analyze the obtained three-dimensional imaging characteristics, obtain the location, scale and groundwater storage of the disaster-causing structure, and complete the prediction of fiber optic earthquake in the shield tunnel.

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