Method, system and equipment for measuring the convergence of surrounding rock of multi-arch tunnel

Abstract

The present application discloses a method, system and device for measuring the convergence of surrounding rock of a multi-arch tunnel. The method includes: obtaining data of multiple pre-buried fiber grating strain sensors to obtain the central wavelength variation of the corresponding position of the surrounding rock of the multi-arch tunnel; performing temperature compensation on the pre-processed central wavelength variation, and calculating the displacement of each measuring point of the measuring section in combination with the effective length of the sensor; constructing a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel based on the theory of elastic-plastic mechanics, so as to calculate the displacement field of the surrounding rock using the displacement; and extracting the radial displacement of each measuring point using the displacement field to calculate the target convergence and convergence rate. Through the scheme of the present application, it is possible to capture the tiny deformation of the surrounding rock and achieve high-precision measurement.

Description

Technical Field

[0001] The present application relates to the field of measurement, and in particular to a method, system and equipment for measuring the convergence of surrounding rock of a multi-arch tunnel. Background Art

[0002] As a special tunnel structure, the stability of the surrounding rock of a multi-arch tunnel is directly related to the safety and service life of the tunnel. The measurement of the convergence of the surrounding rock is one of the key indicators for evaluating the stability of a multi-arch tunnel, and is of great significance for guiding tunnel construction, preventing safety accidents and long-term maintenance. The measurement of the convergence of the surrounding rock of a multi-arch tunnel is mainly used to monitor the deformation of the surrounding rock after tunnel excavation, evaluate the effectiveness of the support structure, and warn of potential instability risks. Its importance is reflected in the following aspects: first, it can timely reflect the changes in the stress state of the surrounding rock and provide a basis for the support design during the construction process; second, through long-term monitoring, the long-term stability of the tunnel can be evaluated and decision support can be provided for maintenance and reinforcement; third, under geological conditions, accurate convergence measurement can help engineers better understand the mechanical behavior of the surrounding rock and optimize the construction plan. At present, the measurement of the convergence of the surrounding rock of a multi-arch tunnel mainly adopts traditional measurement methods, such as total station measurement and convergence meter measurement. The working principle of these methods is to set fixed measurement points in the tunnel, conduct regular manual measurements or use automated equipment for continuous monitoring. Total station measurement calculates the convergence by measuring the change in distance between fixed points, while the convergence meter directly measures the relative displacement between two fixed points. However, these traditional methods have some problems: first, the measurement accuracy is greatly affected by human factors and environmental conditions; second, the measurement frequency is limited, making it difficult to achieve continuous real-time monitoring; third, in harsh tunnel environments, the reliability and durability of the equipment face challenges; finally, these methods can usually only obtain data from a limited number of measurement points, making it difficult to fully reflect the deformation of the entire tunnel section.

[0003] To solve the above problems, researchers have disclosed a variety of improvement methods. For example, using an automated measurement system to increase the measurement frequency and reduce human errors; using laser scanning technology to obtain more comprehensive tunnel section deformation data; introducing wireless sensor network technology to achieve remote real-time monitoring. However, these methods still have some limitations. Although the automated measurement system has improved the measurement efficiency, it still faces the challenges of equipment maintenance and power supply; although laser scanning technology can obtain more data points, the equipment is expensive and data processing; although wireless sensor networks have achieved remote monitoring, the signal transmission is unstable in the tunnel environment, and the life and reliability of the sensor still need to be improved.

[0004] Therefore, there is an urgent need for a technical solution that can capture tiny deformations of the surrounding rock and achieve high-precision measurements. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, the embodiment of the present application provides a method, system and device for measuring the convergence of the surrounding rock of a multi-arch tunnel. The present application solves the technical problems of the prior art such as unstable signal transmission and low measurement accuracy.

[0006] The embodiment of the present application provides a method for measuring the convergence of surrounding rock of a multi-arch tunnel, including: acquiring data of a plurality of pre-buried fiber grating strain sensors to obtain the central wavelength variation at the corresponding position of the surrounding rock of the multi-arch tunnel; performing temperature compensation on the pre-processed central wavelength variation, and calculating the displacement of each measuring point of the measuring section in combination with the effective length of the sensor; including: pre-processing the collected central wavelength variation, removing abnormal values ​​and noise, and performing temperature compensation to calculate the wavelength variation caused by the actual strain; calculating the strain of each measuring point based on the compensated wavelength variation; calculating the displacement of the surrounding rock of each measuring point using the strain and the effective length of the sensor; sorting out the processing results to obtain the displacement of eight measuring points of each measuring section; wherein, performing temperature compensation to calculate the wavelength variation caused by the actual strain includes: ,in, represents the wavelength change caused by the actual strain, represents the total wavelength change measured, represents the temperature sensitivity coefficient of fiber Bragg grating and its value is 6.678×10 -6 / °C, represents the temperature change, represents the initial center wavelength of the fiber Bragg grating; wherein, based on the compensated wavelength change, the strain at each measuring point is calculated, including: ,in, represents the fiber Bragg grating strain, represents the change in fiber Bragg grating wavelength, represents the initial center wavelength of the fiber Bragg grating, represents the strain sensitivity coefficient of the fiber Bragg grating and takes a value of 0.78; based on the theory of elastic-plastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement; the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate.

[0007] In a possible implementation, data of multiple pre-buried fiber grating strain sensors are obtained to obtain the central wavelength change at corresponding positions of the surrounding rock of the multi-arch tunnel, including: pre-buried fiber grating strain sensors around the surrounding rock of the multi-arch tunnel, the sensors are arranged at the arch crown, arch waist, side wall and invert arch, a measurement section is set every 5 meters along the longitudinal direction of the tunnel, and 8 measuring points are arranged in each section; using a spectrum analyzer to measure the central wavelength change of the fiber grating strain sensor.

[0008] In a possible implementation, based on the theory of elastic-plastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement, including: setting the surrounding rock as an isotropic elastic-plastic medium to follow the Mohr-Coulomb yield criterion and determining the stress-strain relationship model equation of the surrounding rock; substituting the displacement into the boundary conditions in the stress-strain relationship model equation; determining the mechanical parameters of the surrounding rock based on on-site geological survey data; the mechanical parameters include elastic modulus, Poisson's ratio, cohesion and internal friction angle; using the finite element method to solve the stress-strain relationship model equation to obtain the surrounding rock stress field and displacement field distribution.

[0009] In a possible implementation, the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate, including: determining the initial radius value of the tunnel before excavation as a reference radius value; after the tunnel is excavated, measuring the radial displacement values ​​of multiple preset measuring points around the tunnel; calculating the convergence value of each measuring point based on the measured radial displacement value of each measuring point; calculating the average convergence value of the entire tunnel based on the convergence values ​​of all measuring points; after a preset time interval, repeatedly calculating the measurement data to obtain a new convergence value; calculating the convergence rate value based on the convergence difference and time interval between two measurements; and outputting the convergence value of each measuring point, the average convergence value of the entire tunnel, and the convergence rate value.

[0010] In one possible implementation, the surrounding rock is set as an isotropic elastic-plastic medium to follow the Mohr-Coulomb yield criterion, and the stress-strain relationship model equation of the surrounding rock is determined, including: ,in, represents the stress tensor, represents the shear modulus, represents the strain tensor, represents the bulk modulus, represents the volume strain, represents the Kroneckerdelta function, represents the direction of plastic flow, represents the yield stress, represents the equivalent plastic strain.

[0011] The embodiment of the present application also provides a system for measuring the convergence of surrounding rock of a multi-arch tunnel, comprising: a sensor unit and a computing unit; wherein the sensor unit is used to obtain data from a plurality of pre-buried fiber grating strain sensors to obtain the central wavelength change at the corresponding position of the surrounding rock of the multi-arch tunnel; the computing unit is used to perform temperature compensation on the pre-processed central wavelength change, and calculate the displacement of each measuring point of the measuring section in combination with the effective length of the sensor; based on the theory of elastic-plastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement; and the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate.

[0012] An embodiment of the present application also provides a device for measuring the convergence of the surrounding rock of a multi-arch tunnel, comprising: a processor, a memory, and a system bus; wherein the processor and the memory are connected via the system bus; the memory is used to store one or more programs, and the one or more programs include instructions, which, when executed by the processor, enable the processor to execute the method described in the above embodiment.

[0013] In the above-provided method, system and device for measuring the convergence of surrounding rock around a multi-arch tunnel, the embodiment of the present application uses fiber Bragg grating sensing technology to deploy a fiber Bragg grating strain sensor array around the surrounding rock of the multi-arch tunnel, and monitors the deformation of the surrounding rock in real time by measuring the change in the fiber Bragg grating wavelength. Combined with the elastic-plastic mechanics model, the relationship between the surrounding rock deformation and the change in the fiber Bragg grating wavelength is established to achieve accurate measurement of the convergence of the surrounding rock around the multi-arch tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 A schematic flow chart of a method for measuring the convergence of surrounding rock of a multi-arch tunnel provided in an embodiment of the present application;

[0016] Figure 2 A schematic diagram of a measurement section of surrounding rock of a multi-arch tunnel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0017] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0018] Those skilled in the art will appreciate that the terms "first", "second" and the like in the embodiments of the present application are only used to distinguish different steps, devices or modules, etc., and do not represent any specific technical meaning, nor do they represent the necessary logical order between them. It should also be understood that in the embodiments of the present application, "multiple" may refer to two or more, and "at least one" may refer to one, two or more. It should also be understood that for any component, data or structure mentioned in the embodiments of the present application, in the absence of explicit limitation or contrary revelation given in the context, it can generally be understood as one or more. In addition, the term "and / or" in the present application is only a kind of association relationship describing the associated objects, indicating that there can be three kinds of relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present application generally indicates that the associated objects before and after are an "or" relationship. It should also be understood that the description of each embodiment in the present application emphasizes the differences between the embodiments, and the same or similar parts can refer to each other. For the sake of brevity, they will not be repeated one by one.

[0019] At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. The techniques, methods and devices known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and devices should be considered as part of the specification. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] Figure 1 A flow chart of a method for measuring the convergence of surrounding rock in a multi-arch tunnel provided in an embodiment of the present application. The multi-arch tunnel refers to a tunnel formed by connecting two or more arch structures, which is usually used for tunnel projects with large spans or geological conditions. Convergence of surrounding rock refers to the phenomenon that the surrounding rock deforms into the interior of the tunnel due to stress redistribution after tunnel excavation, and is an important indicator for evaluating tunnel stability and safety.

[0022] The embodiment of the present application adopts fiber Bragg grating sensing technology to achieve high-precision, real-time measurement of the convergence amount around the surrounding rock of the multi-arch tunnel. Fiber Bragg grating sensing technology is a sensing method based on fiber Bragg grating, which has the advantages of high sensitivity, anti-electromagnetic interference, and distributed measurement. Fiber Bragg grating is a periodic refractive index modulation structure etched in the core of the optical fiber. When the optical fiber is subjected to strain or temperature changes, the central wavelength of the grating will drift accordingly. By measuring this wavelength drift, high-precision strain or temperature measurement can be achieved.

[0023] The embodiment of the present application combines the elastic-plastic mechanics model to establish the relationship between the surrounding rock deformation and the fiber Bragg grating wavelength change, and realizes the accurate conversion from wavelength change to convergence. The elastic-plastic mechanics model is a theoretical model that describes the deformation behavior of materials under external forces, taking into account the elastic and plastic properties of the material. By establishing a relationship model between the surrounding rock deformation and the fiber Bragg grating wavelength change, the measured wavelength change can be converted into the actual surrounding rock deformation, thereby realizing high-precision convergence measurement.

[0024] This method has many advantages, including but not limited to the following aspects: First, high-precision measurement. Fiber Bragg grating sensors have extremely high strain sensitivity and can achieve micron-level deformation measurement. This high-precision measurement capability enables this method to capture tiny deformations of the surrounding rock and provide more accurate data support for tunnel safety assessment. Second, real-time monitoring. This method can perform continuous monitoring and timely reflect the deformation of the surrounding rock. The real-time monitoring capability allows engineers to promptly discover potential safety hazards and take corresponding preventive measures. Third, strong anti-interference ability. Fiber optic sensing is not subject to electromagnetic interference and is suitable for tunnel environments. This feature enables this method to maintain stable measurement performance in various tunnel environments. In addition, distributed measurement capability. This method can simultaneously obtain data from multiple measuring points to fully reflect the deformation distribution of the surrounding rock. Distributed measurement capability allows engineers to fully understand the deformation of the tunnel surrounding rock and provide more comprehensive data support for tunnel design and construction. Finally, good long-term stability. Fiber optic sensors can be buried for a long time and are suitable for full life cycle monitoring of tunnels. This long-term stability enables this method to provide continuous monitoring data throughout the life cycle of the tunnel, providing important support for the long-term safety management of the tunnel.

[0025] The specific implementation steps of the embodiment of this application are as follows:

[0026] like Figure 1As shown, at step S101, data of multiple pre-buried fiber Bragg grating strain sensors are obtained to obtain the central wavelength change at the corresponding position of the surrounding rock of the multi-arch tunnel. The pre-buried fiber Bragg grating strain sensors can be arranged at key positions of the tunnel surrounding rock, such as the arch crown, arch waist, side wall, etc. These sensors are connected to the spectrum analyzer via optical fiber to collect the reflection spectrum of the fiber Bragg grating in real time. By analyzing the change of the reflection spectrum, the central wavelength change at each sensor position can be obtained.

[0027] Specifically, it includes: pre-burying fiber grating strain sensors around the surrounding rock of the multi-arch tunnel, the sensors are arranged at the arch top, arch waist, side wall and invert arch, a measurement section is set every 5 meters along the longitudinal direction of the tunnel, and 8 measuring points are arranged in each section; using a spectrum analyzer to measure the change in the central wavelength of the fiber grating strain sensor.

[0028] The implementation of the embodiments of the present application may include but is not limited to the following aspects: First, the arrangement of the fiber grating sensor may be embedded or surface-mounted. The embedded installation can bury the sensor directly in the surrounding rock, which can better reflect the deformation inside the surrounding rock. The surface-mounted installation can be easily installed on the surface of the tunnel lining, which is suitable for monitoring completed tunnels. Secondly, the data acquisition system can adopt an automated remote monitoring system to achieve real-time transmission and analysis of data. Such a system may include a spectrometer, a data collector, a communication module, and data processing software. Thirdly, temperature compensation can adopt a variety of methods, such as using a temperature self-compensating fiber grating sensor, or arranging an independent temperature sensor near the measuring point.

[0029] In one embodiment, the first parameter collected is the change in the wavelength of the fiber Bragg grating. A fiber Bragg grating strain sensor is pre-buried around the surrounding rock of the multi-arch tunnel, and the change in the central wavelength of the fiber Bragg grating is measured by a spectrum analyzer. The collection positions include (1) laying out fiber Bragg grating sensors at the arch crown, arch waist, side wall and invert of the multi-arch tunnel; (2) laying out a measurement section every 5 meters along the longitudinal direction of the tunnel; (3) laying out 8 measurement points in each measurement section, which are located at: arch crown (1), left and right arch waists (1 each), left and right side walls (1 each), and invert (3).

[0030] When the surrounding rock deforms, the pre-buried fiber Bragg grating will produce strain, causing the grating period to change, which in turn causes the change in the wavelength of the reflected light. By measuring the change in wavelength, the strain of the fiber Bragg grating can be calculated. Fiber Bragg grating sensors have the advantages of high sensitivity, anti-electromagnetic interference, and long-term burial, and are suitable for long-term monitoring of tunnels. Deploying them in key locations can fully reflect the deformation of the surrounding rock. Multi-point deployment can obtain the spatial distribution of surrounding rock deformation.

[0031] At step S102, the change in the central wavelength after preprocessing is temperature compensated, and the displacement of each measuring point of the measuring section is calculated in combination with the effective length of the sensor. Temperature compensation is to eliminate the influence of temperature change on the wavelength of the fiber Bragg grating and improve the measurement accuracy. Temperature compensation can be achieved by arranging a temperature sensor near the measuring point or using a temperature self-compensating fiber Bragg grating sensor. The effective length of the sensor refers to the length of the fiber Bragg grating sensor that actually senses strain. By combining the effective length of the sensor, the wavelength change can be converted into the actual displacement.

[0032] These include: preprocessing the collected central wavelength changes, eliminating outliers and noise, implementing temperature compensation, and calculating the wavelength changes caused by actual strain; calculating the strain at each measuring point based on the compensated wavelength changes; calculating the surrounding rock displacement at each measuring point using the strain and the effective length of the sensor; and collating the processing results to obtain the displacement of eight measuring points on each measuring section.

[0033] In one embodiment, data preprocessing is performed to remove outliers and noises. Temperature compensation is required because temperature changes can also cause fiber Bragg grating wavelength drift.

[0034] Among them, temperature compensation is implemented to calculate the wavelength change caused by actual strain, including: ,in, represents the wavelength change caused by the actual strain, represents the total wavelength change measured, represents the temperature sensitivity coefficient of fiber Bragg grating and its value is 6.678×10 -6 / °C, represents the temperature change, Represents the initial center wavelength of the fiber Bragg grating.

[0035] Next, the strain at each measuring point is calculated: Based on the compensated wavelength change, the strain at each measuring point is calculated, including: ,in, represents the fiber Bragg grating strain, represents the change in fiber Bragg grating wavelength, represents the initial center wavelength of the fiber Bragg grating, represents the fiber Bragg grating strain sensitivity coefficient, and its value includes 0.78. That is, ε_i = Δλ_i / (λ_i Pe) (i = 1, 2, ..., 8). Then, calculate the surrounding rock displacement: u_i = ε_i L_i (i = 1, 2, ..., 8), where u_i represents the displacement of the ith measuring point, and L_i represents the effective length of the fiber Bragg grating sensor. The displacements u_i (i = 1, 2, ..., 8) of the 8 measuring points of each measuring section are obtained through the above calculation. Where ε_i represents the fiber Bragg grating strain measured by the ith sensor ( ), the same goes for u_i and L_i.

[0036] At step S103, based on the theory of elastoplastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement. The theory of elastoplastic mechanics takes into account the elastic deformation and plastic deformation characteristics of the material under the action of external forces, and can more accurately describe the deformation behavior of the surrounding rock. By establishing a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel, the measured displacement can be converted into the displacement field distribution of the entire surrounding rock. This model may include but is not limited to the following factors: mechanical parameters of the surrounding rock (such as elastic modulus, Poisson's ratio, cohesion, internal friction angle, etc.), initial ground stress state, tunnel excavation shape and size, influence of support structure, etc.

[0037] Specifically, the method includes: setting the surrounding rock as an isotropic elastic-plastic medium to follow the Mohr-Coulomb yield criterion and determining the stress-strain relationship model equation of the surrounding rock; substituting the displacement into the boundary conditions in the stress-strain relationship model equation; determining the mechanical parameters of the surrounding rock according to on-site geological survey data; the mechanical parameters include elastic modulus, Poisson's ratio, cohesion and internal friction angle; and solving the stress-strain relationship model equation using the finite element method to obtain the stress field and displacement field distribution of the surrounding rock.

[0038] In one embodiment, based on the theory of elastic-plastic mechanics, a mathematical physical model of the deformation of the surrounding rock of the double-arch tunnel is constructed, wherein the surrounding rock is set as an isotropic elastic-plastic medium to follow the Mohr-Coulomb yield criterion, and the stress-strain relationship model equation of the surrounding rock is determined, including: ,in, represents the stress tensor, represents the shear modulus, represents the strain tensor, represents the bulk modulus, represents the volume strain, represents the Kronecker delta function, represents the direction of plastic flow, represents the yield stress, represents the equivalent plastic strain.

[0039] The theory of elastoplastic mechanics can better describe the stress-strain behavior of surrounding rock during excavation, and the Mohr-Coulomb criterion is suitable for describing the yield characteristics of geotechnical materials.

[0040] After constructing the model, parameters are substituted: the displacement u_i obtained in step S102 is substituted into the boundary conditions of the model, and the mechanical parameters of the surrounding rock (such as elastic modulus E, Poisson's ratio ν, cohesion c, internal friction angle φ, etc.) are determined according to the on-site geological survey data. The above equations are solved using the finite element method to obtain the surrounding rock stress field and displacement field.

[0041] At step S104, the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate. Radial displacement refers to the displacement along the radius of the tunnel cross section, which is a key parameter for evaluating tunnel convergence. By extracting the radial displacement of each measuring point, the convergence amount of the tunnel can be calculated. The convergence amount is usually defined as the distance that the surrounding rock moves into the tunnel after tunnel excavation. The convergence rate is the rate of change of the convergence amount over time, which can reflect the dynamic process of surrounding rock deformation.

[0042] The method includes: determining the initial radius value of the tunnel before excavation as a reference radius value; measuring the radial displacement values ​​of multiple preset measuring points around the tunnel after the tunnel is excavated; calculating the convergence value of each measuring point based on the measured radial displacement value of each measuring point; calculating the average convergence value of the entire tunnel based on the convergence values ​​of all measuring points; repeatedly calculating the measurement data after a preset time interval to obtain a new convergence value; calculating the convergence rate value based on the difference in convergence values ​​and the time interval between two measurements; and outputting the convergence value of each measuring point, the average convergence value of the entire tunnel, and the convergence rate value.

[0043] In an implementation scenario, the convergence amount is first defined as the displacement of the surrounding rock into the tunnel after tunnel excavation, which can be expressed as: S = R_0 – R, where S represents the convergence amount, R_0 represents the tunnel radius before excavation, and R represents the tunnel radius after excavation.

[0044] The calculation steps include: using the displacement field solved in step S103, extracting the radial displacement u_r_i (i = 1, 2, ..., 8) of each measuring point, calculating the convergence amount of each measuring point: S_i = u_r_i (i = 1, 2, ..., 8), and calculating the overall convergence amount of the tunnel: S_avg = (S_1 + S_2 + ... + S_8) / 8.

[0045] Convergence rate calculation: v = ΔS / Δt, where v represents the convergence rate, ΔS represents the difference in convergence between two measurements, and Δt represents the time interval between the two measurements.

[0046] The result output includes: the convergence amount S_i (i = 1, 2, ..., 8) of each measuring point, the overall average convergence amount S_avg of the tunnel, and the convergence rate v.

[0047] In summary, the method for measuring the surrounding rock convergence of a multi-arch tunnel provided by this application realizes high-precision, real-time, anti-interference, distributed and long-term stable surrounding rock deformation monitoring through fiber Bragg grating sensing technology and elastic-plastic mechanics model. This method provides important technical support for the safety assessment and management of tunnel engineering, and helps to improve the safety and reliability of tunnel engineering.

[0048] The embodiments of the present application will be further described below in conjunction with specific application scenarios.

[0049] Figure 2 A schematic diagram of a measurement section of the surrounding rock of a multi-arch tunnel provided in an embodiment of the present application. It should be understood that the structure shown in the figure is exemplary and not restrictive. This means that the structure involved is not limited to a specific form or design, but is presented as an example. In other words, the structure shown in the figure can be regarded as a way of expression to clearly describe related concepts and relationships, and does not exclude other forms of structure. Therefore, when interpreting the structure in the picture, it should be understood that the tunnel has flexibility and diversity, and its purpose is to provide an exemplary description rather than a restrictive provision on a specific form.

[0050] The multi-arch tunnel is a special type of tunnel structure, usually consisting of two or more adjacent arched tunnels connected by a partition wall. This structural design can not only improve the overall stability of the tunnel, but also effectively utilize space and meet multiple functional requirements.

[0051] The construction of a multi-arch tunnel usually adopts a one-way excavation method, that is, gradually advancing from the entrance to the exit. This method can better control the construction progress, and it is also convenient for the management and coordination of various construction links. In the specific operation, the right tunnel is first excavated as the pilot tunnel, starting from the upper step, and advancing from the inside of the tunnel to the outside of the tunnel. This excavation method from the inside to the outside is conducive to maintaining the stability of the tunnel and reducing the risk of surface subsidence.

[0052] In the excavation process, advance support is a key link. Usually, the middle pipe shed is used as the advance support structure, and the construction is carried out from the inside of the tunnel to the outside of the tunnel. The middle pipe shed is a support structure composed of multiple steel pipes, which can effectively control the deformation of the tunnel top and surrounding rock mass and prevent safety accidents such as landslides. This support method can not only improve the safety of construction, but also speed up the construction progress.

[0053] After the excavation of the upper step of the pilot tunnel (right tunnel) is completed, the construction team will continue to excavate the lower step and carry out the secondary lining construction simultaneously. The secondary lining is an important part of the tunnel structure. It can not only further enhance the overall stability of the tunnel, but also improve the internal environment of the tunnel and increase the service life of the tunnel. During this process, the left tunnel's arch and large pipe shed construction will also be carried out simultaneously to prepare for the subsequent excavation of the left tunnel.

[0054] The excavation of the left tunnel (rear tunnel) is the final stage of the entire construction process. At this stage, the middle partition wall is excavated together with the left tunnel. The middle partition wall is a key structure connecting the two arch tunnels, and its stability directly affects the safety of the entire multi-arch tunnel. In order to strengthen the bearing capacity of the foundation of the middle partition wall, anti-pullout anchors are usually used for reinforcement. Specifically, a φ20 mortar anchor with a length of 2.0 meters and a horizontal and vertical dimension of 150 cm is used per linear meter. These anchors are arranged in a plum blossom shape to ensure the stability of the middle partition wall.

[0055] During the entire construction process, both the excavation of the first tunnel and the excavation of the subsequent tunnel are mechanically excavated. Mechanical excavation can not only improve construction efficiency, but also ensure the accuracy of excavation and reduce the safety risks brought by manual operation. At the same time, the construction process follows the principle of "short advance, strong support, initial support closely following the working face, closing as soon as possible, and reducing the exposure time of surrounding rock". This construction principle can effectively control the deformation of surrounding rock, reduce the probability of geological disasters, and ensure the safety of construction.

[0056] Eight fiber Bragg grating sensors were deployed on a measurement section of the multi-arch tunnel. The initial central wavelength of these sensors was 1550 nanometers and the effective length was 1 meter. As a high-precision strain and displacement monitoring device, the fiber Bragg grating sensor can sense the slight changes in the tunnel structure in real time and provide important monitoring data. After a period of monitoring, the wavelength changes at each point measured by the sensor were Δλ_1 = 0.155 nanometers at the arch top, Δλ_2 = 0.124 nanometers at the left arch waist, Δλ_3 = 0.131 nanometers at the right arch waist, Δλ_4 = 0.093 nanometers at the left wall, Δλ_5 = 0.089 nanometers at the right wall, Δλ_6 = 0.062 nanometers at the left invert, Δλ_7 = 0.058 nanometers at the middle invert, and Δλ_8 = 0.065 nanometers at the right invert. At the same time, the temperature change during the measurement was ΔT = 2 degrees Celsius. In order to accurately reflect the actual strain of the tunnel structure, temperature compensation is first required to calculate the actual wavelength change Δλ_real_i of each sensor. The formula is Δλ_real_i = Δλ_i -6.678×10 -6 2 1550, this step is to eliminate the influence of temperature change on wavelength measurement and ensure the accuracy of subsequent strain calculation. Then, through the formula ε_i = Δλ_real_i / (1550 0.78) to calculate the strain ε_i at each point. This process converts the wavelength change into strain value, providing basic data for displacement calculation. Further, through the formula u_i =ε_i 1. Calculate the displacement u_i of each point. Since the effective length of the sensor is 1 meter, the displacement u_i is the direct product of the strain ε_i. Subsequently, based on the tunnel radius R_0 = 5 meters, calculate the convergence amount S_i of each sensor point, that is, S_i = u_i. This value reflects the actual convergence degree of the tunnel at each measurement point. Finally, calculate the average convergence amount S_avg = (S_1+ S_2 + ... + S_8) / 8, and assume that the interval between the two measurements is 7 days, and further calculate the convergence rate v = S_avg / 7. Through these calculation steps, the convergence amount distribution and overall convergence of the measurement section can be fully understood, which is of great reference value for evaluating the safety of tunnel construction. Through precise monitoring and calculation, potential structural problems can be discovered in time, and corresponding reinforcement measures can be taken to ensure the safety and stability of the tunnel construction process.

[0057] The present application discloses a system for measuring the convergence of surrounding rock of a multi-arch tunnel, comprising: a sensor unit and a computing unit; wherein the sensor unit is used to obtain data of a plurality of pre-buried fiber grating strain sensors to obtain the central wavelength variation at corresponding positions of the surrounding rock of the multi-arch tunnel; the computing unit is used to perform temperature compensation on the pre-processed central wavelength variation, and calculate the displacement of each measuring point of the measuring section in combination with the effective length of the sensor; based on the theory of elastic-plastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement; and the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate.

[0058] Furthermore, an embodiment of the present application also provides a device for measuring the convergence of the surrounding rock of a multi-arch tunnel, comprising: a processor, a memory, and a system bus; the processor and the memory are connected via the system bus; the memory is used to store one or more programs, and the one or more programs include instructions, which, when executed by the processor, enable the processor to execute any of the above methods.

[0059] Furthermore, an embodiment of the present application also provides a computer program product, which, when executed on a terminal device, enables the terminal device to execute any of the above methods.

[0060] It can be known from the description of the above implementation mode that those skilled in the art can clearly understand that all or part of the steps in the above-mentioned embodiment method can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a storage medium such as ROM / RAM, a disk, an optical disk, etc., including several instructions for enabling a computer device (which can be a personal computer, a server, or a network communication device such as a media gateway, etc.) to execute the methods described in the various embodiments of the present application or certain parts of the embodiments.

[0061] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0062] It should also be noted that, in the embodiments of the present application, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements that are not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the statement "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

[0063] The above description of the disclosed embodiments enables professionals and technicians in the field to implement or use the present application. Various modifications to these embodiments will be apparent to professionals and technicians in the field, and the general principles defined in the embodiments of the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the embodiments of the present application, but will conform to the widest range consistent with the principles and novel features disclosed in the embodiments of the present application.

Claims

1. A method for measuring the convergence of surrounding rock of a multi-arch tunnel, characterized in that: include: Acquire data from multiple pre-buried fiber Bragg grating strain sensors to obtain the central wavelength change at corresponding positions of the surrounding rock of the multi-arch tunnel; The temperature compensation is performed on the change of the central wavelength after preprocessing, and the displacement of each measuring point of the measuring section is calculated in combination with the effective length of the sensor; These include: pre-processing the collected central wavelength changes, removing outliers and noise, and implementing temperature compensation to calculate the wavelength changes caused by actual strain; calculating the strain at each measuring point based on the compensated wavelength changes; calculating the surrounding rock displacement at each measuring point using the strain and the effective length of the sensor; collating the processing results to obtain the displacement of eight measuring points at each measuring section; Among them, temperature compensation is implemented to calculate the wavelength change caused by actual strain, including: ,in, represents the wavelength change caused by the actual strain, represents the total wavelength change measured, represents the temperature sensitivity coefficient of fiber Bragg grating and its value is 6.678×10 -6 / °C, represents the temperature change, represents the initial center wavelength of the fiber Bragg grating; Among them, based on the compensated wavelength change, the strain amount of each measuring point is calculated, including: ,in, represents the fiber Bragg grating strain, represents the change in fiber Bragg grating wavelength, represents the initial center wavelength of the fiber Bragg grating, It represents the strain sensitivity coefficient of fiber Bragg grating and its value is 0.78; Based on the theory of elastoplastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement; the model includes: setting the surrounding rock as an isotropic elastoplastic medium to follow the Mohr-Coulomb yield criterion and determining the stress-strain relationship model equation of the surrounding rock; substituting the displacement into the boundary conditions in the stress-strain relationship model equation; determining the mechanical parameters of the surrounding rock based on on-site geological survey data; the mechanical parameters include elastic modulus, Poisson's ratio, cohesion and internal friction angle; solving the stress-strain relationship model equation using the finite element method to obtain the distribution of the surrounding rock stress field and displacement field; The surrounding rock is set as an isotropic elastic-plastic medium to follow the Mohr-Coulomb yield criterion, and the stress-strain relationship model equation of the surrounding rock is determined, including: ,in, represents the stress tensor, represents the shear modulus, represents the strain tensor, represents the bulk modulus, represents the volume strain, represents the Kronecker delta function, represents the direction of plastic flow, represents the yield stress, represents the equivalent plastic strain; The radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate.

2. The measuring method according to claim 1, characterized in that: in, The data of multiple pre-buried fiber Bragg grating strain sensors are obtained to obtain the central wavelength change at the corresponding position of the surrounding rock of the multi-arch tunnel, including: Fiber Bragg grating strain sensors are embedded in the surrounding rock of the multi-arch tunnel. The sensors are arranged at the arch crown, arch waist, side wall and invert arch. A measurement section is set every 5 meters along the longitudinal direction of the tunnel, and 8 measuring points are arranged in each section. The optical spectrum analyzer is used to measure the central wavelength variation of the fiber grating strain sensor.

3. The measuring method according to claim 1, characterized in that: in, The radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate, including: Determine the initial radius value of the tunnel before excavation as the reference radius value; After the tunnel is excavated, the radial displacement values ​​of multiple preset measuring points around the tunnel are measured; According to the radial displacement values ​​of each measuring point measured, the convergence value of each measuring point is calculated; Based on the convergence values ​​of all measuring points, calculate the average convergence value of the entire tunnel; After a preset time interval, the measurement data is repeatedly calculated to obtain a new convergence value; Calculate the convergence rate value based on the difference in convergence amount and time interval between two measurements; Output the convergence value of each measuring point, the overall average convergence value of the tunnel and the convergence rate value.

4. A system for measuring the convergence of surrounding rock of a multi-arch tunnel using the measuring method according to any one of claims 1 to 3, characterized in that: include: A sensor unit and a computing unit; wherein, The sensor unit is used to obtain data from a plurality of pre-buried fiber grating strain sensors to obtain a central wavelength change at a corresponding position of the surrounding rock of the multi-arch tunnel; The calculation unit is used to perform temperature compensation on the preprocessed central wavelength variation, and calculate the displacement of each measuring point on the measuring section in combination with the effective length of the sensor; based on the theory of elastic-plastic mechanics, a mathematical and physical model of the deformation of the surrounding rock of the multi-arch tunnel is constructed to calculate the displacement field of the surrounding rock using the displacement; and the radial displacement of each measuring point is extracted using the displacement field to calculate the target convergence amount and convergence rate.

5. A measuring device for the convergence of surrounding rock of a multi-arch tunnel, characterized in that: include: A processor, a memory, and a system bus; wherein the processor and the memory are connected via the system bus; The memory is used to store one or more programs, wherein the one or more programs include instructions, and when the instructions are executed by the processor, the processor executes the method according to any one of claims 1 to 3.

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