Tunnel deformation monitoring system and method based on distributed optical fiber sensing technology

Abstract

The invention provides a tunnel deformation monitoring system and method based on a distributed optical fiber sensing technology, and relates to the technical field of tunnel monitoring. A spiral winding type optical fiber is arranged in the longitudinal axis direction of the surface of a tunnel lining, a transverse optical fiber is arranged on a key section, and the data acquisition frequency is set to be 1Hz. Dividing the optical fiber into a plurality of data acquisition points at equal intervals, obtaining the real-time temperature and Brillouin frequency shift change of each point, measuring the temperature and strain sensitivity coefficient, and calculating the total strain; calculating long-term temperature strain compensation based on the long-term temperature component, generating an instantaneous temperature difference through the real-time temperature and the long-term temperature component, further calculating instantaneous temperature strain compensation, subtracting the two kinds of strain compensation from the total strain to obtain stress strain, and evaluating the deformation level of the tunnel based on the stress strain. And the accuracy of evaluation is judged through clustering analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel monitoring, and in particular to a tunnel deformation monitoring system and method based on distributed optical fiber sensing technology. Background Art

[0002] In tunnel engineering, deformation monitoring is a critical measure to ensure the safety and long-term stability of tunnel structures. Traditional monitoring methods, such as total stations and inclinometers, suffer from sparse deployment, poor real-time performance, and susceptibility to environmental interference, making it difficult to fully capture the dynamic deformation characteristics of tunnel structures. Especially under complex geological conditions, tunnels are susceptible to the combined influence of multiple factors, such as temperature fluctuations and vibration loads. This can lead to distorted monitoring data or delayed early warnings, increasing the safety risks of tunnel operations. With the development of fiber optic sensing technology, distributed fiber optic sensing has been increasingly applied in tunnel deformation monitoring. However, existing methods often lack the ability to comprehensively analyze and dynamically evaluate multi-source data, resulting in insufficient monitoring accuracy. Furthermore, while some methods incorporate temperature compensation, they generally apply corrections based on temperature, ignoring the different effects of long-term and short-term temperatures. Therefore, a tunnel deformation monitoring technology with high precision, strong real-time performance, and the ability to integrate the influence of multiple factors is urgently needed to address the shortcomings of existing tunnel deformation monitoring solutions.

[0003] In the prior art, publication number CN114485449A discloses a method and system for monitoring longitudinal distributed deformation of tunnels based on fiber optic sensing technology. The method connects an optical fiber to a fiber optic demodulator to emit pulsed light. Based on this pulsed light, the temperature change of the ambient temperature of the optical fiber and the frequency shift of the pulsed light are detected. Based on this temperature change and the frequency shift of the pulsed light, the tunnel deformation is generated. This deformation is transmitted to a terminal, which analyzes the deformation to obtain an analysis result, and uses this analysis result to monitor the tunnel. This method involves emitting pulsed light into the optical fiber, monitoring the frequency shift of the pulsed light and the change in ambient temperature, calculating the deformation change of the pulsed light, and calculating the tunnel deformation based on the strain change of the light.

[0004] The main problems with the above scheme are: the monitoring dimension is single, and the tunnel deformation is calculated only through the frequency shift and temperature change of the pulsed light. The actual tunnel deformation is often the result of the combined action of multiple factors. A single monitoring dimension cannot accurately reflect the true deformation of the tunnel; the deformation is corrected by relying on the linear relationship between temperature change and frequency shift, without considering the influence of thermal hysteresis and non-uniform temperature field, resulting in errors in the monitoring results.

[0005] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0006] The object of the present invention is to provide a tunnel deformation monitoring system and method based on distributed optical fiber sensing technology to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions: A tunnel deformation monitoring system based on distributed optical fiber sensing technology, specifically comprising: The data acquisition module is used to arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface and to arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. The strain calculation module is used to divide the spirally wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data collection point. The base temperature of the data collection point is set, and the temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally, and the total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. A long-term compensation calculation module is used to calculate the long-term temperature component of each data collection point based on the temperature sequence of the data collection point during the continuous collection time, and generate long-term temperature strain compensation based on the long-term temperature component and the optical fiber temperature sensitivity coefficient; The instantaneous compensation calculation module is used to generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, calculate the temperature change rate during the acquisition time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; A comprehensive judgment module is used to subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain; The data verification module is used to generate a total temperature compensation for each data collection point based on the sum of the long-term temperature strain compensation and the instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the steps of the above module, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of selected representative points in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

[0008] Furthermore, the key cross-section locations of the tunnel specifically include geological weak zones, lining joints and construction joints, load asymmetry areas, historical fault sections and portal transition sections. The geological weak zones indicate sections where the tunnel passes through water-rich layers, fault fracture zones and expansive rock and soil; the load asymmetry areas indicate areas where there are mountain slopes and cross-tunnels above the tunnel; the historical fault sections indicate sections where abnormal deformation has occurred; and the portal transition section indicates sections within 20m of the tunnel exit and entrance.

[0009] Furthermore, the formula for calculating the change in Brillouin frequency shift is: ; in, represents the change in Brillouin frequency shift at the data acquisition point at time t, represents the time variable, represents the Brillouin frequency shift of the data acquisition point affected by strain and temperature at time t, represents the Brillouin frequency shift of the data collection point when there is no strain and at the reference temperature, represents the total strain at the data collection point at time t, represents the temperature at the data collection point at time t, Indicates the reference temperature of the data collection point, represents the strain sensitivity coefficient, represents the temperature sensitivity coefficient; but .

[0010] Furthermore, the principle behind long-term temperature strain compensation is: For each data collection point, a time window of length L is divided, and the temperature mean within the time window is calculated in real time as the long-term temperature component. The formula is: ; in, represents the long-term temperature component at time t, represents the time variable within the time window; The formula for calculating long-term temperature strain compensation is: ; in, represents the long-term temperature strain compensation, represents the coefficient of thermal expansion, Indicates the reference temperature; The principle for calculating the coefficient of thermal expansion is: In the laboratory, temperature changes are applied to the same distributed optical fiber, and the resulting Brillouin frequency shift changes are measured to calculate the thermal expansion coefficient. The formula used is: ; in, Indicates temperature change, Indicates temperature change The resulting Brillouin frequency shift changes.

[0011] Furthermore, the principle for generating instantaneous temperature strain compensation is: The formula for generating the instantaneous temperature difference is: ; in, represents the instantaneous temperature difference at time t; The temperature change rate at the time of acquisition is calculated based on the following formula: ; in, Indicates time The rate of temperature change, Indicates time temperature, Indicates time temperature, Indicates a time interval; The formula for generating instantaneous temperature strain compensation is: ; in, represents the instantaneous temperature strain compensation, represents the temperature-gauge coefficient, represents the thermal hysteresis coefficient; The calculation principle of thermal hysteresis coefficient is based on: In the laboratory, the same distributed optical fiber is subjected to temperature changes and the apparent strain is calculated based on the formula: ; in, Indicates time The apparent strain, represents the time variable of the experiment, Indicates time Brillouin frequency shift changes under the influence of temperature and strain; The effect of temperature is deducted from the apparent strain to generate the hysteresis strain: ; in, express Time-delayed strain; Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient based on the least squares method: ; in, Represents the thermal hysteresis coefficient.

[0012] Furthermore, the formula for generating stress and strain is: ; in, Indicates that the collection point is Stress and strain at each moment; The principle for determining the deformation level of a tunnel based on stress and strain is as follows: The deformation levels of tunnels are divided into undeformed, slightly deformed, and significantly deformed. The stress and strain corresponding to the historical deformation data of tunnels with known deformation levels are collected. The high-risk strain threshold is generated based on the lowest stress and strain of significantly deformed and the highest stress and strain of slightly deformed. The low-risk strain threshold is generated based on the highest stress and strain of undeformed and the lowest stress and strain of slightly deformed. The formula is as follows: ; ; in, Indicates a high-risk strain threshold, The lowest stress-strain indicating significant deformation, Indicates the highest stress-strain for slight deformation, Indicates the lowest stress strain for slight deformation, represents the highest stress-strain without deformation; when When , the corresponding tunnel area deformation level is undeformed; when , the corresponding tunnel area deformation level is slight deformation; when , the corresponding deformation level of the tunnel area is obvious deformation.

[0013] Furthermore, the principle of cluster analysis of data collection points is as follows: Randomly select several data collection points as initial cluster centers. The number of initial cluster centers ranges from 1 to the total number of data collection points. For each data collection point, assign it to the cluster where the initial cluster center closest to its total temperature compensation is located, and update the mean of all data collection points in the cluster to the new cluster center until all data collection points are assigned to the cluster. In each cluster, several data collection points closest to the cluster center are selected as representative points. The number of representative points is 10% of the total number of data collection points in a cluster. The deformation level of each representative point is calculated according to the steps of the comprehensive judgment module, and the actual deformation level of each representative point is obtained. If the deformation levels are the same, the representative point is marked as accurately judged. The proportion of all accurately judged representative points to the total number of representative points selected for the cluster is counted as the accuracy of the cluster.

[0014] The present invention further provides a tunnel deformation monitoring method based on distributed optical fiber sensing technology. The method is performed by the above-mentioned tunnel deformation monitoring system based on distributed optical fiber sensing technology, and the specific steps include: Step 1: Arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. Step 2: The spirally wound optical fiber and the transverse optical fiber are divided into equal intervals. Each division point is used as a data collection point. The reference temperature of the data collection point is set. The temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally. The total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. Step 3: Based on the temperature sequence of the data acquisition point at the continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate the long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient; Step 4: Generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data collection point, calculate the temperature change rate during the collection time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; Step 5: Subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain; Step 6: For each data collection point, generate a total temperature compensation based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the above steps, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of representative points selected in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses longitudinal spiral optical fiber to cover the entire tunnel, and transverse optical fiber to focus on monitoring key sections, which makes up for the blind spots of single longitudinal optical fiber monitoring and helps to obtain high-resolution, full-coverage data; the optical fiber is equally spaced into several data acquisition points, and the temperature and Brillouin frequency shift changes of each data acquisition point are obtained in real time. It can accurately monitor the temperature impact and strain changes on the optical fiber, thereby improving the accuracy of monitoring, making the strain calculation of each data acquisition point more scientific and reliable, and can effectively distinguish between temperature changes and actual structural deformation, reducing errors caused by temperature changes.

[0016] The present invention also calculates the long-term temperature component of the data collection point to eliminate strain errors caused by long-term slow temperature changes, reduce the interference of environmental changes on tunnel deformation monitoring, and ensure the assessment of the true strain state of the tunnel; by comparing the real-time temperature with the long-term temperature component, the instantaneous temperature difference is calculated, reflecting the impact of short-term temperature changes on structural strain. Instantaneous temperature strain compensation is generated based on the instantaneous temperature difference and the temperature change rate, which can quickly respond to sudden temperature changes, ensure the real-time and accuracy of strain monitoring, and improve the dynamic adaptability of monitoring. The combination of long-term and instantaneous temperature strain compensation allows the monitoring system to comprehensively consider all influencing factors, helps to form more comprehensive strain analysis results, and provides more sufficient data support for tunnel safety assessment. By subtracting the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain, the error caused by temperature change can be eliminated, and more accurate stress and strain data can be obtained, which helps to comprehensively assess the health status of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic block diagram of a tunnel deformation monitoring system based on distributed optical fiber sensing technology in the present invention; Figure 2 Schematic diagram of the method flow of an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0019] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative position relationships. When the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0020] Example: See also Figure 1 , the present invention provides a technical solution: A tunnel deformation monitoring system based on distributed optical fiber sensing technology, specifically comprising: The data acquisition module is used to arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface and to arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. In this embodiment, the key cross-section positions of the tunnel specifically include geological weak zones, lining joints and construction joints, load asymmetric areas, historical fault sections and portal transition sections. The geological weak zones indicate sections where the tunnel passes through water-rich layers, fault fracture zones and expansive rock and soil. The load asymmetric areas indicate areas where there are mountain slopes and cross-tunnels above the tunnel. The historical fault sections indicate sections where abnormal deformation has occurred. The portal transition section indicates sections within 20m of the tunnel exit and entrance.

[0021] The longitudinal axis of the tunnel lining surface is the axis from the tunnel entrance to the exit. A whole spirally wound optical fiber is periodically bent at a fixed angle with the longitudinal axis. The fixed angle with the longitudinal axis is , the distance between each bending point and the longitudinal axis of the tunnel is the pitch, and the pitch is set in the range of 0.3 to 2m according to the actual engineering conditions; the transverse optical fiber is only arranged at the key section, perpendicular to the longitudinal axis of the tunnel, and a single optical fiber is wrapped around the inner wall of the tunnel section, and the ends are fused to form a closed loop. The distance between adjacent transverse optical fibers is set to 20cm, and intensive monitoring is carried out to capture the sudden changes in the key sections. The key section represents a location where the structure is fragile, prone to deformation, or significantly affected by external loads. Therefore, additional optical fibers need to be arranged for monitoring. The geological weak zone means that the tunnel passes through poor geological sections such as water-rich layers, fractured zones, and expansive rock and soil. Such sections are prone to uneven settlement or convergent deformation. The transverse grid can be used to capture sudden changes in circumferential strain including shear cracks; the lining joints and construction joints are the joints of the pipe segments in the tunnel and the construction joints of cast-in-place concrete. The waterproofing of these places is relatively weak and it is easy for the material to deteriorate due to water seepage. The stress at the joints is monitored by the transverse grid. Variable discontinuity; the asymmetric load area indicates the area above the tunnel where there is bias load, such as mountain slopes, adjacent foundation pits, and cross tunnels. Asymmetric loads can easily cause the lining bending moment to exceed the standard, and the bending strain distribution is quantified by transverse optical fiber; the historical fault section indicates the section where abnormal deformation such as cracking and seepage has occurred in the past, and requires key monitoring to avoid recurrence risks; the portal transition section refers to the section within 20m of the tunnel entrance and exit. This section is significantly affected by surface temperature fluctuations and rainwater infiltration, and the surrounding rock constraints vary greatly, so it requires key monitoring.

[0022] The strain calculation module is used to divide the spirally wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data collection point. The base temperature of the data collection point is set, and the temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally, and the total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. In this embodiment, when the spirally wound optical fiber is divided into equal intervals, a division point is selected every 1.0 m along the longitudinal axis, and when the transverse optical fiber is divided into equal intervals, a division point is selected every 0.3 m.

[0023] In this embodiment, the formula for calculating the change in Brillouin frequency shift is: ; in, represents the change in Brillouin frequency shift at the data acquisition point at time t, represents the time variable, represents the Brillouin frequency shift of the data acquisition point affected by strain and temperature at time t, represents the Brillouin frequency shift of the data collection point when there is no strain and at the reference temperature, represents the total strain at the data collection point at time t, represents the temperature at the data collection point at time t, Indicates the reference temperature of the data collection point, represents the strain sensitivity coefficient, represents the temperature sensitivity coefficient; but .

[0024] Base temperature It is a reference for calculating the apparent strain of optical fiber caused by temperature. When the temperature is too high, Too small, the temperature strain compensation is insufficient, and the residual strain may contain more temperature effects that have not been eliminated. When it is large, the temperature difference is too large and the temperature is overcompensated, which may mask the true strain. The specific reference temperature value is determined based on expert evaluation.

[0025] The sensing mechanism of optical fiber depends on the interaction between light and optical fiber material. When the optical fiber is affected by strain or temperature, the frequency of Brillouin scattered light will shift. The effect of temperature on strain is corrected by the change in Brillouin frequency shift. The change in Brillouin frequency shift consists of two parts: the strain contribution term and the and temperature contribution The strain contribution term is the strain generated by the optical fiber under the influence of stress and temperature. It reflects that when the optical fiber is stretched or compressed, its lattice structure changes, resulting in the frequency shift of the Brillouin scattered light. The greater the strain, the higher the Brillouin frequency shift. It represents the strain sensitivity coefficient, which indicates the change in fiber frequency shift caused by unit strain. Its specific value is determined by the material and structure of the fiber. The temperature contribution reflects that the temperature change causes the fiber to expand and contract, thereby changing its refractive index and density, causing Brillouin frequency shift. When the temperature rises, the Brillouin frequency shift increases, and when the temperature drops, the Brillouin frequency shift decreases. It represents the temperature sensitivity coefficient, which represents the frequency shift change caused by a unit temperature change. The specific value is determined by the material and structure of the optical fiber. The Brillouin frequency shift is the result of the interaction of the two, which are linearly superimposed. When external conditions such as temperature, pressure, and strain change, the sound velocity or refractive index of the medium will change, resulting in a change in the Brillouin frequency shift. This change is relative to the original frequency of the incident light. The Brillouin frequency shift of the data acquisition point when no strain is applied and the temperature is the reference temperature is the initial value, that is, .

[0026] A long-term compensation calculation module is used to calculate the long-term temperature component of each data collection point based on the temperature sequence of the data collection point during the continuous collection time, and generate long-term temperature strain compensation based on the long-term temperature component and the optical fiber temperature sensitivity coefficient; In this embodiment, the principle for generating long-term temperature strain compensation is: For each data collection point, a time window of length L is divided, and the temperature mean within the time window is calculated in real time as the long-term temperature component. The formula is: ; in, represents the long-term temperature component at time t, represents the time variable within the time window; The long-term temperature component represents the temperature change trend of the data collection point in the tunnel over a longer time scale, reflecting the slow and continuous impact of the ambient temperature on the tunnel structure. The tunnel structure has a large thermal inertia, and its temperature response lags behind the instantaneous ambient temperature change. It is more significantly affected by the long-term accumulated temperature. By integrating the historical temperature data, the low-frequency component of the temperature is extracted to eliminate the influence of short-term fluctuations. The long-term temperature component is converted into equivalent strain through the thermal expansion coefficient, which is used to correct the influence of long-term temperature on tunnel strain.

[0027] The formula for calculating long-term temperature strain compensation is: ; in, represents the long-term temperature strain compensation, represents the coefficient of thermal expansion, Indicates the reference temperature; Long-term temperature strain compensation reflects the strain caused by long-term temperature changes, such as seasonal temperature differences, which leads to thermal expansion and contraction of tunnel lining materials. It is the long-term cumulative effect related to temperature in structural deformation. The core of tunnel deformation monitoring is to identify strain caused by loads or geological activities. Temperature changes will cause apparent strain in optical fibers. Long-term temperature strain compensation can eliminate the effects of long-term temperature accumulation.

[0028] The principle for calculating the coefficient of thermal expansion is: In the laboratory, temperature changes are applied to the same distributed optical fiber, and the resulting Brillouin frequency shift changes are measured to calculate the thermal expansion coefficient. The formula used is: ; in, Indicates temperature change, Indicates temperature change The resulting Brillouin frequency shift changes.

[0029] The Brillouin frequency shift of optical fiber is affected by temperature, and its change is linearly related to temperature change. When temperature change is applied to the optical fiber, the additional strain generated is , , sorted , ignoring the temperature sensitivity of the optical fiber itself, then The thermal expansion coefficient reflects the expansion / contraction ability of the tunnel lining material to which the optical fiber is attached when the temperature changes. The higher the thermal expansion coefficient, the more intense the expansion / contraction of the tunnel lining material caused by temperature changes.

[0030] The instantaneous compensation calculation module is used to generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, calculate the temperature change rate during the acquisition time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; In this embodiment, the principle for generating instantaneous temperature strain compensation is: The formula for generating the instantaneous temperature difference is: ; in, represents the instantaneous temperature difference at time t; The temperature change rate at the time of acquisition is calculated based on the following formula: ; in, Indicates time The rate of temperature change, Indicates time temperature, Indicates time temperature, Indicates a time interval; The formula for generating instantaneous temperature strain compensation is: ; in, represents the instantaneous temperature strain compensation, represents the temperature-gauge coefficient, Represents the thermal hysteresis coefficient.

[0031] The calculation principle of thermal hysteresis coefficient is based on: In the laboratory, the same distributed optical fiber is subjected to temperature changes and the apparent strain is calculated based on the formula: ; in, Indicates time The apparent strain, represents the time variable of the experiment, Indicates time Brillouin frequency shift changes under the influence of temperature and strain; The effect of temperature is deducted from the apparent strain to generate the hysteresis strain: ; in, express Time-delayed strain; Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient based on the least squares method: ; in, Represents the thermal hysteresis coefficient.

[0032] Instantaneous temperature strain compensation is mainly used to eliminate two effects: the influence of short-term temperature fluctuations and thermal hysteresis effects. It reflects the conversion of the difference between the current temperature and the long-term temperature component into the corresponding strain compensation value. Short-term temperature fluctuations, such as the temperature difference between day and night and the local temperature change caused by ventilation, will cause the optical fiber to produce instantaneous thermal expansion and contraction, thereby introducing noise in the strain measurement. Eliminate false strain caused by short-term temperature changes, temperature-strain coefficient , used to correct the false strain caused by temperature; It is used to eliminate the influence of thermal hysteresis effect. Due to the different heat conduction rates between tunnel lining material and optical fiber, when the temperature changes, the strain response of tunnel lining material will lag behind the temperature change. To eliminate this lag effect, It is the rate of temperature change, which reflects the speed of temperature change. Combined with the thermal hysteresis coefficient, it quantifies the degree to which the material strain response lags behind the temperature change. The instantaneous temperature strain compensation is proportional to the instantaneous temperature difference and the temperature change rate.

[0033] The comprehensive judgment module is used to subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain.

[0034] The formula for generating stress and strain is: ; in, Indicates that the collection point is Stress and strain at each moment; Stress and strain reflect the actual mechanical deformation of the tunnel structure after excluding the influence of temperature, and separate the strain caused by temperature from the total strain; the total strain The strain is obtained based on the change in Brillouin frequency shift directly measured by optical fiber, which includes strain caused by temperature and strain caused by stress. The temperature-induced strain includes long-term temperature effect and instantaneous temperature effect. The stress-induced strain is caused by external loads and affects the actual deformation of the tunnel. The stress-strain is obtained by removing the long-term temperature compensation and instantaneous temperature compensation from the total strain.

[0035] The principle for determining the deformation level of a tunnel based on stress and strain is as follows: The deformation levels of tunnels are divided into undeformed, slightly deformed, and significantly deformed. The stress and strain corresponding to the historical deformation data of tunnels with known deformation levels are collected. The high-risk strain threshold is generated based on the lowest stress and strain of significantly deformed and the highest stress and strain of slightly deformed. The low-risk strain threshold is generated based on the highest stress and strain of undeformed and the lowest stress and strain of slightly deformed. The formula is as follows: ; ; in, Indicates a high-risk strain threshold, The lowest stress-strain indicating significant deformation, Indicates the highest stress-strain for slight deformation, Indicates the lowest stress strain for slight deformation, represents the highest stress-strain without deformation; when When , the corresponding tunnel area deformation level is undeformed; when , the corresponding tunnel area deformation level is slight deformation; when , the corresponding deformation level of the tunnel area is obvious deformation.

[0036] The data verification module is used to generate a total temperature compensation for each data collection point based on the sum of the long-term temperature strain compensation and the instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the steps of the above module, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of selected representative points in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

[0037] In this embodiment, the principle of cluster analysis of data collection points is based on: Randomly select several data collection points as initial cluster centers. The number of initial cluster centers ranges from 1 to the total number of data collection points. For each data collection point, assign it to the cluster where the initial cluster center closest to its total temperature compensation is located, and update the mean of all data collection points in the cluster to the new cluster center until all data collection points are assigned to the cluster. Randomly select the initial cluster centers. The number of initial cluster centers ranges from 1 to the total number of data collection points. If it is greater than 1, at least one cluster must be guaranteed, that is, all data collection points belong to the same cluster. And it must not be greater than the total number of data collection points. However, in practice, the number of initial cluster centers is much smaller than the total number of data collection points. The number of initial cluster centers is determined based on the total number of data collection points. ,in, represents the number of initial cluster centers, Indicates the total number of data collection points; In each cluster, several data collection points closest to the cluster center are selected as representative points. The number of representative points is 10% of the total number of data collection points in a cluster. The deformation level of each representative point is calculated according to the steps of the comprehensive judgment module, and the actual deformation level of each representative point is obtained. If the deformation levels are the same, the representative point is marked as accurately judged. The proportion of all accurately judged representative points to the total number of representative points selected for the cluster is counted as the accuracy of the cluster.

[0038] The data collection points are divided into several clusters, and the total temperature compensation of each data collection point is used as the characteristic variable of the cluster. The total temperature compensation is the long-term temperature strain compensation plus the instantaneous temperature strain compensation. The accuracy of the cluster is reflected by calculating the accuracy of the representative point in each cluster. For clusters with too low accuracy, improper fiber optic layout or environmental interference such as water seepage may occur, and on-site inspection or re-laying of the fiber optic is required.

[0039] See also Figure 2The present invention also provides a tunnel deformation monitoring method based on distributed optical fiber sensing technology. The method is performed by the above-mentioned tunnel deformation monitoring system based on distributed optical fiber sensing technology, and the specific steps include: Step 1: Arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. Step 2: The spirally wound optical fiber and the transverse optical fiber are divided into equal intervals. Each division point is used as a data collection point. The reference temperature of the data collection point is set. The temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally. The total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. Step 3: Based on the temperature sequence of the data acquisition point at the continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate the long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient; Step 4: Generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data collection point, calculate the temperature change rate during the collection time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; Step 5: Subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain; Step 6: For each data collection point, generate a total temperature compensation based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the above steps, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of representative points selected in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

[0040] The above formulas are all dimensionless and numerical calculations. The formulas are obtained by collecting a large amount of data and performing software simulation to obtain the most recent real situation. The preset parameters in the formulas are set by technicians in this field according to actual conditions.

[0041] The above embodiments can be implemented in whole or in part by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed by hardware or software depends on the specific application and design constraints of the technical solution.

[0042] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, and may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment as needed.

[0043] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the scope of protection of the present application.

Claims

1. A tunnel deformation monitoring system based on distributed optical fiber sensing technology, characterized in that: Specifically include: The data acquisition module is used to arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface and to arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. The strain calculation module is used to divide the spirally wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data collection point. The base temperature of the data collection point is set, and the temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally, and the total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. A long-term compensation calculation module is used to calculate the long-term temperature component of each data collection point based on the temperature sequence of the data collection point during the continuous collection time, and generate long-term temperature strain compensation based on the long-term temperature component and the optical fiber temperature sensitivity coefficient; The instantaneous compensation calculation module is used to generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, calculate the temperature change rate during the acquisition time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; A comprehensive judgment module is used to subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain; The data verification module is used to generate a total temperature compensation for each data collection point based on the sum of the long-term temperature strain compensation and the instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the steps of the above module, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of selected representative points in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

2. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 1, characterized in that: The key cross-section positions of the tunnel specifically include geological weak zones, lining joints and construction joints, load asymmetry areas, historical fault sections and portal transition sections. The geological weak zones indicate sections where the tunnel passes through water-rich layers, fault fracture zones and expansive rock and soil. The load asymmetry areas indicate areas where there are mountain slopes and cross-tunnels above the tunnel. The historical fault sections indicate sections where abnormal deformation has occurred. The portal transition section indicates sections within 20m of the tunnel exit and entrance.

3. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 1, characterized in that: The formula for calculating the Brillouin frequency shift change in the strain calculation module is: ； in, represents the change in Brillouin frequency shift at the data acquisition point at time t, represents the time variable, represents the Brillouin frequency shift of the data acquisition point affected by strain and temperature at time t, represents the Brillouin frequency shift of the data collection point when there is no strain and at the reference temperature, represents the total strain at the data collection point at time t, represents the temperature at the data collection point at time t, Indicates the reference temperature of the data collection point, represents the strain sensitivity coefficient, represents the temperature sensitivity coefficient; but .

4. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 3 is characterized by: The principle for generating long-term temperature strain compensation in the long-term compensation calculation module is as follows: For each data collection point, a time window of length L is divided, and the temperature mean within the time window is calculated in real time as the long-term temperature component. The formula is: ； in, represents the long-term temperature component at time t, represents the time variable within the time window; The formula for calculating long-term temperature strain compensation is: ； in, represents the long-term temperature strain compensation, represents the coefficient of thermal expansion, Indicates the reference temperature; The principle for calculating the coefficient of thermal expansion is: In the laboratory, temperature changes are applied to the same distributed optical fiber, and the resulting Brillouin frequency shift changes are measured to calculate the thermal expansion coefficient. The formula used is: ； in, Indicates temperature change, Indicates temperature change The resulting Brillouin frequency shift changes.

5. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 4, characterized in that: The principle for generating instantaneous temperature strain compensation in the instantaneous compensation calculation module is as follows: The formula for generating the instantaneous temperature difference is: ； in, represents the instantaneous temperature difference at time t; The temperature change rate at the time of acquisition is calculated based on the following formula: ； in, Indicates time The rate of temperature change, Indicates time temperature, Indicates time temperature, Indicates a time interval; The formula for generating instantaneous temperature strain compensation is: ； in, represents the instantaneous temperature strain compensation, represents the temperature-gauge coefficient, represents the thermal hysteresis coefficient; The calculation principle of thermal hysteresis coefficient is based on: In the laboratory, the same distributed optical fiber is subjected to temperature changes and the apparent strain is calculated based on the formula: ； in, Indicates time The apparent strain, represents the time variable of the experiment, Indicates time Brillouin frequency shift changes under the influence of temperature and strain; The effect of temperature is deducted from the apparent strain to generate the hysteresis strain: ； in, express Time-delayed strain; Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient based on the least squares method: ； in, Represents the thermal hysteresis coefficient.

6. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 5, characterized in that: The formula for generating stress and strain in the comprehensive judgment module is: ； in, Indicates that the collection point is Stress and strain at each moment; The principle for determining the deformation level of a tunnel based on stress and strain is as follows: The deformation levels of tunnels are divided into undeformed, slightly deformed, and significantly deformed. The stress and strain corresponding to the historical deformation data of tunnels with known deformation levels are collected. The high-risk strain threshold is generated based on the lowest stress and strain of significantly deformed and the highest stress and strain of slightly deformed. The low-risk strain threshold is generated based on the highest stress and strain of undeformed and the lowest stress and strain of slightly deformed. The formula is as follows: ； ； in, Indicates a high-risk strain threshold, The lowest stress-strain indicating significant deformation, Indicates the highest stress-strain for slight deformation, Indicates the lowest stress strain for slight deformation, represents the highest stress-strain without deformation; when When , the corresponding tunnel area deformation level is undeformed; when , the corresponding tunnel area deformation level is slight deformation; when , the corresponding deformation level of the tunnel area is obvious deformation.

7. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 1, characterized in that: The principle of cluster analysis of data collection points in the data verification module is based on: Randomly select several data collection points as initial cluster centers. The number of initial cluster centers ranges from 1 to the total number of data collection points. For each data collection point, assign it to the cluster where the initial cluster center closest to its total temperature compensation is located, and update the mean of all data collection points in the cluster to the new cluster center until all data collection points are assigned to the cluster. In each cluster, several data collection points closest to the cluster center are selected as representative points. The number of representative points is 10% of the total number of data collection points in a cluster. The deformation level of each representative point is calculated according to the steps of the comprehensive judgment module, and the actual deformation level of each representative point is obtained. If the deformation levels are the same, the representative point is marked as accurately judged. The proportion of all accurately judged representative points to the total number of representative points selected for the cluster is counted as the accuracy of the cluster.

8. A tunnel deformation monitoring method based on distributed optical fiber sensing technology, characterized by: The method is performed by the tunnel deformation monitoring system based on distributed optical fiber sensing technology according to any one of claims 1 to 7, and the specific steps include: Step 1: Arrange spirally wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis at key sections of the tunnel. The data acquisition frequency is set to 1 Hz. Step 2: The spirally wound optical fiber and the transverse optical fiber are divided into equal intervals. Each division point is used as a data collection point. The reference temperature of the data collection point is set. The temperature and Brillouin frequency shift change of each data collection point are obtained in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber are measured experimentally. The total strain of the data collection point is generated based on the Brillouin frequency shift change of the data collection point. Step 3: Based on the temperature sequence of the data acquisition point at the continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate the long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient; Step 4: Generate an instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data collection point, calculate the temperature change rate during the collection time, and generate an instantaneous temperature strain compensation based on the instantaneous temperature difference and the temperature change rate; Step 5: Subtract the long-term temperature strain compensation and the instantaneous temperature strain compensation from the total strain to generate stress and strain, and determine the deformation level of the tunnel based on the stress and strain; Step 6: For each data collection point, generate a total temperature compensation based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation, perform cluster analysis on the data collection points, select representative points in each cluster, calculate the deformation level of the representative points based on the above steps, and obtain the actual deformation level of the representative points. The ratio of the number of correct representative points to the number of representative points selected in the cluster based on the deformation level reflects the accuracy of the cluster to which it belongs.

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