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

Abstract

This invention provides a tunnel deformation monitoring system and method based on distributed optical fiber sensing technology, belonging to the field of tunnel monitoring technology. The invention involves arranging helically wound optical fibers along the longitudinal axis of the tunnel lining surface and arranging transverse optical fibers at key sections, setting the data acquisition frequency to 1Hz. The optical fibers are equidistantly divided into multiple data acquisition points to acquire real-time temperature and Brillouin frequency shift changes at each point, and to measure temperature and strain sensitivity coefficients to calculate the total strain. Long-term temperature strain compensation is calculated based on long-term temperature components, and instantaneous temperature difference is generated using real-time temperature and long-term temperature components to calculate instantaneous temperature strain compensation. These two strain compensations are subtracted from the total strain to obtain the stress-strain. The deformation level of the tunnel is assessed based on the stress-strain, and the accuracy of the assessment is determined through cluster analysis.

Description

Technical Field

[0001] This invention relates to the field of tunnel monitoring technology, specifically to a tunnel deformation monitoring system and method based on distributed optical fiber sensing technology. Background Technology

[0002] In tunnel engineering, deformation monitoring is a crucial measure to ensure the safety and long-term stability of tunnel structures. Traditional monitoring methods, such as total stations and inclinometers, suffer from problems such as sparse point deployment, poor real-time performance, and susceptibility to environmental interference, making it difficult to comprehensively capture the dynamic deformation characteristics of tunnel structures. Especially under complex geological conditions, tunnels are susceptible to the combined effects of multiple factors, including temperature changes and vibration loads, leading to distorted monitoring data or delayed early warnings, increasing the safety risks of tunnel operation. With the development of fiber optic sensing technology, distributed fiber optic sensing technology is increasingly being used 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, although some methods consider temperature compensation, they only make general corrections based on temperature, ignoring the different effects of long-term and short-term temperatures. Therefore, there is an urgent need for a high-precision, real-time tunnel deformation monitoring technology that can comprehensively address the shortcomings of existing tunnel deformation monitoring schemes.

[0003] In the prior art, publication number CN114485449A discloses a method and system for longitudinal distributed deformation monitoring of tunnels based on fiber optic sensing technology. The method connects an optical fiber to an optical fiber demodulator, emits pulsed light, and acquires the temperature change and frequency shift of the pulsed light based on the ambient temperature change. Based on the temperature change and frequency shift, a tunnel deformation is generated, and the deformation is transmitted to a terminal. The terminal analyzes the deformation and obtains the analysis results, which are then used to monitor the tunnel. This method involves emitting pulsed light into an optical fiber, monitoring the frequency shift of the pulsed light and changes in ambient temperature, calculating the deformation change of the pulsed light, and then 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 singular, and the tunnel deformation is calculated only by the frequency shift and temperature change of the pulse light. The actual tunnel deformation is often the result of the combined effect of multiple factors, and a single monitoring dimension is difficult to accurately reflect the actual deformation of the tunnel; the deformation is corrected by relying on the linear relationship between temperature change and frequency shift, without considering the effects of thermal hysteresis and non-uniform temperature fields, which leads to errors in the monitoring results.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a tunnel deformation monitoring system and method based on distributed optical fiber sensing technology to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A tunnel deformation monitoring system based on distributed optical fiber sensing technology, specifically comprising:

[0009] The data acquisition module is used to arrange spiral-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 1Hz.

[0010] The strain calculation module is used to divide the spiral wound fiber and the transverse fiber into equal intervals, with each division point serving as a data acquisition point. The reference temperature of the data acquisition point is set, and the temperature and Brillouin frequency shift change of each data acquisition point are acquired in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the fiber are measured experimentally, and the total strain of the data acquisition point is generated based on the Brillouin frequency shift change of the data acquisition point.

[0011] The long-term compensation calculation module is used to calculate the long-term temperature component of each data acquisition point based on the temperature sequence of the data acquisition point during continuous acquisition time, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient.

[0012] The instantaneous compensation calculation module is used to generate instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, and calculate the temperature change rate over the acquisition time. Based on the instantaneous temperature difference and the temperature change rate, instantaneous temperature strain compensation is generated.

[0013] The comprehensive judgment module is used to subtract long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and to determine the deformation level of the tunnel based on the stress strain.

[0014] The data verification module is used to generate a total temperature compensation for each data acquisition point based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation. It performs cluster analysis on the data acquisition points, selects representative points in each cluster, calculates the deformation level of the representative points based on the steps of the above module, and obtains the actual deformation level of the representative points. The proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

[0015] Furthermore, the key cross-sectional locations of the tunnel specifically include geologically weak zones, lining joints and construction joints, areas of asymmetrical loads, historically faulted sections, and tunnel entrance transition sections. The geologically weak zones refer to sections where the tunnel passes through water-rich layers, fault fracture zones, and expansive soil and rock. The areas of asymmetrical loads refer to areas where there are mountain slopes or intersecting tunnels above the tunnel. The historically faulted sections refer to sections where abnormal deformation has occurred. The tunnel entrance transition sections refer to sections within 20m of the tunnel exit and entrance.

[0016] Furthermore, the formula used to calculate the Brillouin frequency shift change is:

[0017] ;

[0018] in, This represents the change in Brillouin frequency shift at time t of the data acquisition point. Represents a time variable. This represents the Brillouin frequency shift at time t caused by strain and temperature at the data acquisition point. This represents the Brillouin frequency shift at the data acquisition point when there is no strain and the temperature is the reference temperature. This represents the total strain at the data acquisition point at time t. This represents the temperature at the data collection point at time t. This indicates the reference temperature of the data acquisition point. Indicates the strain sensitivity coefficient. Indicates the temperature sensitivity coefficient;

[0019] but .

[0020] Furthermore, the principle underlying long-term temperature strain compensation is as follows:

[0021] For each data collection point, a time window of length L is defined, and the average temperature within the time window is calculated in real time as the long-term temperature component. The formula used is as follows:

[0022] ;

[0023] in, This represents the long-term temperature component over time t. Represents the time variable within the time window;

[0024] The formula used to calculate long-term temperature strain compensation is as follows:

[0025] ;

[0026] in, This indicates long-term temperature strain compensation. Indicates the coefficient of thermal expansion. Indicates the reference temperature;

[0027] The principle for calculating the coefficient of thermal expansion is as follows:

[0028] In a laboratory setting, a temperature change was applied to the same distributed optical fiber, and the resulting Brillouin frequency shift was measured. The coefficient of thermal expansion was then calculated using the following formula:

[0029] ;

[0030] in, Indicates temperature change. Indicates temperature change The resulting Brillouin frequency shift.

[0031] Furthermore, the principle underlying the generation of instantaneous temperature strain compensation is as follows:

[0032] The formula used to generate the instantaneous temperature difference is:

[0033] ;

[0034] in, The instantaneous temperature difference representing time t;

[0035] The formula used to calculate the rate of temperature change at the time of data acquisition is:

[0036] ;

[0037] in, Indicates time rate of temperature change Indicates time temperature, Indicates time temperature, Indicates a time interval;

[0038] The formula used to generate instantaneous temperature strain compensation is:

[0039] ;

[0040] in, Indicates instantaneous temperature strain compensation. Indicates the temperature-strain coefficient. Indicates the thermal hysteresis coefficient;

[0041] The principle underlying the calculation of the thermal hysteresis coefficient is as follows:

[0042] In the laboratory, the apparent strain was calculated by applying temperature variations to the same distributed optical fiber using the following formula:

[0043] ;

[0044] in, Indicates time Apparent strain, Represents the time variable of the experiment. Indicates time Below, the Brillouin frequency shift changes under the influence of temperature and strain;

[0045] Subtracting the effect of temperature from the apparent strain, hysteretic strain is generated:

[0046] ;

[0047] in, express Time-delayed response;

[0048] Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient using the least squares method:

[0049] ;

[0050] in, This represents the thermal hysteresis coefficient.

[0051] Furthermore, the formula upon which stress and strain are generated is:

[0052] ;

[0053] in, Indicates the collection point is at Stress and strain at any given moment;

[0054] The principle underlying the determination of tunnel deformation level based on stress and strain is as follows:

[0055] The deformation levels of tunnels are categorized into no deformation, slight deformation, and significant deformation. Historical deformation data corresponding to known deformation levels are collected, and high-risk strain thresholds are generated based on the lowest stress-strain values ​​for significant deformation and the highest stress-strain values ​​for slight deformation. Low-risk strain thresholds are generated based on the highest stress-strain values ​​for no deformation and the lowest stress-strain values ​​for slight deformation. The formula used is as follows:

[0056] ;

[0057] ;

[0058] in, Indicates the high-risk strain threshold. Indicates the minimum stress-strain at which significant deformation occurs. This represents the highest stress-strain value under slight deformation. This represents the minimum stress-strain for slight deformation. Indicates the highest stress-strain without deformation;

[0059] when At that time, the deformation level of the corresponding tunnel area was no deformation;

[0060] when The deformation level of the corresponding tunnel area is slight deformation.

[0061] when The deformation level of the corresponding tunnel area is significant deformation.

[0062] Furthermore, the principle underlying the cluster analysis of data collection points is as follows:

[0063] Randomly select a number of data collection points as initial cluster centers. The number of initial cluster centers is from 1 to the total number of data collection points. For each data collection point, assign it to the cluster containing the initial cluster center that is closest to its total temperature compensation. Update the mean of all data collection points in the cluster to the new cluster center. Continue until all data collection points are assigned to clusters.

[0064] 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 points are marked as accurate. The proportion of all accurately judged representative points to the total number of representative points selected in the cluster is used as the accuracy of the clustering.

[0065] This invention also provides a tunnel deformation monitoring method based on distributed optical fiber sensing technology. The method is executed by the aforementioned tunnel deformation monitoring system based on distributed optical fiber sensing technology, and the specific steps include:

[0066] Step 1: Arrange spiral-wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. Set the data acquisition frequency to 1Hz.

[0067] Step 2: Divide the spiral-wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data acquisition point. Set the reference temperature for each data acquisition point, acquire the temperature and Brillouin frequency shift change of each data acquisition point in real time, and determine the temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber through experiments. Generate the total strain of the data acquisition points based on the Brillouin frequency shift change of the data acquisition points.

[0068] Step 3: Based on the temperature sequence of the data acquisition points during continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient.

[0069] Step 4: Generate instantaneous temperature difference based on real-time temperature and long-term temperature components of data acquisition points, calculate the rate of temperature change over the acquisition time, and generate instantaneous temperature strain compensation based on instantaneous temperature difference and rate of temperature change.

[0070] Step 5: Subtract the long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and determine the deformation level of the tunnel based on the stress strain.

[0071] Step 6: For each data acquisition 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 acquisition 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 proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

[0072] Compared with the prior art, the beneficial effects of the present invention are:

[0073] This invention uses longitudinal spiral optical fibers to cover the entire tunnel, while transverse optical fibers are used to monitor key sections, thus compensating for the blind spots of monitoring with a single longitudinal optical fiber and facilitating the acquisition of high-resolution, full-coverage data. By dividing the optical fibers into several data acquisition points at equal intervals and acquiring the temperature and Brillouin frequency shift changes of each data acquisition point in real time, it is possible to accurately monitor the temperature effects and strain changes on the optical fibers, thereby improving the accuracy of monitoring. This makes the strain calculation of each data acquisition point more scientific and reliable, effectively distinguishing between temperature changes and actual structural deformation, and reducing errors caused by temperature changes.

[0074] This invention also calculates the long-term temperature components at data acquisition points to eliminate strain errors caused by long-term, slow temperature changes, reducing interference from environmental changes on tunnel deformation monitoring and ensuring an accurate assessment of the tunnel's true strain state. By comparing real-time temperature with long-term temperature components, 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 rate of temperature change, enabling rapid response to sudden temperature changes, ensuring the real-time nature and accuracy of strain monitoring, and improving the dynamic adaptability of monitoring. Combining long-term and instantaneous temperature strain compensation allows the monitoring system to comprehensively consider all influencing factors, contributing to a more comprehensive strain analysis and providing more sufficient data support for tunnel safety assessment. By subtracting long-term and instantaneous temperature strain compensation from the total strain, errors caused by temperature changes can be eliminated, resulting in more accurate stress-strain data, which helps to comprehensively assess the tunnel's health status. Attached Figure Description

[0075] Figure 1 This is a schematic block diagram of the tunnel deformation monitoring system based on distributed optical fiber sensing technology in this invention;

[0076] Figure 2 This is a schematic diagram of the method flow of an embodiment of the present invention. Detailed Implementation

[0077] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0078] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0079] Example:

[0080] Please see Figure 1 The present invention provides a technical solution:

[0081] A tunnel deformation monitoring system based on distributed optical fiber sensing technology, specifically comprising:

[0082] The data acquisition module is used to arrange spiral-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 1Hz.

[0083] In this embodiment, the key cross-sectional locations of the tunnel specifically include geologically weak zones, lining joints and construction joints, areas with asymmetrical loads, historically faulted sections, and tunnel entrance transition sections. The geologically weak zones refer to sections where the tunnel passes through water-rich layers, fault fracture zones, and expansive soil and rock. The areas with asymmetrical loads refer to areas where there are mountain slopes or intersecting tunnels above the tunnel. The historically faulted sections refer to sections where abnormal deformation has occurred. The tunnel entrance transition sections refer to sections within 20m of the tunnel exit and entrance.

[0084] The longitudinal axis of the tunnel lining surface is the axis running from the tunnel entrance to the exit. A whole spirally wound optical fiber is periodically bent at a fixed angle to the longitudinal axis. The distance from each bend point to the longitudinal axis of the tunnel is the pitch, which is set within the range of 0.3 to 2m according to the actual engineering conditions. Lateral optical fibers are only deployed at critical sections, perpendicular to the longitudinal axis of the tunnel. A single fiber loops around the inner wall of the tunnel section, with the ends fused together to form a closed loop. The distance between adjacent lateral optical fibers is set at 20cm for dense monitoring to capture abrupt changes at the critical sections. Critical sections represent locations where the structure is fragile, prone to deformation, or significantly affected by external loads; therefore, additional optical fibers are needed for monitoring. Geologically weak zones represent sections where the tunnel passes through water-rich layers, fractured zones, expansive soil, and other unfavorable geological areas. These sections are prone to uneven settlement or convergence deformation, and circumferential strain abrupt changes, including shear cracks, can be captured through the lateral grid. Lining joints and construction joints are the segment assembly joints and cast-in-place concrete construction joints within the tunnel. Waterproofing in these areas is relatively weak, and material deterioration is easily caused by water seepage. The stress at these joints is monitored through the lateral grid. Discontinuity; Asymmetrical load areas indicate areas with eccentric loads above the tunnel, such as mountain slopes, adjacent foundation pits, and intersecting tunnels. Asymmetrical loads can easily cause excessive bending moments in the lining. The distribution of bending strain is quantified by transverse optical fibers. Historical fault sections indicate sections where abnormal deformations such as cracking and seepage have occurred in the past. These sections require key monitoring to avoid the risk of recurrence. The tunnel entrance transition section indicates the section within 20m of the tunnel entrance and exit. This section is significantly affected by surface temperature fluctuations and rainwater seepage, and the surrounding rock constraints vary greatly. It requires key monitoring.

[0085] The strain calculation module is used to divide the spiral wound fiber and the transverse fiber into equal intervals, with each division point serving as a data acquisition point. The reference temperature of the data acquisition point is set, and the temperature and Brillouin frequency shift change of each data acquisition point are acquired in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the fiber are measured experimentally, and the total strain of the data acquisition point is generated based on the Brillouin frequency shift change of the data acquisition point.

[0086] In this embodiment, when dividing the spiral-wound optical fiber at equal intervals, a dividing point is selected every 1.0m along the longitudinal axis, and when dividing the transverse optical fiber at equal intervals, a dividing point is selected every 0.3m.

[0087] In this embodiment, the formula used to calculate the Brillouin frequency shift change is:

[0088] ;

[0089] in, This represents the change in Brillouin frequency shift at time t of the data acquisition point. Represents a time variable. This represents the Brillouin frequency shift at time t caused by strain and temperature at the data acquisition point. This represents the Brillouin frequency shift at the data acquisition point when there is no strain and the temperature is the reference temperature. This represents the total strain at the data acquisition point at time t. This represents the temperature at the data collection point at time t. This indicates the reference temperature of the data acquisition point. Indicates the strain sensitivity coefficient. Indicates the temperature sensitivity coefficient;

[0090] but .

[0091] Reference temperature It serves as a reference for calculating the apparent strain of optical fibers caused by temperature. When it is too high, the temperature difference The value is too small, indicating insufficient temperature strain compensation. The residual strain may contain a significant amount of unremoved temperature effects. When the temperature difference is large, the temperature overcompensation may mask the true strain. Therefore, a specific reference temperature value should be determined based on expert evaluation.

[0092] The sensing mechanism of optical fibers relies on the interaction between light and the fiber material. When the fiber is subjected to strain or temperature, the frequency of the Brillouin scattered light shifts. The effect of temperature on strain is corrected by the change in the Brillouin frequency shift, which consists of two parts: a strain contribution term and a strain contribution term. and temperature contribution The strain contribution term represents the strain generated in the optical fiber under stress and temperature, reflecting the change in its lattice structure when the fiber is stretched or compressed, leading to a frequency shift in the Brillouin scattered light. The greater the strain, the higher the Brillouin frequency shift. The strain sensitivity coefficient represents the change in fiber frequency shift caused by a unit strain, and its specific value is determined by the fiber's material and structure. The temperature contribution term reflects the thermal expansion and contraction of the fiber caused by temperature changes, which in turn alters its refractive index and density, inducing a Brillouin frequency shift. The Brillouin frequency shift increases with increasing temperature and decreases with decreasing temperature. The temperature sensitivity coefficient represents the frequency shift caused by a unit temperature change. Its specific value is determined by the material and structure of the optical fiber. The Brillouin frequency shift is the result of the combined effect of these two factors, which are linearly superimposed. When external conditions, such as temperature, pressure, and strain, change, the sound velocity or refractive index of the medium changes, leading to a change in the Brillouin frequency shift. This change is relative to the original frequency of the incident light. The Brillouin frequency shift at the data acquisition point when no strain is applied and the temperature is at the reference temperature is the initial value. .

[0093] The long-term compensation calculation module is used to calculate the long-term temperature component of each data acquisition point based on the temperature sequence of the data acquisition point during continuous acquisition time, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient.

[0094] In this embodiment, the principle underlying the generation of long-term temperature strain compensation is as follows:

[0095] For each data collection point, a time window of length L is defined, and the average temperature within the time window is calculated in real time as the long-term temperature component. The formula used is as follows:

[0096] ;

[0097] in, This represents the long-term temperature component over time t. Represents the time variable within the time window;

[0098] The long-term temperature component represents the temperature change trend of data acquisition points in the tunnel over a longer time scale, reflecting the slow and continuous influence of ambient temperature on the tunnel structure. The tunnel structure has a large thermal inertia, and its temperature response lags behind the instantaneous changes in ambient temperature. It is more significantly affected by long-term accumulated temperature. By integrating historical temperature data, the low-frequency component of temperature is extracted to eliminate the influence of short-term fluctuations. The long-term temperature component is converted into equivalent strain through the coefficient of thermal expansion to correct the influence of long-term temperature on tunnel strain.

[0099] The formula used to calculate long-term temperature strain compensation is as follows:

[0100] ;

[0101] in, This indicates long-term temperature strain compensation. Indicates the coefficient of thermal expansion. Indicates the reference temperature;

[0102] Long-term temperature strain compensation reflects the strain caused by thermal expansion and contraction of tunnel lining materials due to long-term temperature changes, such as seasonal temperature differences. It is a long-term cumulative effect of temperature in structural deformation. The core of tunnel deformation monitoring is to identify the strain caused by loads or geological activities. Temperature changes will cause optical fibers to produce apparent strain. Long-term temperature strain compensation can eliminate the long-term cumulative effect of temperature.

[0103] The principle for calculating the coefficient of thermal expansion is as follows:

[0104] In a laboratory setting, a temperature change was applied to the same distributed optical fiber, and the resulting Brillouin frequency shift was measured. The coefficient of thermal expansion was then calculated using the following formula:

[0105] ;

[0106] in, Indicates temperature change. Indicates temperature change The resulting Brillouin frequency shift.

[0107] The Brillouin frequency shift of optical fiber is affected by temperature, and the change is linearly related to the temperature variation. When a temperature change is applied to the optical fiber, the additional strain generated is: , Organized If we ignore the temperature sensitivity of the optical fiber itself, then The coefficient of thermal expansion reflects the ability of the tunnel lining material to expand / contract when the temperature changes. The higher the coefficient of thermal expansion, the more intense the expansion / contraction of the tunnel lining material caused by temperature changes.

[0108] The instantaneous compensation calculation module is used to generate instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, and calculate the temperature change rate over the acquisition time. Based on the instantaneous temperature difference and the temperature change rate, instantaneous temperature strain compensation is generated.

[0109] In this embodiment, the principle underlying the generation of instantaneous temperature strain compensation is as follows:

[0110] The formula used to generate the instantaneous temperature difference is:

[0111] ;

[0112] in, The instantaneous temperature difference representing time t;

[0113] The formula used to calculate the rate of temperature change at the time of data acquisition is:

[0114] ;

[0115] in, Indicates time rate of temperature change Indicates time temperature, Indicates time temperature, Indicates a time interval;

[0116] The formula used to generate instantaneous temperature strain compensation is:

[0117] ;

[0118] in, Indicates instantaneous temperature strain compensation. Indicates the temperature-strain coefficient. This represents the thermal hysteresis coefficient.

[0119] The principle underlying the calculation of the thermal hysteresis coefficient is as follows:

[0120] In the laboratory, the apparent strain was calculated by applying temperature variations to the same distributed optical fiber using the following formula:

[0121] ;

[0122] in, Indicates time Apparent strain, Represents the time variable of the experiment. Indicates time Below, the Brillouin frequency shift changes under the influence of temperature and strain;

[0123] Subtracting the effect of temperature from the apparent strain, hysteretic strain is generated:

[0124] ;

[0125] in, express Time-delayed response;

[0126] Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient using the least squares method:

[0127] ;

[0128] in, This represents the thermal hysteresis coefficient.

[0129] Instantaneous temperature strain compensation is mainly used to eliminate two effects: the effects of short-term temperature fluctuations and thermal hysteresis. This reflects the conversion of the difference between the current temperature and the long-term temperature component into a corresponding strain compensation value. Short-term temperature fluctuations, such as diurnal temperature variations and localized temperature changes caused by ventilation, can lead to instantaneous thermal expansion and contraction of the optical fiber, thus introducing noise into the strain measurement. Eliminating spurious strain caused by short-term temperature changes, temperature-strain coefficient It is used to correct spurious strain caused by temperature. To eliminate the effects of thermal hysteresis, since the thermal conductivity of tunnel lining materials differs from that of optical fibers, the strain response of tunnel lining materials lags behind temperature changes. Eliminate this lag effect, It is the rate of temperature change, reflecting how fast or slow the temperature changes. Combined with the thermal hysteresis coefficient, it quantifies the degree to which the material's strain response lags behind the temperature change. Instantaneous temperature strain compensation is proportional to the instantaneous temperature difference and the rate of temperature change.

[0130] The comprehensive judgment module is used to subtract long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and to determine the deformation level of the tunnel based on the stress strain.

[0131] The formula for generating stress and strain is:

[0132] ;

[0133] in, Indicates the collection point is at Stress and strain at any given moment;

[0134] Stress and strain reflect the actual mechanical deformation of the tunnel structure after excluding the effects of temperature. The strain caused by temperature is separated from the total strain; total strain The strain is obtained by directly measuring the Brillouin frequency shift using optical fiber. This includes strain caused by temperature and strain caused by stress. The strain caused by temperature includes long-term temperature effects and instantaneous temperature effects. The strain caused by stress is caused by external loads and affects the actual deformation of the tunnel. The stress strain is obtained by removing long-term temperature compensation and instantaneous compensation from the total strain.

[0135] The principle underlying the determination of tunnel deformation level based on stress and strain is as follows:

[0136] The deformation levels of tunnels are categorized into no deformation, slight deformation, and significant deformation. Historical deformation data corresponding to known deformation levels are collected, and high-risk strain thresholds are generated based on the lowest stress-strain values ​​for significant deformation and the highest stress-strain values ​​for slight deformation. Low-risk strain thresholds are generated based on the highest stress-strain values ​​for no deformation and the lowest stress-strain values ​​for slight deformation. The formula used is as follows:

[0137] ;

[0138] ;

[0139] in, Indicates the high-risk strain threshold. Indicates the minimum stress-strain at which significant deformation occurs. This represents the highest stress-strain value under slight deformation. This represents the minimum stress-strain for slight deformation. Indicates the highest stress-strain without deformation;

[0140] when At that time, the deformation level of the corresponding tunnel area was no deformation;

[0141] when The deformation level of the corresponding tunnel area is slight deformation.

[0142] when The deformation level of the corresponding tunnel area is significant deformation.

[0143] The data verification module is used to generate a total temperature compensation for each data acquisition point based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation. It performs cluster analysis on the data acquisition points, selects representative points in each cluster, calculates the deformation level of the representative points based on the steps of the above module, and obtains the actual deformation level of the representative points. The proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

[0144] In this embodiment, the principle underlying the clustering analysis of data collection points is as follows:

[0145] Randomly select a number of data collection points as initial cluster centers. The number of initial cluster centers is from 1 to the total number of data collection points. For each data collection point, assign it to the cluster containing the initial cluster center that is closest to its total temperature compensation. Update the mean of all data collection points in the cluster to the new cluster center. Continue until all data collection points are assigned to clusters.

[0146] Initial cluster centers are randomly selected. The number of initial cluster centers is between 1 and the total number of data collection points. If the number is greater than 1, it ensures at least one cluster (i.e., all data collection points belong to the same cluster), and the number of initial cluster centers is not 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. Therefore, the number of initial cluster centers is determined based on the total number of data collection points. ,in, Indicates the initial number of cluster centers. Indicates the total number of data collection points;

[0147] 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 points are marked as accurate. The proportion of all accurately judged representative points to the total number of representative points selected in the cluster is used as the accuracy of the clustering.

[0148] By dividing the data acquisition points into several clusters, the total temperature compensation of each data acquisition point is used as the characteristic variable of the cluster. The total temperature compensation is the sum of long-term temperature strain compensation and instantaneous temperature strain compensation. The accuracy of the cluster is reflected by calculating the accuracy of the representative points in each cluster. For clusters with low accuracy, there may be environmental interference such as improper fiber optic deployment or water seepage, which requires on-site investigation or re-deployment of fiber optics.

[0149] Please see Figure 2 The present invention also provides a tunnel deformation monitoring method based on distributed optical fiber sensing technology. The method is executed by the aforementioned tunnel deformation monitoring system based on distributed optical fiber sensing technology, and the specific steps include:

[0150] Step 1: Arrange spiral-wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. Set the data acquisition frequency to 1Hz.

[0151] Step 2: Divide the spiral-wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data acquisition point. Set the reference temperature for each data acquisition point, acquire the temperature and Brillouin frequency shift change of each data acquisition point in real time, and determine the temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber through experiments. Generate the total strain of the data acquisition points based on the Brillouin frequency shift change of the data acquisition points.

[0152] Step 3: Based on the temperature sequence of the data acquisition points during continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient.

[0153] Step 4: Generate instantaneous temperature difference based on real-time temperature and long-term temperature components of data acquisition points, calculate the rate of temperature change over the acquisition time, and generate instantaneous temperature strain compensation based on instantaneous temperature difference and rate of temperature change.

[0154] Step 5: Subtract the long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and determine the deformation level of the tunnel based on the stress strain.

[0155] Step 6: For each data acquisition 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 acquisition 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 proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

[0156] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0157] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples 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 implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0158] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0159] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this 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 spiral-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 1Hz. The strain calculation module is used to divide the spiral wound fiber and the transverse fiber into equal intervals, with each division point serving as a data acquisition point. The reference temperature of the data acquisition point is set, and the temperature and Brillouin frequency shift change of each data acquisition point are acquired in real time. The temperature sensitivity coefficient and strain sensitivity coefficient of the fiber are measured experimentally, and the total strain of the data acquisition point is generated based on the Brillouin frequency shift change of the data acquisition point. The long-term compensation calculation module is used to calculate the long-term temperature component of each data acquisition point based on the temperature sequence of the data acquisition point during continuous acquisition time, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient. The instantaneous compensation calculation module is used to generate instantaneous temperature difference based on the real-time temperature and long-term temperature components of the data acquisition point, and calculate the temperature change rate over the acquisition time. Based on the instantaneous temperature difference and the temperature change rate, instantaneous temperature strain compensation is generated. The comprehensive judgment module is used to subtract long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and to determine the deformation level of the tunnel based on the stress strain. The data verification module is used to generate a total temperature compensation for each data acquisition point based on the sum of long-term temperature strain compensation and instantaneous temperature strain compensation. It performs cluster analysis on the data acquisition points, selects representative points in each cluster, calculates the deformation level of the representative points based on the steps of the above module, and obtains the actual deformation level of the representative points. The proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

2. The tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 1, characterized in that: The key cross-sectional locations of the tunnel specifically include geologically weak zones, lining joints and construction joints, areas of asymmetrical load, historically faulted sections, and tunnel entrance transition sections. The geologically weak zones refer to sections where the tunnel passes through water-rich layers, fault fracture zones, and expansive soil and rock. The areas of asymmetrical load refer to areas where there are mountain slopes above the tunnel or intersecting tunnels. The historically faulted sections refer to sections where abnormal deformation has occurred. The tunnel entrance transition sections refer to 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 used in the strain calculation module to calculate the Brillouin frequency shift change is: ； in, This represents the change in Brillouin frequency shift at time t of the data acquisition point. Represents a time variable. This represents the Brillouin frequency shift at time t caused by strain and temperature at the data acquisition point. This represents the Brillouin frequency shift at the data acquisition point when there is no strain and the temperature is the reference temperature. This represents the total strain at the data acquisition point at time t. This represents the temperature at the data collection point at time t. This indicates the reference temperature of the data acquisition point. Indicates the strain sensitivity coefficient. Indicates the temperature sensitivity coefficient; but .

4. A tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 3, characterized in that: The principle underlying the generation of 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 defined, and the average temperature within the time window is calculated in real time as the long-term temperature component. The formula used is as follows: ； in, This represents the long-term temperature component over time t. Represents the time variable within the time window; The formula used to calculate long-term temperature strain compensation is as follows: ； in, This indicates long-term temperature strain compensation. Indicates the coefficient of thermal expansion. Indicates the reference temperature; The principle for calculating the coefficient of thermal expansion is as follows: In a laboratory setting, a temperature change was applied to the same distributed optical fiber, and the resulting Brillouin frequency shift was measured. The coefficient of thermal expansion was then calculated using the following formula: ； in, Indicates temperature change. Indicates temperature change The resulting Brillouin frequency shift.

5. A tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 4, characterized in that: The principle underlying the instantaneous temperature strain compensation generated in the instantaneous compensation calculation module is as follows: The formula used to generate the instantaneous temperature difference is: ； in, The instantaneous temperature difference representing time t; The formula used to calculate the rate of temperature change at the time of data acquisition is: ； in, Indicates time rate of temperature change Indicates time temperature, Indicates time temperature, Indicates a time interval; The formula used to generate instantaneous temperature strain compensation is: ； in, Indicates instantaneous temperature strain compensation. Indicates the temperature-strain coefficient. Indicates the thermal hysteresis coefficient; The principle underlying the calculation of the thermal hysteresis coefficient is as follows: In the laboratory, the apparent strain was calculated by applying temperature variations to the same distributed optical fiber using the following formula: ； in, Indicates time Apparent strain, Represents the time variable of the experiment. Indicates time Below, the Brillouin frequency shift changes under the influence of temperature and strain; Subtracting the effect of temperature from the apparent strain, hysteretic strain is generated: ； in, express Time-delayed response; Based on the calculated hysteresis strain, and Perform linear regression and fit the thermal hysteresis coefficient using the least squares method: ； in, This represents the thermal hysteresis coefficient.

6. A tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 5, characterized in that: The formula used by the comprehensive judgment module to generate stress and strain is: ； in, Indicates the collection point is at Stress and strain at any given moment; The principle underlying the determination of tunnel deformation level based on stress and strain is as follows: The deformation levels of tunnels are categorized into no deformation, slight deformation, and significant deformation. Historical deformation data corresponding to known deformation levels are collected, and high-risk strain thresholds are generated based on the lowest stress-strain values ​​for significant deformation and the highest stress-strain values ​​for slight deformation. Low-risk strain thresholds are generated based on the highest stress-strain values ​​for no deformation and the lowest stress-strain values ​​for slight deformation. The formula used is as follows: ； ； in, Indicates the high-risk strain threshold. Indicates the minimum stress-strain at which significant deformation occurs. This represents the highest stress-strain value under slight deformation. This represents the minimum stress-strain for slight deformation. Indicates the highest stress-strain without deformation; when At that time, the deformation level of the corresponding tunnel area was no deformation; when The deformation level of the corresponding tunnel area is slight deformation. when The deformation level of the corresponding tunnel area is significant deformation.

7. A tunnel deformation monitoring system based on distributed optical fiber sensing technology according to claim 1, characterized in that: The principle underlying the clustering analysis of data collection points in the data verification module is as follows: Randomly select a number of data collection points as initial cluster centers. The number of initial cluster centers is from 1 to the total number of data collection points. For each data collection point, assign it to the cluster containing the initial cluster center that is closest to its total temperature compensation. Update the mean of all data collection points in the cluster to the new cluster center. Continue until all data collection points are assigned to clusters. 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 points are marked as accurate. The proportion of all accurately judged representative points to the total number of representative points selected in the cluster is used as the accuracy of the clustering.

8. A method for monitoring tunnel deformation based on distributed optical fiber sensing technology, characterized in that: The method is performed by the tunnel deformation monitoring system based on distributed optical fiber sensing technology as described in any one of claims 1-7, and the specific steps include: Step 1: Arrange spiral-wound optical fibers along the longitudinal axis of the tunnel lining surface, and arrange transverse optical fibers perpendicular to the longitudinal axis of the tunnel at key sections of the tunnel. Set the data acquisition frequency to 1Hz. Step 2: Divide the spiral-wound optical fiber and the transverse optical fiber into equal intervals, with each division point serving as a data acquisition point. Set the reference temperature for each data acquisition point, acquire the temperature and Brillouin frequency shift change of each data acquisition point in real time, and determine the temperature sensitivity coefficient and strain sensitivity coefficient of the optical fiber through experiments. Generate the total strain of the data acquisition points based on the Brillouin frequency shift change of the data acquisition points. Step 3: Based on the temperature sequence of the data acquisition points during continuous acquisition time, calculate the long-term temperature component of each data acquisition point, and generate long-term temperature strain compensation based on the long-term temperature component and the fiber temperature sensitivity coefficient. Step 4: Generate instantaneous temperature difference based on real-time temperature and long-term temperature components of data acquisition points, calculate the rate of temperature change over the acquisition time, and generate instantaneous temperature strain compensation based on instantaneous temperature difference and rate of temperature change. Step 5: Subtract the long-term temperature strain compensation and instantaneous temperature strain compensation from the total strain to generate stress strain, and determine the deformation level of the tunnel based on the stress strain. Step 6: For each data acquisition 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 acquisition 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 proportion of the number of representative points with correct deformation level judgment to the number of representative points selected in the cluster reflects the accuracy of the cluster.

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