Shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing

Abstract

The invention relates to the technical field of tunnel construction, in particular to a shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing, and the method comprises the following steps: respectively obtaining laser point cloud data and optical fiber strain data; calculating first laser scanning displacement based on the laser point cloud data, calculating first optical fiber displacement data according to the optical fiber strain data, and performing coordinate conversion to form second optical fiber displacement data; generating a continuous sequence of second laser scanning displacements; the optimal path is solved through dynamic planning, so that the second optical fiber displacement data is aligned with the moment of the second laser scanning displacement; and correcting the second laser displacement data according to the residual error between the second optical fiber displacement data and the second laser scanning displacement. Shield segment displacement monitoring is achieved based on fusion of the laser point cloud data and the optical fiber strain data, and accuracy is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel construction, in particular to a shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing, which realizes real-time accurate detection and risk warning of shield segments by fusing contact-non-contact measurement data. BACKGROUND

[0002] Shield tunnels are the main component of subway engineering. Due to their characteristics of being buried underground and having unclear surrounding conditions, they have problems such as great construction difficulty and insufficient deformation monitoring technology. During the construction and operation of shield tunnels, the displacement of segments is crucial to the structural safety and stability of the tunnel. Traditional monitoring methods often have limitations, such as single-point measurement that cannot fully reflect the overall displacement state of the segments, or insufficient measurement accuracy and untimely data acquisition. Three-dimensional laser scanning and distributed optical fiber technology, as emerging technologies in the field of shield tunnel segment displacement monitoring, have made great progress in recent years.

[0003] Three-dimensional laser scanning technology can quickly obtain three-dimensional spatial information of an object and accurately obtain the overall shape of the segments. However, it is not accurate enough to monitor internal millimeter-level or even sub-millimeter-level micro-displacement in some cases. This is because the point cloud data processing algorithm is easily affected by noise and measurement errors when dealing with small changes, making it difficult to accurately capture these subtle displacement information, and thus missing the early signs of micro-deformation of the segments. Distributed optical fiber technology can measure strain and temperature along the length of the optical fiber, but it has difficulty in presenting three-dimensional spatial information, especially in the spatial resolution perpendicular to the optical fiber direction. This means that for complex deformation of the segment surface, especially when there is uneven deformation in local areas, it may not be able to fully obtain detailed information about the deformation. SUMMARY

[0004] To solve the technical problem of insufficient accuracy of existing shield segment displacement monitoring data and difficulty in achieving accurate early warning, the present application proposes a shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing to achieve high-precision monitoring of shield segments throughout the entire area and life cycle.

[0005] To solve the above technical problems, the technical solution adopted by the present application is as follows: a shield segment displacement monitoring method based on laser scanning and optical fiber sensing, comprising the following steps: Step 1: Obtain laser point cloud data and optical fiber strain data by setting three-dimensional laser scanners and distributed optical fiber sensors in the tunnel, respectively. The optical fiber strain data includes ring strain axial strain radial strain ; Step 2: calculating the displacement field of the segment surface based on the laser point cloud data to obtain first laser scanning displacement, the first laser scanning displacement including laser radial displacement, laser circumferential displacement and laser axial displacement; Step 3: calculating first fiber displacement data including fiber radial displacement, fiber circumferential displacement and fiber axial displacement according to fiber strain data, and then mapping the spatial coordinates corresponding to the first fiber displacement data to the global Cartesian coordinate system of the tunnel, and forming second fiber displacement data according to the spatial coordinates in the global Cartesian coordinate system and the corresponding first fiber displacement data; Step 4: interpolating the first laser scanning displacement by a spline interpolation function to generate a continuous sequence of second laser scanning displacement; Step 5: aligning the time of the second fiber displacement data and the second laser scanning displacement by solving the optimal path through dynamic programming; Step 6: calculating the residual error of the second laser scanning displacement and the second fiber displacement data, and determining whether it is greater than a threshold value, if it is greater, then modifying the second fiber displacement data through a correction coefficient until the residual error is less than the threshold value, and the third fiber displacement data obtained by the modification is the displacement data after data fusion.

[0006] The step 1 further comprises the following steps: In the initial stage of the shield tunnel segment assembly, the pre-global scanning is performed by a three-dimensional laser scanner, the laser point cloud data is associated with the global coordinate system of the tunnel, and the key risk monitoring area is determined; According to the key risk monitoring area, the laying path of the sensing fiber is determined, and the laying density satisfies: the ring joint splicing position of the key risk monitoring area > the longitudinal joint and the position of the main reinforcement of the key risk monitoring area > the ring joint splicing position of the non-key risk monitoring area > the longitudinal joint and the position of the main reinforcement of the non-key risk monitoring area, and an arch-shaped laying method is adopted.

[0007] In the step 3, the calculation formula of the first fiber displacement data is: ; Wherein, 、 、 w respectively represent the fiber radial displacement, the fiber circumferential displacement and the fiber axial displacement in the first fiber displacement data, 、 、 respectively represent the radial strain, the circumferential strain and the axial strain in the fiber strain data, represents the radial strain-displacement coefficient, represents the circumferential strain-radial displacement coefficient Represents the circumferential strain-circumferential displacement coefficient. It represents the axial strain-axial displacement coefficient.

[0008] In step 4, the cubic spline interpolation function is used. Interpolating the first laser scanning displacement generates a continuous sequence of second laser scanning displacements, wherein... , , , The interpolation coefficients are represented by t, and time is represented by t. This represents the interpolation function; it satisfies the boundary conditions during generation: ; ; in, This indicates that the three-dimensional laser scanning occurs at discrete times. The actual displacement values ​​collected Indicates the slope at the scan point; The specific method for step 5 is as follows: calculate the time distance, and the calculation formula is: ; in This represents the i-th value in the time series corresponding to the second laser scanning displacement. This represents the j-th value in the time series corresponding to the second fiber displacement data. This represents the time distance between the i-th value in the time series corresponding to the second laser scanning displacement and the j-th value in the time series corresponding to the second fiber displacement data; This represents the time distance between the (i-1)th value in the time series corresponding to the second laser scanning displacement and the jth value in the time series corresponding to the second fiber displacement data; This represents the time distance between the i-th value in the time series corresponding to the second laser scanning displacement and the (j-1)-th value in the time series corresponding to the second fiber displacement data; This represents the time distance between the (i-1)th value in the time series corresponding to the second laser scanning displacement and the (j-1)th value in the time series corresponding to the second fiber displacement data; Then, the optimal path is solved by dynamic programming to align the timing of the second fiber displacement data with that of the second laser scanning displacement.

[0009] In step 6, the formula for calculating the residual between the second laser scanning displacement and the second fiber displacement data is as follows: ; in, This represents the displacement data of the second fiber corresponding to the i-th point. represents the second laser scanning displacement corresponding to the i-th point, m represents the number of measured points, and e represents a residual error; The formula for correcting the second optical fiber displacement data by the correction coefficient is: ; wherein, represents the third optical fiber displacement data corresponding to the i-th point obtained by correction, represents the correction coefficient.

[0010] The shield segment displacement monitoring method based on laser scanning and optical fiber sensing further comprises a deformation risk early warning step, which specifically comprises the following steps: Step 7: Obtain a three-dimensional displacement initial threshold value and a current scene coefficient, and calculate a three-dimensional displacement actual threshold value under the current scene; Step 8: According to the third optical fiber displacement data, calculate the displacement increment in each direction, and judge whether it is greater than or equal to the early warning displacement threshold value in the corresponding direction, if yes, calculate the displacement rate in the corresponding direction and judge whether it is greater than or equal to the displacement rate threshold value, if yes, calculate the deformation curvature in the corresponding direction, and judge whether the deformation curvature is greater than or equal to the critical curvature, if yes, carry out a first-level early warning; Step 9: Perform quadratic curve fitting on the displacement change trend with time, and determine the predicted remaining time to reach the displacement actual threshold value through the fitting curve , if , calculate a comprehensive risk index, and upgrade the early warning level according to the comprehensive risk index; Step 10: Generate an early warning report, wherein the early warning report comprises a displacement absolute value, a displacement rate, a predicted remaining time and a comprehensive risk index.

[0011] In the step 9, the calculation formula of the comprehensive risk index is: ; ; ; wherein, I represents the comprehensive risk index, represents a normal opening amount of the segment joint, represents a circumferential strain concentration coefficient, represents a segment radial displacement increment obtained after data fusion, represents a circumferential displacement increment obtained after data fusion, represents a joint angle, represents a normal displacement threshold value, represents a circumferential strain, represents a maximum allowable value of the circumferential strain.

[0012] The three-dimensional displacement actual threshold in step 7 includes a normal displacement threshold , a radial displacement threshold and a tangential displacement threshold, and the calculation method is: During construction, the scene coefficient is taken as =1.3, the calculation formula of the normal displacement threshold , the radial displacement threshold and the tangential displacement threshold is: ; ; ; , and respectively represent the initial normal displacement threshold, the initial radial displacement threshold and the initial tangential displacement threshold; During operation, the coefficient is taken as =1.0, and the calculation formula of the normal displacement threshold , the radial displacement threshold and the tangential displacement threshold is: ; ; ; In step 9, the quadratic curve used for fitting is: ; Wherein, a and b are fitting coefficients, and the least square method is used for fitting.

[0013] In addition, the application also provides a shield segment displacement monitoring system based on laser scanning and optical fiber sensing, comprising: a three-dimensional laser scanning subsystem, a distributed optical fiber sensing subsystem and a data fusion analysis module, the three-dimensional laser scanning subsystem is used for acquiring point cloud data of a tunnel segment surface, the distributed optical fiber sensing subsystem is used for acquiring strain distribution of a key part of the tunnel segment; the data fusion analysis module is used for realizing the shield segment displacement monitoring method.

[0014] The shield segment displacement monitoring system based on laser scanning and optical fiber sensing also comprises a warning issuing subsystem, the warning issuing subsystem is used for warning deformation risk according to fused displacement data, and the method for the warning issuing subsystem to warn deformation risk is: Acquiring three-dimensional displacement initial threshold and current scene coefficient, and calculating three-dimensional displacement actual threshold under the current scene; Obtaining the displacement data of the current monitoring point after data fusion, calculating the displacement increment in each direction, and judging whether it is greater than or equal to the actual displacement threshold, if yes, calculating the displacement rate and judging whether it is greater than or equal to the displacement rate threshold, if yes, calculating the deformation curvature, and judging whether the deformation curvature is greater than or equal to the critical curvature, if yes, carrying out a first level early warning; The trend of displacement change over time is fitted by a quadratic curve, and the expected remaining time to reach the actual displacement threshold is determined by the fitting curve , if , calculating the comprehensive risk index, and upgrading the warning level according to the comprehensive risk index; Generating a warning report, the warning report including the absolute value of displacement, displacement rate, expected remaining time, and comprehensive risk index.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application proposes a shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing, which can construct a high-precision monitoring system covering the whole area and whole life cycle of the shield segment by deeply fusing the measurement data of three-dimensional laser scanning and distributed optical fiber, and completely breaks through the limitations of single technology in monitoring range, precision and continuity. Among them, laser scanning realizes high-precision capture and visual presentation of explicit deformation by virtue of its direct measurement capability of segment surface displacement, which provides intuitive basis for macro deformation analysis; and distributed optical fiber captures micro-strain by relying on its distributed and long-distance sensing characteristics, not only fills the monitoring blind area of segment joints inside caused by laser shielding and point cloud dispersion, but also can perceive the trend of micro-strain in the early stage of deformation. Moreover, through the laser-guided optical fiber dynamic deployment strategy, the coverage dead angle of traditional fixed monitoring scheme is further eliminated, and the micro-deformation capture capability of high-risk areas is greatly improved.

[0016] In addition, the present application realizes the synergistic effect of the two types of technology by constructing the optical fiber strain-point cloud displacement conversion, the high-precision displacement data of laser scanning provides a dynamic calibration reference for the optical fiber strain-displacement conversion model, effectively correcting the system error caused by material nonlinearity, model simplification assumption, etc.; the continuous strain sensing of optical fiber makes up for the shortcomings of laser in local details and micro-deformation monitoring, and the two are compared and corrected through displacement residual, and the dynamic adjustment of correction coefficient forms a closed-loop system of "continuous monitoring-global verification". This fusion not only greatly reduces the false alarm rate caused by the dependence of single technology, but also balances the monitoring cost through optimizing the sensor layout, finally provides precise data support and reliable early warning for the whole life cycle safety management of the tunnel, effectively guarantees the structural stability and operation safety. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1A flowchart of a shield segment displacement monitoring method based on laser scanning and optical fiber sensing provided for the first embodiment of the present application is shown in the figure. Figure 2 A schematic diagram of the arrangement of distributed optical fiber sensors in the first embodiment of the present application is shown in the figure, which is a schematic top view of a tunnel. Figure 3 A structural schematic diagram of a shield segment displacement monitoring system based on laser scanning and optical fiber sensing provided for the second embodiment of the present application is shown in the figure. Figure 4 A detailed structural schematic diagram of the second embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0018] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0019] Embodiment one As shown in the figure, the first embodiment of the present application provides a shield segment displacement monitoring method based on laser scanning and optical fiber sensing, which includes the following steps: Figure 1 Step 1: Obtain laser point cloud data and optical fiber strain data through a three-dimensional laser scanner and a distributed optical fiber sensor arranged in a tunnel, wherein the optical fiber strain data includes hoop strain , axial strain , and radial strain .

[0020] Specifically, assuming that the strain measured by the distributed optical fiber sensor is , the hoop strain , axial strain , and radial strain can be calculated through an orthogonal decomposition formula to realize spatial reconstruction of strain components.

[0021] Specifically, the orthogonal decomposition formula is: ; (1) ; (2) ; (3) wherein represents the angle between the optical fiber and the radial direction, represents the angle between the optical fiber and the axial direction.

[0022] ​Further, the embodiment also includes a step of temperature calibration of the optical fiber strain data. The calibration method can be: synchronously laying distributed stress sensing optical fibers and temperature compensation optical fibers on the shield segment, both of which are of the same type of material and are in the same temperature field, and the temperature compensation optical fibers are arranged in the non-stress area of the segment; then synchronously collecting data of the two types of optical fibers by the distributed optical fiber sensor, wherein the stress sensing optical fiber obtains the measured strain , the temperature compensation optical fiber obtains the pure temperature strain, and the difference between the two is calculated to obtain the strain data after temperature correction by removing temperature error .

[0023] Specifically, the embodiment also includes a step of preprocessing the laser point cloud data. First, remove noise points by Gaussian filtering, and the Gaussian filtering formula is: ; (4) wherein, is the filtering radius, and x and y represent the coordinates of the three-dimensional laser scanning data in a certain plane projection, which is used to determine the relative position of the data point in the filtering template. represents the weight value of the Gaussian filter at the coordinates, and the information of the surrounding points is fused according to the weight to remove noise.

[0024] Then, in the point cloud matching stage, the ICP algorithm is used to optimize the transformation matrix T to complete the point cloud registration, wherein the registration error is controlled within 0.03mm.

[0025] The step 1 further includes the following steps: In the initial stage of shield tunnel segment assembly, perform preliminary global scanning by a three-dimensional laser scanner, associate the laser point cloud data with the tunnel global coordinate system, and determine the key risk monitoring area; According to the key risk monitoring area, determine the laying path of the sensing optical fiber in the distributed optical fiber sensor, and when laying, the laying density satisfies: the ring joint splicing position of the key risk monitoring area > the longitudinal joint and the position of the main reinforcement of the key risk monitoring area > the ring joint splicing position of the non-key risk monitoring area > the longitudinal joint and the position of the main reinforcement of the non-key risk monitoring area, and a zigzag laying method is adopted.

[0026] In this embodiment, the three-dimensional laser scanner is selected to have high resolution (0.1 mm accuracy), large scanning range (horizontal 360°, vertical 270°), which can quickly obtain dense point cloud data of the tunnel segment surface. The wavelength of the emitted laser is within a specific range (905 nm) to ensure good reflection effect and measurement accuracy in the tunnel environment. The data transmission cable connects the laser scanner and the data acquisition and control unit, and high-speed, anti-interference optical cable or shielded twisted pair cable is used to ensure stable data transmission with a transmission rate not less than 1 Gbps. In view of the short-term rapid deformation characteristics of the segment during the shield propulsion and segment assembly stage, the scanning frequency is increased to once every 30 minutes in the sensitive area of the tunnel deformation, i.e. within 50 meters behind the shield machine, and the resolution is set to 0.03 mm; in view of the long-term slow deformation characteristics during the operation period, the tunnel connecting channel, curved road and other stress concentration areas are scanned twice a day. In the relatively sensitive area of the tunnel deformation, the scanning frequency can be increased to once every minute, and the resolution is set to 0.05 mm; in the relatively stable area, the scanning frequency and resolution are appropriately reduced to balance the data volume and monitoring effect.

[0027] Specifically, the method for determining the key risk monitoring area is as follows: the three-dimensional laser scanner first performs the preliminary global scanning and key area identification function: the scanning range covers at least 3 complete segment rings of the tunnel, and 1 mm resolution is used to obtain the three-dimensional laser point cloud data of the full ring to generate the three-dimensional model of the initial shape of the segment. The potential key monitoring area is automatically identified by the point cloud data analysis module, the continuity mutation characteristics are used to accurately locate the joint between adjacent segment rings and the joint between segments in the same segment ring, and the stress concentration positions such as the corner of the segment surface curvature mutation are captured; the segment laser point cloud data obtained by the three-dimensional laser scanning is associated with the global coordinate system of the tunnel, the spatial coordinates of each segment are determined, and then the information such as the distribution range of the soft soil layer and the position of the fault fracture zone in the geological survey report is spatially mapped to determine the segment area in these geological risk areas, including the weak structure area, the geological sensitive area and the construction influence area. Finally, the “key monitoring area distribution map” is output, and the boundary coordinates, expected deformation risk level and recommended fiber laying density of each area are determined based on the global coordinate system of the segment.

[0028] In this embodiment, the distributed optical fiber sensor needs to be connected with the light source, demodulation equipment and optical fiber connection and protection device to realize sensing. Meanwhile, it also includes a strain data acquisition and processing module and a temperature compensation module. Specifically, the distributed optical fiber sensor can adopt a Brillouin optical time domain reflection (BOTDR) sensor.

[0029] In this embodiment, the arrangement of sensing fibers in the distributed optical fiber sensor does not adopt a fixed interval pattern, but is dynamically adjusted. Specifically, in high-risk areas such as circumferential joints and segments corresponding to soft soil layers, the spacing at circumferential joints is increased to 0.3 meters, while the spacing at longitudinal joints and main reinforcement positions is 0.5 meters. Figure 2 As shown, a "bow-shaped" deployment is adopted to ensure that the spatial resolution of fiber optic strain monitoring matches the risk level identified by laser scanning. In low-to-medium risk areas such as the non-splicing zone in the middle of the tunnel segment and tunnel segments corresponding to stable strata, the spacing is appropriately widened to 1 meter for circumferential seams and 2 meters for longitudinal seams, reducing the number of sensors used to balance costs. After deployment, the point cloud on the tunnel segment surface is acquired again using 3D laser scanning and compared with the boundary coordinates of the preset key areas to ensure that the fiber optic path covers ≥95% of the key areas. Areas not covered are corrected by adding sensing fibers.

[0030] In this embodiment, the distributed optical fiber sensor uses a broadband light source, whose output power and wavelength stability meet the sensor's operating requirements, with wavelength stability within ±0.1nm. The demodulation device, namely a Brillouin optical time-domain analyzer, can accurately measure the wavelength or frequency changes of the optical signal in the optical fiber, thereby retrieving the strain information of the tube segment. The measurement accuracy needs to reach the micro-strain level (±1με).

[0031] Specifically, in this embodiment, a distributed fiber optic sensor senses the strain changes of the tunnel segment in real time, acquiring data once per minute to continuously obtain fiber optic strain data for key parts of the segment. A 3D laser scanner periodically scans the surface of the segment daily to obtain overall 3D point cloud data. By combining the real-time fiber optic strain data with the periodic overall scan data from the 3D laser scanner, when the distributed fiber optic sensor detects abnormal changes in the fiber optic strain data, it indicates a potential local displacement trend. This triggers the 3D laser scanner to scan, thereby determining in a shorter time whether the overall displacement state of the segment has also changed accordingly, and analyzing the impact of this local displacement on the overall geometry of the segment and the relative positions of adjacent segments. This improves monitoring timeliness and leverages the synergistic advantages of the two monitoring methods in the spatial dimension.

[0032] Step 2: Calculate the displacement field on the surface of the tube segment based on the laser point cloud data to obtain the first laser scanning displacement, which includes laser radial displacement, laser circumferential displacement and laser axial displacement.

[0033] Step 3: Then, based on the fiber strain data, calculate the first fiber displacement data. At the same time, first map the spatial coordinates corresponding to the first fiber strain data to the tunnel global rectangular coordinate system, and then form the second fiber displacement data based on the spatial coordinates in the global rectangular coordinate system and the corresponding first fiber displacement data.

[0034] The spatial coordinates corresponding to the first fiber strain data are mapped to the global rectangular coordinate system of the tunnel, so as to be the same as the spatial coordinate system corresponding to the first laser scanning displacement, thereby facilitating subsequent fusion of the two.

[0035] The first fiber displacement data include radial, circumferential and axial displacement data, i.e., fiber radial displacement , fiber circumferential displacement and fiber axial displacement . The first fiber displacement data are calculated based on the fiber strain data, and each direction displacement corresponds to the position of the fiber measurement point in the global rectangular coordinate system of the tunnel. The specific calculation formula is as follows: ; (4) wherein, is the fiber radial displacement (corresponding to the Y / Z direction of the rectangular coordinate system, reflecting the displacement change of the segment along the horizontal and vertical radial directions), is the radial strain-displacement coefficient associated with the segment thickness, is the circumferential strain-displacement coefficient associated with the segment radius, is the radial strain, is the circumferential strain; is the fiber circumferential displacement (corresponding to the X direction of the rectangular coordinate system, reflecting the displacement of the segment along the circumferential tangent direction), is the circumferential strain-circumferential displacement coefficient associated with the circumferential gage length; is the fiber axial displacement (corresponding to the X direction of the rectangular coordinate system, reflecting the expansion and contraction displacement of the segment along the tunnel axis), is the axial strain-axial displacement coefficient associated with the axial gage length, is the axial strain.

[0036] In actual calculation, the specific values of each strain-displacement coefficient are determined according to the segment design parameters (thickness, radius) and the fiber laying gage length, and then the fiber strain data are substituted into formula (4) to obtain the displacement values in three directions, thereby forming complete first displacement data, which provide displacement reference in a unified coordinate system for subsequent time alignment and residual error calculation of the laser scanning displacement.

[0037] In the spatial coordinate mapping, the starting point of the fiber is selected, and the polar coordinates of the starting point are wherein R is the segment design radius, θ0 is determined in combination with the segment assembly orientation with the segment horizontal radial outside as the 0° reference, X0 is calculated with the tunnel fixed reference point as the origin, according to the segment axial pitch and the segment ring position where the starting point is located; through the polar coordinate to Cartesian coordinate formula, the starting point Cartesian coordinates (X0, Y0, Z0) are obtained, wherein Y0 = R x cos θ0, Z0 = R x sin θ0. For the strain measurement points on the optical fiber data, the circumferential laying segment is determined according to the circumferential laying interval and the circumferential arc length ΔS of the starting point, ΔS = R x Δθ (Δθ is the circumferential angle increment) to determine Δθ, and then the axial distance ΔX of the circumferential segment endpoint is determined according to the axial laying interval, and the polar coordinates corresponding to the strain measurement points can be expressed as: Then, it is converted into the coordinates in the Cartesian coordinates through coordinate conversion, which can be expressed as: , realizing the spatial alignment of the spatial coordinates in the first optical fiber strain data and the tunnel global Cartesian coordinate system.

[0038] Step 4: Interpolating the first laser scanning displacement by a spline interpolation function to generate a continuous sequence of second laser scanning displacement.

[0039] In the step 4, a continuous sequence of the first laser scanning displacement is generated by a cubic spline interpolation function, and the interpolation function is: ; (5) wherein, , , , is an interpolation coefficient, t is time, represents an interpolation function, which is a function of time t, and generates a continuous sequence of laser scanning displacement data that satisfies the boundary conditions at the same time: ; (6) ; (7) wherein, represents the actual displacement value collected by the three-dimensional laser scanning at the discrete time , represents the slope corresponding to the discrete time . Through the interpolation function, the continuity of the laser displacement data in the time dimension can be ensured.

[0040] Step 5: Aligning the time of the second optical fiber displacement data and the second laser scanning displacement by dynamic programming to solve the optimal path.

[0041] In this embodiment, the time alignment of the laser scanning displacement and the optical fiber displacement data is realized by adopting the method of dynamic interpolation combined with elastic regularization.

[0042] Specifically, the specific method of the step 5 is: (1) Calculate the time distance, the formula is: ; (8) Wherein represents the i-th value in the time sequence corresponding to the second laser scanning displacement, represents the j-th value in the time sequence corresponding to the second fiber displacement data, represents the time distance between the i-th value in the time sequence corresponding to the second laser scanning displacement and the j-th value in the time sequence corresponding to the second fiber displacement data; represents the time distance between the i-1-th value in the time sequence corresponding to the second laser scanning displacement and the j-th value in the time sequence corresponding to the second fiber displacement data; represents the time distance between the i-th value in the time sequence corresponding to the second laser scanning displacement and the j-1-th value in the time sequence corresponding to the second fiber displacement data; represents the time distance between the i-1-th value in the time sequence corresponding to the second laser scanning displacement and the j-1-th value in the time sequence corresponding to the second fiber displacement data; (2) Then solve the optimal path by dynamic programming to align the strain sudden increase moment corresponding to the second fiber displacement data with the displacement mutation moment in the second laser scanning displacement, and solve the asynchronous problem of "discrete-continuous" data.

[0043] Step 6: Calculate the residual error of the second laser scanning displacement and the second fiber displacement data to evaluate the consistency of the two, introduce a correction coefficient to correct the first displacement data until the residual error is less than the threshold value, and the third fiber displacement data obtained by correction is the displacement data after data fusion.

[0044] Specifically, whether the residual error of the second laser scanning displacement and the second fiber displacement data is less than the residual error threshold value is judged by calculating the residual error of the second laser scanning displacement and the second fiber displacement data If not, introduce a correction coefficient to correct the second fiber displacement data until the residual error is less than the residual error threshold value , and the third fiber displacement data obtained by correction is the displacement data after data fusion.

[0045] Specifically, in step 6, the residual error calculation formula of the second laser scanning displacement and the second fiber displacement data is: ; (9) e represents the residual error, which is an index for quantifying the difference between the distributed fiber inversion displacement and the three-dimensional laser scanning measured displacement, represents the second fiber displacement data corresponding to the i-th point, represents the second laser scanning displacement corresponding to the i-th point, m represents the number of measurement points, and e represents the residual error; The formula for correcting the second optical fiber displacement data by the correction coefficient is: ; (10) wherein, represents the third optical fiber displacement data corresponding to the i th point after correction, represents the correction coefficient.

[0046] Specifically, in the embodiment, the correction coefficient is dynamically corrected, and the expression is: ; (11) wherein, β is a calibration factor, which is calibrated by experiment, and is usually taken as 0.1-0.5mm-2, for controlling the correction strength. When the residual e satisfies the following condition: the dynamic correction mechanism is triggered, and the residual threshold can be preset by the system. The larger the residual is, the farther it deviates from 1, and the greater the correction amplitude is. In addition, in the embodiment, the residual is calculated after the radial, circumferential and displacement directions of the second optical fiber displacement data are calculated respectively, and then the correction is performed.

[0047] Suppose that the circumferential displacement of a certain measurement point in the second optical fiber displacement data is =2.0mm, and the circumferential displacement in the laser scanning displacement is: =2.2mm, and the residual sum of squares e exceeds the threshold value due to the increased difference of the point, the correction coefficient =1.1 is calculated by the above formula, and then the corrected circumferential displacement is =1.1x2.0=2.2mm, which is consistent with the laser measured value. By quantifying the residual and adjusting the optical fiber data, the influence of the system error is weakened, so that the two types of data maintain their respective advantages (the local precision of the optical fiber and the global integrity of the laser), and form a closed loop of complementary verification, ultimately providing more reliable quantitative basis for segment deformation analysis and early warning.

[0048] Further, the shield segment displacement monitoring method based on laser scanning and optical fiber sensing of the embodiment further includes the step of performing deformation risk early warning, which specifically includes the following steps: Step 7: Obtain the three-dimensional displacement initial threshold and the current scene coefficient, and calculate the three-dimensional displacement actual threshold under the current scene.

[0049] In the step 7, the calculation method of the three-dimensional displacement actual threshold is: During construction, the scene coefficient is taken as =1.3, the normal displacement threshold , the radial displacement threshold and tangential fault threshold The calculation formula is: ; (12) ; (13) ; (14) , and respectively represent the initial normal displacement threshold, the initial radial fault threshold and the initial tangential fault threshold.

[0050] During operation, the scene coefficient takes the value of =1.0, and the superimposed threshold is increased during operation to cope with the impact of train load. Specifically, the calculation formula of the normal displacement threshold , the radial fault threshold and the tangential fault threshold is: ; (15) ; (16) ; (17) In this embodiment, the initial normal displacement threshold is set to 3mm, the initial radial fault threshold 3mm, the initial tangential fault threshold 2mm, and the superimposed threshold =0.3mm.

[0051] Step 8: Obtain the displacement data of the current monitoring point after data fusion, i.e. the third optical fiber displacement data, calculate the displacement increment in each direction, and judge whether it is greater than or equal to the corresponding direction warning displacement threshold. If yes, calculate the displacement rate in the corresponding direction and judge whether it is greater than or equal to the displacement rate threshold. If yes, calculate the deformation curvature in the corresponding direction and judge whether the deformation curvature is greater than or equal to the critical curvature. If it is greater, a first-level warning is performed. Among them, the warning displacement threshold is less than the actual threshold. In this embodiment, the warning displacement threshold is U'=0.8U, wherein U represents the three-dimensional displacement actual threshold.

[0052] In this embodiment, the warning trigger mechanism adopts the "absolute value + change rate" double factor verification. Assuming that the current normal displacement of the monitoring point is , the initial reference displacement in this direction is , the displacement increment is , when , the change rate calculation is started: the displacement rate in the time interval , if , then enters the pre-warning activation state. At this time, the deformation curvature is inversed by fusing data ( s , which is the arc length of the segment), when ( , which is the critical curvature determined by the segment strength calculation), a first-level pre-warning is triggered.

[0053] Step 9: Perform a quadratic curve fitting on the displacement change trend over time, and determine the predicted remaining time to reach the actual threshold of displacement by the fitting curve , if , calculate the comprehensive risk index, and upgrade the pre-warning level according to the comprehensive risk index.

[0054] Specifically, to quantify the risk development trend, a deformation prediction model is constructed based on elastic mechanics: let the displacement change over time satisfy , , which is the rate coefficient, , which is the acceleration coefficient, the value of the coefficient a, b is obtained by least squares fitting to make the residual minimum, then the displacement change curve over time can be obtained, and the predicted remaining time to reach the actual threshold of displacement is calculated according to the curve.

[0055] Specifically, in step 9, the calculation formula of the comprehensive risk index is: ; (18) ; (19) ; (20) wherein I represents the comprehensive risk index, represents the normal opening amount of the segment joint, represents the circumferential strain concentration coefficient, represents the radial displacement increment of the segment obtained after data fusion, represents the circumferential displacement increment obtained after data fusion, represents the joint angle, i.e. the included angle between the segment joint and the circumferential direction (the direction around the tunnel circumference), represents the normal displacement threshold, represents the circumferential strain, represents the maximum allowable value of the circumferential strain.

[0056] Step 10: Generate a pre-warning report, which includes the absolute value of displacement, displacement rate, predicted remaining time and comprehensive risk index.

[0057] Embodiment Two As Figures 3-4As shown, the second embodiment of the present application provides a shield segment displacement monitoring system based on laser scanning and optical fiber sensing, comprising: a three-dimensional laser scanning subsystem, a distributed optical fiber sensing subsystem, a data fusion analysis module, the three-dimensional laser scanning subsystem is used for acquiring point cloud data of the tunnel segment surface, the distributed optical fiber sensing subsystem is used for acquiring strain distribution of the key part of the tunnel segment; the data fusion analysis module is used to realize the shield segment displacement monitoring method of the first embodiment.

[0058] Specifically, as shown in the figure, Figure 4 The distributed optical fiber sensing subsystem includes a distributed optical fiber sensor, a light source and a demodulation device, in addition, it also includes a fiber connection and protection device, the corresponding software settings in the distributed optical fiber sensing subsystem also include strain data acquisition and processing software, and a temperature compensation module; the three-dimensional laser scanning subsystem includes a three-dimensional laser scanner and a data acquisition control unit, wherein the hardware part further includes a mounting bracket of the three-dimensional laser scanner and a corresponding data transmission cable, the software settings in the data acquisition control unit include scanning control software and data preprocessing software.

[0059] Specifically, as shown in the figure, Figure 4 The hardware composition of the data fusion analysis module includes a data acquisition card and a high-performance server, and the software modules set in the high-performance server include a data fusion algorithm module, displacement calculation and analysis software and a database management system.

[0060] Further, the shield segment displacement monitoring system based on laser scanning and optical fiber sensing of the present embodiment further includes a warning release subsystem, the warning release subsystem is used for deformation risk warning according to the displacement data after data fusion, and the method for the warning release subsystem to perform deformation risk warning is: (1) acquiring a three-dimensional displacement initial threshold value and a current scene coefficient, and calculating a three-dimensional displacement actual threshold value under the current scene; (2) acquiring the displacement data after data fusion of the current monitoring point, calculating the displacement increment in each direction, and judging whether it is greater than or equal to the actual displacement threshold value, if yes, calculating the displacement rate and judging whether it is greater than or equal to the displacement rate threshold value, if yes, calculating the deformation curvature, and judging whether the deformation curvature is greater than or equal to the critical curvature, if greater, performing a first-level warning; (3) performing quadratic curve fitting on the change trend of displacement with time, and determining the predicted remaining time to reach the actual displacement threshold value through the fitting curve , if , calculating a comprehensive risk index, and upgrading the warning level according to the comprehensive risk index; (4) generating a warning report, the warning report including the absolute value of displacement, displacement rate, predicted remaining time and comprehensive risk index.

[0061] Further, the embodiment also includes a displacement monitoring database for storing historical fusion data; the early warning issuing subsystem includes a communication module and an audible and light alarm device, the communication module is used for transmitting the early warning signal, and the audible and light alarm device is used for realizing local alarm.

[0062] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing, characterized in that, Includes the following steps: Step 1: Using a 3D laser scanner and distributed fiber optic sensors installed inside the tunnel, laser point cloud data and fiber optic strain data are acquired, including circumferential strain. Axial strain and radial strain ; Step 2: Calculate the displacement field on the surface of the tube segment based on the laser point cloud data to obtain the first laser scanning displacement, which includes laser radial displacement, laser circumferential displacement and laser axial displacement; Step 3: Calculate the first fiber displacement data based on the fiber strain data. The first fiber displacement data includes the fiber radial displacement, fiber circumferential displacement and fiber axial displacement. At the same time, first map the spatial coordinates corresponding to the first fiber displacement data to the tunnel global rectangular coordinate system. Then, based on the spatial coordinates in the global rectangular coordinate system and the corresponding first fiber displacement data, form the second fiber displacement data. Step 4: Interpolate the first laser scanning displacement using a spline interpolation function to generate a continuous sequence of second laser scanning displacements; Step 5: Solve for the optimal path through dynamic programming to align the timing of the second fiber displacement data with that of the second laser scanning displacement; Step 6: Calculate the residual between the second laser scanning displacement and the second fiber displacement data, and determine whether it is greater than the threshold. If it is, correct the second fiber displacement data with a correction coefficient until the residual is less than the threshold. The corrected third fiber displacement data is the displacement data after data fusion.

2. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 1, characterized in that, Step 1 also includes the following steps: In the early stage after the shield tunnel segments are assembled, a three-dimensional laser scanner is used to perform a preliminary full-area scan, and the laser point cloud data is correlated with the tunnel's global coordinate system to determine key risk monitoring areas; Based on the key risk monitoring areas, determine the laying path of the sensing optical fiber. During laying, the laying density should meet the following requirements: circumferential joints in key risk monitoring areas > longitudinal joints and main reinforcement positions in key risk monitoring areas > circumferential joints in non-key risk monitoring areas > longitudinal joints and main reinforcement positions in non-key risk monitoring areas, and adopt a bow-shaped laying method.

3. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 1, characterized in that, In step 3, the formula for calculating the first fiber displacement data is: ； in, , , w These represent the fiber radial displacement, fiber circumferential displacement, and fiber axial displacement in the first fiber displacement data, respectively. , , These represent the radial strain, circumferential strain, and axial strain in the fiber optic strain data, respectively. Indicates the radial strain-displacement coefficient. Indicates the circumferential strain-radial displacement coefficient. Represents the circumferential strain-circumferential displacement coefficient. It represents the axial strain-axial displacement coefficient.

4. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 1, characterized in that, In step 4, the cubic spline interpolation function is used. Interpolating the first laser scanning displacement generates a continuous sequence of second laser scanning displacements, where , , , The interpolation coefficients are denoted by t, which represents time. This represents the interpolation function; it satisfies the boundary conditions during generation: ； ； in, This indicates that the three-dimensional laser scanning occurs at discrete times. The actual displacement values ​​collected Indicates the slope at the scan point; The specific method for step 5 is as follows: calculate the time distance, and the calculation formula is: ； in This represents the i-th value in the time series corresponding to the second laser scanning displacement. This represents the j-th value in the time series corresponding to the second fiber displacement data. This represents the time distance between the i-th value in the time series corresponding to the second laser scanning displacement and the j-th value in the time series corresponding to the second fiber displacement data; This represents the time distance between the (i-1)th value in the time series corresponding to the second laser scanning displacement and the jth value in the time series corresponding to the second fiber displacement data; This represents the time distance between the i-th value in the time series corresponding to the second laser scanning displacement and the (j-1)-th value in the time series corresponding to the second fiber displacement data; This represents the time distance between the (i-1)th value in the time series corresponding to the second laser scanning displacement and the (j-1)th value in the time series corresponding to the second fiber displacement data; Then, the optimal path is solved by dynamic programming to make the second fiber displacement data and the second laser scanning displacement synchronized in time.

5. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 1, characterized in that, In step 6, the formula for calculating the residual between the second laser scanning displacement and the second fiber displacement data is as follows: ； in, This represents the displacement data of the second fiber corresponding to the i-th point. This represents the second laser scanning displacement corresponding to the i-th point, m represents the number of measurement points, and e represents the residual. The formula for correcting the displacement data of the second fiber optic cable using a correction factor is as follows: ； in, This represents the third fiber displacement data corresponding to the i-th point obtained after correction. This represents the correction factor.

6. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 1, characterized in that, It also includes a step for deformation risk warning, which specifically includes the following steps: Step 7: Obtain the initial threshold of 3D displacement and the current scene coefficients, and calculate the actual threshold of 3D displacement in the current scene; Step 8: Based on the displacement data of the third fiber, calculate the displacement increment in each direction and determine whether it is greater than or equal to the warning displacement threshold in the corresponding direction. If so, calculate the displacement rate in the corresponding direction and determine whether it is greater than or equal to the displacement rate threshold. If so, calculate the deformation curvature in the corresponding direction and determine whether the deformation curvature is greater than or equal to the critical curvature. If it is greater, then issue a first-level warning. Step 9: Perform quadratic curve fitting on the displacement-time trend, and determine the estimated remaining time to reach the actual displacement threshold using the fitted curve. ,like Calculate the comprehensive risk index and upgrade the early warning level based on the comprehensive risk index; Step 10: Generate an early warning report, which includes the absolute value of displacement, displacement rate, estimated remaining time, and comprehensive risk index.

7. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 6, characterized in that, In step 9, the formula for calculating the comprehensive risk index is as follows: ； ； ； Where I represents the comprehensive risk index, This indicates the normal opening of the segment joint. Indicates the circumferential strain concentration factor. This represents the radial displacement increment of the tunnel segment obtained after data fusion. This represents the circumferential displacement increment obtained after data fusion. Indicates the seam angle. Indicates the normal displacement threshold. Indicates circumferential strain. This indicates the maximum allowable value of circumferential strain.

8. The method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing according to claim 6, characterized in that, In step 7, the actual three-dimensional displacement threshold includes the normal displacement threshold. Radial misalignment threshold The tangential misalignment threshold is calculated as follows: During construction, the scene coefficient is set to [value]. =1.3, normal displacement threshold Radial misalignment threshold and tangential misalignment threshold The calculation formula is: ； ； ； , and These represent the initial normal displacement threshold, the initial radial misalignment threshold, and the initial tangential misalignment threshold, respectively. The operating period coefficient is taken as: =1.0, normal displacement threshold Radial misalignment threshold and tangential misalignment threshold The calculation formula is: ； ； ； In step 9, the quadratic curve used for fitting is: ； Where a and b are fitting coefficients, and the least squares method is used for fitting.

9. A shield tunnel segment displacement monitoring system based on laser scanning and fiber optic sensing, characterized in that, include: The method comprises a three-dimensional laser scanning subsystem, a distributed optical fiber sensing subsystem, and a data fusion analysis module. The three-dimensional laser scanning subsystem is used to acquire point cloud data of the surface of the tunnel segment, and the distributed optical fiber sensing subsystem is used to acquire the strain distribution of key parts of the tunnel segment. The data fusion analysis module is used to implement the shield tunnel segment displacement monitoring method based on laser scanning and optical fiber sensing as described in any one of claims 1 to 8.

10. A shield tunnel segment displacement monitoring system based on laser scanning and fiber optic sensing according to claim 9, characterized in that, It also includes an early warning release subsystem, which is used to issue early warnings of deformation risks based on the displacement data after data fusion. The method for issuing early warnings of deformation risks by the early warning release subsystem is as follows: Obtain the initial threshold of 3D displacement and the current scene coefficient, and calculate the actual threshold of 3D displacement in the current scene; Obtain the displacement data after data fusion of the current monitoring point, calculate the displacement increment in each direction, and determine whether it is greater than or equal to the actual displacement threshold. If so, calculate the displacement rate and determine whether it is greater than or equal to the displacement rate threshold. If so, calculate the deformation curvature and determine whether the deformation curvature is greater than or equal to the critical curvature. If it is greater, issue a first-level warning. A quadratic curve is fitted to the displacement over time, and the estimated remaining time to reach the actual displacement threshold is determined by the fitted curve. ,like Calculate the comprehensive risk index and upgrade the early warning level based on the comprehensive risk index; Step 10: Generate an early warning report, which includes the absolute value of displacement, displacement rate, estimated remaining time, and comprehensive risk index.

Images