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

Abstract

The 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 comprises the following steps: acquiring laser point cloud data and optical fiber strain data respectively; 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 continuous sequence second laser scanning displacement; aligning the time of the second optical fiber displacement data and the second laser scanning displacement by solving the optimal path through dynamic programming; and correcting the second laser displacement data according to the residual error of the second optical fiber displacement data and the second laser scanning displacement. The application realizes shield segment displacement monitoring based on the fusion of laser point cloud data and optical fiber strain data, and improves the accuracy.

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:

[0006] 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, wherein the optical fiber strain data includes ring strain axial strain radial strain ;

[0007] Step 2: calculate the displacement field of the pipe 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;

[0008] Step 3: according to the fiber strain data, calculate the first fiber displacement data, the first fiber displacement data including fiber radial displacement, fiber circumferential displacement and fiber axial displacement, and then map the spatial coordinates corresponding to the first fiber displacement data to the global rectangular coordinate system of the tunnel, and then form second fiber displacement data according to the spatial coordinates in the global rectangular coordinate system and the corresponding first fiber displacement data;

[0009] Step 4: interpolate the first laser scanning displacement by a spline interpolation function to generate a continuous sequence of second laser scanning displacement;

[0010] Step 5: align the time of the second fiber displacement data and the second laser scanning displacement by solving the optimal path through dynamic programming;

[0011] Step 6: calculate the residual error of the second laser scanning displacement and the second fiber displacement data, and determine whether it is greater than a threshold value, if it is greater, then correct the second fiber displacement data by a correction coefficient 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.

[0012] The step 1 further comprises the following steps:

[0013] At the initial stage of shield tunnel pipe splicing, the three-dimensional laser scanner is used for preliminary global scanning, the laser point cloud data is associated with the global coordinate system of the tunnel, and the key risk monitoring area is determined;

[0014] According to the key risk monitoring area, the laying path of the sensing optical fiber is determined, and the laying density satisfies: the ring joint 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 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 the bow-shaped laying method is adopted.

[0015] In the step 3, the calculation formula of the first fiber displacement data is:

[0016] ;

[0017] Wherein, , , wrespectively represent fiber radial displacement, fiber hoop displacement and fiber axial displacement in the first fiber displacement data, , , respectively represent radial strain, hoop strain and axial strain in the fiber strain data, represents the radial strain-displacement coefficient, represents the hoop strain-radial displacement coefficient represents the hoop strain-hoop displacement coefficient, represents the axial strain-axial displacement coefficient.

[0018] In step 4, the first laser scanning displacement is interpolated by a cubic spline interpolation function to generate a continuous sequence of second laser scanning displacement, wherein, , , , represents the interpolation coefficient, t represents time, represents the interpolation function; when generated, the boundary conditions are satisfied:

[0019] ;

[0020] ;

[0021] wherein, represents the actual displacement value collected by the three-dimensional laser scanning at discrete time , represents the slope at the scanning point;

[0022] The specific method of step 5 is to calculate the time distance, and the calculation formula is:

[0023] ;

[0024] 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; a time distance between an i-1th value in a time sequence corresponding to the second laser scanning displacement and a j-1th value in a time sequence corresponding to the second fiber displacement data;

[0025] Then, the optimal path is solved by dynamic programming to align the time of the second fiber displacement data with the second laser scanning displacement.

[0026] In step 6, the residual calculation formula of the second laser scanning displacement and the second fiber displacement data is:

[0027] ;

[0028] wherein, denotes the second fiber displacement data corresponding to the i th point, denotes the second laser scanning displacement corresponding to the i th point, m represents the number of measurement points, and e represents the residual;

[0029] The formula for correcting the second fiber displacement data by the correction coefficient is:

[0030] ;

[0031] wherein, denotes the third fiber displacement data corresponding to the i th point obtained by correction, denotes the correction coefficient.

[0032] The shield segment displacement monitoring method based on laser scanning and fiber sensing further comprises a deformation risk warning step, which specifically comprises the following steps:

[0033] 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;

[0034] Step 8: According to the third fiber displacement data, calculate the displacement increment in each direction, and determine whether it is greater than or equal to the warning displacement threshold value in the corresponding direction. If yes, calculate the displacement rate in the corresponding direction and determine whether it is greater than or equal to the displacement rate threshold value. If yes, calculate the deformation curvature in the corresponding direction, and determine whether the deformation curvature is greater than or equal to the critical curvature. If yes, a first-level warning is performed.

[0035] 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 warning level according to the comprehensive risk index;

[0036] Step 10: Generate a warning report, wherein the warning report comprises a displacement absolute value, a displacement rate, a predicted remaining time, and a comprehensive risk index.

[0037] The calculation formula of the comprehensive risk index in step 9 is:

[0038] ;

[0039] ;

[0040] ;

[0041] 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, represents the normal displacement threshold value, represents the circumferential strain, represents the maximum allowable value of the circumferential strain.

[0042] In step 7, the three-dimensional displacement actual threshold value includes the normal displacement threshold value , the radial displacement threshold value and the tangential displacement threshold value, and the calculation method is:

[0043] During construction, the scene coefficient takes the value of =1.3, and the calculation formula of the normal displacement threshold value , the radial displacement threshold value and the tangential displacement threshold value is:

[0044] ;

[0045] ;

[0046] ;

[0047] , and respectively represent the initial normal displacement threshold value, the initial radial displacement threshold value, and the initial tangential displacement threshold value;

[0048] During operation, the coefficient takes the value of =1.0, and the calculation formula of the normal displacement threshold value , the radial displacement threshold value and the tangential displacement threshold value is:

[0049] ;

[0050] ;

[0051] ;

[0052] In step 9, the quadratic curve used for fitting is:

[0053] ;

[0054] Wherein, a, b are fitting coefficients, and the least square method is used for fitting.

[0055] 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, wherein 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 key parts of the tunnel segment, and the data fusion analysis module is used for realizing the shield segment displacement monitoring method.

[0056] The shield segment displacement monitoring system based on laser scanning and optical fiber sensing also comprises a pre-warning issuing subsystem, wherein the pre-warning issuing subsystem is used for pre-warning deformation risks according to displacement data after data fusion, and the method for pre-warning deformation risks by the pre-warning issuing subsystem is as follows:

[0057] An initial threshold value of three-dimensional displacement and a current scene coefficient are acquired, and an actual threshold value of three-dimensional displacement under the current scene is calculated;

[0058] The displacement data after data fusion of the current monitoring point are acquired, displacement increments in each direction are calculated, and it is judged whether the displacement increments are greater than or equal to the actual displacement threshold value; if yes, the displacement rate is calculated and it is judged whether the displacement rate is greater than or equal to a displacement rate threshold value; if yes, the deformation curvature is calculated, and it is judged whether the deformation curvature is greater than or equal to a critical curvature; if yes, a first-level pre-warning is performed;

[0059] A quadratic curve fitting is performed on the change trend of displacement with time, and the expected remaining time for reaching the actual threshold value of displacement is determined through the fitting curve , if , a comprehensive risk index is calculated, and the warning level is upgraded according to the comprehensive risk index;

[0060] A pre-warning report is generated, and the pre-warning report comprises an absolute value of displacement, a displacement rate, an expected remaining time and a comprehensive risk index.

[0061] Compared with the prior art, the application has the following beneficial effects:

[0062] The application provides a shield segment displacement monitoring method and system based on laser scanning and optical fiber sensing.

[0063] In addition, the application realizes the synergistic effect of the two types of technologies by constructing a fiber strain-point cloud displacement conversion, the high-precision displacement data of laser scanning provides a dynamic calibration reference for the fiber strain-displacement conversion model, effectively correcting the system error caused by material nonlinearity, model simplification assumption, etc.; the continuous strain sensing of the optical fiber compensates for the shortcomings of laser in local details and micro-deformation monitoring, and the two are compared and corrected through displacement residual and dynamic adjustment of the correction coefficient, forming a closed-loop system of "continuous monitoring-global verification". This fusion not only greatly reduces the false alarm rate caused by the dependence of a single technology, but also balances the monitoring cost through optimizing the sensor layout, finally provides accurate data support and reliable early warning for the safety management of the whole life cycle of the tunnel, effectively guarantees the structural stability and operation safety. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 A flowchart of a shield segment displacement monitoring method based on laser scanning and optical fiber sensing is provided for the first embodiment of the application.

[0065] Figure 2 A schematic diagram of the arrangement of the distributed optical fiber sensor in the first embodiment of the application; the small diagram in the figure is a schematic diagram of the tunnel from the top;

[0066] Figure 3 A structure schematic diagram of a shield segment displacement monitoring system based on laser scanning and optical fiber sensing is provided for the second embodiment of the application.

[0067] Figure 4 A detailed structure schematic diagram of the second embodiment of the application. DETAILED DESCRIPTION

[0068] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] Example 1

[0070] like Figure 1 As shown, Embodiment 1 of the present invention provides a method for monitoring the displacement of tunnel segments based on laser scanning and fiber optic sensing, comprising the following steps:

[0071] 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 .

[0072] Specifically, it is assumed that the strain measured by the distributed fiber optic sensor is... The circumferential strain can then be calculated using the orthogonal decomposition formula. Axial strain and radial strain This enables spatial reconstruction of strain components.

[0073] Specifically, the orthogonal decomposition formula is:

[0074] (1)

[0075] (2)

[0076] (3)

[0077] in, Indicates the angle between the optical fiber and the radial direction. This indicates the angle between the optical fiber and the axis.

[0078] Furthermore, this embodiment also includes a step of temperature calibration of the fiber optic strain data. The calibration method can be as follows: distributed stress-sensing fibers and temperature-compensating fibers are simultaneously laid on the tunnel lining segments. Both fibers are of the same type and material, are in the same temperature field, and the temperature-compensating fibers are arranged in the non-stressed area of ​​the segments. Subsequently, the two types of fiber optic data are simultaneously collected by distributed fiber optic sensors, wherein the stress-sensing fibers acquire the measured strain. Temperature-compensated optical fibers are used to acquire pure temperature strain, and the difference between the two is calculated to obtain temperature-corrected strain data after removing temperature errors. .

[0079] Specifically, this embodiment also includes a step of preprocessing the laser point cloud data. First, noise points are removed using Gaussian filtering. The Gaussian filtering formula is:

[0080] ; (4)

[0081] in, The filter radius is x, y, which represent the coordinates of the 3D laser scanning data projected onto a certain plane and are used to determine the relative position of the data points in the filter template. This represents the weight value of the Gaussian filter at the coordinates, and information from surrounding points is fused based on the weights to remove noise.

[0082] Then, in the point cloud matching stage, the ICP algorithm is used to optimize the transformation matrix T to complete the point cloud registration, where the registration error is controlled within 0.03mm.

[0083] Step 1 also includes the following steps:

[0084] 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;

[0085] Based on the key risk monitoring areas, determine the laying path of the sensing optical fiber in the distributed optical fiber sensor. 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 Z-shaped laying method.

[0086] 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.

[0087] 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 seams between adjacent segment rings and the joint seams of each segment within the same segment ring, and the stress concentration edges and corners 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.

[0088] 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. At the same time, 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.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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.

[0093] 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.

[0094] The spatial coordinates corresponding to the first optical 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.

[0095] The first optical fiber displacement data include radial, circumferential and axial displacement data, i.e., fiber radial displacement , fiber circumferential displacement , and fiber axial displacement The first optical 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, and the specific calculation formula is as follows:

[0096] ; (4)

[0097] 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 diameters), is the radial strain-displacement coefficient associated with the segment thickness, is the circumferential strain-radial 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), 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.

[0098] 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 provides displacement reference in a unified coordinate system for subsequent time alignment and residual error calculation of the laser scanning displacement.

[0099] 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×cosθ0, Z0=R×sinθ0. 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×Δθ (Δθ is the circumferential angle increment) is determined Δθ, and the axial distance ΔX of the circumferential segment end point 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 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.

[0100] Step 4: Interpolating the first laser scanning displacement by a spline interpolation function to generate a continuous sequence of second laser scanning displacement.

[0101] In step 4, a continuous sequence of first laser scanning displacement is generated by a cubic spline interpolation function, and the interpolation function is:

[0102] ; (5)

[0103] 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:

[0104] ; (6)

[0105] ; (7)

[0106] wherein, represents the actual displacement value collected by the three-dimensional laser scanner 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.

[0107] Step 5: Aligning the time of the second optical fiber displacement data and the second laser scanning displacement by solving the optimal path through dynamic programming.

[0108] In this embodiment, the time alignment of the laser scanning displacement and the fiber displacement data is realized by using the method of dynamic interpolation combined with elastic regularization.

[0109] Specifically, the specific method of step 5 is:

[0110] (1) Calculate the time distance, and the calculation formula is:

[0111]

[0112] The i-th value in the time sequence corresponding to the second laser scanning displacement is represented by The j-th value in the time sequence corresponding to the second fiber displacement data is represented by 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 is represented by 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 is represented by 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 is represented by 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 is represented by

[0113] (2) Then, the optimal path is solved by dynamic programming to align the strain sudden increase time corresponding to the second fiber displacement data with the displacement mutation time in the second laser scanning displacement, and to solve the asynchronous problem of "discrete-continuous" data.

[0114] 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.

[0115] 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 determined 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.

[0116] Specifically, in step 6, the residual error calculation formula of the second laser scanning displacement and the second fiber displacement data is:

[0117] ​​ ; (9)

[0118] e represents a residual, which is an index for quantifying the difference between the distributed optical fiber inversion displacement and the three-dimensional laser scanning measured displacement, represents the second optical 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 measured points, and e represents a residual;

[0119] The formula for correcting the second optical fiber displacement data by the correction coefficient is:

[0120] ; (10)

[0121] wherein, represents the third optical fiber displacement data corresponding to the i-th point after correction, represents the correction coefficient.

[0122] Specifically, in the embodiment, the correction coefficient is dynamically corrected, and the expression is:

[0123] ; (11)

[0124] 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.

[0125] Suppose that the circumferential displacement in the second optical fiber displacement data corresponding to a certain measured point 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 increase of the difference of the point, the correction coefficient =1.1 is calculated by the above formula, and then the corrected circumferential displacement is =1.1×2.0=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, finally providing more reliable quantitative basis for segment deformation analysis and early warning.

[0126] Further, the shield segment displacement monitoring method based on laser scanning and optical fiber sensing of the embodiment further includes a step of performing deformation risk early warning, which specifically includes the following steps:

[0127] Step 7: Obtain the three-dimensional displacement initial threshold value and the current scene coefficient, and calculate the three-dimensional displacement actual threshold value under the current scene.

[0128] In the step 7, the calculation method of the three-dimensional displacement actual threshold value is:

[0129] During construction, the scene coefficient takes a value of =1.3, and the calculation formulae of the normal displacement threshold value , the radial displacement threshold value and the tangential displacement threshold value are:

[0130] ; (12)

[0131] ; (13)

[0132] ; (14)

[0133] , and respectively represent the initial normal displacement threshold value, the initial radial displacement threshold value and the initial tangential displacement threshold value.

[0134] During operation, the scene coefficient takes a value of =1.0, and an added threshold value is added in the operation period to cope with the impact of train load, and specifically, the calculation formulae of the normal displacement threshold value , the radial displacement threshold value and the tangential displacement threshold value are:

[0135] ; (15)

[0136] ; (16)

[0137] ; (17)

[0138] In the embodiment, the initial normal displacement threshold value is set to 3 mm, the initial radial displacement threshold value is set to 3 mm, the initial tangential displacement threshold value is set to 2 mm, and the added threshold value is set to =0.3 mm.

[0139] Step 8: Obtain the displacement data after data fusion at the current monitoring point, i.e., the displacement data of the third optical fiber. Calculate the displacement increment in each direction and determine whether it is greater than or equal to the warning displacement threshold for 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, issue a level one warning. The warning displacement threshold is less than the actual threshold. In this embodiment, the warning displacement threshold is U' = 0.8U, where U represents the actual three-dimensional displacement threshold.

[0140] In this embodiment, the early warning triggering mechanism uses a two-factor verification of "absolute value + rate of change". Assume the current normal displacement of the monitoring point is... The initial reference displacement in this direction is Then the displacement increment ,when At that time, the rate of change calculation is initiated: time interval Displacement rate within ,like If this occurs, the system enters an alert activation state. At this time, the curvature is inverted by fusing data. ( s (for the arc length of the tunnel segment), when ( When the critical curvature (determined by segment strength calculation) is reached, a Level 1 warning is triggered.

[0141] 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 At that time, a comprehensive risk index is calculated, and the early warning level is upgraded based on the comprehensive risk index.

[0142] Specifically, to quantify the development trend of risk, a deformation prediction model is constructed based on elasticity mechanics: assuming that the displacement changes with time according to… , For rate coefficient, The acceleration coefficients are obtained by fitting using the least squares method. a, b By finding a value that minimizes the residual, we can obtain the displacement-time curve and calculate the estimated remaining time to reach the actual displacement threshold based on the curve. .

[0143] Specifically, in step 9, the formula for calculating the comprehensive risk index is as follows:

[0144] (18)

[0145] (19)

[0146] ; (20)

[0147] 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 circumference of the tunnel), represents the normal displacement threshold value, represents the circumferential strain, represents the maximum allowable value of the circumferential strain.

[0148] Step 10: generating an early warning report, the early warning report including the absolute value of displacement, displacement rate, predicted remaining time and comprehensive risk index.

[0149] Embodiment two

[0150] As shown in Figures 3-4 , the embodiment two 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 key parts of the tunnel segment; the data fusion analysis module is used to realize the shield segment displacement monitoring method of the embodiment one.

[0151] Specifically, as shown in Figure 4 , the distributed optical fiber sensing subsystem includes a distributed optical fiber sensor and a light source and demodulation device, in addition, it also includes an optical 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.

[0152] Specifically, as shown in Figure 4 , the hardware composition of the data fusion analysis module includes a data acquisition card and a high-performance server, 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.

[0153] Further, the shield segment displacement monitoring system based on laser scanning and optical fiber sensing of the embodiment further comprises a pre-warning issuing subsystem, the pre-warning issuing subsystem is used for pre-warning deformation risk according to the displacement data after data fusion, and the method for pre-warning deformation risk by the pre-warning issuing subsystem is:

[0154] (1) obtaining 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;

[0155] (2) obtaining 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 yes, first-level pre-warning is performed;

[0156] (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;

[0157] (4) generating a pre-warning report, the pre-warning report comprising an absolute value of displacement, a displacement rate, a predicted remaining time, and a comprehensive risk index.

[0158] Further, the embodiment further comprises a displacement monitoring database, the displacement monitoring database is used for storing historical fusion data; the pre-warning issuing subsystem comprises a communication module and an audible and visual alarm device, the communication module is used for transmitting a pre-warning signal, and the audible and visual alarm device is used for realizing local alarm.

[0159] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but 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 that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to 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 shield segment displacement monitoring method based on laser scanning and fiber sensing, characterized in that, The method comprises the following steps: Step 1: Obtain laser point cloud data and fiber strain data respectively through the three-dimensional laser scanner and the distributed optical fiber sensor arranged in the tunnel, wherein the fiber strain data includes hoop strain , axial strain , and 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, wherein the first laser scanning displacement comprises laser radial displacement, laser circumferential displacement and laser axial displacement; Step 3: calculating first fiber displacement data according to the fiber strain data, wherein the first fiber displacement data comprises fiber radial displacement, fiber circumferential displacement and fiber axial displacement, and then mapping the spatial coordinates corresponding to the first fiber displacement data to a global rectangular coordinate system of the tunnel, and then forming second fiber displacement data according to the spatial coordinates in the global rectangular coordinate system and the corresponding first fiber displacement data; Step 4: interpolating the first laser scanning displacement by a spline interpolation function to generate continuous sequence 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 by dynamic programming; Step 6: calculating the residual error of the second laser scanning displacement and the second fiber displacement data, and judging whether the residual error is greater than a threshold value, if yes, modifying the second fiber displacement data by 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; The method further comprises a step of deformation risk early warning, which comprises the following steps: Step 7: obtaining a three-dimensional displacement initial threshold value and a current scene coefficient, and calculating a three-dimensional displacement actual threshold value in the current scene; Step 8: calculating displacement increments in each direction according to the third fiber displacement data, and judging whether the displacement increments in each direction are greater than or equal to a corresponding early warning displacement threshold value, if yes, calculating a displacement rate in the corresponding direction and judging whether the displacement rate is greater than or equal to a displacement rate threshold value, if yes, calculating a deformation curvature in the corresponding direction, and judging whether the deformation curvature is greater than or equal to a critical curvature, if yes, performing a first-level early warning; Step 9: quadratic curve fitting is performed on the trend of displacement change over time, and the expected remaining time to reach the actual threshold of displacement is determined by the fitted curve , if , calculate the comprehensive risk index, and upgrade the warning level according to the comprehensive risk index; Step 10: generating an early warning report, wherein the early warning report comprises displacement absolute value, displacement rate, predicted remaining time and comprehensive risk index.

2. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, The step 1 further comprises the following steps: In the initial stage of shield tunnel segment assembly, a three-dimensional laser scanner is used for early global scanning, the laser point cloud data is associated with a global coordinate system of the tunnel, and a key risk monitoring area is determined; According to the key risk monitoring area, a laying path of the sensing fiber is determined, and the laying density satisfies: joint splicing position in the key risk monitoring area > longitudinal joint and main reinforcement position in the key risk monitoring area > joint splicing position in a non-key risk monitoring area > longitudinal joint and main reinforcement position in the non-key risk monitoring area, and an arch-shaped laying mode is adopted.

3. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, In the step 3, the calculation formula of the first fiber displacement data is: ； wherein, , , w respectively represent fiber radial displacement, fiber hoop displacement and fiber axial displacement in the first fiber displacement data, , , respectively represent radial strain, hoop strain and axial strain in the fiber strain data, represents a radial strain-displacement coefficient, represents a hoop strain-radial displacement coefficient, represents a hoop strain-hoop displacement coefficient, represents an axial strain-axial displacement coefficient.

4. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, In step 4, the first laser scanning displacement is interpolated by a cubic spline interpolation function The first laser scanning displacement is interpolated to generate a continuous sequence of second laser scanning displacements, wherein 、 、 、 is an interpolation coefficient, and t represents time, represents an interpolation function; the boundary conditions are satisfied when generating. ； ； wherein, represents the actual displacement value collected by the three-dimensional laser scanner at the discrete time represents the actual displacement value collected by the three-dimensional laser scanner at the discrete time represents the slope at the scanning point; The specific method of the step 5 is to calculate the time distance, and the calculation formula is: ； wherein represents the i-th value in the time series corresponding to the second laser scan displacement, represents the j-th value in the time series corresponding to the second fiber displacement data, represents the time distance between the i-th value in the time series corresponding to the second laser scan displacement and the j-th value in the time series corresponding to the second fiber displacement data; represents the time distance between the i-1-th value in the time series corresponding to the second laser scan displacement and the j-th value in the time series corresponding to the second fiber displacement data; represents the time distance between the i-th value in the time series corresponding to the second laser scan displacement and the j-1-th value in the time series corresponding to the second fiber displacement data; represents the time distance between the i-1-th value in the time series corresponding to the second laser scan displacement and the j-1-th value in the time series corresponding to the second fiber displacement data; Then, the time of the second fiber displacement data and the second laser scanning displacement is aligned by solving the optimal path by dynamic programming.

5. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, In the step 6, the residual error calculation formula of the second laser scanning displacement and the second fiber displacement data is: ； wherein, represents the second optical 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 modifying the second 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 a correction coefficient.

6. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, In the step 9, the calculation formula of the comprehensive risk index is: ； ； ； wherein I represents a comprehensive risk index, represents a normal opening amount of the segment joint, represents a circumferential strain concentration coefficient, represents a radial displacement increment of the segment 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.

7. The shield segment displacement monitoring method based on laser scanning and fiber sensing according to claim 1, characterized in that, In step 7, the three-dimensional displacement actual threshold value includes a normal displacement threshold value , a radial misalignment threshold value and a tangential misalignment threshold value, which are calculated as follows: During construction, the scene coefficient takes the value of = 1.3, the calculation formula of the normal displacement threshold , the radial displacement threshold and the tangential displacement threshold is: ； ； ； , and respectively represent initial normal displacement threshold, initial radial dislocation threshold, initial tangential dislocation threshold; The operating period coefficient is valued as = 1.0, the normal displacement threshold , the radial displacement threshold and the tangential displacement threshold The calculation formula is: ； ； ； In the step 9, the quadratic curve adopted for fitting is: ； Wherein, a, b are fitting coefficients, the least square method is used in fitting.

8. A shield segment displacement monitoring system based on laser scanning and fiber sensing, characterized in that, Comprise: The three-dimensional laser scanning subsystem, the distributed optical fiber sensing subsystem, the data fusion analysis module, the three-dimensional laser scanning subsystem is used to obtain the point cloud data of the tunnel segment surface, the distributed optical fiber sensing subsystem is used to obtain the strain distribution of the key part of the tunnel segment;The data fusion analysis module is used to realize the method for monitoring the displacement of the shield segment based on laser scanning and optical fiber sensing according to any one of claims 1~7.

9. The shield segment displacement monitoring system based on laser scanning and fiber sensing according to claim 8, characterized in that, Also include early warning release subsystem, the early warning release subsystem is used to carry out deformation risk early warning according to the displacement data after data fusion, the method for early warning of the early warning release subsystem is: Obtain the three-dimensional displacement initial threshold value and the current scene coefficient, calculate the three-dimensional displacement actual threshold value under the current scene; Obtain the displacement data after data fusion of the current monitoring point, calculate the displacement increment in each direction, and judge whether it is greater than or equal to the actual displacement threshold value, if yes, calculate the displacement rate and judge whether it is greater than or equal to the displacement rate threshold value, if yes, calculate the deformation curvature, and judge whether the deformation curvature is greater than or equal to the critical curvature, if greater, then carry out first level early warning; A quadratic curve fitting is performed on the displacement change trend over time, and the expected remaining time to reach the actual threshold of displacement is determined through the fitting curve , if , calculate the comprehensive risk index, and upgrade the warning level according to the comprehensive risk index; Generate early warning report, the early warning report includes displacement absolute value, displacement rate, predicted remaining time, comprehensive risk index.

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