Electric power engineering drainage box culvert monitoring system, construction method and monitoring method

Abstract

The invention relates to the technical field of engineering structure health monitoring, in particular to an electric power engineering drainage box culvert monitoring system, a construction method and a monitoring method. The monitoring system comprises a monitoring element and a data processing unit; the monitoring element comprises a strain sensor and a temperature sensor which are arranged on the inner side of a reinforcement cage of the drainage box culvert; the static leveling instrument is arranged on the concrete surface of the drainage box culvert; the single-axis clinometers are arranged on the central axis of the top plate and the side wall of the drainage box culvert; the flow velocity sensor is fixed on the internal section of the drainage box culvert through a bracket; and the strain sensor, the temperature sensor, the static leveling instrument, the single-axis clinometer and the flow velocity sensor are all connected with the data processing unit. According to the system, the technical problems of discontinuous monitoring, incomplete parameters, weak data association and the like in long-term health monitoring of the large drainage box culvert are solved, and real-time and accurate evaluation and early warning of the safety state of the box culvert are realized.

Description

Technical Field

[0001] This invention relates to the field of engineering structural health monitoring technology, and in particular to a monitoring system, construction method and monitoring method for drainage box culverts in power engineering. Background Technology

[0002] Large drainage box culverts are cast-in-place reinforced concrete underground structures with large cross-sectional dimensions and long extension distances, primarily used for discharging rainwater and sewage or serving as conduits for cables and other facilities. They are typically constructed by splicing together multiple precast or cast-in-place box culvert segments, with expansion joints between segments to accommodate temperature changes and uneven settlement. Due to long-term burial in complex geological environments and the combined effects of overburden loads, surface live loads, internal water erosion, and temperature variations, box culvert structures are prone to uneven settlement, localized deformation, and concrete cracking, directly impacting their drainage function and structural safety. Therefore, real-time and accurate monitoring of deformation, internal forces, and environmental loads throughout the entire lifecycle of the box culvert is crucial.

[0003] Fiber Bragg grating (FBG) sensing technology has been applied to the health monitoring of underground structures due to its advantages such as resistance to electromagnetic interference, corrosion resistance, ease of networking, and ability to achieve quasi-distributed measurements. Existing technology discloses a comprehensive utility tunnel health monitoring system based on fiber Bragg gratings, including a distributed multi-sensor synchronous acquisition device and a host computer. Within the utility tunnel, fiber Bragg grating strain sensors are deployed for monitoring cracks in concrete pipe tunnel joints, fiber Bragg grating hydrostatic levels are deployed for settlement monitoring, fiber Bragg grating displacement sensors are deployed for horizontal displacement monitoring, and fiber Bragg grating strain sensors are deployed for monitoring cracks in pipe flanges. All these sensors are connected to the acquisition device, and the data is ultimately sent to the host computer for processing and display. In this system, for monitoring cracks in pipe tunnel joints, low-temperature sensitive fiber Bragg grating strain sensors are arranged across the joints, with eight sensors typically placed at the four corners and midpoints of the four sides of a rectangular cross-section for each monitoring section; for settlement monitoring, fiber Bragg grating hydrostatic levels are spaced along the pipe tunnel's orientation.

[0004] Applying the aforementioned existing technologies to the long-term monitoring of large drainage culverts in power engineering presents several problems: First, the systems primarily monitor the joints, settlement, and horizontal displacement of the integrated utility tunnel, with relatively discrete sensor deployment schemes. For example, only a limited number of point strain sensors are placed on each cross-section. For large drainage culverts that can reach several kilometers in length and have dynamic water flow loads inside, this discrete point monitoring is insufficient to comprehensively and continuously capture the strain distribution patterns of the culvert's top slab, sidewalls, and bottom slab along the longitudinal and circumferential directions. In particular, it cannot accurately acquire continuous deformation characteristics such as the convergence deformation of the culvert cross-section caused by uneven settlement or water scouring. Second, the existing technologies lack direct monitoring of key environmental loads inside the culvert. The core function of a drainage culvert is drainage, and changes in internal water flow velocity directly reflect the flow capacity and are the main cause of structural scouring and additional dynamic loads. However, the aforementioned systems do not integrate flow velocity monitoring methods, resulting in a lack of data support for assessing the impact of water flow loads on the structure. Furthermore, the monitoring parameters of the system are relatively independent and fail to deeply integrate multi-source information such as strain, settlement, tilt and water flow, making it difficult to achieve overall working status assessment and early warning of box culverts based on multi-parameter coupled analysis. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a monitoring system, construction method, and monitoring method for drainage box culverts in power engineering. This system enables high-density, continuous, and synchronous monitoring of multiple parameters, including strain, temperature, settlement, tilt, and internal flow velocity, within the box culvert structure. Through effective data fusion and processing, it accurately eliminates temperature interference and deeply analyzes the interaction between structural deformation and water flow conditions. This solves the technical problems of discontinuous monitoring, incomplete parameters, and weak data correlation in the long-term health monitoring of large drainage box culverts, enabling real-time and accurate assessment and early warning of the box culvert's safety status.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A monitoring system for large drainage culverts in power engineering includes monitoring elements and a data processing unit. The monitoring elements include: strain sensors and temperature sensors, installed inside the reinforcing cage of the drainage culvert to monitor strain and temperature data; a hydrostatic level installed on the concrete surface of the drainage culvert to monitor settlement; a single-axis inclinometer installed along the central axis of the top slab and side walls of the drainage culvert to monitor the tilt angle; and a flow velocity sensor fixed to the internal cross-section of the drainage culvert by a bracket to monitor water flow velocity. The strain sensor, temperature sensor, hydrostatic level, single-axis inclinometer, and flow velocity sensor are all connected to the data processing unit.

[0007] This invention also provides a construction method for a monitoring system for large drainage box culverts in power engineering, comprising: installing strain sensors and temperature sensors with protective sleeves on the completed box culvert steel cage, and fixing galvanized steel wires at expansion joints; after the box culvert concrete is poured and formed, installing a static level, a single-axis inclinometer, and a flow velocity sensor fixed by a bracket on the concrete surface; converging the leads of each sensor to the interface of the integrated device and marking them, welding them with jumpers, and protecting the welded joints; inserting the sensor leads into protective pipes and leading them to the ground surface, and connecting them to a data processing unit.

[0008] This invention also provides a monitoring method for a large drainage box culvert monitoring system in power engineering, comprising: acquiring signals through strain sensors and temperature sensors installed inside the reinforcing bars, and performing temperature compensation based on the temperature signals to obtain the true strain; calculating the lateral deformation of the box culvert through the true strain acquired by symmetrically installed strain sensors, and calculating the axial deformation of the box culvert through the true strain acquired by strain sensors installed along the length direction; acquiring liquid level signals through a hydrostatic level installed on the surface of the box culvert, and calculating the settlement difference and local settlement of the box culvert based on the liquid level difference; acquiring tilt angle signals through a single-axis inclinometer installed on the central axis and side walls of the box culvert top slab; acquiring water flow velocity signals through a flow velocity sensor installed on the internal cross-section of the box culvert; comparing the calculated deformation data, settlement data, tilt angle data, and flow velocity data with preset thresholds, and issuing an early warning when the data reaches or exceeds the threshold.

[0009] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: This invention provides a multi-parameter collaborative monitoring system for large drainage culverts. The system includes monitoring elements covering multiple dimensions such as structural internal forces, temperature, geometric deformation, and environmental loads. Strain sensors are deployed inside the reinforcing cage of the drainage culvert, thus forming an integral part of the structure after concrete pouring. This allows for continuous or quasi-distributed deployment along the direction of the reinforcing bars, rather than just a few discrete points on the cross-section. This enables continuous sensing of the longitudinal and circumferential strain distribution patterns of the culvert's top, sidewalls, and bottom slabs. This integrated deployment with the structure allows for sensitive capture of continuous deformation characteristics such as overall bending deformation or cross-sectional convergence deformation caused by uneven settlement or water scouring, solving the problems of insufficient coverage and difficulty in reflecting continuous deformation patterns in point-based monitoring. Flow velocity sensors are fixed to the internal cross-section of the drainage culvert using brackets. By monitoring the water flow velocity in real time, key parameters reflecting the culvert's flow capacity can be directly obtained, providing raw data support for assessing the scouring effect and additional dynamic loads caused by water flow on the structure. This addresses the shortcomings of existing monitoring schemes that focus solely on structural deformation while neglecting the main service environment loads, enabling simultaneous monitoring of internal structural forces and external hydraulic loads. Furthermore, five types of heterogeneous data—strain, temperature, settlement, tilt, and flow velocity—are collected simultaneously and aggregated on a single processing platform, creating conditions for subsequent data correlation analysis and coupled modeling. For example, combining settlement and tilt data to analyze deformation patterns, and correlating flow velocity and strain data to assess load response, allows for comprehensive evaluation and early warning of the overall working status of the box culvert based on multi-parameter coupling, breaking the limitations of isolated parameter processing in traditional monitoring.

[0010] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0012] Figure 1 This is a schematic diagram of the overall structure of a large drainage box culvert deformation and stress monitoring system during long-term use; Figure 2 This is a side view of the box culvert; Figure 3 Cross-sectional view of the fiber optic grating sensor layout in the box culvert; Figure 4 Schematic diagram of strain fiber Bragg grating sensor and temperature fiber Bragg grating sensor; Figure 5 This is a partial top view of the box culvert; Figure 6 This is a cross-sectional view of a box culvert. In the diagram: 1. Drainage culvert; 2. Strain sensor; 2a. Length direction; 2b. Perimeter direction; 3. Temperature sensor; 3a. Length direction; 3b. Vertical direction; 4. Grating point; 5. Galvanized steel wire; 6. Static level; 6a. Expansion joint settlement differential static level; 6b. Vertical settlement static level; 7. Single-axis inclinometer; 7a. Top plate longitudinal fiber optic grating single-axis inclinometer; 7b. Side wall transverse fiber optic grating single-axis inclinometer; 8. Sensitive axis; 9. Bolt; 10. Flow velocity sensor; 11. Bracket; 12. Protective sleeve; 13. Integrated device; 14. Tag; 15. Jumper wire; 16. Heat shrink tubing and seamless metal tubing; 17. PVC pipe; 18. Sensor demodulation system; 19. Raw data optimization system; 20. On-site intelligent monitoring system; 21. Monitoring data analysis and remote early warning platform; 22. 5G network; 23. Engineer's electronic receiving equipment; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms include and / or encompass are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0013] Example 1 This embodiment introduces FBG technology into the field of fiber optic grating intelligent monitoring technology for complex geological conditions and long-distance large drainage box culverts. It fully leverages the synergistic deformation characteristics of fiber optic grating sensors and box culvert structures to enhance the accuracy of monitoring data. Fiber optic grating strain and temperature sensors are deployed inside the box culvert's reinforcing steel, while static levels, fiber optic grating single-axis inclinometers, and fiber optic grating flowmeters are deployed on the reinforced concrete surface of the box culvert. This improves the combined monitoring system's ability to monitor the overall deformation of long-distance box culverts. Simultaneously, the data collected by the sensors is combined with the raw data optimization system for noise reduction and smoothing. The on-site intelligent monitoring system then calculates the box culvert deformation, settlement difference, and water flow velocity using formulas, and transmits the results to the monitoring data analysis and remote early warning platform, achieving real-time monitoring of box culvert deformation and stress.

[0014] A monitoring system for large drainage culverts in power engineering includes monitoring elements and a data processing unit. The monitoring elements include: strain sensors and temperature sensors, installed inside the reinforcing cage of the drainage culvert to monitor strain and temperature data; a hydrostatic level installed on the concrete surface of the drainage culvert to monitor settlement; a single-axis inclinometer installed along the central axis of the top slab and side walls of the drainage culvert to monitor the tilt angle; and a flow velocity sensor fixed to the internal cross-section of the drainage culvert by a bracket to monitor water flow velocity. The strain sensor, temperature sensor, hydrostatic level, single-axis inclinometer, and flow velocity sensor are all connected to the data processing unit.

[0015] The strain sensors in this system are deployed inside the reinforcing cage of the drainage culvert, providing continuous monitoring coverage along the longitudinal and circumferential directions, rather than being discretely distributed. Combined with single-axis inclinometers deployed along the central axis of the top slab and side walls, and static levels on the concrete surface, this system collaboratively captures the strain distribution patterns of the culvert's top, side walls, and bottom slabs, accurately acquiring continuous deformation characteristics such as cross-sectional convergence deformation caused by uneven settlement or water erosion. Compared to the discrete monitoring schemes of integrated utility tunnels, this system, through its comprehensive sensor deployment and multi-element collaboration, can meet the continuous monitoring needs of large drainage culverts several kilometers long.

[0016] This system uses a flow velocity sensor fixed to the internal cross-section of the drainage culvert via a bracket to monitor the water flow velocity. It can acquire real-time data on changes in internal water flow velocity, providing direct evidence for assessing flow capacity and key data support for analyzing the additional dynamic loads of water flow scouring on the structure. This makes up for the lack of direct monitoring of water flow loads in existing technologies.

[0017] In this system, strain sensors, temperature sensors, hydrostatic levels, single-axis inclinometers, and flow velocity sensors are all connected to the same data processing unit, forming a unified data acquisition and analysis system. The data processing unit enables centralized integration and coordinated analysis, providing a hardware foundation for multi-parameter coupled analysis. By combining multi-source information such as strain, settlement, tilt, and water flow, the system completes a comprehensive assessment and early warning of the overall working status of the box culvert, solving the problem of independent parameters and difficulty in coordinated analysis in existing technologies.

[0018] The strain sensors include length-direction strain sensors symmetrically arranged on the longitudinal reinforcement of the top slab along the length of the box culvert, and perimeter-direction sensors arranged on the reinforcement of the top slab, bottom slab, and side walls along the perimeter of the box culvert cross-section. The data from the length-direction and perimeter-direction sensors can complement and verify each other, achieving coverage of the strain field of the box culvert structure from lines to surfaces, making the inversion of the overall deformation state of the structure based on strain data more accurate and reliable.

[0019] At the expansion joint between two adjacent box culvert sections, galvanized steel wires are installed that cross the reinforcing cages on both sides, and one sensing point of the length direction strain sensor is fixed to the surface of the galvanized steel wire.

[0020] Sensors used to monitor macroscopic structural strain are transformed into precision detection devices for millimeter-scale or even smaller displacements using galvanized steel wire. This method offers superior sensitivity and specificity compared to indirectly calculating differential settlement by comparing data from independent settlement measurement points on both sides of the culvert. It plays a crucial role in providing early warning of defects such as waterstop failure and structural misalignment caused by excessive differential settlement.

[0021] The temperature sensors include a length direction temperature sensor arranged in the direction of the longitudinal reinforcement of the top slab of the box culvert, and a vertical direction temperature sensor arranged in the direction of the vertical reinforcement of the side wall of the box culvert. The temperature sensors are covered with protective sleeves.

[0022] By deploying bidirectional equipment, more comprehensive structural temperature field information is obtained, rather than single-point temperature. Combined with the isolation effect of the protective sleeve, temperature compensation can more accurately eliminate false readings of strain sensors caused by temperature changes, thereby extracting the true structural mechanical strain and improving the accuracy and reliability of strain monitoring data.

[0023] The static level instruments include expansion joint settlement differential static level instruments arranged on both sides of the expansion joint of the box culvert, and single-section box culvert vertical settlement static level instruments arranged at intervals along the length of the top slab of a single box culvert section.

[0024] The expansion joint settlement differential hydrostatic level is set up on both sides of the expansion joint, connected to liquid tanks on both sides via a connecting pipe. The difference in liquid level between the two measuring points directly reflects the vertical differential settlement between adjacent box culvert sections. For a single-section box culvert, multiple measuring points are spaced along the length of the top slab. All measuring points are connected to a stable benchmark point via a connecting pipe. By comparing the liquid level differences between each measuring point and the benchmark point, the absolute settlement of each point inside the box culvert section can be calculated, allowing analysis of whether the settlement curve is flat or has local depressions.

[0025] The single-axis inclinometer includes a longitudinal inclinometer with its sensitive axis parallel to the length of the box culvert and installed on the central axis of the top plate, and a transverse inclinometer with its sensitive axis perpendicular to the length of the box culvert and symmetrically installed on the left and right side walls.

[0026] Longitudinal tiltmeters are primarily used to monitor changes in the longitudinal slope of box culverts, i.e., whether overall longitudinal tilting or bending has occurred. Transverse tiltmeters are mainly used to monitor whether the sidewalls of box culverts show an inward or outward overturning tendency. Combining tilt data with settlement and strain data can more completely reconstruct the spatial deformation morphology of the box culvert structure, determine whether the deformation is rigid body displacement or structural deflection, and provide more multi-dimensional information for analyzing the causes of defects.

[0027] The data processing unit includes a sensor demodulation system, a raw data optimization system, an on-site intelligent monitoring system, and a monitoring data analysis and remote early warning platform connected in sequence. The on-site intelligent monitoring system is used to calculate the deformation, settlement, and water flow impact force of the box culvert based on the processed data. The monitoring data analysis and remote early warning platform is used to compare the calculation results with the set thresholds and issue early warnings.

[0028] This architecture not only enables unified access and standardized processing of multi-source heterogeneous data, but also transforms raw physical quantity monitoring data into directly usable safety status indicators in engineering terms through professional computing models in the on-site intelligent monitoring system. Furthermore, it enables automatic risk identification and proactive push through the early warning platform, thereby elevating traditional data monitoring to status assessment and early warning, and enhancing the intelligence level and practical value of the monitoring system.

[0029] The following explanation is based on the accompanying drawings: like Figure 1 As shown, the drainage culvert 1 is a reinforced concrete structure. After pouring and curing, it is backfilled underground. Multiple sections of the culvert are spliced ​​together to form a long-distance underground drainage structure. Fiber grating strain sensors 2 and fiber grating temperature sensors 3 are installed on the inner side of the reinforcing steel of the drainage culvert 1 to monitor the strain and temperature changes of the drainage culvert 1 during use. A static level 6 is installed to monitor the settlement and settlement difference of the culvert. A fiber grating single-axis inclinometer 7 is installed to monitor the tilting deformation of the top plate and side walls of the culvert. A fiber grating flow velocity sensor 10 is installed to monitor the water flow velocity inside the culvert.

[0030] The fiber grating strain sensor 2 and fiber grating temperature sensor 3 are arranged inside the reinforcing steel to prevent damage to the sensors during concrete pouring. The hydrostatic level 6, fiber grating single-axis inclinometer 7 and fiber grating flow velocity sensor 10 are all arranged on the surface of the reinforced concrete of the drainage box culvert 1 after it is poured and formed.

[0031] like Figure 2 , Figure 3 , Figure 5As shown, the fiber optic strain sensor 2 is divided into a length direction 2a fiber optic strain sensor and a perimeter direction 2b fiber optic strain sensor according to its deployment path. The fiber optic strain sensor 2 should ensure that the grating point 4 is in close contact with the surface of the reinforcing steel to ensure coordinated deformation. The fiber optic temperature sensor 3 is divided into a length direction 3a fiber optic temperature sensor and a vertical direction 3b fiber optic temperature sensor according to its deployment path. The hydrostatic level 6 is divided into a hydrostatic level 6a for the settlement difference of the expansion joint between multiple box culverts and a hydrostatic level 6b for the vertical settlement of a single box culvert according to the different deformations measured. The fiber optic single-axis tiltmeter 7 is divided into a longitudinal fiber optic single-axis tiltmeter 7a for the top plate and a transverse fiber optic single-axis tiltmeter 7b for the side wall according to its deployment position.

[0032] Two fiber optic strain sensors 2a are installed along the longitudinal reinforcement of the box culvert, ensuring that the two grating points 4 on the same cross section are symmetrically arranged to obtain the strain difference between the upper and lower halves of the box culvert top slab and calculate the vertical deformation of the top slab. A galvanized steel wire 5 is fixed along the longitudinal reinforcement at the expansion joint of the two box culvert sections. The galvanized steel wire 5 is fixed to the box culvert reinforcement cage on both sides with the expansion joint as the axis of symmetry. Its length should be greater than 2m, ensuring it is horizontal and has a certain preload. When the fiber optic strain sensor 2 passes through the expansion joint, it should ensure that a grating point 4 is fixed on the surface of the galvanized steel wire 5 to capture the strain of the galvanized steel wire 5 for calculating the settlement difference between the two box culvert sections. The galvanized steel wire 5 and the fiber optic strain sensor 2 fixed on its surface are protected by a plastic protective sleeve 12 (e.g., Figure 6 As shown, the 3a fiber optic temperature sensor along the length direction can be installed in a specific section of the box culvert under conditions where the hydrogeological conditions do not change significantly. In special circumstances, such as crossing a river or sudden changes in geological conditions, additional sensors can be installed depending on the project requirements. The 3a fiber optic temperature sensor along the length direction is protected by a plastic protective sleeve 12 to keep it relaxed and unaffected by box culvert deformation. It is installed on the longitudinal reinforcement of the box culvert top slab to obtain the temperature change along the length direction of the box culvert.

[0033] Two 2b fiber optic strain sensors are symmetrically arranged along the horizontal reinforcement of the top and bottom slabs and the vertical reinforcement of the side walls. After circling the box culvert once, they are arranged along the longitudinal reinforcement of the bottom slab to the next box culvert section. This process is repeated until the monitoring section is completed. The 3b fiber optic temperature sensor in the vertical direction can be selected for installation in a box culvert section under conditions where the hydrogeological conditions do not change significantly. In special circumstances, such as underpassing a river or sudden changes in geological conditions, additional sensors can be installed as needed. The vertical fiber optic temperature sensor is protected by a plastic protective sleeve 12 to keep it relaxed and unaffected by box culvert deformation. It is installed on the vertical reinforcement of the side walls to obtain the temperature changes in the vertical direction of the box culvert.

[0034] The static level 6 is selected as the reference point on the stable foundation outside the main structure of the drainage culvert 1, i.e., 10 meters away from the end of the culvert. The expansion joint settlement differential static level 6a is installed on each side of the top plate of the adjacent culvert expansion joint, 1 meter away from the expansion joint, and connected by a connecting pipe to form a monitoring unit. It should be ensured that there are measuring points on both sides of the expansion joint. When the uneven settlement of the foundation causes a height difference between the two culverts, the difference in liquid level in the level instrument is directly converted into the settlement difference at the expansion joint. The single-section culvert vertical settlement static level 6b is installed on the single-section culvert... Multiple hydrostatic leveling instruments are installed along the length of the culvert's top slab, with one measuring point every 5 meters, covering key areas such as the mid-span and supports. The measuring points within the same culvert maintain a consistent height. By measuring the liquid level difference between the measuring points, localized settlement within a single section of the culvert can be detected. The hydrostatic leveling instrument 6 is fixed to the reinforced concrete surface of the culvert using bolts 9. A silicone tube is used as a connecting pipe to connect the inlet and outlet of all hydrostatic leveling instruments. The connecting pipe is secured to the culvert's reinforcing steel bars every 50 cm using clips. The hydrostatic leveling instrument 6 and the connecting pipe must be fitted with a stainless steel protective shell to prevent damage from the backfill soil.

[0035] like Figure 3 , Figure 4 As shown, the longitudinal fiber optic grating single-axis inclinometer 7a on the top slab is continuously deployed along the central axis of the box culvert top slab. The inclinometer's sensitive axis 8 is parallel to the length direction of the box culvert. The inclinometer is fixed to the crossarm by bolts 9. One transverse fiber optic grating single-axis inclinometer 7b is deployed on each of the left and right walls of the box culvert. Each measuring point is 50cm from the top of the side wall, and the measuring points on the left and right side walls are horizontally aligned. The sensitive axis 8 is perpendicular to the length direction of the box culvert. The inclinometer 7b is fixed to the vertical reinforcement of the side wall by bolts 9. Both the longitudinal and transverse fiber optic grating single-axis inclinometers 7a on the top slab and the transverse fiber optic grating single-axis inclinometer 7a are deployed every 25m along the regular section of the box culvert. In case of [unspecified event], [further details are needed]. Additional inclinometers can be installed at river crossings, road sections, and on the outer sidewalls of box culvert bends, depending on the project requirements. At critical sections such as the ends and corners of the box culvert, a fiber optic grating top plate longitudinal single-axis inclinometer 7a needs to be installed within 1m of the end to obtain the inclination angle along the length of the box culvert. One inclinometer is installed on each side of the expansion joint to obtain the longitudinal misalignment inclination angle at the expansion joint. After installation, the single-axis inclinometer 7 needs to be calibrated to ensure that the sensor is initially tilt-free. The fiber optic grating single-axis inclinometer is covered with a stainless steel protective shell, and the exposed part of the fixing bolt 9 is covered with an anti-corrosion protective sleeve. The head of the bolt 9 is coated with an anti-rust agent to adapt to the underground humid and corrosive environment.

[0036] The fiber optic grating velocity sensor 10 is fixed by the bracket 11 at a depth of 2 / 3 above the vertical line of the box culvert cross-section, at a distance greater than 0.5m from the inner wall of the side wall and greater than 0.3m from the bottom of the box culvert. The fiber optic grating velocity sensor 10 is installed without intruding into the main flow zone. The sensitive axis 8 is aligned with the flow direction to accurately capture the main flow velocity of the cross-section. A measuring point is set every 25m in the conventional section of the box culvert cross-section. Additional measuring points are required at the box culvert inlet and outlet, river crossing section, uneven foundation section, and bend section to capture sudden changes in water flow velocity. A stainless steel protective shell is added to the outside of the fiber optic grating velocity sensor 10 to reduce sediment adhesion. The part where the fiber optic grating velocity sensor 10 is connected and fixed to the bracket 11 is covered with an anti-corrosion protective sleeve. The bolt head is coated with anti-rust agent to prevent damage caused by water erosion.

[0037] After the fiber optic strain sensor 2 and fiber optic temperature sensor 3 are installed, they need to be led out to the integrated device 13. After the sensors are marked with tags 14, they are fused with jumpers 15. The fused joint is protected with heat shrink tubing and seamless metal tubing 16 to facilitate long-term data acquisition. The lead-out section needs to be protected by PVC pipe 17 and buried in the soil to prevent external loads from damaging the sensors.

[0038] The jumper 15 is connected to the fiber Bragg grating sensor demodulation system 18. The hydrostatic level 6, the fiber Bragg grating single-axis inclinometer 7, and the fiber Bragg grating flow velocity sensor 10 are connected to the fiber Bragg grating sensor demodulation system 18 via the 5G network 22. The fiber Bragg grating sensor demodulation system 18 can automatically match the location of the monitored object according to the grating point signal, collect grating point data, and obtain strain, temperature, settlement, tilt angle, and flow velocity.

[0039] The fiber grating sensor demodulation system 18 is connected to the raw data optimization system 19, and transmits the initial fiber grating strain, temperature signal, sedimentation signal, tilt angle signal and flow velocity signal to the raw data optimization system for noise reduction and smoothing.

[0040] The raw data optimization system 19 is connected to the on-site intelligent monitoring system 20, and transmits the processed strain, temperature, settlement, tilt angle and flow velocity data to the on-site intelligent monitoring system. The on-site intelligent monitoring system processes the received strain, temperature, settlement, tilt angle and flow velocity signals to obtain the box culvert deformation, settlement data and water flow velocity, and displays them in the form of charts.

[0041] The on-site intelligent monitoring system 20 transmits the deformation and settlement data of the box culvert to the monitoring data analysis and remote early warning platform 21. The monitoring data analysis and remote early warning platform automatically stores and analyzes the deformation and settlement data of the box culvert and compares it with the built-in threshold. When the rate or magnitude of deformation or settlement of a certain section of the box culvert approaches the threshold, an early warning is issued. When the rate or magnitude of deformation or settlement of a certain section of the box culvert reaches the threshold, a warning is issued.

[0042] The monitoring data analysis and remote early warning platform 21 transmits early warning and warning signals to the project engineer's electronic receiving device 23 via the 5G network 22, facilitating the engineer's early intervention and prevention of risky segments.

[0043] In summary, this system symmetrically deploys fiber optic grating sensors on both sides of the top slab reinforcement of a large drainage box culvert to acquire the culvert strain; simultaneously, a section of steel strand is deployed with the expansion joint of the two box culvert sections as the axis of symmetry; temperature-compensated fiber optic gratings are deployed on several sections of the box culvert reinforcement cage to acquire the temperature changes of the box culvert concrete and eliminate the interference of temperature on strain; the fiber optic grating sensors are integrated into the fiber optic grating signal processor to calculate the axial deformation of the box culvert through axial strain; the lateral deformation of the box culvert is calculated through the strain acquired by the two symmetrically arranged fiber optic grating sensors; and the strain is measured at both ends of the expansion joint and the box culvert. A static level is installed on the top slab to obtain the differential settlement and local settlement of the box culvert; fiber optic grating single-axis inclinometers are installed on the central axis and side walls of the box culvert top slab to obtain the inclination angles in the longitudinal and length directions of the box culvert; fiber optic grating flow velocity sensors are installed on the cross-section of the box culvert to obtain the flow velocity of the water inside the box culvert; this invention applies advanced FBG technology to the field of monitoring large drainage box culverts, and uses strain and temperature fiber optic grating sensors to monitor the deformation and temperature changes of the box culvert in real time and accurately. By using multiple methods to monitor strain, flow velocity and settlement, it solves the current problem that it is difficult to meet the long-term and stable monitoring requirements for large drainage box culverts.

[0044] Compared to existing technologies, it has the following advantages: (1) For large reinforced concrete structures such as drainage box culverts, existing technologies mostly focus on monitoring a single or a few parameters, such as cracks, settlement, and displacement, and have not yet formed a joint monitoring capability for the stress, deformation, and seepage of the entire drainage box culvert section. This invention combines FBG technology with automated data acquisition, and by analyzing strain, temperature, settlement, inclination angle and flow velocity information, it realizes multi-dimensional monitoring of the stress, deformation and water flow state of the box culvert, making up for the shortcomings of traditional monitoring methods that are single and discrete.

[0045] (2) FBG technology is suitable for monitoring long-distance structures. A single sensor can be connected in series with dozens to hundreds of grating sensors to achieve quasi-distributed, multi-point synchronous real-time measurement along the longitudinal direction of the box culvert for hundreds or even thousands of meters. It fully covers key parts such as the top plate, side walls and expansion joints, and realizes continuous monitoring of structural deformation, internal force distribution and temperature changes. It fundamentally solves the technical problems of low monitoring density, limited coverage and difficulty in capturing the overall response law of long-distance structures by traditional means.

[0046] (3) Compared with traditional monitoring methods, which are difficult to continuously and effectively obtain the internal response of the structure after the box culvert is backfilled and buried in the soil, the FBG technology adopted in this invention allows the sensor to be directly tied to the steel cage and cast integrally with the box culvert concrete, becoming part of the structure. During the backfilling and long-term operation phases, it can continuously and stably sense the strain and temperature changes inside the box culvert, overcoming the problems of traditional point sensors or external measuring equipment being inaccessible after backfilling, easily affected by environmental interference, or having monitoring interruptions. In addition, casting the fiber optic grating sensor integrally with the box culvert concrete can ensure the survival rate of the sensor under backfill soil pressure, groundwater erosion, water flow scouring, and long-term operation. At the same time, through multi-layer composite protection and active protection of key parts of the fiber optic grating sensor, it effectively resists the damage to the sensor caused by the load during construction steps such as concrete pouring and box culvert backfilling, ensuring the structural integrity and functional stability of the fiber optic grating sensor throughout the construction process and long-term operation, overcoming the technical problem of low survival rate of traditional deployment methods.

[0047] (4) By combining wavelet denoising, temperature compensation, and strain decoupling algorithms, the system effectively filters out complex on-site noise and extracts the true structural response. The system incorporates calculation models related to box culvert deformation, settlement data, and water flow load, deeply integrating flow velocity data with strain and settlement data. When monitoring data is abnormal, the system can not only provide remote early warnings but also identify the source of the anomaly through cross-analysis of various data.

[0048] Example 2 This embodiment provides a construction method for a monitoring system for large drainage box culverts in power engineering. It applies high-precision, digital FBG technology to large drainage box culverts, tightly binding fiber optic grating sensors to the main reinforcing bars of the culvert's main structure, allowing them to deform in tandem with the concrete structure. A static level, a fiber optic grating single-axis inclinometer, and a fiber optic grating flow velocity sensor are fixed to the concrete surface of the box culvert. During the backfilling of the foundation pit and long-term operation phases, it can continuously monitor the long-term strain and deformation of the box culvert under the combined action of earth pressure, internal water pressure, and ground live load, solving the current problem of difficulty in achieving long-term, stable monitoring.

[0049] A construction method for the monitoring system of large drainage box culverts in power engineering, comprising: Strain sensors and temperature sensors with protective sleeves are installed on the completed box culvert steel cage, and galvanized steel wires are fixed at the expansion joints. After the box culvert concrete is poured and formed, a static level, a single-axis inclinometer, and a flow velocity sensor fixed by a bracket are installed on the concrete surface. The leads of each sensor are connected to the interface of the integrated device and marked, then fused with jumpers, and the fused joints are protected. The sensor lead-out section is inserted into a protective pipe and led to the ground surface, where it is connected to the data processing unit.

[0050] Specifically, the following steps are included: (1) Determine the monitoring section range and select a drainage box culvert 1 in which the side plate reinforcement cage has been tied; (2) After the steel cage is made, the strain sensor 2 is installed and the grating point 4 is symmetrically positioned and fixed with cable ties. The galvanized steel wire 5 at the expansion joint needs to be fixed before the two sections of the steel cage are joined together. Then fix the grating point 4. The strain sensor 2 and the temperature sensor 3 are both covered with plastic protective sleeves 12. (3) After the concrete of the box culvert is poured, a support 11, a static level 6, a fiber optic grating single-axis inclinometer 7 and a fiber optic grating flow velocity sensor 10 are installed on the concrete surface. All sensors are covered with stainless steel protective shells, and the exposed parts of the fixed support 11 and bolts 9 are covered with anti-corrosion protective sleeves.

[0051] (4) All sensor leads are connected to the interface of the box culvert side wall integration device 13, and the types are distinguished by the label 14. They are then fused with the jumper wire 15. (5) Heat shrink tubing and seamless metal tubing are fitted at the weld joint; (6) A PVC pipe 17 is installed in the lead-out section and extends along the outside of the steel cage to the pre-set system installation pit on the ground surface. The joint between the PVC pipe 17 and the drainage box culvert 1 is sealed with waterproof glue. (7) After the concrete pouring, curing and backfilling of the box culvert are completed, the hardware is connected in the surface system installation pit; (8) Long-term monitoring and threshold warning of large drainage box culverts are achieved through on-site intelligent monitoring system 20 and remote early warning platform 21.

[0052] This embodiment provides a standardized and operable construction process to ensure that the monitoring sensors can be correctly and securely installed in complex construction site environments, and that their signal transmission lines are effectively protected. This method clarifies the interface between sensor installation and the main structure construction process, avoiding mutual interference and guaranteeing the survival rate and long-term reliability of the monitoring system itself—a prerequisite for achieving long-term stable monitoring.

[0053] Example 3 A monitoring method for a large drainage culvert monitoring system in power engineering includes: The strain is obtained by collecting signals through strain sensors and temperature sensors installed inside the steel bars, and temperature compensation based on the temperature signals is performed on the strain signals. The lateral deformation of the box culvert is calculated by using the real strain obtained from symmetrically arranged strain sensors, and the axial deformation of the box culvert is calculated by using the real strain obtained from strain sensors arranged along the length direction. The liquid level height signal is collected by a hydrostatic level instrument installed on the surface of the box culvert, and the settlement difference and local settlement of the box culvert are calculated based on the liquid level height difference. Inclination angle signals were collected by single-axis inclinometers installed on the central axis and side walls of the box culvert top slab. Water flow velocity signals are collected by flow velocity sensors installed inside the cross-section of the box culvert. The calculated deformation data, settlement data, tilt angle data, and flow velocity data are compared with preset thresholds, and an early warning is issued when the data reaches or exceeds the threshold.

[0054] This method systematically integrates multi-source monitoring information and specifies a clear data processing path. It not only realizes multi-parameter monitoring but also the fusion and comprehensive judgment of multi-parameter information, enabling the system to conduct safety early warning based on comprehensive data support, thereby improving the scientific nature and accuracy of the early warning.

[0055] The calculation of settlement difference based on liquid level difference includes: directly converting the liquid level difference from the hydrostatic level on both sides of the expansion joint into settlement difference; the calculation of water flow impact force based on flow velocity data includes: calculating the dynamic shear stress of water flow on the culvert wall using fluid mechanics formulas based on water flow velocity, water density, and culvert cross-sectional dimensions. Specific quantitative methods for key safety indicators (settlement difference and impact force) are clearly defined, transforming the monitoring method from a theoretical description into an executable algorithm. The system not only monitors the original physical quantity (flow velocity) but also, through a built-in engineering mechanics model, transforms it into load parameters (impact force) that directly affect structural safety, thus achieving a deep transformation from monitoring data to engineering risk assessment and enhancing the professionalism and practical value of the monitoring system.

[0056] The monitoring methods will be explained in conjunction with the system's construction process: (1) Level the box culvert construction area, use a total station to mark the center line, edge line and expansion joint position of the box culvert, determine the sensor layout point 4 and PVC pipe burial path 17, and mark the points on the reinforcing bars.

[0057] (2) Excavate drainage ditches along the perimeter of the construction area, set up water collection wells, and pump groundwater down to below the bottom plate of box culvert 1 to avoid water accumulation affecting the sensor installation.

[0058] (3) After the reinforcing cage is tied and before the box culvert is poured, grind the surface of the reinforcing steel in the area marked with grating point 4 and clean it with chemical reagents to ensure that there is no oxide layer or oil on the surface, so as to provide a base surface with the maximum adhesion for subsequent bonding. Apply epoxy resin evenly to the metal substrate of grating point 4, and quickly and steadily press the strain sensor 2a onto the pre-treated surface of the reinforcing steel, applying constant pressure along the axial direction of the fiber optic grating sensor. When pasting, it is necessary to ensure that the fiber optic grating sensor is aligned with the direction of the principal stress to be measured, and then bind it with cable ties. Arrange the perimeter direction sensor 2b around the reinforcing steel of the top plate, bottom plate, and side wall, leaving a 5cm slack at the turning point to avoid stress concentration.

[0059] (4) Secure the temperature sensor 3, which is covered by the plastic protective sleeve 12, with cable ties to ensure that the sensor is in a relaxed state without stress and can freely expand and contract inside the sleeve. Before the two sections of the steel cage are joined together, fix the galvanized steel wire 5 and apply pre-tension, then fix the strain sensor grating point 4 at the midpoint of the steel wire and cover it with the plastic protective sleeve 12.

[0060] (5) Before the two sections of the box culvert steel cage are finally joined together, install the galvanized steel wire 5 of the differential settlement monitoring unit. First, pass one end of the galvanized steel wire through the pre-embedded clip of the reinforcing cage and use a hydraulic wire rope clamp for initial tightening. At the other end, use a hydraulic tensioner to apply a constant pre-tension force to the wire. Precisely set the pre-tension force of the galvanized steel wire 5 to 200N±10N. The lower limit of the value must overcome the maximum sag of the wire under its own weight to ensure that it is in a nearly horizontal straight state under actual working conditions. The upper limit of the value must be much lower than the yield strength of the wire and ensure that its anchoring point will not cause visible deformation or displacement to the binding point of the reinforcing cage. Use a calibrated tension gauge for real-time monitoring and verification. After maintaining the tension stability, complete the final anchoring of the other end. Both ends of the wire must be fixed back to back with at least two U-shaped clamps. Finally, fix the strain sensor grating point 4, which is specially used for expansion joint monitoring, to the midpoint of the wire with epoxy glue of the same grade. Under the action of pre-tension force, the mid-span of the galvanized steel wire 5 is most sensitive to the relative displacement of the two ends, with the largest strain response amplitude and the best linearity.

[0061] (6) Pour impermeable concrete in layers, with each layer ≤50cm thick. Avoid the vibrator touching the sensor and PVC pipe 17 during vibration. Cover the surface of the box culvert 1 with geotextile for at least 28 days to keep it moist. During the curing period, regularly check the integrity of the PVC pipe 17 leading out to avoid damage from external forces.

[0062] (7) The reference point of the static level 6 is established in an absolutely stable area outside the deformation influence zone of the main structure of the box culvert. It is usually selected at a location with good geological conditions, at least 10 meters outside the starting or ending point of the box culvert. At this site, a C30 reinforced concrete reference pier is poured on site, and anti-slip tenons are set at the bottom of the pier and embedded in the original soil. This pier structure provides anti-pull-out and anti-overturning stability, fundamentally ensuring the long-term reliability of the reference. After the box culvert concrete is poured, stainless steel brackets 11 are installed at the predetermined measuring points on the top plate of the box culvert. The top plate of the bracket is finely leveled with a level to ensure that its levelness error is within the standard range. The static level 6 is fixed to the stainless steel bracket 11 with bolts 9, and a stainless steel protective cover is added to the outside. Food-grade silicone transparent hoses are used as connecting pipes to connect the inlets and outlets of all static level 6 in series. The pipes are fixed with stainless steel clips, allowing the pipe body to expand and contract freely when the temperature changes. To prevent the instruments and pipelines from being damaged by the enormous earth pressure during backfilling, all static levels and their connected pipelines must be fitted with stainless steel protective sleeves.

[0063] (8) The concrete surface of the box culvert is usually uneven. Direct installation of the inclinometer will introduce a huge initial inclination error and the fixation will not be firm. Before installation, the concrete base surface is roughened and a square flat base is poured using non-shrink high-strength grout. Before installation, the horizontal arm of the mounting base of the top plate inclinometer 7a needs to be checked for straightness on the platform. During installation, it is fixed to the top plate with bolts 9. The side wall transverse fiber optic grating single-axis inclinometer 7b is arranged on the left and right side walls and fixed to the concrete surface with bolts 9. The concrete surface of the side wall may be uneven, so the installation area needs to be locally leveled to form a flat base. The inclinometer body is initially fixed to the prepared base with bolts 9. After the bolts are initially fixed, a fine adjustment margin is reserved. The initial installation deviation angle is measured using an electronic inclinometer as a reference and input into the configuration parameters of the corresponding inclinometer in the on-site intelligent monitoring system 20. After calibration, all fixing bolts 9 are finally tightened. The exposed bolt parts are covered with nylon anti-corrosion protective sleeves, and the entire inclinometer is covered with a stainless steel protective cover.

[0064] (9) Determine the installation position of the fiber optic grating velocity sensor 10 on the cross-section, i.e., 2 / 3 of the water depth above the vertical line. This position is considered to be the average velocity point of the rectangular cross-section. The bracket 11 is firmly installed at the design elevation of the lower middle part of the box culvert side wall using anchor bolts. The fiber optic grating velocity sensor 10 is installed on the bracket 11 using bolts 9, and the direction of the sensor is adjusted so that its sensitive axis 8 is strictly consistent with the theoretical mainstream direction of the water flow in the box culvert. A densely perforated stainless steel protective mesh is installed on the outside of the sensor. The surface of the protective mesh is coated with an anti-stick coating. Anti-corrosion protective sleeves are installed at the connection between the sensor and the bracket, and at all bolt connections. The bolt heads are coated with anti-rust agent.

[0065] (10) All sensor leads are connected to the interface of the box culvert sidewall integrated device 13, and the types are distinguished by label 14, such as type-section-serial number.

[0066] (11) The welding protection adopts a double-layer protection structure. The inner layer is heat shrink tubing and seamless metal tubing 16. The outer layer is uniformly inserted into PVC pipe 17 after being gathered, and extends along the outside of the steel cage to the ground surface integrated device 13. The gap between PVC pipe 17 and the box culvert 1 template is sealed with fireproof mud to prevent concrete from seeping in. All pipe joints and penetrations through walls and slabs are sealed with water-resistant adhesive.

[0067] (12) Before backfilling the box culvert, connect the fiber optic grating sensor demodulation system 18, the raw data optimization system 19, and the on-site intelligent monitoring system 20 to the surface integrated device 13. Collect initial data, verify the sensor survival rate (100%), and use infrared lamps to heat the temperature sensor to verify the temperature compensation function.

[0068] (13) The system collects data once every 10 minutes, automatically completes noise reduction, temperature compensation and deformation calculation, and monitors the data analysis and remote early warning platform 21 to display in real time; when the settlement difference of a certain box culvert is close to the set threshold, the platform pops up a yellow warning pop-up window and provides audio and visual prompts; when the threshold is reached or exceeded, a red warning is triggered and the location of the risk section is locked.

[0069] (14) After receiving the warning signal, the engineer’s electronic receiving device 23 shall make timely adjustments and take corresponding emergency measures to avoid the expansion of hidden dangers.

[0070] Specifically: like Figure 1 As shown, according to the monitoring layout diagram, a waterproof marker was used to precisely mark the bonding position of each fiber optic grating point 4, the fixing point of the galvanized steel wire 5, and the sensor lead path on the main reinforcement of the already bound steel cage. This ensures that all subsequent monitoring data accurately corresponds to the spatial location. Before concrete pouring, the installation of all pre-embedded sensors was completed. For the marked grating point 4 positions, the surface of the steel reinforcement was first ground to ensure the bonding surface was clean. The grating point 4 was tightly attached to the surface of the steel reinforcement with epoxy resin adhesive and then fixed in both directions with nylon cable ties to ensure that the grating point 4 deformed together with the steel reinforcement and that there was no relative displacement between the grating point and the steel reinforcement. After all strain sensor 2 grating points 4 were installed, a detector was used to monitor the signal transmission to ensure that the signal strength of the grating point 4 met the standard.

[0071] Temperature sensors are crucial for temperature compensation in strain measurement. After being inserted into a flexible plastic protective sleeve 12, they are loosely secured to the reinforcing bars at predetermined locations using cable ties. This ensures the sensor remains naturally relaxed within the sleeve, allowing for some deformation allowance, and ensures it only senses changes in ambient temperature without being affected by structural mechanical strain. A length-direction temperature sensor 3a is installed along the longitudinal reinforcement of the culvert top slab to obtain the temperature distribution along the culvert's length. In conventional sections, one sensor is installed for every five culvert sections, with denser installation in sections crossing the river. Sensor 3 is encased in a plastic protective sleeve 12 and loosely secured with cable ties to maintain sensor relaxation and prevent interference from culvert deformation. A vertical-direction temperature sensor 3b is installed along the sidewall reinforcement to obtain the vertical temperature difference of culvert 1. In conventional sections, one sensor is installed for every ten culvert sections, with one sensor installed for each section in special conditions. Sensor 3 extends from the bottom of the sidewall to the top of the slab, with grating dots 4 spaced 50cm apart. It is also encased in a plastic protective sleeve 12, with a redundancy allowance at the bottom.

[0072] After the box culvert 1 is poured and formed, static level instrument 6 benchmark points are set on the concrete surface. A reinforced concrete benchmark pier is poured 10m outside the starting point of the box culvert, with a silty clay layer embedded at the bottom and a stainless steel bracket installed on top. The benchmark static level instrument 6 is fixed to the bracket 11 with expansion bolts 9 and calibrated with an electronic level. A stainless steel protective cover is added to the outside of the benchmark pier. Expansion joint settlement differential static level instrument 6a is set up 1m away from the expansion joint on both sides of the top plate of the adjacent box culvert 1 expansion joint, with one instrument fixed by a stainless steel bracket 11, which is then fixed to the concrete surface with bolts 9. Single-section box culvert vertical settlement static level instrument 6b is set up every 5m along the length of the top plate of the single-section box culvert, covering key parts such as the mid-span and supports. All measuring points within the same box culvert maintain a consistent height. It directly measures the difference in liquid level height, and the total settlement of the box culvert and the differential settlement between adjacent box culvert sections can be calculated. Food-grade silicone tubing was used as the connecting pipe for the hydrostatic level, connecting all the inlet and outlet ports of the hydrostatic level. The pipeline route was laid along the steel reinforcement of the culvert side wall, and fixed to the steel reinforcement with clips every 50cm. The on-site intelligent monitoring system 20 analyzed and performed pattern recognition on the data collected by the hydrostatic level 6, and could distinguish the settlement type.

[0073] One transverse fiber optic grating single-axis inclinometer 7b is installed on each of the left and right side walls of the box culvert. Each measuring point is 50cm from the top of the side wall, and the measuring points on the left and right side walls are horizontally aligned. One inclinometer is installed every 25m in the standard section, with increased density in sections crossing rivers and roads. The sensor 7b is fixed to the concrete surface corresponding to the vertical reinforcement of the side wall using bolts 9. The sensitive axis 8 is perpendicular to the length of the box culvert. After installation, an electronic level is used to calibrate the initial state to ensure no tilt, thus obtaining the inclination deformation of the box culvert. The inclinometer 7b is covered with a stainless steel protective cover, which is fixed to the bracket using bolts 9. The exposed parts of the fixing bolts 9 are covered with nylon anti-corrosion protective sleeves, and the bolt heads are coated with rust inhibitor.

[0074] All sensor leads converge to the interface of the pre-designed integrated device 13, which is made of stainless steel. Before the sensors are led out, they are labeled with tags 14 according to type, cross-section, and serial number, and then fused with jumpers 15. The fusion joint is first protected with heat-shrink tubing and then covered with a seamless metal tube 16, with both ends of the tube sealed with waterproof adhesive. The lead-out section is entirely covered with a PVC pipe 17, buried in the soil along the side wall of the culvert, and the end connects to the surface integrated device 13. Jumpers 15 connect to the fiber optic grating sensor demodulation system 18, which automatically matches the monitoring position based on the signal of grating point 4, collects grating point data, and obtains strain, temperature, settlement, tilt angle, and flow velocity data. The fiber optic grating sensor demodulation system 18 transmits the data signal to the raw data optimization system 19, which has a built-in wavelet denoising algorithm to remove noise caused by construction vibration and electromagnetic interference, outputting clean data. The original data optimization system 19 and the on-site intelligent monitoring system 20 are built and deployed in the site monitoring room. Equipped with a deformation calculation module, the system processes the received data signals, calculates the vertical deformation of the top slab and the settlement difference of the expansion joints, and visualizes the data in real time using line graphs and heat maps. System 20 has built-in calculation formulas to calculate the overall settlement or local uneven settlement of the box culvert, which may cause the bottom of the structure to bulge or the sidewalls to tilt inward, reducing the area of ​​the originally designed rectangular or square water passage. Settlement leads to a reduction in the effective water passage area, which, under constant flow conditions, leads to an increase in flow velocity. Uneven longitudinal settlement of the box culvert will cause tilting, directly changing its hydraulic gradient and thus affecting drainage capacity. Conversely, flowing water will generate dynamic water pressure on the structural surface, and sudden changes in flow velocity will also act as a load feedback effect on the structure.

[0075] ; Q – Traffic volume, m 3 / s; V—Average flow velocity across the cross section, m / s; B—Original width of the box culvert cross-section, in meters; ΔB — Width change, in meters; H—Original height of the box culvert cross-section, in meters; ; ΔH — Change in altitude, in meters (m).

[0076] i actual — Actual hydraulic gradient, dimensionless; i design —Design hydraulic gradient, dimensionless; Δs — differential settlement, in meters; L – Length of flow between two cross sections, in meters.

[0077] The monitoring data analysis and remote early warning platform 21 calculates the settlement rate and settlement acceleration from the hydrostatic level at each measuring point in real time. It allows setting thresholds for strain and settlement difference. When the box culvert deformation or settlement difference approaches or exceeds the set threshold, the platform 21 transmits the data to the engineer's mobile app and computer platform 23 via the 5G network 22, and automatically stores historical data. The built-in algorithm formula of the monitoring data analysis and remote early warning platform 21 can convert the real-time flow velocity v from the current meter into the impact force of the water flow on the sidewall of the box culvert using fluid dynamics formulas. This data can be superimposed and compared with the concrete surface strain data measured by the fiber optic strain sensor 2 at the corresponding location.

[0078] ; V s —Settlement rate, m / s; s t —Real-time settlement data from a hydrostatic level, in meters; s t-Δt —Real-time settlement data from a hydrostatic level, in meters; ; Δt — time interval, seconds.

[0079] ; A s —Settlement acceleration, m / s 2 .

[0080] P—Impact force on the sidewall of the box culvert, MPa; ρ — density of water, kg / m³ 3 ; V – Flow velocity, m / s; B—Original width of the box culvert cross-section, in meters; ΔB — Width change, in meters; H—Original height of the box culvert cross-section, in meters; ΔH — Change in altitude, in meters (m).

[0081] When the fiber optic strain sensor 2b along the perimeter detects inward convergence deformation of the culvert sidewall or upward bulging of the bottom plate, the on-site intelligent monitoring system 20 can calculate the reduction in the actual water-carrying area of ​​that section. This data, combined with the actual flow velocity measured by the fiber optic flow velocity sensor 10, can calculate the percentage loss of water flow capacity at that section, providing data support for the operation of the drainage system. When the hydrostatic level 6 detects uniform settlement in a section of the culvert, the system will automatically calculate the actual hydraulic gradient of that section of the culvert by combining data from upstream and downstream measuring points. If the settlement leads to a decrease in gradient, the monitoring data analysis and remote early warning platform 21 can predict and alert the flow velocity in that section, thereby reducing the risk of siltation.

[0082] The monitoring data analysis and remote early warning platform 21 assimilates the raw data transmitted by the fiber optic grating sensor demodulation system 18. FBG is a wavelength-selective reflective device based on optical fiber, with a reflection center wavelength λ. B With the effective refractive index n of the fiber core eff And the grating period Λ satisfies: λ B =2n eff Λ; Strain and temperature are the causes of λ B The two main physical quantities of the drift. Under the action of axial strain Δε, the center wavelength drift Δλ. BS It can be represented as: Δλ BS =λ B (1-P C )Δε; Where P C As the effective photoelastic coefficient, under the influence of a temperature change ΔT, due to the combined effects of thermal expansion and thermo-optical effects, the center wavelength shift Δλ BT for: Δλ BT =λ B (α+ξ)ΔT; Where α is the coefficient of thermal expansion and ξ is the thermo-optical coefficient. In summary, the total wavelength shift Δλ at the center of the FBG is... B This can be expressed as a linear superposition of the effects of strain and temperature: Δλ B =K e *Δε+K T *ΔT; In the formula, Ke is the strain sensitivity coefficient, K T The temperature sensitivity coefficient is denoted by λ, and both can be obtained through experimental calibration. To achieve temperature decoupling of strain measurement, this invention employs a reference FBG temperature sensor for real-time temperature compensation; the sensor only senses temperature changes. Let Δλ be the wavelength drift caused by the temperature measured by the reference temperature sensor. T BT The total wavelength of the strain sensor is Δλ B The wavelength shift Δλ caused by pure strain BS It can be calculated using the following formula: Δλ BS =Δλ B -Δλ e BT ; Δλ e BT =K e T *ΔT=K e T / KT T *Δλ e BT ; In the formula, ΔT is the temperature change value, K e T K T T These are the temperature sensitivity coefficients of the temperature sensor and the strain sensor, respectively. The drift measured by the fiber optic strain sensor 2 is only the drift under the influence of temperature. Combined with the temperature compensation signal, strain decoupling is first performed to eliminate the influence of temperature and obtain the true mechanical strain. The fiber optic strain sensor is affected by temperature while deforming in tandem with the box culvert. Then, stress inversion converts the strain into stress. Substituting the strain and temperature data into the above formula, the temperature change ΔT and the box culvert strain Δε can be obtained, and then the stress of the box culvert sidewall and top plate can be calculated. Based on the flow velocity v measured by the fiber optic velocity sensor 10, the dynamic shear stress of the water flow on the box culvert wall can be calculated for the turbulence near the box culvert sidewall using the built-in fluid dynamics formula. This is the key to evaluating scour and local loads. Based on the data from the hydrostatic level 6 and the fiber optic single-axis inclinometer 7, the settlement distribution curve and spatial state matrix of the box culvert are calculated.

[0083] ; T w(t) — Wall shear stress, MPa; f—coefficient of friction, dimensionless; ρ—fluid density, kg / m³ 3 ; [v(t)] 2 —The square of the instantaneous flow velocity, (m / s) 2 .

[0084] like Figure 2 As shown, two fiber optic strain sensors with a length direction of 2a are symmetrically arranged along the longitudinal reinforcement of the top slab of box culvert 1. The sensors are 50cm from the edge of the top slab. Two grating points 4 on the same cross section are located in the upper and lower halves of the top slab, respectively, and are symmetrically arranged. Each sensor covers a single section of the box culvert, with a lead-out section reserved. The lead-out section is fixed to the inside of the reinforcing cage with cable ties. This is used to obtain the strain difference between the upper and lower parts of the box culvert top slab and to calculate the vertical deformation of the top slab. Two fiber optic strain sensors with a perimeter direction of 2b are symmetrically arranged along the longitudinal reinforcement of the top slab, the transverse reinforcement of the bottom slab, and the vertical reinforcement of the side walls of the box culvert. Each sensor goes around the box culvert once, with a 5cm relaxation allowance reserved at the turning point to avoid stress concentration that could damage the sensor. The extension extends along the longitudinal reinforcement of the bottom slab to the next section of the box culvert. The extension section is fixed tightly against the longitudinal reinforcement. The grating points 4 are continuously distributed without monitoring breaks until the entire box culvert is covered. This is used to obtain the strain difference between the inside and outside of the box culvert perimeter.

[0085] like Figure 3As shown, the longitudinal fiber optic grating single-axis inclinometer 7a is continuously deployed along the central axis of the box culvert top plate. All inclinometer mounting bases must be flat. After installation, an electronic level is used immediately for initial zero-point calibration, setting the initial state to zero tilt angle. The inclinometer is used to monitor the rigid body rotation or flexural deformation of the box culvert under lateral loads such as uneven soil pressure and water scouring. One inclinometer is deployed every 25m in the conventional section, and one inclinometer is deployed at the end of the box culvert, at the corner, and on both sides of the expansion joint. The sensor 7a is fixed by the bracket 11, and the sensitive axis 8 is parallel to the length direction of the box culvert 1. When the static level 6 detects significant uneven settlement in a box culvert section, the on-site intelligent monitoring system 20 will immediately call up the data of the fiber optic grating single-axis inclinometer 7 of the settlement section and adjacent sections to analyze its rigid body rotation trend, and simultaneously check the data change pattern of the fiber optic strain sensor 2 in the settlement area to determine whether the settlement has triggered bending moment and stress redistribution within the structure.

[0086] like Figure 4 As shown, the core function of a large drainage box culvert is water flow. Its internal structure is subjected to dynamic scouring by water flow and static additional loads generated by siltation over a long period of time. High-speed water flow generates continuous shear stress on the base slab and the root of the side walls, which is a key factor leading to concrete surface wear, aggregate spalling, and steel corrosion. Uneven siltation can cause deformation of the box culvert. It is necessary to quantify this environmental load parameter and conduct a correlation analysis between it and the structural strain. The fiber optic grating flow velocity sensor 10 is installed at a depth of 2 / 3 above the vertical line of the box culvert cross section. This position is an approximate location of the average flow velocity of the rectangular cross section, which can most effectively represent the flow capacity of the cross section. The sensor 10 is 0.8m from the inner wall of the side wall and 0.8m from the bottom of the box culvert 1. In the conventional section, a cross section measuring point is installed every 25m. The sensor 10 is densely installed at the box culvert inlet and outlet, the river crossing section, the uneven foundation section, and the turning section. A stainless steel bracket 11 is used. The vertical arm of the bracket 11 is fixed to the lower middle part of the side wall with bolts 9. The sensor 10 is fixed to the end of the horizontal arm with stainless steel bolts 9. The sensitive axis 8 is aligned with the water flow direction to ensure that it does not intrude into the main flow area. A stainless steel protective net is installed on the outside of the sensor 10. The surface of the protective net is coated with a polytetrafluoroethylene anti-stick coating. A stainless steel protective cover is added to the outside to prevent the adhesion of silt and sand and the impact of floating objects.

[0087] like Figure 5As shown, the expansion joints of the box culvert, designed to adapt to temperature and settlement, directly and continuously bear the seepage thrust of internal water pressure and the compression of external soil. They are more prone to complex multi-dimensional displacement in the vertical, longitudinal, and transverse directions, making them a weak link in the overall stability of large drainage box culverts. At the expansion joints of both box culverts, before the two sections of the box culvert's reinforcing cage are joined, a galvanized steel wire 5 is fixed along the longitudinal reinforcement direction. The wire needs to be pre-stretched with the expansion joint as the axis of symmetry. Applying pre-tension ensures that the wire accurately captures the relative displacement of the two box culverts. When the box culverts on both sides of the expansion joint experience slight vertical displacement due to uneven foundation, the tension of the wire will immediately change. Both ends are fixed to the reinforcing cages of the box culverts on both sides with stainless steel clips. The fixing point is 1m away from the expansion joint, and the total length of the galvanized steel wire is 2.5m. Pre-tension is applied before deployment. When the strain sensor passes through the expansion joint, a grating point 4 is fixed to the midpoint of the steel wire with epoxy adhesive. Plastic protective sleeves 12 are fitted around the steel wires before and after the grating point 4, and the ends of the sleeves are sealed with heat shrink tubing. The design captures 5° strain on galvanized steel wire to calculate the differential settlement between two box culvert sections. This design is extremely sensitive to minute, dynamic changes in elevation on both sides of the expansion joint, making it a monitoring solution specifically for this unique location.

[0088] like Figure 6 As shown, the plastic protective sleeve is a flexible hose with corrosion resistance and a certain compressive strength. Both the fiber optic strain sensor 2 and the fiber optic temperature sensor 3 are fitted with plastic protective sleeves 12 to prevent damage to the sensors from the external environment. Before inserting the sleeve, the sensor itself must be carefully inspected to ensure that its armor layer is free of scratches and creases. To prevent cement slurry from seeping into the sleeve along the port during concrete pouring and vibration, a small amount of waterproof sealant is first filled into the gap between the sleeve port and the sensor body. Then, high-performance electrical insulating tape or corrosion-resistant fine metal wire is used for binding and fixing.

[0089] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A monitoring system for large drainage culverts in power engineering, characterized in that, Includes monitoring components and data processing units; The monitoring element includes: Strain sensors and temperature sensors are installed inside the steel cage of the drainage culvert to monitor strain and temperature data. A hydrostatic level is installed on the concrete surface of the drainage culvert to monitor settlement. A single-axis inclinometer is installed on the central axis of the top slab and the side walls of the drainage culvert to monitor the tilt angle. A flow velocity sensor, fixed to the internal cross-section of the drainage culvert by a bracket, is used to monitor the water flow velocity; The strain sensor, temperature sensor, hydrostatic level, single-axis inclinometer, and flow velocity sensor are all connected to the data processing unit.

2. The monitoring system for large drainage culverts in power engineering as described in claim 1, characterized in that, The strain sensors include length direction strain sensors symmetrically arranged on the longitudinal reinforcement of the top slab along the length of the box culvert, and circumferential direction strain sensors arranged on the reinforcement of the top slab, bottom slab and side walls along the perimeter of the box culvert cross section.

3. The monitoring system for large drainage culverts in power engineering as described in claim 2, characterized in that, At the expansion joint between two adjacent box culvert sections, galvanized steel wires are installed that cross the reinforcing cages on both sides, and one sensing point of the length direction strain sensor is fixed to the surface of the galvanized steel wire.

4. The monitoring system for large drainage culverts in power engineering as described in claim 1, characterized in that, The temperature sensors include a length direction temperature sensor arranged in the direction of the longitudinal reinforcement of the top slab of the box culvert, and a vertical direction temperature sensor arranged in the direction of the vertical reinforcement of the side wall of the box culvert. The temperature sensors are covered with protective sleeves.

5. The monitoring system for large drainage culverts in power engineering as described in claim 1, characterized in that, The static level instruments include expansion joint settlement differential static level instruments arranged on both sides of the expansion joint of the box culvert, and single-section box culvert vertical settlement static level instruments arranged at intervals along the length of the top slab of a single box culvert section.

6. The monitoring system for large drainage culverts in power engineering as described in claim 1, characterized in that, The single-axis inclinometer includes a longitudinal inclinometer with its sensitive axis parallel to the length of the box culvert and installed on the central axis of the top plate, and a transverse inclinometer with its sensitive axis perpendicular to the length of the box culvert and symmetrically installed on the left and right side walls.

7. The monitoring system for large drainage culverts in power engineering as described in claim 1, characterized in that, The data processing unit includes a sensor demodulation system, a raw data optimization system, an on-site intelligent monitoring system, and a monitoring data analysis and remote early warning platform connected in sequence. The on-site intelligent monitoring system is used to calculate the deformation, settlement, and water flow impact force of the box culvert based on the processed data. The monitoring data analysis and remote early warning platform is used to compare the calculation results with the set thresholds and issue early warnings.

8. A construction method for a monitoring system for large drainage culverts in power engineering as described in any one of claims 1-7, characterized in that, include: Strain sensors and temperature sensors with protective sleeves are installed on the completed box culvert steel cage, and galvanized steel wires are fixed at the expansion joints. After the box culvert concrete is poured and formed, a static level, a single-axis inclinometer, and a flow velocity sensor fixed by a bracket are installed on the concrete surface. The leads of each sensor are connected to the interface of the integrated device and marked, then fused with jumpers, and the fused joints are protected. Insert the sensor lead into a protective tube and lead it to the ground surface to connect it to the data processing unit.

9. A monitoring method for a large drainage culvert monitoring system for power engineering as described in any one of claims 1-7, characterized in that, include: The strain is obtained by collecting signals through strain sensors and temperature sensors installed inside the steel bars, and temperature compensation based on the temperature signals is performed on the strain signals. The lateral deformation of the box culvert is calculated by using the real strain obtained from symmetrically arranged strain sensors, and the axial deformation of the box culvert is calculated by using the real strain obtained from strain sensors arranged along the length direction. The liquid level height signal is collected by a hydrostatic level instrument installed on the surface of the box culvert, and the settlement difference and local settlement of the box culvert are calculated based on the liquid level height difference. Inclination angle signals were collected by single-axis inclinometers installed on the central axis and side walls of the box culvert top slab. Water flow velocity signals are collected by flow velocity sensors installed inside the cross-section of the box culvert. The calculated deformation data, settlement data, tilt angle data, and flow velocity data are compared with preset thresholds, and an early warning is issued when the data reaches or exceeds the threshold.

10. The monitoring method as described in claim 9, characterized in that, The calculation of settlement difference based on liquid level difference includes: directly converting the liquid level difference between the two sides of the expansion joint into the settlement difference; the calculation of water flow impact force based on flow velocity data includes: calculating the dynamic shear stress of water flow on the box culvert wall based on water flow velocity, water density and box culvert cross-sectional dimensions using fluid mechanics formulas.

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