Real-time monitoring system and method for frost heaving of power transmission and transformation tower footing in cold region

Abstract

The invention relates to the field of health monitoring of civil engineering structures, in particular to a real-time monitoring system and method for frost heaving of a power transmission and transformation tower footing in a cold region, and the system comprises a sensing unit, a demodulation unit, and a data processing and early warning unit. A plurality of measuring points are vertically arranged on all the optical fibers at intervals; the strain sensing optical fiber encloses a sensing column and senses the strain of a measuring point; the temperature reference optical fiber is arranged in the sensing column and is not stressed at all; the demodulation unit is connected with the sensing unit, transmits laser pulses to each optical fiber, receives backward Brillouin scattering signals and obtains strain and temperature data of each optical fiber at each time point. And the data processing and early warning unit is connected with the demodulation unit, and constructs a frost heaving event discrimination model based on the strain and temperature data to obtain graded early warning and identify a frost heaving event. And the change of the temperature and the strain field can be simultaneously sensed in the whole life cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of civil engineering structure health monitoring, in particular to a real-time monitoring system and method for frost heaving of a power transmission tower foundation in cold regions. BACKGROUND

[0002] In cold regions, the frost heaving effect of foundation soil is one of the main reasons for the cracking, upheaval and instability of concrete structures such as building foundations, bridge piers, power transmission tower foundations, etc. Frost heaving is a complex physical process driven by temperature field, involving water field and responding to stress field. Its damage has the characteristics of concealment, accumulation and suddenness. Therefore, real-time, accurate and reliable monitoring of the frost heaving process inside the foundation is the key to early warning and safe operation of the structure.

[0003] Currently, the monitoring of foundation frost heaving mainly relies on traditional technical means, i.e. point measurement technology. Point measurement technology generally uses electrical point sensors such as resistance strain gauges and vibrating wire sensors. However, this technology has defects such as discontinuous monitoring, poor anti-interference ability and difficulty in accurate positioning, which often brings difficulties to subsequent repair and treatment.

[0004] Distributed optical fiber sensing technology such as Brillouin optical time domain analysis (BOTDR) has been applied to the field of structure monitoring due to its outstanding advantages such as distribution, long distance, anti-electromagnetic interference and intrinsic safety. The existing patents and technical solutions mainly apply BOTDR to power cable icing monitoring or pile foundation deformation measurement. The sensing object, layout method and discrimination model are designed for specific scenarios and cannot be directly applied to the frost heaving monitoring of foundation mass concrete. The core of frost heaving monitoring is to distinguish between thermal expansion and cold contraction effect and ice crystal expansion effect. The existing solutions lack systematic decoupling design for this "temperature-strain" cross-sensitivity problem, and there is no effective discrimination and early warning model matched with the mechanism of foundation frost heaving.

[0005] Therefore, the present application provides a solution designed specifically for foundation frost heaving monitoring. The solution can monitor the changes of temperature and strain field throughout the life cycle from the pouring period, accurately locate the height, depth and degree of frost heaving occurrence and development, and ultimately establish an effective early warning mechanism. SUMMARY

[0006] The present application provides a foundation frost heaving monitoring system based on distributed optical fiber sensing. The system pre-buries a sensing optical fiber based on Brillouin scattering effect when pouring the foundation. The optical fiber serves as both a sensor and a transmission medium, allowing for the monitoring of micro-strain and temperature changes throughout the foundation, accurate positioning of the location and degree of frost heaving occurrence, and early warning. The technical solution of the present application to solve the above technical problems is as follows: A real-time monitoring system for frost heave of power transmission tower foundations in cold regions includes a sensing unit, a demodulation unit, and a data processing and early warning unit. The sensing unit includes multiple strain sensing optical fibers and a temperature reference optical fiber embedded in the concrete foundation. Each strain sensing optical fiber and temperature reference optical fiber has m measurement points arranged vertically at intervals, and the starting height of the measurement points is the same. One strain sensing fiber is placed at the center of the concrete foundation, and the remaining strain sensing fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The strain sensing fibers are used to sense the strain at the measurement point. The temperature reference fiber is laid inside the sensing column and is in a completely stress-free state. The demodulation unit is a distributed fiber optic demodulator connected to the sensing unit. It is used to emit laser pulses to the strain sensing fiber and the temperature reference fiber, respectively, and to receive backscattered Brillouin signals, thereby acquiring the height z of each strain sensing fiber and the temperature reference fiber at each time point t. j The strain ε at the j-th measurement point 0j (z) j, t) and temperature data, j=1, 2...m; The data processing and early warning unit is connected to the demodulation unit and is used to perform temperature compensation on the strain at all measurement points to obtain the pure mechanical strain ε. j (z) j, t), based on pure mechanical strain ε j (z) j, A frost heave event discrimination model is constructed using t) and temperature data to obtain graded early warnings and identify frost heave events.

[0007] A method for real-time monitoring of frost heave of power transmission tower foundations in cold regions using a real-time monitoring system for frost heave of power transmission tower foundations in cold regions includes: Multiple strain sensing optical fibers and one temperature reference optical fiber are pre-embedded in the concrete foundation. One strain sensing optical fiber is arranged in the center of the concrete foundation, and the remaining strain sensing optical fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The temperature reference fiber is laid inside the sensing column and is in a completely stress-free state. Each strain sensing fiber and temperature reference fiber has multiple measurement points arranged at vertical intervals, and the multiple measurement points have the same height. Laser pulses are emitted into all strain sensing fibers and temperature reference fibers, and the backscattered light signals to Brillouin are received. Through signal analysis, strain and temperature data of all measurement points of each strain sensing fiber and temperature reference fiber at each time point are obtained; The strain data is denoised and temperature compensated to eliminate the thermal expansion and contraction effect, and the pure mechanical strain at the measurement point is obtained. Based on pure mechanical strain and temperature data, a frost heave event discrimination model is used to conduct graded early warning and identify frost heave events.

[0008] The present invention has the following beneficial effects: By pre-embedding Brillouin optical time-domain analysis (BOTDR) optical fibers during foundation pouring, which serve as both sensors and transmission media, the micro-strain and temperature changes of the foundation can be monitored throughout the entire process. This allows for precise location and extent of frost heave, enabling early warning and dynamic tracking throughout the entire process. It can monitor the advancement of the freezing front and the accumulation of frost heave strain in real time, achieving a leap from "static result monitoring" to "dynamic process perception," thus providing the possibility for advanced early warning.

[0009] The problem of temperature drift interference has been fundamentally solved: through the unique scheme of co-deploying "strain sensing fiber" and "temperature reference fiber", the thermal expansion and contraction effect is effectively eliminated, ensuring the accuracy and reliability of the data.

[0010] High degree of automation and accurate early warning: The system can automatically collect, process and judge data, and issue graded early warnings based on a multi-level logical discrimination model, which greatly reduces the reliance on manual labor and improves the scientific nature and accuracy of early warnings. Attached Figure Description

[0011] Figure 1 This is a top-view diagram showing the sensor unit's position within the concrete foundation. Figure 2 This is a schematic diagram showing the internal location of the sensing unit in the concrete foundation. Figure 3 This is a flowchart of a method for real-time monitoring of frost heave in power transmission tower foundations in cold regions.

[0012] In the diagram: 1. Concrete foundation; 2. Strain sensing fiber; 3. Temperature reference fiber. Detailed Implementation

[0013] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0014] A real-time monitoring system for frost heave of power transmission tower foundations in cold regions includes a sensing unit, a demodulation unit, and a data processing and early warning unit. The sensing unit includes multiple strain sensing optical fibers and one temperature reference optical fiber embedded in the concrete foundation. Each strain sensing optical fiber and temperature reference optical fiber has multiple measurement points arranged vertically at intervals, and the starting height of the multiple measurement points is the same, that is, the number and height of measurement points on each optical fiber are the same; the heights of the measurement points on each optical fiber are z1, z2, z3...z m，m represents the total number of measurement points on each strain sensing fiber or temperature reference fiber.

[0015] One strain sensing fiber is placed at the center of the concrete foundation, and the remaining strain sensing fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The strain sensing fibers are used to sense the strain at the measurement point. The cross-section of the sensing column can be circular, square, rectangular, etc., with circular being preferred.

[0016] A temperature reference fiber is laid inside the sensing column. The temperature reference fiber is a fiber laid near the sensing column that is in a completely stress-free state and is used to measure the temperature at the measurement point of the temperature reference fiber. The demodulation unit is a distributed fiber optic demodulator connected to the sensing unit. It is used to emit laser pulses into the strain sensing fiber and the temperature reference fiber, respectively, and to receive the backscattered Brillouin signals, thereby acquiring the height z of each strain sensing fiber and the temperature reference fiber at each time point t. j The strain ε at the j-th measurement point 0j (z) j, t) and temperature data T j (t), j=1, 2...m. A total strain data array ε is formed for each time point t. 0i (z) and temperature data array T(z), i=1, 2...n, where n is the number of strain sensing fibers, ε 0i (z)={ε i (z) 1, t), ε 0i (z) 2, t), ε 0i (z) 3, t)……ε 0i (z) m, t)},ε 0i (z) 1, t), ε 0i (z) 2, t), ε 0i (z) 3, t)……ε 0i (z) m, T(z) is the strain data from m measurement points on the i-th strain sensing fiber. T(z) = {T1(t), T2(t), T3(t), ..., T} m (t)}. T1(t), T2(t), T3(t)……T m (t) represents the temperature at each measurement point on the temperature reference fiber.

[0017] The demodulation unit periodically acquires data according to a preset sampling time interval ΔT, where time point t is the sampling moment. The sampling time interval ΔT can be set and adjusted according to actual monitoring needs and season. For example, during active frost heave phases such as freezing or thawing periods, a shorter sampling interval (e.g., 1 minute to 30 minutes) can be used; during stable phases such as non-freezing periods, a longer sampling interval (e.g., 1 hour to 12 hours) can be used to save energy and data storage space. Those skilled in the art can flexibly set the interval according to actual conditions to ensure that strain and temperature changes during the occurrence and development of frost heave can be captured.

[0018] The data processing and early warning unit is connected to the demodulation unit to perform temperature compensation on the strain of all measurement points to obtain pure mechanical strain. Based on the pure mechanical strain and temperature data, a frost heave event discrimination model is constructed to obtain graded early warning and identify frost heave events.

[0019] Indicative, such as Figure 1 As shown, the sensing unit contains five vertically arranged strain sensing fibers 2 under stress and one unstressed temperature reference fiber 3. Each strain sensing fiber 2 is threaded through a stainless steel flexible tube, forming a "loose-fitting" structure, and is mainly used to sense the strain of the strain sensing fiber in the fiber direction, vertical direction, and height z. j The strain at this point. This strain is the result of the combined effects of thermal expansion and contraction and external mechanical strain (such as frost heave). The temperature reference fiber is threaded through a PVC pipe with a larger inner diameter and injected with lubricating material to ensure it is completely stress-free, used to accurately measure the temperature value distributed along the fiber. All fibers in the demodulation unit and sensing unit (i.e., Figure 1 The six optical fibers shown are connected separately. The demodulation unit is a distributed fiber optic demodulator based on Brillouin Optical Time Domain Analysis (BOTDR). Its function is to emit laser pulses to all fibers and receive the backscattered light signals into the Brillouin. Through signal analysis, the demodulation unit outputs two key raw strain and temperature data to the data processing and early warning unit. The data processing and early warning unit is electrically connected to the demodulation unit to construct a frost heave event discrimination model to obtain graded early warnings and identify frost heave events.

[0020] More specifically, a cross-shaped stress-strain sensing fiber 2 and a stress-free temperature reference fiber 3 are arranged on the cast-in-place concrete foundation 1. The strain sensing fiber 2 is required to be arranged with one fiber at the center of the pile foundation and at least four fibers around the pile body.

[0021] The strain sensing fiber optic cable 2 is encased in a nylon flexible tube. The inner diameter of the flexible tube should be larger than the outer diameter of the fiber optic cable, forming a "loose-fitting" structure to ensure the fiber optic cable can freely expand and contract, accurately sensing variations. In areas with intensive concrete pouring and vibration (mainly the bottom and top of the foundation), the aforementioned nylon flexible tube is then inserted into a thicker HDPE corrugated pipe or galvanized steel pipe, forming double protection.

[0022] The temperature reference fiber 3 is housed in a relatively large-diameter PVC solid-wall tube. Silicone grease is injected into the tube to ensure that the fiber is completely relaxed and unstressed within it.

[0023] Both the strain sensing fiber 2 and the temperature reference fiber 3 are gently secured to the vertical reinforcing bars with nylon or stainless steel cable ties, each with a protective sleeve. The fixing spacing is approximately 1-1.5 meters.

[0024] After the strain sensing fiber 2 and temperature reference fiber 3 are bundled inside the concrete foundation 1, they emerge uniformly from the exit hole reserved in the side wall of the foundation. A galvanized steel pipe is pre-embedded between this exit hole and the protective junction box on the ground as a lead wire conduit, through which the fiber bundle enters the junction box. At the exit hole and inside the junction box, a redundancy length of no less than 5 meters must be reserved for each fiber, and it must be coiled into a loop with a diameter greater than 15cm to cope with possible settlement or deformation of the foundation.

[0025] In a preferred embodiment, the number of strain sensing fibers is at least five, which is sufficient to ensure the accuracy of the graded early warning results.

[0026] In a preferred embodiment, the strain sensing fiber is threaded within a stainless steel or nylon flexible conduit, the inner diameter of which is larger than the outer diameter of the fiber. This significantly improves system survivability and durability: the fiber protection design ensures a high survival rate of the sensing unit during concrete pouring and long-term use, and the fiber itself is corrosion-resistant, resistant to electromagnetic interference, and has a long lifespan. Preferably, the stainless steel or nylon flexible conduit is further encased in an HDPE corrugated pipe or galvanized steel pipe.

[0027] In a preferred embodiment, the temperature reference fiber is dynamically inserted into a PVC pipe, which is filled with lubricating material to ensure that the fiber is completely stress-free. This significantly improves the system's survivability and durability: the fiber protection design ensures a high survival rate of the sensing unit during concrete pouring and long-term use, and the fiber itself is corrosion-resistant, electromagnetic interference-resistant, and has a long lifespan.

[0028] In a preferred embodiment, the data processing and early warning unit is also used to preprocess the strain and temperature data, including moving average filtering or wavelet noise reduction.

[0029] In a preferred embodiment, temperature compensation is performed on the strain at each measurement point to obtain the pure mechanical strain ε. j (z) j, t) is: ε j (z) j, t)=ε 0j (z) j, t)-α · ΔT(z j ), εj (z) j ) represents the height z j The pure mechanical strain at the j-th measurement point, α represents the thermal expansion coefficient of concrete, and ΔT(z) is the temperature change of the j-th measurement point at time t relative to the reference temperature T0. The reference temperature T0 is the temperature data of the j-th measurement point measured by the temperature reference fiber optic cable after the concrete foundation is poured and before the start of the first freeze-thaw cycle.

[0030] The data processing and early warning unit performs temperature compensation calculations on the denoised data. Specifically, for time t, the temperature compensation calculation is performed on the i-th strain sensing fiber at height z. j The total strain measured at each measurement point is compared with the temperature measured at the corresponding height on the reference fiber, and then substituted into the compensation formula to calculate the pure mechanical strain at that point. This process is repeated until all measurement points on all fibers at all times have been processed.

[0031] Specifically, the data processing and early warning unit performs noise reduction processing on the received strain and temperature data (such as moving average filtering), and then calculates the pure mechanical strain data distributed along the fiber optic distance after eliminating the thermal expansion and contraction effect by performing temperature compensation through the compensation formula.

[0032] Raw data acquisition and noise reduction: The demodulation unit uses an optical switch to cyclically scan or process optical connections to all fiber optic paths simultaneously and in parallel. For each fiber, the distributed fiber demodulator performs a distributed measurement and outputs a set of "measurement point height-strain or temperature" data arrays for each time point corresponding to that fiber. Specifically: For the five strain sensing fibers 2, each sensing fiber outputs a total strain data array ε distributed along the fiber distance z. 0i (z)” (where i = 1, 2, 3, 4, 5, representing the i-th strain sensing fiber). This total strain data array ε 0i (z) includes the strain generated by the thermal expansion and contraction of concrete and external mechanical loads (such as frost heave).

[0033] For temperature reference fiber 3, the output is a "temperature data array T(z) distributed along the fiber distance". Since this fiber is in a completely stress-free state, the strain measured is negligible. Therefore, this data array directly reflects the temperature field distribution inside the foundation.

[0034] The above ε obtained from the six fiber optic paths 01 (z), ε 02 (z), ..., ε 05 T(z) and T(z) represent the raw data collected by the system. Subsequently, the system performs noise reduction processing on these raw data arrays, that is, for each group of ε...0i The T(z) and T(z) data are subjected to moving average filtering or wavelet denoising along the vertical direction to suppress the inherent random noise of the optical system and improve the signal-to-noise ratio. The denoised data will be used for subsequent temperature compensation calculations.

[0035] Temperature compensation processing: Total strain ε measured from the force path 0i In (z), the thermal expansion and contraction strain components caused by simple temperature changes are removed, and the mechanical strain caused purely by external mechanical effects (such as frost heave) is separated. Specifically, the noise-reduced temperature data T(z) is used to compensate for the total strain data of each strain sensing fiber after noise reduction and data preprocessing.

[0036] ΔT(z) represents the position z j The temperature change at the measurement point relative to the reference temperature T0 is calculated from T(z) - T0. Here, T(z) comes directly from the measurement results of the temperature reference fiber optic 3.

[0037] After the above preprocessing and temperature compensation, the system obtained five sets of spatially distributed pure mechanical strain field data that accurately reflect the internal stress state of the foundation, as well as one set of temperature field data, providing an accurate data foundation for subsequent frost heave event identification. The system fundamentally solves the temperature drift interference problem: through a unique scheme of co-deploying strain sensing optical fibers and temperature reference optical fibers, combined with a dedicated algorithm, the thermal expansion and contraction effect is effectively eliminated, ensuring the accuracy and reliability of the data.

[0038] In a preferred embodiment, the frost heave event discrimination model includes: First-level judgment: Determine whether the temperature of the measurement point on the strain sensing fiber 2 is lower than the freezing threshold Ts. The temperature of the measurement point on the strain sensing fiber 2 is equal to the temperature of the measurement point at the same height as the temperature reference fiber 3. Second-level judgment: For measurement points that satisfy the first-level judgment, determine whether the pure mechanical strain at the measurement point exceeds the critical strain threshold ε. s And whether the strain rate exceeds the critical rate threshold ν s ; Third-level judgment: For measurement points that satisfy the second-level judgment, check whether there are multiple consecutive measurement points in the adjacent spatial region [z-ΔL, z+ΔL] that simultaneously satisfy the first-level and second-level judgments; When the number of measurement points exceeding a preset proportion meets the first-level judgment but does not meet the second-level judgment, a first-level warning is issued. If the second-level judgment is met but the third-level judgment is not met, a second-level warning is issued. When the criteria for Level 3 are met, a frost heave event is confirmed and a Level 3 warning is issued.

[0039] The severity of frost heave is measured by the frost heave index (FHI), FHI(z, t) = ε j (z) j, t) – ε j (z j The larger the FHI value (t0), the more severe the cumulative effect of frost heave. ε j (z) j, t) represents the height z j The pure mechanical strain at measurement point j at the current time point t; ε j (z j , t0) represents at height z j The pure mechanical strain at measurement point j at reference time t0; t0 is the height z j The measurement point is the starting time at which the first-level judgment condition is met consecutively for the first time within a preset freezing period. The preset freezing period refers to a typical seasonal cycle in the project location where frost heave is likely to occur, usually a complete winter or a major freeze-thaw cycle. Its duration can be set according to local meteorological conditions, for example, 3 to 6 months. The specific value of t0 is determined by the height z. j The starting time of the measurement point j, whose temperature data first begins and continues to satisfy the first-level judgment condition (i.e., T(z) ≤ Ts).

[0040] Specifically, the first level of judgment (temperature judgment): For each measurement point, determine whether its temperature data T(z) is lower than the freezing threshold T. s Second-level judgment (strain anomaly judgment): For measurement points that meet the first-level judgment, determine whether their pure mechanical strain exceeds the critical strain threshold ε. s And whether the strain rate ∂ε(z) / ∂t exceeds the critical rate threshold ν. s Third-level judgment (spatial consistency confirmation): For a measuring point that meets the second-level judgment, check whether there are multiple consecutive measuring points in its adjacent spatial region [z-ΔL, z+ΔL] that simultaneously meet the first-level and second-level conditions.

[0041] For frost heave events confirmed through the above three-level judgment, the frost heave severity index FHI(z, t) is calculated. This index is based on the change in the pure mechanical strain data ε(z) at the measurement point over time. Finally, based on the conclusions of the above three-level judgment, the system issues corresponding graded early warning information.

[0042] High degree of automation and accurate early warning: The system can automatically collect, process and judge data, and issue graded early warnings based on a multi-level logical discrimination model and frost heave index, which greatly reduces reliance on manual labor and improves the scientific nature and accuracy of early warning.

[0043] The first level of judgment is a freezing state assessment. The freezing threshold Ts is set and can be slightly lower than 0°C, such as -0.5°C, to account for supercooling. It determines whether the measurement point is in a temperature environment where frost heave may occur. If "No," then there is currently no risk of frost heave at that point. If "Yes," proceed to the second level of judgment.

[0044] The second level of judgment is the strain anomaly judgment, and the judgment condition is ε. i (z, t) ≥ ε s And the strain change rate ε j (z) j, t) / ∂t ≥ ν s Where εᵢ(z, t) represents the purely mechanical strain value at time t at the measurement point at spatial location z on the i-th strain sensing fiber. It is the strain caused by external mechanical forces (such as frost heave or load), and the effects of thermal expansion and contraction have been eliminated. s The critical strain threshold indicates that a strain value is only of concern when it exceeds the minimum background noise level. The strain rate ε j (z) j, t) / ∂t represents the instantaneous rate of change of the purely mechanical strain εᵢ at time t at the measurement point at spatial location z on the i-th strain sensing fiber, i.e., the strain rate. Its physical meaning is the increment of strain per unit time, intuitively reflecting the "rate of strain growth" at that measurement point. s The critical strain rate threshold ε is used to distinguish between frost heave (rapid increase) and slow creep. In a frozen state, the second-level judgment checks for abnormal, rapidly increasing tensile strain. If both conditions are met simultaneously, it is preliminarily determined as a "suspected frost heave event," triggering the third-level judgment. s and critical rate threshold ν s The settings need to be determined comprehensively based on the material properties of the concrete, the accuracy of the sensor, and the climatic conditions of the project location. ε s The value of ε should be greater than the strain fluctuation range of the measurement system under steady-state conditions (typically ±20~50µε). Therefore, ε s It can be set from 50µε to 100µε (micro-strain). ν s The value can be set according to the typical local frost heave development rate, with a typical range of 5µε / hour to 20µε / hour.

[0045] The third level of judgment is spatial consistency confirmation. A single measurement point signal may be noise or a local defect, while true frost heave has a certain spatial continuity. The judgment condition is: check whether there are multiple consecutive measurement points (3 or more measurement points on the same optical fiber) that also simultaneously satisfy the conditions of the first and second levels. If they are satisfied, then a frost heave event has finally been confirmed to have occurred near the measurement point z. The judgment condition is: check whether there are multiple consecutive measurement points (3 or more measurement points on the same optical fiber) that simultaneously satisfy the conditions of the first and second levels. If they are satisfied, then a frost heave event has finally been confirmed to have occurred near the measurement point z. The third level of judgment will greatly improve the reliability of the judgment.

[0046] In the tiered early warning system, the first-level warning condition is that when more than a preset proportion (e.g., 50%) of the measurement points meet the first-level judgment (temperature below the freezing threshold T), the warning is triggered. s At this point, the system will enter "Frozen Monitoring Mode." The second-level warning alerts staff to pay attention to a specific location. The third-level warning indicates the specific measurement point location (z-coordinate) and severity (FHI value), suggesting the need for manual intervention (such as heating or unloading).

[0047] This invention achieves three-dimensional dynamic tracking and precise early warning of the basic frost heave process through innovative fiber optic deployment structure and dedicated algorithm. It effectively solves the industry problems of discontinuous traditional point monitoring, poor anti-interference and cross-sensitivity to temperature strain. The system has high reliability and long life.

[0048] A method for real-time monitoring of frost heave of power transmission tower foundations in cold regions using a real-time monitoring system for frost heave of power transmission tower foundations in cold regions includes: Multiple strain sensing optical fibers and one temperature reference optical fiber are pre-embedded in the concrete foundation. One strain sensing optical fiber is arranged in the center of the concrete foundation, and the remaining strain sensing optical fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The temperature reference fiber is laid inside the sensing column and is in a completely stress-free state. Each strain sensing fiber and temperature reference fiber has multiple measurement points arranged at vertical intervals, and the multiple measurement points have the same height. Laser pulses are emitted into all strain sensing fibers and temperature reference fibers, and the backscattered light signals to Brillouin are received. Through signal analysis, strain and temperature data of all measurement points of each strain sensing fiber and temperature reference fiber at each time point are obtained; The strain data is denoised and temperature compensated to eliminate the thermal expansion and contraction effect, and the pure mechanical strain at the measurement point is obtained. Based on pure mechanical strain and temperature data, a frost heave event discrimination model is used to conduct graded early warning and identify frost heave events.

[0049] The frost heave event discrimination model includes a first-level judgment: judging whether the temperature of the measurement point on the strain sensing fiber 2 is lower than the freezing threshold Ts, and the temperature of the measurement point on the strain sensing fiber 2 is equal to the temperature of the measurement point at the same height as the temperature reference fiber 3. Second-level judgment: For measurement points that satisfy the first-level judgment, determine whether the pure mechanical strain at the measurement point exceeds the critical strain threshold ε. s And whether the strain rate exceeds the critical rate threshold ν s ; Third-level judgment: For measurement points that satisfy the second-level judgment, check whether there are multiple consecutive measurement points in the adjacent spatial region [z-ΔL, z+ΔL] that simultaneously satisfy the first-level and second-level judgments; When the number of measurement points exceeding a preset proportion meets the first-level judgment but does not meet the second-level judgment, a first-level warning is issued. If the second-level judgment is met but the third-level judgment is not met, a second-level warning is issued. When the criteria for Level 3 are met, a frost heave event is confirmed and a Level 3 warning is issued; The severity of frost heave is measured by the frost heave index (FHI), FHI(z, t) = ε j (z) j, t) – ε j (z j The larger the FHI value (t0), the more severe the cumulative effect of frost heave. ε j (z) j, t) represents the height z j The pure mechanical strain at measurement point j at the current time point t; ε j (z j , t0) represents at height z j The pure mechanical strain at measurement point j at reference time t0; t0 is the height z j The starting time when the measurement point first continuously meets the first-level judgment condition within a preset freezing period.

Claims

1. A real-time monitoring system for frost heave of power transmission tower foundations in cold regions, characterized in that, Includes a sensing unit, a demodulation unit, and a data processing and early warning unit: The sensing unit includes multiple strain sensing optical fibers and a temperature reference optical fiber embedded in the concrete foundation. Each strain sensing optical fiber and temperature reference optical fiber has m measurement points arranged vertically at intervals, and the starting height of the measurement points is the same. One strain sensing fiber is placed at the center of the concrete foundation, and the remaining strain sensing fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The strain sensing fibers are used to sense the strain at the measurement point. The temperature reference fiber is laid inside the sensing column and is in a completely stress-free state. The demodulation unit is a distributed fiber optic demodulator connected to the sensing unit. It is used to emit laser pulses to the strain sensing fiber and the temperature reference fiber, respectively, and to receive backscattered Brillouin signals, thereby acquiring the height z of each strain sensing fiber and the temperature reference fiber at each time point t. j The corresponding strain ε at the j-th measurement point 0j (z) j, t) and temperature data, j=1, 2...m; The data processing and early warning unit is connected to the demodulation unit and is used to perform temperature compensation on the strain at all measurement points on the strain sensing fiber to obtain the pure mechanical strain ε. j (z) j, t), based on pure mechanical strain ε j (z) j, A frost heave event discrimination model is constructed using t) and temperature data to obtain graded early warnings and identify frost heave events.

2. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 1, characterized in that, The number of the plurality of strain sensing fibers is at least five.

3. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 1, characterized in that, The strain sensing fiber is inserted inside a stainless steel hose or a nylon hose, and the inner diameter of the stainless steel hose or nylon hose is larger than the outer diameter of the strain sensing fiber.

4. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 1, characterized in that, The temperature reference fiber is movably inserted inside a PVC pipe, and lubricating material is injected into the PVC pipe to ensure that the temperature reference fiber is in a completely stress-free state.

5. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 1, characterized in that, The data processing and early warning unit is also used to preprocess the strain and temperature data, including moving average filtering or wavelet noise reduction.

6. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 5, characterized in that, Temperature compensation is applied to the strain at each measurement point at time t to obtain the pure mechanical strain ε. j (z) j, The formula for calculating t is: ε j (z) j, t)=ε 0j (z) j, t)-α · ΔT(z j ), ε j (z) j ) represents the height z j The pure mechanical strain at the j-th measurement point, α represents the thermal expansion coefficient of concrete, and ΔT(z) is the temperature change of the j-th measurement point at time t relative to the reference temperature T0. The reference temperature T0 is the temperature data of the j-th measurement point measured by the temperature reference fiber optic cable after the concrete foundation is poured and before the first freeze-thaw cycle begins.

7. The real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 1, characterized in that, The frost heave event discrimination model includes: First-level judgment: Determine whether the temperature of the measurement point on the strain sensing fiber 2 is lower than the freezing threshold Ts. The temperature of the measurement point on the strain sensing fiber 2 is equal to the temperature of the measurement point at the same height as the temperature reference fiber 3. Second-level judgment: For measurement points that satisfy the first-level judgment, determine whether the pure mechanical strain at the measurement point exceeds the critical strain threshold ε. s And whether the strain rate exceeds the critical rate threshold ν s ; Third-level judgment: For measurement points that satisfy the second-level judgment, check whether there are multiple consecutive measurement points in the adjacent spatial region [z-ΔL, z+ΔL] that simultaneously satisfy the first-level and second-level judgments; When the number of measurement points exceeding a preset proportion meets the first-level judgment but does not meet the second-level judgment, a first-level warning is issued. If the second-level judgment is met but the third-level judgment is not met, a second-level warning is issued. When the criteria for Level 3 are met, a frost heave event is confirmed and a Level 3 warning is issued.

8. A real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to claim 7, characterized in that, The severity of frost heave is measured by the frost heave index (FHI), FHI(z, t) = ε j (z) j, t) – ε j (z j The larger the FHI value (t0), the more severe the cumulative effect of frost heave. ε j (z) j, t) represents the height z j The pure mechanical strain at measurement point j at the current time point t; ε j (z j , t0) represents at height z j The pure mechanical strain at measurement point j at reference time t0; t0 is the starting time when measurement point j first continuously meets the first-level judgment condition within a preset freezing period.

9. A method for real-time monitoring of frost heave of power transmission tower foundations in cold regions based on the real-time monitoring system for frost heave of power transmission tower foundations in cold regions according to any one of claims 1-8, characterized in that, include: Multiple strain sensing optical fibers and one temperature reference optical fiber are pre-embedded in the concrete foundation. One strain sensing optical fiber is arranged in the center of the concrete foundation, and the remaining strain sensing optical fibers are arranged around the center of the concrete foundation to form a vertical sensing column. The temperature reference fiber is laid inside the sensing column and is in a completely stress-free state. Each strain sensing fiber and temperature reference fiber has multiple measurement points arranged at vertical intervals, and the multiple measurement points have the same height. Laser pulses are emitted into all strain sensing fibers and temperature reference fibers, and the backscattered light signals to Brillouin are received. Through signal analysis, strain and temperature data of all measurement points of each strain sensing fiber and temperature reference fiber at each time point are obtained; The strain data is denoised and temperature compensated to eliminate the thermal expansion and contraction effect, and the pure mechanical strain at the measurement point is obtained. Based on pure mechanical strain and temperature data, a frost heave event discrimination model is used to conduct graded early warning and identify frost heave events.

10. The method for real-time monitoring of frost heave of power transmission tower foundations in cold regions according to claim 9, characterized in that, The frost heave event discrimination model includes a first-level judgment: judging whether the temperature of the measurement point on the strain sensing fiber 2 is lower than the freezing threshold Ts, and the temperature of the measurement point on the strain sensing fiber 2 is equal to the temperature of the measurement point at the same height on the temperature reference fiber 3. Second-level judgment: For measurement points that satisfy the first-level judgment, determine the pure mechanical strain ε of the measurement point. j (z) j, t) Whether the critical strain threshold ε is exceeded. s And whether the strain rate exceeds the critical rate threshold ν s ; Third-level judgment: For measurement points that satisfy the second-level judgment, check whether there are multiple consecutive measurement points in the adjacent spatial region [z-ΔL, z+ΔL] that simultaneously satisfy the first-level and second-level judgments; When the number of measurement points exceeding a preset proportion meets the first-level judgment but does not meet the second-level judgment, a first-level warning is issued. If the second-level judgment is met but the third-level judgment is not met, a second-level warning is issued. When the criteria for Level 3 are met, a frost heave event is confirmed and a Level 3 warning is issued; The severity of frost heave is measured by the frost heave index (FHI), FHI(z, t) = ε j (z) j, t) – ε j (z j The larger the FHI value (t0), the more severe the cumulative effect of frost heave. ε j (z) j, t) represents the height z j The pure mechanical strain at measurement point j at the current time point t; ε j (z j , t0) represents at height z j The pure mechanical strain at measurement point j at reference time t0; t0 is the starting time when measurement point j first continuously meets the first-level judgment condition within a preset freezing period.

Images