Subgrade layered settlement monitoring system and monitoring method thereof

Abstract

The present application relates to a kind of roadbed layered settlement monitoring system and its monitoring method, including perception layer, data acquisition and transmission layer and data analysis platform, perception layer is by the optical fiber integrated intelligent geotextile of being laid in each structural layer of roadbed, and distributed optical fiber strain sensor is implanted in intelligent geotextile, and it is horizontally laid layer by layer in each structural layer filling top surface, data acquisition and transmission layer gathers the strain distribution data of each layer optical fiber along line and is transmitted to data analysis platform, and data analysis platform includes strain settlement reconstruction module and layered settlement analysis module;Strain settlement reconstruction module reconstructs horizontal strain distribution into vertical displacement distribution;Layered settlement analysis module takes roadbed top surface absolute settlement as boundary condition, and recursively calculates each structural layer absolute settlement and interlayer differential settlement from ground surface downwards layer by layer, and this technical solution does not need deep physical reference point, and can realize full-section continuous settlement field monitoring.

Description

Technical Field

[0001] This invention relates to the field of safety monitoring technology for transportation engineering infrastructure, specifically to a roadbed layered settlement monitoring system and its monitoring method. Background Technology

[0002] The roadbed is an important component of railway and highway engineering. The settlement and deformation of the roadbed directly affect the safety and comfort of vehicle operation. During the long-term service of the roadbed, the cyclic dynamic load generated by the repeated passage of trains, automobiles and other vehicles will cause different degrees of cumulative plastic deformation in each structural layer of the roadbed. Since the roadbed is a layered system composed of multiple layers such as the subbase, base course and base course, the stiffness, thickness and compaction of each layer material are different. Under the action of cyclic dynamic load, the deformation response of each layer is inconsistent, which can easily lead to stratified settlement (i.e., uneven settlement between layers), which in turn causes engineering defects such as interlayer voids, reflective cracks and pumping, seriously affecting the long-term service performance of the roadbed.

[0003] Currently, the following technical methods are mainly used for monitoring roadbed settlement.

[0004] The method of manually observing settlement plates and multi-point displacement gauges mainly uses point sensors such as settlement plates and multi-point displacement gauges. By drilling holes in the roadbed and burying the sensors at different depths, the layered settlement can be measured. This method requires drilling to the bedrock or immovable layer at each monitoring section to bury the reference anchor head. The construction process is complicated and causes great damage to the integrity of the roadbed. Moreover, the reference anchor head is prone to loosening or failure during long-term service, resulting in a decrease in measurement accuracy. In addition, this method relies on manual periodic measurement, which has low data acquisition efficiency, poor real-time performance, and difficulty in capturing the continuous evolution process of roadbed settlement.

[0005] Regarding the settlement measurement method based on the principle of electromagnetic induction, Chinese patent CN101476337B discloses an automatic monitoring device for the vertical settlement and lateral displacement of roadbed layers. It adopts laser measurement technology to integrate a laser displacement sensing unit, a laser angle sensing unit, a measurement signal control unit and a data transmission unit to achieve simultaneous automatic monitoring of vertical settlement and lateral displacement. Chinese patent CN209114288U discloses a real-time monitoring system for layered deformation inside a roadbed, comprising a settlement cap, a settlement plate, carbon fiber rods, and displacement sensors. The carbon fiber rods are arranged side by side with increasing lengths, and the longest rod is anchored at its bottom end in a borehole. However, the above-mentioned device still requires drilling holes in the roadbed to embed measuring rods or settlement tubes. The magnetic ring spring claw has weak anchoring force, making it difficult to firmly grip the borehole wall. Furthermore, the gap between the settlement tube and the magnetic ring is easily filled by soil, creating resistance and leading to measurement errors. At the same time, this type of device is still a discrete point monitoring system with a limited number of measuring points, making it difficult to obtain a continuous settlement field distribution across the entire cross-section of the roadbed.

[0006] In recent years, distributed optical fiber sensing technology has been gradually introduced into the field of roadbed settlement monitoring due to its advantages such as large range, long distance and resistance to electromagnetic interference. Chinese patent CN206818159U discloses an intelligent geotextile suitable for high-speed railway subgrade deformation monitoring and control. In the process of weaving and forming high-strength geotextile, distributed optical fiber strain sensors and distributed optical fiber temperature sensors are implanted into the geotextile as additional geotextile fibers along the warp direction. The implanted distributed optical fiber sensors are used to locate the subgrade deformation position and determine the amount of deformation. Chinese invention patent application CN117822389A provides a method and system for monitoring roadbed and pavement based on three-layer buried distributed optical fiber. The method involves burying encapsulated distributed optical fiber in the road structure and calculating the structural settlement values ​​at the locations where the optical fiber is buried in the pavement surface layer, pavement base layer, and bottom of the roadbed based on the strain and temperature distribution changes along the optical fiber. Chinese patent CN211178334U discloses a roadbed deformation monitoring system based on distributed optical fiber dynamic and static strain testing, which achieves high-precision static strain and low-precision dynamic strain testing by setting different data acquisition conditions. However, the aforementioned existing technologies based on distributed optical fibers still have the following shortcomings: First, existing settlement monitoring methods based on distributed optical fibers, such as CN117822389A, still rely on deep physical benchmarks. These methods require the establishment of physical benchmarks (such as settlement plates or benchmark anchors) at the bottom of the roadbed or bedrock to provide an absolute reference for settlement calculations. This not only increases the amount of drilling and engineering costs, but also makes it difficult to guarantee the long-term stability of the benchmarks. In soft soil areas or high embankment sections, it is difficult to find a truly "fixed layer" as a benchmark. Even if one is found, the long-term anchoring reliability of the benchmark anchors under cyclic dynamic loads and groundwater environments is also highly questionable. Once the benchmarks are displaced, it will lead to a systematic deviation in the entire settlement monitoring data.

[0007] Second, the monitoring data is discrete point data rather than a continuous field. Whether it is a traditional multi-point displacement meter or an existing distributed optical fiber solution, the settlement calculation results are all settlement values ​​of a finite number of discrete points. For example, CN117822389A can only calculate the settlement values ​​of a few structural layers at the "location where the optical fiber is buried", and cannot obtain the continuous settlement field distribution of the entire cross section of the roadbed, making it difficult to accurately capture the detailed characteristics of local uneven settlement.

[0008] Third, it is difficult to obtain the differential settlement between layers in stratified settlement. Although existing technologies can obtain the absolute settlement values ​​of several layers, there is a lack of effective technical means to accurately obtain the relative settlement between layers (i.e., the differential settlement between adjacent structural layers). The differential settlement between layers is precisely the direct cause of defects such as interlayer voids and reflective cracks.

[0009] Fourth, strain-settlement conversion relies on empirical formulas or simplified models. Existing technologies mostly use empirical formulas or simplified models to convert fiber strain into settlement values, lacking rigorous mathematical derivation based on mechanical theory. The conversion accuracy under large deformation or complex load conditions is difficult to guarantee.

[0010] In summary, existing roadbed layered settlement monitoring technologies suffer from problems such as reliance on deep physical benchmarks, discretization of monitoring data, difficulty in obtaining differential settlement between layers, and lack of mechanical theoretical basis for strain-settlement conversion. There is an urgent need for a new technical solution that can solve these problems. Summary of the Invention

[0011] In view of this, the purpose of the present invention is to provide a roadbed layered settlement monitoring system and monitoring method to solve the problems of existing roadbed layered settlement monitoring technology, such as reliance on deep physical benchmarks, discretization of monitoring data, difficulty in obtaining differential settlement between layers, and lack of mechanical theoretical basis for strain settlement conversion.

[0012] This invention is achieved through the following technical solution: A roadbed layered settlement monitoring system includes: The sensing layer is composed of fiber-optic integrated smart geotextiles laid in each structural layer of the roadbed. Distributed fiber-optic strain sensors are embedded in the smart geotextiles. The smart geotextiles are laid horizontally layer by layer on the top surface of each structural layer of the roadbed. The distributed fiber-optic strain sensors in each layer of smart geotextiles sense the horizontal strain distribution generated by the corresponding structural layer under load. The data acquisition and transmission layer includes a distributed fiber optic demodulator and a data transmission module connected to the distributed fiber optic strain sensors of each layer. The distributed fiber optic demodulator acquires strain distribution data along the fiber optic lines of each layer, and the data transmission module transmits the acquired data to the data analysis platform. The data analysis platform includes a strain settlement reconstruction module and a layered settlement analysis module; The strain settlement reconstruction module reconstructs the horizontal strain distribution measured by each layer of smart geotextile into the vertical displacement distribution of the corresponding structural layer based on the mathematical relationship between the axial strain and vertical displacement of the optical fiber. The layered settlement analysis module uses the absolute settlement of the top surface of the roadbed as the boundary condition, and calculates the absolute settlement of each structural layer layer by layer from the ground surface downwards, and calculates the interlayer differential settlement between adjacent structural layers.

[0013] Further specifying, during the weaving and forming process of the high-strength geotextile, a distributed optical fiber strain sensor is implanted as an additional geotextile fiber along the warp direction of the geotextile. The distributed optical fiber temperature sensor 72 is implanted parallel to and spaced apart from the distributed optical fiber strain sensor in the high-strength geotextile. Multiple sensor positioning marks are spaced apart in the warp direction of the high-strength geotextile for physical distance positioning of the distributed optical fiber strain sensor.

[0014] Furthermore, the distributed optical fiber strain sensors in the intelligent geotextile are arranged in a serpentine or U-shaped continuous loop, with both the starting and ending ends of the optical fiber leading out of the roadbed slope and connected to the optical fiber junction box on the roadside.

[0015] Further specifying, the layered settlement analysis module uses the following recursive formula to calculate the absolute settlement of each structural layer: in, For the first The absolute settlement of the layered structure. This represents the absolute settlement of the adjacent structural layer above. For the first The vertical compression of the layered structure; By the The difference between the vertical displacement of the top surface and the vertical displacement of the bottom surface of the layered structure is determined.

[0016] Furthermore, the strain settlement reconstruction module uses the following formula to convert the axial strain distribution of the optical fiber into a vertical displacement distribution: (1) in The strain distribution along the axial direction of the optical fiber. This represents the vertical displacement distribution.

[0017] Furthermore, the absolute settlement of the top surface of the roadbed is obtained by receiver measurement and serves as the sole external boundary condition input for the layered settlement analysis module.

[0018] Further specifying, the distributed fiber optic demodulator employs Brillouin optical time-domain analysis technology, with a spatial resolution of no more than 1m and a strain resolution of no more than 10. .

[0019] Furthermore, the data analysis platform also includes a static-dynamic separation module, which decomposes the strain distribution data into static and dynamic components. The static components are used to calculate the long-term cumulative settlement of the roadbed, and the dynamic components are used to analyze the stiffness decay of each structural layer under cyclic dynamic loading.

[0020] Furthermore, the data analysis platform also includes a three-dimensional settlement field reconstruction module, which reconstructs a three-dimensional settlement cloud map of the entire roadbed section based on multi-section and multi-layer strain distribution data using a three-dimensional interpolation method.

[0021] A monitoring method for the above-mentioned roadbed layered settlement monitoring system includes the following steps: S1: During the roadbed filling construction, fiber-optic integrated smart geotextile is laid layer by layer on the top surface of each structural layer, and distributed fiber-optic strain sensors are embedded in the smart geotextile. S2: After the smart geotextile layers are laid, the initial strain distribution data along the optical fiber of each layer is collected by a distributed optical fiber demodulator as the zero strain reference for each layer. S3: During the operation of the roadbed, real-time strain distribution data along each layer of optical fiber is collected at a preset frequency using a distributed optical fiber demodulator. S4: The strain settlement reconstruction module reconstructs the horizontal strain distribution measured by each layer of smart geotextile into the real-time vertical displacement distribution of the corresponding structural layer based on the mathematical relationship between the axial strain and vertical displacement of the optical fiber. S5: Using the absolute settlement of the top surface of the roadbed as the boundary condition, the layered settlement analysis module calculates the absolute settlement of each structural layer from the ground surface down layer by layer, and calculates the interlayer differential settlement between adjacent structural layers. S6: When the absolute settlement of any structural layer or the differential settlement between layers exceeds the preset threshold, an early warning signal is issued.

[0022] The beneficial effects of this invention are as follows: This technical solution uses only the absolute settlement of the top surface of the roadbed as the boundary condition, and calculates the absolute settlement of each structural layer layer by layer from the ground surface downwards. This completely avoids the dependence on deep physical benchmarks, greatly simplifies the construction process, eliminates the long-term stability risks of benchmarks, and eliminates the need for deep physical benchmarks.

[0023] This technical solution utilizes the fully distributed characteristics of distributed optical fibers to obtain strain data continuously distributed along the entire length of the optical fiber, thereby reconstructing a continuous settlement field along the entire cross-section along the line direction and depth direction, and realizing the monitoring of the continuous settlement field along the entire cross-section.

[0024] This technical solution lays intelligent geotextiles at the interfaces of each structural layer, which can accurately obtain the vertical displacement of the top and bottom surfaces of each structural layer, thereby accurately calculating the compression of each structural layer and the differential settlement between adjacent structural layers. This provides direct data support for early warning of defects such as interlayer voids and reflective cracks, and accurately obtains the differential settlement between layers.

[0025] This technical solution derives the mathematical relationship between the axial strain and vertical displacement of optical fibers based on elasticity mechanics, avoiding the conversion errors caused by empirical formulas or simplified models in existing technologies.

[0026] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the roadbed layered settlement monitoring system of the present invention; Figure 2 This is a schematic diagram showing the layout of the distributed optical fiber strain sensor and the distributed optical fiber temperature sensor in the intelligent geotextile of this invention. Figure 3 This is a flowchart of the roadbed layered settlement monitoring method of the present invention; In the diagram: 1. Top surface of the roadbed; 2. Base course; 3. Subbase course; 4. Subgrade; 5. Foundation; 6. Smart geotextile; 71. Distributed fiber optic strain sensor; 72. Distributed fiber optic temperature sensor; 8. Fiber optic junction box; 9. Distributed fiber optic demodulator; 10. Data transmission module; 11. Data analysis platform; 12. GNSS receiver. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the above description of the present invention, it should be noted that the terms "one side," "the other side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is conventionally placed during use. These terms are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] Furthermore, terms such as "identical" do not imply that components must be absolutely identical; minor differences are permissible. The term "perpendicular" simply means that the positional relationship between components is more perpendicular than "parallel," not that the structure must be perfectly perpendicular; a slight tilt is acceptable.

[0033] Example 1 like Figure 1 As shown, the roadbed layered settlement monitoring system of this embodiment includes a sensing layer, a data acquisition and transmission layer, and a data analysis platform 11.

[0034] The sensing layer consists of fiber optic integrated smart geotextile 6 laid in each structural layer of the roadbed. The roadbed consists of three layers from bottom to top: cushion layer 4, subbase layer 3 and base layer 2. On the top surface of each structural layer, namely the top surface of cushion layer 4, the top surface of subbase layer 3 and the top surface of base layer 2, a layer of smart geotextile 6 is laid horizontally layer by layer. Distributed fiber optic strain sensor 71 and distributed fiber optic temperature sensor 72 are embedded in the smart geotextile 6. The manufacturing method of the intelligent geotextile 6 is as follows: During the weaving and forming process of the high-strength geotextile, distributed optical fiber strain sensors 71 and distributed optical fiber temperature sensors 72 are embedded into the high-strength geotextile as additional geofibers along the warp direction of the geotextile; the distributed optical fiber temperature sensors 72 and distributed optical fiber strain sensors 71 are embedded in parallel and at intervals; multiple sensor positioning marks are embedded at certain intervals in the warp direction of the high-strength geotextile for physical distance positioning of the distributed optical fiber strain sensors 71 and distributed optical fiber temperature sensors 72 on the high-strength geotextile. like Figure 2 As shown, the distributed optical fiber strain sensor 71 in the smart geotextile 6 is arranged in a serpentine continuous loop. The starting end and the end of the optical fiber are led out of the roadbed slope and connected to the optical fiber junction box 8 on the roadside. The optical fiber junction box 8 has an IP68 protection level. The data acquisition and transmission layer includes a distributed fiber optic demodulator 9 and a data transmission module 10. The distributed fiber optic demodulator 9 employs Brillouin optical time-domain analysis technology, with a spatial resolution of no more than 1 m and a strain resolution of no more than 10. The distributed optical fiber demodulator 9 is connected to the optical fiber led out from each layer of smart geotextile 6 through an optical switch to realize multi-channel polling acquisition. The data transmission module 10 adopts a 4G / 5G wireless communication module to transmit the acquired data to the data analysis platform 11 in real time. The data analysis platform 11 is deployed on a cloud server and includes a strain settlement reconstruction module, a layered settlement analysis module, a dynamic-static separation module, and a three-dimensional settlement field reconstruction module. The strain settlement reconstruction module, based on the principles of elasticity, uses the following formula to convert the axial strain distribution of the optical fiber into a vertical displacement distribution: (1) in The strain distribution along the axial direction of the optical fiber. The vertical displacement distribution; The layered settlement analysis module uses the absolute settlement of the top surface 1 of the roadbed as the boundary condition. This absolute settlement is obtained by measuring with GNSS receiver 12 and is calculated layer by layer from the ground surface downwards. The specific recursive process is as follows: For base course 2, the absolute settlement of its top surface (i.e., top surface 1 of the roadbed) is known to be... (Measured by GNSS receiver 12), the compression of base layer 2 The vertical displacement is determined by the difference between the top and bottom surfaces of the base layer 2 (the vertical displacement of the top surface is...). The vertical displacement of the bottom surface is obtained by reconstructing the strain data measured by the intelligent geotextile 6 embedded in the bottom surface of the base layer 2 using formula (1). Then the absolute settlement of the bottom surface of the base layer 2 is... ; For the base course 3, the absolute settlement of its top surface (i.e., the bottom surface of base course 2) is known to be... Compression of base layer 3 The absolute settlement of the bottom surface of base course 3 is determined by the difference in vertical displacement between the top and bottom surfaces. ; For subbase layer 4, the same principle applies. ; Therefore, the absolute settlement of each structural layer can be obtained. , , , and the compression of each structural layer , , This allows for differential settlement between adjacent structural layers; The static-dynamic separation module decomposes the strain distribution data into static and dynamic components through digital filtering. The static component reflects the cumulative plastic deformation of the subgrade under its own weight and long-term load, and is used to calculate the long-term cumulative settlement. The dynamic component reflects the elastic vibration response under traffic cycle dynamic load, and is used to analyze the attenuation of the dynamic elastic modulus of each structural layer. The three-dimensional settlement field reconstruction module reconstructs a three-dimensional settlement cloud map of the entire roadbed section based on strain distribution data from multiple monitoring sections and multiple structural layers, using a three-dimensional cubic spline interpolation method.

[0035] like Figure 3 As shown, the monitoring method includes the following steps: S1: During the subgrade filling construction, fiber-optic integrated smart geotextile 6 is laid layer by layer on the top surface of each structural layer. Specifically, after the subbase 4 is filled, compacted to the design elevation and leveled, the first layer of smart geotextile 6 is laid on the top surface of the subbase 4; then the base course 3 is backfilled and compacted to the design elevation, and the second layer of smart geotextile 6 is laid on the top surface of the base course 3; then the base course 2 is backfilled and compacted to the design elevation, and the third layer of smart geotextile 6 is laid on the top surface of the base course 2. Each layer of smart geotextile 6 should be stretched flat and tightly attached to the fill surface, without wrinkles or gaps, and the overlap width between adjacent sections should not be less than 30cm. S2: Within 24 hours after the completion of each layer of smart geotextile 6, the initial strain distribution data along the optical fiber of the layer is collected by the distributed optical fiber demodulator 9 and used as the strain zero reference of the layer. S3: During the operation of the roadbed, the distributed optical fiber demodulator 9 collects real-time strain distribution data along each layer of optical fiber at a preset frequency. The normal collection frequency is once per hour. When the strain change rate is detected to exceed 3 times the daily fluctuation threshold, it automatically switches to the encrypted collection mode with a sampling rate of not less than 1Hz. S4: The strain settlement reconstruction module reconstructs the horizontal strain distribution measured by each layer of smart geotextile 6 into the real-time vertical displacement distribution of the corresponding structural layer based on formula (1). S5: Using the absolute settlement of the top surface 1 of the roadbed (obtained by GNSS receiver 12) as the boundary condition, the layered settlement analysis module calculates the absolute settlement of each structural layer from the ground surface downwards, and calculates the compression of each structural layer and the differential settlement between adjacent structural layers. S6: The data analysis platform 11 has a built-in three-level early warning threshold. When the settlement rate of any structural layer exceeds 70% of the design value, a yellow warning is triggered; when the settlement rate exceeds the design value, an orange warning is triggered; when the differential settlement between layers exceeds the allowable value or the settlement rate continues to increase, a red warning is triggered. The warning information is pushed simultaneously through three channels: Web, mobile APP and SMS.

[0036] Effect verification To verify the actual effectiveness of this embodiment and technical solution, a comparative monitoring test was conducted on a test section of a highway (200m long, 6m high, including a three-layer structure of subbase, base course, and base course). Both the technical solution and the traditional electromagnetic stratified settlement meters were deployed, and a 10-month comparative monitoring test was carried out. Measurement points for both monitoring schemes were set up at the same cross-section and layer. The monitoring data are compared below: Table 1 Comparison of monitoring results between this technical solution and the electromagnetic stratified settlement meter (cumulative settlement over 10 months, unit: mm) Table 2 Performance Comparison of the Two Monitoring Schemes Comparative results show that the measurement deviation between this technical solution and the electromagnetic stratified settlement meter is between 0.2 and 0.3 mm, and the measurement accuracy meets the requirements of engineering monitoring. At the same time, this technical solution is superior to the existing technology in terms of measuring point density, degree of automation, and ability to obtain interlayer differential settlement. In addition, the accuracy of the strain settlement reconstruction algorithm in this technical solution was verified by indoor model test: smart geotextile was pre-embedded in the fill soil, and high-precision displacement sensors (accuracy 0.01mm) were buried at the same depth as a control. Vertical loads were applied step by step, and the settlement under each load was recorded. The test results show that: During the small deformation stage (settlement less than 10mm), the relative error between the reconstructed settlement value and the measured value by the displacement sensor in this technical solution is 3.2% to 5.6%. The relative error during the large deformation stage (settlement of 10-30 mm) was 4.8%-8.1%; the overall average relative error was approximately 6%. During the 10-month monitoring period, the system in this embodiment achieved unattended continuous operation with a data acquisition success rate of 97.3%. A total of two yellow alerts and one orange alert were triggered during the monitoring period, and all alert information was pushed to the management personnel's terminal within one minute. In terms of construction efficiency, under the same number of cross sections (5 monitoring sections), this technical solution does not require drilling and can be carried out simultaneously with the filling construction, saving about 3 days of construction time compared with the traditional drilling and installation solution, and does not take up extra construction time. Example 2 The difference between this embodiment and embodiment 1 is that the distributed optical fiber strain sensor 71 in the smart geotextile 6 is arranged in a U-shaped continuous loop (instead of a serpentine shape), which is suitable for scenarios with a small roadbed width or a short monitoring section. The rest of the structure and monitoring method are the same as in embodiment 1. Effect verification To verify the applicability of the U-shaped layout method in narrow roadbed scenarios, a section with a roadbed width of 12m was selected in a secondary highway reconstruction project. Smart geotextiles were laid using both serpentine and U-shaped layouts to compare the strain measurement effects of the two methods. Two smart geotextiles were laid on the top surface of the base course at the same cross-section: one using a serpentine loop (fiber optic cable spacing 1.0m) and the other using a U-shaped loop (fiber optic cable spacing 1.2m). Strain data were collected synchronously and continuously for 30 days, yielding a total of 720 sets of valid data. The comparison results are as follows: Table 3 Comparison of strain measurement results between serpentine and U-shaped layouts (unit: ) The test results show that the strain measurement deviation between the serpentine and U-shaped layouts at each measuring point is between -0.7% and +1.1%, and the measurement results of the two layout methods have good consistency. Under narrow roadbed conditions (width less than 15m), the number of bends in the U-shaped layout is reduced by about 40% compared to the serpentine layout, and the number of fiber optic splice points is reduced accordingly. The average fiber survival rate increases from 96.2% in the serpentine layout to 98.5%. At the same time, the U-shaped layout can save about 15% of fiber usage. This shows that in scenarios with narrow roadbeds, the U-shaped layout has a higher fiber survival rate and lower material cost than the serpentine layout, and is more economical without sacrificing measurement accuracy. Example 3 The difference between this embodiment and embodiment 1 is that the subgrade structure has four layers (subbase, base course, base course, and functional layer at the bottom of the surface course). A layer of intelligent geotextile 6 is laid on the top surface of each structural layer. The recursive calculation of the layered settlement analysis module is extended to four layers. The remaining structure and monitoring methods are the same as in embodiment 1. Effect verification To verify the applicability of the recursive algorithm in this technical solution for a four-layer structure scenario, a section with a roadbed height of 8m (including four layers: subbase, base course, base course, and bottom functional layer of the surface course) was selected as a test section of a newly built highway. The technical solution and the manual leveling method were compared and verified. A smart geotextile was laid on the top surface of each structural layer, and settlement observation points were simultaneously installed at the roadbed slopes of the same layer. A precision level (accuracy 0.1mm) was used for manual measurement as a control. Monitoring began immediately after each layer was laid and continued for 6 months. The cumulative settlement data for each layer are as follows: Table 4 Comparison of this technical solution and leveling measurement results under four-layer structure conditions (cumulative settlement over 6 months, unit: mm) Table 5 Comparison of monitoring effects between the three-layer structure (Example 1) and the four-layer structure (Example 3) The comparison results show that under the four-layer structure condition, the deviation between the proposed technical solution and the precision leveling measurement results is 0.2-0.3 mm, which is comparable to the measurement accuracy under the three-layer structure condition. This indicates that the recursive algorithm in the proposed technical solution can still maintain good measurement accuracy when the number of structural layers increases. When the number of recursive calculation steps increases from 3 to 4, the cumulative settlement error increases from ≤0.5 mm to ≤0.7 mm, but it is still within the acceptable range for engineering (usually ≤1 mm is required), meeting the engineering monitoring accuracy requirements. Example 3 verifies the applicability of the proposed technical solution in multi-layer roadbed structures and proves that the recursive algorithm has good scalability.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A roadbed layered settlement monitoring system, characterized in that: include: The sensing layer is composed of fiber-optic integrated smart geotextiles laid in each structural layer of the roadbed. Distributed fiber-optic strain sensors are embedded in the smart geotextiles. The smart geotextiles are laid horizontally layer by layer on the top surface of each structural layer of the roadbed. The distributed fiber-optic strain sensors in each layer of smart geotextiles sense the horizontal strain distribution generated by the corresponding structural layer under load. The data acquisition and transmission layer includes a distributed fiber optic demodulator and a data transmission module connected to the distributed fiber optic strain sensors of each layer. The distributed fiber optic demodulator acquires strain distribution data along the fiber optic lines of each layer, and the data transmission module transmits the acquired data to the data analysis platform. The data analysis platform includes a strain settlement reconstruction module and a layered settlement analysis module; The strain settlement reconstruction module reconstructs the horizontal strain distribution measured by each layer of smart geotextile into the vertical displacement distribution of the corresponding structural layer based on the mathematical relationship between the axial strain and vertical displacement of the optical fiber. The layered settlement analysis module uses the absolute settlement of the top surface of the roadbed as the boundary condition, and calculates the absolute settlement of each structural layer layer by layer from the ground surface downwards, and calculates the interlayer differential settlement between adjacent structural layers.

2. The roadbed layered settlement monitoring system according to claim 1, characterized in that: During the weaving and forming process of the high-strength geotextile, distributed optical fiber strain sensors are embedded as additional geotextile fibers along the warp direction of the geotextile. Distributed optical fiber temperature sensors 72 are embedded in the high-strength geotextile parallel to and at intervals with the distributed optical fiber strain sensors. Multiple sensor positioning marks are set at intervals in the warp direction of the high-strength geotextile for physical distance positioning of the distributed optical fiber strain sensors.

3. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The distributed optical fiber strain sensors in the intelligent geotextile are arranged in a serpentine or U-shaped continuous loop, with the starting and ending ends of the optical fiber leading out of the roadbed slope and connected to the optical fiber junction box on the roadside.

4. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The layered settlement analysis module uses the following recursive formula to calculate the absolute settlement of each structural layer: in, For the first The absolute settlement of the layered structure. This represents the absolute settlement of the adjacent structural layer above. For the first The vertical compression of the layered structure; By the The difference between the vertical displacement of the top surface and the vertical displacement of the bottom surface of the layered structure is determined.

5. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The strain settlement reconstruction module uses the following formula to convert the axial strain distribution of the optical fiber into a vertical displacement distribution: （1） in The strain distribution along the axial direction of the optical fiber. This represents the vertical displacement distribution.

6. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The absolute settlement of the top surface of the roadbed is obtained by measuring with a GNSS receiver and serves as the sole external boundary condition input for the layered settlement analysis module.

7. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The distributed fiber optic demodulator employs Brillouin optical time-domain analysis technology, with a spatial resolution of no more than 1m and a strain resolution of no more than 10. .

8. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The data analysis platform also includes a static-dynamic separation module, which decomposes the strain distribution data into static and dynamic components. The static components are used to calculate the long-term cumulative settlement of the roadbed, and the dynamic components are used to analyze the stiffness decay of each structural layer under cyclic dynamic loads.

9. The roadbed layered settlement monitoring system according to claim 1, characterized in that: The data analysis platform also includes a three-dimensional settlement field reconstruction module, which reconstructs a three-dimensional settlement cloud map of the entire roadbed section based on multi-section and multi-layer strain distribution data and using a three-dimensional interpolation method.

10. A method for monitoring the layered settlement of roadbed using the system described in any one of claims 1-9, characterized in that: Includes the following steps: S1: During the roadbed filling construction, fiber-optic integrated smart geotextile is laid layer by layer on the top surface of each structural layer, and distributed fiber-optic strain sensors are embedded in the smart geotextile. S2: After the smart geotextile layers are laid, the initial strain distribution data along the optical fiber of each layer is collected by a distributed optical fiber demodulator as the zero strain reference for each layer. S3: During the operation of the roadbed, real-time strain distribution data along each layer of optical fiber is collected at a preset frequency using a distributed optical fiber demodulator. S4: The strain settlement reconstruction module reconstructs the horizontal strain distribution measured by each layer of smart geotextile into the real-time vertical displacement distribution of the corresponding structural layer based on the mathematical relationship between the axial strain and vertical displacement of the optical fiber. S5: Using the absolute settlement of the top surface of the roadbed as the boundary condition, the layered settlement analysis module calculates the absolute settlement of each structural layer from the ground surface down layer by layer, and calculates the interlayer differential settlement between adjacent structural layers. S6: When the absolute settlement of any structural layer or the differential settlement between layers exceeds the preset threshold, an early warning signal is issued.

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