A slope stress and flow field coupling monitoring device and method based on optical fiber sensing

Abstract

This invention discloses a slope stress and flow field coupling monitoring device and method based on fiber optic sensing, belonging to the field of slope stability monitoring technology. The device comprises a base at the bottom of a housing, with a lifting assembly located below one end of the base. The housing is filled with experimental soil, with optical fibers embedded both inside and on the surface of the soil. A rainfall assembly is located above the housing, and several pore water pressure sensors are positioned above the base. The outputs of the pore water pressure sensors and the optical fibers are connected to the input of a Brillouin optical time domain reflectometer (OTDR). The output of the OOTDR is connected to the input of a main control module, which controls the lifting assembly, the rainfall assembly, and generates early warning signals. This invention solves the problems of missing multi-field coupling and discontinuous monitoring in existing technologies, improving the simulation realism of slope rainfall-induced instability processes.

Description

Technical Field

[0001] This invention belongs to the field of open-pit coal mine slope stability monitoring technology, and particularly relates to a slope stress and flow field coupling monitoring device and method based on fiber optic sensing. Background Technology

[0002] Existing slope monitoring models and technologies have the following main shortcomings: 1. Simplified boundary condition simulation: Traditional physical models often use a single constraint method, which does not fully consider the actual stress characteristics of the slope. Boundary disturbances can easily lead to distortion of internal stress distribution, making it impossible to accurately simulate the lateral deformation free characteristics of an infinite slope. 2. Lack of multiphysics coupling simulation: Existing models mostly consider stress field or static seepage field separately, without systematically integrating dynamic rainfall simulation. They ignore the interaction between rainfall-induced seepage field changes and mechanical field. In fact, slope instability is mostly induced by rainfall, resulting in a large deviation between monitoring results and actual engineering. 3. Poor coupling effect between optical fiber and soil: Optical fiber is often laid by surface bonding or direct pre-embedding, which can easily lead to problems such as air gaps and suspension, resulting in stress transfer failure and inability to accurately obtain data on the internal strain evolution of the slope during rainfall. 4. Insufficient dynamic monitoring capabilities: Existing technologies are unable to capture real-time dynamic changes in pore water pressure, strain, and displacement during rainfall, and lack linkage monitoring of rainfall intensity, seepage, and stress response; 5. Lack of close integration between experiments and numerical methods: The rainfall simulation in the physical model is disconnected from the fluid-structure interaction calculation in the numerical model. Experimental data cannot effectively calibrate the numerical model, resulting in insufficient accuracy of the coupling analysis. Summary of the Invention

[0003] To address the technical problems existing in the prior art, this invention provides a device and method for monitoring slope stress and flow field coupling based on fiber optic sensing.

[0004] According to a first aspect of the technical solution of the present invention, a slope stress and flow field coupling monitoring device based on fiber optic sensing is provided, which includes a box, a base at the bottom of the box, a lifting component below one end of the base, experimental soil filling the box, optical fibers being provided inside and on the surface of the experimental soil, a rainfall component being provided on the hillside of the box, and a plurality of pore water pressure sensors being provided above the base. The output ends of the plurality of pore water pressure sensors and the optical fibers are all connected to the input end of a Brillouin optical time domain reflectometer. The output end of the Brillouin optical time domain reflectometer is connected to the input end of a main control module. The main control module is used to control the lifting component and the rainfall component, and the main control module is also used to generate an early warning signal based on the input of the Brillouin optical time domain reflectometer. The optical fiber includes surface optical fibers uniformly arranged on the surface of the experimental soil and internal optical fibers inserted into the experimental soil. The arrangement direction of the surface optical fibers is perpendicular to the direction in which the experimental soil forms a slope. The internal optical fibers include several vertical optical fibers inserted vertically into the experimental soil and several horizontal optical fibers inserted horizontally into the experimental soil. The soil used in the experiment, from bottom to top, includes bedrock, a weak layer, and a landslide body; The top of the landslide body is equipped with a deep water channel.

[0005] A further improvement of the present invention is that the optical fiber installed inside the experimental soil is installed using a shallow trench pre-embedding method.

[0006] A further improvement of the present invention is that: the boundary of the slope formed by the experimental soil is set as a free permeability boundary, the bottom boundary of the slope formed by the experimental soil is set as a water-impermeable layer, and the two side boundaries of the slope formed by the experimental soil are set as weakly permeable boundaries.

[0007] A further improvement of the present invention is that: the bottom boundary of the box body is provided with a fixed constraint, and the two side boundaries of the box body are provided with a rolling constraint.

[0008] A further improvement of the present invention is that the optical fiber is waterproofed and bend-resistant where it passes through the housing.

[0009] A further improvement of the present invention is that the maximum included angle between the base and the bottom of the box is 30°.

[0010] A further improvement of the present invention is that the box body is made of plexiglass and the base is made of steel plate.

[0011] A further improvement of the present invention is that the rainfall intensity adjustment range of the rainfall component is 0 mm / h-100 mm / h, and the rainfall uniformity is ≥90%.

[0012] According to a second aspect of the technical solution of the present invention, a method for monitoring slope stress and flow field coupling based on fiber optic sensing is provided, and a slope stress and flow field coupling monitoring device based on fiber optic sensing as described above includes the following steps: Step S1: Fill the base inside the box with experimental soil in layers, lay optical fibers inside and on the surface of the experimental soil, and lay several pore water pressure sensors above the base. Step S2: Connect the output end of the optical fiber to the input end of the Brillouin optical time domain reflectometer, and connect the output end of the pore water pressure sensor to the input end of the Brillouin optical time domain reflectometer. Step S3: Adjust the tilt angle of one end of the base by controlling the lifting component through the main control module; Step S4: Control the rainfall component through the main control module to apply simulated rainfall to the experimental soil surface above the box; Step S5: Real-time acquisition of fiber frequency shift data and pore water pressure data from pore water pressure sensor using Brillouin optical time domain reflectometer, and transmission to main control module; Step S6: The main control module generates slope stress-seepage field coupling state information based on the frequency shift data and pore water pressure data, and generates an early warning signal based on the slope stress-seepage field coupling state information.

[0013] A further improvement of the present invention is that step S6 specifically includes the following steps: The frequency shift data and the pore water pressure data are preprocessed first; The preprocessed frequency shift data and pore water pressure data are subjected to feature extraction to obtain several feature data. The acquired feature data is input into a preset coupled analysis model to obtain the slope stress-seepage field coupled state information.

[0014] Compared with the prior art, the above-mentioned technical solution of the present invention has the following beneficial technical effects: 1. This invention integrates a slope physical model, distributed fiber optic sensing, dynamic rainfall simulation, and a multi-parameter collaborative monitoring system to achieve full-process, distributed, and real-time coupled monitoring of the internal stress field and seepage field of a slope under rainfall conditions. It solves the key problems in existing technologies, such as boundary simulation distortion, lack of multi-field coupling, discontinuous monitoring, and disconnect between experiments and numerical analysis. It improves the simulation realism of the slope rainfall-induced instability process, the spatiotemporal resolution of monitoring data, and the accuracy and timeliness of disaster early warning.

[0015] 2. Based on the multi-directional arrangement of optical fibers on and inside the slope, this invention realizes three-dimensional monitoring of the transverse strain of the slope surface, the vertical compression of the deep layer, and the horizontal shear deformation. It solves the problem of insufficient spatial coverage of traditional point monitoring and improves the ability to capture potential sliding surfaces and strain concentration areas.

[0016] 3. This invention uses a shallow trench pre-embedding process to arrange internal optical fibers, which achieves tight coupling between the optical fibers and the surrounding soil, avoids suspension and gaps, solves the problem of monitoring data distortion caused by stress transmission failure, and improves the accuracy and reliability of strain monitoring.

[0017] 4. This invention simulates the actual geological composition of slopes based on the layered soil structure, enabling differentiated observation of the mechanical and seepage behaviors of different soil and rock materials under rainfall conditions. It solves the problem that the homogeneous soil model does not match the actual engineering geological conditions and improves the engineering reference value of the test results.

[0018] 5. This invention adopts boundary settings that conform to actual hydrogeological conditions, realizing a realistic simulation of rainfall infiltration, runoff and lateral seepage. It solves the problem of distortion of the seepage field caused by overly simplified boundary conditions in traditional models, and improves the simulation realism of the seepage-stress coupling process.

[0019] 6. This invention adopts a constraint method of bottom fixation and side rolling, which realizes a reasonable simulation of the stable rock layer at the bottom of the slope and the free characteristics of lateral deformation. It solves the problem of stress distribution distortion caused by excessive traditional boundary constraints and improves the simulation accuracy of slope mechanical response.

[0020] 7. This invention achieves long-term stable operation of optical fiber in humid environments through waterproof sealing and anti-bending protection measures, solves the problems of signal attenuation, fiber breakage and water seepage affecting the continuity of monitoring, and improves the reliability and durability of the device in rainfall tests.

[0021] 8. By setting an adjustable slope range, this invention enables the simulation of various slope types, from gentle to steep slopes, solving the problem of limited applicability of fixed slope models and improving the adaptability and testing flexibility of the device for different engineering slope conditions.

[0022] 9. This invention uses a combination of an organic glass box and a steel plate base to achieve a balance between observation transparency and structural stability. It solves the problems of traditional models being inconvenient for internal observation or prone to deformation, and improves the visualization of the experimental process and the overall rigidity of the model. Attached Figure Description

[0023] The accompanying drawings are provided to better understand the invention and are not intended to unduly limit the scope of the invention. Wherein: Figure 1 This is a schematic diagram of the structure of a slope stress and flow field coupling monitoring device based on fiber optic sensing according to the present invention. Figure 2 This is a schematic diagram of the soil layering structure used in the experimental part of a slope stress and flow field coupling monitoring device based on fiber optic sensing according to the present invention. Figure 3 This is a schematic diagram of the fiber arrangement structure in a fiber optic sensing-based slope stress and flow field coupling monitoring device of the present invention. Figure 4 This is a schematic diagram of the geometric and fluid-structure coupling boundary of the numerical model in an embodiment of a slope stress and flow field coupling monitoring device based on fiber optic sensing according to the present invention.

[0024] The reference numerals in the attached figures are as follows: 1. Housing; 2. Base; 3. Lifting assembly; 4. Rainfall assembly; 5. Pore water pressure sensor; 6. Brillouin optical time domain reflectometer. Detailed Implementation

[0025] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0026] This invention discloses a slope stress and flow field coupling monitoring device and method based on fiber optic sensing, belonging to the field of slope stability monitoring technology. The device comprises a base at the bottom of a housing, with a lifting assembly located below one end of the base. The housing is filled with experimental soil, with optical fibers embedded both inside and on the surface of the soil. A rainfall assembly is located above the housing, and several pore water pressure sensors are positioned above the base. The outputs of the pore water pressure sensors and the optical fibers are connected to the input of a Brillouin optical time domain reflectometer (OTDR). The output of the OOTDR is connected to the input of a main control module, which controls the lifting assembly, the rainfall assembly, and generates early warning signals. This invention solves the problems of missing multi-field coupling and discontinuous monitoring in existing technologies, improving the simulation realism of slope rainfall-induced instability processes.

[0027] The following describes in detail the slope stress and flow field coupling monitoring device and method based on fiber optic sensing of the present invention, with reference to the embodiments and accompanying drawings.

[0028] Example 1 like Figure 1As shown, a slope stress and flow field coupling monitoring device based on fiber optic sensing is provided. It includes a housing 1, with a base 2 at the bottom of the housing 1. A lifting assembly 3 is located below one end of the base 2. The housing 1 is filled with experimental soil. Fiber optic cables are installed inside and on the surface of the experimental soil. A rainfall assembly 4 is located above the housing 1. Several pore water pressure sensors 5 are located above the base 2. The output ends of the pore water pressure sensors and the fiber optic cables are connected to the input end of a Brillouin optical time domain reflectometer 6. The output end of the Brillouin optical time domain reflectometer 6 is connected to the input end of a main control module. The main control module controls the lifting assembly 3 and the rainfall assembly 4, and also generates an early warning signal based on the input of the Brillouin optical time domain reflectometer 6. Experimental soil is layered and filled inside the housing 1 to simulate a slope structure, and the tilt angle of one end of the base 2 is adjusted by the lifting assembly 3 to simulate natural slopes with different gradients. A fiber optic sensing network is deployed inside and on the surface of the soil, while pore water pressure sensors 5 are embedded at key locations. A rainfall component 4 simulates rainfall conditions of varying intensities and durations above the enclosure 1. Rainfall infiltration increases soil moisture content and pore water pressure, thereby altering the effective stress and strain state of the soil. The fiber optic cables embedded in the soil exhibit Brillouin frequency shifts due to soil deformation. These shifts are collected in real-time by a Brillouin optical time-domain reflectometer 6 and converted into distributed strain data. Combined with data from the pore water pressure sensors 5, the main control module calculates the stress distribution using Hooke's law and analyzes the dynamic coupling process between the stress field and the seepage field. When a sudden strain change, a rapid increase in pore water pressure, or a calculated safety factor falls below the warning threshold is detected, the main control module automatically generates a warning signal, achieving early warning of slope instability. This system enables full-process, distributed, and dynamic coupled monitoring of slope stress and seepage fields under rainfall conditions, overcoming the shortcomings of insufficient spatial coverage in traditional point-based monitoring. By combining physical models with fiber optic sensing technology, it can accurately capture the spatiotemporal correlation between internal slope strain evolution and pore water pressure diffusion, providing real and continuous data support for the study of rainfall-induced landslide mechanisms. The built-in intelligent early warning mechanism can identify potential hazards in advance based on multi-parameter fusion analysis, significantly improving the accuracy and timeliness of slope disaster early warning. The device has a flexible structure and can be adapted to the simulation monitoring needs of different types of slopes by adjusting rainfall parameters, slope, and soil composition, making it highly applicable to engineering and applicable to widespread use.

[0029] Specifically, the optical fibers include surface optical fibers uniformly arranged on the surface of the experimental soil and internal optical fibers inserted into the experimental soil. The arrangement direction of the surface optical fibers is perpendicular to the direction in which the experimental soil forms the slope. The internal optical fibers include several vertically inserted vertical optical fibers and several horizontally inserted horizontal optical fibers. Based on the above optical fiber arrangement, the slope model formed in the box 1 can achieve full-section, multi-directional strain monitoring: the surface optical fibers are distributed laterally (perpendicular to the slope direction), which can sensitively capture the lateral tensile and compressive strain of the slope surface and the possible crack propagation; among the internal optical fibers, the vertical optical fibers are used to monitor the compression or settlement deformation of the soil along the depth direction, while the horizontal optical fibers are used to reveal the phenomenon of horizontal shear strain concentration near the potential sliding surface. This spatially gridded optical fiber layout, combined with the pore water pressure sensor 5, enables the Brillouin optical time domain reflectometer 6 to acquire the coupled evolution data of the three-dimensional strain field and seepage field of the slope during rainfall infiltration, thereby providing a more comprehensive and three-dimensional information basis for the early warning judgment of the main control module.

[0030] Specifically, the optical fibers embedded within the experimental soil are installed using a shallow trench pre-embedding method. During the layered filling and compaction of the experimental soil, a shallow trench is excavated on the surface of each compacted layer. The optical fibers are then placed within the trench along a predetermined path, and backfilled and compacted with filler of the same material as the experimental soil, ensuring close contact between the optical fibers and the surrounding soil without any gaps or suspension. This shallow trench pre-embedding method avoids the bending and damage that can occur with direct burial, and overcomes the problem of insufficient fiber-soil coupling when directly surface-bonded. It ensures that soil deformation is effectively transmitted to the optical fiber sensing unit, thereby improving the accuracy and reliability of strain monitoring. Furthermore, this method is simple to construct, causes minimal disturbance to the soil, and helps maintain the original state of the slope model and the consistency of the experiment.

[0031] Specifically, the experimental soil, from bottom to top, includes bedrock, a weak layer, and a landslide mass. The parameters corresponding to each layer are shown in Table 1. In addition to Table 1, the following supplementary parameters are also included: landslide mass elastic modulus 3e7 Pa, Poisson's ratio 0.36; weak layer elastic modulus 1e7 Pa, Poisson's ratio 0.35; bedrock elastic modulus 9.4e8 Pa, Poisson's ratio 0.27; fluid density 1e3 kg / m³, fluid modulus 2e5 Pa.

[0032] Table 1

[0033] Specifically, the slope boundary formed by the experimental soil is set as a free permeable boundary, the bottom boundary of the slope formed by the experimental soil is set as an impermeable layer, and the two side boundaries of the slope formed by the experimental soil are set as weakly permeable boundaries. The free permeable boundary allows runoff of non-infiltrating rainwater, the impermeable layer is used to simulate the impermeability of bedrock, and the weakly permeable boundary is used to restrict lateral seepage. The above boundary conditions enable the device to more realistically simulate the hydrological boundary behavior of natural slopes during rainfall: the free permeable boundary of the slope realistically reflects the distribution process of surface runoff and infiltration during rainfall; the bottom impermeable boundary simulates the restrictive effect of underlying bedrock or relatively impermeable layers on groundwater movement; and the two weakly permeable boundaries on both sides better reproduce the hydrogeological conditions of limited but not completely isolated lateral seepage in actual slopes. This boundary system provides a realistic hydraulic driving environment for rainfall infiltration simulated by the rainfall component 4, pore pressure response monitored by the pore water pressure sensor 5, and soil strain sensed by optical fiber, thereby significantly improving the realism of the slope fluid-structure interaction process simulation and the engineering reference value of the monitoring data.

[0034] Specifically, the bottom boundary of the box 1 is provided with fixed constraints, and the two side boundaries of the box 1 are provided with rolling constraints. The fixed constraints are used to limit vertical and horizontal displacements to simulate the stable underlying rock layer of the slope, while the rolling constraints are used to limit horizontal displacement but allow vertical displacement to simulate the free lateral deformation of an infinite slope. The setting of boundary constraints effectively reduces the interference of the model boundaries on the stress and deformation distribution inside the slope: the bottom fixed constraint realistically simulates the fixed connection between the bottom of the slope and the stable bedrock, ensuring the reasonable transmission of the slope's self-weight stress field; the two side rolling constraints allow vertical deformation of the soil (such as settlement) while avoiding unrealistic stress concentration caused by excessive lateral constraints. This combination of boundary conditions enables the slope physical model constructed in the box 1 to better reflect the deformation characteristics of "fixed bottom and relatively free lateral movement" in natural slopes, thus providing a more realistic mechanical basis for the strain data monitored by optical fibers and the slope stability state obtained based on this data analysis.

[0035] Specifically, the optical fiber is waterproofed and bend-resistant at the point where it passes through housing 1. A sealing ring and waterproof sealant are applied at the wall penetration hole of the optical fiber exiting housing 1 to create a multi-layered seal, preventing external moisture from seeping into the housing or leaking along the fiber. Simultaneously, a corrugated protective tube is fitted over the fiber exit section, maintaining a minimum bending radius of 5cm to prevent signal attenuation or fiber breakage due to excessive bending. These measures ensure the reliability and durability of the optical fiber in long-term rainfall simulation tests and potentially high-humidity environments: the waterproofing prevents moisture from intruding along the fiber and affecting signal quality and monitoring stability, while the bend-resistant treatment ensures the fiber is not easily damaged during installation, testing, and disassembly, maintaining normal optical signal transmission. These detailed designs further improve the operational stability and data accuracy of the entire monitoring device under complex test conditions, ensuring the continuity and reliability of the slope stress-seepage coupling monitoring process.

[0036] Specifically, the maximum angle between the base 2 and the bottom of the housing 1 is 30°. This angle range covers the typical slopes of common natural and engineering slopes, enabling the device to simulate various working conditions from gentle to steep slopes. By adjusting the tilt angle of the base 2 through the lifting component 3, different slope angles can be flexibly set, thereby studying the impact of slope changes on rainfall infiltration, pore water pressure distribution, soil stress-strain response, and overall slope stability. This significantly improves the device's simulation adaptability and experimental research value for different types of slope engineering.

[0037] Specifically, the enclosure 1 is made of plexiglass, and the base 2 is made of steel plate. The plexiglass enclosure has good light transmittance, facilitating direct observation of soil deformation, seepage paths, and potential failure modes within the slope during the experiment; it also boasts strong sealing and corrosion resistance, enabling it to withstand long-term rainfall. The steel plate base 2 provides sufficient rigidity and stability, ensuring minimal deformation when adjusting the slope and bearing the soil's own weight, thus providing a robust and reliable support foundation for the upper slope model. The combination of these two materials balances ease of observation, environmental tolerance, and structural stability, effectively supporting the long-term and reliable operation of the slope rainfall-coupled monitoring experiment.

[0038] Preferably, the housing 1 uses an organic glass frame measuring 1.5m (length) × 1.2m (width) × 1.0m (height), with a non-deformable steel plate base (simulating exposed bedrock). The tilt angle is adjustable (preferably 30°), and the frame joints are sealed (to prevent rainwater leakage). The main control module is based on a FLAC3D model, with the model range being X∈[0,120], Y∈[0,50], Z∈[0,40] (unit: m). Figure 2 and 4As shown, the landslide is divided into three regions: the landslide body, the weak layer, and the bedrock. The top boundary is set as the rainfall action surface. The core loads include self-weight (achieved by the material's own unit weight) and rainfall load (dynamic fluid load), which work together to simulate the stress state of a natural slope. The optical fiber used has an elastic modulus of 72e9Pa, a cross-sectional area of ​​1e-6m², and a density of 2600kg / m³. The grouting perimeter is 0.01256m, the grouting stiffness is 1e10Pa / m, the grouting bond strength is 1e6N / m, the friction angle is 35°, and the yield tensile strength is 3e6N. Figure 3 As shown, the surface optical fibers (N1~N3): N1 (slope top) is arranged laterally along the slope shoulder, N2 (slope middle) is arranged laterally along the middle of the slope surface, and N3 (slope toe) is arranged laterally above the toe arc. They are bonded with low-modulus epoxy resin (thickness ≤0.5mm) to avoid constraining fiber strain. The internal optical fibers (L1~L2 / V1~V3): 2 horizontal optical fibers (L1~L2) and 3 vertical optical fibers (V1~V3) are installed using a shallow trench pre-embedding method. Each layer of material is first compacted, then a shallow trench is excavated, and the optical fibers are placed in and filled and compacted with the same material, ensuring close contact between the optical fibers and the soil without any gaps. For fiber lead-out and protection, all ends of the optical fibers are led out of the model box and connected to the BOTDR device, with waterproof and bend-resistant protection provided at the lead-out ends.

[0039] Specifically, the main control module includes a data acquisition terminal, an industrial computer, and a PLC controller. The data acquisition terminal is used to acquire the output data of the Brillouin optical time-domain reflectometer 6. The industrial computer is used to run slope stability analysis algorithms and generate control commands and early warning signals based on the analysis results. The PLC controller is used to receive commands from the industrial computer and control the start / stop and parameter adjustment of the lifting component 3 and the rainfall component 4. This architecture realizes automatic acquisition of monitoring data, real-time analysis of slope status, and precise control of test conditions, forming a closed-loop intelligent monitoring and control system, which significantly improves the automation level and response efficiency of slope rainfall coupling tests.

[0040] Specifically, the rainfall component 4 is an artificial rainfall system with an adjustable rainfall intensity range of 0-100 mm / h. A rainfall intensity of 50 mm / h is set for a duration of 24 hours, with a rainfall uniformity ≥90%. The rainfall intensity is converted into a surface flow rate (50 mm / h = 1.389e-5 m / s), and a uniform surface flow rate is applied at the top boundary (X∈[0,120], Y∈[0,50], Z=40) to simulate rainfall infiltration. Pore water pressure is monitored in real time during rainfall (pore water pressure sensors are installed in the middle and at the toe of the slope), and data is collected synchronously to capture stress and strain changes caused by seepage. The FLAC3D fluid-structure interaction switch (model configure fluid-mechanical) is turned on, and seepage-mechanical iterative coupling is set. Mechanical parameters (friction angle and cohesion are dynamically adjusted with saturation) are updated every 5 steps of the seepage field solution.

[0041] Specifically, during the experiment, the chamber 1 is filled with soil, consisting of bedrock, a weak layer, and a landslide body from bottom to top. A deep-water trench is located at the top of the landslide body. This trench can preset and stably control the groundwater level at the bottom / side of the experimental soil, replicating the occurrence of bedrock fissure water and shallow groundwater in natural slopes. This solves the problem of traditional models relying solely on rainfall infiltration to simulate seepage and lacking groundwater base recharge. It allows the slope seepage field to be driven by both rainfall infiltration and groundwater action, better reflecting the actual hydrogeological conditions of engineering projects. In conjunction with the "upward infiltration" of the rainfall component 4, the deep-water trench can achieve "downward / lateral water replenishment" or "drainage," simulating complex hydrological scenarios such as groundwater level rises and falls, river level changes, and groundwater runoff recharge. It can conduct slope stress-seepage coupling tests under different groundwater conditions, overcoming the limitations of single rainfall simulation scenarios. The experimental soil in the device is equipped with an impermeable layer at the bottom and weakly permeable boundaries on both sides. The deep-water trench can be arranged to fit the impermeable layer / weakly permeable boundary. By controlling the water head difference between the water level in the trench and the experimental soil, the water-blocking effect of the impermeable layer and the lateral seepage law of the weakly permeable boundary are accurately simulated. This solves the problem of distortion in the simulation of seepage gradient in traditional boundary settings, making the pore pressure distribution monitored by the pore water pressure sensor more realistic. Moreover, rainfall infiltration will increase soil saturation and pore pressure, and the groundwater head in the deep-water trench will interact with the rainfall infiltration, thereby changing the effective stress and strain distribution of the soil. The fiber optic sensor network can capture the strain evolution inside the slope during this process, and the pore water pressure sensor can simultaneously monitor the spatiotemporal changes of pore pressure. The addition of the deep-water trench allows the monitoring system to capture the multi-field coupled response driven by both rainfall and groundwater factors, improving the engineering reference value of the experimental data.

[0042] Specifically, the device in Embodiment 1 can achieve the following technical effects: 1. High accuracy of fluid-structure interaction simulation: It realizes the coupling of the entire process of rainfall-seepage-stress, with a rainfall infiltration monitoring error of ≤3% and a dynamic response capture delay of pore water pressure of ≤10min, which can accurately recreate the physical process of rainfall-induced slope instability; 2. Realistic Boundary and Load Simulation: Layered constraint design reduces boundary disturbances by more than 80%, and the simulation of the synergistic effect of self-weight and rainfall loads achieves 95% consistency with the stress state of natural slopes; 3. High reliability of fiber optic coupling: The "shallow trench pre-embedding method" and waterproof protection technology ensure a 100% survival rate of optical fibers during rainfall, with strain monitoring error ≤ ±3µε and stress transfer efficiency of 98%; 4. Outstanding dynamic monitoring capabilities: Real-time monitoring of multiple parameters during rainfall, with 70% more data dimensions than existing technologies, can capture the complete evolution chain of slope from stability to critical instability to instability; 5. Accurate linkage between experiments and numerical models: The error in strain and pore water pressure data between the physical model and the numerical model is ≤4%, and the error in the safety factor calculation is ≤5%, providing dual verification for fluid-structure interaction analysis.

[0043] Example 2 This embodiment provides a method for monitoring slope stress and flow field coupling based on fiber optic sensing, and is based on a fiber optic sensing-based slope stress and flow field coupling monitoring device in Embodiment 1, including the following steps: Step S1: Fill the test soil in layers above the base 2 inside the box 1, lay optical fibers inside and on the surface of the test soil, and lay several pore water pressure sensors 5 above the base 2. Step S2: Connect the output end of the optical fiber to the input end of the Brillouin optical time domain reflectometer 6, and connect the output end of the pore water pressure sensor 5 to the input end of the Brillouin optical time domain reflectometer 6. Step S3: Adjust the tilt angle of one end of the base 2 by controlling the lifting component 3 through the main control module; Step S4: Control the rainfall component 4 through the main control module to apply simulated rainfall to the experimental soil surface above the box 1; Step S5: Real-time acquisition of fiber frequency shift data and pore water pressure data from pore water pressure sensor using Brillouin optical time domain reflectometer 6, and transmission to main control module; Step S6: The main control module generates slope stress-seepage field coupling state information based on the frequency shift data and pore water pressure data, and generates an early warning signal based on the slope stress-seepage field coupling state information.

[0044] Specifically, the frequency shift data and the pore water pressure data are first preprocessed, and then feature extraction is performed on the preprocessed data to obtain several feature data (e.g., maximum strain value, strain gradient, and temperature drift). The obtained feature data is then input into a preset coupled analysis model for numerical simulation and theoretical calculation. The numerical simulation uses the finite difference software FLAC3D, the constitutive model adopts the Mohr-Coulomb convergence criterion, the mesh is divided into hexahedral elements, and the step size is 0.01s. The theoretical calculation, based on the feature data and the Mindlin solution of elasticity, derives the shear stress transmission equation at the fiber-soil interface: ; in, For fiber strain, To correct the characteristic coefficients, This represents the effective free strain of the rock and soil mass.

[0045] Calculation process of safety factor for fiber-optic coupled slope stress-seepage field monitoring model: I. Core Basis and Prerequisites for Calculation 1. Strength Criterion: The classic Mohr-Coulomb yield criterion for geotechnical engineering is adopted. The criterion for determining slope instability is that the shear stress of the soil and rock mass reaches the shear strength. The shear strength formula is: ; In the formula: The shear strength of the soil and rock mass (Pa); Cohesion of soil and rock mass (Pa); The normal stress (Pa) on the shear plane; The friction angle within the rock and soil is (°).

[0046] 2. Calculation method: In FLAC3D, the strength reduction method (SRM) is used. By gradually reducing the cohesion c and internal friction angle φ of the soil and rock mass, the slope reaches the limit equilibrium state. The reduction factor at this time is the slope safety factor (FOS).

[0047] 3. Dynamic parameter adaptation: Considering the changes in soil saturation caused by rainfall seepage, the cohesion c and internal friction angle φ are dynamically adjusted with the saturation (φ drops to 20° when saturation > 0.4, and to 18° when saturation > 0.8), and this dynamic parameter is adapted synchronously during the reduction process.

[0048] 4. Convergence Criterion: The local convergence ratio 1e-4 is used as the criterion for determining the limit equilibrium in numerical calculations. That is, when the ratio of the unbalanced force calculated by the model to the maximum force is ≤1×10⁻⁴. -4 When the slope reaches the equilibrium state under the reduction factor, it is determined that the slope has reached the equilibrium state.

[0049] 5. Calculation scope: Covers the three-layer structure of landslide body, weak layer and bedrock, with a focus on calculating the safety factor of the weak layer (core sliding surface of slope instability). The geometric parameters of the calculation scope of the physical model and the numerical model correspond one-to-one.

[0050] II. Core Formula of Strength Reduction Method 1. Strength parameter reduction formula Regarding cohesion c and internal friction angle After proportional reduction, the parameters are as follows: ; ; In the formula: , c represents the reduced cohesion and internal friction angle; F is the strength reduction factor; c represents the strength reduction factor. These are the original physical and mechanical parameters of the rock and soil mass.

[0051] 2. Safety Factor Determination Formula When the reduction factor is At this point, the slope reaches its limit equilibrium state (local convergence ratio = 1e-4). This is the slope safety factor, which satisfies: ; In the formula: This represents the actual shear stress on the slope sliding surface. This represents the reduced shear strength of the soil and rock mass.

[0052] III. Steps for Calculating the Safety Factor of a FLAC3D Numerical Model In conjunction with the FLAC3D fluid-structure interaction solution process of this invention, the safety factor calculation and the seepage field-mechanical field coupling iteration are performed simultaneously. The mechanical parameters are updated once every 5 solution steps, and a safety factor trial calculation is completed simultaneously. The specific steps are as follows: Step 1: Initialize calculation parameters and boundaries; Step 2: Set the trial calculation range for the strength reduction factor; Based on the initial stable state of the slope (before rainfall) and the instability trend induced by rainfall, a trial calculation interval for the reduction coefficient F is defined: before rainfall, the slope is in a stable state, and the trial calculation interval F∈[1.0,2.0]; during / after rainfall, the slope saturation increases and the strength parameter decreases, and the trial calculation interval F∈[1.0,1.5]. A bisection method is used for trial calculation to reduce the number of iterations and improve computational efficiency.

[0053] Step 3: Iterative calculation of strength reduction under fluid-structure interaction; Step 3 specifically includes the following steps: 1. Input the initial reduction factor F1, and calculate according to the reduction formula. , , if the saturation degree of the rock and soil mass > 0.4 / 0.8, update it first and then perform reduction; 2. Execute the FLAC3D fluid-solid coupling solution command model solve to synchronously calculate the seepage field and the mechanical field, and output the convergence ratio of the model imbalance force; 3. If the convergence ratio > 1e-4, it means that the slope is still in a stable state under F1. Increase the reduction coefficient to F2 (F2 > F1), and repeat steps 1-2; 4. If the convergence ratio < 1e-4, it means that the slope has become unstable under F2. Reduce the reduction coefficient to F3 (F1 < F3 < F2), and repeat steps 1-2; 5. Iterate repeatedly until the reduction coefficient Fcr satisfies the convergence ratio = 1e-4. At this time, Fcr is the slope safety factor at this stage.

[0054] IV. Verification calculation of the safety factor of the physical model experiment 1. Extract the core data of physical monitoring: Obtain the fiber strain data through the BOTDR device and convert it into the stress distribution of the landslide body / soft layer , τ; Obtain the normal effective stress of the sliding surface through the pore water pressure sensor ( , is the pore water pressure); 2. Back-calculate the actual shear strength: According to the Mohr-Coulomb criterion, back-calculate the actual shear strength of the rock and soil mass from the monitored τ, ; 3. Calculate the safety factor of the physical model: Combine the original , of the rock and soil mass in the physical model, substitute it into the formula to obtain the safety factor of the physical model; 4. Calibration of numerical and physical results: Compare the Fcr of the numerical model with the F of the physical model. If the error > 5%, adjust the saturation-intensity parameter correlation function in FLAC3D and re-iterate the calculation until the error ≤ 5%.

[0055] Example 3 Based on the experimental method of a slope stress and flow field coupling monitoring device based on fiber optic sensing in Example 1, material preparation needs to be carried out before the experiment. The materials include an acrylic frame (1.5m × 1.2m × 1.0m, with seams sealed), an invariable steel plate base, adjustable struts, similar materials (barite powder, bentonite, gypsum, etc.), an artificial rainfall system (rainfall intensity 0 - 100mm / h, uniformity ≥ 90%), optical fibers, a BOTDR strain sensing optical system, FLAC3D software, low modulus epoxy resin, and waterproof tape.

[0056] Site requirements: The laboratory floor should be level, with a stable power supply and drainage, and the temperature should be controlled at 20±5℃; a waterproof mat should be installed to prevent rainwater leakage from affecting the experimental environment.

[0057] The experimental method based on the fiber optic sensing-based slope stress and flow field coupling monitoring device in this embodiment includes the following steps: Step S1B: Physical model preparation; specifically including the following steps: 1. Mix similar materials (barite powder, bentonite, gypsum, quicklime or surfactant) according to the specified ratio to ensure uniform bulk density; 2. Fill the model frame in layers, each layer is 5cm thick, and compact each layer (uniform compaction) to avoid the formation of voids; 3. Pre-embed internal optical fibers (L1~L2 / V1~V3): After each layer of material is compacted, a shallow groove with a width of 1cm and a depth of 0.8cm is dug, the optical fiber is placed in the groove, and the material with the same ratio is filled and compacted to ensure that the optical fiber is in close contact with the material. 4. Surface fiber bonding (N1~N3): Low modulus epoxy resin is used for bonding, with the thickness controlled at 0.3mm, covering key areas such as the slope shoulder, middle of the slope, and toe of the slope; 5. Fiber Optic Outlet Treatment: Lead all fiber optic cables out of the model box at both ends, and protect them from water (wrapping with waterproof tape) and bending (leaving a 5cm bending radius) before connecting them to the BOTDR device; 6. Model settling: After molding, the model is settling for 36 hours. Frequency shift data is collected once every 6 hours using BOTDR. When the frequency shift change is ≤10MHz (corresponding to strain ≤15µε) and the pore water pressure change is ≤5kPa, the self-weight stress and the initial seepage field are considered to have reached a steady state.

[0058] Step S2B: Rainfall simulation system debugging and startup; specifically including the following steps: 1. Rainfall equipment debugging: Install the artificial rain system 1.5m above the top of the model, adjust the nozzle angle to cover the entire top of the slope with rain (coverage area 1.5m×1.2m); set the rainfall intensity to 50mm / h, start the system to pre-spray for 10 minutes, calibrate the rainfall uniformity with a rain gauge (ensure ≥90%), and adjust the position of the diversion channel to avoid local erosion of the slope; 2. Physical model rainfall simulation: The rainfall system was activated and rainfall continued for 24 hours. During the rainfall, BOTDR full-fiber frequency shift data and pore water pressure data were collected every hour, and slope morphology changes were recorded simultaneously with a camera. The infiltration rate at the top of the slope and the slope runoff were measured every 6 hours to ensure data integrity. 3. Emergency handling: If local erosion is found on the slope, immediately reduce the rainfall intensity to 30 mm / h, and restore the set intensity after the slope stabilizes; if the fiber optic frequency shift signal changes abruptly, stop the rainfall, check the integrity of the fiber optic cable, and continue the experiment after troubleshooting.

[0059] Step S3B: Numerical model construction and fluid-structure interaction solution; specifically including the following steps: 1. Basic model building: Open FLAC3D software, restore the "landslide model 1.sav" model, turn off the large strain mode, and define the landslide body, weak layer, and bedrock groupings; 2. Material parameters and constitutive assignment: The basic parameters are assigned using the "setup_parameters" function of the fish function, and a dynamic correlation function of saturation-friction angle is added (the friction angle decreases to 20° when saturation > 0.4, and to 18° when saturation > 0.8). 3. Boundary conditions and rainfall settings: Mechanical boundaries: fixed bottom constraint, rolling constraints on both sides, and free boundary on the slope; Seepage boundary: bottom impermeable (velocity-z=0), sides impermeable, top rainfall boundary; Rainfall load application: Execute "zone faceapply flow-rate 1.389e-5 range position-z 40" at the top boundary (X∈[0,120], Y∈[0,50], Z=40) to simulate a rainfall intensity of 50 mm / h; 4. Fluid-structure interaction solution: Initialize the seepage field: Open the fluid module, set the seepage constitutive parameters and porosity and permeability coefficient parameters, initialize the saturation and pore pressure, solve the seepage field separately for 864000s, and save the file "water_2.sav"; Mechanical-seepage coupling solution: Activate the mechanical module, close the fluid module, execute "model solve" to perform coupled calculations, and simultaneously record BOTDR frequency shift data and numerical model monitoring parameters; Step S4B: Data Acquisition and Coupling Analysis; specifically including the following steps: 1. Physical Experiment Data Processing: After the rainfall ended, monitoring continued for 24 hours (data was collected every 6 hours) until the pore water pressure stabilized; the BOTDR frequency shift data was converted into distributed strain, and then converted into stress using Hooke's law. The changes in tensile stress at the top of the slope and compressive stress at the toe of the slope before and after the rainfall were compared; the evolution curve of pore water pressure with rainfall duration was analyzed to determine the stabilization time of the seepage field. 2. Numerical model data processing: Extract strain and stress data and pore water pressure distribution cloud map of the fiber optic arrangement location in the numerical model; compare the strain peak value and pore water pressure peak value of the physical experiment with those of the numerical model, and control the error within 5%; 3. Stability analysis: Calculate the slope safety factor (local convergence ratio 1e-4) before rainfall, 12 hours after rainfall, 24 hours after rainfall, and 24 hours after rainfall, and analyze the influence of rainfall on slope stability.

[0060] Step S5B: Post-experimental processing; specifically including the following steps: 1. Equipment disassembly and inspection: Turn off the rain system, remove the fiber optic protection device, collect the last set of BOTDR frequency shift curves, and check whether the fiber optic cable is broken (if a certain segment of signal disappears, exclude that segment of data). 2. Model profile analysis: Disassemble the plexiglass frame and observe the internal failure morphology of the slope (focusing on the sliding signs at the interface between the weak layer and the landslide body). Compare the results with the locations of strain abrupt changes in the monitoring data to verify the effectiveness of fluid-structure interaction monitoring. 3. Data archiving: Organize data on strain, stress, pore water pressure, rainfall intensity, and infiltration from physical experiments, along with the coupling calculation results and safety factor curves from numerical models, to form a complete fluid-structure interaction monitoring report.

[0061] (3) Implementation effect verification Fluid-structure interaction response: 12 hours after rainfall, the pore water pressure at the toe of the slope increased from the initial 12 kPa to 85 kPa, and the tensile strain at the shoulder of the slope increased from 5 µε to 35 µε, with a deviation of ≤3% from the numerical model calculation results; Stability changes: The slope safety factor was 1.8 before rainfall, dropped to 1.1 (critical stable state) 24 hours after rainfall, and rebounded to 1.3 24 hours after rainfall, which is consistent with the actual engineering law of rainfall-induced slope instability; Fiber optic reliability: No fiber optic breaks were observed throughout the entire rainfall process, and strain monitoring data remained continuous, verifying the rationality of the waterproof protection and coupling arrangement.

[0062] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0063] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A slope stress and flow field coupling monitoring device based on fiber optic sensing, characterized in that, The device includes a housing (1), a base (2) at the bottom of the housing (1), a lifting assembly (3) at one end of the base (2), experimental soil inside the housing (1), optical fibers inside and on the surface of the experimental soil, a rainfall assembly (4) above the housing (1), and several pore water pressure sensors (5) above the base (2). The output ends of the several pore water pressure sensors (5) and the optical fibers are connected to the input end of a Brillouin optical time domain reflectometer (6). The output end of the Brillouin optical time domain reflectometer (6) is connected to the input end of a main control module. The main control module is used to control the lifting assembly (3) and the rainfall assembly (4). The main control module is also used to generate a warning signal based on the input of the Brillouin optical time domain reflectometer (6). The optical fiber includes surface optical fibers uniformly arranged on the surface of the experimental soil and internal optical fibers inserted into the experimental soil. The arrangement direction of the surface optical fibers is perpendicular to the direction in which the experimental soil forms a slope. The internal optical fibers include several vertical optical fibers inserted vertically into the experimental soil and several horizontal optical fibers inserted horizontally into the experimental soil. The soil used in the experiment, from bottom to top, includes bedrock, a weak layer, and a landslide body; The top of the landslide body is equipped with a deep water channel.

2. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The optical fibers installed inside the experimental soil were installed using a shallow trench pre-embedding method.

3. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The slope boundary formed by the experimental soil is set as a free permeability boundary, the bottom boundary of the slope formed by the experimental soil is set as a water-impermeable layer, and the two side boundaries of the slope formed by the experimental soil are set as weakly permeable boundaries.

4. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The bottom boundary of the box (1) is provided with a fixed constraint, and the two side boundaries of the box (1) are provided with a rolling constraint.

5. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The optical fiber is waterproofed and bend-resistant at the point where it passes through the housing (1).

6. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The maximum angle between the base (2) and the bottom of the box (1) is 30°.

7. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The box body (1) is made of plexiglass, and the base (2) is made of steel plate.

8. The slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 1, characterized in that, The rainfall intensity adjustment range of the rainfall component (4) is 0 mm / h-100 mm / h, and the rainfall uniformity is ≥90%.

9. A method for coupled monitoring of slope stress and flow field based on fiber optic sensing, comprising a device for coupled monitoring of slope stress and flow field based on fiber optic sensing as described in any one of claims 1-7, characterized in that, Includes the following steps: Step S1: Fill the experimental soil in layers above the base (2) inside the box (1), lay optical fibers inside and on the surface of the experimental soil, and lay several pore water pressure sensors (5) above the base (2). Step S2: Connect the output end of the optical fiber to the input end of the Brillouin optical time domain reflectometer (6), and connect the output end of the pore water pressure sensor (5) to the input end of the Brillouin optical time domain reflectometer (6). Step S3: Control the lifting component (3) through the main control module to adjust the tilt angle of one end of the base (2); Step S4: Control the rainfall component (4) through the main control module to apply simulated rainfall to the experimental soil surface above the box (1); Step S5: Real-time acquisition of fiber frequency shift data and pore water pressure data from pore water pressure sensor using Brillouin optical time domain reflectometer (6), and transmission to main control module; Step S6: The main control module generates slope stress-seepage field coupling state information based on the frequency shift data and pore water pressure data, and generates an early warning signal based on the slope stress-seepage field coupling state information.

10. The method for a slope stress and flow field coupling monitoring device based on fiber optic sensing according to claim 9, characterized in that, Step S6 specifically includes the following steps: The frequency shift data and the pore water pressure data are preprocessed first; The preprocessed frequency shift data and pore water pressure data are subjected to feature extraction to obtain several feature data. The acquired feature data is input into a preset coupled analysis model to obtain the slope stress-seepage field coupled state information.

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