A distributed fiber high-coupling backfill structure and method for landslide deep monitoring
By using three layers of backfill material with gradually varying elastic modulus and LiDAR data correction, the problem of low coupling efficiency between distributed fiber optic sensors and landslide soil and rock was solved, enabling efficient, reliable transmission and accurate reflection of deep landslide monitoring data.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HOHAI UNIV
- Filing Date
- 2026-05-27
- Publication Date
- 2026-07-14
AI Technical Summary
In existing technologies, the coupling efficiency between distributed fiber optic sensors and landslide soil and rock is low, resulting in distorted monitoring data that cannot accurately reflect the deformation of deep soil and rock masses.
A three-layer backfill material with gradually varying elastic modulus is used, including an inner layer of epoxy resin-based adhesive, a middle layer of polymer-modified cement mortar, and an outer layer of cement-based grouting material. Combined with a multi-layer composite sheath and a layered grouting process, a highly coupled backfill structure is formed, and the monitoring results are corrected using LiDAR data.
It achieves a smooth mechanical transition between optical fiber and soil, improves strain transfer efficiency, ensures the authenticity and reliability of monitoring data, eliminates interface strain attenuation and reflection, and forms a highly coupled structure without voids or debonding.
Smart Images
Figure CN122384701A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of geotechnical engineering and geological disaster monitoring technology, specifically to a distributed optical fiber high-coupling backfill structure and method for deep landslide monitoring. Background Technology
[0002] Distributed fiber optic sensing technology is an important means of monitoring deep deformation in landslides. This technology usually involves drilling holes in the landslide body, inserting monitoring optical cables that integrate distributed fiber optic sensors, and backfilling materials to restore the continuity of the strata. The deformation of the rock and soil body is inverted by demodulating the strain or temperature signals of the optical fibers.
[0003] However, the accuracy of monitoring data heavily depends on the strain transfer efficiency between the optical fiber and the surrounding soil and rock mass, i.e., their coupling state. Currently, engineering projects commonly use a single material, such as cement grout or cement mortar, to backfill the entire borehole in a single injection. This conventional method has the following significant drawbacks:
[0004] Firstly, in terms of materials, the mechanical parameters of a single backfill material, especially the elastic modulus, are difficult to match simultaneously with the sheath modulus of the fiber optic sensor and the modulus of the surrounding rock in the borehole, which can easily lead to abrupt changes in mechanical properties at the interface. When the landslide deforms, this "soft-hard-soft" or "hard-soft-hard" interlayer structure can cause severe strain attenuation or reflection at the interface, resulting in distorted monitoring data.
[0005] Secondly, in terms of process, one-time injection makes it difficult to ensure that the backfill material uniformly and densely wraps the optical fiber in the annular borehole space, which can easily generate air bubbles, segregation or shrinkage gaps, forming "debonding" or "voids", further disrupting the continuity of strain transfer.
[0006] The aforementioned defects in materials and processes collectively lead to low coupling efficiency between the distributed fiber optic sensors in the borehole and the surrounding rock. This results in monitoring data that cannot accurately reflect the actual deformation of the deep soil and rock mass, limiting the reliable application of this technology. Therefore, developing a borehole backfill structure and corresponding construction and calibration methods that can ensure long-term, reliable, and efficient coupling between the distributed fiber optics and the landslide soil and rock is an urgent engineering need for improving the accuracy and reliability of deep landslide monitoring data. Summary of the Invention
[0007] This invention aims to address the problems of existing backfill materials easily forming abrupt changes in mechanical properties at the interface, and the easy generation of air bubbles, segregation, or shrinkage cracks in one-time injection backfill materials. Instead, it provides a distributed optical fiber high-coupling backfill structure and method for deep landslide monitoring.
[0008] To achieve the above objectives, the present invention adopts the following technical solution:
[0009] A distributed optical fiber high-coupling backfill structure for deep landslide monitoring is installed inside boreholes in the landslide body, comprising:
[0010] A distributed optical fiber monitoring cable, wherein the monitoring cable comprises, from the inside out, a fiber core, a coating layer, and a layered composite sheath;
[0011] And, a layered backfill material filling the space between the borehole wall and the monitoring optical cable;
[0012] The layered backfill body includes at least an inner layer of backfill material, a middle layer of backfill material, and an outer layer of backfill material arranged radially from the inside to the outside;
[0013] The elastic modulus of the inner backfill material is close to that of the layered composite sheath of the monitoring optical cable, the elastic modulus of the outer backfill material is close to that of the surrounding rock of the borehole, and the elastic modulus of the middle backfill material is between that of the inner and outer backfill materials.
[0014] By using radial three-layer elastic modulus gradual matching, abrupt changes in the mechanical interface between the optical fiber sheath and the backfill, and between the backfill and the surrounding rock, are eliminated, achieving smooth strain transfer, improving the coupling efficiency between the optical fiber and the soil, and ensuring the authenticity and reliability of the monitoring data.
[0015] Furthermore, the inner backfill material is an epoxy resin-based adhesive layer with an elastic modulus of 0.1 GPa to 1.0 GPa; the middle backfill material is a polymer-modified cement mortar layer with an elastic modulus of 1.0 GPa to 5.0 GPa; and the outer backfill material is a cement-based grouting material layer with an elastic modulus of 5.0 GPa to 20 GPa.
[0016] By combining materials with specific elastic modulus ranges, a continuous mechanical transition from the optical fiber sheath to the landslide soil and rock mass can be achieved, avoiding strain attenuation, reflection, and decoupling, thereby improving the accuracy and stability of deep deformation monitoring.
[0017] Furthermore, the inner backfill material has the smallest thickness, the outer backfill material has the next largest thickness, and the middle backfill material has a thickness greater than both the inner and outer backfill materials.
[0018] As one embodiment, the thickness of the inner backfill material is 2mm to 5mm, the thickness of the middle backfill material is 40mm to 45mm, and the thickness of the outer backfill material is 3mm to 8mm.
[0019] By thickening the intermediate layer, the stress transition and deformation coordination are fully utilized; the inner layer is thin and dense to ensure tight bonding with the optical cable; the outer layer is thin and close-fitting to ensure coordinated deformation with the landslide rock mass, forming a highly coupled structure without voids or debonding.
[0020] Furthermore, the layered composite sheath of the monitoring optical cable is a multi-layered structure that is coaxially wrapped sequentially, including: a tight-buffered layer that directly covers the optical fiber; a tensile reinforcement layer wrapped around the tight-buffered layer; and a wear-resistant and corrosion-resistant outer sheath covering the outermost layer.
[0021] By using a multi-layered composite sheath, the tensile strength, abrasion resistance, and corrosion resistance of the optical cable are improved, making it suitable for drilling construction and long-term underground environments. At the same time, the elastic modulus of the sheath is kept stable, which facilitates modulus matching with backfill materials.
[0022] Preferably, the tensile reinforcement layer is a fiber reinforcement layer, and the fiber reinforcement layer material is selected from aramid fiber, glass fiber, carbon fiber or basalt fiber.
[0023] Using lightweight, high-strength fibers, the axial tensile strength of the optical cable is significantly improved without significantly changing the overall elastic modulus of the sheath, ensuring that strain transmission is not affected.
[0024] Preferably, the tensile reinforcement layer is a metal reinforcement layer, which is a stranded steel wire layer or a braided steel wire layer.
[0025] The metal-reinforced structure significantly improves the overall stiffness and tensile strength of the optical cable, making it suitable for deep-hole, long-distance, and high-load construction scenarios, and ensuring that the optical cable does not break or slip during construction and service.
[0026] A construction method for a distributed optical fiber high-coupling backfill structure includes the following steps:
[0027] S1. Drilling and fiber optic cable guidance and positioning: Drill monitoring holes at the designed location of the landslide body, and install a centering guide in the borehole. Pass the distributed fiber optic monitoring cable through the centering guide and fix it at the center of the borehole axis.
[0028] S2, Layered Grouting Forming: Three grouting pipes are used for construction. The three grouting pipes are respectively connected to grouting equipment that stores the inner, middle and outer layers of backfill material. The grouting operation is carried out in sequence from the inside to the outside and at the set time intervals to ensure that the previous grout enters the initial gelation state before the subsequent grout arrives, so as to form micro-penetration at the interface without macro-mixing, and construct a radially layered composite structure.
[0029] S3. Pressure maintenance and curing constraint: After the layered grouting is completed, a continuous pressure is applied to the borehole until the backfill material is completely cured, so that the cured layered backfill body forms a composite structure with the monitoring optical cable and the surrounding rock of the borehole in a coordinated deformation.
[0030] Preferably, in step S2, the grouting pressure when injecting the inner layer backfill material is 0.1 MPa to 0.3 MPa, the grouting pressure when injecting the middle layer backfill material is 0.3 MPa to 0.6 MPa, and the grouting pressure when injecting the outer layer backfill material is 0.6 MPa to 1.0 MPa.
[0031] In step S3, the constraint pressure is 0.2 MPa to 0.5 MPa, and the constraint pressure is maintained for 2 hours to 6 hours.
[0032] By gradually increasing the pressure during grouting, the grout is filled radially in an orderly manner and with clear stratification. By using specific stabilizing pressure and stabilizing time, the backfill is ensured to be fully compacted, without shrinkage or voids, thereby further improving the long-term coupling stability between the optical fiber and the soil.
[0033] Furthermore, following step S3, a coupling coefficient calibration step is also included:
[0034] S4. Set up permanent control points in the stable area of the landslide surface, acquire LiDAR scanning data of the landslide surface at the permanent control points at at least two different time points, and calculate the landslide surface deformation field based on the data.
[0035] S5. Simultaneously acquire the deep strain data of the landslide monitored by the distributed optical fiber monitoring cable;
[0036] S6. Based on the spatial correspondence between the surface deformation field and the deep strain data, determine the actual strain coupling coefficient of the distributed optical fiber monitoring cable in the deep soil and rock mass of the landslide.
[0037] S7. In subsequent monitoring, the monitoring data of the distributed optical fiber monitoring cable are corrected using the actual strain coupling coefficient.
[0038] By using high-precision LiDAR displacement on the ground as the true reference, the actual coupling coefficient in the field is obtained through inversion. The original fiber optic data is then corrected to eliminate systematic errors caused by incomplete coupling, ensuring that the monitoring results truly reflect the actual deformation of the soil and rock mass from the data level.
[0039] Further, in step S6, establishing the spatial correspondence includes:
[0040] Based on the center coordinates of the borehole opening and the borehole trajectory, a three-dimensional spatial coordinate transformation model is constructed from the surface to the depth of the borehole.
[0041] Using the coordinate transformation model, the surface displacement field data obtained by the LiDAR scan is spatially matched with the strain profile data distributed along the borehole depth obtained by the distributed optical fiber monitoring cable within the same time period or a set time window.
[0042] By achieving precise spatial matching, a strict correspondence between surface displacement and deep strain is realized, ensuring accurate and reliable coupling coefficient inversion and improving the accuracy and reliability of subsequent data correction.
[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0044] By using backfill material with three layers of gradually varying elastic modulus, the abrupt change in mechanical properties at the interface of traditional single materials is eliminated, and a smooth mechanical transition from the optical fiber sheath to the landslide rock mass is achieved. This effectively suppresses the attenuation and reflection of strain at the interface and ensures high-fidelity transmission of deformation information.
[0045] By centering the positioning, the optical cable is uniformly wrapped around its perimeter; by using multiple grouting pipes to inject grout at different times, combined with the gradient control of the initial setting time of the grout, the three layers of material are orderly layered and tightly stacked in the radial direction of the borehole, effectively avoiding interlayer mixing; combined with the pressure stabilization and curing process, defects are eliminated, forming a highly coupled backfill structure.
[0046] This invention innovatively introduces a deep coupling coefficient calibration method based on surface LiDAR deformation data. It uses a high-precision surface displacement field to infer the actual strain transfer efficiency of deep optical fibers, providing a basis for on-site verification and correction of monitoring data, making the monitoring results closer to the true deformation state of the soil and rock.
[0047] This invention constructs a complete technical solution from physical coupling to data correction through the integrated design of material structure, construction method, and online calibration. It significantly improves the strain transfer efficiency between optical fiber and landslide rock mass, fundamentally ensuring the authenticity and reliability of deep landslide monitoring data, and has important engineering application value. Attached Figure Description
[0048] Figure 1 This is a schematic diagram of the borehole axial section of a distributed optical fiber high-coupling backfill structure in one embodiment.
[0049] Figure 2 for Figure 1 Enlarged schematic diagram of the radial cross-section of the monitoring optical cable.
[0050] Figure 3 This is a process flow diagram of the construction method in one embodiment.
[0051] The markings in the diagram are as follows: 1-Drill hole; 2-Monitoring optical cable; 3-Layered backfill; 31-Inner layer backfill material; 32-Middle layer backfill material; 33-Outer layer backfill material; 4-Drill hole surrounding rock; 5-Center guide; 21-Fiber core; 22-Coating layer; 23-Layered composite sheath; 231-Tight-fitting layer; 232-Tensile reinforcement layer; 233-Outer sheath. Detailed Implementation
[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it.
[0053] Example 1: Backfill Structure
[0054] In this embodiment, the deep deformation of a typical rock landslide was monitored. The landslide body is mainly composed of moderately weathered sandstone, and its elastic modulus is approximately 12 GPa according to on-site testing.
[0055] like Figure 1 As shown, the backfill structure in this embodiment is set inside the borehole 1 of the landslide body, including a distributed optical fiber monitoring cable 2 and a layered backfill body 3 filled between the borehole wall of the borehole 1 and the monitoring cable 2.
[0056] like Figure 2 As shown, the monitoring optical cable 2, from the inside out, includes a fiber core 21, a coating layer 22, and a layered composite sheath 23. In this embodiment, the diameter of the fiber core 21 is 2mm. The layered composite sheath 23 is a multi-layered structure that is coaxially wrapped, and from the inside out, it includes:
[0057] Tight-fitting layer 231: Directly wrapped around the optical fiber coating layer 22, made of high-toughness polyacrylate material, with a thickness of about 0.2 mm and an elastic modulus of about 0.8 GPa, which plays a preliminary buffering and protection role;
[0058] Tensile reinforcement layer 232: Wound around the tight sleeve layer 231, it is formed by aramid fibers cross-wound at a helix angle of 15°, with a single layer thickness of about 0.3 mm and a tensile strength greater than 1500 MPa, and is used to withstand axial tensile forces during construction and operation;
[0059] Outer sheath 233: Covers the outermost layer, made of wear-resistant and corrosion-resistant thermoplastic polyurethane elastomer, with a thickness of about 0.5mm and a Shore hardness of 95A, used to resist shear damage during drilling and backfilling construction and long-term erosion by groundwater.
[0060] like Figure 1 As shown, the layered backfill body 3 is formed by backfilling with three different materials, which are backfilled sequentially from the inside to the outside in the radial direction:
[0061] Inner backfill material 31: Epoxy resin-based adhesive with an elastic modulus of 0.6 GPa, which is close to the equivalent modulus (approximately 0.8 GPa) of the layered composite sheath 23 of the monitoring optical cable. It also has excellent bonding performance to ensure a strong interface bond with the surface of the optical cable.
[0062] Intermediate layer backfill material 32: Polymer modified cement mortar is used, which is modified by adding 10% acrylic emulsion. Its elastic modulus is 2.8 GPa, which is between the inner layer and the outer layer, and plays a role in the transition of mechanical properties.
[0063] Outer backfill material 33: Ordinary silicate cement-based grouting material with a water-cement ratio of 0.45 and an elastic modulus of 10.5 GPa, which is close to the modulus of the borehole surrounding rock 4 (12 GPa), ensuring coordinated deformation with the rock mass.
[0064] The thickness of each layer is designed as follows: 3mm for the inner layer, 45mm for the middle layer, and 5mm for the outer layer. The thickness of the middle layer is significantly greater than that of the inner and outer layers to fully utilize its stress transition function.
[0065] Example 2, Construction Method
[0066] like Figure 3 In this embodiment, the construction method includes the following steps:
[0067] S1. Drilling and fiber optic cable guidance and positioning
[0068] At the selected landslide monitoring point, a vertical monitoring borehole 1 with a diameter of 110 mm and a depth of 35 m was drilled using a geological drilling rig to ensure that the borehole penetrated the potential slip surface. After drilling, the borehole was cleaned. Subsequently, the monitoring optical cable 2 was lowered, with expandable rubber stabilizers 5 tied to the cable at 5 m intervals as centering guides. After the stabilizers expand upon contact with water inside the borehole, they press firmly against the borehole wall, thereby reliably positioning the monitoring optical cable 2 at the center of the borehole 1.
[0069] Intumescent rubber stabilizers are an existing technology, also known as water-swellable rubber or water-swellable sealing strips. They utilize hydrophilic groups to absorb moisture, causing volume expansion, and the resulting expansion pressure is sufficient to fix lightweight optical cables in the center of the borehole.
[0070] S2, Layered Grouting Molding
[0071] Three grouting pipes, named Grouting Pipe A, Grouting Pipe B, and Grouting Pipe C, are used for construction. These pipes are connected to grouting equipment storing the inner, middle, and outer layers of backfill material, respectively. Grouting operations are performed sequentially from the inside out, coordinated with the slow lifting of the grouting pipes.
[0072] Injecting the inner layer material: First, start the inner layer grouting pump to allow the epoxy resin-based adhesive (inner layer backfill material 31) to flow out from the outlet at the bottom of the grouting pipe A. Control the grouting pressure to approximately 0.15 MPa and the grouting rate to approximately 2 L / min, while simultaneously raising the grouting pipe A at a uniform speed of approximately 0.5 m / min to ensure the adhesive fully wraps the monitoring optical cable.
[0073] Injecting intermediate layer material: After the grouting pipe A is raised a certain distance, start the intermediate layer grouting pump and start grouting through the grouting pipe B. Inject polymer-modified cement mortar, increase the grouting pressure to about 0.45MPa, the grouting rate to about 5L / min, and coordinate with a pipe lifting speed of 0.5m / min.
[0074] After grouting pipe A is raised a certain distance, the inner layer grout has initially set. The middle layer grouting pump is then started. If the middle layer grout is injected only after the inner layer grout has fully cured, cold joints will form between the layers, hindering strain transfer. The interval between each grout injection layer should be controlled within the initial setting time of the first grout injection to ensure microscopic diffusion and penetration at the interface, forming a physical-mechanical interlock and avoiding the formation of a weak mechanical interface.
[0075] After the grouting pipe A has been raised a certain distance, that is, after the inner layer grouting has been completed for 10-20 minutes, the middle layer grouting will begin. If the ambient temperature is high, the time may need to be shortened to less than 10 minutes.
[0076] Injecting the outer layer material: After the grouting pipe B has been raised a certain distance, that is, after the middle layer material has been grouted for 30-45 minutes and the grouting of the middle layer has initially set, start the outer layer grouting pump and inject ordinary cement-based grouting material (outer layer backfill material 33). Further increase the grouting pressure to about 0.8 MPa and control the grouting rate at about 8 L / min.
[0077] By injecting grout at staggered times through three grouting pipes, and utilizing the differences in rheological properties of each grout layer and the gradual increase in grouting pressure, the subsequently injected grout can tightly encapsulate and compress the grout that has already entered the gelling state under pressure constraint. This results in an ordered, layered backfill structure with an inner layer of 3mm, a middle layer of 45mm, and an outer layer of 5mm radially within a 110mm diameter borehole. This process effectively avoids large-area mixing or scouring and replacement between layers, ensuring a smooth transition of the mechanical properties of the backfill from the inside out.
[0078] S3, Pressure Curing Constraint
[0079] After grouting is completed, the borehole is immediately sealed, and pressure is added to the borehole through the grouting pipe to maintain a constraint pressure of approximately 0.35 MPa throughout the curing process. The pressure stabilization time is approximately 4 hours, until the material initially sets. This process effectively inhibits material shrinkage, ensuring a tight bond between the backfill and the optical cable and surrounding rock, ultimately forming a composite structure with overall coordinated deformation.
[0080] Example 3: Coupling Coefficient Calibration
[0081] After the backfill structure is completed and put into operation, the coupling coefficient is calibrated on site, and the deep fiber optic monitoring results are corrected using high-precision surface deformation data. The specific steps are as follows:
[0082] S4. Acquisition of LiDAR data on the Earth's surface and calculation of deformation field
[0083] Permanent control points were set up in the stable area of the landslide surface, and a ground-based three-dimensional laser scanner was used to scan at two key time points: T0 was the time when the backfill structure was completed and the monitoring system was initialized; T1 was the time after a monitoring cycle (such as the rainy season or after excavation disturbance).
[0084] Both scans simultaneously acquired the entire landslide surface point cloud and the coordinates of stability control points. Upon completion of the backfill structure and initialization of the monitoring system, the scanner performed a full-coverage scan of the entire landslide slope, obtaining the original 3D point cloud before significant deformation. Each point had precise X / Y / Z 3D coordinates, along with reflection intensity, RGB color, scan time, and point number, serving as baseline data. After one monitoring cycle (after the rainy season / excavation / drift), a second scan was performed using the same instrument, at the same location, and with the same parameters, yielding the latest 3D point cloud after landslide deformation. This new point cloud also contained complete X / Y / Z coordinates, along with reflection intensity, color, and a timestamp, for comparison with T0.
[0085] The point cloud data acquired from the two scans were imported into the data processing system. First, using permanent stable control points as constraints, the global coordinates of the two point clouds were unified and rigid displacements were corrected. Then, using the T0 period reference point cloud, the T1 period point cloud was registered with high precision. After removing rigid displacements and noise through differential processing, the three-dimensional displacement field of the landslide surface during the T0 to T1 period was calculated. The displacement field, centered on the monitoring orifice, achieves a spatial resolution of [missing information]. The displacement measurement accuracy is better than 5mm.
[0086] S5. Synchronous acquisition of deep strain data
[0087] During the same time period as the surface LiDAR scan (T0 to T1), the Brillouin scattering signal of monitoring optical cable 2 was continuously acquired using a distributed fiber optic demodulator. Two sets of raw measurement data corresponding to times T0 and T1 were extracted, and the strain distribution along the borehole depth was obtained after demodulation. and Then, the deep strain increment profile during this period is calculated. The spatial resolution of fiber optic data in the depth direction is 0.5m.
[0088] To ensure data comparability, LiDAR scanning and fiber optic data acquisition adopt a synchronous triggering mechanism, that is, the initial measurement at time T0 is initiated by the same control command, and then synchronously triggered again at time T1, ensuring that the surface and deep monitoring data strictly correspond to the same deformation period.
[0089] S6. Establishment of Spatial Correspondence and Determination of Coupling Coefficients
[0090] This step establishes an accurate spatial coordinate transformation model to achieve spatial matching between the surface deformation field and deep strain data, and then inverts to obtain the actual strain transfer efficiency of the deep optical fiber.
[0091] (1) Construction of spatial coordinate transformation model
[0092] A local coordinate system O-XYZ is established with the center O of the borehole opening of monitoring hole 1 as the origin. The Z-axis follows the borehole trajectory (perpendicular to the borehole, i.e., vertically), while the X and Y axes form a horizontal plane. Since the actual borehole may be inclined, the inclination angle at each depth needs to be obtained using a borehole inclinometer. and azimuth This describes the spatial trajectory of the borehole.
[0093] For any point P in the LiDAR point cloud on the Earth's surface, its coordinates in the geodetic coordinate system are: Transform it to a local coordinate system using the following steps:
[0094] First, a translation transformation is performed using the center O of the borehole as the reference point, shifting the origin of the geodetic coordinates to point O, thus obtaining the translated coordinates. .
[0095] Secondly, the orientation of the local coordinate system at each depth is determined based on the borehole trajectory data. Since the surface deformation field is a three-dimensional curved surface, we need to project it onto a vertical profile containing the borehole axis to compare it with the one-dimensional fiber optic strain data distributed along the depth. Specifically, for any point on the surface, the horizontal distance d from it to the borehole axis is calculated, and the deformation vector at that point is decomposed into a projected component along the borehole axis and a component perpendicular to the axis. In this embodiment, the focus is on the deformation component along the borehole axis, as it is directly related to the axial strain measured by the fiber optic cable.
[0096] Through the above coordinate transformation and projection processing, the three-dimensional surface displacement field is... Transformed into a one-dimensional equivalent surface displacement profile along borehole depth z Based on the deformation compatibility principle, the surface displacement is equal to the integral of the strain of the deep rock and soil mass along the depth. The true strain of the deep landslide rock and soil mass in the borehole can be obtained by inversion using this principle. .
[0097] (2) Inversion of strain coupling coefficients
[0098] Define the strain coupling coefficient that varies along the depth direction. Let be the function to be determined, and its physical meaning be the proportional relationship between the measured strain of the optical fiber and the actual strain of the landslide soil and rock mass, i.e.
[0099]
[0100] in, This represents the actual strain of the landslide rock and soil mass. This represents the original measured strain of the optical fiber.
[0101] According to the deformation compatibility principle, the integral of the true strain of the landslide soil and rock mass along the borehole depth from the borehole opening (depth 0) to the bottom (depth H) is equal to the displacement component of the ground surface along the borehole axis. Therefore, the following optimization objective equation is established to find the optimal coupling coefficient K(z) to minimize the error between the theoretical ground displacement obtained by integrating after fiber strain correction and the LiDAR measured displacement:
[0102]
[0103] in, This represents the theoretical surface displacement obtained from the corrected fiber strain integral. This represents the surface displacement along the borehole axis, as measured by LiDAR.
[0104] Considering This may vary continuously with depth; this embodiment uses a piecewise constant model to... Discretization is performed: the borehole depth range is divided into N equally spaced intervals, and within each interval... constant The optimization problem described above is then transformed into a standard linear least squares problem:
[0105]
[0106] Among them, matrix The vector b, obtained by integrating fiber strain data, is composed of the projected values of surface deformation. Let be the vector of coupling coefficients to be determined. By solving this least-squares problem, the optimal coupling coefficients within each depth interval can be obtained. .
[0107] In this embodiment, the 35m drilling depth is divided into 35 intervals (each interval is 1m), and the truncated singular value decomposition algorithm is used to solve the above least squares problem to avoid the instability of the solution caused by data noise.
[0108] S7, Monitoring Data Correction
[0109] The coupling coefficient obtained in step S6 (or discretized) This applies to all subsequent fiber optic monitoring data. For any given monitoring time t, the raw strain data... Corrected actual landslide soil and rock strain Calculate using the following formula:
[0110]
[0111] The corrected strain data eliminates systematic errors caused by incomplete coupling between the optical fiber and the surrounding rock, and can more realistically reflect the actual deformation state of the deep soil and rock mass of the landslide. In this embodiment, subsequent monitoring cycles all use the data obtained from the initial calibration. Perform calibration; if the landslide deformation mode changes significantly, the S4-S7 calibration process can be repeated every six months or one year to update the coupling coefficients.
Claims
1. A distributed optical fiber high-coupling backfill structure for deep landslide monitoring, installed within boreholes in the landslide body, characterized in that, include: A distributed optical fiber monitoring cable, wherein the monitoring cable comprises, from the inside out, a fiber core, a coating layer, and a layered composite sheath; And, the layered backfill material filling the space between the borehole wall and the monitoring optical cable; The layered backfill body includes at least an inner layer of backfill material, a middle layer of backfill material, and an outer layer of backfill material arranged radially from the inside to the outside; The elastic modulus of the inner backfill material is close to that of the layered composite sheath of the monitoring optical cable, the elastic modulus of the outer backfill material is close to that of the surrounding rock of the borehole, and the elastic modulus of the middle backfill material is between that of the inner and outer backfill materials.
2. The backfill structure according to claim 1, characterized in that, The inner backfill material is an epoxy resin-based adhesive layer with an elastic modulus of 0.1 GPa to 1.0 GPa; the middle backfill material is a polymer-modified cement mortar layer with an elastic modulus of 1.0 GPa to 5.0 GPa; and the outer backfill material is a cement-based grouting material layer with an elastic modulus of 5.0 GPa to 20 GPa.
3. The backfill structure according to claim 1 or 2, characterized in that, The inner backfill material has the smallest thickness, followed by the outer backfill material, and the middle backfill material has a thickness greater than both the inner and outer backfill materials.
4. The backfill structure according to claim 1, characterized in that, The layered composite sheath of the monitoring optical cable is a multi-layered structure that is coaxially wrapped sequentially, including: a tight-buffered layer that directly covers the optical fiber; a tensile reinforcement layer that is wound around the tight-buffered layer; and a wear-resistant and corrosion-resistant outer sheath that covers the outermost layer.
5. The backfill structure according to claim 4, characterized in that, The tensile reinforcement layer is a fiber reinforcement layer, and the fiber reinforcement layer material is selected from aramid fiber, glass fiber, carbon fiber or basalt fiber.
6. The backfill structure according to claim 4, characterized in that, The tensile reinforcement layer is a metal reinforcement layer, which is a stranded steel wire layer or a braided steel wire layer.
7. A construction method for implementing the distributed optical fiber high-coupling backfill structure as described in claim 1, characterized in that, Includes the following steps: S1. Drilling and fiber optic cable guidance and positioning: Drill monitoring holes at the designed location of the landslide body, and install a centering guide in the borehole. Pass the distributed fiber optic monitoring cable through the centering guide and fix it at the center of the borehole axis. S2, Layered Grouting Forming: Three grouting pipes are used for construction. The three grouting pipes are respectively connected to grouting equipment that stores the inner, middle and outer layers of backfill material. The grouting operation is carried out in sequence from the inside to the outside and at the set time intervals to ensure that the previous grout enters the initial gelation state before the subsequent grout arrives, so as to form micro-penetration at the interface without macro-mixing, and construct a radially layered composite structure. S3. Pressure maintenance and curing constraint: After the layered grouting is completed, a continuous pressure is applied to the borehole until the backfill material is completely cured, so that the cured layered backfill body forms a composite structure with the monitoring optical cable and the surrounding rock of the borehole in a coordinated deformation.
8. The construction method according to claim 7, characterized in that, In step S2, the grouting pressure when injecting the inner layer backfill material is 0.1 MPa to 0.3 MPa, the grouting pressure when injecting the middle layer backfill material is 0.3 MPa to 0.6 MPa, and the grouting pressure when injecting the outer layer backfill material is 0.6 MPa to 1.0 MPa. In step S3, the constraint pressure is 0.2 MPa to 0.5 MPa, and the constraint pressure is maintained for 2 hours to 6 hours.
9. The construction method according to claim 7, characterized in that, Following step S3, a coupling coefficient calibration step is also included: S4. Set up permanent control points in the stable area of the landslide surface, acquire LiDAR scanning data of the landslide surface at the permanent control points at at least two different time points, and calculate the landslide surface deformation field based on the data. S5. Simultaneously acquire the deep strain data of the landslide monitored by the distributed optical fiber monitoring cable; S6. Based on the spatial correspondence between the surface deformation field and the deep strain data, determine the actual strain coupling coefficient of the distributed optical fiber monitoring cable in the deep soil and rock mass of the landslide. S7. In subsequent monitoring, the monitoring data of the distributed optical fiber monitoring cable are corrected using the actual strain coupling coefficient.
10. The construction method according to claim 9, characterized in that, In step S6, establishing the spatial correspondence includes: Based on the center coordinates of the borehole opening and the borehole trajectory, a three-dimensional spatial coordinate transformation model is constructed from the surface to the depth of the borehole. Using the coordinate transformation model, the surface displacement field data obtained by the LiDAR scan is spatially matched with the strain profile data distributed along the borehole depth obtained by the distributed optical fiber monitoring cable within the same time period or a set time window.