Distributed optical fiber based physical similar test method for deformation of mining top and bottom plate

Abstract

This invention discloses a physical similarity test method for roof and floor deformation during mining based on distributed optical fibers. It constructs an integrated optical fiber observation network for the roof and floor within a similar physical model, supplemented by low-temperature lattice coding calibration and orthogonal strain coupling at intersection points. This invention achieves full-field, continuous, and high-resolution acquisition of the roof and floor deformation field and fracture development process under mining conditions, significantly improving the spatial resolution and strain measurement accuracy of roof and floor deformation monitoring during mining. It enables synchronous distributed monitoring and unified spatial coordinate calibration of the roof and floor at different height interfaces. Furthermore, it achieves continuous and detailed observation of the entire roof and floor deformation process during mining, providing reliable experimental evidence and data support for evaluating the stability of the roof and floor in coal mines.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology and relates to a physical similarity test method for deformation of the roof and floor during mining based on distributed optical fiber sensing. Background Technology

[0002] In coal mining, the decompression, subsidence, and floor deformation and uplift caused by the advancement of the working face are among the main causes of coal mine disasters such as roadway instability, support failure, and even rockbursts. Especially under deep, high-stress, or intense mining conditions, the deformation and failure of the coal seam's roof and floor directly affect the safety of the working face support and production efficiency. Therefore, it is necessary to systematically study the deformation mechanism and failure evolution of the roof and floor under mining conditions through controlled indoor model tests. Existing indoor tests for monitoring roof and floor deformation mostly rely on discretely deployed stress gauges, pressure gauges, and acoustic emission sensors. These point-based or limited-section monitoring methods have poor spatial continuity and can only obtain limited measurement point information. They cannot comprehensively reflect the continuous deformation field inside the roof and floor under mining influence, nor can they accurately characterize different evolution stages. Distributed Strain Sensing (DSS), a technology within Distributed Fiber Optic Sensing (DFOS), can continuously acquire high spatial resolution strain distributions along the entire length of an optical fiber. It possesses advantages such as strong resistance to electromagnetic interference and long-term service capability when embedded within the medium, and has been gradually applied to structural deformation monitoring and early damage identification in civil engineering, tunnels, and slope protection. However, existing fiber optic monitoring in model tests often employs a one-dimensional or single-line two-dimensional deployment method, which has limited ability to perceive complex deformation fields within the roof and floor slabs, making it difficult to accurately identify the specific locations of deformation and their spatial evolution during coal mining. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a physical similarity test method for roof and floor deformation during mining operations based on distributed optical fibers. This method constructs an integrated optical fiber observation network for the roof and floor in a similar physical model, supplemented by low-temperature lattice coding calibration and orthogonal strain coupling at intersection points. It focuses on solving the following technical problems: First, it overcomes the limitation of poor spatial continuity in traditional point-based monitoring methods such as stress gauges, pressure gauges, and acoustic emission, achieving full-field, continuous, and high-resolution acquisition of the roof and floor deformation field and crack development process under mining conditions. Second, it overcomes the shortcomings of existing model tests where optical fibers are mostly one-dimensional or single-line deployments, making it difficult to reflect the complex deformation characteristics of the roof and floor, achieving synchronous distributed monitoring and unified spatial coordinate calibration of the roof and floor at different height interfaces. Third, it solves the problem that existing test methods cannot quantitatively characterize and intuitively display the entire process of crack initiation, propagation, and penetration in the roof and floor, achieving continuous and precise observation of the entire roof and floor deformation process during mining operations, providing reliable experimental basis and data support for the stability evaluation of the roof and floor in coal mines.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A physical similarity test method for the deformation of mining-induced top and bottom plates based on distributed optical fibers includes the following steps: Step 1, Construct the base plate planar fiber optic observation network: In the base plate model plane, use a single fiber to make an S-shaped back-and-forth loop along the x direction to cover the base plate monitoring area. Then, make an S-shaped back-and-forth loop along the y direction to form a base plate fiber optic grid in the base plate model plane. Step 2, synchronous calibration of the fiber with low temperature dot matrix encoding on the base plate: a low temperature calibration point is preset at the intersection of the fiber segment in the x direction and the fiber segment in the y direction to form a regular low temperature dot matrix encoding. Using the low temperature dot matrix encoding fiber synchronous calibration method, the mapping relationship between the fiber length coordinates on the base plate and the spatial coordinates on the base plate is established to realize the conversion of the fiber length coordinates to the spatial geometric coordinates of the base plate, and obtain the precise spatial position of each intersection point of the fiber in the model. Step 3, Laying of similar materials for the bottom plate and the minable coal seam area: The similar materials for the bottom plate are evenly spread and formed within the fiber optic grid of the bottom plate; the minable coal seam area is arranged using a combination of capsules and water-soluble materials, and the boundary of the fiber optic observation network is always anchored within the stable coal pillar; Step 4, construct the top plate planar fiber optic observation network: the bottom plate fiber tails laid in Step 1 are vertically raised to the top plate at the edge of the bottom plate to form a vertical fiber segment connecting the bottom plate and the top plate, and the fiber is wound in an S-shape first in the y direction and then in the x direction in the top plate plane to form a top plate fiber optic grid. Step 5, synchronous calibration of the top plate low temperature dot matrix coded fiber: a low temperature calibration point is preset at the intersection of the x and y directions of the fiber. The intersection point of the top plate fiber is calibrated using the low temperature dot matrix coded fiber synchronous calibration method to obtain the mapping relationship between the length coordinates of the top plate fiber and the spatial coordinates of the top plate. Step 6, Laying similar material on the top plate: The similar material on the top plate is evenly spread and formed within the fiber optic mesh area of ​​the top plate; Step 7: Establish an OFDR dual-end synchronous measurement system and obtain reference data before sampling: Lead out the bottom plate head end and top plate tail end of the optical fiber respectively, and connect them to the two measurement channels of the OFDR to synchronously collect optical fiber signals and obtain the initial reference data along the entire optical fiber before sampling. Step 8: Start the sampling loading and obtain the spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates: Perform sampling loading on the model and continuously monitor the entire optical fiber in real time throughout the sampling process to obtain the distributed axial strain field of the top and bottom plates at each sampling stage, and form a spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates that varies with the sampling cutter sequence. Step 9: Extract bidirectional strain at intersection points and perform orthogonal coupling analysis: Based on the spatiotemporal dataset of the strain of the entire optical fiber in the top and bottom plates obtained in Step 8, and according to the spatial coordinates of each intersection point and its corresponding optical fiber length position determined in Steps 2 and 5, the axial strain time series of the x-direction and y-direction fiber segments at each intersection point are extracted respectively. The average normal strain field at each intersection point of the top and bottom plates under different mining stages is calculated. and differential strain field This enables quantitative characterization of the local strain state of the top and bottom plates, and obtains the intersection point coupling analysis results required for crack initiation, propagation, and identification of strong deformation zones. Step 10: Construct waterfall plots and identify deformation and failure characteristics of the top and bottom plates: Based on the spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates obtained in Step 8 and the average normal strain field and differential strain field of each intersection point obtained in Step 9, waterfall plots of strain changes of the top and bottom plates under different mining stages are constructed using the spatial coordinates of the top and bottom plates and the average normal strain, respectively. At the same time, differential strain is used as an auxiliary identification quantity to assist in the identification of anisotropic regions of local deformation.

[0006] The present invention also includes the following technical features: Specifically, the optical fibers are laid out along the x and y directions to form multiple intersection points, with a spacing of 10cm between adjacent intersection points.

[0007] Specifically, the low-temperature dot matrix encoded optical fiber synchronous calibration method includes: starting from the first intersection point corresponding to the optical fiber incident end, selecting each intersection point sequentially along the fiber's x-direction laying direction, performing short-term spray cooling on each intersection point in sequence, and measuring the optical fiber using a high-precision distributed optical fiber strain demodulator (OFDR). In the obtained along-path signal, the low-temperature excitation position is manifested as a high-resolution narrow peak that is significantly higher than the background signal. By selecting each point on the OFDR intensity-distance curve and manually picking the peak position of each peak, the coordinates of the corresponding low-temperature event on the optical fiber are determined, thereby extracting the peak position of the low-temperature event along the path, obtaining the low-temperature event sequence of the optical fiber in the length-distance coordinate system, completing the unified transformation from the optical fiber length coordinate to the base plate spatial coordinate system, and obtaining the precise spatial position of each intersection point of the optical fiber in the model.

[0008] Specifically, the raw materials for the base plate similar material and the top plate similar material include sand, heavy calcium carbonate powder, paraffin wax and butter.

[0009] Specifically, when local damage or fiber breakage occurs within the model, the complete signal along the entire optical fiber is reconstructed according to the dual-channel data splicing rules. The dual-channel data splicing rules include: taking the fiber break location as the boundary, keeping the original length direction of the fiber segment data before the break point obtained by the first-end channel, rearranging the fiber segment data after the break point obtained by the tail-end channel in reverse according to the fiber length coordinate, and splicing it after the data of the first-end channel after length translation according to the actual length of the whole fiber, so as to reconstruct the complete signal along the entire fiber.

[0010] Specifically, step 8 includes: During the mining process, the mineable coal seam is divided into 20 sections. Each section is simulated by flushing water onto the corresponding mineable coal seam capsule. At each sampling moment, OFDR synchronously acquires the along-path signals of the bottom plate head channel and the top plate tail channel, compares the along-path measurement data of the whole optical fiber obtained at each sampling moment with the initial along-path reference data before sampling, and obtains the axial strain distribution along the whole optical fiber. Combining the mapping relationship between the fiber length coordinates of the bottom plate and the spatial coordinates of the bottom plate established in step 2, and the mapping relationship between the fiber length coordinates of the top plate and the spatial coordinates of the top plate established in step 5, the strain data along the fiber length direction is transformed into the corresponding spatial coordinate systems of the top plate and the bottom plate, thereby obtaining the distributed axial strain field of the top plate and the bottom plate under each mining stage, and forming a spatiotemporal dataset of the strain of the entire fiber of the top and bottom plates that varies with the mining sequence.

[0011] Specifically, the axial strain time series of the x-direction fiber segment and the y-direction fiber segment at each intersection point is as follows: Let the axial strain time series of the x-direction fiber segment at the i-th intersection point be... The axial strain time series of the y-direction fiber segment is as follows ;and , ,in These represent the normal strains of the rock mass at the intersection point in the x and y directions, respectively. The average normal strain field : ,when At the intersection point, tensile deformation predominates, exhibiting a tendency to open and tear; when At this time, the intersection point is dominated by compression deformation, and has a tendency to compaction and closure; The differential strain field : ,when When the value exceeds a preset threshold, the difference in deformation in the x and y directions at the intersection point becomes significant, making bending and shear deformation more likely, corresponding to a region prone to shear cracks or tension-shear combined cracks; when When the value is less than or equal to the preset threshold, the deformation in both directions at the intersection point is consistent, with pure tensile or pure compressive deformation being the main form.

[0012] Specifically, in step 10, the high-strain stripes that appear continuously in the waterfall diagram correspond to the actual locations of crack development areas and strong deformation zones in the top or bottom plate of the model. By analyzing the location of the high-strain stripes, their extension direction, intensity changes, and temporal evolution, the range of mining influence, the location of the leading edge of the failure zone, and the failure transmission path of the top and bottom plates can be identified during the working face advancement process.

[0013] Specifically, in the waterfall plot, when the average normal strain of a certain area is consistently positive, it indicates that the area is dominated by tensile deformation and is prone to crack opening and tensile cracking. When the average positive strain in a certain region is continuously negative and the amplitude gradually increases, it indicates that the region is dominated by compressive deformation and is a region with significant compaction and closure deformation. When the differential strain in a certain area increases significantly, it indicates that the deformation in the x and y directions of that area is not coordinated, and it belongs to a region prone to shear cracks and tension-shear combined cracks.

[0014] Specifically, by comparing and analyzing the waterfall diagrams of the roof and floor, we can obtain the differences in deformation strength, influence range, and failure evolution between the roof and floor during the mining process. This enables us to intuitively identify and quantitatively determine the distribution of cracks, strong deformation zones, and overall deformation and failure characteristics of the roof and floor in the goaf.

[0015] Compared with the prior art, the present invention has the following technical effects: This invention constructs an integrated fiber optic observation network for the roof and floor. By continuously deploying single optical fibers in an S-shape along the x and y directions in the roof and floor respectively, a high-density fiber optic grid is formed. The fiber boundaries are then anchored within the coal pillars, enabling synchronous distributed strain monitoring of the roof and floor layers within the same working face area, thereby obtaining quasi-three-dimensional deformation information with spatial correspondence.

[0016] This invention proposes a low-temperature dot matrix coded fiber synchronous calibration method. By setting regular low-temperature dot matrices on the top and bottom plates of the model and using OFDR to obtain the distributed response along the fiber, a one-to-one correspondence is established between the fiber length position corresponding to the low-temperature event and the known spatial calibration points in the model. This achieves accurate mapping of fiber length coordinates to the spatial coordinates of the top and bottom plates, improves the spatial positioning accuracy of the full-field strain data, and ensures the consistency and comparability between the monitoring results of the top and bottom plates.

[0017] This invention proposes an orthogonal strain coupling method at the intersection point. By extracting the axial strain data of two orthogonal fiber segments at the intersection point of the fiber optic mesh and performing averaging and differential processing, a two-dimensional coupling index of average normal strain and differential strain at the intersection point is constructed. This enables quantitative characterization of the local two-dimensional strain state of the top and bottom plates, and improves the ability to identify local deformation characteristics such as crack opening, compaction, and tension-shear combined deformation.

[0018] This invention enables continuous and precise monitoring of roof and floor deformation and crack evolution during mining operations. Compared to traditional point-based or limited-section monitoring methods, this invention can continuously acquire the spatiotemporal evolution characteristics of the deformation field inside the roof and floor throughout the entire mining process. It has advantages such as high spatial resolution, good measurement continuity, wide monitoring range, and strong anti-interference ability, and can provide reliable experimental methods and data support for the stability evaluation of coal mine roof and floor and the study of disaster mechanisms. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a fiber optic network deployment.

[0020] Figure 2 This is a waterfall diagram showing the strain changes of the top and bottom plates during the mining process.

[0021] Figure 3 This is a waterfall diagram showing the strain changes in the roof and floor of the goaf. Detailed Implementation

[0022] This invention provides a physical similarity test method for the deformation of mining-induced top and bottom plates based on distributed optical fibers, comprising: Construct an integrated fiber optic observation network for the roof and floor: Use a single optical fiber to form a high-density grid by laying it in an S-shape along the x and y directions on the floor and roof respectively, and anchor the fiber boundary in the coal pillar to realize synchronous distributed strain monitoring of the roof and floor layers within the same working face, and obtain "quasi-three-dimensional" deformation information with a high degree of correspondence. Low-temperature dot matrix encoding fiber synchronous calibration method: a low-temperature dot matrix is ​​formed at a fixed interval on the top and bottom plates of the model using liquid nitrogen. At the same time, the distributed response of the fiber is measured using OFDR. The low-temperature event is used as a "spatial control point". The fiber length coordinate is accurately mapped to the upper and lower spatial coordinate systems to ensure the spatial positioning accuracy of the strain data in the whole field and the consistent comparison between the top and bottom plates. Intersection point orthogonal strain coupling method: Physical coupling is performed using the strain data of two orthogonal fiber segments at the intersection point of the grid. By averaging and differentiating the strain data, a two-dimensional coupling index of average normal strain and differential strain at the intersection point is constructed, thereby realizing the quantitative characterization of the local two-dimensional strain state of the top and bottom plates and the identification of crack deformation characteristics. The above technical solutions significantly improve the spatial resolution and strain measurement accuracy of roof and floor deformation monitoring during mining, enabling continuous and precise observation of roof and floor deformation throughout the mining process, and providing reliable experimental basis and data support for the stability evaluation of roof and floor in coal mines.

[0023] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0024] Example: This embodiment provides a physical similarity test method for the deformation of mining top and bottom plates based on distributed optical fibers, including the following steps: Step 1: Constructing the base plate planar fiber optic observation network: Using a single fiber, first, make an S-shaped back-and-forth loop along the x-direction within the base plate model plane to cover the entire monitoring area. Then, make another S-shaped loop along the y-direction to form an approximately regular fiber optic grid within the base plate model plane. This S-shaped layout achieves high-density, continuous coverage of the base plate area without increasing fiber optic connectors. Furthermore, it ensures that the fiber orientations correspond one-to-one with the orthogonal x and y directions, facilitating accurate mapping of fiber length coordinates to the spatial coordinates of the base plate plane. This also provides a regular grid foundation for subsequent low-temperature lattice coding calibration and orthogonal strain coupling at intersection points. Specifically, as follows... Figure 1 As shown, the solid lines and dashed lines represent optical fibers running in the x and y directions, respectively.

[0025] Specifically, the distance between the S-bend angles in the x and y directions of the base plate is 10cm, thus forming several intersection points on the base plate plane. The spatial coordinates of these intersection points are unique and the interval is 10cm.

[0026] Step 2, synchronous calibration of the base plate low-temperature dot matrix encoded fiber: A low-temperature calibration point is preset at the intersection of the x-direction fiber segment and the y-direction fiber segment to form a regular low-temperature dot matrix code. Using the low-temperature dot matrix encoded fiber synchronous calibration method, the movable liquid nitrogen nozzle is sprayed with short-term cooling on each calibration point in a predetermined order to form a local low-temperature pulse. The mapping relationship between the fiber length coordinates of the base plate and the spatial coordinates of the base plate is established to realize the conversion of the fiber length coordinates to the spatial geometric coordinates of the base plate and obtain the precise spatial position of each intersection point of the fiber in the model. The specific steps of the cryogenic dot-matrix coded fiber synchronous calibration method include: starting from the first intersection point corresponding to the fiber's incident end, sequentially selecting each intersection point along the fiber's x-direction laying direction; performing short-term cooling on each intersection point in sequence; measuring the fiber using a high-precision distributed fiber strain demodulator (OFDR); and determining the cryogenic excitation position in the obtained along-path signal as a high-resolution narrow spike significantly higher than the background signal. By selecting each point on the OFDR intensity-distance curve and manually picking the peak position of each spike, the coordinates of the corresponding cryogenic event on the fiber are determined, thereby extracting the peak position of the cryogenic event along the path and obtaining the cryogenic event sequence of the fiber in the length-distance coordinate system. OFDR can only provide coordinates along the fiber length, not the geometric coordinates of each intersection point in the substrate. The installation was pre-determined through measurements and model geometry. The length and position on the OFDR curve can be established using a low-temperature calibration method. With the known geometric coordinates in the base plate ( The one-to-one correspondence between the fiber length coordinates and the spatial coordinates is used as the control points for establishing the mapping relationship between the length coordinates and the spatial coordinates of the base plate. Specifically, the purpose of low-temperature calibration is to find the correspondence between the fiber length coordinates and the actual spatial coordinates of the base plate. Since the OFDR outputs the corresponding information along the length of the fiber, it needs to be converted to the spatial coordinates corresponding to the actual model base plate. By calibrating the low-temperature points, the corresponding lengths of the spatial positions and the abrupt change points of the OFDR curve can be found. On this basis, the mapping relationship is established through linear or piecewise linear fitting methods, thereby completing the unified conversion from the fiber length coordinates to the base plate spatial coordinate system and obtaining the precise spatial positions of each intersection point of the fiber in the model.

[0027] Step 3, Laying of Similar Materials for the Bottom Plate and Minable Coal Seams: After completing the fiber optic laying of the bottom plate, the similar materials for the bottom plate and the minable coal seams are laid sequentially. The similar material for the bottom plate is prepared by mixing sand, heavy calcium carbonate powder, paraffin wax, and butter in a ratio of 153:46:1:20, and is evenly spread within the fiber optic grid area of ​​the bottom plate. In the minable coal seam area, a combination of capsules and water-soluble materials is used. To ensure that the boundary of the fiber optic observation network remains anchored within a stable coal pillar and its spatial position remains unchanged during mining, the planar dimensions of the coal seam similar material are reduced by 10 cm in both length and width directions compared to the similar material for the bottom plate, so that the fiber optic grid boundary falls within the coal pillar area.

[0028] Step 4, Construct the Top-Plane Planar Fiber Optic Observation Network: The fiber optic tails laid in Step 1 are vertically raised from the edge of the bottom plate to the top plate, forming a vertical fiber segment connecting the bottom and top plates. The fiber optic network is then repeatedly wound in an S-shape in the y-direction followed by an S-shape in the x-direction within the plane of the top plate, forming the top-plate fiber optic grid. Specifically, as shown below... Figure 1 As shown.

[0029] Step 5, synchronous calibration of the top plate low-temperature dot matrix encoded fiber: Pre-set a low-temperature calibration point at each intersection point of the fiber in the x and y directions. Use the low-temperature dot matrix encoded fiber synchronous calibration method to calibrate the intersection points of the top plate fiber and obtain the mapping relationship between the length coordinates of the top plate fiber and the spatial coordinates of the top plate. The low-temperature dot matrix encoded fiber synchronous calibration method is the same as step 2.

[0030] Step 6, laying of roof similar material: Laying of roof similar material. The roof similar material is also prepared by mixing sand, heavy calcium carbonate powder, paraffin wax and butter in a predetermined mass ratio. However, the ratio can be appropriately adjusted compared with the bottom plate according to the actual mining stress conditions and structural requirements.

[0031] Finally, the integrated layout of similar materials for the floor, coal seam, and roof with the fiber optic observation network was completed.

[0032] Step 7: Establish an OFDR dual-end synchronous measurement system and acquire pre-sampling reference data: Lead out the bottom and top ends of the optical fiber and connect them to the two measurement channels of the OFDR. Set the sampling interval, sampling frequency, and single acquisition duration, and conduct joint debugging tests to ensure that the two channels synchronously acquire optical fiber signals within the same sampling period. During the joint debugging process, perform continuity and correspondence checks on the signals obtained from the first and last channels. If local damage or fiber breakage occurs inside the model in subsequent steps, follow the dual-channel data splicing rules: using the fiber breakage location as the boundary, keep the original length direction of the fiber segment data before the breakage point obtained from the first channel, and rearrange the fiber segment data after the breakage point obtained from the last channel in reverse according to the fiber length coordinates. Then, splice the data after the first channel data after length translation according to the actual length of the entire fiber. This allows for the reconstruction of the complete fiber-to-line signal, effectively preventing the complete failure of the entire measurement line due to local fiber breakage inside the model, and improving the system reliability and data integrity. After completing the joint commissioning and confirming that the two channels are measuring normally, the initial reference data along the entire optical fiber before sampling is obtained as a reference for strain calculation at each moment in subsequent steps and data reconstruction after fiber breakage.

[0033] Step 8: Begin mining loading and acquire spatiotemporal dataset of fiber strain along the entire roof and floor: After step 7, begin model mining loading and continuously monitor the entire fiber in real time throughout the mining process. During mining, the mineable coal seam is divided into 20 sections. Each section is simulated by flushing water onto the corresponding mineable coal seam capsule. Mining of one simulated coal seam takes approximately 40 minutes. After each section is mined, the seam is left to stand for 1 hour to collect and analyze the fiber monitoring data for that stage, thus achieving precise monitoring of the entire mining process. At each sampling moment, OFDR simultaneously acquires the along-path signals of the first channel of the floor and the last channel of the roof. When a fiber break occurs locally within the model, complete data is acquired according to the dual-channel data splicing rules determined in step 7. Furthermore, the along-path measurement data of the entire fiber obtained at each sampling moment is compared with the initial along-path reference data before mining to obtain the axial strain distribution along the entire fiber. Combining the mapping relationship between the fiber length coordinates of the base plate and the spatial coordinates of the base plate established in step 2, and the mapping relationship between the fiber length coordinates of the top plate and the spatial coordinates of the top plate established in step 5, the strain data along the fiber length direction is transformed into the corresponding spatial coordinate systems of the top and bottom plates. This yields the distributed axial strain fields of the top and bottom plates at each mining stage, forming a spatiotemporal dataset of the strain along the entire fiber of the top and bottom plates that varies with the mining sequence. Since the ambient temperature changes are small during the model test, the impact on the strain measurement results is negligible; therefore, no separate temperature compensation processing is performed in this embodiment.

[0034] Step 9: Extract bidirectional strain at intersection points and perform orthogonal coupling analysis: Based on the spatiotemporal dataset of the strain of the entire optical fiber in the top and bottom plates obtained in Step 8, and according to the spatial coordinates of each intersection point and its corresponding fiber length position determined in Steps 2 and 5, the axial strain time series of the x-direction and y-direction fiber segments at each intersection point are extracted respectively. The average normal strain field at each intersection point of the top and bottom plates under different mining stages is calculated. and differential strain field This enables quantitative characterization of the local strain state of the top and bottom plates, and obtains the intersection point coupling analysis results required for crack initiation, propagation, and identification of strong deformation zones.

[0035] Let the axial strain time series of the fiber segment in the x-direction at the i-th intersection point be... The axial strain time series of the y-direction fiber segment is as follows Since the tangent directions of the two fiber segments at the intersection point are approximately distributed along the x and y directions, respectively, the two axial strains mentioned above can be approximated as two orthogonal normal strain components in the local continuous medium plane strain state at the intersection point, that is: , (1) in These represent the normal strains of the rock mass at the intersection point in the x and y directions, respectively. The average normal strain at the intersection point is defined. for: (2) when At the intersection point, tensile deformation predominates, exhibiting a tendency to open and tear; when At the intersection point, compressive deformation predominates, exhibiting a tendency towards compaction and closure. Further, the differential strain at the i-th intersection point is defined. for: (3) when When the value exceeds a preset threshold, the difference in deformation in the x and y directions at the intersection point becomes significant, making bending and shear deformation more likely, corresponding to a region prone to shear cracks or tension-shear combined cracks; when When the value is less than or equal to a preset threshold, the bidirectional deformation at the intersection point is relatively consistent, mainly consisting of pure tensile or pure compressive deformation. The preset threshold is used for judgment. The determination value representing the degree of difference in biaxial deformation is a preset threshold that is set in advance according to the test conditions and monitoring requirements before the test begins.

[0036] Therefore, the average normal strain field at each intersection point of the roof and floor under different mining stages can be obtained. and differential strain field This study enables quantitative characterization of the local strain state of the top and bottom plates and obtains the intersection point coupling analysis results required for crack initiation, propagation, and identification of strong deformation zones. These results can serve as the basis for constructing waterfall plots and identifying the deformation and failure characteristics of the top and bottom plates in the next step.

[0037] Step 10: Construct waterfall plots and identify deformation and failure characteristics of the top and bottom plates: Based on the spatiotemporal dataset of strain along the entire optical fiber of the top and bottom plates obtained in Step 8, and the average normal strain field and differential strain field at each intersection point obtained in Step 9, waterfall plots of strain changes of the top and bottom plates under different mining stages are constructed using the spatial coordinates of the top and bottom plates and the average normal strain, respectively. Simultaneously, differential strain is used as an auxiliary identification quantity to assist in the identification of anisotropic regions of local deformation, such as... Figure 2 .

[0038] Since the edges of the fiber optic observation networks for the floor and roof are anchored within the coal pillars on both sides, the grid as a whole does not undergo significant rigid displacement or overall torsion during mining. Therefore, the relative positions of the intersection points in the spatial coordinate systems of the roof and floor remain basically stable. Based on this, the continuous high-strain bands appearing in the waterfall plot can directly correspond to the actual locations of crack development zones and strong deformation zones in the model's roof or floor. By analyzing the location, extension direction, intensity changes, and temporal evolution of the high-strain bands, the mining influence range, the location of the leading edge of the failure zone, and the failure transmission path of the roof and floor can be identified during the working face advancement.

[0039] Furthermore, when the average positive strain in a certain area of ​​the waterfall diagram remains positive, it indicates that the area is dominated by tensile deformation, making it prone to crack opening and tensile fracturing. When the average positive strain in a certain area remains negative and the amplitude gradually increases, it indicates that the area is dominated by compressive deformation, making it a significant area for compaction and closure deformation. When the differential strain in a certain area increases significantly, it indicates that the deformation in the x and y directions is not coordinated, making it prone to shear fractures and tension-shear composite fractures. By comparing and analyzing the waterfall diagrams of the roof and floor, the differences in deformation intensity, influence range, and failure evolution between the roof and floor during mining can also be obtained, thereby enabling intuitive identification and quantitative determination of the distribution of cracks, strong deformation zones, and overall deformation and failure characteristics of the roof and floor in the goaf.

[0040] from Figure 2 The system can clearly record the specific location information of the mining operation, analyze the impact range of mining, the location of the leading edge of the failure zone, and the failure transmission path of the roof and floor. Meanwhile, comparative analysis reveals that the deformation of the roof is significantly greater than that of the floor. This phenomenon indicates that during mining, the roof experiences more drastic stress changes, and its structural stability is more easily affected than that of the floor.

[0041] Ultimately Figure 3It can identify the tensile and compression zones of the top and bottom plates after the working face advances, and obtain the spatial distribution results of the crack development zone, strong deformation zone and failure evolution path of the top and bottom plates throughout the mining process, so as to achieve continuous and fine characterization of the entire deformation and failure process of the top and bottom plates.

[0042] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0043] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0044] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers, characterized in that, Includes the following steps: Step 1, Construct the base plate planar fiber optic observation network: In the base plate model plane, use a single fiber to make an S-shaped back-and-forth loop along the x direction to cover the base plate monitoring area. Then, make an S-shaped back-and-forth loop along the y direction to form a base plate fiber optic grid in the base plate model plane. Step 2, synchronous calibration of the fiber with low temperature dot matrix encoding on the base plate: a low temperature calibration point is preset at the intersection of the fiber segment in the x direction and the fiber segment in the y direction to form a regular low temperature dot matrix encoding. Using the low temperature dot matrix encoding fiber synchronous calibration method, the mapping relationship between the fiber length coordinates on the base plate and the spatial coordinates on the base plate is established to realize the conversion of the fiber length coordinates to the spatial geometric coordinates of the base plate, and obtain the precise spatial position of each intersection point of the fiber in the model. Step 3, Laying of similar materials for the bottom plate and the minable coal seam area: The similar materials for the bottom plate are evenly spread and formed within the fiber optic grid of the bottom plate; the minable coal seam area is arranged using a combination of capsules and water-soluble materials, and the boundary of the fiber optic observation network is always anchored within the stable coal pillar; Step 4, construct the top plate planar fiber optic observation network: the bottom plate fiber tails laid in Step 1 are vertically raised to the top plate at the edge of the bottom plate to form a vertical fiber segment connecting the bottom plate and the top plate, and the fiber is wound in an S-shape first in the y direction and then in the x direction in the top plate plane to form a top plate fiber optic grid. Step 5, synchronous calibration of the top plate low temperature dot matrix coded fiber: a low temperature calibration point is preset at the intersection of the x and y directions of the fiber. The intersection point of the top plate fiber is calibrated using the low temperature dot matrix coded fiber synchronous calibration method to obtain the mapping relationship between the length coordinates of the top plate fiber and the spatial coordinates of the top plate. Step 6, Laying similar material on the top plate: The similar material on the top plate is evenly spread and formed within the fiber optic mesh area of ​​the top plate; Step 7: Establish an OFDR dual-end synchronous measurement system and obtain reference data before sampling: Lead out the bottom plate head end and top plate tail end of the optical fiber respectively, and connect them to the two measurement channels of the OFDR to synchronously collect optical fiber signals and obtain the initial reference data along the entire optical fiber before sampling. Step 8: Start the sampling loading and obtain the spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates: Perform sampling loading on the model and continuously monitor the entire optical fiber in real time throughout the sampling process to obtain the distributed axial strain field of the top and bottom plates at each sampling stage, and form a spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates that varies with the sampling cutter sequence. Step 9: Extract bidirectional strain at intersection points and perform orthogonal coupling analysis: Based on the spatiotemporal dataset of the strain of the entire optical fiber in the top and bottom plates obtained in Step 8, and according to the spatial coordinates of each intersection point and its corresponding fiber length position determined in Steps 2 and 5, the axial strain time series of the x-direction and y-direction fiber segments at each intersection point are extracted respectively. The average normal strain field at each intersection point of the top and bottom plates under different mining stages is calculated. and differential strain field This enables quantitative characterization of the local strain state of the top and bottom plates, and obtains the intersection point coupling analysis results required for crack initiation, propagation, and identification of strong deformation zones. Step 10: Construct waterfall plots and identify deformation and failure characteristics of the top and bottom plates: Based on the spatiotemporal dataset of strain of the entire optical fiber of the top and bottom plates obtained in Step 8 and the average normal strain field and differential strain field of each intersection point obtained in Step 9, waterfall plots of strain changes of the top and bottom plates under different mining stages are constructed using the spatial coordinates of the top and bottom plates and the average normal strain, respectively. At the same time, differential strain is used as an auxiliary identification quantity to assist in the identification of anisotropic regions of local deformation.

2. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, The optical fibers are laid out along the x and y directions to form multiple intersection points, with a spacing of 10cm between adjacent intersection points.

3. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, The low-temperature dot matrix encoded optical fiber synchronous calibration method includes: starting from the first intersection point corresponding to the optical fiber incident end, selecting each intersection point sequentially along the fiber's x-direction laying direction, performing short-term spray cooling on each intersection point in sequence, and measuring the optical fiber using a high-precision distributed optical fiber strain demodulator (OFDR). In the obtained along-path signal, the low-temperature excitation position is manifested as a high-resolution narrow peak that is significantly higher than the background signal. By selecting each point on the OFDR intensity-distance curve and manually picking the peak position of each peak, the coordinates of the corresponding low-temperature event on the optical fiber are determined, thereby extracting the peak position of the low-temperature event along the path, obtaining the low-temperature event sequence of the optical fiber in the length-distance coordinate system, completing the unified transformation from the optical fiber length coordinate to the base plate spatial coordinate system, and obtaining the precise spatial position of each intersection point of the optical fiber in the model.

4. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, The raw materials for the base plate similar material and the top plate similar material include sand, heavy calcium carbonate powder, paraffin wax and butter.

5. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, When local damage or fiber breakage occurs inside the model, the complete signal along the entire optical fiber is reconstructed according to the dual-channel data splicing rules. The dual-channel data splicing rules include: taking the fiber break location as the boundary, keeping the original length direction of the fiber segment data before the break point obtained by the first-end channel, rearranging the fiber segment data after the break point obtained by the tail-end channel in reverse according to the fiber length coordinate, and splicing it after the data of the first-end channel after length translation according to the actual length of the whole fiber, so as to reconstruct the complete signal along the entire fiber.

6. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, Step 8 includes: During the mining process, the mineable coal seam is divided into 20 sections. Each section is simulated by flushing water onto the corresponding mineable coal seam capsule. At each sampling moment, OFDR synchronously acquires the along-path signals of the bottom plate head channel and the top plate tail channel, compares the along-path measurement data of the whole optical fiber obtained at each sampling moment with the initial along-path reference data before sampling, and obtains the axial strain distribution along the whole optical fiber. Combining the mapping relationship between the fiber length coordinates of the bottom plate and the spatial coordinates of the bottom plate established in step 2, and the mapping relationship between the fiber length coordinates of the top plate and the spatial coordinates of the top plate established in step 5, the strain data along the fiber length direction is transformed into the corresponding spatial coordinate systems of the top plate and the bottom plate, thereby obtaining the distributed axial strain field of the top plate and the bottom plate under each mining stage, and forming a spatiotemporal dataset of the strain of the entire fiber of the top and bottom plates that varies with the mining sequence.

7. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, The axial strain time series of the x-direction fiber segment and y-direction fiber segment at each intersection point are as follows: Let the axial strain time series of the x-direction fiber segment at the i-th intersection point be... The axial strain time series of the y-direction fiber segment is as follows ;and , ,in These represent the normal strains of the rock mass at the intersection point in the x and y directions, respectively. The average normal strain field : ,when At the intersection point, tensile deformation predominates, exhibiting a tendency to open and tear; when At this time, the intersection point is dominated by compression deformation, and has a tendency to compaction and closure; The differential strain field : ,when When the value exceeds a preset threshold, the difference in deformation in the x and y directions at the intersection point becomes significant, making bending and shear deformation more likely, corresponding to a region prone to shear cracks or tension-shear combined cracks; when When the value is less than or equal to the preset threshold, the deformation in both directions at the intersection point is consistent, with pure tensile or pure compressive deformation being the main form.

8. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 1, characterized in that, In step 10, the high-strain stripes that appear continuously in the waterfall diagram correspond to the actual locations of crack development areas and strong deformation zones in the top or bottom plate of the model. By analyzing the location of the high-strain stripes, their extension direction, intensity changes, and temporal evolution, the range of mining influence, the location of the leading edge of the failure zone, and the failure transmission path of the top and bottom plates can be identified during the working face advancement.

9. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 8, characterized in that, In the waterfall diagram, when the average normal strain of a certain area is consistently positive, it indicates that the area is dominated by tensile deformation and is prone to crack opening and tensile cracking. When the average positive strain in a certain region is continuously negative and the amplitude gradually increases, it indicates that the region is dominated by compressive deformation and is a region with significant compaction and closure deformation. When the differential strain in a certain area increases significantly, it indicates that the deformation in the x and y directions of that area is not coordinated, and it belongs to a region prone to shear cracks and tension-shear combined cracks.

10. The physical similarity test method for deformation of mining-induced top and bottom plates based on distributed optical fibers as described in claim 8, characterized in that, By comparing and analyzing the waterfall diagrams of the roof and floor, we can obtain the differences in deformation intensity, influence range, and failure evolution between the roof and floor during the mining process. This enables us to intuitively identify and quantitatively determine the distribution of cracks, strong deformation zones, and overall deformation and failure characteristics of the roof and floor in the goaf.

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