Coal mining cave stability analysis and early warning method based on three-dimensional reconstruction numerical simulation

Abstract

The invention discloses a coal mining cave stability analysis and early warning method based on three-dimensional reconstruction numerical simulation, and the method comprises the steps: firstly carrying out the low-altitude shooting through employing an unmanned plane, obtaining the high-resolution image data of a mining area terrain, carrying out the processing and analysis of the data, and generating a high-precision three-dimensional model; then collecting drilling data of a mining area, establishing basic reference information of stratigraphic stratification through the drilling data, and constructing a stratum surface and a geologic body; carrying out three-dimensional reconstruction to generate a three-dimensional model of the coal mining cave after carrying out image data acquisition on the coal mining cave area, and carrying out numerical simulation after establishing a numerical model; analyzing according to a numerical simulation result, and evaluating the stability state of the coal mining cave; and finally, an early warning index of the stability of the coal mining cave is established according to a stability analysis result, the coal mining cave is monitored in real time, and an early warning signal is sent out when monitoring data reach or exceed the early warning index. The method can provide theoretical basis and data support for stability analysis and early warning of the coal mining cave.

Description

Technical Field

[0001] The present invention relates to a method for analyzing and warning the stability of a coal mining cave, specifically a method for analyzing and warning the stability of a coal mining cave based on image three-dimensional reconstruction numerical simulation for shallow buried coal seams, belonging to the technical field of safe coal mining. Background Art

[0002] Traditional coal mining methods have many challenges. For example, during the coal mining process, the coal seam has a large degree of fracturing, and the geological conditions are complex and uneven, resulting in problems such as low mining efficiency, high costs, and environmental pollution. To solve these problems, in recent years, researchers have begun to focus on the physical fluidization mining technology of underground cross-layer drilling. As a new type of coal mining method, the physical fluidization mining technology has advantages such as improving resource recovery rate and reducing potential safety hazards. Among them, the coal mining method using surface drilling for physical fluidization mining has been gradually popularized in coal mines due to advantages such as less upfront investment and low coal mining costs.

[0003] During the physical fluidization mining process, the stability of the coal mining cave is the key to ensuring safe production. Especially for shallow buried coal seams with complex geological conditions, coal mining activities often cause disturbances to the surrounding rock of the coal mining cave, which may further lead to safety problems such as deformation, damage, and even collapse of the surrounding rock. Therefore, accurately evaluating the stability of the coal mining cave and timely detecting potential safety hazards are of great significance for ensuring the safety and efficiency of coal mine production.

[0004] Currently, in the field of coal mining, the evaluation of the stability of coal mining caves mainly relies on traditional geological exploration, on-site monitoring, and numerical simulation methods. However, these methods have certain limitations in practical applications: Although geological exploration can provide information about coal seam occurrence, geological structure, etc., it is difficult to accurately reflect the specific impact of coal mining activities on the stability of the surrounding rock; On-site monitoring installs monitoring equipment to monitor the deformation and stress state of the surrounding rock in real time, but the monitoring range is limited, and it is affected by factors such as the environment and equipment, making it difficult to comprehensively reflect the stability status of the coal mining cave; Although numerical simulation can simulate various mechanical behaviors during the coal mining process, the accuracy and reliability of the model are often affected by various factors, such as the selection of model parameters and the setting of boundary conditions. Summary of the Invention

[0005] Aiming at the problems existing in the above-mentioned prior art, the present invention provides a method for analyzing and warning the stability of a coal mining cave based on three-dimensional reconstruction numerical simulation, which has advantages such as high precision, high efficiency, and strong real-time performance, and can provide a theoretical basis and data support for the analysis and warning of the stability of the coal mining cave. It is particularly suitable for accurately evaluating and warning the stability of a coal mining cave during the physical fluidization mining of shallow buried coal seams with complex geological conditions by surface drilling.

[0006] To achieve the above object, the method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation specifically includes the following steps:

[0007] Step1, on-site terrain investigation: Use a drone to conduct low-altitude shooting to obtain high-resolution image data of the mining area terrain, and then process and analyze these data to generate a high-precision three-dimensional model;

[0008] Step2, geological modeling: Collect borehole data of the mining area, establish basic reference information for stratigraphic layering through the borehole data, and construct geological strata and geological bodies;

[0009] Step3, cave scanning reconstruction and simulation: After collecting image data of the coal mining cave area, perform three-dimensional reconstruction to generate a three-dimensional model of the coal mining cave, establish a numerical model based on the three-dimensional model of the coal mining cave, and conduct numerical simulation based on the numerical model;

[0010] Step4, stability analysis and evaluation: Analyze according to the numerical simulation results, evaluate the stability state of the coal mining cave, and determine whether there are potential instability factors or safety hazards in the coal mining cave according to the stability analysis results; Combine the actual situation and the numerical simulation results to conduct a comprehensive evaluation of the stability of the coal mining cave;

[0011] Step5, warning and response: According to the stability analysis results, establish warning indicators for the stability of the coal mining cave, conduct real-time monitoring of the coal mining cave, and issue a warning signal when the monitoring data reaches or exceeds the warning indicators.

[0012] Furthermore, in Step5, the warning indicators include primary risk warning indicators, intermediate risk warning indicators, and high-level risk warning indicators. Define as the primary risk warning, define as the intermediate risk warning, and define as the high-level risk warning, where u represents the displacement of coal and rock, and d represents the number of days.

[0013] Furthermore, when the coal mining cave bare hole is in the elastic state during physical fluidized bed mining, the relationship between the radius r0 of the coal mining cave bare hole and the displacement u of coal and rock is:

[0014]

[0015] In the formula: r0 is the radius of the coal mining cave bare hole; r is the radius of a certain point in the elastic region of the coal mining cave bare hole; σ0 is the original rock stress; μ and η are constants related to the spring and damper in the Maxwell viscoelastic model; t is the time;

[0016] When plastic deformation occurs in the coal mining cave bare hole during physical fluidized bed mining, the relationship between the radius r0 of the coal mining cave bare hole and the displacement u of coal and rock is:

[0017]

[0018] In the formula: E is Young's modulus; v is Poisson's ratio; f(t) is an undetermined function, which is obtained from the displacement continuity at r = r p where r p is the plastic radius; v p is the plastic volume expansion, generally assumed to be a constant value; σ r and σ θ are respectively the radial stress and circumferential stress of the surrounding rock at a point with radius r in the elastic region of the bare hole of the coal mining cave.

[0019] Furthermore, the specific process of Step1 is as follows:

[0020] Step1-1, Determine the modeling boundary: Determine the boundary range of the modeling according to the research purpose and geological information;

[0021] Step1-2, UAV aerial photography: Plan the flight route and set the shooting parameters according to the actual situation of the mining area, and then use the UAV and photography equipment for aerial photography;

[0022] Step1-3, Image preprocessing: Perform preprocessing operations on the acquired image data to correct the geometric distortion and radiation distortion of the images;

[0023] Step1-4, Feature extraction and matching: Use the feature extraction algorithm to extract key feature information from the preprocessed images, and match the features in different images through the feature matching algorithm to establish the corresponding relationship between the images;

[0024] Step1-5, Aerial triangulation: According to the feature matching results, use the aerial triangulation technology to solve the exterior orientation elements of the images;

[0025] Step1-6, Multi-view image dense matching: On the basis of aerial triangulation, use the multi-view image dense matching technology to generate high-precision three-dimensional point cloud data;

[0026] Step1-7, 3D model construction: Use 3D modeling software to convert the three-dimensional point cloud data into a 3D model;

[0027] Step1-8, Texture mapping: Map the texture information in the original image data onto the 3D model.

[0028] Furthermore, the specific process of Step2 is as follows:

[0029] Step2-1, Data collection and collation: Collect the borehole data of the mining area, including borehole location, borehole depth, and lithology information;

[0030] Step2-2, Data preprocessing: Process the drilling data, remove outliers, missing values and duplicate data, and convert the data into a unified format;

[0031] Step2-3, Establish a drilling model: Import the processed drilling data into the modeling software to form a drilling database, and establish a drilling model;

[0032] Step2-4, Formation stratification and interface modeling: Based on the drilling model, and through analyzing the lithology changes in the boreholes, conduct formation stratification and establish a formation interface model;

[0033] Step2-5, Geological body modeling: Based on the formation interface model, construct each geological body model.

[0034] Furthermore, the specific process of Step3 is as follows:

[0035] Step3-1, Data acquisition: Use image acquisition equipment to collect multi-angle and multi-scale image data of the coal mining cave area;

[0036] Step3-2, 3D reconstruction: Use the image 3D reconstruction algorithm to process the collected image data and generate a 3D model of the coal mining cave;

[0037] Step3-3, Establish a numerical model: On the basis of 3D reconstruction, use numerical simulation software to establish a numerical model of the coal mining cave;

[0038] Step3-4, Set simulation parameters: Set the boundary conditions, load conditions, and material parameters of the numerical model according to the actual situation;

[0039] Step3-5, Numerical simulation: Use numerical simulation software to conduct simulation analysis on the stability of the coal mining cave.

[0040] Furthermore, the specific process of Step3-4 is as follows:

[0041] Divide the coal-rock strata within the analysis range into multiple small units, conduct joint grouping and mesh division on the divided coal-rock strata, use the generalized Hoek-Brown strength criterion to assign parameters to the already divided coal / rock strata, and apply boundary constraints and boundary conditions according to the actual mining situation.

[0042] Furthermore, the generalized Hoek-Brown strength criterion is expressed as:

[0043]

[0044] In the formula: σ θ and σ r are the major principal stress and minor principal stress respectively; σ cis the uniaxial compressive strength of the rock mass; m, s, and a are the strength parameters of the generalized H-B criterion. m reflects the hardness of the rock, s reflects the degree of rock mass fragmentation, and a reflects the non-linearity of the material;

[0045] The values of m, s, and a are as follows:

[0046]

[0047] In the formula: m i is a dimensionless material parameter, and there are detailed value-taking methods for various rocks; GSI is the geological strength index; D is the degree of disturbance caused by the blasting influence and stress release process.

[0048] Compared with the prior art, the method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation first uses an unmanned aerial vehicle (UAV) route planning software for route planning, image data collection, and three-dimensional model browsing to obtain an accurate three-dimensional model of the surface terrain. Based on the borehole point data within the mining area and information such as coal seam occurrence and geological structure, high-resolution image technology is used to perform three-dimensional reconstruction on the shallow-buried coal seam mining caves to obtain an accurate three-dimensional model of the mining caves. Then, combined with geomechanics theory and numerical simulation technology, an in-depth analysis of the stability of the mining caves is carried out to obtain the stability state of the shallow-buried coal seam mining caves under different mining conditions, including the deformation and failure trends of the caves, etc., and the numerical simulation results of the overlying rock displacement and stress analysis of the mining caves formed by coal seam cavity formation are obtained, and the characteristics of overlying rock instability of the shallow-buried coal seam physical fluidization mining caves formed by coal seam cavity formation are obtained. Then, a warning system is constructed, which can issue a warning in a timely manner when the numerical simulation results show that there are potential risks in the cave stability, reminding relevant personnel to take necessary preventive measures to ensure the safe progress of coal mine mining. It has the advantages of high precision, high efficiency, and strong real-time performance, and can provide a theoretical basis and data support for the stability analysis and warning of coal mining caves, and is especially suitable for accurately evaluating and warning the stability of coal mining caves during the physical fluidization mining of shallow-buried coal seams with complex geological conditions by surface drilling. Brief Description of the Drawings

[0049] Figure 1 is the flow chart of the present invention;

[0050] Figure 2 is a schematic diagram of obtaining low-altitude multi-angle aerial images of the mining area terrain by using an unmanned aerial vehicle in an embodiment of the present invention;

[0051] Figure 3 is a schematic diagram of borehole data in an embodiment of the present invention;

[0052] Figure 4 is a schematic diagram of the three-dimensional model of the coal mining cave in an embodiment of the present invention;

[0053] Figure 5Schematic diagram of the aperture shrinkage displacement of the three-dimensional model in the embodiments of the present invention;

[0054] Figure 6 Partial enlarged view of the aperture shrinkage displacement of the coal mining cave in the embodiments of the present invention;

[0055] Figure 7 Schematic diagram of the change of the aperture shrinkage displacement of the coal mining cave with time in the embodiments of the present invention. Detailed implementation manners

[0056] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0057] As Figure 1 shown, the method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation specifically includes the following steps:

[0058] Step1, on-site terrain investigation: Use a drone for low-altitude shooting, obtain high-resolution image data of the mining area terrain through photogrammetry technology, and then process and analyze these data to finally generate a high-precision three-dimensional model. Specifically as follows:

[0059] Step1-1, determine the modeling boundary: Determine the boundary range of the modeling according to the research purpose and geological information.

[0060] Step1-2, drone aerial photography: Use a drone and photographic equipment to plan the flight route and set the shooting parameters according to the actual situation of the mining area. During the aerial photography process, it is necessary to ensure that the image data has sufficient overlap and resolution for subsequent three-dimensional reconstruction.

[0061] Step1-3, image preprocessing: Perform preprocessing operations such as denoising and correction on the obtained image data to improve the data quality. Correct the geometric distortion and radiation distortion of the image to ensure the accuracy and reliability of the image.

[0062] Step1-4, feature extraction and matching: Use feature extraction algorithms to extract key information such as feature points and feature lines from the preprocessed images. Through feature matching algorithms, match the features in different images to establish the corresponding relationship between the images.

[0063] Step1-5, aerotriangulation: According to the feature matching results, use aerotriangulation technology to solve the exterior orientation elements of the images, that is, determine parameters such as the position and attitude of the images during shooting. Aerotriangulation is one of the key steps in three-dimensional reconstruction, and its accuracy directly affects the accuracy of the subsequent three-dimensional model.

[0064] Step1-6, Multi-view Image Dense Matching: Based on the aerial triangulation measurement, use the multi-view image dense matching technology to generate high-precision 3D point cloud data. The multi-view image dense matching technology can make full use of the overlap and resolution of images to generate dense and accurate 3D point clouds.

[0065] Step1-7, 3D Model Construction: Use 3D modeling software or algorithms to convert the 3D point cloud data into a 3D model. When constructing the 3D model, appropriate modeling methods and parameters need to be selected to ensure the accuracy and fidelity of the model.

[0066] Step1-8, Texture Mapping: Map the texture information in the original image data onto the 3D model to make the model more realistic and vivid. Texture mapping is the last step in 3D model construction and an important means to improve the fidelity and visual effect of the model.

[0067] Step2, Borehole Geological Modeling: Borehole data usually includes information such as borehole location, borehole depth, and lithology description. Through these data, establish the basic reference information for stratigraphic layering and construct the stratigraphic surface and geological bodies. Specifically as follows:

[0068] Step2-1, Data Collection and Sorting: Collect borehole data in the mining area, including information such as borehole location, depth, and lithology. Sort the data to ensure the accuracy and integrity of the data.

[0069] Step2-2, Data Preprocessing: Process the borehole data to remove outliers, missing values, and duplicate data. Convert the data into a unified format for subsequent processing and modeling.

[0070] Step2-3, Establish Borehole Model: Import the processed borehole data into the modeling software to form a borehole database and establish a borehole model. This usually involves the description and representation of borehole location, depth, and lithology.

[0071] Step2-4, Stratigraphic Layering and Interface Modeling: Conduct stratigraphic layering based on the borehole model. This is usually achieved by analyzing the lithology changes in the boreholes. Establish a stratigraphic interface model to describe the boundaries and relationships between strata.

[0072] Step2-5, Geological Body Modeling: Based on the stratigraphic interface model, construct models of individual geological bodies. This usually involves the description and representation of the morphology, location, and properties of geological bodies.

[0073] Step3, Cave Scanning Reconstruction and Simulation: After collecting image data of the shallow-buried coal seam mining cave area, conduct 3D reconstruction to generate a 3D model of the mining cave. Based on the 3D model of the mining cave, establish a numerical model and conduct numerical simulation. Specifically as follows:

[0074] Step3-1, Data acquisition: Use high-resolution image acquisition devices (such as drones, terrestrial photogrammetry systems, etc.) to collect multi-angle and multi-scale image data of the shallow-buried coal seam mining cave area, ensuring that the collected image data has sufficient overlap and clarity.

[0075] Step3-2, 3D reconstruction: Use image 3D reconstruction algorithms (such as structured light method, stereo vision method, etc.) to process the collected image data and generate a 3D model of the mining cave. This model should be able to accurately reflect the shape, structure, and spatial distribution characteristics of the mining cave.

[0076] Step3-3, Establish a numerical model: On the basis of 3D reconstruction, use numerical simulation software (such as MIDAS, FLAC3D, ABAQUS, etc.) to establish a numerical model of the mining cave. The numerical model should fully consider factors such as the geological characteristics of the coal seam, mining conditions, and cave shape to ensure the accuracy of the simulation results. The model should include the mechanical properties of the coal seam, roof, floor, and surrounding rock mass.

[0077] Step3-4, Set simulation parameters: Set the boundary conditions, load conditions, material parameters, etc. of the numerical model according to the actual situation to ensure that the simulation parameters can truly reflect the actual situation of the mining cave.

[0078] Divide the coal-rock strata within the analysis range into multiple small units, i.e., grids, conduct joint grouping and grid division on the divided coal-rock strata. The coal-rock yield adopts the Generalized Hoek-Brown strength criterion. Assign parameters to the already divided coal / rock strata and apply boundary constraints according to the actual mining situation. The grid division should consider the mechanical properties of the coal / rock strata and the stress changes during the mining process to ensure the accuracy of the analysis results. According to the actual situation of the mined coal seam, apply appropriate boundary conditions on the boundary of the model. The boundary conditions may include fixed boundaries, free boundaries, or constrained boundaries, etc.

[0079] The principle of the Generalized Hoek-Brown strength criterion is based on the fact that the strength of rock is affected by internal friction and cohesion effects as well as the strength of rock blocks and can be expressed as:

[0080]

[0081] In the formula: σ θ and σ r are the major principal stress and minor principal stress respectively; σ cis the uniaxial compressive strength of the rock mass; m, s, and a are the strength parameters of the generalized Hoek-Brown criterion. m reflects the hardness of the rock, s reflects the degree of rock mass fragmentation, with a value of 1.0 for a complete rock mass, and a reflects the degree of material nonlinearity.

[0082] The values of m, s, and a are as follows:

[0083]

[0084] where: m i is a dimensionless material parameter, and there are detailed methods for obtaining values for various rocks; GSI is the Geological Strength Index; D is the degree of disturbance caused by the blasting effect and stress release process.

[0085] Once the above parameters are determined, the generalized Hoek-Brown strength criterion can be applied to the evaluation of the rock mass strength in numerical software.

[0086] Step3-5, Numerical simulation: Use numerical simulation software to simulate and analyze the stability of the coal mining cave. During the simulation process, key indicators such as the stress distribution, displacement changes, and plastic zone evolution around the cave should be focused on.

[0087] Step4, Stability analysis and evaluation: Analyze based on the numerical simulation results to evaluate the stability status of the coal mining cave. According to the stability analysis results, determine whether there are potential instability factors or safety hazards in the coal mining cave; combine the actual situation and numerical simulation results to comprehensively evaluate the stability of the coal mining cave. During the evaluation process, the influence of factors such as the shape, structure, geological conditions, and mining method of the cave on stability should be fully considered.

[0088] Step5, Early warning and response: Based on the stability analysis results, establish early warning indicators for the stability of the coal mining cave. The early warning indicators should be able to reflect the change trend and potential risks of the cave stability; use sensors, monitoring equipment, etc. to monitor the coal mining cave in real time. The monitoring data should be able to reflect the changes in key indicators such as the stress, displacement, and plastic zone of the cave in real time; when the monitoring data reaches or exceeds the early warning indicators, issue an early warning signal, and corresponding emergency response measures can be taken according to the level of the early warning signal and the actual situation to ensure the safety and stability of the coal mining cave.

[0089] The early warning indicators include primary risk early warning indicators, intermediate risk early warning indicators, and high-level risk early warning indicators. Define as the primary risk early warning, define as the intermediate risk early warning, and define as the high-level risk early warning, where u represents the displacement of coal and rock, and d represents the number of days.

[0090] When the coal mining cave bare hole is in the elastic state during physical fluidized bed mining, based on the Maxwell viscoelastic model, the relationship between the radius r0 of the coal mining cave bare hole and the displacement u of the coal and rock is:

[0091]

[0092] In the formula: r0 is the radius of the coal mining cave bare hole; r is the radius of a certain point in the elastic region of the coal mining cave bare hole; σ0 is the virgin rock stress; μ and η are constants related to the spring and damper in the Maxwell viscoelastic model; t is the time.

[0093] As continuous coal breaking progresses, the radius of the coal mining cave continuously increases and plastic deformation occurs. Based on the Fritz elasto-viscoplastic model, the relationship between the radius r0 of the coal mining cave bare hole and the displacement u of the coal and rock is:

[0094]

[0095] In the formula: E is the Young's modulus; v is the Poisson's ratio; f(t) is an undetermined function, which is obtained from the displacement continuity at r = r p where r p is the plastic radius; v p is the plastic volume expansion, generally assumed to be a constant value; σ r and σ θ are respectively the radial stress and circumferential stress of the surrounding rock at the radius r of a certain point in the elastic region of the coal mining cave bare hole.

[0096] Taking the physical fluidized bed mining of a certain coal seam in a certain mine as an example, the present invention will be further described in conjunction with the accompanying drawings.

[0097] The geological data of this coal seam are shown in Table 1 below.

[0098] Table 1 Physical and mechanical parameters of coal and rock strata

[0099]

[0100] The coal mining cave is in the shape of a columnar hole. According to the on-site situation, a three-dimensional geometric model of the coal mining cave with height × radius = 10 m × 5 m is constructed as shown in Figure 4 shown.

[0101] First, the Altizure mobile software is used to plan the UAV flight path, which can efficiently plan the flight path for multiple DJI UAVs and complete the image acquisition at vertical and oblique angles, as shown in Figure 2As shown, a drone is used to obtain low-altitude multi-angle aerial images of the mining area terrain. The image data is sorted by terrain category and imported into the Smart3D Capture software for review. After the review is error-free, aerial triangulation measurement is performed. In the 3D view interface, the positional relationship between the photos and the model can be observed, and the specific positions of the photos in the model can be previewed. After the aerial triangulation measurement is completed, select the reconstruction option to generate a three-dimensional model of the terrain. Smart3D Capture supports exporting three-dimensional images or mesh models in various formats, and can be further processed through three-dimensional design software to generate physical-level three-dimensional models or three-dimensional meshes. The model is imported into the reverse engineering software Geomagic, converted into the.iges format, and after mesh optimization, it is imported into the preprocessing module of the numerical software for finite element analysis.

[0102] Secondly, collect the borehole data of the mining area as Figure 3 shown. The borehole data usually includes information such as borehole location, borehole depth, and lithology description. Based on these data, the basic reference information for stratigraphic layering is established, and then the stratigraphic surface and geological bodies are constructed.

[0103] Next, use the terrestrial photogrammetry system to collect multi-angle and multi-scale image data of the shallow-buried coal seam mining cave area; use the structured light method to process the collected image data to generate a three-dimensional model of the mining cave as Figure 4 shown.

[0104] Then, on the basis of three-dimensional reconstruction, use numerical simulation software to establish a numerical model of the mining cave and perform numerical simulation based on the numerical model. From on-site experience, it is known that the roof subsidence amount / aperture shrinkage amount in coal seam stability is the most intuitive index for caving. First, perform numerical simulation of coal seam mining, and the aperture shrinkage displacement diagram of the mining cave under the condition of hard roof of shallow-buried coal seam as Figure 5 shown can be obtained. The vertical displacement of the aperture of the mining cave under the condition of hard roof of shallow-buried coal seam, that is, the subsidence amount, is less than 1 m, indicating that the roof has not caved. In the corresponding displacement diagram (as Figure 5 shown), it can also be clearly seen that there is no situation where the red displacement is too large in the hard roof of the shallow-buried coal seam; however, the horizontal displacement of the aperture of the mining cave under the condition of hard roof of shallow-buried coal seam, that is, the aperture shrinkage amount, is greater than 1 m, indicating that the lateral coal body has caved. In the corresponding displacement diagram (such as Figure 5 、 Figure 6The red caving area of the aperture shrinkage can also be clearly seen (as shown). Conduct a detailed analysis of the numerical simulation results to evaluate the stability state of the coal mining cave; according to the analysis results, determine whether there are potential instability factors or safety hazards in the cave. Combining the actual situation and the numerical simulation results, conduct a comprehensive evaluation of the stability of the coal mining cave. During the evaluation process, fully consider the influence of factors such as the shape, structure, and geological conditions of the cave on the stability. Use the method of coal seam water jet coal breaking and lifting to conduct a simulation analysis of coal seam cavity mining. After calculating the deformation characteristics of the coal mining cave under the condition of coal seam water jet coal breaking and lifting, save and extract the data; extract and analyze the simulation data of the coal mining cave under the condition of coal seam water jet coal breaking and lifting, analyze the stress distribution, deformation conditions, and possible failure modes around the coal mining cave, etc., to obtain the instability characteristics of the surrounding rock of the coal mining cave in the in-situ fluidized mining of shallow buried coal seams with coal seam cavity formation.

[0105] Finally, according to the stability analysis results, establish early warning indicators for the stability of the coal mining cave, and define as the primary risk early warning, and define as the intermediate risk early warning, and define as the high-level risk early warning; use sensors, monitoring equipment, etc. to conduct real-time monitoring of the coal mining cave, and issue an early warning signal when the monitoring data reaches or exceeds the early warning indicators.

[0106] Based on the viscoelastic model and the elastoplastic-viscoplastic model, set the relevant parameters of the springs and dampers, use numerical simulation software to establish a numerical model of the coal mining cave, and conduct a numerical simulation of the fluidized mining of the coal seam. The schematic diagram of the change of the aperture shrinkage displacement of the coal mining cave over time as shown in Figure 7 can be obtained. In this example, within 0-15h, the aperture shrinkage displacement of the coal mining cave reaches 230m. According to the early warning indicators of the stability of the coal mining cave, it is a high-level risk early warning (150mm ≤ |u| / d = 368mm). In addition, the displacement diagrams established based on the elastoplastic model above (as shown in Figure 5 , Figure 6 ) are also verified. The lateral coal body of the coal mining cave collapses in the corresponding red caving area of the aperture shrinkage. Through the time effect analysis of the above numerical simulation results, it shows the effectiveness of the stability analysis and early warning method of the coal mining cave based on three-dimensional reconstruction numerical simulation.

[0107] The stability analysis and early warning method for coal mining caves based on 3D reconstruction numerical simulation first uses an unmanned aerial vehicle route planning software for route planning, image data collection, and 3D model browsing to obtain an accurate 3D model of the surface terrain, and collects the data of exploration borehole points in the mining area to obtain information on coal seam occurrence, geological structure, etc. It uses high-resolution imaging technology to perform 3D reconstruction on the shallow-buried coal seam mining caves to obtain an accurate 3D model of the caves; then, combined with geomechanics theory and numerical simulation technology, it deeply analyzes the stability of the coal mining caves, obtains the stability status of the shallow-buried coal seam mining caves under different mining conditions, including the deformation and failure trends of the caves, etc., obtains the numerical simulation results of the overlying rock displacement and stress analysis of the coal seam mining caves with cavity formation, and obtains the characteristics of overlying rock instability of the shallow-buried coal seam in-situ physical fluidization mining caves with cavity formation; then constructs an early warning system. When the numerical simulation results show potential risks in the cave stability, the early warning system can issue an early warning in a timely manner to remind relevant personnel to take necessary preventive measures to ensure the safe progress of coal mine mining. It has the advantages of high precision, high efficiency, and strong real-time performance, and can provide a theoretical basis and data support for the stability analysis and early warning of coal mining caves, and is especially suitable for accurately evaluating and warning the stability of coal mining caves during the ground borehole physical fluidization mining of shallow-buried coal seams with complex geological conditions.

Claims

1. A coal mining cave stability analysis and early warning method based on three-dimensional reconstruction numerical simulation, characterized in that: The specific steps include: Step 1, on-site terrain survey: Use drones to take low-altitude photos to obtain high-resolution image data of the mining area terrain, and then process and analyze these data to generate a high-precision 3D model; Step 2, geological modeling: collect drilling data from the mining area, establish basic reference information for stratigraphic stratification through drilling data, and construct stratigraphic layers and geological bodies; Step 3, cave scanning reconstruction and simulation: after collecting image data of the coal mining cave area, perform 3D reconstruction to generate a 3D model of the coal mining cave, establish a numerical model based on the 3D model of the coal mining cave, and perform numerical simulation based on the numerical model; Step 4, stability analysis and evaluation: Analyze and evaluate the stability of the coal mining cave according to the numerical simulation results. According to the stability analysis results, determine whether there are potential unstable factors or safety hazards in the coal mining cave; combine the actual situation and the numerical simulation results to conduct a comprehensive evaluation of the stability of the coal mining cave; Step 5, early warning and response: Based on the results of stability analysis, establish early warning indicators for coal mining cave stability, conduct real-time monitoring of coal mining caves, and issue early warning signals when the monitoring data reaches or exceeds the early warning indicators.

2. The method for coal mining cave stability analysis and early warning based on three-dimensional reconstruction numerical simulation according to claim 1 is characterized in that: In Step 5, the early warning indicators include primary risk early warning indicators, intermediate risk early warning indicators and advanced risk early warning indicators. Defined as a primary risk warning, Defined as a medium risk warning, It is defined as an advanced risk warning, where u represents coal-rock displacement and d represents the number of days.

3. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 2 is characterized in that: In the elastic state of the open hole of the coal mining cave in physical fluidization mining, the relationship between the open hole radius r0 of the coal mining cave and the coal-rock displacement u is: Where: r0 is the radius of the open hole of the coal mining cave; r is the radius of a point in the elastic area of ​​the open hole of the coal mining cave; σ0 is the original rock stress; μ and η are constants related to the spring and damper in the Maxwell viscoelastic model; t is time; When plastic deformation occurs in the open hole of the coal mining cave in physical fluidization mining, the relationship between the radius r0 of the open hole of the coal mining cave and the coal-rock displacement u is: Where: E is Young's modulus; v is Poisson's ratio; f(t) is the function to be determined, through r = r p The displacement continuity at the position is obtained, where r p is the plastic radius; v p is the plastic volume expansion, which is generally assumed to be a constant value; σ r , σ θ They are respectively the radial stress and annular stress of the surrounding rock at a point with radius r in the elastic area of ​​the bare hole of the coal mining cave.

4. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 1, 2 or 3, characterized in that: Step 1 The specific process is as follows: Step 1-1, determine the modeling boundary: determine the modeling boundary range according to the research purpose and geological information; Step 1-2, drone aerial photography: plan the route and set the shooting parameters according to the actual situation of the mining area, and then use drones and photography equipment to take aerial photos; Step 1-3, image preprocessing: preprocess the acquired image data to correct the geometric distortion and radiation distortion of the image; Step 1-4, feature extraction and matching: Use feature extraction algorithm to extract key feature information from the preprocessed image, and use feature matching algorithm to match the features in different images to establish the correspondence between images; Step 1-5, aerial triangulation: Based on the feature matching results, the exterior orientation elements of the image are solved using aerial triangulation technology; Step 1-6, multi-view image dense matching: Based on aerial triangulation, multi-view image dense matching technology is used to generate high-precision 3D point cloud data; Step 1-7, 3D model construction: Use 3D modeling software to convert 3D point cloud data into 3D models; Step 1-8, texture mapping: map the texture information in the original image data to the three-dimensional model.

5. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 1, 2 or 3, characterized in that: Step 2 The specific process is as follows: Step 2-1, data collection and collation: collect drilling data in the mining area, including drilling location, drilling depth, and lithology information; Step 2-2, data preprocessing: process the drilling data, remove outliers, missing values ​​and duplicate data, and convert the data into a unified format; Step 2-3, establish a drilling model: import the processed drilling data into the modeling software to form a drilling database, and establish a drilling model; Step 2-4, stratigraphic stratification and interface modeling: Based on the borehole model and by analyzing the lithology changes in the borehole, stratigraphic stratification is performed to establish a stratigraphic interface model; Step 2-5, geological body modeling: construct each geological body model based on the stratigraphic interface model.

6. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 1, 2 or 3, characterized in that: Step 3 The specific process is as follows: Step 3-1, data collection: Use image acquisition equipment to collect multi-angle and multi-scale image data of the coal mining cave area; Step 3-2, 3D reconstruction: using the image 3D reconstruction algorithm to process the collected image data and generate a 3D model of the coal mining cave; Step 3-3, establish a numerical model: on the basis of three-dimensional reconstruction, use numerical simulation software to establish a numerical model of the coal mining cave; Step 3-4, set simulation parameters: set the boundary conditions, load conditions, and material parameters of the numerical model according to the actual situation; Step 3-5, numerical simulation: Use numerical simulation software to simulate and analyze the stability of coal mining caves.

7. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 6 is characterized in that: Step 3-4 The specific process is as follows: The coal-rock strata within the analysis range are divided into multiple small units, the divided coal-rock strata are grouped by joints and meshed, the generalized Hoek-Brown strength criterion is used to assign parameters to the divided coal / rock strata, and boundary constraints and boundary conditions are imposed according to the actual mining situation.

8. The method for analyzing and warning the stability of coal mining caves based on three-dimensional reconstruction numerical simulation according to claim 7 is characterized in that: The generalized Hoek-Brown strength criterion is expressed as: Where: θ and σ r are the major and minor principal stresses respectively; σ c is the uniaxial compressive strength of the rock mass; m, s and a are the strength parameters of the generalized HB criterion, m reflects the hardness of the rock, s reflects the degree of rock mass crushing, and a reflects the nonlinearity of the material; The values ​​of m, s, and a are as follows: Where: m i It is a dimensionless material parameter, and various rocks have detailed value selection methods; GSI is the geological strength index; D is the degree of disturbance caused by blasting impact and stress release process.

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