A Simulation Analysis Method for Directional Pre-splitting in Fully Mechanized Longwall Mines of Extra-Thick Coal Seams Based on 3D Modeling

Abstract

This invention belongs to the field of directional pre-fracture simulation technology for extra-thick coal seams, specifically involving a directional pre-fracture simulation analysis method for extra-thick coal seam fully mechanized caving mining areas based on 3D modeling. Through geological exploration of the extra-thick coal seam fully mechanized caving mining area, pre-fracture boreholes are laid out and a 3D model is built. The detonation sequence is determined according to a predetermined directional pre-fracture path. Based on this, a gradient detonation time difference is designed to form multiple pre-fracture simulation test groups. Then, the 3D model of the extra-thick coal seam fully mechanized caving mining area is used to conduct detonation under each pre-fracture simulation test group. During the detonation process, the fracture propagation path conformity and environmental risk monitoring and assessment are carried out simultaneously. Based on the assessment results, a suitable detonation time difference is determined. This method achieves the determination of a suitable detonation time difference based on a balance between fracture propagation path conformity and environmental risk, greatly reducing the incidence of forced mining interruptions and promoting sustainable coal seam mining.

Description

Technical Field

[0001] This invention belongs to the field of directional pre-fracture simulation technology for extra-thick coal seams, specifically involving a directional pre-fracture simulation and analysis method for fully mechanized longwall mining of extra-thick coal seams based on three-dimensional modeling. Background Technology

[0002] Extra-thick coal seams refer to coal seams with a thickness exceeding 6 meters. Due to their substantial thickness, the surrounding rock in the roadway experiences significant stress during mining, making them prone to deformation and collapse. Consequently, traditional mining methods struggle to achieve full-thickness mining, resulting in the ineffective recovery of some coal resources and significant resource waste. In response to this challenge, fully mechanized longwall mining emerged. By installing supports at the bottom of the working face and gradually lowering the top coal, full-thickness mining is achieved, and this method has gradually become the mainstream approach for extra-thick coal seam mining.

[0003] Given the high strength and hardness of the top coal in extra-thick coal seams, traditional mining methods struggle to achieve uniform top coal fracturing and caving, resulting in low resource recovery rates. To address this, it's necessary to introduce fractures to provide more fracturing paths for the top coal, allowing it to cave more rapidly and uniformly after the support force is released. However, the complex and variable geological conditions of extra-thick coal seams, along with significant differences in the mechanical properties of the coal seam and surrounding rock, all influence fracture propagation paths. Therefore, directional pre-fracture is achieved by pre-arranging multiple boreholes in the coal seam and determining the detonation sequence according to a predetermined path to guide fracture propagation along that path. This reduces the overall strength of the top coal, promoting its fracturing and caving along the predetermined path, thereby improving the efficiency and resource recovery rate of fully mechanized longwall mining.

[0004] In directional pre-splitting, the time difference between adjacent boreholes significantly impacts the fracture propagation path when boreholes are blasted according to a predetermined sequence. Improperly set time differences can cause the fracture propagation path to deviate from the predetermined direction, thus affecting the crushing effect of top coal and the efficiency of fully mechanized longwall mining. Therefore, rationally controlling the time difference is crucial in directional pre-splitting operations, typically requiring simulation analysis to select an appropriate time difference. However, existing methods for selecting time differences often overemphasize the conformity of the fracture propagation path, neglecting the impact of the time difference on environmental risks such as coal seam vibration and surface subsidence. This singular evaluation criterion may result in a selected time difference that, while ensuring a high degree of conformity between the fracture propagation path and the predetermined path, could trigger significant environmental risks, potentially leading to forced mining interruptions and hindering sustainable coal seam mining. Summary of the Invention

[0005] In view of this, the present invention aims to propose a simulation analysis method for directional pre-splitting in fully mechanized longwall mining of extra-thick coal seams based on three-dimensional modeling, which effectively solves the problems mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solution: a directional pre-splitting simulation analysis method for fully mechanized longwall mining of extra-thick coal seams based on three-dimensional modeling, comprising the following steps: S1, conducting geological exploration of the extra-thick coal seam, thereby laying out pre-splitting boreholes.

[0007] S2. Based on the geological exploration results of the extra-thick coal seam, a three-dimensional model of the extra-thick coal seam is built using three-dimensional modeling software.

[0008] S3. Determine the detonation sequence based on the spatial distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and design a gradient detonation time difference to form multiple pre-splitting simulation groups, with each pre-splitting simulation group corresponding to a detonation time difference.

[0009] S4. Using the constructed three-dimensional model of the extra-thick coal seam, detonation was carried out under each pre-splitting simulation group. During the detonation process, crack propagation and environmental risk monitoring were carried out simultaneously to obtain the crack propagation path and environmental risk indicators corresponding to each pre-splitting simulation group. The environmental risk indicators include the coal seam vibration frequency and surface subsidence displacement.

[0010] S5. Based on the crack propagation path and environmental risk indicators corresponding to each pre-crack simulation group, assess the compliance of crack propagation path and the environmental risk of crack propagation.

[0011] S6. Determine the appropriate detonation time difference based on the crack propagation path conformity and crack propagation environment risk assessment results corresponding to each pre-splitting simulation group.

[0012] Combining all the above technical solutions, the positive effects of this invention are as follows: This invention determines the layout of pre-splitting boreholes through geological exploration of fully mechanized longwall mining in extra-thick coal seams and builds a three-dimensional model. Then, based on a predetermined directional pre-splitting path, it determines the detonation sequence and designs multiple pre-splitting simulation groups with different gradient detonation time differences. The three-dimensional model is then used to simulate detonation in each test group, simultaneously monitoring the conformity of the fracture propagation path and environmental risks. Finally, based on the evaluation results, a suitable detonation time difference that balances fracture propagation path and environmental risks is determined. This method effectively reduces the incidence of mining interruptions and ensures efficient, safe, and sustainable mining of coal seams. Attached Figure Description

[0013] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0014] Figure 1 This is a diagram illustrating the implementation steps of the method of the present invention.

[0015] Figure 2 This is a schematic diagram of the linear layout of pre-splitting boreholes in this invention.

[0016] Figure 3 This is a schematic diagram of the pre-splitting borehole mesh layout in this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] See Figure 1 As shown, the present invention proposes a directional pre-splitting simulation analysis method for fully mechanized longwall mining of extra-thick coal seams based on three-dimensional modeling, including the following steps: S1, geological exploration of the fully mechanized longwall mining of extra-thick coal seams, thereby laying out pre-splitting boreholes.

[0019] When applied to the above scheme, the main purpose of geological exploration is to understand in detail the key parameters such as the geological structure, thickness, dip angle, and stress distribution of extra-thick coal seams, so as to provide accurate data support for subsequent pre-splitting borehole layout, three-dimensional model building, and blasting design.

[0020] The geological structure exploration mentioned above is to understand the geological structural features of the coal seam, including geological structures such as faults, folds, and joints. For example, exploration methods can be carried out by rock sampling drilling, specifically by obtaining core samples of the coal seam and surrounding rock for geological structure analysis. Another example is the use of seismic wave methods (such as high-resolution three-dimensional seismic exploration technology) to detect the distribution and morphology of underground geological structures.

[0021] The aforementioned coal seam thickness exploration exemplifies the use of a method that directly measures the coal seam thickness by obtaining core samples through drilling. Another exemplary method uses ground-penetrating radar technology to detect coal seam thickness based on the reflection characteristics of electromagnetic waves underground.

[0022] The above-mentioned coal seam dip angle exploration exemplifies the following methods: obtaining coal seam core samples through drilling to directly measure the dip angle of the coal seam; using an inclined logging tool to measure the dip angle within the borehole to estimate the coal seam dip angle; and obtaining the three-dimensional structural information of the coal seam through 3D seismic exploration to measure the dip angle.

[0023] The above-mentioned exemplary exploration method for stress distribution exploration is to directly measure the stress in the coal seam and surrounding rock using a stress measuring instrument. The stress measurement points should be reasonably arranged according to the distribution characteristics of the coal seam to ensure coverage of the entire mining area.

[0024] As a preferred option, the pre-splitting borehole layout follows the process described below: extract stress distribution information from the geological exploration results of the extra-thick coal seam, divide the extra-thick coal seam into several stress regions, number the divided stress regions, and mark the stress value of each stress region.

[0025] It should be added that when dividing extra-thick coal seams into stress regions based on stress distribution information, clustering methods can be used to group regions with similar stress values ​​into the same category to form different stress regions.

[0026] Extract the boundary contours of each stress region, and construct a set of surrounding adjacent stress regions corresponding to each stress region, with each stress region as the center.

[0027] The stress value of each stress region is compared with the stress value of each adjacent stress region using an expression. The stress concentration SC corresponding to each stress region is obtained. i In the formula F i This represents the stress value of the i-th stress region, where i represents the stress region number, i = 1, 2, ..., K, n. ij Let j represent the stress value of the adjacent stress region corresponding to the i-th stress region, where j = 1, 2, K, m, and m represents the number of adjacent stress regions.

[0028] As an explanation of the above expression, the stress concentration is 0 when the stress value of a stress region is less than that of an adjacent stress region. The stress concentration is greater only when the stress values ​​of all stress regions are greater than those of their adjacent stress regions.

[0029] The stress concentration corresponding to each stress region is compared with the preset effective stress concentration. For example, the effective stress concentration is 0.8. If the stress concentration corresponding to a certain stress region reaches the effective stress concentration, then the stress region is taken as the pre-crack target region. If the stress concentration corresponding to all stress regions does not reach the effective stress concentration, then the stress region corresponding to the maximum stress value is selected as the pre-crack target region based on the stress value of each stress region.

[0030] It's important to understand that the main purpose of calculating stress concentration after stress zoning is to assess whether the stress level in each stress zone is significantly higher than its surrounding areas, thereby determining the pre-cracking target area. Specifically, if the stress value within a stress zone is generally higher than its neighboring areas, this zone is considered a stress concentration zone and is selected as the pre-cracking target area. When no stress concentration zone can be identified based on stress concentration calculations, the stress zone corresponding to the maximum stress value is selected as the pre-cracking target area. This is because both the maximum stress zone and stress concentration zone are the starting points and main directions of crack propagation. Selecting these areas for pre-cracking can effectively guide crack propagation. A stress concentration zone refers to a specific location where the stress value is significantly higher than the surrounding area within a localized range. Due to stress concentration, these areas are more likely to trigger crack initiation and propagation, making them ideal targets for pre-cracking operations. The maximum stress zone refers to the area with the highest stress value within a specific range. Although the maximum stress zone does not necessarily exhibit stress concentration, its high stress level can still lead to rapid crack propagation. Therefore, selecting the maximum stress zone as the pre-cracking target area is reasonable when there is no obvious stress concentration zone. Therefore, by calculating stress concentration areas and selecting these areas as pre-cracking targets, it is possible to effectively guide crack propagation, release local stress, and prevent the formation of irregular cracks.

[0031] The shape of the pre-splitting target area is identified based on the boundary contour of the pre-splitting target area, and the pre-splitting borehole locations are then laid out accordingly. The specific layout is as follows: the shape of the pre-splitting target area is matched with the shape of the pre-splitting area suitable for various layout methods in the layout reference library to obtain the pre-splitting borehole layout method corresponding to the pre-splitting target area, where the layout methods include linear layout and mesh layout.

[0032] As a concrete implementation of the above scheme, the suitable shape for the pre-splitting area when arranged linearly is a long strip, and the suitable shape for the pre-splitting area when arranged in a mesh is a square, rectangular, or irregular shape.

[0033] See Figure 2 As shown, when the pre-splitting boreholes corresponding to the pre-splitting target area are laid out in a linear pattern, the starting and ending points of the linear arrangement are determined according to the boundary of the pre-splitting target area.

[0034] Pre-splitting boreholes are evenly distributed between the starting and ending points of the linear arrangement.

[0035] The spacing between adjacent pre-splitting boreholes mentioned above should not be too large or too small. If the spacing is too large, the stress waves generated between adjacent boreholes will attenuate rapidly during propagation, making it difficult to form effective stress superposition in the target area. This will result in the cracks not being fully connected between adjacent boreholes, forming a discontinuous crack network. If the spacing is too small, the stress waves generated by adjacent boreholes will interfere with each other, leading to an enhanced interference effect of the stress waves, which will weaken the effective role of the stress waves. This may result in uneven crack expansion or even crack closure, affecting the pre-splitting effect. In addition, too small a borehole spacing will require more boreholes, increasing construction time and cost. At the same time, too many boreholes will also increase the number of detonation devices, further increasing material and labor costs. Specifically, the spacing can be determined according to the length of the target pre-splitting area. Generally, the spacing can be between 0.5 and 2 meters. Assuming that the target pre-splitting area is a long strip area with a length of 50 meters and a width of 5 meters, the spacing between adjacent pre-splitting boreholes can be 2 meters, which can result in 25 pre-splitting boreholes.

[0036] See Figure 3 As shown, when the pre-splitting borehole layout corresponding to the pre-splitting target area is a mesh layout, the pre-splitting target area is evenly divided into several small meshes, and staggered meshes are selected from the divided meshes, and then a pre-splitting borehole is arranged in each staggered mesh.

[0037] The size of the grid mentioned above can be determined based on the area of ​​the pre-splitting target region, which is usually 2 to 5 meters square.

[0038] It is important to understand that the purpose of staggering the pre-splitting boreholes in the divided grid is to improve the connectivity and propagation effect of the cracks. The staggered arrangement can be used between different grids, that is, the borehole positions are staggered in adjacent grids to form staggered stress wave superposition, which guides the cracks to propagate along a specific path.

[0039] The coal seam thickness and dip angle are extracted from the geological exploration results of extra-thick coal seams, thereby determining the drilling depth and drilling angle of each pre-splitting borehole in the pre-splitting target area.

[0040] As a specific implementation of the above scheme, the borehole depth is usually determined to penetrate the entire coal seam to ensure that stress waves can propagate fully within the coal seam. If the borehole depth is insufficient, the range of stress waves will be limited, which may result in cracks failing to penetrate the entire coal seam, affecting the pre-splitting effect.

[0041] As a specific implementation of the above scheme, when determining the drilling angle, if the coal seam has an inclination angle, it is necessary to ensure that the drilling angle is perpendicular to the top or bottom of the coal seam so that the stress wave can propagate along the effective direction inside the coal seam, avoiding excessive reflection or scattering of the stress wave at the interface between the coal seam and the surrounding rock. This helps to improve the propagation efficiency of the stress wave and ensure that the crack can fully expand.

[0042] S2. Based on the geological exploration results of extra-thick coal seams, a three-dimensional model of the extra-thick coal seam is built using three-dimensional modeling software. This model can accurately reproduce the geological structure of the extra-thick coal seam, providing a real and reliable geological background for pre-fracture simulation and ensuring the accuracy of the simulation results.

[0043] S3. Determine the detonation sequence based on the spatial distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and design a gradient detonation time difference to form multiple pre-splitting simulation groups, with each pre-splitting simulation group corresponding to a detonation time difference.

[0044] The specific process for determining the detonation sequence is as follows: Based on the directional pre-splitting path, extract the pre-splitting boreholes along the path and arrange them according to their order on the path. This arrangement of the pre-splitting boreholes is then used as the detonation sequence. This method ensures that each detonation guides the cracks to gradually expand along the predetermined path, ultimately forming a continuous and directional crack network. This approach effectively controls the direction and speed of crack expansion, ensuring the accuracy and controllability of the pre-splitting effect.

[0045] It should be added that the directional pre-splitting path can be determined based on geological conditions and engineering requirements.

[0046] More specifically, the design of gradient detonation time differences can begin by obtaining the minimum detonation time difference, which can be calculated by dividing the spacing of the pre-splitting boreholes by the propagation speed of the stress wave. The propagation speed of the stress wave can be obtained through laboratory testing. Of course, if laboratory testing conditions are limited, it can be estimated based on empirical values ​​under similar geological conditions. Typically, the propagation speed of the stress wave in the coal seam ranges from 1500 to 4000 m / s. After obtaining the minimum detonation time difference, an upper limit value for the detonation time difference is designed. Then, several detonation time differences are selected at equal intervals between the minimum detonation time difference and the upper limit value as the gradient detonation time differences.

[0047] S4. Using the constructed three-dimensional model of the extra-thick coal seam, detonation was carried out under each pre-splitting simulation group. During the detonation process, crack propagation and environmental risk monitoring were carried out simultaneously to obtain the crack propagation path and environmental risk indicators corresponding to each pre-splitting simulation group. The environmental risk indicators include the coal seam vibration frequency and surface subsidence displacement.

[0048] In the optimized implementation of the above operations, the environmental risk indicators are monitored in the following process: During the detonation simulation of each pre-splitting simulation group, the coal seam vibration frequency and surface subsidence displacement data generated after the detonation of each pre-splitting borehole are collected in real time by virtual sensors to form coal seam vibration frequency dataset and surface subsidence displacement dataset.

[0049] It is important to emphasize that when using the three-dimensional model of an extra-thick coal seam to simulate the initiation of each pre-splitting simulation group, it is essential to ensure that the simulation environmental conditions remain consistent, including parameters such as temperature, humidity, and atmospheric pressure. This helps to eliminate the influence of environmental factors on the test results and ensure the comparability of the data. When necessary, the simulation environmental conditions should be made as close as possible to the actual natural environmental conditions of the extra-thick coal seam. This can reduce the interference of external factors on the simulation results and ensure that the simulation results can truly reflect the behavior of the extra-thick coal seam during the actual mining process.

[0050] It is further important to emphasize that when using the three-dimensional model of the extra-thick coal seam to simulate the detonation of each pre-splitting simulation group, the three-dimensional model should be restored to its initial state after each simulation to ensure that the next pre-splitting simulation is not affected by the previous pre-splitting simulation.

[0051] S5. Based on the crack propagation path and environmental risk indicators corresponding to each pre-crack simulation group, assess the compliance of crack propagation path and the environmental risk of crack propagation.

[0052] Specifically, the crack propagation path conformity assessment process is as follows: the crack propagation path corresponding to each pre-splitting simulation group is overlapped with the directional pre-splitting path to obtain the overlapped path length, and the number of branch paths and the length of each branch path are identified, which are then substituted into the statistical formula. Obtain the crack propagation path conformity CP conformity In the formula, l represents the length of the coincident path, l0 represents the length of the directional pre-splitting path, s represents the average length of the branch path, k represents the number of branch paths, and R represents the proportional adjustment coefficient. The value of R can be 1 or 10, which reflects the degree of amplification of the calculation results. When the value is 1, the calculation results remain the same. When the value is 10, the calculation results are amplified by 10 times. By adjusting the value of R, the small range of the curve value due to the original calculation results being too small can be avoided when constructing the crack propagation path conformity curve in the subsequent process, making it difficult to clearly identify and analyze.

[0053] It should be noted that during pre-cracking simulation, although the crack propagation path can generally develop along the predetermined directional pre-cracking path, there may still be branch paths. Branch paths are unintended propagation paths formed by local stress concentrations of the crack. The number and length of branch paths reflect the irregularity of crack propagation. Fewer and shorter branch paths mean that crack propagation is more concentrated and controllable. The higher the overlap between the crack propagation path and the predetermined path, the closer the crack propagation is to the predetermined path.

[0054] Specifically, the environmental risk of crack propagation is assessed as follows: The difference between the coal seam vibration frequency and surface settlement displacement corresponding to adjacent pre-fracturing boreholes in the coal seam vibration frequency dataset and surface settlement displacement dataset corresponding to each pre-fracturing simulation group is divided by the coal seam vibration frequency and surface settlement displacement corresponding to the previous pre-fracturing borehole to obtain the coal seam vibration amplification degree and surface settlement amplification degree corresponding to adjacent pre-fracturing boreholes. Then, the average value of the coal seam vibration amplification degree and surface settlement amplification degree corresponding to each adjacent pre-fracturing borehole is taken to calculate the coal seam vibration amplification degree and surface settlement amplification degree.

[0055] It is important to know that during pre-splitting simulation, the pre-splitting boreholes that are detonated later will be affected by the aftershocks of the previously detonated boreholes. Therefore, throughout the detonation process, coal seam vibration and surface subsidence will gradually accumulate and continue to increase.

[0056] The maximum coal seam vibration frequency and maximum surface subsidence displacement were extracted from the coal seam vibration frequency dataset and surface subsidence displacement dataset corresponding to each pre-splitting simulation group.

[0057] The maximum coal seam vibration frequency and maximum surface subsidence displacement corresponding to each pre-splitting simulation group were compared with the warning coal seam vibration frequency and warning surface subsidence displacement of extra-thick coal seams. Furthermore, these values ​​were combined with the increase in coal seam vibration and the increase in surface subsidence and substituted into the statistical formula. Obtain the environmental risk level CP for crack propagation risk In the formula f max d max f represents the maximum coal seam vibration frequency and the maximum surface subsidence displacement, respectively. a d a σ represents the warning coal seam vibration frequency and the warning surface subsidence displacement in a fully mechanized longwall mining area for extra-thick coal seams, respectively. f σ d represents the increase in coal seam vibration and the increase in surface subsidence, respectively, and e represents the natural constant.

[0058] S6. Determine the appropriate detonation time difference from the assessment results of crack propagation path conformity and crack propagation environment risk for each pre-splitting simulation group. The specific process is as follows: Construct a coordinate system with the gradient detonation time difference as the horizontal axis and the crack propagation path conformity and crack propagation environment risk as the vertical axes. Then, plot the crack propagation path conformity curve and crack propagation environment risk curve in the constructed coordinate system for the detonation time difference, crack propagation path conformity, and crack propagation environment risk for each pre-splitting simulation group.

[0059] It should be noted that, in order to ensure the rationality and accuracy of the curve, the number of sample points should be increased as much as possible when designing the detonation time difference.

[0060] In the plotted crack propagation path conformity curve and crack propagation environmental risk curve, mark the horizontal axis corresponding to the maximum crack propagation path conformity and the minimum crack propagation environmental risk, respectively, and determine whether they are the same detonation time difference. If they are the same detonation time difference, it means that under this time difference, the crack propagation path best conforms to the predetermined path and the environmental risk is the lowest. Then, the detonation time difference is taken as the appropriate detonation time difference.

[0061] If the time difference between the two detonations is determined to be different, the detonation time difference along the horizontal axis where the intersection of the crack propagation path conformity curve and the crack propagation environmental risk curve is located is taken as the appropriate detonation time difference. This is because the time difference at the intersection point means that, under that time difference, the crack propagation path conformity and environmental risk reach a relatively balanced state, ensuring both the pre-fracture effect and controlling the environmental risk.

[0062] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined by the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A simulation analysis method for directional pre-splitting in fully mechanized longwall mining of extra-thick coal seams based on 3D modeling, characterized in that, Includes the following steps: S1. Conduct geological exploration of extra-thick coal seams, and then lay out pre-splitting boreholes. S2. Based on the geological exploration results of the extra-thick coal seam, a three-dimensional model of the extra-thick coal seam is built using three-dimensional modeling software. S3. Determine the detonation sequence based on the spatial distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and design a gradient detonation time difference to form multiple pre-splitting simulation groups, with each pre-splitting simulation group corresponding to a detonation time difference. S4. Using the constructed three-dimensional model of the extra-thick coal seam, detonation was carried out under each pre-splitting simulation group. During the detonation process, crack propagation and environmental risk monitoring were carried out simultaneously to obtain the crack propagation path and environmental risk indicators corresponding to each pre-splitting simulation group. The environmental risk indicators include coal seam vibration frequency and surface subsidence displacement. S5. Based on the crack propagation path and environmental risk indicators corresponding to each pre-cracking simulation group, assess the compliance of crack propagation path and the environmental risk of crack propagation. S6. Determine the appropriate detonation time difference based on the crack propagation path conformity and crack propagation environment risk assessment results corresponding to each pre-splitting simulation group.

2. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 1, characterized in that: The pre-splitting borehole layout is described in the following process: Stress distribution information is extracted from the geological exploration results of extra-thick coal seams, and the extra-thick coal seams are divided into several stress regions based on this information. The stress regions are numbered and the stress values ​​of each stress region are marked. Extract the boundary contours of each stress region, and construct a set of surrounding adjacent stress regions corresponding to each stress region as the center. The stress concentration of each stress region is obtained by comparing and analyzing the stress values ​​of each stress region with the stress values ​​of each adjacent stress region. The stress concentration of each stress region is compared with the preset effective stress concentration. If the stress concentration of a certain stress region reaches the effective stress concentration, then the stress region is taken as the pre-crack target region. If the stress concentration of all stress regions does not reach the effective stress concentration, then the stress region corresponding to the maximum stress value is selected as the pre-crack target region based on the stress value of each stress region. The shape of the pre-splitting target area is identified based on the boundary contour of the pre-splitting target area, and the location of the pre-splitting boreholes is then determined accordingly. The coal seam thickness and dip angle are extracted from the geological exploration results of extra-thick coal seams, thereby determining the drilling depth and drilling angle of each pre-splitting borehole in the pre-splitting target area.

3. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 2, characterized in that: The layout of the pre-splitting borehole locations includes the following process: The shape of the pre-splitting target area is matched with the shape of the pre-splitting area suitable for various layout methods in the layout reference library to obtain the pre-splitting borehole layout method corresponding to the pre-splitting target area, wherein the layout method includes linear layout and mesh layout. When the pre-splitting boreholes corresponding to the pre-splitting target area are laid out in a linear pattern, the starting and ending points of the linear arrangement are determined according to the boundary of the pre-splitting target area. Pre-splitting boreholes are evenly distributed between the starting and ending points of the linear arrangement.

4. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 3, characterized in that: The layout of the pre-splitting borehole locations also includes the following process: When the pre-splitting boreholes corresponding to the pre-splitting target area are laid out in a mesh pattern, the pre-splitting target area is evenly divided into several small meshes, and staggered meshes are selected from the divided meshes. Then, a pre-splitting borehole is arranged in each staggered mesh.

5. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 1, characterized in that: The process for determining the detonation sequence is as follows: Based on the directional pre-splitting path, the pre-splitting boreholes along the path are extracted and arranged in order of their sequence on the path. The arrangement order of the pre-splitting boreholes is then used as the detonation sequence.

6. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 1, characterized in that: The environmental risk indicators are described in the monitoring process below: During the detonation simulation of each pre-splitting simulation group, virtual sensors are used to collect data on the coal seam vibration frequency and surface subsidence displacement generated after the detonation of each pre-splitting borehole in real time, forming coal seam vibration frequency datasets and surface subsidence displacement datasets.

7. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 6, characterized in that: The crack propagation path conformity includes the following evaluation process: The crack propagation path corresponding to each pre-splitting simulation group is overlapped with the directional pre-splitting path to obtain the overlap path length. The number of branch paths and the length of each branch path are identified, and the crack propagation path conformity is analyzed.

8. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 7, characterized in that: The assessment of the environmental risk level for crack propagation includes the following process: The difference between the coal seam vibration frequency and surface settlement displacement corresponding to adjacent pre-splitting boreholes in each pre-splitting simulation group's coal seam vibration frequency dataset and surface settlement displacement dataset, and then divided by the coal seam vibration frequency and surface settlement displacement corresponding to the previous pre-splitting borehole, yields the coal seam vibration amplification rate and surface settlement amplification rate. The maximum coal seam vibration frequency and the maximum surface subsidence displacement are extracted from the coal seam vibration frequency dataset and the surface subsidence displacement dataset corresponding to each pre-splitting simulation group. The maximum coal seam vibration frequency and maximum surface subsidence displacement corresponding to each pre-splitting simulation group were compared with the warning coal seam vibration frequency and warning surface subsidence displacement of extra-thick coal seams, and then combined with the coal seam vibration amplification rate and surface subsidence amplification rate to comprehensively analyze the environmental risk of crack propagation.

9. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 8, characterized in that: The process for determining the appropriate detonation time difference is as follows: A coordinate system was constructed with the gradient initiation time difference as the horizontal axis and the crack propagation path conformity and crack propagation environmental risk as the vertical axes. Crack propagation path conformity curves and crack propagation environmental risk curves were plotted in the constructed coordinate system for the initiation time difference, crack propagation path conformity and crack propagation environmental risk of each pre-crack simulation group. Mark the horizontal axis corresponding to the maximum crack propagation path conformity curve and the minimum crack propagation environmental risk curve, respectively, and determine whether they are the same detonation time difference. If they are the same detonation time difference, then the detonation time difference is taken as the appropriate detonation time difference.

10. The method for directional pre-splitting simulation analysis of ultra-thick coal seam fully mechanized caving mining based on three-dimensional modeling as described in claim 9, characterized in that: Determining the appropriate detonation time difference also includes the following process: If it is determined that the detonation time difference is not the same, the intersection point of the crack propagation path conformity curve and the crack propagation environmental risk curve is captured, and the detonation time difference on the horizontal axis where the intersection point is located is taken as the appropriate detonation time difference.

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