Three-dimensional modeling-based directional presplitting simulation analysis method for fully-mechanized caving stope of extra-thick coal seam

Abstract

The invention belongs to the technical field of ultra-thick coal seam directional presplitting simulation, and particularly relates to an ultra-thick coal seam fully-mechanized caving stope directional presplitting simulation analysis method based on three-dimensional modeling, and the method comprises the steps: carrying out the geological exploration of an ultra-thick coal seam fully-mechanized caving stope, and carrying out the presplitting drill hole layout and three-dimensional model building; a detonation sequence is formulated according to a preset directional pre-splitting path, and meanwhile, a gradient detonation time difference is designed on this basis to form a plurality of pre-splitting simulation test groups, so that detonation is carried out under each pre-splitting simulation test group by utilizing the built ultra-thick coal seam fully-mechanized caving stope three-dimensional model; and crack propagation path coincidence and environmental risk monitoring evaluation are synchronously performed in the detonating process, so that the appropriate detonating time difference is determined according to the evaluation result, the appropriate detonating time difference is determined on the basis of consideration of crack propagation path coincidence and environmental risk balance, the occurrence rate of forced interruption of mining is greatly reduced, and the exploiting efficiency is improved. And sustainable mining of the coal seam is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of directional pre - splitting simulation of extra - thick coal seams, and particularly relates to a method for simulating and analyzing directional pre - splitting in fully - mechanized caving mining fields of extra - thick coal seams based on three - dimensional modeling. Background Technique

[0002] An extra - thick coal seam refers to a coal seam with a thickness exceeding 6 meters. Due to its large thickness, the surrounding rock of the roadway bears great stress during the mining process, and problems such as deformation and collapse are likely to occur. Therefore, traditional coal - mining methods are difficult to achieve full - thickness mining, resulting in prominent problems of waste of some coal resources that cannot be effectively recovered. In this case, fully - mechanized caving mining emerged. By setting supports at the bottom of the working face and gradually caving the top coal, full - thickness mining is realized, and it has gradually become the mainstream method for mining extra - thick coal seams.

[0003] Given that the top coal in extra - thick coal seams usually has high strength and hardness, it is difficult for traditional coal - mining methods to achieve uniform fragmentation and caving of the top coal, resulting in low resource recovery rates. To solve this problem, it is necessary to introduce cracks to provide more fracture paths for the top coal, so that the top coal can collapse more quickly and uniformly after the support force of the support is released. However, the geological conditions of extra - thick coal seams are complex and variable, and the mechanical properties of coal seams and surrounding rocks vary significantly, which will affect the propagation path of cracks. Therefore, by pre - arranging multiple boreholes in the coal seam and determining the initiation sequence according to a predetermined path to guide the crack path to expand along the predetermined path to achieve directional pre - splitting, the overall strength of the top coal can be reduced, promoting its fragmentation and caving along the predetermined path, thereby improving the efficiency of fully - mechanized caving mining and the resource recovery rate.

[0004] During the directional pre - splitting process, when detonating boreholes according to the predetermined initiation sequence, the initiation time difference between adjacent boreholes has a significant impact on the crack propagation path. If the initiation time difference is set improperly, it may cause the crack propagation path to deviate from the predetermined direction, thereby affecting the fragmentation effect of the top coal and the efficiency of fully - mechanized caving mining. Therefore, in the directional pre - splitting operation, it is crucial to reasonably control the initiation time difference, and usually, simulation analysis is required to select an appropriate initiation time difference. However, the existing selection of the initiation time difference often overly relies on the conformity of the crack propagation path, while ignoring the impact of the initiation time difference on environmental risks such as coal - seam vibration and surface subsidence. This single evaluation criterion may lead to the selected initiation time difference that can make the crack propagation path highly coincide with the predetermined path, but may cause greater environmental risks, easily resulting in the interruption of mining and being unfavorable to the sustainable mining of coal seams. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for simulating and analyzing directional pre - splitting in fully - mechanized caving mining fields of extra - thick coal seams based on three - dimensional modeling, effectively solving the problems mentioned in the background technique.

[0006] The object of the present invention can be achieved by the following technical solutions: A method for simulating and analyzing directional pre-splitting in a fully-mechanized caving stope of an extra-thick coal seam based on 3D modeling, comprising the following steps: S1. Conduct geological exploration on the extra-thick coal seam, and accordingly arrange pre-splitting boreholes.

[0007] S2. Based on the geological exploration results of the extra-thick coal seam, use 3D modeling software to build a 3D model of the extra-thick coal seam.

[0008] S3. Determine the initiation sequence according to the spatial position distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and on this basis, design a gradient initiation time difference to form multiple pre-splitting simulation groups, where each pre-splitting simulation group corresponds to an initiation time difference.

[0009] S4. Use the built 3D model of the extra-thick coal seam to initiate under each pre-splitting simulation group, and synchronously monitor the crack propagation and environmental risk during the initiation process to obtain the crack propagation path and environmental risk indicators corresponding to each pre-splitting simulation group, where the environmental risk indicators include the coal seam vibration frequency and the surface settlement displacement.

[0010] S5. Evaluate the compliance of the crack propagation path and the environmental risk degree of crack propagation based on the crack propagation path and environmental risk indicators corresponding to each pre-splitting simulation group.

[0011] S6. Determine the appropriate initiation time difference according to the evaluation results of the compliance of the crack propagation path and the environmental risk degree of crack propagation corresponding to each pre-splitting simulation group.

[0012] Combining all the above technical solutions, the positive effects of the present invention are as follows: The present invention determines the arrangement of pre-splitting boreholes through geological exploration of the fully-mechanized caving stope of the extra-thick coal seam, builds a 3D model, then determines the initiation sequence based on the predetermined directional pre-splitting path, and at the same time designs different gradient initiation time differences to form multiple pre-splitting simulation groups. Furthermore, it uses the 3D model to conduct simulated initiation under each test group, synchronously monitors the compliance of the crack propagation path and the environmental risk, and finally determines the appropriate initiation time difference that takes into account both the crack propagation path and the environmental risk according to the evaluation results. This method effectively reduces the incidence of mining interruption and ensures the efficient, safe and sustainable mining of the coal seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation to the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the following drawings.

[0014] Figure 1 It is a flowchart of the method implementation steps of the present invention.

[0015] Figure 2 It is a schematic diagram of the linear arrangement of pre-splitting boreholes in the present invention.

[0016] Figure 3 It is a schematic diagram of the mesh arrangement of pre-splitting drilling holes in the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] See also Figure 1 As shown, the present invention proposes a directional pre-splitting simulation analysis method for a fully-mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling, comprising the following steps: S1, conducting geological exploration of the fully-mechanized caving mining area in an extra-thick coal seam, and arranging pre-splitting drilling holes accordingly.

[0019] Applied to the above scheme, the main purpose of geological exploration is to understand in detail the key parameters of the extra-thick coal seams, such as geological structure, thickness, inclination, stress distribution, etc., so as to provide accurate data support for the subsequent pre-splitting drilling layout, three-dimensional model construction and detonation design.

[0020] The geological structure exploration mentioned above is to understand the geological structural characteristics of coal seams, including faults, folds, joints and other geological structures. The exploration method can exemplarily adopt rock sampling drilling, specifically obtaining core samples of coal seams and surrounding rocks through drilling for geological structural analysis. Another example is to use seismic wave method (such as high-resolution three-dimensional seismic exploration technology) to detect the distribution and morphology of underground geological structures.

[0021] The above-mentioned coal seam thickness exploration method exemplarily adopts the exploration method of obtaining core samples of the coal seam by drilling to directly measure the thickness of the coal seam. Another exemplary method is to use geological radar technology to detect the thickness of the coal seam through the reflection characteristics of electromagnetic waves underground.

[0022] The above-mentioned coal seam dip angle exploration method is exemplarily adopted to directly measure the dip angle of the coal seam by obtaining core samples of the coal seam through drilling. Another exemplary method is to use an inclination logging instrument to measure the inclination angle in the borehole to infer the dip angle of the coal seam. Another exemplary method is to obtain the three-dimensional structural information of the coal seam through three-dimensional seismic exploration to measure the dip angle of the coal seam.

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

[0024] As the above preferred solution, the layout of pre-splitting drill holes is as follows: Extract the stress distribution information from the geological exploration results of the extra-thick coal seam, divide the extra-thick coal seam into several stress regions based on this, number the divided stress regions, and mark the stress values of each stress region.

[0025] It should be added that when dividing the extra-thick coal seam into stress regions according to the stress distribution information, a clustering method 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 respectively, and construct a set of surrounding adjacent stress regions corresponding to each stress region with each stress region as the center.

[0027] Compare the stress value of each stress region with the stress value of each adjacent stress region in the set of surrounding adjacent stress regions through the expression to obtain the stress concentration degree SC corresponding to each stress region i , where F i represents the stress value of the i-th stress region, i represents the stress region number, i = 1, 2, …, n, F ij represents the stress value of the adjacent stress region in the set of surrounding adjacent stress regions corresponding to the i-th stress region, j = 1, 2, …, m, and m represents the number of adjacent stress regions in the set of surrounding adjacent stress regions.

[0028] As an explanation of the above expression, when the stress value of a stress region is less than the stress value of the adjacent stress region, the stress concentration degree is 0, and the stress concentration degree is only larger when the stress values of all stress regions are greater than the stress values of the adjacent stress regions.

[0029] Compare the stress concentration degree corresponding to each stress region with the preset effective stress concentration degree. Exemplarily, the effective stress concentration degree is 0.8. If the stress concentration degree corresponding to a certain stress region reaches the effective stress concentration degree, then take this stress region as the pre-splitting target region. If the stress concentration degrees corresponding to all stress regions do not reach the effective stress concentration degree, then select the stress region corresponding to the maximum stress value based on the stress values of each stress region as the pre-splitting target region.

[0030] It should be noted that the main purpose of calculating the stress concentration after completing the stress area division is to evaluate whether the stress level in each stress area is significantly higher than that in its surrounding areas, so as to determine the pre-splitting target area. Specifically, if the stress values in a certain stress area are generally higher than those in its adjacent areas, then this area is regarded as a stress concentration area, and the stress concentration area is selected as the pre-splitting target area. When no stress concentration area can be screened out based on the calculation of stress concentration, the stress area corresponding to the maximum stress value is selected as the pre-splitting target area. The reason for this is that both the maximum stress area and the stress concentration area are the starting points and main development directions of crack propagation. Selecting these areas for pre-splitting can effectively guide the crack propagation. The stress concentration area refers to a specific location where the stress value is significantly higher than that in the surrounding area within a local range. Due to stress concentration in these areas, it is easier to initiate and expand cracks, so they are ideal targets for pre-splitting operations. The maximum stress area refers to the area with the highest stress value within a specific range. Although the maximum stress area does not necessarily show stress concentration, its high stress level may also lead to the rapid expansion of cracks. Therefore, when there is no obvious stress concentration area, it is also reasonable to select the maximum stress area as the pre-splitting target area. Thus, by calculating the stress concentration to screen out the stress concentration area and preferentially selecting these areas as the pre-splitting target, the crack propagation can be effectively guided, the local stress can be released, and the formation of irregular cracks can be prevented.

[0031] Identify the shape of the pre-splitting target area based on the boundary contour of the pre-splitting target area, and then arrange the positions of pre-splitting drill holes as follows: Match the shape of the pre-splitting target area with the shapes of pre-splitting areas suitable for various arrangement methods in the arrangement reference library to obtain the pre-splitting drill hole arrangement method corresponding to the pre-splitting target area, where the arrangement methods include linear arrangement and mesh arrangement.

[0032] As a specific implementation of the above solution, the shape of the pre-splitting area suitable for linear arrangement is strip-shaped, and the shapes of the pre-splitting areas suitable for mesh arrangement are square, rectangular, irregular, etc.

[0033] See Figure 2 As shown, when the pre-splitting drill hole arrangement method corresponding to the pre-splitting target area is linear arrangement, determine the starting point and ending point of the linear arrangement according to the boundary of the pre-splitting target area.

[0034] Uniformly arrange the positions of pre-splitting drill holes between the starting point and the ending point of the linear arrangement.

[0035] The spacing between adjacent pre-splitting drill holes mentioned above should neither be too large nor too small. When the drill hole spacing is too large, the stress waves generated between adjacent drill holes will rapidly attenuate during propagation, making it difficult to form effective stress superposition in the target area. This will result in the inability of cracks to fully connect between adjacent drill holes, forming a discontinuous crack network. If the spacing is too small, the stress waves generated by adjacent drill holes will interfere with each other, leading to an enhanced interference effect of the stress waves, which will instead weaken the effective action of the stress waves. This may cause uneven crack propagation and even crack closure, affecting the pre-splitting effect. In addition, too small a drill hole spacing will require more drill holes to be arranged, increasing the construction time and cost. At the same time, too many drill holes will also increase the number of initiation devices, further increasing the material and labor costs. Specifically, it can be determined according to the length of the pre-splitting target area. Generally, the spacing can be between 0.5 and 2 meters. Assuming the pre-splitting target area is a long strip area with a length of 50 meters and a width of 5 meters, the spacing between adjacent pre-splitting drill holes selected at this time can be 2 meters, and 25 pre-splitting drill holes can be arranged in this way.

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

[0037] The size of the above-mentioned grid can be determined according to the area size of the pre-splitting target area, usually 2 to 5 meters square.

[0038] It should be understood that arranging the pre-splitting drill holes in a staggered manner from the divided grids is to improve the connectivity and propagation effect of the cracks. The staggered arrangement method can be adopted between different grids, that is, the drill hole positions are staggered in adjacent grids to form a staggered stress wave superposition and guide the cracks to propagate along a specific path.

[0039] Extract the coal seam thickness and coal seam dip angle from the geological exploration results of the extra-thick coal seam, and thus determine the drill hole depth and drill hole angle of each pre-splitting drill hole in the pre-splitting target area.

[0040] As a specific implementation of the above scheme, when determining the drill hole depth, the drill hole depth usually needs to penetrate the entire coal seam to ensure that the stress waves can fully propagate inside the coal seam. If the drill hole depth is insufficient, the action range of the stress waves is limited, which may cause the cracks to not penetrate the entire coal seam, affecting the pre-splitting effect.

[0041] As a specific implementation of the above solution, when determining the drilling angle, when there is an inclination in the coal seam, it is necessary to ensure that the drilling angle is perpendicular to the roof or floor 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 junction of the coal seam and the surrounding rock. This helps to improve the propagation efficiency of the stress wave and ensure that the cracks can fully expand.

[0042] S2. Based on the geological exploration results of the extra-thick coal seam, use 3D modeling software to build a 3D model of the extra-thick coal seam, which can accurately reproduce the geological structure of the extra-thick coal seam. This provides a real and reliable geological background for the pre-splitting simulation and ensures the accuracy of the simulation results.

[0043] S3. Determine the detonation sequence according to the spatial position distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and on this basis, design a gradient detonation time difference to form multiple pre-splitting simulation groups, where each pre-splitting simulation group corresponds to a detonation time difference.

[0044] Specifically, the process for determining the detonation sequence is as follows: Extract the pre-splitting boreholes passing through on the path according to the directional pre-splitting path, and arrange them in the order of their sequence on the path. Then, take the arrangement result of the pre-splitting boreholes as the detonation sequence. In this way, it can be ensured that each detonation can guide the cracks to gradually expand along the predetermined path, and finally form a continuous and directional crack network. In this way, the expansion direction and speed of the cracks can be effectively controlled, ensuring the accuracy and controllability of the pre-splitting effect.

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

[0046] Further specifically, when designing the gradient detonation time difference, the minimum detonation time difference can be obtained first. The minimum detonation time difference can be obtained by dividing the layout spacing of the pre-splitting boreholes by the propagation speed of the stress wave, and the propagation speed of the stress wave can be obtained through laboratory tests. Of course, if the laboratory test conditions are limited, it can be estimated according to the empirical values under similar geological conditions. Generally, the propagation speed range of the stress wave in the coal seam is 1500 to 4000 m / s. After obtaining the minimum detonation time difference, further design an upper limit value of the detonation time difference, and then select several detonation time differences at equal intervals between the minimum detonation time difference and the upper limit value of the detonation time difference as the gradient detonation time difference.

[0047] S4. Use the built 3D model of the extra-thick coal seam to initiate detonation under each pre-splitting simulation group, and synchronously monitor the crack expansion and environmental risks during the detonation process to obtain the crack expansion paths and environmental risk indicators corresponding to each pre-splitting simulation group, where the environmental risk indicators include the vibration frequency of the coal seam and the surface settlement displacement.

[0048] In the optimized implementation of the above operations, the environmental risk indicators are as follows in the monitoring process: during the detonation simulation of each pre-splitting simulation group, the coal seam vibration frequency and surface settlement displacement data generated after the detonation of each pre-splitting borehole are collected in real time through virtual sensors to form a coal seam vibration frequency data set and a surface settlement displacement data set.

[0049] It should be emphasized that when using the three-dimensional model of the extra-thick coal seam for the detonation simulation of each pre-splitting simulation group, it is necessary 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, ensure the comparability of data, and 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, which 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 actual mining.

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

[0051] S5. Evaluate the compliance degree of the crack propagation path and the environmental risk degree of the crack propagation based on the crack propagation paths and environmental risk indicators corresponding to each pre-splitting simulation group.

[0052] Specifically, the evaluation process of the compliance degree of the crack propagation path is as follows: the crack propagation paths corresponding to each pre-splitting simulation group are overlapped with the directional pre-splitting path to obtain the overlapping path length, and the number of branch paths existing in the crack propagation path and the lengths of each branch path are identified, and then substituted into the statistical formula to obtain the compliance degree CP of the crack propagation path conformity , where l represents the overlapping path length, l 0 represents the directional pre-splitting path length, s represents the average length of the branch paths, 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 magnification ratio of the calculation result. When the value is 1, the calculation result remains unchanged, and when the value is 10, the calculation result is magnified 10 times. By adjusting the value of R, it can be avoided that the value range span of the curve is too small due to the too small original calculation result when constructing the compliance curve of the crack propagation path in the follow-up, making it difficult to clearly identify and analyze.

[0053] It should be noted that when conducting pre-splitting simulation, although the crack propagation path can generally develop along the predetermined directional pre-splitting path, there may still be branch paths. The branch path is an unexpected propagation path formed by local stress concentration during crack propagation. The number and length of the branch paths reflect the irregularity of crack propagation. The fewer the number and the shorter the length of the branch paths, the more concentrated and controllable the crack propagation is, and the higher the coincidence degree between the crack propagation path and the predetermined path indicates that the crack propagation is closer to the predetermined path.

[0054] Specifically, the evaluation process of the crack propagation environmental risk degree is as follows: Subtract the coal seam vibration frequency and surface settlement displacement corresponding to adjacent pre-splitting boreholes in the coal seam vibration frequency dataset and surface settlement displacement dataset corresponding to each pre-splitting simulation group, and then divide by the coal seam vibration frequency and surface settlement displacement corresponding to the previous pre-splitting borehole to obtain the coal seam vibration increase amplitude and surface settlement increase amplitude corresponding to adjacent pre-splitting boreholes. Then, take the average value of the coal seam vibration increase amplitude and surface settlement increase amplitude corresponding to each adjacent pre-splitting borehole to calculate the coal seam vibration increase amplitude and surface settlement increase amplitude.

[0055] It should be known that during pre-splitting simulation, since the post-initiated pre-splitting boreholes will be affected by the aftershocks of the previously initiated boreholes, during the entire initiation process, the coal seam vibration and surface settlement will gradually accumulate and continuously increase.

[0056] Extract the maximum coal seam vibration frequency and maximum surface settlement displacement from the coal seam vibration frequency dataset and surface settlement displacement dataset corresponding to each pre-splitting simulation group.

[0057] Compare the maximum coal seam vibration frequency and maximum surface settlement displacement corresponding to each pre-splitting simulation group with the warning coal seam vibration frequency and warning surface settlement displacement of the extra-thick coal seam, and substitute them into the statistical formula in combination with the coal seam vibration increase amplitude and surface settlement increase amplitude to obtain the crack propagation environmental risk degree CP risk , where f max , d max represent the maximum coal seam vibration frequency and maximum surface settlement displacement respectively, f a , d a represent the warning coal seam vibration frequency and warning surface settlement displacement of the fully-mechanized caving face in the extra-thick coal seam respectively, σ f , σ d represent the coal seam vibration increase amplitude and surface settlement increase amplitude respectively, and e represents the natural constant.

[0058] S6. Determine the appropriate detonation time difference from the evaluation results of the crack propagation path compliance and the crack propagation environmental risk degree corresponding to each pre-splitting simulation group. The specific process is as follows: Taking the gradient detonation time difference as the horizontal axis and the crack propagation path compliance and the crack propagation environmental risk degree as the vertical axes respectively, construct a coordinate system. Thus, for each pre-splitting simulation group, plot the crack propagation path compliance curve and the crack propagation environmental risk curve within the constructed coordinate system for the detonation time difference, the crack propagation path compliance, and the crack propagation environmental risk degree.

[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] Mark the horizontal axes corresponding to the maximum crack propagation path compliance and the minimum crack propagation environmental risk degree respectively in the plotted crack propagation path compliance curve and the crack propagation environmental risk curve, and determine whether they are the same detonation time difference. If it is determined that they are the same detonation time difference, it means that at this time difference, the crack propagation path is most in line with the predetermined path and the environmental risk is the lowest. Then, take this detonation time difference as the appropriate detonation time difference.

[0061] If it is determined that they are not the same detonation time difference, then take the detonation time difference on the horizontal axis corresponding to the intersection point of the crack propagation path compliance curve and the crack propagation environmental risk curve as the appropriate detonation time difference. This is because the time difference at the intersection point means that at this time difference, the crack propagation path compliance and the environmental risk degree reach a relatively balanced state, which not only ensures the pre-splitting effect but also controls the environmental risk.

[0062] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments 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 fall within the protection scope of the present invention.

Claims

1. A directional pre-splitting simulation and analysis method for fully mechanized caving mining in extra-thick coal seams based on three-dimensional modeling, characterized in that: The steps include: S1. Conduct geological exploration of extra-thick coal seams and arrange pre-splitting drilling holes accordingly; S2. Based on the geological exploration results of the extra-thick coal seam, a 3D model of the extra-thick coal seam is constructed using 3D modeling software; S3, formulating an initiation sequence according to the spatial position distribution of each pre-splitting borehole and the predetermined directional pre-splitting path, and on this basis designing a gradient initiation time difference to form a plurality of pre-splitting simulation groups, wherein each pre-splitting simulation group corresponds to an initiation time difference; S4. Detonate under each pre-splitting simulation group using the constructed three-dimensional model of the extra-thick coal seam, and simultaneously monitor the crack extension and environmental risk during the detonation process to obtain the crack extension path and environmental risk indicators corresponding to each pre-splitting simulation group, where the environmental risk indicators include the vibration frequency of the coal seam and the surface settlement displacement; S5. Based on the crack propagation paths and environmental risk indicators corresponding to each pre-cracking simulation group, the compliance of the crack propagation paths and the environmental risk of crack propagation are evaluated; S6. Determine the appropriate detonation time difference based on the crack propagation path compliance and crack propagation environment risk assessment results corresponding to each pre-cracking simulation group.

2. The method for directional pre-splitting simulation and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 1, characterized in that: The pre-splitting drilling arrangement is described in the following process: Extract stress distribution information from geological exploration results of extra-thick coal seams, divide the extra-thick coal seams into several stress areas, number the divided stress areas, and mark the stress values ​​of each stress area; Extract the boundary contours of each stress region respectively, and construct a set of surrounding adjacent stress regions corresponding to each stress region with each stress region as the center; The stress value of each stress area is compared with the stress value of each adjacent stress area in the surrounding adjacent stress areas to obtain the stress concentration corresponding to each stress area; Compare the stress concentration corresponding to each stress region with the preset effective stress concentration. If the stress concentration corresponding to a certain stress region reaches the effective stress concentration, then the stress region is used as the pre-cracking target region. If the stress concentration corresponding to all stress regions does not reach the effective stress concentration, then based on the stress values ​​of each stress region, the stress region corresponding to the maximum stress value is selected as the pre-cracking target region. Identify the shape of the pre-splitting target area according to the boundary contour of the pre-splitting target area, and arrange the pre-splitting drilling position accordingly; The thickness and inclination of the coal seam are extracted from the geological exploration results of the extra-thick coal seam, 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 and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 2, characterized in that: The pre-splitting drilling position is arranged as follows: The shape of the pre-splitting target area is matched with the shapes of the pre-splitting areas suitable for various layout modes in the layout reference library to obtain the pre-splitting drilling layout mode corresponding to the pre-splitting target area, wherein the layout mode includes linear layout and mesh layout; When the pre-splitting drilling arrangement corresponding to the pre-splitting target area is a linear arrangement, the starting point and the ending point of the linear arrangement are determined according to the boundary of the pre-splitting target area; The pre-splitting drilling positions are evenly arranged between the starting point and the ending point of the linear arrangement.

4. The method for directional pre-splitting simulation and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 3, characterized in that: The pre-splitting drilling position arrangement also includes the following process: When the pre-splitting drill hole layout mode corresponding to the pre-splitting target area is a mesh layout, the pre-splitting target area is evenly divided into a number of small grids, and staggered grids are selected from the divided grids, and then a pre-splitting drill hole is arranged in each staggered grid.

5. The method for directional pre-splitting simulation and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 1, characterized in that: The detonation sequence is formulated as follows: The pre-splitting boreholes passing through the directional pre-splitting path are extracted and arranged in order on the path, and then the arrangement order of the pre-splitting boreholes is used as the detonation order.

6. The method for directional pre-splitting simulation and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 1, characterized in that: The environmental risk indicators are shown in the following monitoring process: During the detonation simulation process of each pre-splitting simulation group, the coal seam vibration frequency and surface settlement displacement data generated after the detonation of each pre-splitting borehole are collected in real time through virtual sensors to form a coal seam vibration frequency data set and a surface settlement displacement data set.

7. The method for directional pre-splitting simulation and analysis of a fully mechanized caving mining area in an extra-thick coal seam based on three-dimensional modeling according to claim 6, characterized in that: The crack extension path compliance is evaluated as follows: The crack propagation paths corresponding to each pre-cracking simulation group are overlapped with the directional pre-cracking path to obtain the overlapped path length, and the number of branch paths in the crack propagation path and the length of each branch path are identified to analyze the conformity of the crack propagation path.

8. The method for directional pre-splitting simulation and analysis of fully mechanized caving mining field in extra-thick coal seams based on three-dimensional modeling according to claim 7, characterized in that: The crack extension environmental risk assessment process is as follows: The coal seam vibration frequency data set corresponding to each pre-splitting simulation group and the coal seam vibration frequency and surface settlement displacement corresponding to the adjacent pre-splitting boreholes in the surface settlement displacement data set are subtracted and divided by the coal seam vibration frequency and surface settlement displacement corresponding to the previous pre-splitting borehole to obtain the coal seam vibration amplitude and surface settlement amplitude; Extract the maximum coal seam vibration frequency and the maximum surface settlement displacement from the coal seam vibration frequency data set and the surface settlement displacement data set corresponding to each pre-splitting simulation group; The maximum coal seam vibration frequency and maximum surface settlement displacement corresponding to each pre-cracking simulation group are compared with the warning coal seam vibration frequency and warning surface settlement displacement of the extra-thick coal seam, and then combined with the coal seam vibration amplitude and surface settlement amplitude to comprehensively analyze the environmental risk of crack expansion.

9. The method for directional pre-splitting simulation and analysis of fully mechanized caving mining area in extra-thick coal seams based on three-dimensional modeling according to claim 8, characterized in that: The determination of the appropriate detonation time difference refers to the following process: A coordinate system is constructed with the gradient detonation time difference as the horizontal axis and the crack extension path conformity and crack extension environmental risk as the vertical axes, thereby drawing a crack extension path conformity curve and a crack extension environmental risk curve in the constructed coordinate system for the detonation time difference, crack extension path conformity and crack extension environmental risk of each pre-cracking simulation group; In the drawn crack extension path compliance curve and crack extension environmental risk curve, the horizontal axes corresponding to the maximum crack extension path compliance and the minimum crack extension environmental risk are marked respectively, and it is determined whether they are the same detonation time difference. If it is determined to be the same detonation time difference, the detonation time difference is used as the appropriate detonation time difference.

10. The method for directional pre-splitting simulation and analysis of fully mechanized caving mining area in extra-thick coal seams based on three-dimensional modeling according to claim 9, characterized in that: Determining the appropriate detonation time difference also includes the following process: If it is judged that they are not the same detonation time difference, the intersection point corresponding to the crack extension path compliance curve and the crack extension 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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