L-shaped drill hole pressure relief and shock absorption method for thick and hard roof of island working face
By analyzing the key layer theory and microseismic data of the thick and hard roof of the isolated working face, a stratum overburden structure model was constructed and L-shaped borehole pressure relief operations were carried out, which solved the mine seismic problem induced by the high-level thick and hard roof and improved the safety and stability of coal mining.
Patent Information
- Application Number
- CN202511785668.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-02-17
AI Technical Summary
In the process of coal mining, especially when the main coal seam is buried at a large depth and there is a low-lying thick and hard roof, the strong dynamic load formed by high static load and fracture is prone to induce rock bursts and mine tremors. Existing technologies are difficult to effectively control the frequent mine tremors caused by high-lying thick and hard roofs. In particular, the rock strata above the isolated working face are distributed at a high height, which increases the safety risk.
By using key layer theory and microseismic data analysis, the location of the induced rock layer above the isolated working face was identified, an overburden structure model was constructed, the main control layer and sub-control layer causing the disaster were determined, and L-shaped borehole decompression operations were carried out, including layered fracturing and retreating segmented fracturing, to cover the key layer and sub-control layer to reduce energy release.
It effectively reduces the risk of seismic activity in isolated working faces with thick, hard roofs, lowers the probability of rockbursts, and improves the safety and stability of coal mining.
Smart Images
Figure CN121539352A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of safety technology in underground coal mining, and in particular to a method for pressure relief and vibration reduction through L-shaped boreholes in thick, hard roofs of isolated working faces. Background Technology
[0002] Coal is a crucial basic energy source in my country. Although the proportion of coal consumption in my country's total primary energy consumption has been declining in recent years, the absolute amount of coal consumption has continued to grow due to the continuous increase in total energy consumption. In areas where the main coal seams are buried at depths of approximately 600-750 meters, the high static load caused by the low-lying thick and hard roof, combined with the strong dynamic load resulting from its fracture, easily induces rockbursts. Meanwhile, the fracture of the high-lying thick and hard roof releases a large amount of elastic energy, easily leading to frequent surface seismic events. Actual monitoring has revealed that a large number of seismic events occur above 200 meters in the roof, exceeding the scope of current underground technologies. Rockbursts and seismic events have become major challenges restricting safe coal mining in this region.
[0003] In the process of coal mining, after the working faces on both sides are mined out, an isolated working face is formed. The isolated working face is also prone to safety problems due to the high distribution of rock strata induced by mine seismic activity. Summary of the Invention
[0004] The present invention aims to at least partially solve one of the technical problems in the related art.
[0005] To achieve the above objectives, this invention proposes a method for pressure relief and vibration reduction through L-shaped drilling in a thick, hardened roof plate on an isolated working face, comprising: S1. Based on the critical layer theory, critical layer analysis is performed on the thick and hard top plate above the isolated working face to confirm the location of the main critical layer and multiple sub-critical layers. S2. Collect microseismic data of the roof of the working face during mining, statistically analyze the distribution of microseismic data in each key layer, identify the location of the key layer where the main induced rock layer above the isolated working face is located, and analyze the occurrence characteristics of the thick and hard roof. S3. Based on the identification results of the main induced rock layer locations in S2, a corresponding overburden structure model for abnormal mining pressure induced by the energy transfer of key layer failure in isolated working faces is constructed. The mining pressure induction conditions of thick and hard roof in isolated working faces are analyzed from three aspects: energy release of key induced rock layers, energy level of large energy events triggered by key layer failure inducing abnormal mining pressure, and energy decay law of key layer failure. The induced rock layer in the overburden structure model is determined by the induced rock layer induced by the rock layer, and the main control layer and multiple sub-control layers causing disaster are identified. S4. Conduct L-shaped drilling to relieve pressure on the main disaster-causing layer and multiple sub-disaster-causing layers.
[0006] This invention identifies the key layer containing the induced rock strata in the thick, hard roof of an isolated working face by utilizing key layer theory and microseismic data analysis. It also constructs a model of the overburden structure above the isolated working face and, through theoretical analysis, identifies the main disaster-causing layers and multiple sub-disaster-causing control layers in multiple induced rock strata areas. The invention determines the distribution location of the main disaster-causing control layer and the sub-disaster-causing control layers, thereby enabling the arrangement of ultra-long boreholes and pressure relief operations.
[0007] Optionally, in step S2, statistically analyzing the distribution of microseismic data across various key layers includes the following steps: S21. Vertically locate all microseismic events to the rock strata within a predetermined height range above the roof corresponding to the geological borehole or core borehole of the working face. Plot the microseismic data and key layer distribution into charts and graphs to form the vertical total energy / frequency curve and the vertical average energy / frequency curve of each rock stratum. S22. Based on the rock stratum thickness, calculate the total energy and frequency of microseismic events corresponding to each key stratum, determine the disaster-causing capacity of each key stratum, identify the location of the main induced rock stratum in the working face, and determine the vertical distance of the disaster-causing key stratum from the coal seam.
[0008] Furthermore, in S3, when analyzing the energy release from the perspective of the key layer of the induced impact, based on the analysis results of the key layer above the isolated working face and combined with the microseismic data in S2, the microseismic events inside the low-level and middle-high-level sandstone layers during the mining period of the adjacent working face or the adjacent mining area working face are selected for energy, frequency and propulsion analysis. The influence of mining speed on the energy release inside the low-level and middle-high-level sandstone layers is analyzed, and the disaster-causing capacity and energy release cycle of the low-level and middle-high-level key layers are obtained.
[0009] Furthermore, in S3, when analyzing from the perspective of the energy level of the high-energy event triggered by the failure of the key layer inducing abnormal mining pressure, a "large-small cycle" failure model of the thick and hard overburden is established based on the energy release law of the key layer and the characteristics of the high-energy event. A mechanical formula is established to quantitatively calculate the magnitude of the bending elastic energy released when the low-level and middle-high-level key layers fail, revealing the mechanism and triggering conditions of the roof mining pressure disaster.
[0010] Furthermore, a mechanical formula was established to quantitatively calculate the magnitude of the flexural elastic energy released when the low-level critical layer fails. The formula is as follows: The basic roof, serving as a thick and rigid roof during working face mining, has the following elastic energy released upon initial fracture, calculated as a fixed-support beam: ; In the formula, The initial fracture of the basic top releases elastic energy; The unit length equivalent load is the self-weight of the basic top and the additional load of the overlying rock strata. The elastic modulus of the beam at the basic top; The tensile strength of the basic top rock layer; The thickness of the basic top; The span of the suspended structure at the initial fracture of the basic top; The elastic energy released when the thick-layer main roof experiences periodic failure, calculated based on a cantilever beam, is: ; In the formula, The basic top cycle is broken to release elastic energy; The unit length equivalent load is the self-weight of the basic top cantilever beam model and the additional load of the overlying rock strata. This refers to the suspended span when the basic top cycle breaks.
[0011] Furthermore, a mechanical formula was established to quantitatively calculate the magnitude of the flexural elastic energy released when the critical layer in the middle and upper reaches fails. The formula is as follows: The elastic energy released during the initial and periodic fractures of the high-level, thick, and rigid roof slab is: ; In the formula, , To release elastic energy for the initial and periodic fracture of high-level, thick, key layers; , The unit length equivalent load is calculated for its initial and periodic self-weight and the additional load of its overlying rock strata. The elastic modulus of the beam in the high-level, thick, critical layer; Its tensile strength; Its thickness; , The initial and periodic breakage step distances; , It refers to the suspended span at the time of its initial and periodic failure.
[0012] Furthermore, in S4, when performing L-shaped borehole decompression operation, the fracturing range of the horizontal section of the L-shaped borehole needs to completely cover the rock stratum where the target disaster-causing layer is located. Other disaster-causing layers penetrated by the vertical section of the L-shaped borehole are subjected to retreat-type segmented fracturing during the fracturing process, and fracturing operations are carried out on the disaster-causing layers that are passed through.
[0013] Furthermore, the L-shaped boreholes are arranged from the two sides of the isolated working face towards the roof, and the horizontal range of the borehole fracturing should preferentially cover the area above the roadway. An unfractured area is allowed to remain in the roof area corresponding to the center of the working face, wherein the horizontal radius of the unfractured area does not exceed 80m.
[0014] Furthermore, in S4, after arranging L-shaped boreholes, the fracturing radius of each L-shaped borehole is in the range of 40-60m.
[0015] Furthermore, in S4, the number of L-shaped boreholes is based on the number of boreholes required to cover the working face with the maximum horizontal range of fracturing.
[0016] Furthermore, during fracturing operations, a layered fracturing process is adopted, prioritizing the fracturing of the rock strata containing the main disaster-causing layer, and then sequentially fracturing the rock strata containing each sub-disaster-causing layer in a direction away from the main disaster-causing layer.
[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the method steps for a method of decompression and vibration reduction in an L-shaped borehole of a thick, hard top plate in an isolated working face according to the present invention. Figure 2 This is a schematic diagram of the structure of the main critical layer and multiple sub-critical layers confirmed by the critical layer theory in step S1 of the L-shaped drilling pressure relief and vibration reduction method for thick hard top plate of isolated working face according to the present invention. Figure 3 This is a graph showing the total vertical energy / frequency of each rock layer in step S2 of a method for decompression and vibration reduction of L-shaped boreholes in an isolated working face according to the present invention. Figure 4 The S2 step of the present invention is the vertical average energy / frequency curve of each rock layer in the L-shaped borehole pressure relief and vibration reduction method for thick and hard roof plate of isolated working face according to the present invention. Figure 5 This is a schematic diagram of the overburden structure model of an isolated working face constructed in step S2 of the L-shaped borehole pressure relief and vibration reduction method for a thick, hard roof plate of an isolated working face according to the present invention. Figure 6 This is a schematic diagram of the unbroken model of the low-position and mid-high-position hard rock strata in the "large-small cycle" fracture model of the L-shaped borehole pressure relief and vibration reduction method for thick hard roof plate of isolated working face according to the present invention. Figure 7 This is a schematic diagram of the low- and mid-high-level hard rock simultaneous fracture model in the "large-small cycle" fracture model of the L-shaped borehole pressure relief and vibration reduction method for thick hard roof plate of isolated working face according to the present invention. Figure 8 This is a schematic diagram of the L-shaped drilling arrangement structure of a method for decompression and vibration reduction of a thick, hard top plate in an isolated working face according to the present invention. Detailed Implementation
[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0020] A method for pressure relief and vibration reduction through L-shaped drilling in a thick, hard roof plate of an isolated working face, comprising: S1. Based on the critical layer theory, critical layer analysis is performed on the thick and hard top plate above the isolated working face to confirm the location of the main critical layer and multiple sub-critical layers. S2. Collect microseismic data of the roof of the working face during mining, statistically analyze the distribution of microseismic data in each key layer, identify the location of the key layer where the main induced rock layer above the isolated working face is located, and analyze the occurrence characteristics of the thick and hard roof. S3. Based on the identification results of the main induced rock layer locations in S2, a corresponding overburden structure model for abnormal mining pressure induced by the energy transfer of key layer failure in isolated working faces is constructed. The mining pressure induction conditions of thick and hard roof in isolated working faces are analyzed from three aspects: energy release of key induced rock layers, energy level of large energy events triggered by key layer failure inducing abnormal mining pressure, and energy decay law of key layer failure. The induced rock layer in the overburden structure model is determined by the induced rock layer induced by the rock layer, and the main control layer and multiple sub-control layers causing disaster are identified. S4. Conduct L-shaped drilling to relieve pressure on the main disaster-causing layer and multiple sub-disaster-causing layers.
[0021] This invention identifies the key layer containing the induced rock strata in the thick, hard roof of an isolated working face by utilizing key layer theory and microseismic data analysis. It also constructs a model of the overburden structure above the isolated working face and, through theoretical analysis, identifies the main disaster-causing layers and multiple sub-disaster-causing control layers in multiple induced rock strata areas. The invention determines the distribution location of the main disaster-causing control layer and the sub-disaster-causing control layers, thereby enabling the arrangement of ultra-long boreholes and pressure relief operations.
[0022] In some embodiments, the step S2, which involves statistically analyzing the distribution of microseismic data across key layers, includes the following steps: S21. Vertically locate all microseismic events to the rock strata within a predetermined height range above the roof corresponding to the geological borehole or core borehole of the working face. Plot the microseismic data and key layer distribution into charts and graphs to form the vertical total energy / frequency curve and the vertical average energy / frequency curve of each rock stratum. S22. Based on the rock stratum thickness, calculate the total energy and frequency of microseismic events corresponding to each key stratum, determine the disaster-causing capacity of each key stratum, identify the location of the main induced rock stratum in the working face, and determine the vertical distance of the disaster-causing key stratum from the coal seam.
[0023] In some embodiments, in S1, based on the critical layer theory, assuming a certain rock layer is a critical layer and the area controlled by this rock layer reaches the nth layer, then the condition for the (n+1)th layer to become the second critical layer is: ; In the formula: —Calculate the load on the first critical layer when the calculation reaches the (n+1)th layer; —is the thickness of the rock strata; —is the unit weight of the rock strata; It is the elastic modulus of the rock strata; Then, based on the stiffness conditions of the key layer, the object to be judged for strength conditions is determined, namely: ; If the above formula holds true, the calculated rock layer may become the key layer. The calculation is repeated until the last layer of hard rock is reached. The composition is judged from bottom to top until the position of the last layer is determined.
[0024] In some embodiments, the step S2, which involves statistically analyzing the distribution of microseismic data across key layers, includes the following steps: S21. Vertically locate all microseismic events to the rock strata within a predetermined height range above the roof corresponding to the geological borehole or core borehole at the working face. Plot the microseismic data and the distribution of key layers into charts, forming the vertical total energy / frequency curve and the vertical average energy / frequency curve for each rock stratum. The predetermined height is generally 200m. Based on the key layer theory, the layer distribution and thickness of each key layer are preliminarily calculated and analyzed. The height and thickness of the key layer are marked on the vertical total energy / frequency curve and the vertical average energy / frequency curve of each rock layer, so as to intuitively identify the distribution of microseismic events in each key layer. S22. Based on the rock stratum thickness, calculate the total energy and frequency of microseismic events corresponding to each key stratum, determine the disaster-causing capacity of each key stratum, identify the location of the main induced rock stratum in the working face, and determine the vertical distance of the disaster-causing key stratum from the coal seam.
[0025] In some embodiments, in S3, when analyzing the energy release from the perspective of the key layer of the induced impact, based on the analysis results of the key layer above the isolated working face and combined with the microseismic data in S2, the microseismic events inside the low-level and middle-high-level sandstone layers during the mining period of the adjacent working face or adjacent mining area working face (if there is no adjacent working face or adjacent mining area working face, the working face in the mine with similar conditions in this area can be referred to) are analyzed for energy, frequency and propulsion. The influence of mining speed on the energy release inside the low-level and middle-high-level sandstone layers is analyzed to obtain the disaster-causing capacity and energy release cycle of the low-level and middle-high-level key layers.
[0026] In some embodiments, in step S3, when analyzing from the perspective of the energy level of the high-energy event triggered by the failure of the key layer inducing abnormal mining pressure, a "large-small cycle" failure model of the thick and hard overburden is established based on the energy release law of the key layer and the characteristics of the high-energy event. The "large-small cycle" failure model includes a model where the low-level and middle-high-level hard rock layers are not broken, and a model where the low-level and middle-high-level hard rock layers are broken simultaneously. Mechanical formulas are established based on different models to quantitatively calculate the magnitude of the bending elastic energy released when the low-level and middle-high-level key layers fail, thereby revealing the mechanism and triggering conditions of the roof mining pressure disaster.
[0027] Specifically, when quantitatively calculating the magnitude of the flexural elastic energy released upon failure of the low-level critical layer, the following formula is established: The basic roof, serving as a thick and rigid roof during working face mining, has the following elastic energy released upon initial fracture, calculated as a fixed-support beam: ; In the formula, The initial fracture of the basic top releases elastic energy; The unit length equivalent load is the self-weight of the basic top and the additional load of the overlying rock strata. The elastic modulus of the beam at the basic top; The tensile strength of the basic top rock layer; The thickness of the basic top; The span of the suspended structure at the initial fracture of the basic top; The elastic energy released when the thick-layer main roof experiences periodic failure, calculated based on a cantilever beam, is: ; In the formula, The basic top cycle is broken to release elastic energy; The unit length equivalent load is the self-weight of the basic top cantilever beam model and the additional load of the overlying rock strata. The suspended span when the basic top cycle breaks; When quantitatively calculating the magnitude of the flexural elastic energy released upon failure of the high-level critical stratum, the following formula is established: The elastic energy released during the initial and periodic fractures of the high-level, thick, and rigid roof slab is: ; In the formula, , To release elastic energy for the initial and periodic fracture of high-level, thick, key layers; , The unit length equivalent load is calculated for its initial and periodic self-weight and the additional load of its overlying rock strata. The elastic modulus of the beam in the high-level, thick, critical layer; Its tensile strength; Its thickness; , The initial and periodic breakage step distances; , It refers to the suspended span at the time of its initial and periodic failure.
[0028] In some embodiments, during the L-shaped borehole decompression operation in S4, the horizontal section of the L-shaped borehole needs to completely cover the rock stratum where the target disaster-causing layer is located. Other disaster-causing layers penetrated by the vertical section of the L-shaped borehole are subjected to retreat-type segmented fracturing during the fracturing process, and fracturing operations are carried out on the disaster-causing layers that are passed through.
[0029] In some embodiments, L-shaped boreholes are arranged from both sides of the isolated working face toward the roof, and the horizontal range of the borehole fracturing should preferably cover the roadway above. The pressure zone should cover the entire roof above the isolated working face as much as possible. In some working conditions, it is not possible to completely cover the roof above the isolated working face. In this case, an unfractured area is allowed in the roof area corresponding to the center of the working face. The horizontal radius of the unfractured area shall not exceed 80m. Depending on the actual situation, in a few working conditions, the horizontal radius of the unfractured area may not exceed 100m.
[0030] In some embodiments, in step S4, after arranging L-shaped boreholes, the fracturing radius of each L-shaped borehole is in the range of 40-60m.
[0031] In some embodiments, in step S4, the number of L-shaped boreholes is based on the number of boreholes required to cover the working face at the maximum horizontal range of fracturing.
[0032] In some embodiments, when performing fracturing operations, a layered fracturing process is adopted, prioritizing the fracturing of the rock strata containing the main disaster-causing layer, and then sequentially fracturing the rock strata containing each sub-disaster-causing layer in a direction away from the main disaster-causing layer.
[0033] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0035] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0037] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0038] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A method for pressure relief and vibration reduction through L-shaped drilling in a thick, hard roof plate of an isolated working face, characterized in that, include: S1. Based on the critical layer theory, critical layer analysis is performed on the thick and hard top plate above the isolated working face to confirm the location of the main critical layer and multiple sub-critical layers. S2. Collect microseismic data of the roof of the working face during mining, statistically analyze the distribution of microseismic data in each key layer, identify the location of the key layer where the main induced rock layer above the isolated working face is located, and analyze the occurrence characteristics of the thick and hard roof. S3. Based on the identification results of the main induced rock layer locations in S2, a corresponding overburden structure model for abnormal mining pressure induced by the energy transfer of key layer failure in isolated working faces is constructed. The mining pressure induction conditions of thick and hard roof in isolated working faces are analyzed from three aspects: energy release of key induced rock layers, energy level of large energy events triggered by key layer failure inducing abnormal mining pressure, and energy decay law of key layer failure. The induced rock layer in the overburden structure model is determined by the induced rock layer induced by the rock layer, and the main control layer and multiple sub-control layers causing disaster are identified. S4. Conduct L-shaped drilling to relieve pressure on the main disaster-causing layer and multiple sub-disaster-causing layers.
2. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate, as described in claim 1, is characterized in that... In step S2, the statistical analysis of the distribution of microseismic data in each key layer includes the following steps: S21. Vertically locate all microseismic events to the rock strata within a predetermined height range above the roof corresponding to the geological borehole or core borehole of the working face. Plot the microseismic data and key layer distribution into charts and graphs to form the vertical total energy / frequency curve and the vertical average energy / frequency curve of each rock stratum. S22. Based on the rock stratum thickness, calculate the total energy and frequency of microseismic events corresponding to each key stratum, determine the disaster-causing capacity of each key stratum, identify the location of the main induced rock stratum in the working face, and determine the vertical distance of the disaster-causing key stratum from the coal seam.
3. The method for pressure relief and vibration reduction through L-shaped drilling in a thick, hardened roof plate on an isolated working face as described in claim 1, characterized in that... In S3, when analyzing the energy release from the perspective of the key layer of the induced impact, based on the analysis results of the key layer above the isolated working face and combined with the microseismic data in S2, the energy, frequency and propulsion of microseismic events inside the low-level and middle-high-level sandstone layers during the mining period of the adjacent working face or the adjacent mining area working face are selected for analysis. The influence of mining speed on the energy release inside the low-level and middle-high-level sandstone layers is analyzed, and the disaster-causing capacity and energy release cycle of the low-level and middle-high-level key layers are obtained.
4. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 3, characterized in that... In S3, when analyzing from the perspective of the energy level of the high-energy event triggered by the failure of the key layer inducing abnormal mining pressure, a "large-small cycle" failure model of the thick and hard overburden is established based on the energy release law of the key layer and the characteristics of the high-energy event. A mechanical formula is established to quantitatively calculate the magnitude of the bending elastic energy released when the low-level and middle-high-level key layers fail, revealing the mechanism and triggering conditions of the roof mining pressure disaster.
5. The method for pressure relief and vibration reduction through L-shaped drilling in a thick, hard top plate of an isolated working face as described in claim 4, characterized in that... To quantitatively calculate the magnitude of flexural elastic energy released when the low-level critical layer fails, a mechanical formula is established as follows: The basic roof, serving as a thick and rigid roof during working face mining, has the following elastic energy released upon initial fracture, calculated as a fixed-support beam: ； In the formula, The initial fracture of the basic top releases elastic energy; The unit length equivalent load is the self-weight of the basic top and the additional load of the overlying rock strata. The elastic modulus of the beam at the basic top; The tensile strength of the basic top rock layer; The thickness of the basic top; The span of the suspended structure at the initial fracture of the basic top; The elastic energy released when the thick-layer main roof experiences periodic failure, calculated based on a cantilever beam, is: ； In the formula, The basic top cycle is broken to release elastic energy; The unit length equivalent load is the self-weight of the basic top cantilever beam model and the additional load of the overlying rock strata. This refers to the suspended span when the basic top cycle breaks.
6. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 4, characterized in that... A mechanical formula was established to quantitatively calculate the magnitude of the flexural elastic energy released when the critical layer in the middle and upper reaches fails. The formula is as follows: The elastic energy released during the initial and periodic fractures of the high-level, thick, and rigid roof slab is: ； In the formula, , To release elastic energy for the initial and periodic fracture of high-level, thick, key layers; , The unit length equivalent load is calculated for its initial and periodic self-weight and the additional load of its overlying rock strata. The elastic modulus of the beam in a high-level, thick, critical layer; Its tensile strength; Its thickness; , The initial and periodic breakage step distances; , It refers to the suspended span at the time of its initial and periodic failure.
7. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 1, characterized in that... In S4, when performing L-shaped borehole decompression operation, the horizontal section of the L-shaped borehole needs to completely cover the rock stratum where the target disaster-causing layer is located. Other disaster-causing layers penetrated by the vertical section of the L-shaped borehole are subjected to retreat-type segmented fracturing during the fracturing process, and fracturing operations are carried out on the disaster-causing layers that are passed through.
8. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 7, characterized in that... The L-shaped boreholes are arranged from the two sides of the isolated working face towards the roof. The horizontal range of the borehole fracturing should first cover the area above the roadway. An unfractured area is allowed in the roof area corresponding to the center of the working face, and the horizontal radius of the unfractured area shall not exceed 80m.
9. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 8, characterized in that... In S4, after arranging L-shaped boreholes, the fracturing radius of each L-shaped borehole is in the range of 40-60m.
10. The method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate as described in claim 9, characterized in that... In S4, the number of L-shaped boreholes is based on the number of boreholes required to cover the working face with the largest horizontal range of fracturing.
11. A method for pressure relief and vibration reduction through L-shaped drilling in an isolated working face with a thick, hard top plate, as described in any one of claims 7-10, characterized in that... When carrying out fracturing operations, a layered fracturing process is adopted, prioritizing the fracturing of the rock strata containing the main disaster-causing layer, and then sequentially fracturing the rock strata containing each sub-disaster-causing layer in a direction away from the main disaster-causing layer.