Determination method of pressure relief range in mining area of ​​protective layer of outburst coal seam

Abstract

The present invention relates to a method for measuring the pressure relief range of the mining area of ​​the protruding coal seam protective layer, and belongs to the field of coal mining. The measuring method comprises: S1, constructing a directional long borehole from the protective layer to the protected layer; S2, installing a sensing optical fiber and a grouting hose in the borehole; S3, after blocking one end of the borehole, grouting is injected into the borehole through the grouting hose to couple the sensing optical fiber with the rock layer; S4, repeating steps S1 to S3, completing the construction of a borehole and the laying of the sensing optical fiber on both sides of the protected layer respectively; S5, based on the measurement data obtained by the sensing optical fiber, performing strain and deformation rate analysis of the protected layer and the spacer layer, and then determining the pressure relief range and the pressure relief angle. The pressure relief range of the protected layer measured by the method of the present invention is larger, and the result is more accurate, simple and convenient, and real-time dynamic measurement is realized, without the need for manual downhole, and the drilling trajectory can be adjusted in time to always keep it at the target layer. The number of drilling holes is small, the engineering workload is small, and the construction is simple.

Description

Technical Field

[0001] The invention belongs to the field of coal mining and relates to a method for measuring the pressure relief range of a mining area of ​​a protruding coal seam protective layer. Background Art

[0002] In areas with poor natural conditions for coal mines, the geological conditions of coal fields are complex, the gas content of coal seams is high, and the permeability is generally (0.1~1.0)×10 -6 μm 2 , which is generally low, making gas extraction from pristine coal seams very difficult. However, mining practice has shown that even low-permeability coal seams can experience tens, hundreds, or even thousands of times more permeability after coal seam mining causes deformation and movement, creating favorable conditions for gas migration and extraction. Therefore, coal mine gas extraction in these areas primarily relies on underground protective layer decompression extraction.

[0003] Protective layer mining is to first mine the coal seam (called the protective layer) adjacent to the protruding coal seam (called the protected layer), thereby improving the permeability of the protruding coal seam itself, reducing gas pressure and gas content, and reducing the risk of outburst. According to the relative position relationship between the protective layer and the protected layer, it is divided into upper protective layer mining and lower protective layer mining. When the protective layer is located above the protruding coal seam, it is called the upper protective layer, and when it is located below the protruding coal seam, it is called the lower protective layer. Specifically, after the protective layer is mined, the adjacent protruding coal seam (protected layer) undergoes displacement and expansion deformation under the influence of mining, and the surrounding rock stress is also redistributed. The displacement and expansion deformation of the protruding coal seam causes a significant increase in the permeability and permeability of the protruding coal seam, that is, the protected layer experiences a pressure relief and permeability-enhancing effect. The large amount of gas stored in the protected layer is desorbed and released, which significantly reduces the gas pressure and gas content of the protected layer, thereby reducing or even eliminating its outburst risk. Therefore, protective layer mining is currently considered to be the most economical, safe and efficient technical method to eliminate the danger of coal seam outbursts. The measures to prevent outbursts in the mining protective layer area have the advantages of a large outburst elimination range, good outburst elimination effect and high economic benefits.

[0004] At present, the commonly used measurement methods are ground point measurement method and downhole point measurement method. Both of these measurement methods have a small number of measuring points and can only reflect the changes of one point, but cannot fully reflect the stress changes of the rock formation. The measurement accuracy is not high, and only a single indicator can be measured. The pressure relief angle and the protective vertical distance cannot be measured, and thus a more accurate pressure relief range cannot be obtained. In addition, due to the limitations of terrain conditions, manual on-site collection is required underground, and the construction is more difficult. If you want to improve the measurement accuracy, you need to increase the number of drill holes, which increases the difficulty of construction. The convenience of construction and measurement accuracy cannot be achieved at the same time. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer, which can accurately measure the pressure relief range, has a large test coverage range, can realize online automatic collection, and is convenient for construction.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for determining the pressure relief range of the mining area of ​​the protective layer of a protruding coal seam, wherein both sides of the protective layer are protected layers;

[0008] The determination method comprises the following steps:

[0009] S1, constructing a directional long drill hole from the protective layer to the protected layer;

[0010] S2, installing the sensing optical fiber and grouting hose in the borehole;

[0011] S3, after plugging one end of the borehole, grouting is injected into the borehole through a grouting hose provided in the plugging section to complete the coupling between the sensing optical fiber and the rock formation;

[0012] S4, repeating steps S1 to S3, adjusting the angle between the drilling direction and the axial direction of the protective layer, completing the construction of several drilling holes with different angles and the laying of sensing optical fibers;

[0013] S5, based on the measurement data obtained by the sensing optical fiber, the strain and deformation rate are analyzed to determine the pressure relief range and pressure relief angle.

[0014] Optionally, in step S5, points on the sensing optical fiber where the deformation rate is greater than or equal to 3‰ are determined, and a range enclosed by connecting these points is the pressure relief range.

[0015] Optionally, in step S5, the angle formed by connecting the points on the sensing optical fibers of the two drilled holes on both sides of the protected layer with a deformation rate equal to 3‰ and closest to the drilling point with the axial direction of the protective layer is the pressure relief angle; the pressure relief angle also includes the angle formed by connecting the points on the sensing optical fibers of the two drilled holes with a deformation rate equal to 3‰ and closest to the drilling point with the axial direction of the protective layer.

[0016] Optionally, in step S2, when installing the sensing optical fiber and the grouting hose, connect the drill bit to one end of the sensing optical fiber and the grouting hose, and pull the connecting end of the sensing optical fiber, the grouting hose and the drill bit back into the return air channel of the protective layer when retracting the drill.

[0017] Optionally, in step S2, one end of the sensing optical fiber is connected to the optical cable junction cabinet, and then the measurement data measured by the sensing optical fiber is transmitted to the BOTDA demodulator to complete demodulation to achieve real-time dynamic measurement; before the formal measurement, the spatial resolution of the BOTDA demodulator is set to 0.2m, and the initial strain data of the sensing optical fibers in the four boreholes are measured respectively, and then the spatial position is matched with the actual trajectory of the borehole to determine the position of the point on the sensing optical fiber corresponding to the borehole.

[0018] Optionally, there is a spacer layer between the protected layer and the protective layer; the protected layer includes a first protected layer located on the upper part of the protective layer and a second protected layer located on the lower part; directional long drill holes are constructed on both sides of the first protected layer and the second protected layer.

[0019] Optionally, a first return air channel is provided on the protective layer, a second return air channel is provided on the first protected layer, and a third return air channel is provided on the second protected layer; the upper portion of the first protected layer is a roof rock layer, and the lower portion of the second protected layer is a floor rock layer;

[0020] There are four directional long boreholes, namely the first borehole, the second borehole, the third borehole and the fourth borehole; the first borehole starts from the first return air channel and penetrates the interval layer and the first protected layer in sequence, then drills into the top rock layer, and then connects to the second return air channel; the second borehole starts from the first return air channel and penetrates the interval layer and then connects to the second return air channel; the third borehole starts from the first return air channel and penetrates the interval layer and then connects to the third return air channel; the fourth borehole starts from the first return air channel and penetrates the interval layer and the second protected layer in sequence, then drills into the bottom rock layer, and then connects to the third return air channel.

[0021] Optionally, in step S3, when sealing the borehole, first insert a return pipe into the borehole, and then use polyurethane to seal the inserted section of the return pipe, with the sealing length being less than or equal to the length of the return pipe; and install a valve at the end of the return pipe facing the return air channel.

[0022] Optionally, in step S3, cement slurry is injected from the end of the grouting hose located at the protected layer. When the cement slurry flows out of the return grouting pipe located at the protective layer, the valve is closed and grouting is continued for 5 minutes; then the grouting hose is gradually pulled out from the orifice at one end of the drilled hole close to the protected layer until the cement slurry overflows from the orifice.

[0023] Optionally, the sensing optical fiber is an armored multi-core single-mode optical cable.

[0024] The beneficial effects of the present invention are:

[0025] (1) The pressure relief range determined by the measurement method of the present invention is significantly increased, and the delineation of the pressure relief range is more accurate;

[0026] (2) The directional long drilling technology that has been popularized in recent years is adopted. Compared with the conventional drilling process used previously, the drilling trajectory adjustment is more timely and convenient, and the number of drilling holes and construction costs can be reduced;

[0027] (3) The present invention utilizes BOTDA distributed fiber optic measurement technology, enabling distributed measurement. This significantly increases the test range and number of measurement points, improving test accuracy. The distance between measurement points is only 0.1 to 2 meters, and the shorter the sensing fiber, the denser the measurement point spacing. For example, a sensing fiber laid in a 1 km long directional borehole can achieve a measurement distance of 0.2 meters, meaning 5,000 measurement points, or even more.

[0028] (4) The selection of drilling sites is more flexible. As long as the drill hole can cover the roof and floor areas of the coal mining face, it can be used. In addition, there are fewer auxiliary devices and only one sensing optical fiber at the hole mouth. The drilling workload is small and the overall process is simple.

[0029] (5) The deformation data during the observation period are all collected online automatically, without the need for manual on-site collection underground, which is more convenient.

[0030] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0032] Figure 1 Schematic diagram of the protective layer, protected layer, drilling hole and measuring point of the present invention;

[0033] Figure 2 This is an enlarged schematic diagram of the directional long drilling plugging section;

[0034] Figure 3 Flow chart of the steps of the determination method of the present invention.

[0035] Reference numerals:

[0036] 1 protective layer, 11 first return air channel, 2 first protected layer, 21 second return air channel, 3 second protected layer, 31 third return air channel, 4 interval layer, 5 borehole, 51 first borehole, 52 second borehole, 53 third borehole, 54 fourth borehole, 6 sensing optical fiber, 7 grouting hose, 8 valve, 9 return slurry pipe, 10 coal mining working face, 12 pressure relief range envelope, 13 blocking section, 14 return air channel, 15 transport channel, 16 goaf. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0038] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0039] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0040] See also Figure 3, is a method for determining the decompression range of the mining area of ​​the protective layer of the outburst coal seam, because the mining of the protective layer has been listed as one of the two types of regional outburst prevention measures in relevant laws and regulations. Article 4 of the "Technical Specifications for Protective Layer Mining" stipulates the applicable conditions and selection principles of protective layer mining: (1) When mining a coal seam group in an outburst mine, it is necessary to adopt the mining of the protective layer to prevent and control outbursts. (2) Coal seams without outburst hazards should be selected as protective layers first; when there are several coal seams in a coal seam group that can be used as protective layers, the best one should be selected based on a comprehensive comparison and analysis of safety, technology, and economic rationality; when all coal seams in the mine have outburst hazards, coal seams with a smaller degree of outburst hazard can be selected as protective layers; if the mineable coal seam cannot be mined as a protective layer, the adjacent unmineable coal seam can be selected as a protective layer under economically reasonable conditions. (3) The upper protective layer should be selected first; when the lower protective layer is mined, the mining conditions of the protected layer must not be destroyed. Article 61 of the "Detailed Rules for Preventing and Controlling Coal and Gas Outbursts" stipulates: In outburst hazard areas with the conditions for mining the protective layer, the protective layer must be mined. The following principles should be followed when selecting protective layers: (1) Coal seams without outburst hazards should be selected as protective layers first. When all coal seams in a mine have outburst hazards, coal seams with a lower degree of outburst hazards should be selected as protective layers; (2) When there are several coal seams in a coal seam group that can be used as protective layers, the coal seam with the best protection effect should be mined first; (3) The upper protective layer should be selected first. When mining the lower protective layer, the mining conditions of the protected layer must not be damaged; (4) When mining a coal seam group, if there is a coal seam with a thickness of 0.5m or more without outburst hazards within the effective protection vertical distance, it should be mined first as a protective layer, except when the distance to the outburst coal seam is too close to threaten the safety of the protective layer working face or may damage the mining conditions of the outburst coal seam.

[0041] The present invention proposes a method for determining the pressure relief range of the mining area of ​​the outburst coal seam protective layer, such as Figures 1-2 As shown, the two sides of the protective layer 1 are defined as protected layers; the spacer layer 4 is defined between the protective layer 1 and the protected layer, and the spacer layer 4 is a rock layer formed by natural sedimentation; the protected layer includes a first protected layer 2 located on the upper part of the protective layer 1 and a second protected layer 3 located on the lower part, the upper rock layer of the first protected layer 2 is the roof rock layer, and the lower rock layer of the second protected layer 3 is the bottom rock layer; a first return air channel 11 is provided on the protective layer 1, a second return air channel 21 is provided on the first protected layer 2, and a third return air channel 31 is provided on the second protected layer 3.

[0042] The determination method comprises the following steps:

[0043] S1, before the protective layer 1 coal mining working face 10 is mined, a directional long drill hole 5 is constructed from the protective layer 1 toward the protected layer; in some embodiments of the present invention, the drill hole 5 adopts a directional long drill hole technology, and the diameter of the drill hole 5 ranges from 94mm to 153mm.

[0044] Directional long-hole drilling is a drilling technique that controls the direction of the drill string by adjusting the drill bit. Using an adjustable drill bit on the drill pipe, directional long-hole drilling can extend the borehole in different directions, allowing the operator to drill a specific location. This technology is equipped with a remote control device that receives remote control commands, allowing the operator to precisely control the drilling direction from the surface. Because the strength and stability of the drill pipe affect the drilling direction, drill pipe adjustment techniques are often used to ensure accurate drilling direction. Directional long-hole drilling offers the advantages of high drilling accuracy, high construction efficiency, and low cost. A guide device controls the drill bit along a predetermined trajectory, enabling long-distance, high-precision directional drilling. This technology also reduces the risk of gas outbursts and coal-gas outbursts, improving mine safety. In mine gas control, directional long-hole drilling can effectively extract coal seam gas, reduce gas concentrations, and prevent gas explosions. This technology is particularly suitable for mines with high gas content, coal-gas outbursts, and complex geological structures with unstable coal seams.

[0045] S2, installing the sensing optical fiber 6 and the grouting hose 7 in the borehole 5;

[0046] In step S2, when installing the sensing optical fiber 6 and the grouting hose 7, the drill bit is connected to one end of the sensing optical fiber 6 and the grouting hose 7. When retracting the drill, the connection end of the sensing optical fiber 6, the grouting hose 7 and the drill bit is pulled back into the return air channel of the protective layer 1; after the installation is completed, the integrity of the sensing optical fiber 6 and the grouting hose 7 is retested in the return air channel;

[0047] Connect one end of the sensing fiber 6 to the optical cable junction cabinet, and then transmit the measurement data measured by the sensing fiber 6 to the BOTDA demodulator for demodulation to achieve real-time dynamic measurement. Before the formal measurement, the spatial resolution of the BOTDA demodulator is set to 0.2m, and three initial strain data measurements are performed on the sensing fibers 6 in the four boreholes 5. The spatial positions are then matched with the actual trajectories of the boreholes 5 to determine the corresponding positions of the points on the sensing fiber 6 on the boreholes 5.

[0048] The BOTDA interrogator is a key device in the field of fiber optic sensing, primarily used for long-distance (up to tens of kilometers) distributed temperature and strain measurement. It analyzes the frequency shift of Brillouin signal light reflected from various points on the fiber to determine the strain distribution along the fiber. It offers numerous advantages, including continuous distributed detection, no blind spots, long monitoring distance, low power consumption, high reliability, an embedded design, simple installation and maintenance, flexible expansion, and online self-diagnosis.

[0049] Armored multi-core single-mode optical fiber cable is an optical signal transmission and sensing device, primarily used for optical signal transmission and sensing changes in measured physical quantities. It is generally composed of optical fiber, casing, filler, reinforcing core, waterproof layer, and armor layer. Each segment of the optical fiber serves as both a sensing unit and a transmission medium, achieving both "transmission" and "sensing."

[0050] S3, after plugging one end of the borehole 5, grouting is injected into the borehole 5 through the grouting hose 7 provided in the plugging section to complete the coupling between the sensing optical fiber 6 and the rock formation;

[0051] Optionally, in step S3, when sealing the borehole 5, first insert a 5m long return pipe 9 into the borehole 5, and then use polyurethane to seal the inserted section of the return pipe 9 to form a sealing section 13. The sealing length is 4m. In actual operation, the sealing length needs to be less than or equal to the length of the return pipe 9 to ensure that both ends of the return pipe 9 are unobstructed; and a valve 8 is installed at the end of the return pipe 9 facing the return air channel.

[0052] Optionally, in step S3, cement slurry is injected from the end of the grouting hose 7 located in the second return air channel 21, and whether cement slurry flows out from the valve 8 of the return slurry pipe 9 in the first return air channel 11. When cement slurry flows out of the return slurry pipe 9 in the first return air channel 11, the valve 8 is closed and the grouting is continued for 5 minutes; then the grouting hose 7 is gradually lifted up from the second return air channel 21, and the lifting speed is determined according to the grouting amount, but it should be ensured that the slurry outlet of the grouting hose 7 is always placed in the slurry until the cement slurry overflows from the orifice, until the cement slurry overflows from the orifice of the first borehole 51 close to one end of the second return air channel 21, and the grouting hose 7 is lifted up from the orifice to complete the laying of the sensing optical fiber 6 of the first borehole 51.

[0053] S4, repeat steps S1 to S3, adjust the angle between the direction of the drill hole 5 and the axial direction of the protective layer 1, and complete the construction of several drill holes 5 with different angles and the laying of their sensing optical fibers 6; directional long drill holes 5 are constructed on both sides of the first protected layer 2 and the second protected layer 3, that is, four directional long drill holes 5 are set.

[0054] The four boreholes 5 are the first borehole 51, the second borehole 52, the third borehole 53 and the fourth borehole 54; the first borehole 51 starts from the first return air channel 11 and penetrates the interval layer 4 and the first protected layer 2 in sequence, then drills into the top rock layer, and then connects to the second return air channel 21; the second borehole 52 starts from the first return air channel 11 and penetrates the interval layer 4 and then connects to the second return air channel 21; the third borehole 53 starts from the first return air channel 11 and penetrates the interval layer 4 and then connects to the third return air channel 31; the fourth borehole 54 starts from the first return air channel 11 and penetrates the interval layer 4 and the second protected layer 3 in sequence, then drills into the bottom rock layer, and then connects to the third return air channel 31.

[0055] S5, performing strain and deformation rate analysis based on the measurement data obtained by the sensing optical fiber 6, and then determining the pressure relief range and pressure relief angle.

[0056] In step S5, before the coal mining face 10 of the protective layer 1 advances to within 100 meters of the borehole 5, the modem is set to continuous dynamic measurement, and data is stored for strain and deformation rate analysis. This monitoring continues until the mining face passes through the borehole 5 and moves 100 meters away from it. Based on the strain and deformation rate analysis of the measured data, points on the sensing fiber 6 with a deformation rate greater than or equal to 3‰ are identified. The range enclosed by connecting these points is the pressure relief range. The angle formed by connecting the points on the sensing fibers 6 of two adjacent boreholes 5 with a deformation rate equal to 3‰ and closest to the entry point with the axial direction of the protective layer 1 is the pressure relief angle. The pressure relief angle also includes the angle formed by connecting the points with a deformation rate equal to 3‰ and closest to the exit point with the axial direction of the protective layer. Since BOTDA only requires single-end measurement, if the sensing fiber 6 breaks due to rock formation movement, measurements can be performed on both ends of the broken sensing fiber 6 in the first, second, and third return airways 11, 21, and 31 to still obtain strain data.

[0057] like Figure 1 As shown, the areas where the deformation rate of the sensing optical fiber 6 in the first borehole 51 is greater than 3‰ are the A1A3, A4A5, and A6A7 sections; the area where the deformation rate of the sensing optical fiber 6 in the second borehole 52 is greater than 3‰ is the B1B2 section; the area where the deformation rate of the sensing optical fiber 6 in the third borehole 53 is greater than 3‰ is the C1C2 section; and the areas where the deformation rate of the sensing optical fiber 6 in the fourth borehole 54 is greater than 3‰ are the D1D3, D4D5, and D6D7 sections; the points on the sensing optical fiber 6 where the deformation rate is equal to 3‰ are A1, A2, B1, B2, C1, C2, D1, and D2, respectively; the angle between the line A1B1 and the protective layer 1 is the pressure relief angle δ1, the angle between the line A2B2 and the protective layer 1 is the pressure relief angle δ2, the angle between the line C1D1 and the protective layer 1 is the pressure relief angle δ3, and the angle between the line C2D2 and the protective layer 1 is the pressure relief angle δ4. The envelope obtained by connecting points B0, B1, A1, A3, A4, A5, A6, A7, A2, B2, B3, C2, D2, D7, D6, D5, D4, D3, D2, D1, and C1 in sequence is the pressure relief range; among them, B0 and B3 are the two ends of the coal mining working face 10 in the protective layer 1, respectively.

[0058] In the present invention, in addition to the above-mentioned return air lanes, a number of return air lanes 14 and transport lanes 15 are also connected and arranged. The return air lane 14 refers to the lane through which the return air flows, and is mainly used to discharge the dirty gases generated in the coal mine (such as gas, exhaust gas generated by diesel rubber-wheeled vehicles, and foul air exhaled by workers) out of the mine to ensure the cleanliness and safety of the air underground in the coal mine. The transport lane 15, especially the main transport lane, is the main lane in coal mine production and is used for uninterrupted transportation of coal. Depending on the specific conditions of the coal mine, the transport lane 15 may be equipped with a belt conveyor (inclined shaft) or a skip (vertical shaft) to transport coal. In addition, the transport lane 15 also undertakes the task of ventilation, providing fresh air for the entire coal mine.

[0059] The goaf 16 is the space left after the coal mining face is mined. The coal and rock layers above and below the goaf will move and deform to produce a certain pressure relief range, causing a large amount of gas to flow into the coal mining face.

[0060] In some embodiments of the present invention, the sensing optical fiber 6 is an armored sensing optical fiber 6. The present invention utilizes directional long drilling, and the trajectory of the drilling hole 5 can be adjusted in real time as needed. The drilling is carried out to the layer and position most favorable for investigating the pressure relief range, and can cover the entire roof and floor coal and rock mass of the rectified protective layer 1 coal mining working face 10. This provides a wide test coverage range, more test data, and a more accurate analysis of the pressure relief range.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for determining the pressure relief range of a mining area in a protruding coal seam protective layer, characterized by: The two sides of the protective layer (1) are protected layers; The determination method comprises the following steps: S1, constructing a directional long drill hole (5) from the protective layer (1) toward the protected layer; S2, installing a sensing optical fiber (6) and a grouting hose (7) in the borehole (5); S3, after plugging one end of the borehole (5), grouting is injected into the borehole (5) through a grouting hose (7) provided in the plugging section to complete the coupling between the sensing optical fiber (6) and the rock formation; S4, repeating steps S1 to S3, adjusting the angle between the direction of the drilling hole (5) and the axial direction of the protective layer (1), completing the construction of several drilling holes (5) with different angles and the laying of the sensing optical fiber (6); S5, performing strain and deformation rate analysis based on the measurement data obtained by the sensing optical fiber (6), and then determining the pressure relief range and pressure relief angle; In step S5, points on the sensing optical fiber (6) with a deformation rate greater than or equal to 3‰ are determined, and the range enclosed by connecting these points is the pressure relief range; the angle formed by connecting the points on the sensing optical fibers (6) of the two drill holes (5) located on both sides of the protected layer with a deformation rate equal to 3‰ and closest to the drilled-in point with the axial direction of the protective layer (1) is the pressure relief angle; the pressure relief angle also includes the angle formed by connecting the points with a deformation rate equal to 3‰ and closest to the drilled-out point with the axial direction of the protective layer (1).

2. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 1, characterized in that: In step S2, when installing the sensing optical fiber (6) and the grouting hose (7), the drill bit is connected to one end of the sensing optical fiber (6) and the grouting hose (7), and when retracting the drill bit, the connection end of the sensing optical fiber (6), the grouting hose (7) and the drill bit is pulled back into the return air channel of the protective layer (1).

3. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 2, characterized in that: In step S2, one end of the sensing optical fiber (6) is connected to the optical cable junction cabinet, and the measurement data measured by the sensing optical fiber (6) is transmitted to the BOTDA demodulator to complete demodulation to achieve real-time dynamic measurement; before the formal measurement, the spatial resolution of the BOTDA demodulator is set to 0.2m, and the initial strain data of the sensing optical fibers (6) in the four boreholes (5) are measured respectively, and then the spatial position is matched with the actual trajectory of the borehole (5), so as to determine the position of the point on the sensing optical fiber (6) corresponding to the borehole (5).

4. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 1, characterized in that: A spacer layer (4) is provided between the protected layer and the protective layer (1); the protected layer comprises a first protected layer (2) located above the protective layer (1) and a second protected layer (3) located below the protective layer (1); and directional long drill holes (5) are constructed on both sides of the first protected layer (2) and the second protected layer (3).

5. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 4, characterized in that: A first return air channel (11) is provided on the protective layer (1), a second return air channel (21) is provided on the first protected layer (2), and a third return air channel (31) is provided on the second protected layer (3); the upper portion of the first protected layer (2) is a roof rock layer, and the lower portion of the second protected layer (3) is a floor rock layer; The directional long boreholes (5) are provided with four, namely a first borehole (51), a second borehole (52), a third borehole (53) and a fourth borehole (54); the first borehole (51) starts from the first return air channel (11) and sequentially penetrates the spacer layer (4) and the first protected layer (2), then drills into the top rock layer, and then connects to the second return air channel (21); the second borehole (52) starts from the first return air channel (11) and penetrates the spacer layer (4), then connects to the second return air channel (21); the third borehole (53) starts from the first return air channel (11) and penetrates the spacer layer (4), then connects to the third return air channel (31); the fourth borehole (54) starts from the first return air channel (11) and sequentially penetrates the spacer layer (4) and the second protected layer (3), then drills into the bottom rock layer, and then connects to the third return air channel (31).

6. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 1, characterized in that: In step S3, when the borehole (5) is blocked, a return slurry pipe (9) is first inserted into the borehole (5), and then the inserted section of the return slurry pipe (9) is blocked with polyurethane, with the blocking length being less than or equal to the length of the return slurry pipe (9); and a valve (8) is installed at one end of the return slurry pipe (9) facing the return air channel.

7. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 1, characterized in that: In step S3, cement slurry is injected from the end of the grouting hose (7) located at the protected layer. When the cement slurry flows out of the return grouting pipe (9) located at the protective layer (1), the valve (8) is closed and the grouting is continued for 5 minutes. Then, the grouting hose (7) is gradually pulled out from the hole at the end of the drill hole (5) close to the protected layer until the cement slurry overflows from the hole.

8. The method for determining the pressure relief range of the mining area of ​​the protruding coal seam protective layer according to claim 1, characterized in that: The sensing optical fiber (6) is an armored multi-core single-mode optical cable.

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