Method for probing a coal mine roof cantilever

Abstract

This invention discloses a method for cantilever beam exploration in coal mines. It utilizes borehole inspection to detect the surrounding rock integrity level of each cantilever exploration hole, establishing the surrounding rock integrity level and its corresponding indicators to improve the accuracy of cantilever exploration. Low-pressure water injection is used to detect the water leakage of each cantilever exploration hole, allowing for segmented water injection and high-precision leakage measurement. While borehole inspection directly reveals the fractures within the hole, the results are often unclear due to water seepage and fogging caused by temperature differences between the inside and outside of the lens. Although low-pressure water injection passively reflects the fracture condition, it is unaffected by lens blur and provides a more reliable numerical reflection of fracture expansion. By cross-validating the borehole inspection and low-pressure water injection methods, the error in cantilever beam exploration is further reduced. This systematizes the cantilever beam exploration method, making the exploration more refined and minimizing errors.

Description

Technical Field

[0001] This invention belongs to the field of coal mine rockburst disaster prevention and control technology, and relates to a method for detecting cantilever beams on the roof of coal mines. Background Technology

[0002] In recent years, with the increasing depth and complexity of coal mining conditions in my country, coal mine rockbursts have become a major hazard restricting safe and efficient coal mine production. One type of rockburst, widely found in mines across the country, is the roof-type rockburst. Its basic principle is that as the coal seam is mined, the overlying thick, hard rock strata are easily disturbed and fractured, generating significant elastic energy that can induce a coal mine rockburst. The intensity of the rockburst is positively correlated with the length of the cantilever beam of the overlying thick, hard rock strata. Therefore, determining the length of the cantilever beam of the overlying thick, hard rock strata is of great significance for the prevention and control of coal mine rockburst hazards.

[0003] Currently, the cantilever beam exploration of coal seam overlying strata is generally carried out using the borehole inspection method, which determines the approximate length of the cantilever beam by observing the borehole fractures. However, this method often results in large errors due to unclear imaging, and it has not formed a systematic method, with significant human interference factors. This poses a technical challenge to the precise exploration of cantilever beams in thick and hard overlying strata of coal seams. Therefore, it is urgent to propose a refined method for exploring cantilever beams in coal mine roofs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting cantilever beams on the roof of coal mines, which solves the problem of large errors in the detection results caused by unclear imaging in the existing borehole inspection method for detecting cantilever beams.

[0005] The technical solution adopted in this invention is a method for detecting cantilever beams on the roof of coal mines, comprising: Step 1: Open a cantilever exploration hole in the adjacent goaf of the longwall face; Step 2: Drill and inspect the cantilever inspection hole and calculate the vertical height and length of the cantilever beam; Step 3: Perform segmented low-pressure water injection detection on the cantilever inspection hole from top to bottom and calculate the vertical height and length of the cantilever beam; Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam.

[0006] The invention is further characterized by: In step 1, S1, extract the columnar sections of several boreholes near the cantilever beam exploration area. Assume the rock strata within a 100m range above the coal seam are sequentially designated as layers 1, 2, 3…m…n. Determine the rock strata type and thickness for each layer. , bulk density Elastic modulus Ultimate tensile strength parameter, ; S2, based on the above parameters, calculate and identify the key layers in each rock stratum; substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0007] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; when

[0008] At that time, the first The layer is the key layer; S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0009] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0010] In step 2, A1, borehole inspection is performed on the opened cantilever exploration hole to obtain fracture images at various depths of the cantilever exploration hole, and surrounding rock information is obtained from the fracture images; A2, classifying the rock integrity level based on surrounding rock information and the corresponding rock integrity index for each level; The integrity of the surrounding rock is classified into grades I to VI, with grade I corresponding to the highest integrity index. The volumetric joint number of the rock mass corresponding to each grade is also introduced. Rock mass joint number Actual measurements were conducted using direct measurement methods. The corresponding indicators for Grade I are rock mass integrity and the number of joints in the rock mass volume. The borehole walls are smooth or exhibit large-scale ripple marks, with no visible cracks; Grade II corresponds to a relatively intact rock mass and a high number of volumetric joints. The borehole wall is generally intact, with a few closed or slightly open cracks visible, and the crack spacing is >0.5m; the corresponding index for Grade III is moderately intact rock mass, and the number of volumetric joints in the rock mass is [missing information]. A clear network of fractures was visible on the borehole wall, with fracture spacing of 0.2-0.5m. A small number of delaminations or slightly fractured zones were observed, but the main rock mass still maintained its structure. The corresponding index for Grade IV is relatively fractured rock mass, with a high number of volumetric joints. The borehole wall exhibits densely developed fractures with a spacing of 0.1-0.2m, and multiple fracture zones are visible. The rock mass is cut into small to medium-sized blocks with a diameter of 20-30cm. The borehole wall shows slight spalling or unevenness. Grade V corresponds to rock mass fracture and a high number of volumetric joints. The borehole wall is severely fractured, with very dense fissures, spacing <0.1m, forming a grid pattern. The fractured zones are continuous, and the rock mass is in the form of fragments or gravel. During the drilling process, blocks continue to fall, and the borehole shape is irregular. The corresponding indicator for Grade VI is borehole collapse, and the borehole sighting instrument cannot continue to explore deeper, with no sighting image. A3. Record the integrity level of the surrounding rock at each depth of each cantilever exploration hole, and calculate the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole.

[0011] In the formula, For the first Vertical height of the cantilever beam of the cantilever exploration hole For the first The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the rock integrity level of the cantilever borehole at various depths, the depth value with the highest rock integrity index was selected, and the cantilever borehole was considered to have reached the required depth. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

[0012] In step 3, B1, starting from the bottom of the hole, the cantilever exploration hole is divided into sections with a length of... of part; In B1, ; B2, for the first section, involves filling the upper and lower sealing holes with water, maintaining a distance between the upper and lower sealing holes. The water injection volume is more than twice the volume of the space between the upper and lower sealing holes; the water injection volume is recorded as... ; B3, open the lower sealing hole. The water inside the sealing hole will flow out naturally due to gravity. Record the outflow volume. ; B4, calculate the water leakage rate and record it as follows: , ; B5. Repeat steps B2-B4, sequentially injecting water into the upper and lower sealing holes of each section, and measuring the water leakage of each section. To conduct statistics; B6. Repeat steps B1 to B5 to calculate the segmented water leakage of each cantilever inspection hole and calculate the vertical height and length of the cantilever corresponding to each cantilever inspection hole.

[0013] In the formula, The first calculation based on water leakage Vertical height of the cantilever beam of the cantilever exploration hole The first calculation based on water leakage The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the statistical analysis of water leakage in each segment of the cantilever borehole, the depth at which the water leakage from the borehole opening to the bottom first increases, then decreases, and finally remains stable is selected. This depth is considered the optimal depth for the cantilever borehole. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

[0014] In step 4, C1, extract the surrounding rock integrity information at different depths of each cantilever exploration hole from the borehole inspection in step 2 (A1) and the segmented water injection leakage of each cantilever exploration hole from the low-pressure water injection detection in step 3 (B6). Observe the borehole inspection images of each cantilever exploration hole. If the borehole inspection images are clear and the fracture images at different depths of the cantilever exploration holes clearly identify fractures of different degrees, then use the borehole inspection to verify the low-pressure water injection detection results. and This is the result of the cantilever beam exploration at this stratum; if the borehole inspection imaging is unclear, and it is difficult to identify fractures of different degrees from different depths in the exported images of the cantilever inspection borehole, then low-pressure water injection detection is used to verify the borehole inspection results. and The results of the cantilever beam exploration corresponding to the cantilever exploration hole; C2 records the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole at the top of the coal seam.

[0015] The beneficial effects of this invention are: By referencing the surrounding rock information of each cantilever exploration hole through borehole inspection, the integrity level of the surrounding rock of the cantilever exploration hole and its corresponding integrity index are finely classified, improving the accuracy of cantilever borehole inspection. The water leakage of each cantilever exploration hole is detected by segmented low-pressure water injection, and the segment length is adjusted for high-precision leakage measurement. While borehole inspection can directly observe the fractures within the hole, the results are generally unclear due to water inflow and fogging caused by temperature differences between the inside and outside of the lens. Although low-pressure water injection passively reflects the fracture condition within the hole, it is not affected by lens blurring, and the obtained numerical value reflects the degree of fracture propagation more reliably. By cross-validating the two inspection methods of borehole inspection and low-pressure water injection, the error of cantilever beam inspection is further reduced. This systematizes the cantilever beam inspection method, making the inspection more refined and minimizing errors. Attached Figure Description

[0016] Figure 1 This is a flowchart of the coal mine roof cantilever beam exploration method of the present invention; Figure 2 This is a contour diagram of the cantilever situation after mining out of an adjacent working face, implemented in the coal mine roof cantilever beam exploration method of the present invention. Figure 3 This invention relates to the cantilever inspection hole used in the coal mine roof cantilever beam inspection method. l 1. Statistical chart of the integrity levels of surrounding rock at different depths; Figure 4 This invention relates to the cantilever inspection hole used in the coal mine roof cantilever beam inspection method. l 1. Bar chart of water leakage in segmented injection sections; Figure 5 This is a contour diagram of the cantilever situation after mining out of adjacent working faces in the second implementation of the coal mine roof cantilever beam exploration method of the present invention; Figure 6 This is a contour diagram of the cantilever situation after mining out of adjacent working faces in the third implementation of the coal mine roof cantilever beam exploration method of the present invention. Detailed Implementation

[0017] The following detailed description is provided in conjunction with specific implementation methods.

[0018] Example 1 This embodiment discloses a method for detecting cantilever beams on the roof of a coal mine, such as... Figure 1 As shown, the process includes: Step 1: Opening a cantilever exploration hole in the adjacent goaf of the longwall face; Step 2: Drilling and inspecting the cantilever exploration hole and calculating the vertical height and length of the cantilever beam; Step 3: Performing segmented low-pressure water injection detection from top to bottom on the cantilever exploration hole and calculating the vertical height and length of the cantilever beam; Step 4: Verifying the drilling and inspection detection with the low-pressure water injection detection to determine the vertical height and length of the cantilever beam.

[0019] In this embodiment, to conduct cantilever beam exploration work on one side of an adjacent goaf in the advanced section of the longwall face, it is first necessary to open cantilever exploration holes in the coal seam roof of the adjacent goaf. Then, by drilling and observing the cantilever exploration holes, the surrounding rock information at different depths of each cantilever exploration hole is detected, and the vertical height and length of the cantilever beam are calculated. By performing segmented low-pressure water injection from top to bottom on each cantilever exploration hole, the water leakage is detected, and the vertical height and length of the cantilever beam are calculated. Drilling and observing can directly see the fractures inside the hole, but the observation results are generally unclear due to water in the hole, temperature difference between the inside and outside of the lens, etc. Although segmented low-pressure water injection passively reflects the fracture conditions inside the hole, it is not affected by the unclear lens, and the numerical value obtained reflects the degree of fracture expansion more reliably. The two methods of drilling and observing are mutually verified, and finally the vertical height and length of the cantilever beam at each layer are determined.

[0020] Example 2 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0021] Table For the serial number rock strata type, ; S2, Based on the above parameters, calculate and identify the key layers in each rock stratum. Substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0022] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0023] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0024] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0025] Specifically, based on the calculations in S3, the key layers are designated as layer 2 and layer 4, and the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows. Figure 2 As shown in the dashed box in the figure. L 2. L 4 represents the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam. Based on the cantilever profile diagram, three cantilever exploration holes are opened. l 1. l 2. l 3. All three cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway and extend from the adjacent goaf roadway toward the roof of the goaf area. The three cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0026] Step 2: Drill and inspect the cantilever exploration holes and calculate the vertical height and length of the cantilever beam; specifically, for the three cantilever exploration holes drilled in S4 of Step 1... l 1. l 2. l 3. Conduct borehole inspection and calculate the vertical height and length of the cantilever beam.

[0027] Step 3: Conduct segmented low-pressure water injection testing of the cantilever probe holes from top to bottom and calculate the vertical height and length of the cantilever beam; specifically, for the three cantilever probe holes... l 1. l 2. l 3. Perform segmented low-pressure water injection detection and calculate the vertical height and length of the cantilever beam. The detection is carried out from the bottom of the hole, which simplifies the segmented low-pressure water injection detection process.

[0028] Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; specifically, refer to Steps 2 and 3 for the three cantilever inspection holes. l 1. l 2. l If the borehole inspection imaging in step 2 is clear and the exported images of fractures at different depths of the cantilever inspection hole clearly identify fractures of different degrees, then borehole inspection is used to verify the low-pressure water injection detection results; otherwise, low-pressure water injection is used to verify the borehole inspection detection results.

[0029] Example 3 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0030] Table For the serial number rock strata type, ; S2, based on the above parameters, calculate and identify the key layers in each rock stratum; substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0031] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0032] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0033] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. Multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture areas of the cantilever in each key layer.

[0034] Specifically, based on the calculations in S3, the key layers are designated as layer 2 and layer 4, and the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows. Figure 2 As shown in the dashed box in the figure. L 2. L 4 represents the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam. Based on the cantilever profile diagram, three cantilever exploration holes are opened. l 1. l 2. l 3. All three cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway and extend from the adjacent goaf roadway toward the roof of the goaf area. The three cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0035] Step 2: Drill and inspect the cantilever inspection hole and analyze and calculate the vertical height and length of the cantilever beam; In step 2, A1, borehole inspection is performed on the opened cantilever exploration hole to obtain fracture images at various depths of the cantilever exploration hole, and surrounding rock information is obtained from the fracture images; A2, classify the rock integrity level of the cantilever exploration hole and the corresponding rock integrity index for each level based on the surrounding rock information; The integrity of the surrounding rock is classified into grades I to VI, with grade I corresponding to the highest integrity index. The volumetric joint number of the rock mass corresponding to each grade is also introduced. Rock mass joint number The table below shows the correspondence between the number of volumetric joints in rock mass and the degree of borehole fractures, obtained through direct measurement.

[0036] A3. Record the integrity level of the surrounding rock at each depth of each cantilever exploration hole, and calculate the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole.

[0037] In the formula, For the first Vertical height of the cantilever beam of the cantilever exploration hole For the first The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the rock integrity level of the cantilever borehole at various depths, the depth value with the highest rock integrity index was selected, and the cantilever borehole was considered to have reached the required depth. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam; Specifically, such as Figure 3 As shown, this is a cantilevered exploration hole. l 1. A statistical chart of the integrity levels of surrounding rock at different depths, with a gradient of 5m. The chart shows the results at different depths during cantilever exploration. l 1. The rock integrity grade of the exploratory borehole in the 80-85m section with inclined length decreases significantly from high to low, approaching level I, indicating the highest rock integrity. This suggests that fractures are not well-developed in this section of the borehole, thus evaluating the cantilever exploration borehole. l 1. At a depth of 80-85m, the rock mass is intact; this location marks the starting point of the cantilever. Figure 2 As shown, cantilever exploration hole l 1. Angle with the coal seam ,have

[0038] In the formula Take 80m~85m, and get The elevation ranges from 56.57m to 60.10m. The range is 56.57m to 60.10m.

[0039] Step 3: Conduct segmented low-pressure water injection testing and verification of the cantilever probe hole from top to bottom, and calculate the vertical height and length of the cantilever beam; specifically, for the cantilever probe hole... l 1. Perform segmented low-pressure water injection detection and calculate the vertical height and length of the cantilever beam. The detection is carried out from the bottom of the hole, which simplifies the segmented low-pressure water injection detection process.

[0040] Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; specifically, refer to Steps 2 and 3 for the cantilever inspection borehole. lIf the borehole inspection imaging in step 2 is clear and the images of fractures at different depths of the cantilever inspection hole clearly identify fractures of different degrees, then borehole inspection is used to verify the low-pressure water injection detection results; otherwise, low-pressure water injection is used to verify the borehole inspection results.

[0041] Example 4 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0042] Table For the serial number rock strata type, ; S2, based on the above parameters, calculate and identify the key layers in each rock stratum; substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0043] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0044] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0045] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0046] Specifically, based on the calculations in S3, the key layers are designated as layer 2 and layer 4, and the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows. Figure 2 As shown in the dashed box in the figure. L 2. L 4 represents the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam. Based on the cantilever profile diagram, three cantilever exploration holes are opened. l 1. l 2. l 3. All three cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway and extend from the adjacent goaf roadway toward the roof of the goaf area. The three cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0047] Step 2: Drill and inspect the cantilever inspection hole and calculate the vertical height and length of the cantilever beam; In step 2, A1, borehole inspection is performed on the opened cantilever exploration hole to obtain fracture images at various depths of the cantilever exploration hole, and surrounding rock information is obtained from the fracture images; A2. Based on the surrounding rock information, the surrounding rock integrity is classified into grades and corresponding integrity indices for each grade. The surrounding rock integrity grades are divided into I to VI, with grade I having the highest integrity index. The number of rock mass joints corresponding to each grade is also introduced. Rock mass joint number The table below shows the correspondence between the number of volumetric joints in rock mass and the degree of borehole fractures, obtained through direct measurement.

[0048] A3. Record the integrity level of the surrounding rock at each depth of each cantilever exploration hole, and calculate the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole.

[0049] In the formula, For the first Vertical height of the cantilever beam of the cantilever exploration hole For the first The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the rock integrity level of the cantilever borehole at various depths, the depth value with the highest rock integrity index was selected, and the cantilever borehole was considered to have reached the required depth. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam; Specifically, such as Figure 3 As shown, this is a cantilevered exploration hole. l 1. A statistical chart of the integrity levels of surrounding rock at different depths, with a gradient of 5m. The chart shows the results at different depths during cantilever exploration. l 1. The rock integrity grade of the exploratory borehole in the 80-85m section with an inclined length decreases significantly from high to low, approaching level I, indicating the highest rock integrity. This suggests that fractures are not well-developed in this section of the borehole, and it is considered a cantilever exploratory borehole. l 1. At a depth of 80-85m, the rock mass is intact; this location marks the starting point of the cantilever. Figure 2 As shown, cantilever exploration hole l 1. Angle with the coal seam ,have

[0050] In the formula Take 80m~85m, and get The elevation ranges from 56.57m to 60.10m. The range is 56.57m to 60.10m.

[0051] Step 3: Perform segmented low-pressure water injection detection on the cantilever inspection hole from top to bottom and calculate the vertical height and length of the cantilever beam; In step 3, B1, starting from the bottom of the hole, the cantilever exploration hole is divided into sections with a length of... of part; B2, for the first section, involves filling the upper and lower sealing holes with water, maintaining a distance between the upper and lower sealing holes. The water injection volume is more than twice the volume of the space between the upper and lower sealing holes; the water injection volume is recorded as... ; B3, open the lower sealing hole. The water inside the sealing hole will flow out naturally due to gravity. Record the outflow volume. ; B4, calculate the water leakage rate and record it as follows: , ; B5. Repeat steps B2-B4, sequentially injecting water into the upper and lower sealing holes of each section, and measuring the water leakage of each section. To conduct statistics; B6. Repeat steps B1 to B5 to calculate the segmented water leakage of each cantilever inspection hole and calculate the vertical height and length of the cantilever corresponding to each cantilever inspection hole.

[0052] In the formula, The first calculation based on water leakage Vertical height of the cantilever beam of the cantilever exploration hole The first calculation based on water leakage The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the statistical analysis of water leakage in each segment of the cantilever borehole, the depth at which the water leakage from the borehole opening to the bottom first increases, then decreases, and finally remains stable is selected. This depth is considered the optimal depth for the cantilever borehole. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

[0053] Specifically, such as Figure 4 As shown, this is a cantilevered exploration hole. l A histogram of segmented water leakage for section 1, showing the leakage at the cantilever inspection borehole. l 1. Divide the borehole into 20 sections, each 5m long, starting from the bottom. For the first section, seal the upper and lower boreholes and fill with water, maintaining a 5m distance between them. The water volume is 50L. Open the lower borehole; the water inside will flow out naturally due to gravity. Record the outflow volume. The amount of water leakage is calculated and recorded as follows: , Starting from the bottom of the hole and moving backward, water was injected into each section in sequence, sealing the top and bottom of the hole. The water leakage of each section was measured. To conduct statistics; from Figure 4 The leakage rate shows that the leakage first increases and then decreases from the orifice to the bottom, finally stabilizing at around 16L. Therefore, it can be determined that the leakage from the cantilevered exploration borehole... l The basic leakage rate is around 16L, meaning the leakage rate is around 16L when the borehole wall is intact. Areas with a leakage rate greater than 16L indicate the presence of fractures. The greater the leakage rate (greater than 16L), the more developed the fractures at that depth. Figure 4 It can be seen that the fractures develop at a depth of about 80m in the inclined hole, and the fractures do not develop beyond that depth. According to the cantilever exploration hole l The segmented water injection leakage rate of 1 is calculated by determining the vertical height and length of the cantilever corresponding to the cantilever inspection hole.

[0054] In the formula Take 80m, ,get It is 56.57m. It is 56.57m.

[0055] Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; specifically, refer to Steps 2 and 3 for the cantilever inspection borehole. l If the borehole inspection imaging in step 2 is clear and the images of fractures at different depths of the cantilever inspection hole clearly identify fractures of different degrees, then borehole inspection is used to verify the low-pressure water injection detection results; otherwise, low-pressure water injection is used to verify the borehole inspection results.

[0056] Example 5 Based on Example 4, in step 2A2, the rock integrity level of the cantilever exploration hole and the corresponding rock integrity index for each level can be further refined into levels I to IX, as shown in the table below. Level I corresponds to the highest rock integrity index.

[0057] In step 3, B1, The value is adjusted according to the required detection accuracy. Adjust the rock integrity grade of the cantilever exploration borehole and the distance between the upper and lower sealing holes. It can control the accuracy of cantilever exploration and meet the accuracy requirements of cantilever exploration under different working conditions.

[0058] Example 6 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0059] Table For the serial number rock strata type, ; S2, based on the above parameters, calculate and identify the key layers in each rock stratum; substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0060] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0061] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0062] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0063] Specifically, based on the calculations in S3, the key layers are designated as layer 2 and layer 4, and the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows. Figure 2 As shown in the dashed box in the figure. L 2. L 4 represents the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam. Based on the cantilever profile diagram, three cantilever exploration holes are opened. l 1. l 2. l 3. All three cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway and extend from the adjacent goaf roadway toward the roof of the goaf area. The three cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0064] Step 2: Drill and inspect the cantilever inspection hole and calculate the vertical height and length of the cantilever beam; In step 2, A1, borehole inspection is performed on the opened cantilever exploration hole to obtain fracture images at various depths of the cantilever exploration hole, and surrounding rock information is obtained from the fracture images; A2. Based on the surrounding rock information, the surrounding rock integrity is classified into grades and corresponding integrity indices for each grade. The surrounding rock integrity grades are divided into I to VI, with grade I having the highest integrity index. The number of rock mass joints corresponding to each grade is also introduced. Rock mass joint number The table below shows the correspondence between the number of volumetric joints in rock mass and the degree of borehole fractures, obtained through direct measurement.

[0065] A3. Record the integrity level of the surrounding rock at each depth of each cantilever exploration hole, and calculate the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole.

[0066] In the formula, For the first Vertical height of the cantilever beam of the cantilever exploration hole For the first The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the rock integrity level of the cantilever borehole at various depths, the depth value with the highest rock integrity index was selected, and the cantilever borehole was considered to have reached the required depth. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam; Specifically, such as Figure 3 As shown, this is a cantilevered exploration hole. l 1. A statistical chart of the integrity levels of surrounding rock at different depths, with a gradient of 5m. The chart shows the results at different depths during cantilever exploration. l 1. The rock integrity grade of the exploratory borehole in the 80-85m section with an inclined length decreases significantly from high to low, approaching level I, indicating the highest rock integrity. This suggests that fractures are not well-developed in this section of the borehole, and it is considered a cantilever exploratory borehole. l 1. At a depth of 80-85m, the rock mass is intact; this location marks the starting point of the cantilever. Figure 2 As shown, cantilever exploration hole l 1. Angle with the coal seam ,have

[0067] In the formula Take 80m~85m, and get The elevation ranges from 56.57m to 60.10m. The range is 56.57m to 60.10m.

[0068] Step 3: Perform segmented low-pressure water injection detection on the cantilever inspection hole from top to bottom and calculate the vertical height and length of the cantilever beam; In step 3, B1, starting from the bottom of the hole, the cantilever exploration hole is divided into sections with a length of... of part; B2, for the first section, involves filling the upper and lower sealing holes with water, maintaining a distance between the upper and lower sealing holes. The water injection volume is more than twice the volume of the space between the upper and lower sealing holes; the water injection volume is recorded as... ; B3, open the lower sealing hole. The water inside the sealing hole will flow out naturally due to gravity. Record the outflow volume. ; B4, calculate the water leakage rate and record it as follows: , ; B5. Repeat steps B2-B4, sequentially injecting water into the upper and lower sealing holes of each section, and measuring the water leakage of each section. To conduct statistics; B6. Repeat steps B1 to B5 to calculate the segmented water leakage of each cantilever inspection hole and calculate the vertical height and length of the cantilever corresponding to each cantilever inspection hole.

[0069] In the formula, The first calculation based on water leakage Vertical height of the cantilever beam of the cantilever exploration hole The first calculation based on water leakage The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the statistical analysis of water leakage in each segment of the cantilever borehole, the depth at which the water leakage from the borehole opening to the bottom first increases, then decreases, and finally remains stable is selected. This depth is considered the optimal depth for the cantilever borehole. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

[0070] Specifically, such as Figure 4 As shown, this is a cantilevered exploration hole. lA histogram of segmented water leakage for section 1, showing the leakage at the cantilever inspection borehole. l 1. Divide the borehole into 20 sections, each 5m long, starting from the bottom. For the first section, seal the upper and lower boreholes and fill with water, maintaining a 5m distance between them. The water volume is 50L. Open the lower borehole; the water inside will flow out naturally due to gravity. Record the outflow volume. The amount of water leakage is calculated and recorded as follows: , Starting from the bottom of the borehole and moving backward, water is injected into each section sequentially, sealing both the top and bottom, until the opening of the cantilever exploration borehole is reached. The water leakage rate of each section is then measured. To conduct statistics; from Figure 4 The leakage rate shows that the leakage first increases and then decreases from the orifice to the bottom, finally stabilizing at around 16L. Therefore, it can be determined that the leakage from the cantilevered exploration borehole... l The basic leakage rate is around 16L, meaning the leakage rate is around 16L when the borehole wall is intact. Areas with a leakage rate greater than 16L indicate the presence of fractures. The greater the leakage rate (greater than 16L), the more developed the fractures at that depth. Figure 4 It can be seen that the fractures develop at a depth of about 80m in the inclined hole, and the fractures do not develop beyond that depth. According to the cantilever exploration hole l The segmented water injection leakage rate of 1 is calculated by determining the vertical height and length of the cantilever corresponding to the cantilever inspection hole.

[0071] In the formula Take 80m, ,get It is 56.57m. It is 56.57m.

[0072] Step 4: Cross-verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; In step 4, C1, extract the surrounding rock integrity information at different depths of each cantilever exploration hole from the borehole inspection in step 2 (A1) and the segmented water injection leakage of each cantilever exploration hole from the low-pressure water injection detection in step 3 (B6). Observe the borehole inspection images of each cantilever exploration hole. If the borehole inspection images are clear and the fracture images at different depths of the cantilever exploration holes clearly identify fractures of different degrees, then use the borehole inspection to verify the low-pressure water injection detection results. and This is the result of the cantilever beam exploration at this stratum; if the borehole inspection imaging is unclear, and it is difficult to identify fractures of different degrees from different depths in the exported images of the cantilever inspection borehole, then low-pressure water injection detection is used to verify the borehole inspection results. and The results of the cantilever beam exploration corresponding to the cantilever exploration hole; In this embodiment, the cantilever inspection hole for borehole exploration is extracted. l 1. Statistical chart of the integrity level of surrounding rock at different depths, such as Figure 3 As shown in the figure, a bar chart of segmented water injection leakage for low-pressure water injection detection is presented, as follows: Figure 4 As shown, the observation cantilever probe hole l The borehole inspection imaging (BEM) of image 1 is clear, and the exported images of fractures at different depths in the cantilever inspection hole clearly distinguish fractures of varying degrees. Therefore, borehole inspection was used to verify the low-pressure water injection detection results. and For cantilever exploration holes l The cantilever beam exploration results corresponding to 1; C2 records the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole at the top of the coal seam.

[0073] Example 7 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0074] Table For the serial number rock strata type, ; S2, Based on the above parameters, calculate and identify the key layers in each rock stratum. Substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0075] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0076] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0077] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0078] Specifically, based on the key layers calculated in S3, which are layer 1, layer 2, and layer 4, the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows. Figure 5 As shown in the dashed box in the figure. L 1. L 2. L 4 represents the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam. Based on the cantilever profile diagram, four cantilever exploration holes are opened. l 1. l 2. l 3. l 4. All four cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway and extend from the adjacent goaf roadway toward the roof of the goaf area. The four cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0079] Step 2: Drill and inspect the cantilever exploration holes and calculate the vertical height and length of the cantilever beam; specifically, for the four cantilever exploration holes drilled in S4 of Step 1... l 1 、l 2 、l 3 、l 4. Conduct borehole inspection and calculate the vertical height and length of the cantilever beam.

[0080] Step 3: Conduct segmented low-pressure water injection detection of the cantilever probe holes from top to bottom and calculate the vertical height and length of the cantilever beam; specifically, for the four cantilever probe holes... l 1 、l 2 、l 3 、l4. Perform segmented low-pressure water injection detection and calculate the vertical height and length of the cantilever beam. The detection is carried out from the bottom of the hole, which simplifies the segmented low-pressure water injection detection process.

[0081] Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; specifically, refer to Steps 2 and 3 for the four cantilever inspection holes. l 1 、l 2 、l 3 、l If the borehole inspection imaging in step 2 is clear and the exported images of fractures at different depths of the cantilever inspection hole clearly identify fractures of different degrees, then borehole inspection is used to verify the low-pressure water injection detection results; otherwise, low-pressure water injection is used to verify the borehole inspection detection results.

[0082] Example 8 The coal mine roof cantilever beam exploration method provided in this embodiment includes: Step 1: Opening a cantilever exploration hole in the adjacent roadway of the longwall face; In step 1, S1, extract the columnar diagrams of several boreholes near the cantilever beam exploration area. Assume that the rock strata within 100m above the coal seam are the 1st, 2nd, 3rd...m...nth layers in sequence. The geological and mechanical parameters of each rock strata are shown in the table below. Schematic table of borehole geomechanical parameters

[0083] Table For the serial number rock strata type, ; S2, Based on the above parameters, calculate and identify the key layers in each rock stratum. Substitute the parameters of each rock stratum into the key layer discrimination formula for calculation, thereby determining the location of each key layer.

[0084] In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata For the first Thickness of rock strata ; When the When the bending subsidence of the lower strata is greater than the bending subsidence of the current stratum, the first... If the rock layers above the strata do not require the underlying rock layers to bear the load, then the following will definitely occur:

[0085] At this time, the The layer is the key layer; similarly, other key layers can be calculated. S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. ,

[0086] In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

[0087] Specifically, based on the key layers calculated in S3, which are layer 1, layer 4, layer 5 (composite layer), layer 8, and layer 10, the outline diagram of the cantilever situation after the adjacent working faces are mined out is drawn as follows: Figure 6 As shown in the dashed box in the figure. L 1. L 4+5 , L 8. L 10 To determine the ultimate caving step distance of the cantilever beams at the top of each key layer of the coal seam, five cantilever exploration holes were drilled based on the cantilever profile diagram. l 1. l 2. l 3. l 4. l 5. All five cantilever exploration holes are perpendicular to the axial direction of the adjacent goaf roadway, extending from the adjacent goaf roadway towards the roof of the goaf area. The five cantilever exploration holes are distributed in a dispersed manner, covering the fracture area of ​​the cantilever in each key layer.

[0088] Step 2: Drill and inspect the cantilever exploration holes and calculate the vertical height and length of the cantilever beam; specifically, for the five cantilever exploration holes drilled in S4 of Step 1... l 1 、l 2 、l 3 、l 4 、l 5. Conduct borehole inspection and calculate the vertical height and length of the cantilever beam.

[0089] Step 3: Conduct segmented low-pressure water injection detection of the cantilever probe holes from top to bottom and calculate the vertical height and length of the cantilever beam; specifically, for 5 cantilever probe holes...l 1 、l 2 、l 3 、l 4 、l 5. Perform segmented low-pressure water injection detection and calculate the vertical height and length of the cantilever beam. The detection is carried out from the bottom of the hole, which simplifies the segmented low-pressure water injection detection process.

[0090] Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam; specifically, refer to Steps 2 and 3 for the five cantilever inspection holes. l 1 、l 2 、l 3 、l 4 、l If the borehole inspection imaging in step 2 is clear and the exported images of fractures at different depths of the cantilever inspection hole clearly identify fractures of different degrees, then borehole inspection is used to verify the low-pressure water injection detection results; otherwise, low-pressure water injection is used to verify the borehole inspection results.

Claims

1. A method for detecting cantilever beams on the roof of a coal mine, characterized in that, include: Step 1: Open a cantilever exploration hole in the adjacent goaf of the longwall face; Step 2: Drill and inspect the cantilever inspection hole and calculate the vertical height and length of the cantilever beam; Step 3: Perform segmented low-pressure water injection detection on the cantilever inspection hole from top to bottom and calculate the vertical height and length of the cantilever beam; Step 4: Verify the borehole inspection and low-pressure water injection detection to determine the vertical height and length of the cantilever beam.

2. The method for detecting cantilever beams in coal mine roofs according to claim 1, characterized in that, In step 1, S1, extract the columnar sections of several boreholes near the cantilever beam exploration area. Assume the rock strata within a 100m range above the coal seam are sequentially designated as layers 1, 2, 3…m…n. Determine the rock strata type and thickness for each layer. , bulk density Elastic modulus Ultimate tensile strength parameter, ; S2, based on the above parameters, calculate and identify the key layers in each rock stratum; S3, Calculate the ultimate collapse step distance of the cantilever beams in each key layer. , In the formula: For the first Thickness of rock strata For the first Ultimate tensile strength of rock strata For the first The load exerted by the layered rock on the first layer of rock; S4, based on the ultimate collapse step distance of the cantilever beams in each key layer calculated in S3. Multiple cantilever exploration holes were opened, all of which are perpendicular to the axial direction of the adjacent roadway and extend from the adjacent roadway toward the roof of the goaf. The multiple cantilever exploration holes are distributed in a dispersed manner to cover the fracture area of ​​the cantilever in each key layer.

3. The method for detecting cantilever beams in coal mine roofs according to claim 2, characterized in that, In step S2 of step 1, the parameters of each rock layer are substituted into the key layer discrimination formula for calculation, thereby determining the location of each key layer. In the formula: For the first The load formed by the layered rock layers on the first layer of rock. For the first The density of the rock strata For the first The elastic modulus of the rock strata ; when At that time, the first The layer is the key layer.

4. The method for detecting cantilever beams on the roof of a coal mine according to claim 3, characterized in that, In step 2, A1, the cantilevered exploration hole is drilled for inspection and exploration to obtain fracture images at various depths of the cantilevered exploration hole, and the surrounding rock information is obtained from the fracture images; A2, classifying the rock integrity level based on surrounding rock information and the corresponding rock integrity index for each level; A3. Record the integrity level of the surrounding rock at each depth of each cantilever exploration hole, and calculate the vertical height and length of the cantilever corresponding to each cantilever exploration hole. In the formula, For the first Vertical height of the cantilever beam of the cantilever exploration hole For the first The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the rock integrity level of the cantilever borehole at various depths, the depth value with the highest rock integrity index was selected, and the cantilever borehole was considered to have reached the required depth. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

5. The method for detecting cantilever beams in coal mine roofs according to claim 4, characterized in that, In step 2, A2, the surrounding rock integrity is classified into grades I to VI, with grade I corresponding to the highest surrounding rock integrity index. The number of volumetric joints corresponding to each grade is then introduced. Rock mass joint number Actual measurements were conducted using direct measurement methods. The corresponding indicators for Grade I are rock mass integrity and the number of joints in the rock mass volume. The borehole walls are smooth or exhibit large-scale ripple marks, with no visible cracks; Grade II corresponds to a relatively intact rock mass and a high number of volumetric joints. The borehole wall is generally intact, with a few closed or slightly open cracks visible, and the crack spacing is >0.5m; the corresponding index for Grade III is moderately intact rock mass, and the number of volumetric joints in the rock mass is [missing information]. A clear network of fractures was visible on the borehole wall, with fracture spacing of 0.2-0.5m. A small number of delaminations or slightly fractured zones were observed, but the main rock mass still maintained its structure. The corresponding index for Grade IV is relatively fractured rock mass, with a high number of volumetric joints. The borehole wall exhibits densely developed fractures with a spacing of 0.1-0.2m, and multiple fracture zones are visible. The rock mass is cut into small to medium-sized blocks with a diameter of 20-30cm. The borehole wall shows slight spalling or unevenness. Grade V corresponds to rock mass fracture and a high number of volumetric joints. The borehole wall is severely fractured, with very dense fissures, spaced <0.1m apart, forming a grid pattern. The fractured zones are connected, and the rock mass is in the form of fragments or gravel. During the drilling process, blocks continuously fall off, and the borehole shape is irregular. The corresponding indicator for Grade VI is borehole collapse. The borehole inspection instrument cannot continue to explore deeper and there is no inspection image.

6. The method for detecting cantilever beams in coal mine roofs according to claim 5, characterized in that, In step 3, B1, starting from the bottom of the hole, the cantilever exploration hole is divided into sections with a length of... of part; B2, for the first section, involves filling the upper and lower sealing holes with water, maintaining a distance between the upper and lower sealing holes. The water injection volume is more than twice the volume of the space between the upper and lower sealing holes; the water injection volume is recorded as... ; B3, open the lower sealing hole. The water inside the sealing hole will flow out naturally due to gravity. Record the outflow volume. ; B4, calculate the water leakage rate and record it as follows: , ; B5. Repeat steps B2-B4, sequentially injecting water into the upper and lower sealing holes of each section, and measuring the water leakage of each section. To conduct statistics; B6. Repeat steps B1 to B5 to calculate the segmented water leakage of each cantilever inspection hole and calculate the vertical height and length of the cantilever corresponding to each cantilever inspection hole. In the formula, The first calculation based on water leakage Vertical height of the cantilever beam of the cantilever exploration hole The first calculation based on water leakage The length of the cantilever beam for each cantilever exploration hole For the first A cantilevered exploration hole at a depth Length and depth of the cantilever exploration hole at that time Based on the statistical analysis of water leakage in each segment of the cantilever borehole, the depth at which the water leakage from the borehole opening to the bottom first increases, then decreases, and finally remains stable is selected. This depth is considered the optimal depth for the cantilever borehole. At that time, the rock mass was intact, and this location was the starting point of the cantilever. For the first The angle between the cantilevered exploration hole and the coal seam.

7. The method for detecting cantilever beams in coal mine roofs according to claim 6, characterized in that, In step 3, B1, .

8. The method for detecting cantilever beams on the roof of a coal mine according to claim 5, characterized in that, In step 4, C1, extract the surrounding rock integrity information at different depths of each cantilever exploration hole from the borehole inspection in step 2 (A1) and the segmented water injection leakage of each cantilever exploration hole from the low-pressure water injection detection in step 3 (B6). Observe the borehole inspection images of each cantilever exploration hole. If the borehole inspection images are clear and the fracture images at different depths of the cantilever exploration holes clearly identify fractures of different degrees, then use the borehole inspection to verify the low-pressure water injection detection results. and This is the result of the cantilever beam exploration at this stratum; if the borehole inspection imaging is unclear, and it is difficult to identify fractures of different degrees from different depths in the exported images of the cantilever inspection borehole, then low-pressure water injection detection is used to verify the borehole inspection results. and The results of the cantilever beam exploration corresponding to the cantilever exploration hole; C2 records the vertical height and length of the cantilever beam corresponding to each cantilever exploration hole at the top of the coal seam.

Images