Method for reducing roadway surrounding rock deformation and damage by implementing roof cutting / bottom cutting pressure relief in high drainage roadway

Abstract

The invention discloses a method for reducing roadway surrounding rock deformation and damage by implementing roof cutting / bottom cutting pressure relief in a high drainage roadway, belongs to the field of coal mining, and aims to solve the problems of roadway wall caving, roof caving, floor heaving and the like caused by the dynamic pressure influence on the roadway due to fracture of a far-field hard rock stratum covering a roadway roof in the stoping process. According to the method, holes are drilled in the high drainage roadway closer to the far-field hard rock stratum, and the nearby far-field hard rock stratum is cut off in cooperation with a blasting fracturing or hydraulic fracturing top-cutting / bottom-cutting pressure relief method, so that the dynamic pressure influence caused by fracture of the far-field hard rock stratum is reduced, and deformation and damage of surrounding rock of a mining roadway are reduced. Top cutting / bottom cutting pressure relief is carried out in the high drainage roadway to cut off the nearby far-field hard rock stratum, the dynamic pressure influence generated when the far-field hard rock stratum is broken is reduced, and surrounding rock deformation damage of the roadway is reduced. And meanwhile, the engineering quantity is small, and the investment is less.

Description

Technical Field

[0001] The invention relates to the field of coal mining, and in particular to a method for implementing top cutting / bottom cutting pressure relief in a high-extraction lane to reduce deformation and damage of lane surrounding rocks. Background Art

[0002] With the increase of underground mining depth and mining intensity, the deformation and damage of the tunnels have become more and more serious. Some coal mine tunnels have mining pressure disturbance phenomena such as roof sinking, bottom bulging, two sides squeezing, irregular falling, and even worse, serious mining dynamic disasters such as impact ground pressure have occurred.

[0003] The reason is that as the working face advances, the far-field hard rock layer overlying the roof is not completely broken and is in a delamination state, which causes a large amount of elastic deformation energy to accumulate inside it, which is quickly transferred to the deep overburden when it breaks. Due to the instantaneous release and transfer of energy, the stress field of the surrounding rock mass changes dramatically, which in turn causes the stress on the tunnel surrounding rock to far exceed its bearing limit, the surrounding rock structure is severely damaged, a large number of joints and fissures are developed, the integrity of the rock mass is reduced, and finally the tunnel surrounding rock is severely deformed. Therefore, it is of great significance to find a method to reduce the deformation and damage of the surrounding rock caused by the breaking of the far-field hard rock layer.

[0004] In terms of tunnel surrounding rock control (such as: CN101749034A, CN101839140A, etc.), in the past, it was mostly handled by increasing the width of the coal pillars and combining strong support measures. The disadvantage is that it wastes coal resources and reduces the excavation rate. Nowadays, in order to save coal resources, it is mostly handled by combining strong support and top cutting (here refers to the rock layer above the mining surface) pressure relief measures without increasing the width of the coal pillars or even reducing the width of the coal pillars. The control effect is good in some areas, but the deformation and damage of the tunnels in some areas are still serious. The reason may be that only the near-field hard rock layer is treated without the far-field hard rock layer.

[0005] At present, the treatment of far-field hard rock formations is mainly carried out by drilling and fracturing in the mining tunnel or fracturing from the ground, which has a series of problems, such as: large amount of cutting work and high project cost.

[0006] Therefore, in order to address the two problems of the dynamic pressure effect on the mining tunnel when the far-field hard rock layer is broken and the large amount of engineering work and high engineering cost when the mining tunnel is cut off to relieve pressure, and based on the distance characteristic of the high-extraction tunnel being 20 to 30 meters above the mining tunnel, this patent proposes a method of drilling holes in the high-extraction tunnel and cutting off the nearby thick hard rock layer to cut off the thick hard rock layer near the high-extraction tunnel, thereby reducing the dynamic pressure effect on the tunnel when the far-field hard rock layer is broken, reducing the deformation and damage of the tunnel surrounding rock, and at the same time reducing the engineering work and saving engineering cost. Summary of the invention

[0007] The invention provides a method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks, aiming to solve the problems of the prior art.

[0008] The specific scheme of this application is as follows:

[0009] A method for implementing top cutting / bottom cutting to relieve pressure in a high-extraction tunnel to reduce deformation and damage of tunnel surrounding rocks, wherein holes are drilled in the roof of the high-extraction tunnel and the top cutting / bottom cutting method is used in conjunction with hydraulic fracturing or blasting fracturing to cut off the nearby far-field hard rock layer, thereby reducing the impact of dynamic pressure caused by the breaking of the far-field hard rock layer and reducing deformation and damage of tunnel surrounding rocks.

[0010] A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks comprises the following steps:

[0011] S1, collect basic data of mining face;

[0012] S2, determine the position of the far-field hard rock layer that affects the deformation of the tunnel surrounding rock and the position relationship between the far-field hard rock layer and the high-extraction tunnel;

[0013] S3, determine the top cutting / bottom cutting method and top cutting / bottom cutting parameters according to the stratigraphic relationship between the high-extraction laneway and the far-field hard rock layer;

[0014] S4, cutting off the far-field hard rock layer above the mining roadway using the top cutting / bottom cutting method in step S3.

[0015] Further, the method for determining the position of the far-field hard rock layer that affects the deformation of the tunnel surrounding rock in step S2 is: determining whether the rock layer on the mining working face is a far-field hard rock layer one by one;

[0016] Among them, any rock layer must meet both the stiffness judgment condition and the strength judgment condition, that is, it is judged as a far-field hard rock layer;

[0017] (1) Stiffness judgment condition: The rock layers from bottom to top of the mining working face are 1st to mth layers. The loads exerted by two adjacent rock layers on the first layer are judged from bottom to top. When the following conditions are met: q 1 | n+1 <q 1 | n When , the n+1th rock layer meets the stiffness judgment condition;

[0018]

[0019] Among them, q 1 | n ,q 1 | n+1 Respectively represent the loads exerted by the nth and n+1th rock layers on the first rock layer (MPa); E irepresents the elastic modulus of the i-th rock layer, GPa; h i represents the thickness of the i-th rock layer, m; γ i Represents the bulk density of the i-th rock layer, KN / m 3 ;

[0020] (2) Strength judgment condition: Determine the breaking distance of two adjacent rock layers from bottom to top, and when it meets the following conditions: L n+1 >L n When , the n+1th rock layer meets the strength judgment condition;

[0021]

[0022] Among them, L n+1 , L n Respectively represent the breaking distance of the n+1th and nth rock layers (m); h n+1 、h n Respectively represent the thickness of the n+1th and nth rock layers (m); σ n+1 , σ n Respectively represent the tensile strength of the n+1th and nth layers of rock (MPa); q n+1 ,q n Vertical load borne by the top surfaces of the n+1 and nth rock layers (MPa).

[0023] Furthermore, the stratigraphic relationship between the high-extraction tunnel and the far-field hard rock layer is as follows: if the far-field hard rock layer is located above the high-extraction tunnel, the method of cutting the top upward to relieve pressure is adopted in the high-extraction tunnel to cut off the overlying far-field hard rock layer; if the far-field hard rock layer is located below the high-extraction tunnel, the method of cutting the bottom downward to relieve pressure is adopted to cut off the underlying far-field hard rock layer.

[0024] Further, the top cutting / bottom cutting parameters in step S3 include the bottom cutting height L 1 , cutting height L 2 , cutting angle α 1 , cutting angle α 2 ( Figure 1 A schematic diagram of the above parameters is given), and the determination method is as follows:

[0025]

[0026] Where: L 1 , L 2 Indicates the cutting bottom and cutting top height; α 1 , α 2 Respectively represent the angle between the bottom cutting and top cutting drilling trajectory lines and the normal direction of the high extraction roadway bottom plate or top plate; h 1 Indicates the cumulative thickness of the rock layer from the bottom plate of the high-drawn roadway to the bottom of the far-field hard rock layer cut; h 2It represents the cumulative thickness of the rock layer between the top plate of the high-extraction tunnel and the top of the hard rock layer in the far field; H represents the vertical distance between the high-extraction tunnel and the return air chute in the projection direction; b represents the horizontal distance between the high-extraction tunnel and the return air chute in the projection direction.

[0027] Furthermore, the top cutting / bottom cutting method is a hydraulic fracturing or explosive fracturing method;

[0028] If the top cutting / bottom cutting method adopts hydraulic fracturing, the top cutting / bottom cutting parameters also include: drilling parameters and hydraulic fracturing parameters; the drilling parameters include: drilling layer position, drilling inclination, drilling azimuth, drilling start position, drilling end position, horizontal distance between drilling holes, drilling length, the relationship between the number of horizontal layers of drilling holes and the thickness of the hard roof to be cut; the hydraulic fracturing parameters include: fracturing initiation pressure, fracturing direction, and fracturing section;

[0029] If the top / bottom cutting method is blasting cutting, the top / bottom cutting parameters also include: blasthole depth, blasthole angle, blasthole diameter, blasthole spacing, sealing depth, etc.

[0030] Furthermore, the horizontal spacing x of the boreholes is calculated using the following formula:

[0031]

[0032] Wherein, R represents the fracturing radius of the roof rock formation; H represents the vertical spacing between the boreholes m.

[0033] Furthermore, the crack initiation pressure P sc The calculation is done using the following formula:

[0034] P sc =2R 0 +R L

[0035] Among them, R 0 Indicates the surrounding rock stress at the crack initiation location; R L Indicates the ultimate tensile strength of rock.

[0036] Furthermore, the basic data of step S1 include: a drilling column chart of the mining face and mechanical parameters of each rock layer.

[0037] Furthermore, it also includes S5, monitoring the deformation of the surrounding rock of the mining tunnel below the high-extraction tunnel, and optimizing the top cutting / bottom cutting parameters according to the deformation of the surrounding rock of the tunnel.

[0038] The beneficial effects of this application are:

[0039] First, the basic concept of the present application is: in order to solve the problem of tunnel spalling, roof collapse, bottom bulging and other phenomena caused by the dynamic pressure of the tunnel caused by the breaking of the far-field hard rock layer overlying the tunnel roof during the mining process, the present application proposes to drill holes in the high-extraction tunnel closer to the far-field hard rock layer and cooperate with blasting fracturing or hydraulic fracturing top / bottom cutting to unload the pressure to cut off the nearby far-field hard rock layer, thereby reducing the dynamic pressure caused by the breaking of the far-field hard rock layer and reducing the deformation and damage of the surrounding rock of the mining tunnel.

[0040] In the high-drawn tunnel, the top / bottom cutting is carried out to relieve pressure and cut off the hard rock layer in the nearby far field, which reduces the dynamic pressure effect generated when the hard rock layer in the far field breaks and reduces the deformation and damage of the surrounding rock of the tunnel. At the same time, the engineering volume is small and the investment is less.

[0041] Second, the present application proposes a method for determining the rock position of a far-field hard rock layer: the rock layer can be determined to be a far-field hard rock layer only when both the stiffness determination condition and the strength determination condition are met simultaneously.

[0042] If the first condition is missing, it means that the rock layer cannot play a leading and controlling role in the deformation of a larger range of rock layers and can only locally affect the adjacent rock layers; if the second condition is missing, even if the rock layer can bear the load, it will break due to insufficient strength and lose its control over the overall structure.

[0043] (1) Stiffness judgment condition: The rock layers from bottom to top of the mining working face are 1st to mth layers. The loads exerted by two adjacent rock layers on the first layer are judged from bottom to top. When the following conditions are met: q 1 | n+1 <q 1 | n When , the n+1th rock layer meets the stiffness judgment condition;

[0044]

[0045] Among them, q 1 | n ,q 1 | n+1 Respectively represent the loads exerted by the nth and n+1th rock layers on the first rock layer (MPa); E i represents the elastic modulus of the i-th rock layer, GPa; h i represents the thickness of the i-th rock layer, m; γ i Represents the bulk density of the i-th rock layer, KN / m 3 ;

[0046] (2) Strength judgment condition: Determine the breaking distance of two adjacent rock layers from bottom to top, and when it meets the following conditions: L n+1 >L n When , the n+1th rock layer meets the strength judgment condition;

[0047]

[0048] Among them, L n+1 , L n Respectively represent the breaking distance of the n+1th and nth rock layers (m); h n+1 、h n Respectively represent the thickness of the n+1th and nth rock layers (m); σ n+1 , σ n Respectively represent the tensile strength of the n+1th and nth layers of rock (MPa); q n+1 ,q n Vertical load borne by the top surfaces of the n+1 and nth rock layers (MPa). BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Graph of corresponding parameters for the top / bottom cutting height formula.

[0050] Figure 2 This is a top view of a mine in Example 1.

[0051] Figure 3 It is a top view II cross-sectional view of a mine in Example 1 (the red frame represents the high extraction lane, and the red oblique line represents the top cut).

[0052] Figure 4 This is the II-II cross-section of a mine in Example 1 (the red oblique line is the top cutting line, and the area below the top cutting line is the high extraction lane).

[0053] Figure 5 This is a top view of a mine in Example 2.

[0054] Figure 6 This is the Ι-Ι cross-section diagram of a certain mine in Example 2 (the red frame represents the high extraction lane, and the red oblique line represents the bottom cutting).

[0055] Figure 7 This is the II-II cross-section diagram of a certain mine in Example 2 (the red oblique line is the bottom line, and the high-extraction lane is above the bottom line).

[0056] Figure 8 This is a top view of a certain mine in Example 3.

[0057] Fig. 9 This is the Ι-Ι cross-section diagram of a certain mine in Example 3 (the red frame represents the high-extraction lane, and the red oblique line represents the cut).

[0058] Fig.10 This is the II-II cross-section of a certain mine in Example 3. DETAILED DESCRIPTION

[0059] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0060] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0061] Example 1: A mine

[0062] A method for implementing top cutting and pressure relief in a high-extraction tunnel to reduce deformation and damage of tunnel surrounding rock is carried out in the following steps.

[0063] Step S1, conduct on-site investigation of the mine engineering geological conditions and test and analyze the geomechanical characteristics of the surrounding rock of the tunnel.

[0064] The surrounding rock geomechanical characteristics include: rock structure and thickness, physical and mechanical properties of surrounding rock, hydrogeological conditions, structural conditions, mining impact, etc. According to the borehole column chart and geological report overview, the coal seam mined by the working face of the mine is 6.2m thick, the high extraction roadway is located directly above the mining working face, with a horizontal projection of 35.4m to the return air chute and a vertical projection of 18.0m to the return air chute. The full rock roadway is 3.0m wide, 2.7m high, and has a cross-sectional area of ​​8.1m. 2 , bottom drum 1.8m, two side deformation 2.0m.

[0065] Step S2, from the comprehensive columnar diagram of the lithology of the top and bottom plates of the coal seams provided by the mine, it can be seen that the top plate rock layers are mainly siltstone, fine-grained sandstone, sandy mudstone and mudstone. According to calculations, there is only one layer of far-field hard rock layer above the mining working face, which is fine-grained sandstone 18.9m away from the top plate of the coal seam, that is, this layer is the main key layer that needs to be fractured. According to the mine's information and the above calculations, it can be seen that the far-field hard rock layer is located above the high-drawn roadway. The specific spatial position relationship is shown in Figure 1 to Figure 3 shown.

[0066] Step S3, the present invention uses a hydraulic fracturing method to perform top / bottom cutting and pressure relief on the far-field hard rock layer of the mine. This step requires determining drilling parameters and hydraulic fracturing top / bottom cutting key parameters.

[0067] The drilling parameters include the drilling layer position, drilling angle, horizontal distance between boreholes, drilling length, the relationship between the number of horizontal layers of drilling and the thickness of the hard roof cut; the hydraulic fracturing parameters include the initiation pressure and fracturing section.

[0068] The cut rock layer (i.e., the far-field hard rock layer) is a fine-grained sandstone with a thickness of 8.2 m. Drill holes are drilled in the top plate along the excavation direction of the high-extraction lane, and the drill holes are arranged in the middle of the fracturing layer;

[0069] The horizontal spacing of the boreholes is calculated as 2 times the fracturing radius, which is 2R, or about 6.0m;

[0070] It is calculated that the cutting height is 37.0m and the cutting angle is 76.0°.

[0071] The cracking pressure can be calculated according to the following formula:

[0072] P sc =2R 0 +R L

[0073] Where: R 0 : surrounding rock stress at the crack initiation position, R L : The ultimate tensile strength of rock, the fracture pressure is 19.0MPa

[0074] Step S4, based on the position of the far-field hard rock layer that affects the surrounding rock of the roadway obtained in the above steps, the stratigraphic relationship between the high-extraction roadway and the far-field hard rock layer, and the top cutting parameters, a hydraulic fracturing top cutting pressure relief technology is implemented in the high-extraction roadway. The technical steps are as follows:

[0075] After determining the drilling parameters and hydraulic fracturing parameters, a hole is drilled every 6.0m.

[0076] After the drilling arrangement is completed, hydraulic fracturing construction is carried out. The hydraulic fracturing construction can be divided into three parts, namely sealing the hole, injecting high-pressure water, and continuously injecting pressure to retain water. The fracturing site adopts single-hole multiple retreat fracturing, and it is set to be fracturing every 6 to 8 meters. The number of fracturing times for a single hole is about 10 to 13 times. When the corresponding part of the far-field hard rock layer above the hole is broken, the fracturing is stopped. The specific hydraulic fracturing process is to connect the hole sealer → drill the hole to connect the water injection pipe → pass the high-pressure water pump → seal the hole and pressurize → inject water for fracturing → stop the pump after the adjacent hole produces water or injects liquid for 30 minutes → unload the pressure → start the second stage of fracturing → cyclic fracturing.

[0077] Step S5, a cross surrounding rock displacement monitoring point is set in the mining tunnel below the high extraction tunnel to monitor the deformation of the tunnel during the entire mining process of the working face, and the results show that the bottom heave is reduced from 1.8m to 0.4m, and the deformation of the two sides is reduced from 2.0m to 0.6m.

[0078] Example 2: A certain mine

[0079] A method for implementing bottom cutting and pressure relief in a high-extraction tunnel to reduce deformation and damage of tunnel surrounding rocks is carried out in the following steps.

[0080] Step S1, conduct on-site investigation of the engineering geology of the mine, and test and analyze the geomechanical characteristics of the surrounding rock of the tunnel, such as the rock structure and thickness, physical and mechanical properties of the surrounding rock, hydrogeological conditions, structural conditions, mining impact, etc. According to the borehole column chart and geological report overview, the working face adopts fully mechanized caving mining, with an average coal thickness of 6.05m (mining height 1.6m, coal caving height 4.45m), and the high extraction tunnel is located directly above the mining working face, with a horizontal projection of 15m with the return air chute and a vertical projection of 15m with the return air chute. The full rock tunnel is 3m wide, 2.7m high, and has a cross-sectional area of ​​8.1m 2 , bottom drum 1.6m, two side deformation 2.2m.

[0081] Step S2, from the comprehensive lithology column chart of the top and bottom plates of the coal seams at the working face provided by the mine, it can be seen that the overlying rock strata are mainly mudstone, limestone, fine-grained sandstone, siltstone and sandy mudstone.

[0082] According to calculations, the far-field hard rock layer above the mining face is limestone 10.2m away from the coal seam roof.

[0083] According to the mine data and the above calculations, it can be known that the far-field hard rock layer is located below the high-drawn roadway. The specific spatial position relationship is shown in Figures 4 to 6 .

[0084] Step S3, the present invention uses blasting to cut the bottom and relieve pressure on the hard rock layer in the far field of the mine. This step requires determining key parameters for blasting and cutting the top (see Table 1 for details).

[0085] It is calculated that the cutting height is 12m and the cutting angle is about 37°.

[0086] Taking into account factors such as blasting effect, construction machinery and drilling workload, the diameter of the blasthole for pre-splitting blasting is determined to be 55mm based on deep hole pre-splitting blasting theory and experience.

[0087] The drilling spacing was determined to be 500mm through on-site tests.

[0088] To ensure safety and blasting effect, the sealing length should be greater than 1 / 3 of the blasting hole length. After charging, a roll of water cannon mud (or water sand bag) is used to extinguish the flame, and the remaining blast holes are all sealed with yellow sand and yellow mud as sealing materials. The sealing length is determined to be 4m.

[0089] Table 1 Summary of blasting design parameters

[0090]

[0091]

[0092] Charge structure:

[0093] The roof pre-splitting blasting uses O-type energy-gathering tubes without coupling and charging. The charging is carried out at the underground operation site, and the current charge is used during the shift. The outer diameter of the O-type energy-gathering tube is 42mm, the inner diameter is 35mm, the length of a single energy-gathering tube is 2m, and each blast hole is equipped with 4 energy-gathering tubes. The pre-splitting blasting uses third-level coal mine emulsion explosives, the length of the explosive roll is 200mm, the diameter is 35mm, and the weight is 200g / roll. Each energy-gathering tube is equipped with 10 rolls of explosive rolls. The charge per meter of the O-type energy-gathering tube is 1.0kg. The coal mine allows the use of 8# detonators (instantaneous or the same level) for detonation.

[0094] Blast hole arrangement:

[0095] The pressure relief blastholes are arranged in the high-draw tunnel, which is 661.2m long. The blastholes are arranged in the top plate of the high-draw tunnel and are arranged in the center. The hole spacing is 500mm, the blasthole diameter is Φ55mm, the depth is 12m, and the blasthole inclination is 37°. According to the hole spacing of 500mm, a total of 1322 blastholes are arranged, numbered 1, 2, 3, 4...1322.

[0096] Detonation method:

[0097] The blasting uses a BF-200 detonator, with group charges and batch blasting. The connection of one batch of guns is carried out in an "overall series" manner, and no more than 6 holes can be detonated each time in the early stage. The blasting sequence is 1, 2, 3 + 4 (empty holes) + 5, 6, 7 + 8 (empty holes) → 9, 10, 11 + 12 (empty holes) + 13, 14, 15 + 16 (empty holes) → ... → 33, 34, 35 + 36 (empty holes) → ... → 1322. The blasting sequence is based on the previous blasting, and the number of blasting holes for one blasting can be optimized and adjusted. According to the advancement of the on-site working face and the speed of blasting construction, the charging blasting method can adopt 3-hole continuous charging (the spacing between blasting holes is 1200mm) and blasting every other hole.

[0098] Step S4, based on the position of the far-field hard rock layer that affects the tunnel surrounding rock, the stratigraphic relationship between the high-extraction tunnel and the far-field hard rock layer, and the cut-off parameters obtained in the previous steps, implement the cut-off pressure relief technology in the high-extraction tunnel to cut off the far-field hard rock layer, reduce the impact on the tunnel surrounding rock, and ensure safe and efficient production of the coal mine.

[0099] Step S5, a cross surrounding rock displacement monitoring point is set in the mining tunnel below the high extraction tunnel to monitor the deformation of the tunnel during the entire mining process of the working face. It is found that the bottom heave is reduced from 1.6m to 0.2m, and the deformation of the two sides is reduced from 2.2m to 0.6m.

[0100] Example 3: A certain mine

[0101] A method for implementing top cutting and bottom cutting to relieve pressure in a high-extraction tunnel to reduce deformation and damage of tunnel surrounding rocks is carried out in the following steps.

[0102] Step S1, based on the on-site investigation of the mine engineering geological conditions, test and analyze the surrounding rock geomechanical characteristics of the tunnel, such as rock structure and thickness, surrounding rock physical and mechanical properties, hydrogeological conditions, structural conditions, mining impact, etc. According to the borehole column chart and geological report overview, the average thickness of the coal seam mined this time is 5.8m (using fully mechanized caving mining, machine mining height of 3.2m, top coal caving height of 2.6m), the high extraction tunnel is located directly above the mining face, with a horizontal projection distance of 30m from the return air chute, and a vertical projection of 26.5m from the return air chute in the main view. The full rock tunnel is 3m wide, 2.7m high, and has a cross-sectional area of ​​8.1m 2 , bottom drum 1.8m, two side deformation 2.2m.

[0103] Step S2, from the 503 borehole column chart provided by the mine, it can be seen that the overlying rock strata of the No. 10 coal seam are mainly fine sandstone, medium sandstone, mudstone, sandy mudstone, limestone, coarse sandstone and siltstone.

[0104] According to calculations, the far-field hard rock layers above the mining face are limestone at 17.2m and limestone at 28.8m from the roof.

[0105] According to the above calculations and the mine data, it can be known that there are two layers of far-field hard rock layer, and the high-extraction roadway is located in the middle of the far-field hard rock layer. The specific spatial position relationship is shown in Figures 7 to 9 shown.

[0106] Step S3, the present invention uses blasting to remove the top and bottom pressure of the hard rock layer in the far field of the mine. This step requires determining the key parameters of blasting and cutting the top (the summary of blasting design parameters is shown in Table 2).

[0107] It is calculated that the top cutting height and bottom cutting height are 10m and 32m respectively, and the corresponding top cutting and bottom cutting angles are approximately 53° and 72° respectively.

[0108] Taking into account factors such as blasting effect, construction machinery and drilling workload, the diameter of the blasthole for pre-splitting blasting is determined to be 65mm based on deep hole pre-splitting blasting theory and experience.

[0109] The drilling spacing was determined to be 500mm through on-site tests.

[0110] To ensure safety and blasting effect, the length of the sealing hole should be greater than 30% of the length of the blasting hole. After charging, a roll of water cannon mud (or water sand bag) is used to extinguish the flame, and the remaining blast holes are all sealed with yellow sand and yellow mud as sealing materials. The length of the sealing mud is 4m when cutting the bottom, and 12m when cutting the top. The sealing hole must be sealed tightly but not too tight, and the detonator foot line must not be damaged.

[0111] Table 2 Summary of blasting design parameters

[0112]

[0113]

[0114] Charge structure:

[0115] The pre-splitting blasting of the roof adopts O-type energy-gathering tubes without coupling and charging. The charging is carried out at the underground operation site, and the current charge is used during the shift. The outer diameter of the O-type energy-gathering tube is 42mm, the inner diameter is 35mm, and the length of a single energy-gathering tube is 2m. Three energy-gathering tubes are installed in each blast hole of the bottom plate, and 10 energy-gathering tubes are installed in each blast hole of the roof. The pre-splitting blasting adopts the third-level coal mine emulsion explosive, the length of the explosive roll is 200mm, the diameter is 35mm, and the weight is 200g / roll. Each energy-gathering tube is equipped with 10 rolls of explosive rolls. The charge per meter of the O-type energy-gathering tube is 1.0kg. The coal mine allows the use of 8# detonators (instantaneous or the same level) for detonation.

[0116] Blast hole arrangement:

[0117] The blast holes for top cutting and pressure relief are arranged in the high-drawing tunnel, which is 1252m long. The blast holes are arranged in the center of the roof of the high-drawing tunnel. The hole spacing is 500mm, the blast hole diameter is Φ65mm, the bottom cutting and top cutting depths are 10m and 32m respectively, and the blast hole inclination angles are 53° and 72°. Calculated based on the hole spacing of 500mm, 1424 blast holes are arranged on the roof and bottom plates respectively, and the numbers are 1, 2, 3, 4...2848 in sequence.

[0118] Detonation method:

[0119] The blasting uses a BF-200 detonator, which is divided into groups and blasted in batches. The connection of one batch of blasting is carried out in the "overall series" mode, and no more than 4 holes can be detonated each time in the early stage. The blasting sequence is 1, 2, 3, 4 → 5 (empty holes) → 6, 7, 8, 9 → 10 (empty holes) → ... → 30 (empty holes) → 31, 32, 33, 34 → ... → 2848. The blasting sequence is based on the previous blasting, and the number of blasting holes for one blasting can be optimized and adjusted. According to the advancement of the on-site working face and the speed of blasting construction, the charging blasting method can adopt 4 holes of continuous charging and blasting every other hole.

[0120] Step S4, based on the position of the far-field hard rock layer that affects the tunnel surrounding rock, the stratigraphic relationship between the high-extraction tunnel and the far-field hard rock layer, and the top cutting parameters obtained in the previous steps, implement the top cutting and pressure relief technology in the high-extraction tunnel to cut off the far-field hard rock layer, reduce the impact on the tunnel surrounding rock, and ensure safe and efficient production of the coal mine.

[0121] Step S5, a cross surrounding rock displacement monitoring point is set in the mining tunnel below the high extraction tunnel to monitor the deformation of the tunnel during the entire mining process of the working face, and the results show that the bottom heave is reduced from 1.8m to 0.5m, and the deformation of the two sides is reduced from 2.2m to 0.8m.

[0122] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the description of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the relevant technical field, if they do not depart from the scope of the technical features of the present invention, can make equivalent embodiments by partial changes or modifications to the technical contents disclosed in the present invention, and they still fall within the scope of the technical features of the present invention without departing from the technical features of the present invention.

Claims

1. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks, characterized in that: A method of drilling holes in the roof of a high-extraction tunnel and using hydraulic fracturing or blasting to cut off the nearby far-field hard rock layer, thereby reducing the impact of dynamic pressure caused by the breaking of the far-field hard rock layer and reducing deformation and damage to the tunnel surrounding rock.

2. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks, characterized in that: The steps include: S1, collect basic data of mining face; S2, determine the position of the far-field hard rock layer that affects the deformation of the tunnel surrounding rock and the position relationship between the far-field hard rock layer and the high-extraction tunnel; S3, determine the top cutting / bottom cutting method and top cutting / bottom cutting parameters according to the stratigraphic relationship between the high-extraction laneway and the far-field hard rock layer; S4, cutting off the far-field hard rock layer above the mining roadway using the top cutting / bottom cutting method in step S3.

3. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that: The method for determining the position of the far-field hard rock layer that affects the deformation of the tunnel surrounding rock in step S2 is: determining whether the rock layers on the mining working face are far-field hard rock layers one by one; Among them, any rock layer must meet both the stiffness judgment condition and the strength judgment condition, that is, it is judged as a far-field hard rock layer; (1) Stiffness judgment condition: The rock layers from bottom to top of the mining working face are 1st to mth layers. The loads exerted by two adjacent rock layers on the 1st layer are judged from bottom to top. When the following conditions are met: q1| n+1 <q1| n When , the n+1th rock layer meets the stiffness judgment condition; Among them, q1| n 、q1| n+1 They represent the loads exerted by the nth and n+1th rock layers on the first rock layer respectively; E i represents the elastic modulus of the i-th rock layer; h i represents the thickness of the i-th rock layer; γ i represents the bulk density of the i-th rock layer; (2) Strength judgment condition: Determine the breaking distance of two adjacent rock layers from bottom to top, and when it meets the following conditions: L n+1 >L n When , the n+1th rock layer meets the strength judgment condition; Among them, L n+1 , L n Respectively represent the breaking distances of the n+1th and nth rock layers; h n+1 、h n Respectively represent the thickness of the n+1th and nth rock layers; σ n+1 , σ n Respectively represent the tensile strength of the n+1th and nth layers of rock; q n+1 ,q n Vertical loads borne by the top surfaces of the n+1 and nth rock layers.

4. The method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that: The stratigraphic relationship between the high-extraction tunnel and the far-field hard rock layer is as follows: if the far-field hard rock layer is located above the high-extraction tunnel, the method of cutting the top upward to relieve pressure is adopted in the high-extraction tunnel to cut off the overlying far-field hard rock layer; if the far-field hard rock layer is located below the high-extraction tunnel, the method of cutting the bottom downward to relieve pressure is adopted to cut off the underlying far-field hard rock layer.

5. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that ； The top cutting / bottom cutting parameters in step S3 include the bottom cutting height L1, the top cutting height L2, the bottom cutting angle α1, and the top cutting angle α2, and the determination method is as follows: Among them: L1 and L2 represent the bottom cutting and top cutting heights; α1 and α2 represent the angles between the bottom cutting and top cutting drilling trajectory lines and the normal direction of the bottom plate or top plate of the high-extraction roadway respectively; h1 represents the cumulative thickness of the rock layer between the bottom plate of the high-extraction roadway and the bottom of the hard rock layer cut in the far field; h2 represents the cumulative thickness of the rock layer between the top plate of the high-extraction roadway and the top of the hard rock layer cut in the far field; H represents the vertical distance between the high-extraction roadway and the return air chute in the projection direction; b represents the horizontal distance between the high-extraction roadway and the return air chute in the projection direction.

6. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that: The top cutting / bottom cutting method is a hydraulic fracturing or explosive fracturing method; If the top / bottom cutting method adopts hydraulic fracturing, the drilling parameters include the drilling layer position, drilling angle, horizontal distance between boreholes, drilling length, the relationship between the number of horizontal layers of the borehole and the thickness of the hard top plate cut, and the hydraulic fracturing parameters include the initiation pressure and the fracturing section. If the top cutting / bottom cutting method is blasting, the top cutting / bottom cutting parameters also include: blast hole depth, blast hole angle, blast hole diameter, blast hole spacing, sealing depth, etc.

7. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 6, characterized in that: The horizontal spacing x of the drilling holes is calculated using the following formula: Wherein, R represents the fracturing radius of the roof rock formation; H represents the vertical spacing between the boreholes m.

8. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 7, characterized in that: Cracking pressure P sc The calculation is done using the following formula: P sc =2R0+R L Where R0 represents the surrounding rock stress at the crack initiation position; R L Indicates the ultimate tensile strength of rock.

9. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that: The basic data of step S1 include: a drilling column chart of the mining face and mechanical parameters of each rock layer.

10. A method for implementing top cutting / bottom cutting to relieve pressure in a high-pressure extraction tunnel to reduce deformation and damage of tunnel surrounding rocks according to claim 2, characterized in that: It also includes S5, which monitors the deformation of the surrounding rock of the mining tunnel below the high-extraction tunnel and optimizes the top cutting / bottom cutting parameters according to the deformation of the surrounding rock of the tunnel.

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