Large-diameter drilling depth design method based on roadway surrounding rock energy storage partition

Abstract

The invention discloses a large-diameter drilling depth design method based on roadway surrounding rock energy storage partitions, and belongs to the technical field of deep-buried roadway rock burst disaster prevention and control. Step B, coal rock mechanical property determination; c, a roadway near-field surrounding rock partition energy storage theory is established; d, numerical simulation calculation; step E, performing energy monitoring; f, constructing a roadway surrounding rock dynamic energy partition evolution model; step G, designing the depth of the large-diameter pressure relief drill hole according to the range of the energy storage area of the surrounding rock of the roadway; and H, checking and optimizing. According to the method, the energy storage area range is analyzed by building the roadway surrounding rock dynamic energy partition evolution model through a numerical simulation means, so that the large-diameter drilling depth design depth in coal body construction is determined, and whether the large-diameter drilling depth design is reasonable or not is determined by judging whether the roadway surrounding rock energy storage area range descends or moves to the deep part or not; therefore, the pressure relief effect of the surrounding rock of the roadway in the energy storage partition is evaluated more accurately.

Description

Technical Field

[0001] The invention belongs to the technical field of prevention and control of rock burst disasters in deep buried tunnels, and in particular relates to a method for designing the depth of a large-diameter borehole based on energy storage zoning of tunnel surrounding rocks. Background Art

[0002] As the mining depth of coal mines increases year by year, the stress environment of the tunnel surrounding rock becomes more complex, and the frequency and intensity of rock burst continue to increase, posing a serious threat to mine production and personnel safety. At present, large-diameter drilling pressure relief is one of the main means of preventing and controlling rock burst in China. Reasonable large-diameter drilling parameters can not only reduce the damage to the tunnel surrounding rock, but also effectively prevent and control the occurrence of rock burst.

[0003] The parameters of large-diameter drilling mainly include diameter, spacing and depth. The diameter of large-diameter drilling is generally 150-200mm, and the spacing is generally 1-3m according to national standards and the degree of impact danger of the working face. The depth is generally summarized according to the thickness of the coal seam and the production practice experience of each mine, generally 15m, 20m, and 25m. However, the occurrence of rock burst is closely related to the mechanical properties of coal and rock mass. There is a lack of corresponding theoretical guidance for simply determining the depth of large-diameter drilling according to the thickness of the coal seam. In fact, rock burst is a phenomenon of coal-rock instability driven by energy. Before the occurrence of rock burst, it will be accompanied by the accumulation of elastic energy areas. This area is generally called the energy storage area. After the rock burst occurs, the stored energy is converted into kinetic energy and released in the form of coal-rock collapse and splash. Therefore, studying the energy storage zoning law of tunnel surrounding rock from the perspective of energy, and then destroying the surrounding rock structure of the energy storage area through large-diameter drilling, reducing the surrounding rock energy storage limit, can effectively prevent the occurrence of rock burst.

[0004] For conventional fixed large-diameter drilling depth, under different tunnel surrounding rock conditions, there are often serious deformation and damage of tunnel surrounding rock and failure of anchor support structure caused by excessive pressure unloading, as well as impact ground pressure caused by accumulation of elastic energy of coal body due to insufficient pressure unloading. It is very necessary to unload the tunnel surrounding rock reasonably and appropriately. Therefore, a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning is urgently needed. Summary of the invention

[0005] The purpose of the present invention is to improve the pressure relief effect of large-diameter drilling and avoid the problem of insufficient or excessive pressure relief of coal seams caused by the empirical design of large-diameter drilling depth in the tunnel, and to propose a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning.

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

[0007] A method for designing the depth of a large-diameter borehole based on the energy storage zoning of surrounding rock in a tunnel comprises the following steps:

[0008] Step A. Collect on-site data;

[0009] Step B. Determination of mechanical properties of coal and rock;

[0010] Step C. Energy storage theory of surrounding rock partitions in the near-field of the tunnel;

[0011] Step D. numerical simulation calculation;

[0012] Step E. Perform energy monitoring;

[0013] Step F. constructing a dynamic energy partition evolution model of tunnel surrounding rock;

[0014] Step G. designing the depth of the large-diameter pressure relief drilling hole according to the range of the surrounding rock energy storage area of ​​the tunnel;

[0015] Step H. Inspection and optimization.

[0016] As a further description of the above technical solution: the field data mainly include: drilling column chart, ground stress distribution law research report, etc., which are used to determine the type and thickness of coal and rock layers, the stress environment of tunnel surrounding rocks, etc.; by collecting the above data, we can have a preliminary understanding of the field situation and provide data support for the design of parameters such as numerical model size and boundary conditions.

[0017] As a further description of the above technical solution: In the step B, drilling and sampling are carried out in the research target area, and the cores taken out on site are processed into standard test pieces. By conducting indoor uniaxial compression tests, Brazilian splitting tests, triaxial tests, etc., the mechanical properties of the coal rock formations are obtained, which mainly include bulk modulus, cohesion, internal friction angle, tensile strength, etc., to provide data support for the design of numerical model parameters.

[0018] As a further description of the above technical solution: in the step C, during the occurrence of rock burst, the shallow coal bodies on both sides of the tunnel belong to the energy release zone, and will eventually be destroyed due to stress overload or energy overlimit; the roof on both sides of the tunnel and the coal bodies in the deep elastic zone belong to the energy storage zone. At the moment of shallow coal body destruction, the lateral restraint force below the roof and the deep coal body suddenly decreases, the compressed roof recovers its deformation, and the constrained coal body expands laterally, both of which release strain energy to the shallow coal body, which is converted into dissipated energy for crack expansion in the shallow coal body and kinetic energy of coal blocks ejected; therefore, the "energy release zone + energy storage zone" jointly affect whether rock burst occurs and the severity of its occurrence.

[0019] As a further description of the above technical solution: in the step D, firstly, since there will be initial stress inside the rock mass in the natural state without being disturbed by artificial excavation, ground stress should be applied to the model to make the model stress condition closer to the actual situation; secondly, the field data collected in the preliminary preparation step A and the parameters measured by the coal rock mechanics test in step B are assigned to the model; finally, the working face mining activities are simulated.

[0020] As a further description of the above technical solution: In the step E, first, the energy calculation program is written using the relevant language in the numerical simulation software such as FLAC3D, and the energy density U of the model unit i is calculated as follows:

[0021]

[0022] In the formula, σ1, σ2, σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress of unit i, respectively, in MPa; μ is the Poisson's ratio of the unit; E is the elastic modulus of the unit, in GPa. The energy density U of the surrounding rock of the tunnel is calculated using numerical simulation software; if the numerical simulation software has this function, there is no need to program and proceed directly to the next step;

[0023] Secondly, energy measurement lines are arranged in the constructed numerical model. Considering that rock burst generally occurs 300m behind the tunnel excavation and 500m in front of the stope, the measurement lines are generally arranged on both sides and the top and bottom plates of the tunnel. The specific number and spacing of measurement lines are determined according to the model and the complexity of the actual engineering stress, such as Figure 1 As shown; Finally, according to the numerical simulation results, the data on the energy measurement lines arranged at different positions in each tunnel are sorted and output, and the elastic energy density zoning curve of the tunnel surrounding rock is drawn through data analysis software such as Origin, as shown in Figure 2 As shown in the figure, the area with elastic energy density lower than E is defined as the energy release area, and the area with elastic energy density greater than 1.3E is defined as the energy storage area, thus obtaining the distribution characteristics of elastic energy density of tunnel surrounding rock during working face mining.

[0024] As a further description of the above technical solution: In the step F, based on the data analysis results and the output elastic energy density partition curve, establish Figure 3 The energy storage model of tunnel near-field surrounding rock zoning is shown in the figure. According to this model, the tunnel surrounding rock can be divided into energy release zone and energy storage zone. Before tunnel excavation, the roof and floor plates close to the tunnel accumulate elastic energy under the initial ground stress. After tunnel excavation, the elastic energy stored in the roof and floor plates is released to form an energy release zone. Since coal seams are easier to store elastic energy than rock seams, an energy storage zone appears in front of the tunnel. For the coal body on the side of the tunnel, the elastic energy stored in the coal body close to the tunnel is released to form an energy release zone. The coal body within a certain range from the tunnel and the front of the tunnel form an energy storage zone, such as Figure 3shown.

[0025] As a further description of the above technical solution: in the step G, first, the design of the depth of the large-diameter pressure relief drilling hole should be in line with the actual production. According to the thickness of the coal seam and the production practice experience of the mine, when the coal seam mining thickness is less than 3.5m, the drilling depth is generally not less than 15m; when the coal seam mining thickness is 3.5m to 8m, the drilling depth is generally not less than 20m; when the coal seam mining thickness is greater than 8m, the drilling depth is generally not less than 25m;

[0026] Table 1 Large diameter drilling depth based on coal seam thickness

[0027] Coal thickness / m ≤3.5 3.5～8 ≥8 Hole depth / m 15 20 25

[0028] Therefore, the drilling design depth of the present invention does not exceed the range of 10-20m when the coal seam mining thickness is less than 3.5m; the drilling depth range does not exceed 15-25m when the coal seam mining thickness is 3.5m to 8m; the drilling depth range does not exceed 20-30m when the coal seam mining thickness is greater than 8m;

[0029] Secondly, the fundamental basis for the design of drilling depth is the scope of the tunnel surrounding rock energy storage area. In principle, the design depth should exceed the scope of the tunnel surrounding rock energy storage area. Figure 4 The design guidance of large-diameter pressure relief borehole depth based on the energy storage zoning of tunnel surrounding rock is given, such as Figure 4 As shown in (a), during tunnel excavation, the energy storage area is roughly distributed in a "U" shape on both sides and the front of the tunnel. Therefore, the arrangement of large-diameter boreholes should exceed the energy storage area; Figure 4 As shown in (b), during the mining of the working face, the energy storage area is roughly distributed in a strip shape at a certain distance in front of the mining working face, and large-diameter drill holes are arranged on both sides of the tunnel, and the depth exceeds the range of the energy storage area.

[0030] As a further description of the above technical solution: in the step H, first, the geological structure ahead is detected by advance drilling; if special geological structures such as faults and folds are encountered, whether it is a normal fault or a reverse fault, the mining disturbance and the stress superposition generated by it are one of the necessary conditions for the occurrence of fault impact ground pressure; therefore, when the borehole is close to geological structures such as coal seam faults, the borehole depth should be no less than 3.5 times the coal seam thickness, and the borehole depth needs to be appropriately increased on the basis of the original borehole depth; secondly, by using the numerical simulation method, combined with the actual situation on site, such as the influence of goafs and coal pillars, additional boreholes are added on the basis of the original model, and the designed large-diameter pressure relief borehole depth parameters are substituted into the tunnel surrounding rock energy zoning evolution model, and the data is output to observe whether its energy change conforms to the decline in the energy storage area or transfers to the deep part; finally, the on-site inspection method is adopted to observe the mine pressure in the tunnel and use a borehole stress meter or a drill cuttings method to check whether the designed large-diameter borehole depth has an ideal pressure relief effect;

[0031] The above two methods are used to judge whether the design of the large-diameter pressure relief drilling depth is reasonable. If the range of the tunnel surrounding rock energy storage area decreases or moves to a deeper level, it is reasonable and large-diameter drilling can continue to be carried out on-site; if the range does not decrease or move, it is unreasonable and further optimization of the large-diameter drilling depth design is required and it must pass the inspection again before on-site construction can be carried out.

[0032] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0033] 1. In the present invention, numerical simulation is used to analyze the range of the energy storage area by constructing a dynamic energy zoning evolution model of the tunnel surrounding rock, so as to determine the design depth of the large-diameter drilling hole in coal body construction. By judging whether the range of the tunnel surrounding rock energy storage area decreases or moves deeper, it is determined whether the design of the large-diameter drilling depth is reasonable. Therefore, the evaluation of the pressure relief effect of the tunnel surrounding rock in the energy storage zone is more accurate.

[0034] 2. In the present invention, the actual coal seam thickness and on-site construction experience are taken into consideration, and the large-diameter drilling depth design can meet the on-site construction conditions and is more in line with the actual on-site conditions, thus avoiding the situation where on-site construction cannot be carried out due to the deviation of theoretical calculation results from the actual conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic flow chart of a method for designing the depth of a large-diameter borehole based on energy storage zoning of surrounding rock in a tunnel proposed by the present invention;

[0036] Figure 2 A schematic diagram of survey line arrangement for a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning proposed by the present invention;

[0037] Figure 3It is an elastic energy density zoning curve diagram of a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning proposed by the present invention;

[0038] Figure 4 A schematic diagram of a dynamic energy zoning evolution model of tunnel surrounding rock based on a large-diameter drilling depth design method for tunnel surrounding rock energy storage zoning proposed by the present invention;

[0039] Figure 5 A large-diameter pressure relief drilling depth design diagram of a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning proposed by the present invention;

[0040] Figure 6 A numerical model of a 2307 excavation working face based on a large-diameter drilling depth design method for tunnel surrounding rock energy storage zoning proposed by the present invention;

[0041] Figure 7 The elastic energy density zoning curve of the two sides of the tunnel for the large-diameter drilling depth design method based on the tunnel surrounding rock energy storage zoning proposed by the present invention;

[0042] Figure 8 A schematic diagram of a dynamic energy zoning evolution model of a tunnel surrounding rock according to a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning proposed by the present invention;

[0043] Fig. 9 The present invention provides a large-diameter pressure relief drilling depth design diagram for a certain tunnel, based on a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Combination Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 8 As shown, a specific implementation method of a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning provided by the present invention is described.

[0046] The existing large-diameter drilling depth is usually constructed at a uniform depth based on engineering experience, and the depth will be densely arranged in different impact risk areas to reduce the possibility of rock burst. However, there is little research on the large-diameter drilling depth under different tunnel surrounding rock conditions. For this problem, the dynamic evolution process of tunnel surrounding rock energy is studied by using theoretical analysis and numerical simulation methods, and the evolution law of tunnel surrounding rock energy zoning is analyzed. Then, a dynamic energy zoning evolution model of tunnel surrounding rock is constructed. Based on the energy zoning of tunnel surrounding rock, the large-diameter anti-bumping drilling depth is designed, and the practicality of this design method is verified by combining numerical simulation and field testing methods. The results show that: (1) The pressure relief effect of the large-diameter drilling depth designed based on coal seam thickness and engineering experience is quite different. In fact, rock burst is an energy-driven coal rock state instability phenomenon. Therefore, it is more universal to study the large-diameter drilling depth from the energy perspective and in combination with engineering practice. (2) With the effective "destruction" of the large-diameter drilling on the energy storage area, the range of the tunnel surrounding rock energy storage area gradually decreases or moves to the depth, resulting in a decrease in the release of elastic energy stored in the coal body energy storage area, achieving the expected pressure relief effect. (3) The rationality of the designed large-diameter drilling depth is tested by numerical simulation and field testing to achieve better pressure relief effect.

[0047] Through field practice, under normal circumstances, the depth of large-diameter drilling in construction is mostly: when the coal seam mining thickness is less than 3.5m, the drilling depth is generally not less than 15m, and 15m is taken; when the coal seam mining thickness is 3.5m-8m, the drilling depth is generally not less than 20m, and 20m is taken; when the coal seam mining thickness is greater than 8m, the drilling depth is generally not less than 25m, and 25m is taken. However, rock burst is an energy-driven coal rock state instability phenomenon. Before the rock burst occurs, it will inevitably be accompanied by the accumulation of elastic energy areas. When the elastic energy accumulation exceeds the energy storage limit of the surrounding rock, the stored energy is converted into kinetic energy and released in the form of coal rock collapse and splashing. In order to solve this problem, the present invention provides a large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning.

[0048] Taking the actual working face of a mine as an example, the design method of large-diameter drilling depth based on tunnel surrounding rock energy storage zoning is further explained. The specific steps include:

[0049] Step A. Collect field data. The 2307 working face of a certain mine is arranged in the 3 coal seams, with an average coal thickness of 3.5m and an average working face burial depth of 815m. The working face adopts a double tunnel layout, with the track chute connected to the track tunnel of the west wing of the second mining area, with a total length of 538.3m, and the belt chute connected to the belt tunnel of the west wing of the second mining area, with a total length of 503.9m, and the working face cut length is 200.1m. The northeast sides of the working face are solid coal areas, the south side is the west wing of the second mining area, and the west side is the 1308 working face of the first mining area. The direct top of the coal seam is mudstone, the basic top is siltstone, the direct bottom is mudstone, and the basic bottom is fine sandstone. Overall, the 2307 working face is buried deep, which has the basic conditions for rock burst. In addition, the track chute is close to the goaf, and is greatly affected by the lateral support pressure of the goaf. There is a certain risk of rock burst during tunnel excavation. Collect the plan view, bar graph, and research report on the distribution of geostress of the 2307 working face, organize and summarize the required information such as rock formation type, rock formation thickness, and geostress distribution law, and provide data support for the design of parameters such as numerical model size and boundary conditions.

[0050] Step B. Determination of mechanical properties of coal and rock. Drill holes and take samples at the 2307 working face. The cores taken out on site are processed into standard specimens. The mechanical properties of the relevant coal and rock formations are obtained by conducting core mechanical tests. The specific parameters are shown in the following table.

[0051] Table 2 Parameters of coal and rock strata model of 2307 working face

[0052]

[0053] Step C. Energy storage theory of surrounding rock zoning in the near field of the roadway. Based on the theory that the shallow coal bodies on both sides of the roadway release energy, and the roof and deep elastic zone coal bodies on both sides of the roadway store energy, the relevant parameters obtained in steps A and B are input into the numerical model for simulation.

[0054] Step D. Numerical simulation calculation. According to the design plan of the 2307 working face, a FLAC3D numerical model is established, and ground stress is applied to the numerical model and parameters are assigned. The model size is X×Y×Z=600m×800m×62m. The model includes the 2307 working face and part of the goaf of the adjacent 1306, 1308, and 1310 working faces. The model height extends from 15m below the coal seam to 47m above the coal seam, including the main rock strata of the coal seam and its roof and floor, such as Figure 5 Table 2 shows the mechanical parameters of the coal-rock layer of the model. The displacement boundary conditions are used for the front, back, left, right and bottom surfaces of the model, and the stress boundary conditions are used for the top surface of the model. According to the buried depth of the coal-rock layer, it is converted to 19.2MPa. First, the 1308 working face is excavated, and the 2307 working face tunnel is excavated after 2000 time steps.

[0055] Step E. Perform energy monitoring. First, use the fish language in FLAC3D to write an energy calculation program. The energy density U of the model unit i is calculated as follows:

[0056]

[0057] Where σ1, σ2, σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress of unit i, respectively, in MPa; μ is the Poisson's ratio of the unit; E is the elastic modulus of the unit, in GPa. The energy density U of the tunnel surrounding rock is calculated using numerical simulation software.

[0058] Secondly, energy measurement lines were arranged 10m behind the head of the track chute of the 2307 working face and 10m behind the head of the belt chute of the 2307 working face. In order to quantitatively analyze the evolution law of the elastic energy density of the surrounding rock during the excavation of the track chute and the belt chute, the model energy density data was extracted. The elastic energy density zoning curve of the tunnel surrounding rock was drawn using the Origin data analysis software, as shown in Figure 6 As shown, the changing trend of elastic energy density of the energy measurement line is analyzed.

[0059] Step F: Construct the dynamic energy partition evolution model of tunnel surrounding rock. Figure 7 The energy storage model of the tunnel near-field surrounding rock zoning is shown. According to this model, the tunnel surrounding rock can be divided into an energy release zone and an energy storage zone. The tunnel height H is 4m and the width L is 5m. Before the tunnel excavation, the top and bottom plates close to the tunnel accumulate elastic energy under the initial ground stress. After the tunnel excavation, the elastic energy stored in the top and bottom plates is released, and an energy release zone 0-5H (0-20m) is formed between the top and bottom plates of the tunnel and the two sides of the coal body; the rock layer far from the tunnel (>20m) is less affected by the excavation disturbance, and the energy change is not obvious; because the coal seam is easier to store elastic energy than the rock layer, an energy storage zone appears about 15-20m in front of the tunnel head. For the tunnel side coal body, the elastic energy stored in the coal body close to the tunnel is released, forming an energy release zone (0-5m); and the area about 10-15m away from the two sides and the coal body about 15-20m away from the head form an energy storage zone.

[0060] Step G. Design the depth of the large-diameter pressure relief drilling hole according to the range of the tunnel surrounding rock energy storage area. First, the design of the depth of the large-diameter pressure relief drilling hole should be in line with the actual production. Since the average coal thickness of the 2307 working face is 3.5m, the design range of the depth of the large-diameter pressure relief drilling hole should be within the range of 10-25m.

[0061] Secondly, the design basis of large diameter drilling depth is that the design depth should exceed the range of the tunnel surrounding rock energy storage area. Therefore, considering the range of the energy storage area and the coal seam thickness of 3.5m, in order to prevent drilling into the rock layer, the drilling depth of the two sides of the solid coal is determined to be 15m, and the head drilling depth is 20m. Figure 8 shown.

[0062] Step H. Inspection and optimization. Through on-site inspection, after adopting the large-diameter drilling depth decompression and emergency relief measures designed in step F, no microseismic warning events occurred during the track tunnel excavation. Overall, the use of this large-diameter drilling depth for decompression can effectively "destroy" the surrounding rock energy storage area, and the 2307 working face has achieved safe excavation and penetration. No obvious dynamic phenomenon occurred during the excavation process, which indirectly verified the rationality of the large-diameter decompression drilling depth design, so the on-site construction can continue.

[0063] The large-diameter drilling depth design method based on tunnel surrounding rock energy storage zoning is obtained through theoretical calculation, numerical simulation, subsequent graphics drawing, and data calculation. Under the condition of fully considering the influence of coal seam thickness, a reasonable and effective large-diameter pressure relief drilling depth is obtained, avoiding the problem of insufficient pressure relief caused by large-diameter drilling parameters designed by engineering experience. This method provides reference and guidance for the prevention and control of rock burst problems, and further ensures the safe production of coal mines.

[0064] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning, characterized in that: The following steps are involved: Step A. Collect on-site data; Step B. Determination of mechanical properties of coal and rock; Step C. Energy storage theory of surrounding rock partitions in the near-field of the tunnel; Step D. numerical simulation calculation; Step E. Perform energy monitoring; Step F. constructing a dynamic energy partition evolution model of tunnel surrounding rock; Step G. designing the depth of the large-diameter pressure relief drilling hole according to the range of the surrounding rock energy storage area of ​​the tunnel; Step H. Inspection and optimization.

2. A method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1, characterized in that: The field data mainly include: drilling column chart, ground stress distribution law research report, which are used to determine the type and thickness of coal and rock layers, and the stress environment of tunnel surrounding rocks; by collecting the above data, we can have a preliminary understanding of the field situation and provide data support for the design of numerical model size and boundary condition parameters.

3. A method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1, characterized in that: In step B, drilling and sampling are carried out in the target area, and the cores taken out on site are processed into standard specimens. By carrying out indoor uniaxial compression tests, Brazilian splitting tests, and triaxial tests, the mechanical properties of the coal strata are obtained, which mainly include bulk modulus, cohesion, internal friction angle, and tensile strength, providing data support for the design of numerical model parameters.

4. A method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1, characterized in that: In step C, during the occurrence of rock burst, the shallow coal bodies on both sides of the tunnel belong to the energy release zone, and will eventually be destroyed due to stress overload or energy overlimit; the roof on both sides of the tunnel and the coal bodies in the deep elastic zone belong to the energy storage zone. At the moment of shallow coal body destruction, the lateral restraint force below the roof and the deep coal body suddenly decreases, the compressed roof recovers its deformation, and the restrained coal body expands laterally, both of which release strain energy to the shallow coal body, which is converted into dissipated energy for crack expansion in the shallow coal body and kinetic energy of coal blocks ejected; therefore, the "energy release zone + energy storage zone" jointly affect whether rock burst occurs and the severity of its occurrence.

5. The method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1 is characterized in that: In the step D, firstly, since there will be initial stress inside the rock mass in the natural state without being disturbed by artificial excavation, ground stress should be applied to the model so that the stress condition of the model is closer to the actual situation; Secondly, the field data collected in the preliminary preparation step A and the parameters measured by the coal and rock mechanics test in step B are assigned to the model; finally, the mining activities of the working face are simulated.

6. A method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1, characterized in that: In step E, first, the energy calculation program is written using the relevant language in the FLAC3D numerical simulation software, and the energy density U of the model unit i is calculated as follows: In the formula, σ1, σ2, σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress of unit i, respectively, in MPa; μ is the Poisson's ratio of the unit; E is the elastic modulus of the unit, in GPa. The energy density U of the surrounding rock of the tunnel is calculated using numerical simulation software; if the numerical simulation software has this function, there is no need to program and proceed directly to the next step; Secondly, energy measurement lines are arranged in the constructed numerical model. Considering that rock burst generally occurs 300m behind the tunnel excavation head and 500m in front of the mining area, the measurement lines are generally arranged on both sides and the top and bottom plates of the tunnel. The specific number and spacing of measurement lines are determined according to the complexity of the model and actual engineering stress, as shown in Figure 1. Finally, according to the numerical simulation results, the data on the energy measurement lines arranged at different positions in each tunnel are sorted and output, and the elastic energy density zoning curve of the tunnel surrounding rock is drawn by Origin data analysis software, as shown in Figure 2. In the figure, the area with elastic energy density lower than E is defined as the energy release area, and the area greater than 1.3E is the energy storage area, so as to obtain the distribution characteristics of the elastic energy density of the tunnel surrounding rock during the mining of the working face.

7. The method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1 is characterized in that: In the step F, based on the data analysis results and the output elastic energy density zoning curve, the tunnel near-field surrounding rock zoning energy storage model shown in Figure 3 is established; according to this model, the tunnel surrounding rock can be divided into an energy release zone and an energy storage zone; before tunnel excavation, the top and bottom plates closer to the tunnel accumulate elastic energy under the action of initial ground stress, and after tunnel excavation, the elastic energy stored in the top and bottom plates is released to form an energy release zone; since coal seams are easier to store elastic energy than rock strata, an energy storage zone appears in front of the tunnel head; for the coal body on the side of the tunnel, the elastic energy stored in the coal body closer to the tunnel is released to form an energy release zone; and the coal body within a certain range from the tunnel and in front of the tunnel head form an energy storage zone, as shown in Figure 3.

8. The method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1 is characterized in that: In step G, first, the design of the depth of the large-diameter pressure relief drilling hole must be in accordance with actual production; Secondly, the fundamental basis for drilling depth design is the scope of the tunnel surrounding rock energy storage area. In principle, the design depth should exceed the scope of the tunnel surrounding rock energy storage area.

9. The method for designing the depth of large-diameter drilling holes based on tunnel surrounding rock energy storage zoning according to claim 1 is characterized in that: In the step H, first, the geological structure ahead is detected by advance drilling; if a special geological structure such as a fault or a fold is encountered, whether it is a normal fault or a reverse fault, the mining disturbance and the stress superposition generated by it are one of the necessary conditions for the occurrence of fault impact ground pressure; therefore, when the borehole is close to the coal seam fault geological structure, the borehole depth should be no less than 3.5 times the coal seam thickness, and the borehole depth needs to be appropriately increased on the basis of the original borehole depth; secondly, by using the numerical simulation method, combined with the actual situation on site, such as the influence of goaf and coal pillars, additional boreholes are added on the basis of the original model, and the designed large-diameter pressure relief borehole depth parameters are substituted into the tunnel surrounding rock energy zoning evolution model, and the data is output to observe whether its energy change conforms to the decline in the energy storage area or the transfer to the deep; finally, the on-site inspection method is adopted to observe the mine pressure in the tunnel and use a borehole stress meter or a drill cuttings method to check whether the designed large-diameter borehole depth has an ideal pressure relief effect.

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