A method for determining construction parameters and early warning critical values of drilling cuttings method for rock burst coal seams

Abstract

The present invention provides a method for determining construction parameters and critical values of early warning for a rock burst coal seam drilling method, which relates to the field of mine safety technology. The method first obtains the rock mechanical parameters of the coal body in the surrounding rock of the roadway to be drilled for early warning, and calculates the critical parameters for the occurrence of rock burst in the roadway to be drilled for early warning; then, based on the calculated critical softening zone radius for the occurrence of rock burst in the roadway, the depth of the drilling hole for the drilling method construction in the surrounding rock of the roadway to be monitored and warned is determined; then, the critical mining stress index engineering value for the actual occurrence of rock burst in the same coal seam roadway where the roadway to be warned is determined; finally, the critical value of the graded early warning index for the maximum single-meter amount of drilled chips in the roadway to be drilled for early warning and the critical value of the graded early warning index for the depth of the surrounding rock where the maximum single-meter amount of drilled chips appears in the drill hole of the roadway to be drilled for early warning are determined, and the hazard level of the roadway to be drilled for early warning is determined. This method makes the construction design of the drilling method and the determination of the critical parameter values for early warning more scientific, more universal, and applicable to coal rocks of different strengths.

Description

Technical Field

[0001] The present invention relates to the field of mine safety technology, and in particular to a method for determining construction parameters and early warning critical values of a rock burst coal seam drilling method. Background Art

[0002] In recent years, rock burst accidents have occurred frequently, causing a large number of damages to tunnels and equipment, casualties, threatening the lives of underground workers, and seriously restricting economic development. More than 95% of rock bursts in my country occur in tunnels. Monitoring and early warning of rock bursts are the first prerequisite for rock burst control. Among them, the drill cuttings method has simple equipment, intuitive monitoring results of drill cuttings volume, and is easy to operate and identify on-site. It is an important method for monitoring and early warning of rock burst hazards. The drill cuttings method is a method of using a pneumatic drill or an electric drill to drill small diameter holes (42 to 50 mm in diameter) in the coal seam, and identifying rock burst hazards based on the amount of coal powder discharged at different depths, its changing pattern, and related dynamic effects.

[0003] Determining the construction depth of coal drilling and the critical value of coal dust discharge at different depths to warn of rock burst are key to determining when and where to prevent and control rock burst. Currently, the critical value for warning of drill cuttings is determined by multiplying the normal amount of coal dust, unaffected by mining stress, by the drill dust rate index. However, in recent years, the increasing occurrence of soft coal and high-moisture coal in deep mining projects has led to inappropriately defined critical values for drill cuttings, resulting in frequent over-warnings and significantly reduced production efficiency.

[0004] The main problems currently exist are as follows: 1) When using the drill dust rate index and normal drill cuttings volume to determine the critical warning value, the drill dust rate index is often artificially and mechanically set to a value (1.5 to 3.0). This value is not quantitatively correlated with the brittleness and strength properties of the coal material, the drill hole size, and other factors, resulting in low universality and accuracy of the critical value determination method. 2) The determination of the critical warning value relies entirely on experimental testing and engineering experience. The index value is not correlated with the critical stress for rock burst, and there is a lack of criteria for predicting rock burst hazards. 3) The current national standard proposes that the drilling depth be 3 to 4 times the roadway height. This depth determination lacks theoretical basis, and insufficient drilling depth will not fully reflect the stress distribution in the elastic zone of the roadway surrounding rock. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for determining the construction parameters and warning critical values of the drilling method for rock burst coal seams in response to the deficiencies of the above-mentioned existing technologies, which is used to determine the construction parameters and warning critical values of the drilling method for rock burst coal seams.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for determining construction parameters and warning critical values of rock burst coal seam drilling method, comprising the following steps:

[0007] Step 1: Obtain rock mechanical parameters of the coal body in the surrounding rock of the roadway to be drilled; the rock mechanical parameters include uniaxial compressive strength σ c , elastic modulus E, impact modulus index K = λ1 / E, residual degradation modulus λ2 and residual strength coefficient ξ; where λ1 is the post-peak softening modulus;

[0008] Step 2: Calculate the critical crushing zone radius ρ for rock burst in the tunnel to be drilled. fcr , critical softening zone radius ρ cr , critical softening depth of surrounding rock L pcr , critical ground stress P cr And the optimized critical mining peak stress P for the occurrence of rock burst in the roadway to be warned mcr * ;

[0009] Step 3: Determine the depth L of the drilling hole in the surrounding rock of the monitored warning tunnel. drill-bits ;

[0010] The critical softening zone radius ρ of the tunnel rock burst calculated in step 2 cr , determine the depth L of the drilling hole constructed by the cuttings method in the surrounding rock of the monitored warning tunnel drill-bits =η drill ρ cr , where η drill The drilling depth margin factor for cuttings;

[0011] Step 4: Define the critical mining stress index K for calculating rock burst in tunnels cr , and then determine the critical mining stress index engineering value K of the actual rock burst in the same coal seam where the warning roadway is located fcr ;

[0012] Step 4.1: Define the critical mining stress index K for calculating rock burst in tunnels cr , as shown in the following formula:

[0013]

[0014] Where, P m is the mining peak stress in the surrounding rock of the roadway;

[0015] Step 4.2: Obtain the actual mining peak stress P of the rock burst in the same coal seam where the roadway to be warned is located. mf Based on the definition of the critical mining stress index for rock burst in the roadway, the engineering value of the critical mining stress index for the actual rock burst in the same coal seam of the roadway to be warned is calculated.

[0016] If the coal seam in the drill cuttings warning area has not experienced rock burst, the critical mining stress index engineering value K of rock burst is calculated based on the coal seam with the same rock burst tendency that has experienced rock burst. fcr ;

[0017] Step 5: Determine the maximum amount of drilling cuttings per meter M in the lane to be drilled for warning max The critical value M of the graded warning indicator max(弱) 、M max(中等) With M max(强) , and then determine the danger level of the roadway to be drilled cuttings warning;

[0018] Step 5.1: Determine the distance u from the borehole wall diameter of the roadway to be drilled cuttings warning a ;

[0019] Set drilling and crushing area r d <r<r f The coal body is incompressible, so the borehole wall diameter is moved closer u a , as shown in the following formula:

[0020]

[0021] Where r d is the radius of the crushing zone of the drill hole; r f is the radius of the plastic softening zone of the drill hole; r0 is the drill hole radius or the drill bit cutting radius;

[0022] Step 5.2: Determine the critical conditions for the occurrence of drilling impact;

[0023] Calculate the critical crushing zone radius r where drilling impact occurs dcr , radius of critical plastic softening zone r pcr and critical environmental stress P hcr , as shown in the following formula:

[0024]

[0025]

[0026]

[0027] in, is the stress of the surrounding rock crushing zone on the plastic softening zone when drilling impact occurs, d is the drill hole diameter or the drill bit cutting diameter, d = 2r0; m is an intermediate variable, is the internal friction angle of coal-rock medium in the crushing zone;

[0028] Step 5.3: Based on the physical principle of drill bit cuttings generation, determine the maximum amount of cuttings per meter in the laneway to be drilled for warning.max , as shown in the following formula:

[0029]

[0030] Where γ is the bulk density of coal;

[0031] Step 5.4: Set the critical crushing zone radius of the drill hole Substitute r into formula (6) d , and obtain the critical maximum single-meter cuttings volume M before the impact starts maxcr , as shown in the following formula:

[0032]

[0033] Step 5.5: Determine the critical maximum amount of drill cuttings per meter M max The graded warning value M max(弱) 、M max(中等) With M max(强) , and then determine the danger level of the roadway to be drilled cuttings warning;

[0034] The critical maximum single-meter cuttings amount M maxcr The graded warning value M max(弱) 、M max(中等) With M max(强) As shown in the following formula:

[0035]

[0036] When 0<M max <0.25K fcr M maxcr , wait for the drilling cuttings warning lane to be free of impact danger warning; when 0.25K fcr M maxcr ≤M max <0.5K fcr M maxcr , wait for the drilling cuttings warning lane to be a weak impact danger warning; when 0.5K fcr M maxcr ≤M max <0.75K fcr M maxcr , the cuttings warning lane is a medium impact hazard warning; when M max ≥0.75K fcr M maxcr , the drilling cuttings warning tunnel is a strong impact danger warning;

[0037] Step 6: Determine the maximum amount of drill cuttings per meter in the drilling hole of the tunnel to be drilled cuttings warning max The depth of surrounding rock L p The critical value L of the graded warning indicator p(弱) 、L p(中等)With L p(强) , further determine the danger level of the tunnel to be drilled cuttings warning;

[0038] The surrounding rock depth L p The critical value L of the graded warning indicator p(弱) 、L p(中等) With L p(强) As shown in the following formula:

[0039]

[0040] When 0<L p <0.25K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is that there is no impact hazard warning; when 0.25K fcr L pcr ≤L p <0.5K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is a weak impact hazard warning; when 0.5K fcr L pcr ≤L p <0.75K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is medium impact hazard warning; when L p ≥0.75K fcr L pcr , and the evaluation of the drilling cuttings warning tunnel is a strong impact hazard warning.

[0041] The beneficial effect of adopting the above technical solution is that: the present invention provides a method for determining the construction parameters and warning critical values of the drilling method for impact ground pressure coal seams, wherein the method for determining the construction parameters and critical index values of the drilling method is directly related to the coal rock mechanical parameters, drilling hole structure parameters, tunnel structure parameters and current environmental stress, making the drilling construction design parameters of the drilling method more scientific, and the method for determining the drilling cuttings warning critical value is more universal for coal rocks of different strengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flowchart of a method for determining construction parameters and warning critical values of a rock burst coal seam drilling method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0044] This embodiment takes a coal seam in a mine as an example, and adopts the rock burst coal seam drilling cuttings construction parameter and warning critical value determination method of the present invention to determine the drilling cuttings construction parameter and drilling warning critical index value of the coal seam. Among them, the drilling cuttings construction parameter mainly refers to the drilling depth; the drilling warning critical index is the critical maximum single meter drilling cuttings volume M maxcr And the maximum amount of drilling cuttings per meter in the drilling hole of the drilling cuttings warning lane M max The depth of surrounding rock L p .

[0045] In this embodiment, a method for determining construction parameters and early warning critical values of rock burst coal seam drilling method is provided. Figure 1 As shown, the following steps are included:

[0046] Step 1: Obtain rock mechanical parameters of the coal body in the surrounding rock of the roadway to be drilled; the rock mechanical parameters include uniaxial compressive strength σ c , elastic modulus E, impact modulus index K = λ1 / E, residual degradation modulus λ2 and residual strength coefficient ξ; where λ1 is the post-peak softening modulus;

[0047] Step 2: Calculate the critical crushing zone radius ρ for rock burst in the tunnel to be drilled. fcr , critical softening zone radius ρ cr , critical softening depth of surrounding rock L pcr , critical ground stress P cr And the optimized P of the rock burst in the roadway to be warned mcr ;

[0048] Step 2.1: Obtain the support stress p of the roadway to be warned s ;

[0049] Step 2.2: Calculate the critical crushing zone radius ρ for rock burst in the roadway to be monitored and warned fcr and the critical softening zone radius ρ cr , as shown in the following formulas:

[0050]

[0051]

[0052] Calculation of critical softening depth L of surrounding rock for rock burst initiation pcr , as shown in the following formula:

[0053]

[0054] Among them, B is the width of the tunnel to be drilled for anti-blowout construction. It is the internal friction angle of coal-rock medium in the plastic softening zone of the tunnel surrounding rock.

[0055] Calculate the critical ground stress P for the occurrence of rock burst in the tunnel to be monitored and warned cr for:

[0056]

[0057] Among them, ρ0 is the radius of the roadway after the roadway to be monitored is equivalent to a homogeneous, continuous and isotropic circular roadway; m is an intermediate variable, is the internal friction angle of coal rock medium in the plastic softening zone, p fcr is the stress exerted by the surrounding rock crushing zone on the plastic softening zone when the tunnel impact starts, as shown in the following formula:

[0058]

[0059] in, is the internal friction angle of coal-rock medium in the crushing zone,

[0060] Step 2.3: Calculate the critical mining peak stress P for the occurrence of rock burst in the roadway to be warned mcr ;

[0061] Step 2.4: Optimize the critical mining peak stress P for rock burst in the roadway to be warned based on the cross-sectional shape of the roadway to be warned mcr , as shown in the following formula:

[0062] P mcr * =n1×P mcr

[0063] Among them, P mcr * is the optimized critical mining peak stress for rock burst in the roadway to be warned, and n1 is the cross-section correction coefficient. When the cross-section of the roadway to be warned is rectangular, trapezoidal, straight-wall arched, and circular, n1 is 0.89, 0.92, 0.95, and 0.98, respectively.

[0064] Step 3: Determine the depth L of the drilling hole in the surrounding rock of the monitored warning tunnel. drill-bits ;

[0065] The critical softening zone radius ρ of the tunnel rock burst calculated in step 2 cr , determine the depth L of the drilling hole constructed by the cuttings method in the surrounding rock of the monitored warning tunnel drill-bits =η drill L pcr , where η drill The drilling depth margin coefficient for cuttings is generally 1.1 to 1.3.

[0066] Step 4: Define and calculate the critical mining stress index K for rock burst in the tunnel cr , and then determine the critical mining stress index engineering value K of the actual rock burst in the same coal seam where the warning roadway is located fcr ;

[0067] Step 4.1: Define and calculate the critical mining stress index K for rock burst in the tunnel cr , as shown in the following formula:

[0068]

[0069] Where, P m is the mining peak stress in the surrounding rock of the roadway, MPa;

[0070] Step 4.2: Use the common method of surrounding rock mining stress testing to obtain the actual mining peak stress P of the same coal seam where the warning roadway is located. mf Based on the critical mining stress index of rock burst in the roadway, the engineering value of the critical mining stress index of the actual rock burst in the same coal seam of the roadway to be warned is calculated.

[0071] Step 4.3: If the coal seam in the drill cuttings warning area has not experienced rock burst, the critical mining stress index engineering value K of the actual occurrence of rock burst can be calculated by referring to the coal seams with the same rock burst tendency that have experienced rock burst. fcr .

[0072] Step 5: Determine the critical maximum per-meter cuttings volume M of the roadway to be drilled cuttings warning maxcr The critical value M of the graded warning indicator max(弱) 、M max(中等) With M max(强) ;

[0073] Step 5.1: Determine the distance u from the borehole wall diameter of the roadway to be drilled cuttings warning a The calculation method and analytical formula of ;

[0074] Set drilling and crushing area (r d <r<r f ) Coal is incompressible, then ε r +ε θ =0, that is Solution so Equivalent strain Because the boundary between the crushing zone and the plastic softening zone meets have to Therefore, the borehole wall diameter is moved closer by u a :

[0075]

[0076] Where r d is the radius of the crushing zone of the drill hole, in m; r f is the radius of the softening zone of the drill hole, in m;

[0077] Step 5.2: Determine the critical conditions for the occurrence of drilling impact;

[0078] Calculate the critical crushing zone radius r where drilling impact occurs dcr , radius of critical plastic softening zone r pcr and critical environmental stress P hcr , as shown in the following formula:

[0079]

[0080]

[0081]

[0082] in, is the stress of the surrounding rock crushing zone on the plastic softening zone when drilling impact occurs, r0 is the drilling radius or the drill bit cutting radius;

[0083] Step 5.3: Based on the physical principle of drill bit cuttings generation, determine the maximum amount of cuttings per meter in the laneway to be drilled for warning. max , as shown in the following formula:

[0084]

[0085] Where γ is the bulk density of coal;

[0086] Step 5.4: Set the critical crushing zone radius of the drill hole Substitute r into formula (11) d , and obtain the critical maximum single-meter cuttings volume M before the impact starts maxcr , as shown in the following formula:

[0087]

[0088] Step 5.5: Determine the critical maximum amount of drill cuttings per meter M maxcr The graded warning value M max(弱) 、M max(中等) With M max(强) ;

[0089]

[0090] When 0<M max <0.25K fcr M maxcr, wait for the drilling cuttings warning lane to be free of impact danger warning; when 0.25K fcr M maxcr ≤M max <0.5K fcr M maxcr , wait for the drilling cuttings warning lane to be a weak impact danger warning; when 0.5K fcr M maxcr ≤M max <0.75K fcr M maxcr , the cuttings warning lane is a medium impact hazard warning; when M max ≥0.75K fcr M maxcr , the drilling cuttings warning tunnel is a strong impact danger warning;

[0091] Step 6: Determine the maximum amount of drill cuttings per meter in the drilling hole of the tunnel to be drilled cuttings warning max The depth of surrounding rock L p The critical value L of the graded warning indicator p(弱) 、L p(中等) With L p(强) ;

[0092]

[0093] When 0<L p <0.25K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is that there is no impact hazard warning; when 0.25K fcr L pcr ≤L p <0.5K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is a weak impact hazard warning; when 0.5K fcr L pcr ≤L p <0.75K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is medium impact hazard warning; when L p ≥0.75K fcr L pcr , and the evaluation of the drilling cuttings warning tunnel is a strong impact hazard warning.

[0094] In this example, the coal seam has an average thickness of 7.03 m, a dip of 13°, and an average burial depth of 984 m. The coal mass has an average uniaxial compressive strength of 11.12 MPa. The coal seam has a weak impact tendency, with the roof having a weak impact tendency and the floor having no impact tendency. The results of determining the coal rock physical parameters, support strength, roadway geometric characteristic parameters, and warning threshold values are detailed in Table 1.

[0095] Table 1 Results of tunnel parameters and warning critical values determined by drilling method for rock burst coal seams

[0096]

[0097]

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for determining construction parameters and early warning critical values of a rock burst coal seam drilling method, characterized by: The following steps are involved: Step 1: Obtain rock mechanical parameters of the coal body in the surrounding rock of the roadway to be drilled cuttings warning; Step 2: Calculate the critical crushing zone radius ρ for rock burst in the tunnel to be drilled. fcr , critical softening zone radius ρ cr , critical softening depth of surrounding rock L pcr , critical ground stress P cr And the optimized critical mining peak stress P for the occurrence of rock burst in the roadway to be warned mcr * ; Step 3: The critical softening zone radius ρ of the roadway rock burst calculated in step 2 cr , determine the depth L of the drilling hole constructed by the cuttings method in the surrounding rock of the monitored warning tunnel drill-bits ; Step 4: Define the critical mining stress index K for calculating rock burst in tunnels cr , and then determine the critical mining stress index engineering value K of the actual rock burst in the same coal seam where the warning roadway is located fcr ; Step 5: Determine the maximum amount of drilling cuttings per meter M in the lane to be drilled for warning max The critical value M of the graded warning indicator max(弱) 、M max(中等) With M max(强) , and then determine the danger level of the roadway to be drilled cuttings warning; Step 5.1: Determine the distance u from the borehole wall diameter of the roadway to be drilled cuttings warning a ; Step 5.2: Determine the critical conditions for the occurrence of drilling impact; Step 5.3: Based on the physical principle of drill bit cuttings generation, determine the maximum amount of cuttings per meter in the laneway to be drilled for warning. max ; The maximum amount of drilling cuttings per meter in the tunnel to be drilled cuttings warning is determined as M max As shown in the following formula: Among them, γ is the bulk density of coal, r d is the radius of the crushing zone of the drill hole; r0 is the drill hole radius or the drill bit cutting radius; σ c is the uniaxial compressive strength; E is the elastic modulus; ξ is the residual strength coefficient; λ1 is the post-peak softening modulus; Step 5.4: Set the critical crushing zone radius of the drill hole Substitute r into formula (6) d , and obtain the critical maximum single-meter cuttings volume M before the impact starts maxcr , as shown in the following formula: in, λ2 is the residual drop modulus; Step 5.5: Determine the critical maximum amount of drill cuttings per meter M max The graded warning value M max(弱) 、M max(中等) With M max(强) , and then determine the danger level of the roadway to be drilled cuttings warning; The critical maximum single-meter cuttings amount M maxcr The graded warning value M max(弱) 、M max(中等) With M max(强) As shown in the following formula: When 0<M max <0.25K fcr M maxcr , wait for the drilling cuttings warning lane to be free of impact danger warning; when 0.25K fcr M maxcr ≤M max <0.5K fcr M maxcr , wait for the drilling cuttings warning lane to be a weak impact danger warning; when 0.5K fcr M maxcr ≤M max <0.75K fcr M maxcr , the cuttings warning lane is a medium impact hazard warning; when M max ≥0.75K fcr M maxcr , the drilling cuttings warning tunnel is a strong impact danger warning; Step 6: Determine the maximum amount of drill cuttings per meter in the drilling hole of the tunnel to be drilled cuttings warning max The depth of surrounding rock L p The critical value L of the graded warning indicator p(弱) 、L p(中等) With L p(强) , further determine the danger level of the tunnel to be drilled cuttings warning; The surrounding rock depth L p The critical value L of the graded warning indicator p(弱) 、L p(中等) With L p(强) As shown in the following formula: When 0<L p <0.25K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is that there is no impact hazard warning; when 0.25K fcr L pcr ≤L p <0.5K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is a weak impact hazard warning; when 0.5K fcr L pcr ≤L p <0.75K fcr L pcr , the evaluation of the tunnel to be drilled cuttings warning is medium impact hazard warning; when L p ≥0.75K fcr L pcr , and the evaluation of the drilling cuttings warning tunnel is a strong impact hazard warning.

2. The method for determining construction parameters and early warning critical values of the rock burst coal seam drilling method according to claim 1, characterized in that: The rock mechanics parameters include uniaxial compressive strength σ c , elastic modulus E, impact modulus index K=λ1 / E, residual degradation modulus λ2 and residual strength coefficient ξ; where λ1 is the post-peak softening modulus.

3. The method for determining construction parameters and early warning critical values of the rock burst coal seam drilling method according to claim 2, characterized in that: Step 3 is based on the critical softening zone radius ρ of the tunnel rock burst calculated in step 2. cr , determine the depth L of the drilling hole constructed by the cuttings method in the surrounding rock of the monitored warning tunnel drill-bits =η drill ρ cr , where η drill It is the depth margin coefficient for drilling cuttings.

4. The method for determining construction parameters and early warning critical values of the rock burst coal seam drilling method according to claim 3, characterized in that: The specific method of step 4 is: Step 4.1: Define the critical mining stress index K for calculating rock burst in tunnels cr , as shown in the following formula: Where, P m is the mining peak stress in the surrounding rock of the roadway; Step 4.2: Obtain the actual mining peak stress P of the rock burst in the same coal seam where the roadway to be warned is located. mf Based on the definition of the critical mining stress index for rock burst in the roadway, the engineering value of the critical mining stress index for the actual rock burst in the same coal seam of the roadway to be warned is calculated. If the coal seam in the drill cuttings warning area has not experienced rock burst, the critical mining stress index engineering value K of rock burst is calculated based on the coal seam with the same rock burst tendency that has experienced rock burst. fcr .

5. The method for determining construction parameters and early warning critical values of rock burst coal seam drilling method according to claim 4, characterized in that: The step 5.1 determines the distance u from the borehole wall diameter of the lane to be drilled cuttings warning a The specific method is: Set drilling and crushing area r d <r<r f The coal body is incompressible, so the borehole wall diameter is moved closer u a , as shown in the following formula: Where r d is the radius of the crushing zone of the drill hole; r f is the radius of the plastic softening zone of the drill hole; r0 is the drill hole radius or the drill bit cutting radius; The critical conditions for the occurrence of drilling impact determined in step 5.2 include the critical crushing zone radius r of the drilling impact dcr , radius of critical plastic softening zone r pcr and critical environmental stress P hcr , as shown in the following formula: in, is the stress of the surrounding rock crushing zone on the plastic softening zone when drilling impact occurs, d is the drill hole diameter or the drill bit cutting diameter, d = 2r0; m is an intermediate variable, is the internal friction angle of the coal rock medium in the crushing zone.

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