Method for determining roof cutting angle of pre-splitting blasting for gob-side entry retaining under condition of direct overburden thick and hard roof

Abstract

The application discloses a method for determining a cutting roof angle of pre-splitting blasting under the condition of directly covering thick and hard roof and gob-side entry retaining, and is implemented according to the following steps: step 1, collecting engineering geological data of a working face to be mined; step 2, determining a cutting roof height; step 3, determining a critical angle of sliding instability of thick and hard direct roof; step 4, determining a blasting damage radius; and step 5, determining the cutting roof angle according to the cutting roof height, the critical angle of sliding instability of thick and hard direct roof and the blasting damage radius. The application solves the problem that the design of the pre-splitting cutting roof angle in the prior art fails to fully consider the disturbance influence of the blasting damage radius on the roof of the roadway.

Description

Technical Field

[0001] This invention belongs to the technical field of methods for determining coal mining parameters, and relates to a method for determining the roof cutting angle of pre-splitting blasting in roadway retention under conditions of direct overburden thick hard roof. Background Technology

[0002] Goaf retention technology is an important pillarless mining technique that improves coal recovery rate and reduces roadway excavation. Among them, directional pre-splitting blasting to cut the roof and relieve pressure is the key to ensuring the success of goaf retention. Its core is to carry out directional blasting on the roof of the goaf side of the roadway to pre-create a weak surface, so that the roof of the goaf can collapse neatly along the weak surface, forming a natural support for the roadway side, thereby reducing the stress of the surrounding rock and maintaining the stability of the roadway.

[0003] However, under conditions of thick and hard roof strata, traditional directional pre-splitting blasting often fails to achieve effective roof cutting due to the hardness and integrity of the roof rock layers, necessitating the use of large-diameter pre-splitting blasting technology. Currently, the design of pre-splitting roof cutting angles focuses primarily on the cutting effect, failing to fully consider the disturbance impact of large-diameter pre-splitting blasting on the roadway roof. If the cutting angle is too small, the damage zone generated by the pre-splitting blasting may extend to the roadway roof, compromising its integrity and stability, and similarly jeopardizing the safety of the roadway. Therefore, there is an urgent need for a method that can scientifically and quantitatively determine the cutting angle to simultaneously meet the two core requirements of "effective cutting" and "no damage to the roadway." Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the roof cutting angle of pre-splitting blasting in roadway retention under conditions of direct overburden thick hard roof, which solves the problem in the prior art that the design of the pre-splitting roof cutting angle fails to fully consider the disturbance effect of the blasting damage radius on the roadway roof.

[0005] The technical solution adopted in this invention is a method for determining the roof-cutting angle of pre-splitting blasting in goaf-retention roadways under conditions of direct overburden with thick, hard roof, which is implemented according to the following steps: Step 1: Collect engineering geological data of the working face to be mined; Step 2, determine the cutting height; Step 3: Determine the critical angle for the slippage and instability of the thick, hard direct top; Step 4: Determine the radius of blast damage; Step 5: Determine the cutting angle based on the cutting height, the critical angle for slippage and instability of the thick and hard direct roof, and the radius of blast damage.

[0006] Further, step 1 specifically involves: collecting engineering geological data of the working face to be mined, including borehole columnar sections, coal seam mining height M, and the thickness of each stratum. , bulk density ,tensile strength Cohesion internal friction angle There are m layers of rock above the coal seam.

[0007] Furthermore, step 2 specifically involves: based on the thickness of each rock stratum above the coal seam... Coefficient of fragmentation Based on the coal seam mining height M, the roof cutting height was determined. , .

[0008] Furthermore, the cutting height Obtain it using the following formula:

[0009] in, M This refers to the coal seam thickness, in meters (m). H 1, H 2, H m They are respectively the first layer, the second layer, and the third layer. m Thickness of rock strata, in meters; K p The average coefficient of rock strata swelling. , K 1, K 2, K m They are respectively the first layer, the second layer, and the third layer. m The coefficient of fragmentation of the rock strata.

[0010] Furthermore, step 3 specifically involves: Thick, hard, direct top slippage instability critical angle Obtain it using the following formula:

[0011] in, The friction angle between the rock blocks is expressed in degrees (°). h The thickness of the basic top is expressed in meters (m). This represents the subsidence of the rock block, expressed in meters (m). L The length of the basic top rock block is expressed in meters (m).

[0012] Further, step 4 specifically involves: determining, based on theoretical and empirical formulas, the maximum radius R of the damage zone generated by pre-splitting blasting in the roof strata under given charge quantity, explosive type, and sealing conditions, specifically:

[0013] in, This refers to the density of the explosive, expressed in kg / m³. 3 ; The velocity of the explosive is expressed in m / s; The radius of the medicine roll is in mm; is the borehole radius in mm; n is the stress amplification factor caused by the collision of explosive gases with the rock wall. denoted as the pressure attenuation coefficient; the coefficient b is related to the Poisson's ratio of the rock and the stress propagation distance. The value of b is larger in the near-explosion zone, but decreases rapidly with increasing distance. It is taken as 0.80.

[0014] Furthermore, step 5 specifically involves determining the minimum safe distance based on the tunnel cross-section diagram, the roof cutting height, and the blasting damage radius. And determine the minimum safe angle for cutting the top based on geometric relationships. When the top is cut at a safe angle Less than the critical angle for slip instability At that time, the cutting angle is When the top is cut at a safe angle Angle greater than or equal to the critical angle of slippage instability At that time, the cutting angle is When the top is cut at a safe angle equal to the critical angle of slippage and instability At that time, the angle of the cutting tip .

[0015] Furthermore, minimum safety angle Obtain it using the following formula: .

[0016] Furthermore, the cutting angle The value can be: ; in, for The maximum value in.

[0017] The beneficial effects of this invention are: The method for determining the cutting angle of pre-splitting blasting for roadway retention with thick, hard roof provided by this invention, based on the achievement of roadway roof cutting, precisely optimizes the cutting angle by introducing the dual constraints of blasting damage radius and roadway roof safety distance, effectively avoiding damage to the stability of the roadway roof caused by blasting operations. Thus, while ensuring the long-term safety of the roadway, it significantly improves the success rate of roadway retention under thick, hard roof conditions, and has certain practical applications. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view of the pre-splitting blasting cut-off angle in the goaf-retaining roadway pre-splitting blasting method of the present invention under the condition of direct overlay of thick hard roof.

[0019] In the diagram: 1. Reserved roadway, 2. Thick and hard direct roof, 3. Basic roof, 4. Pre-splitting cut, 5. Sealing length of pre-splitting blast hole, 6. Pre-splitting blast hole, 7. Roof-cutting collapse goaf. Detailed Implementation

[0020] The following detailed description is provided in conjunction with specific implementation methods.

[0021] Example 1 The method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under conditions of direct overburden with a thick, hard roof, as described in this invention, is implemented according to the following steps: Step 1: Collect engineering geological data of the working face to be mined; Step 2, determine the cutting height; Step 3: Determine the critical angle for the slippage and instability of the thick, hard direct top; Step 4: Determine the radius of blast damage; Step 5: Determine the cutting angle based on the cutting height, the critical angle for slippage and instability of the thick and hard direct roof, and the radius of blast damage.

[0022] Example 2 Based on Example 1, Step 1 specifically involves: collecting engineering geological data of the working face to be mined, including borehole columnar section, coal seam mining height M, and thickness of each stratum. , bulk density ,tensile strength Cohesion internal friction angle There are m layers of rock above the coal seam.

[0023] Step 2 specifically involves: determining the thickness of each rock stratum above the coal seam. Coefficient of fragmentation Based on the coal seam mining height M, the roof cutting height was determined. , .

[0024] Cutting height Obtain it using the following formula:

[0025] in, M This refers to the coal seam thickness, in meters (m). H 1, H 2, H m They are respectively the first layer, the second layer, and the third layer. m Thickness of rock strata, in meters; K p The average coefficient of rock strata swelling. , K 1, K 2, Km They are respectively the first layer, the second layer, and the third layer. m The coefficient of fragmentation of the rock strata, K p It is usually 1.2~1.5.

[0026] Example 3 Based on Example 2, step 3 specifically includes: Thick, hard, direct top slippage instability critical angle Obtain it using the following formula:

[0027] in, The friction angle between the rock blocks is expressed in degrees (°). h The thickness of the basic top is expressed in meters (m). This represents the subsidence of the rock block, expressed in meters (m). L The length of the basic top rock block is expressed in meters (m).

[0028] Example 4 Based on Example 3, step 4 specifically involves: determining, according to theoretical empirical formulas, the maximum radius R of the damage zone generated by pre-splitting blasting in the roof strata under given charge amount, explosive type, and sealing conditions, specifically:

[0029] in, This refers to the density of the explosive, expressed in kg / m³. 3 ; The velocity of the explosive is expressed in m / s; The radius of the medicine roll is in mm; is the borehole radius in mm; n is the stress amplification factor caused by the collision of explosive gases with the rock wall. denoted as the pressure attenuation coefficient; the coefficient b is related to the Poisson's ratio of the rock and the stress propagation distance. The value of b is larger in the near-explosion zone, but decreases rapidly with increasing distance. It is taken as 0.80.

[0030] Example 5 Based on Example 4, step 5 specifically involves: Figure 1 The diagram shows a cross-section of a pre-splitting blasting cut in a goaf-preserving roadway. It includes the pre-splitting roadway (1), thick, hard immediate roof (2), main roof (3), pre-splitting cut (4), pre-splitting blast hole sealing lengths (5, 6), pre-splitting blast holes (6), and the goaf area (7). Based on the roadway cross-section, cut height, and blast damage radius, the minimum safe distance is determined. And determine the minimum safe angle for cutting the top based on geometric relationships. When the top is cut at a safe angle Less than the critical angle for slip instability At that time, the cutting angle is When the top is cut at a safe angle Angle greater than or equal to the critical angle of slippage instability At that time, the cutting angle is When the top is cut at a safe angle equal to the critical angle of slippage and instability At that time, the angle of the cutting tip .

[0031] Minimum safe angle Obtain it using the following formula: .

[0032] Cutting angle The value can be: ; in, for The maximum value in.

[0033] Example 6 Based on Example 5, this example further illustrates the present invention using a certain mine as an example.

[0034] The mine uses a pillarless roof cutting and goaf-side roadway retention method to retain the ventilation roadway of the longwall mining face.

[0035] The method for determining the roof-cutting angle for pre-splitting blasting in roadways with goaf-side retention for directly overlying thick and hard roofs includes the following steps: Step S1: Collect engineering geological data for the working face to be mined. The coal seam has a mining height of M=2.8m and a thick, hard roof. =14m, tensile strength 8.06 MPa, cohesion c = 9 MPa, internal friction angle =46°, compressive strength =120MPa, initial density =2700kg / m 3 .

[0036] Step S2, based on the thickness of the hard roof above the coal seam. =14m, coefficient of fragmentation K Given a coal seam height of 1.20 m and a mining height of M = 2.8 m, the required roof cutting height is determined.

[0037] Step S3: Perform stress analysis on the cut surface of the thick, hard direct top to ensure that, at a given cut height, the critical angle for slippage and instability of the thick, hard direct top is within acceptable limits.

[0038] in, h The thickness of rock block B is 4m; The subsidence of rock block B is 0.2m; L The length of rock block B is 16m.

[0039] Step S4, Explosion Damage Radius =2.875m; in, The density of the explosive is 1.10 × 10⁻⁶. 3 kg / m 3 ; The velocity of the explosive is 3200 m / s; The radius of the medicine roll is 31.5 mm; is the borehole radius, 47 mm; n is the stress amplification factor caused by the collision of explosive gas with the rock wall, taken as 11; The pressure attenuation coefficient is taken as 1.20; the coefficient b is related to the Poisson's ratio of the rock and the stress propagation distance. The b value is larger in the near-explosion zone, but decreases rapidly with increasing distance, and is taken as 0.80.

[0040] In step S5, the minimum safe angle for cutting the top.

[0041] Furthermore, in step S5, the cutting angle... .

[0042] This invention provides a method for determining the cutting angle of pre-splitting blasting in gob-side retention of thick, hard roofs. Through reasonable theoretical derivation, it provides a method for determining the cutting angle of pre-splitting blasting in gob-side retention of thick, hard roofs. The calculation results are relatively accurate and, to a certain extent, effectively avoid damage to the stability of the retained roadway roof caused by blasting operations. Thus, while ensuring the long-term safety of the retained roadway, it significantly improves the success rate of gob-side retention under thick, hard roof conditions and has certain practical applications.

Claims

1. A method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under conditions of direct overburden with a thick, hard roof, characterized in that, The specific steps are as follows: Step 1: Collect engineering geological data of the working face to be mined; Step 2, determine the cutting height; Step 3: Determine the critical angle for the slippage and instability of the thick, hard direct top; Step 4: Determine the radius of blast damage; Step 5: Determine the cutting angle based on the cutting height, the critical angle for slippage and instability of the thick, hard direct roof, and the radius of blasting damage. Specifically: Based on the tunnel cross-section diagram, the cut-off height, and the blasting damage radius, the minimum safe distance is determined. , The radius of blast damage is given; and the minimum safe angle for cutting the top is determined based on geometric relationships. When the top is cut at a safe angle Less than the critical angle for slip instability At that time, the cutting angle is When the top is cut at a safe angle Angle greater than or equal to the critical angle of slippage instability At that time, the cutting angle is When the top is cut at a safe angle equal to the critical angle of slippage and instability At that time, the angle of the cutting tip ; The minimum safe angle Obtain it using the following formula: ； in, This refers to the cutting height. The cutting angle The value can be: ； in, for The maximum value in.

2. The method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under the condition of directly overlying thick hard roof as described in claim 1, characterized in that, Step 1 specifically involves: collecting engineering geological data of the working face to be mined, including borehole columnar section, coal seam mining height M, and thickness of each stratum. , bulk density ,tensile strength Cohesion internal friction angle There are m layers of rock above the coal seam.

3. The method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under the condition of directly overlying thick hard roof as described in claim 2, characterized in that, Step 2 specifically involves: determining the thickness of each rock stratum above the coal seam. Coefficient of fragmentation Based on the coal seam mining height M, the roof cutting height was determined. , .

4. The method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under the condition of directly overlying thick hard roof as described in claim 3, characterized in that, The cutting height Obtain it using the following formula: in, M This refers to the coal seam thickness, in meters (m). H 1, H 2, H m They are respectively the first layer, the second layer, and the third layer. m Thickness of rock strata, in meters; K p The average coefficient of rock strata swelling. , K 1, K 2, K m They are respectively the first layer, the second layer, and the third layer. m The coefficient of fragmentation of the rock strata.

5. The method for determining the roof-cutting angle by pre-splitting blasting in a goaf-retaining roadway under the condition of directly overlying thick hard roof as described in claim 4, wherein step 3 specifically comprises: Thick, hard, direct top slippage instability critical angle Obtain it using the following formula: in, The friction angle between the rock blocks is expressed in degrees (°). h The thickness of the basic top is expressed in meters (m). This represents the subsidence of the rock block, expressed in meters (m). L The length of the basic top rock block is expressed in meters (m).

6. The method for determining the roof-cutting angle of pre-splitting blasting in a goaf-retaining roadway under the condition of directly overlying thick and hard roof as described in claim 5, wherein step 4 specifically comprises: determining, based on theoretical empirical formulas, the maximum radius R of the damage zone generated by the pre-splitting blasting in the roof strata under given charge amount, explosive type, and hole sealing conditions, specifically: in, This refers to the density of the explosive, expressed in kg / m³. 3 ; The velocity of the explosive is expressed in m / s; The radius of the medicine roll is in mm; is the borehole radius in mm; n is the stress amplification factor caused by the collision of explosive gases with the rock wall. is the pressure attenuation coefficient; coefficient b is related to the Poisson's ratio of the rock and the stress propagation distance.

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