A method for determining roof pre-splitting drilling parameters for preventing rock bursts in the working face

Abstract

A method for determining the parameters of roof pre-splitting boreholes for preventing rock bursts in the working face. By relying on the evaluation report of the rock burst risk in the working face, the area with rock burst risk in the working face is determined. Rock cores are taken from the roof of the roadway in the area with rock burst risk to determine the lithology, thickness of the roof rock layer and the distance from the coal seam. The key layer position is determined based on the key layer theory. The roof of the area with rock burst risk in the working face is subjected to pre-splitting blasting along the roadway strike. One pre-splitting borehole along the roadway strike is arranged every 10 - 15 m. The roof of the area with rock burst risk in the working face is subjected to pre-splitting blasting along the roadway dip. One group of pre-splitting boreholes along the roadway strike is arranged every 10 - 15 m, and each group contains n pre-splitting boreholes along the roadway dip, where n ≥ 2. The present invention realizes the accurate determination of the parameters of the pre-splitting boreholes, accurately fractures the coal seam roof, achieves better pressure relief effect and early prevention of rock bursts, and ensures the safe production of the mine.

Description

Technical Field

[0001] The present invention relates to a method for determining roof pre-splitting drilling parameters for preventing rock bursts in a working face, belonging to the technical field of safe coal mining. Background Art

[0002] Rock burst is a typical mine dynamic phenomenon, which is extremely harmful to the normal production of coal mines. The hard roof above the coal mining face is one of the main factors affecting rock burst disasters. The thicker the hard rock layer, the less likely it is to collapse, the longer the suspended roof length formed, and the larger the suspended area, thus accumulating more elastic energy. When the working face is in the stage of square, sub-key layer or main key layer fracture, the impact risk is relatively high, and prevention measures need to be taken to make the hard roof fracture in advance to avoid rock bursts in the working face.

[0003] Due to the complex geological conditions of the mine, there are significant differences in the thickness of the roof rock layers in different areas of the coal mining face. To prevent rock bursts, it is necessary to fracture the hard roof rock layer above the working face in advance. At present, the pre-splitting drilling parameters for fracturing the hard roof above the working face are mostly determined based on experience or borehole columnar diagrams. Due to strong subjectivity, the accuracy of the parameters is difficult to guarantee, and it is impossible to meet the requirement of reasonably fracturing the hard roof by pre-splitting drilling, and ultimately it is difficult to achieve the goal of preventing the sudden collapse of the long suspended roof from inducing rock bursts. Summary of the Invention

[0004] The object of the present invention is to provide a method for determining roof pre-splitting drilling parameters for preventing rock bursts in a working face, which can improve the accuracy of roof pre-splitting drilling parameters, reasonably fracture the hard roof, achieve the early prevention of rock bursts, and ensure the safety of mine production.

[0005] To achieve the above object, the present invention provides a method for determining roof pre-splitting drilling parameters for preventing rock bursts in a working face, including the following steps:

[0006] S1. Determine the area with impact risk in the working face according to the impact risk assessment report of the working face. Drill cores from the roof of the roadway in the impact risk area to determine the lithology, thickness and distance from the coal seam of the roof rock layer, and determine the key layer position according to the key layer theory;

[0007] S2. Conduct strike pre-splitting blasting on the roof of the working face area with impact risk along the roadway strike. The strike pre-splitting drill holes for strike pre-splitting blasting are arranged one every 10 - 15 m along the roadway strike;

[0008] S3. Conduct dip pre-splitting blasting on the roof of the working face area with impact risk along the roadway dip. The dip pre-splitting drill holes for dip pre-splitting blasting are arranged in groups one every 10 - 15 m along the roadway strike, and each group contains n dip pre-splitting drill holes, where n ≥ 2.

[0009] Furthermore, the angle between the strike pre-splitting borehole and the working face mining direction is not less than 70°, the borehole depth is 15 - 20 m, the borehole diameter is 42 - 100 mm, the charging section length is not less than 1 / 2 of the borehole depth, and the hole sealing section length is not less than 1 / 3 of the borehole depth.

[0010] Furthermore, in S3, each group of dip pre-splitting boreholes includes dip pre-splitting borehole A and dip pre-splitting borehole B; the angle between dip pre-splitting borehole A and the horizontal plane is tan -1 (H / L), and takes an integer value that is a multiple of 5. The borehole length of dip pre-splitting borehole A is and takes an integer value that is a multiple of 5, the borehole diameter is 42 - 100 mm, the charging section length is 1 / 2 of the borehole depth, and the hole sealing section length is not less than 1 / 3 of the borehole depth; where L is the horizontal projection of the key stratum roof, and H is the vertical height of the roof.

[0011] Dip pre-splitting borehole B blasts the topmost key stratum rock formation within the vertical height H′, the angle with the horizontal plane is 70°, the borehole depth of dip pre-splitting borehole B is H / sin70°, the borehole diameter is 42 - 100 mm, the charging section length is 1 / 2 of the borehole depth, and the hole sealing section length is not less than 1 / 3 of the borehole depth; where H′ is the theoretical pre-splitting height, with the unit of m.

[0012] Furthermore, the roof vertical height H is determined by the theoretical pre-splitting height H′. If H′≥50, then H is the vertical height from the upper interface of the topmost key stratum rock formation to the roadway roof in H′; if H′<50, then H = 50; the calculation formula for H′ is:

[0013]

[0014] In the formula, ∑M is the cumulative mining thickness, with the unit of m; R c is the uniaxial mine pressure strength, with the unit of MPa.

[0015] Furthermore, the horizontal projection L of the key stratum roof satisfies:

[0016]

[0017] In the formula, σ ti is the tensile strength of the i-th key stratum rock formation within the vertical height H′, with the unit of MPa;

[0018] k i is the cracking coefficient of the i-th key stratum rock formation within the vertical height H′, k = 0.25 - 0.75;

[0019] m i is the thickness of the i-th key stratum rock formation within the vertical height H′, with the unit of m;

[0020] b is the inclined length of the working face, with the unit of m;

[0021] γ i is the bulk density of the i-th key stratum within the vertical height H′, with the unit of N / m 3 ;

[0022] α is the dip angle of the working face.

[0023] Furthermore, the opening position of the inclined pre-splitting borehole is located at the roof on the working-face side of the roadway, and the spacing between adjacent inclined pre-splitting borehole groups is D. The calculation formula for D is:

[0024]

[0025] In the formula, S is the adjustment coefficient; r b is the radius of the blast hole, with the unit of m; f is the rock toughness coefficient.

[0026] Furthermore, in the case of (H / tan70° - L) / 10 > 1, the calculation formula for the number n of each group of inclined pre-splitting boreholes is:

[0027]

[0028] When n > 2, the rock stratum between the intersection points of the inclined pre-splitting borehole A and the inclined pre-splitting borehole B in the uppermost key stratum is equally divided according to the value of (H / tan70° - L) / 10 + 1. The final hole positions of the added inclined pre-splitting boreholes are located at the equally divided positions. The diameter of the added boreholes is 42 - 100 mm, the charge length needs to be 1 / 2 of the borehole depth, and the sealing length is not less than 1 / 3 of the borehole depth.

[0029] Furthermore, in the impact hazard area, the core length taken from the roof borehole of the roadway is at least 100 m; both the strike pre-splitting borehole and the inclined pre-splitting borehole are at least 200 m ahead of the working face of the coal mining face.

[0030] The present invention determines the areas with impact hazards on the working face based on the impact hazard assessment report of the working face. In the areas with impact hazards, boreholes are drilled in the roadway roof to obtain rock cores, so as to determine the lithology, thickness of the roof rock layer and the distance from the coal seam, and determine the key layer horizon according to the key layer theory. The roof of the area with impact hazards on the working face is subjected to pre-splitting blasting along the roadway strike. One pre-splitting borehole for strike pre-splitting blasting is arranged every 10 - 15 m along the roadway strike. The roof of the area with impact hazards on the working face is subjected to pre-splitting blasting along the roadway dip. One group of dip pre-splitting boreholes for dip pre-splitting blasting is arranged every 10 - 15 m along the roadway strike, and each group contains n dip pre-splitting boreholes, where n≥2, and the parameters of the dip pre-splitting boreholes are determined according to the theoretical pre-splitting height and the ultimate length of the roof cantilever. The present invention realizes the accurate determination of the parameters of the pre-splitting boreholes, avoids the occurrence of the phenomenon that the main key layer is broken due to too long borehole length and the key layer cannot be effectively broken due to too short borehole length, accurately fractures the coal seam roof, realizes better pressure relief effect and early prevention of rock burst, ensures the safety of mine production, and has a wide application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic plan view of the layout of the roof strike pre-splitting boreholes and dip pre-splitting boreholes of the present invention;

[0032] Figure 2 is a schematic layout view of the roof strike pre-splitting boreholes of the present invention;

[0033] Figure 3 is a schematic layout view when the number n of the roof dip pre-splitting boreholes of the present invention is 2;

[0034] Figure 4 is a schematic layout view when the number n of the roof dip pre-splitting boreholes of the present invention is >2. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described below with reference to the drawings.

[0036] As Figure 1 shown, a method for determining the parameters of the roof pre-splitting boreholes for preventing and controlling rock burst on the working face includes the following steps:

[0037] S1. Determine the areas with impact hazards on the working face based on the impact hazard assessment report of the working face. In the areas with impact hazards, boreholes are drilled in the roadway roof to obtain rock cores, so as to determine the lithology, thickness of the roof rock layer and the distance from the coal seam, and determine the key layer horizon according to the key layer theory;

[0038] S2. As Figure 2 shown, the roof of the area with impact hazards on the working face is subjected to pre-splitting blasting along the roadway strike. One pre-splitting borehole for strike pre-splitting blasting is arranged every 10 - 15 m along the roadway strike;

[0039] S3. As shown in Figure 3 , pre-splitting blasting is carried out along the dip of the roadway on the roof of the area with impact risk on the working face. A group of dip pre-splitting drill holes for pre-splitting blasting is arranged every 10 - 15 m along the roadway strike. Each group contains n dip pre-splitting drill holes, and n ≥ 2.

[0040] As a preferred embodiment, as shown in Figure 2 , the included angle between the strike pre-splitting drill hole and the working face mining direction is not less than 70°, the hole depth is 15 - 20 m, the drill hole diameter is 42 - 100 mm, the charging section length is not less than 1 / 2 of the drill hole depth, and the hole sealing section length is not less than 1 / 3 of the drill hole depth.

[0041] As a preferred embodiment, as shown in Figure 3 , in S3, each group of dip pre-splitting drill holes includes dip pre-splitting drill hole A and dip pre-splitting drill hole B; the included angle between the dip pre-splitting drill hole A and the horizontal plane is tan -1 (H / L), and it takes an integer value that is a multiple of 5. The drill hole length of the dip pre-splitting drill hole A is and it takes an integer value that is a multiple of 5. The drill hole diameter is 42 - 100 mm, the charging section length is 1 / 2 of the drill hole depth, and the hole sealing section length is not less than 1 / 3 of the drill hole depth; where L is the horizontal projection of the key layer roof, and H is the vertical height of the roof.

[0042] The dip pre-splitting drill hole B blasts the topmost key layer rock formation within the vertical height H'. The included angle with the horizontal plane is 70°. The hole depth of the dip pre-splitting drill hole B is H / sin70°, the drill hole diameter is 42 - 100 mm, the charging section length is 1 / 2 of the drill hole depth, and the hole sealing section length is not less than 1 / 3 of the drill hole depth; where H' is the theoretical pre-splitting height, with the unit of m.

[0043] As a preferred embodiment, the roof vertical height H is determined by the theoretical pre-splitting height H'. If H' ≥ 50, then H is the vertical height from the upper interface of the topmost key layer rock formation to the roadway roof in H'; if H' < 50, then H = 50; where the calculation formula for H' is:

[0044]

[0045] In the formula, ∑M is the cumulative mining thickness, with the unit of m; R c is the uniaxial mine pressure strength, with the unit of MPa.

[0046] As a preferred embodiment, the horizontal projection L of the key layer roof satisfies:

[0047]

[0048] Where, σ ti is the tensile strength of the i-th key stratum within the vertical height H', with the unit of MPa;

[0049] k i is the cracking coefficient of the i-th key stratum within the vertical height H', and k = 0.25 - 0.75;

[0050] m i is the thickness of the i-th key stratum within the vertical height H', with the unit of m;

[0051] b is the inclined length of the working face, with the unit of m;

[0052] γ i is the unit weight of the i-th key stratum within the vertical height H', with the unit of N / m 3 ;

[0053] α is the dip angle of the working face.

[0054] As a preferred embodiment, the opening position of the inclined pre-splitting borehole is located at the roof on the working face side of the roadway, and the spacing between adjacent inclined pre-splitting borehole groups is D. The calculation formula for D is:

[0055]

[0056] Where, S is the adjustment coefficient; r b is the radius of the blast hole, with the unit of m; f is the rock hardness coefficient.

[0057] In order to improve the effect of roof pressure relief in the area with impact risk on the working face, when (H / tan70° - L) / 10 > 1, the calculation formula for the number n of each group of inclined pre-splitting boreholes is:

[0058]

[0059] As Figure 4 shown, when n > 2, the strata between the intersection points of the inclined pre-splitting borehole A and the inclined pre-splitting borehole B in the uppermost key stratum are equally divided according to the value of (H / tan70° - L) / 10 + 1. The end hole position of the added inclined pre-splitting borehole is located at the equal division position, the diameter of the added borehole is 42 - 100 mm, the length of the charging section needs to be 1 / 2 of the borehole depth, and the length of the hole sealing section is not less than 1 / 3 of the borehole depth.

[0060] In order to improve the accuracy of rock property judgment of the strata, the core length taken from the roof borehole of the roadway in the impact risk area is at least 100 m; in order to prevent affecting the working face, both the strike pre-splitting borehole and the inclined pre-splitting borehole are at least 200 m ahead of the working face extraction face.

Claims

1. A method for determining the roof pre-splitting drilling parameters for preventing rock bursts in the working face, characterized in that, The steps are as follows: S1. Determine the areas with impact hazards on the working face according to the impact hazard assessment report of the working face. Drill for rock cores on the roof of the roadway in the impact hazard areas to determine the lithology, thickness of the roof strata and the distance from the coal seam, and determine the key stratum positions according to the key stratum theory; S2. Conduct strike pre-splitting blasting on the roof of the areas with impact hazards on the working face along the roadway strike. One strike pre-splitting borehole for strike pre-splitting blasting is arranged every 10 - 15 m along the roadway strike; the angle between the strike pre-splitting borehole and the working face mining direction is not less than 70°, the hole depth is 15 - 20 m, the borehole diameter is 42 - 100 mm, the charging section length is not less than 1 / 2 of the borehole depth, and the hole sealing section length is not less than 1 / 3 of the borehole depth; S3. Conduct dip pre-splitting blasting on the roof of the working face in the area with impact risk along the dip of the roadway. The dip pre-splitting boreholes for dip pre-splitting blasting are arranged in groups every 10 - 15 m along the roadway strike, and each group contains dip pre-splitting boreholes, ; Each group of dip presplitting drill holes includes dip presplitting drill hole A and dip presplitting drill hole B; the included angle between the dip presplitting drill hole A and the horizontal plane is , and it takes an integer value that is a multiple of 5. The drilling length of the dip presplitting drill hole A is , and it takes an integer value that is a multiple of 5. The drilling diameter is 42 - 100 mm, the charging section length is 1 / 2 of the drilling depth, and the hole sealing section length is not less than 1 / 3 of the drilling depth; among them, L is the horizontal projection of the key stratum roof, H is the vertical height of the roof The inclined pre-splitting borehole B blasts the uppermost key stratum within the vertical height H', and the angle with the horizontal plane is 70°. The depth of the inclined pre-splitting borehole B is , the borehole diameter is 42 - 100 mm, the charge length is half of the borehole depth, and the hole-sealing length is not less than one-third of the borehole depth; where H' is the theoretical pre-splitting height, with the unit of m.

2. The method for determining the roof pre-splitting borehole parameters for preventing rock bursts on the working face according to claim 1, wherein The vertical height of the roof plate H is determined by the theoretical pre-splitting height H'. If H'≥50, then H it is the vertical height from the upper interface of the key stratum in the uppermost layer in H' to the roof of the roadway. If H'<50, then H = 50. The calculation formula for H' is as follows: H ' = ; In the formula, is the cumulative mining thickness, with the unit of m; is the uniaxial mine pressure strength, with the unit of MPa.

3. The method for determining the roof pre-splitting borehole parameters for preventing rock bursts in the working face according to claim 1, wherein The horizontal projection of the key layer roof L satisfies: ； In the formula, is the tensile strength of the th key stratum within the vertical height H', with the unit of MPa; is the cracking coefficient of the key strata of the layer within the vertical height H'; k = 0.25 to 0.75; is the thickness of the key stratum in the layer within the vertical height H', with the unit of m; b is the inclined length of the working face, with the unit of m; is the unit weight of the key stratum rock within the vertical height H', with the unit of N / m3; for the nth layer; is the dip angle of the working face.

4. The method for determining the roof pre-splitting borehole parameters for preventing rock bursts on the working face according to claim 1, characterized in that, The opening position of the inclined pre-splitting borehole is located on the roof of the roadway near the working face side, and the spacing between adjacent inclined pre-splitting borehole groups is D , D The calculation formula is: ； Wherein, S is the adjustment coefficient; is the blasthole radius, with the unit of m; is the coefficient of rock hardness.

5. The method for determining the roof pre-splitting borehole parameters for preventing rock bursts on the working face according to claim 1, characterized in that , When, the number of each group of inclined pre-splitting drill holes The calculation formula is: ； When > 2, the rock formation between the intersection points of the key rock formation in the uppermost layer of the dip presplit boreholes A and B is equally divided according to the value. The final hole positions of the additional dip presplit boreholes are located at the equally divided positions. The diameter of the additional boreholes is 42 - 100 mm, the charging section length needs to be 1 / 2 of the borehole depth, and the hole sealing section length is not less than 1 / 3 of the borehole depth.

6. The method for determining the roof pre-splitting drilling parameters for preventing rock bursts on the working face according to claim 1, characterized in that, The length of the rock cores drilled from the roof of the roadway in the impact hazard areas is at least 100 m; both the strike pre-splitting boreholes and the dip pre-splitting boreholes are at least 200 m ahead of the working face extraction face.

Images