A method for determining the reasonable spacing of drilling holes in composite blasting pre-splitting hard roof

Abstract

The present invention provides a method for determining a reasonable spacing of holes drilled in a hard roof pre-splitting by composite blasting, the method comprising the following steps: first, conducting a core test on the roof rock layer on site to obtain relevant physical and mechanical parameters thereof; second, establishing a numerical simulation model for shaped jet penetration based on the specifications of the perforating bullet to obtain the average velocity at the beginning of jet penetration, the maximum velocity of the head, and the time required for the jet to be formed and to start penetration; third, obtaining the length of the shaped jet penetration channel based on the quasi-steady theory of shaped jet; fourth, obtaining the attenuation coefficient and the geometric shape factor based on the stress intensity factor theory of fracture mechanics; fifth, obtaining the crack extension length under the action of the explosion stress wave and the crack extension length under the action of the explosive gas based on the fracture mechanics, the Griffith strength criterion, and the explosive blasting theory; and sixth, theoretically superposing and calculating the shaped jet penetration channel length and the crack extension length under the action of the explosion stress wave and the action of the explosive gas to obtain a reasonable spacing of holes drilled in a hard roof pre-splitting by composite blasting.

Description

Technical Field

[0001] The present invention relates to a method for determining a reasonable spacing of drill holes in a composite blasting pre-splitting hard roof. The method mainly aims at the rock burst problem under mining conditions of a hard roof coal seam, and determines the reasonable spacing of drill holes when pre-splitting the hard roof is controlled by using a composite blasting directional cracking technology. Background Art

[0002] The manifestation of mining pressure in the mining area is closely related to the characteristics of roof fracture. Especially under the conditions of hard roof mining, due to the high strength of the rock layer, a large amount of elastic energy is easily accumulated. After the working face is mined, the hanging roof will have characteristics such as large step distance and long hanging roof time. This makes the tunnel support bear great pressure, the coal pillars are crushed and unstable under pressure, and the surrounding rock is easy to deform and difficult to maintain. In order to reduce the degree of rock burst damage under the conditions of hard roof mining and prevent the occurrence of rock burst accidents, the composite blasting directional cracking technology is used to directional pre-crack the hard roof and effectively control the mining area pressure. Reasonable drilling spacing can ensure the effectiveness of composite blasting directional roof cutting, so it is crucial to determine the appropriate drilling spacing. Summary of the Invention

[0003] The present invention aims to solve the problem of determining the reasonable spacing of drill holes when using composite blasting technology to pre-crack and control the roof under hard roof mining conditions, and provides a method for determining the spacing of drill holes in composite blasting pre-cracked hard roof.

[0004] The method for determining the reasonable spacing of drill holes for composite blasting pre-cracking of a hard roof described in the present invention is based on fracture mechanics and the Griffith strength criterion, and on the theory of the interaction between explosion stress waves and explosive gases to obtain a formula for reasonable spacing of drill holes. The formula can be used to guide the arrangement of drill holes in engineering practice and ensure the directional pre-cracking control effect of composite blasting on a hard roof. The method comprises the following steps: a. performing a core test on the roof rock layer on site to obtain its relevant physical and mechanical parameters, where the rock density and tensile strength are denoted as ρ, respectively. T and σ t ;

[0005] b. According to the parameters of the perforating bullet, a numerical simulation model of shaped jet penetration is established to simulate the jet penetration process and obtain the average velocity V at the beginning of jet penetration. j , the maximum head velocity V0 and the time t0 required from jet formation to the start of penetration;

[0006] c. Let the perforating charge height be S and the jet density be ρ J , the square root of the ratio of rock density to jet density is γ. According to the quasi-steady penetration theory of shaped charge jet, the penetration channel length p of shaped charge jet is obtained;

[0007] d. Based on the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient α and the crack geometry factor β are obtained;

[0008] e. Let the density, detonation velocity, critical pressure and average detonation pressure of the explosive be ρ respectively. e , D e , p k and p w , the isentropic index during the explosion process is k1, the adiabatic index is γ1, the drilling radius is r, and the charge radius is r e , the charge coefficient of the blast hole is l e ;

[0009] f. After the explosive explodes, an explosion stress wave and explosive gas are generated. According to the Griffith strength criterion and explosive explosion theory, the length of the crack generated by the explosion stress wave, r1, is obtained;

[0010] g. According to the Griffith strength criterion and explosive explosion theory, the length r2 of the crack generated by the explosive gas is obtained;

[0011] h. Theoretical superposition calculation of the shaped charge jet penetration channel length p, the crack length r1 generated by the blast stress wave, and the crack length r2 generated by the blast gas was performed to obtain the reasonable spacing l of the holes drilled in the hard roof for composite blasting pre-cracking;

[0012] in, l=2(r+p+r1+r2).

[0013] The present invention provides a method for determining the reasonable spacing of drilling holes in a composite blasting directional seam-making and top-cutting technology for the rock burst problem under hard roof mining conditions, thereby ensuring the composite blasting directional seam-making effect and guaranteeing safe, high-yield and efficient mining of the working face.

[0014] The method described in the present invention has the following advantages: 1) it takes into account the theory of the combined action of explosion stress waves and explosive gases, calculates the crack extension lengths under the action of explosion stress waves and the crack extension lengths under the action of explosive gases, and performs theoretical superposition calculations; 2) it fully considers the theory of fracture mechanics, and calculates the crack extension length based on the stress intensity factor theory and the Griffith strength criterion; 3) the method has strong applicability, the calculation results are accurate and reliable, and it has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the arrangement of drilling holes for pre-cracking hard roof by composite blasting.

[0016] Figure 2 Schematic diagram for calculating the reasonable spacing of drilling holes for pre-cracking hard roof by composite blasting (i.e. Figure 1 (enlarged view of A in Figure 3).

[0017] In the figure: 1-roof rock layer, 2-perforating charge, 3-explosive, 4-shaped jet penetrating the channel, 5-cracks generated by the action of explosion stress wave, 6-cracks generated by the action of explosive gas, 7-perforating tube string, 8-drill hole, 9-drill hole spacing, 10-hole sealing, 11-detonating cord, 12-detonator, 13-detonator. DETAILED DESCRIPTION

[0018] The present invention will be further described below by taking the composite blasting pre-splitting control of a hard roof of a mine in Shanxi as an example with reference to the accompanying drawings:

[0019] Figure 1 3 is a schematic diagram of the arrangement of the composite blasting pre-splitting hard roof drilling of the present invention. Multiple holes are drilled through the roof from top to bottom. A perforating tube string is installed in each hole. The distance between two adjacent perforating tube strings is the distance between the holes.

[0020] like Figure 2 The figure shows a schematic diagram of calculating the reasonable spacing of holes in a method for determining the reasonable spacing of holes in a composite blasting pre-splitting hard roof according to the present invention. The specific steps of the technique are:

[0021] a. Conduct core testing on the roof rock layer 1 on site to obtain its relevant physical and mechanical parameters. The rock density and tensile strength Poisson's ratio are 2500 kg / m 3 and 10MPa;

[0022] b. Based on the parameters of perforating charge 2, a numerical simulation model for shaped charge penetration was established. The penetration process was simulated, resulting in an average velocity of 2900 m / s at the start of penetration, a maximum velocity of 4234 m / s at the head, and a time of 20 μs from jet formation to the start of penetration. The numerical simulation model for jet penetration was typically established using LSDYNA numerical simulation software. These parameters can also be obtained through physical testing. This method is conventional in the art.

[0023] c. The blast height of perforating bullet 2 is 15 mm, and the jet density is 8960 kg / m 3 The square root of the ratio of rock density to jet density is 0.53. According to the quasi-steady penetration theory of shaped jet, the length of shaped jet penetration channel 4 is 158.35 mm.

[0024] d. Based on the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient is 0.2, and the fracture geometry factor is 1.15. Both parameters are empirical and can be selected based on actual site conditions.

[0025] e. The density, detonation velocity, critical pressure and average detonation pressure of explosive 3 are 1787 kg / m 3, 8390m / s, 200MPa and 12.52GPa, the isentropic index during the explosion of the explosive is 1.3, the adiabatic index is 4, the drilling radius is 37.5mm, the charging radius is 22.5mm, and the blasthole charging coefficient is 0.4;

[0026] f explosives 3 explosion produces an explosion stress wave and explosive gas, according to the Griffith strength criterion and explosive explosion theory, the length of the crack 5 generated by the explosion stress wave is 140.98mm;

[0027] g. According to the Griffith strength criterion and explosive explosion theory, the length of the crack 6 generated by the explosive gas is 419.67mm;

[0028] h. Theoretical superposition calculations were performed on the length p of the shaped charge jet penetration channel 4, the length r1 of the crack 5 generated by the explosion stress wave, and the length r2 of the crack 6 generated by the explosive gas, and the reasonable spacing of the drill holes in the composite blasting pre-cracked hard roof was obtained as 1513 mm.

[0029] Figure 2 It can be seen that under reasonable drilling spacing, the cracks generated by the perforating string in each borehole can be connected to each other (the sum of the lengths of the cracks on the left and right sides is the drilling spacing).

[0030] The drill hole spacing was set at 1500mm. After composite blasting pre-cracking control, observations using a borehole peephole instrument revealed good joint formation. Simultaneously, mine pressure monitoring indicated a significant reduction in mine pressure during the working face mining process. This validated the rationality of the drill hole spacing and the method for determining the optimal drill hole spacing for composite blasting pre-cracking of hard roof. This method is crucial for ensuring the effectiveness of composite blasting pre-cracking in controlling hard roof and for safe and efficient mining at the working face.

Claims

1. A method for determining the reasonable spacing of drill holes in composite blasting pre-cracking hard roof, based on fracture mechanics and Griffith strength criterion, and based on the theory of the interaction between explosion stress waves and explosive gases, obtains a formula for the reasonable spacing of drill holes; characterized by: The steps include: a. Conduct core sampling test on the roof rock layer (1) to obtain its relevant physical and mechanical parameters. The rock density and tensile strength are ρ T and σ t ; b. According to the parameters of perforating bullet (2), a numerical simulation model of shaped jet penetration is established to simulate the jet penetration process and obtain the average velocity V at the beginning of jet penetration. j , the maximum head velocity V0 and the time t0 required from jet formation to the start of penetration; c. Record the explosion height of the perforating bullet (2) as S , the jet density is ρ J , the square root of the ratio of rock density to jet density is γ. According to the quasi-steady penetration theory of shaped charge jet, the length p of the shaped charge jet penetration channel (4) is obtained; d. Based on the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient α and the crack geometry factor β are obtained; e. Let the density, detonation velocity, critical pressure and average detonation pressure of explosive (3) be ρ e , D e , p k and p w , the isentropic index during the explosion process is k1, the adiabatic index is γ1, the drilling radius is r, and the charge radius is r e , the charge coefficient of the blast hole is l e ; f. After the explosion of explosives (3), an explosion stress wave and explosive gas are generated. According to the Griffith strength criterion and explosive explosion theory, the length r1 of the crack (5) generated under the action of the explosion stress wave is obtained; g. According to the Griffith strength criterion and explosive explosion theory, the length r2 of the crack (6) generated by the explosive gas is obtained; h. Theoretical superposition calculation of the length p of the shaped energy jet penetration channel (4), the length r1 of the crack (5) generated under the action of the stress wave, and the length r2 of the crack (6) generated under the action of the explosive gas is performed to obtain the reasonable spacing l of the holes drilled in the hard roof pre-cracked by the composite blasting; in,

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