Method for determining reasonable drill hole spacing of composite blasting presplitting hard roof

Abstract

The invention provides a method for determining a reasonable distance between drill holes of a composite blasting presplitting hard roof, which comprises the following steps of: 1, performing coring test on a roof rock stratum on site to obtain related physical and mechanical parameters of the roof rock stratum; secondly, according to the specification of a perforating bullet, an energy-gathered jet penetration numerical simulation model is established, and the average speed at the beginning of jet penetration, the maximum speed of the head and the time needed by jet from formation to penetration starting are obtained; thirdly, the energy-gathered jet penetration duct length is obtained based on the energy-gathered jet quasi-steady theory; 4, obtaining an attenuation coefficient and a geometrical shape factor according to a fracture mechanics stress intensity factor theory; 5, according to fracture mechanics, a Griffus strength criterion and an explosive blasting theory, obtaining a crack propagation length under the action of an explosion stress wave and a crack propagation length under the action of an explosion gas; and 6, theoretical superposition calculation is conducted on the length of the energy-gathered jet penetration hole channel and the crack extension length under the action of the explosion stress waves and the action of the explosion gas, and the reasonable interval of the composite blasting presplitting hard roof drill holes is obtained.

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, mainly aiming at the rock burst problem under the condition of hard roof coal seam mining, and determining a reasonable spacing of drill holes when pre-splitting the hard roof is controlled by using a composite blasting directional seam making technology. Background Art

[0002] The law of the mine pressure in the mining area is closely related to the characteristics of the 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, there will be characteristics such as large suspended roof step distance and long suspended roof time, which makes the tunnel support bear large pressure, the coal pillar is crushed and unstable under pressure, and the surrounding rock is easy to deform and difficult to maintain. In order to reduce the degree of impact ground pressure under hard roof mining conditions and prevent the occurrence of impact ground pressure accidents, the composite blasting directional cracking technology is used to directional pre-crack the hard roof and efficiently control the mine pressure in the mining area. Reasonable drilling spacing can ensure the directional cutting effect of composite blasting, so it is very important to determine the reasonable spacing of drilling holes. Summary of the invention

[0003] The invention provides a method for determining the spacing of holes in a composite blasting pre-splitting hard roof to solve the problem of determining the reasonable spacing of holes when a composite blasting technology is used to pre-splitting and control the roof under hard roof mining conditions.

[0004] The method for determining the reasonable spacing of the holes in the composite blasting pre-cracking hard roof described in the present invention obtains a formula for the reasonable spacing of the holes based on the theory of the interaction of the explosion stress wave and the explosion gas according to fracture mechanics and the Griffith strength criterion, and can be used to guide the arrangement of holes in engineering practice to ensure the directional pre-cracking control effect of the composite blasting hard roof, including the following steps: a. Conducting a coring test on the roof rock layer on site to obtain its related physical and mechanical parameters, and recording the rock density and tensile strength as ρ T With σ t ;

[0005] b. According to the parameters of the perforating bullet, a numerical simulation model of shaped energy 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 beginning of penetration;

[0006] c. The explosion height of the perforating bullet is S, and 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 energy jet, the penetration channel length p of shaped energy jet is obtained;

[0007] d. According to 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 e , D e , p k and p w , the isentropic index of the explosive explosion 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 explosion of explosives, explosion stress waves and explosive gases are generated. According to the Griffith strength criterion and the theory of explosive explosion, the length of the crack generated under the action of the explosion stress wave, r1, is obtained;

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

[0011] h. Theoretical superposition calculation is performed on the length p of the shaped energy jet penetration channel, the length r1 of the crack generated by the explosion stress wave, and the length r2 of the crack generated by the explosion gas, and the reasonable spacing l of the holes drilled in the composite blasting pre-cracking hard roof is obtained;

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

[0013] The present invention provides a method for determining a reasonable spacing of holes in a composite blasting directional seam-making and top-cutting technology for rock burst problems 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) the theory of the combined action of explosion stress wave and explosion gas is taken into consideration, the crack extension length under the action of explosion stress wave and the crack extension length under the action of explosion gas are calculated respectively, and theoretical superposition calculation is performed; 2) the fracture mechanics theory is fully considered, based on the stress intensity factor theory, combined with the Griffith strength criterion, the crack extension length is calculated; 3) the method has strong applicability, the calculation results are accurate and reliable, and the application prospect is broad. 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 (A in the figure).

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

[0018] The following is a further description of the present invention 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 The figure is a schematic diagram of the arrangement of the composite blasting pre-splitting hard roof drilling of the present invention. A plurality of boreholes are drilled through the roof from top to bottom, a perforating tube string is installed in each borehole, and the distance between two adjacent perforating tube strings is the borehole distance.

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

[0021] a. Carry out core sampling test 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 2500kg / m 3 and 10MPa;

[0022] b. According to the parameters of perforating bullet 2, a numerical simulation model of shaped energy jet penetration is established to simulate the jet penetration process, and the average velocity at the beginning of jet penetration is 2900m / s, the maximum velocity of the head is 4234m / s, and the time required for the jet from formation to the beginning of penetration is 20μs; generally, the numerical simulation model of jet penetration is established using LSDYNA numerical simulation software, and of course, these parameters can also be obtained through physical experiments. The above method is a conventional technical means in this field;

[0023] c. The explosion 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 energy jet, the length of shaped energy jet penetration channel 4 is 158.35 mm.

[0024] d. According to the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient is 0.2 and the crack geometry factor is 1.15. The above two parameters are empirical parameters and can be selected according to the actual situation on site;

[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 blast hole charging coefficient is 0.4;

[0026] f. After the explosion of explosive 3, an explosion stress wave and explosion gas are generated. According to the Griffith strength criterion and the theory of explosive explosion, the length of the crack 5 generated under the action of the explosion stress wave is 140.98 mm;

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

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

[0029] Figure 2 It can be seen that under reasonable drilling spacing, the cracks generated by the perforating pipe 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 borehole spacing was set to 1500mm. After the composite blasting pre-cracking control, the composite blasting seam formation was observed through the borehole peep instrument. At the same time, the mine pressure monitoring showed that the mine pressure intensity during the mining process of the working face was significantly reduced, which verified the rationality of the borehole spacing and the correctness of the method for determining the reasonable spacing of the composite blasting pre-cracking hard roof. The above method for determining the reasonable spacing of the boreholes is of great significance for ensuring the effect of composite blasting pre-cracking to control the hard roof and the safe and efficient mining of the working face.

Claims

1. A method for determining the reasonable spacing of 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 wave and explosion gas, obtains a formula for the reasonable spacing of holes; it is characterized by: The steps include: a. Conduct core sampling test on the roof rock layer (1) on site to obtain its relevant physical and mechanical parameters. The rock density and tensile strength are ρ T With σ t ; b. According to the parameters of the perforating bullet (2), a numerical simulation model of shaped energy 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 beginning 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 focused jet, the length p of the penetration channel (4) of the focused jet is obtained; d. According to 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 of the explosive explosion 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 the explosive (3), an explosion stress wave and explosion gas are generated. According to the Griffith strength criterion and the theory of explosive explosion, 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 explosion gas is obtained; h. Theoretical superposition calculation is performed on the length p of the shaped energy jet penetration channel (4), the length r1 of the cracks (5) generated under the action of the stress wave, and the length r2 of the cracks (6) generated under the action of the explosive gas, and the reasonable spacing l of the holes drilled in the composite blasting pre-cracking hard roof is obtained; in,

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