Method for determining model of perforation pipe string of composite blasting presplitting hard roof

Abstract

The invention provides a method for determining the model of a perforation pipe string for a composite blasting presplitting hard roof, which aims at solving the problem that no scientific calculation method is provided for the model of the perforation pipe string in the existing composite blasting directional fracture-forming top-cutting technology, and comprises the following steps of: 1, carrying out coring test on a roof rock stratum on site to obtain related physical and mechanical parameters of the roof rock stratum; 2, 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 3, performing theoretical superposition calculation on the crack extension length under the action of the explosion stress wave and the crack extension length under the action of the explosion gas to obtain the distance between the adjacent same-phase perforating bullets. 4, the theoretical hole density of the perforating pipe string is determined according to the distance between every two adjacent perforating bullets; 5, the theoretical outer diameter of the perforation pipe string is determined according to the radius of the drilled hole; and 6, determining the model of the perforation pipe string according to the theoretical hole density and the theoretical outer diameter of the perforation pipe string. The method is reasonable and accurate, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to a method for determining a model of a composite blasting pre-splitting hard roof perforating pipe string, which mainly aims at the rock burst problem under the condition of hard roof coal seam mining, and determines the model of the perforating pipe string when the composite blasting directional seam making technology is used to pre-splitting the hard roof. Background Art

[0002] The law of mine 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, it is easy to accumulate a large amount of elastic energy. Once it collapses suddenly, the elastic energy will be released instantly, resulting in impact mine pressure, large-area pressure and other mine pressure disasters and hurricanes. The suspended roof may also cause gas explosions, coal spontaneous combustion and other derivative disasters, causing serious damage to the working face, mining area and even the entire mine. In order to reduce the degree of impact ground pressure hazards under hard roof mining conditions and prevent the occurrence of impact ground pressure accidents, the composite blasting directional seam making technology is used to directional pre-crack control of the hard roof to efficiently control the mine pressure in the mining area. The perforating pipe string is the key equipment of the composite blasting directional seam making technology. Selecting the appropriate perforating pipe string model is crucial to ensure the effect of composite blasting directional seam making. Summary of the invention

[0003] The invention provides a method for determining the model of a perforating pipe string for pre-splitting a hard roof using a composite blasting technology to solve the problem of determining the model of a perforating pipe string when pre-splitting a roof using a composite blasting technology under hard roof mining conditions.

[0004] The method for determining the model of a composite blasting pre-cracking hard roof perforating pipe string of the present invention obtains the theoretical pore density and theoretical outer diameter of the perforating pipe string based on fracture mechanics and Griffith strength criterion, based on the theory of the interaction of explosion stress wave and explosion gas, and determines the model of the perforating pipe string, which can be used to guide the selection of perforating pipe strings in engineering practice, and includes the following steps: a. Conducting a coring test on the roof rock formation on site to obtain its related physical and mechanical parameters: denoted as σ t and μ, we get the stress wave attenuation index K;

[0005] b. According to the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient α and the crack geometry factor β are obtained;

[0006] c. 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 process is k1, the adiabatic index is γ, the drilling radius is r, and the charge radius is r e , the charge coefficient of the blast hole is l e ;

[0007] d. 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;

[0008] e. According to the Griffith strength criterion and explosive explosion theory, the length of the crack generated by the explosion gas, r2, is obtained;

[0009] f. The length of cracks generated by explosion stress wave r1 and the length of cracks generated by explosion gas r2 are theoretically superimposed and calculated to obtain the spacing l between adjacent perforating bullets of the same phase in the perforating pipe string;

[0010] g. According to the spacing l between adjacent perforating bullets of the same phase in the perforating string, determine the theoretical density of the perforating string as m, and round up the calculated result to an even number;

[0011] h. According to the drilling radius r, determine the theoretical outer diameter of the perforating tube string as d;

[0012] i. Select a perforating pipe string model with a theoretical pore density of m and a theoretical outer diameter of d;

[0013] in,

[0014] The present invention provides a method for determining the model of a perforating pipe string for 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.

[0015] 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

[0016] Figure 1 This is a schematic diagram of the calculation of perforating string parameters for composite blasting pre-cracking hard roof.

[0017] In the figure: 1-roof rock layer, 2-perforating tube string, 3-perforating bullet, 4-explosive, 5-cracks generated by the action of explosion stress wave, 6-cracks generated by the action of explosion gas. 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 in conjunction with the accompanying drawings:

[0019] a. Conduct core sampling test on the roof rock layer 1 on site to obtain its relevant physical and mechanical parameters. The tensile strength and Poisson's ratio are 10 MPa and 0.15 respectively, and the stress wave attenuation index is 2.18;

[0020] b. According to the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient is 0.1 and the fracture geometry factor is 1.2; the above two parameters are empirical parameters and can be selected according to the actual situation on site;

[0021] c. The density, detonation velocity, critical pressure and average detonation pressure of explosive 4 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;

[0022] d. After the explosion of explosive 4, 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 72.20 mm;

[0023] e. According to the Griffith strength criterion and explosive explosion theory, the length of the crack 6 generated by the explosion gas is 37.20 mm;

[0024] f. The length r1 of the crack 5 generated by the explosion stress wave and the length r2 of the crack 6 generated by the explosion gas are theoretically superimposed and calculated, and the spacing between adjacent perforating bullets 3 in the same phase in the perforating pipe string 2 is 218.82 mm;

[0025] g. According to the spacing between adjacent perforating bullets 3 of the same phase in the perforating string 2, the theoretical hole density of the perforating string 2 is determined to be 10 holes / m, and the calculated result is rounded up and is an even number;

[0026] h. According to the drilling radius of 37.5 mm, the theoretical outer diameter of the perforating tube string 2 is determined to be 65 mm;

[0027] i. Select the perforating pipe string 2 model with a theoretical hole density of 10 holes / m and a theoretical outer diameter of 65 mm.

[0028] A perforating pipe string with a hole density of 10 holes / m and an outer diameter of 65 mm was selected. After composite blasting pre-cracking control, it was observed through a borehole peep instrument that the composite blasting seam formation was good. 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, verifying the correctness of the method for determining the model of the perforating pipe string for composite blasting pre-cracking hard roof. The above-mentioned perforating pipe string model determination method is of great significance for ensuring the composite blasting pre-cracking control of hard roof and safe and efficient mining of the working face.

Claims

1. A method for determining the model of a composite blasting pre-cracking hard roof perforating pipe string, according to fracture mechanics and Griffith strength criterion, based on the theory of the interaction between explosion stress wave and explosion gas, obtains the theoretical pore density and theoretical outer diameter of the perforating pipe string, and determines the model of the perforating pipe string, 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: tensile strength and Poisson's ratio are σ t and μ, we get the stress wave attenuation index K; b. According to the fracture mechanics stress intensity factor theory, the blasthole pressure attenuation coefficient α and the crack geometry factor β are obtained; c. Let the density, detonation velocity, critical pressure and average detonation pressure of explosive (4) be ρ e , D e , p k and p w , the isentropic index of the explosive explosion process is k1, the adiabatic index is γ, the drilling radius is r, and the charge radius is r e , the charge coefficient of the blast hole is l e ; d. After the explosion of the explosive (4), 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; e. According to the Griffith strength criterion and the explosive explosion theory, the length r2 of the crack (6) generated by the explosion gas is obtained; f. The length r1 of the crack (5) generated by the explosion stress wave and the length r2 of the crack (6) generated by the explosion gas are theoretically superimposed and calculated to obtain the spacing l between adjacent perforating bullets (3) with the same phase in the perforating pipe string (2); g. According to the spacing l between adjacent perforating bullets (3) with the same phase in the perforating string (2), the theoretical hole density of the perforating string (2) is determined to be m, and the calculated result is rounded up and is an even number; h. According to the drilling radius r, determine the theoretical outer diameter of the perforating tube string (2) as d; i. Select a perforating pipe string (2) model with a theoretical pore density of m and a theoretical outer diameter of d; in,

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