PSI - Issue 32

S.S. Andreiko et al. / Procedia Structural Integrity 32 (2021) 3–9 V.Anikin/ Structural Integrity Procedia 00 (2021) 000–000

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2. The Subject of the Research In the classical theories of explosive destruction and in the practical conduct of blasting works, the pressure of the gases formed during the explosion is taken as the main factor of destruction, while the time during which the strain acts on the destroyed object is usually not taken into account due to a short duration of the explosion process [2-7]. In this article, the main destruction factor is considered to be the explosion pulse (hereinafter - explosion pulse), equal to the product of strain and the duration of its impact on the object of destruction [2-9]. Taking into account the fact that with an increase in the distance from the charge center, the strain of the explosive gases (detonation products of the explosive charge) decreases in a power law dependence, the change in the explosion pulse with the distance is proposed to be determined by the equation [8]: ( ) = ∙ ∙ ( ) ∙ 0 . 5 ⁄ (1) where ( ) is the explosion pulse in a rock mass at a distance , Pa·s; is the clearance coefficient; is the calculated initial strain in the charge chamber, Pa; is the relative (dimensionless) distance from the charge center, expressed in the radii of the charge chamber; is an indicator of the degree of the explosion strain (and pulse) damping with a distance, depends on the type of rock and the used E; ( ) is the duration of the explosion pulse at distance from the charge center, s; is the charge length, m. 2.1. Clearance Coefficient To simulate the formation of a strain pulse in the borehole clearance in the process of numerous reflections of the detonation wave front from the borehole walls and from the collision of waves in the charge center during their opposite motion from the borehole walls, the clearance coefficient is introduced: = ∆ ⁄ (2) = ( 0 ⁄ ) 6 (3) Δ = ( − 0 ) 0 ⁄ (4) where is the coefficient characterizing the decrease in the explosion strain in the volume of the radial clearance with the expansion of the detonation products; Δ is the relative radial clearance; is an empirical indicator of the strain damping degree in the radial clearance, depending on the magnitude of this clearance; 0 is the cartridge radius, m; is the charge chamber radius (borehole, well), m. For the optimal relative clearance ∆ 0 = 0.3125, the value of the empirical indicator of the strain damping degree in the radial clearance is = 3.4 for an explosive of the ammonite 6ZhV type. The coefficient is derived from the law of expansion of the volume of the explosion products V at high strains : ∙ 3 = [3]. Considering that the volume of a cylindrical borehole (and a radial clearance ) is proportional to the square of its radius, the degree when calculating the value of the coefficient in expression (3) is equal to: 3·2 = 6. Due to the presence of a radial clearance, the pulse duration and magnitude increase due to multiple reflections in the process of strain stabilization. In the absence of a radial clearance (when the borehole is fully charged), most of the energy is spent on deformation, overgrinding and heating of the rocks of the borehole's boundary layer.

2.2. Pulse Duration

The pulse duration is determined by expression (5) from [6]: ( ) = [ + 0,21 ∙ ( − 1)] ∙ 10 −3 , = 0,21 + 1000 ∙ (0) ⁄ ,

(5)

(6)