PSI - Issue 32

S.S. Andreiko et al. / Procedia Structural Integrity 32 (2021) 3–9 V.Anikin/ Structural Integrity Procedia 00 (2021) 000–000 The stress 2 for the same distance is determined by the value of the known experimental stress in granite and the ratio of the acoustic stiffness of the studied rock and granite [6]: 2 ( ′ ) = г ( ′ ) ∙ ∙ г ∙ г ⁄ (18) where г and г are the density and speed of longitudinal vibrations of granite. The magnitude of the stress in granite г (100)=10.3 MPa was taken from the experimental graph of the radial stresses presented in [6, Fig. 58]. At this distance in the rock, the experimental values of the strain and duration of the explosion pulse were measured with a constant diameter of the elongated explosive charge at various radial clearances created by changing the diameter of the borehole. When extrapolating the strain damping curve to a zero clearance (the case of the full borehole charging), the optimal pulse increases by about 10-11 times. The pulse increase due to the radial clearance is determined by the value of the clearance coefficient according to formula (2), which gives the best convergence with the results [6]. Results of the experimental determination of the radius of the crack formation zone in four dolomite rocks during blasting with AP-5ZhV ammonite safety explosive ( = 3.79 MJ/kg, = 1050 kg/m 3 , = 3700 m/s) in cartridges with a diameter of 36 mm with a charge length 1.2 m showed that the average radius of the crack formation zone was 0.5 m [12]. Table 2 shows the physicomechanical characteristics of dolomite rocks and the radius of the crack formation zone for AP-5ZhV ammonite for these rocks [12–14]. The calculated parameters of Table 2 were determined from the parameters of the theoretical explosion of AP-5ZhV ammonite in granite according to formulas (1-15), which were then taken as reference for dolomite rocks. The calculated values of the radii of their fracture zones are close to the experimental values. 6

8

Table 2. Calculated values of the radius of the crack formation zoneof dolomite rocks for ammonite AP-5ZhV

, kg/m3 , m/s

4

m 6

μ, unit fraction

, MPa

,

Rock

1

2

3

5

Dolomite

2640 2640 2640 2640

6206 5785 5800 6444

68.9 58.7 58.5 59.5

0.28 0.22 0.22 0.22

0.49 0.58 0.52 0.49

Clay dolomite Dense dolomite

Limestone dolomite

The maximum discrepancy (clayey dolomite and dense dolomite) is 6 %, the minimum is 2 % (dolomite and limestone dolomite), the average (for four rocks in absolute value) is 4 %. The resistance of a rock to dynamic impact depends on the type and nature of the impact. Under explosive action, the dynamic strength depends on an explosive type and the conditions of the explosion. 5. Conclusions 1. The use of the strain pulse of detonation products in elongated charges makes it possible to calculate the radius of the zone of the effective crack formation from the action of the primary compressive explosion wave in rocks of almost any strength. 2. We determined the degree of pulse damping with the distance and the radius of the crack formation zone for 17 rocks with strength from 30 MPa (sylvinite = 1.05 m) to 335 MPa (quartz porphyrite = 0.26 m) for a borehole charge with a length of 1.6 m when using explosive ammonite 6ZhV in cartridges with a diameter of 32 mm and a diameter of holes 42 mm. 3. A good convergence of the theoretical (calculated) radius of the crack formation zone with the results of the experimental measurements of the crack formation radius during the experimental blasting was obtained for four dolomite rocks (the average deviation in absolute value is 4 %) with a changed relative radial clearance of the