Norilsk Nickel’s Polar Division, Norilsk, Russia:

A. S. Koretskiy, Manager at Drilling and Blasting Department at Mining Office of Mining Practice Department, KoretskiyAS@nornik.ru

Global Mining Explosive–Russia, Moscow, Russia:
I. Yu. Maslov, Chief Engineer, Candidate of Engineering Sciences

When sensitizing emulsion explosives (EE) with gas microbubbles (GMB), the size of the latter has a significant effect on the detonation and susceptibility of EE to the initiating pulse. With a decrease in the total porosity of EE below a certain limit, it loses the ability of detonation decomposition, and with an increase above a certain limit, it loses the aggregate stability due to the fusion of GMB. At the same time, too small or too large GMBs do not form ‘hot spots’ that serve as ignition centers when initiating EE. When conducting blasting operations in monolithic rocks, both zones of increased and decreased density are formed in the upward borehole charges of EE under the influence of gravitational forces compared to the density of EE at atmospheric pressure. Therefore, in the lower part of the charge, due to the excessive hydrostatic pressure from the charge column, there is a decrease in the size of GMB and a decrease in the total porosity of the EE, while in the upper part there is an increase in the size of GMB and an increase in the total porosity of the EE. These circumstances serve as a source of failures during blasting of upward boreholes, therefore, the identification of patterns of changes in the size of GMB along the length of this charge is of great practical importance. The paper provides a theoretical assessment of the size of GMB sensitizing EE along the length of upward boreholes. It is shown that the range of changes in the size of GMB along the length of an upward EE charge can vary within the limits significantly exceeding the range of changes in the size of GMD in the downward charges. The porosity and radius of GMB in EE based on a heavier matrix emulsion decrease with an increasing distance from the bottomhole faster than in EE with a lighter matrix emulsion. When initiating upward borehole EE charges sensitized by GMB, it is advisable to have an upper location of the intermediate detonator due to the likely development of unstable detonation modes when initiating a charge from the wellhead side. The obtained patterns are of interest to specialists involved in both the use of EE and the improvement of this type of industrial explosives.

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