Delay intervals for quality fragmentation of jointed rock mass by blasting in open pit mines

The mechanism of fragmentation quality improvement in short-delay blasting in
jointed rock mass is substantiated. The fragmentation quality improvement is achieved owing to closure of natural joints under the action of deformation waves in the target areas (in interwell space) and due to the more uniform distribution of energy of destructive stress waves. The theoretical formula is obtained to calculate the delay intervals that ensure closure of joints in the target areas of rock mass. A delay interval is governed by the explosion and geometrical parameters of explosives, characteristics of a large-scale blast, density of rocks and rock jointing. It is found that in short-delay blasting at the improved fragmentation quality (for instance, at rock jointing category III), it is required to blast the first 20 groups of explosive charges at the increased delay intervals starting from 150 ms and to gradually decrease them to 70 ms. The subsequent groups of explosive charges should be blasted at the delay interval of 50 ms. Such delay intervals ensure four-fold stressing of the interwell spaces by the waves of stresses and deformation. The appropriateness of the studies is confirmed by the practical experience gained by different authors in blasting at the effective delay intervals variable from 30 to 200 ms. At the delay interval larger than 50 ms, it is unrecommended to use detonating cords because of potential cord damage and faulting.

Tyupin V. N. Delay intervals for quality fragmentation of jointed rock mass by blasting in open pit mines. MIAB. Mining Inf. Anal. Bull. 2023;(12):70-78. [In Russ]. DOI: 10.25018/0236_1493_2023_12_0_70.

V.N. Tyupin, Dr. Sci. (Eng.), Professor, Belgorod State National Research University, 308015, Belgorod, Russia, e-mail: tyupinvn@mail.ru, ORCID ID: 0000-0002-3709-0957.

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