Saint-Petersburg Mining University, Saint-Petersburg, Russia:

V. N. Kovalevskiy, Associate Professor, Candidate of Engineering Sciences, vladimir_kovalevskiy@mail.ru
K. R. Argimbaev, Assistant, Candidate of Engineering Sciences

The article describes an integrated approach to study generation of an explosive jet and its penetration depth in marble and granite under directional destruction with elongated jet charges. It is found that the basic condition of an explosive jet (knife) penetration is that the pressure at the interface exceeds dynamic compressive strength of rocks. The X-ray pattern of the process of the explosive jet penetration in a rock slab is presented together with the data of lab tests on jet penetration depths in case of different focus distances to a rock block. The tests show that penetration rate of an explosive jet in rocks is much less than the explosive jet velocity in air. Also, the penetration rate of an explosive jet lowers as penetration depth grows, and the explosive jet gets longer during penetration. The scheme of interaction between the explosive jet elements and rocks is presented. Based on the test results, the conclusions have been drawn that: deceleration rate of the jet elements is lower in granite than in marble, consequently, the penetration depth value of the explosive jet behaves the same way; the focus distance is higher in granite than in marble; the values of the focus distances are lower than the value of the distance at which an explosive jet is decomposed into elements. The analysis of the laboratory testing result shows that the length of a main crack in the model blocks is greatly influenced by the length of a primary crack: the former is longer with the longer primary crack. Accordingly, generation of long main cracks requires maximized penetration depth of an explosive jet (knife). The data obtained in the research into directional destruction of rocks by long jet charges are recommended for use in actual separation and splitting of stone blocks, in bench design, perimeter control blasting, etc.

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