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

V. A. Isheyskiy, Assistant, Candidate of Engineering Sciences, vd07@bk.ru
M. M. Yakubovskiy, Associate Professor, Candidate of Engineering Sciences

The article presents the integrated research data on influence of blast energy on strength characteristics of blasted rocks and on yield of sub-standard size grades in different areas of explosive fracture. After a series of simulation experiments using equivalent materials, the mechanism of strength loss in blasted rocks and the quantity of sub-standard size yield in different zones of explosive fracture were obtained. The full-scale experiments revealed relationships between average size of a blasted rock fragment, energy input, strength reduction factor and distance to a blast source. The comparison of the relationships obtained to calculate strength of an average rock fragment in the field conditions and in the simulation experiments using equivalent materials has allowed the conclusion to be drawn that the theoretical relationship satisfactorily approximates the experimental data and is applicable to the determination of strength of an average rock fragment and of a rock damage zone based on the data on energy input of an explosive. The quality of rock mass blasting has great influence on preservation of minerals and on economic efficiency of a mine. When hard rocks are blasted to produce break stone, there is much yield of undersize and oversize rejects, the amount of which is governed by strength characteristics of rocks. It is of the current concern to study effect of drilling and blasting parameters on strength of blasted rocks, which is important both as the theory and applications. This article describes a full-scale experiment carried out in a broken stone quarry. The experiment was aimed to relate strength of rock pieces after blasting, considering damage zones in rock mass, and the blast energy. There were three series of blasts. The explosive was Nitronit E-70, the powder factor of the explosive was varied by changing blasthole patterns (4.5×4.5 m, 4×4.5 m, 4×4 m). The key parameters of drilling-and-blasting remained unaltered. In order to find the effect of the blast energy on the strength of blasted rocks, the selected specimens were subjected to compression tests on MTS servohydraulic testing machine. The full-scale experiments produced the relationships between the strength of an average size rock fragment, blast energy input, strength reduction factor and the distance from the blast source. The published results were obtained in the framework of R&D under the governmental assignment issued for higher education and scientific institutions.

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