Effect of detonator position on rock fragmentation: Full-scale field tests at Kevitsa open pit mine

Abstract

The effect of detonator position on rock fragmentation was studied at the Kevitsa open pit mine. Five full-scale field tests were conducted where the blasts were divided into test and reference areas, and compared with each other. In the test areas, the detonators were placed at or near the middle point of the explosive column, and in the reference areas, corresponding to the conventional blasts used in the Kevitsa mine, the detonators were placed about 1–2 m above the bottom of the blast holes. The rock fragment sizes from both test and reference areas were measured and studied using shovel-mounted machine vision cameras and image analysis. Both theoretical and field studies indicated that the detonator position plays an important role in rock fragmentation, and that the detonator position in the middle of the explosive column yielded significant improvement in rock fragmentation. For example, percentages of fragment sizes x20, x50, and x80 are reduced by 10–27%, 11–30%, and 8–31%, respectively; percentage of large size fragments (>1.0 m) is reduced by 29–99%; percentage of small size fragments (<2.5 cm) is increased by 6–49%. • Detonator location was studied for open pit bench blasting. • The best detonator position is the middle of the explosive charge length. • The middle detonator position significantly improved rock fragmentation. • Fragment size x50 was reduced by 11–24% in the field tests.