Effect of detonator position on fragmentation at Kevitsa open pit mine

Abstract. Blasting is one of the main operations in open pit mining and effective rock blasting can have a major impact on the overall economy of the mine. To obtain optimal rock fragmentation by blasting, explosive energy must be well-utilized, well-distributed, and targeted to the rock mass that we aim to fragment. A position of a detonator in a blasthole affects all of the above. The aim of this thesis was to study the effect of detonator position on fragmentation at the Kevitsa open pit mine. The theoretical optimum for the detonator position in the explosive column was defined and tested in practice. In addition, the effects on bench floor conditions were investigated. The practical study consisted of blasted test fields within production blasts, where the current blasting practice used in Kevitsa was compared to the test design representing the theoretical optimum. The effects were measured and studied with shovel-mounted machine vision cameras, test drillings, and loading machine operator feedback forms. Considering optimal fragmentation and less damage below the bench floor level, 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 allows for significant improvement in rock fragmentation and bench floor conditions. The results of this study can be applied more generally in open pit blasting

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%