A case study on blasting for controlled casting of high over-burden bench

Abstract

The primary objective of any blasting program to overcast the overburden is to enormously increase the heave (or throw) of the burden rock mass. Fragment size control assumes less significance in this type of casting program. However, casting of the muck piles by blasting, as discussed in this paper, refers to considerable lateral spreading of the overburden rock on the lower berm face of the bench largely with an objective to facilitate the loading of the muck by the loaders. As such, the present paper highlights the important blast design parameters for vertical lowering and lateral spreading of the blasted muck in large-scale blasts on a sandstone bench of a surface coal mine. A series of field-scale blasts were conducted on a high (22-24 m) sandstone bench which was excavated by 10 m3 rope shovel with a maximum digging height of 14 m only. Keeping in mind the hazards faced by shovel while loading a blasted bench much higher than its maximum digging height capability, it was desired to drop down the blasted muck pile by innovative controlled blasting technique in order to facilitate the loading operation. Furthermore, it was essential to control the fragment size in the blasted muck pile for its efficient digging by the shovel. For this, the blast rounds were suitably designed and fired on row to-row firing pattern at higher inter-row delay and with increased explosive charge in the complete round. The paper describes the blast design changes and their impact on the fragment size and shovel performance. The state of-art image analysis technique was used to evaluate the fragment size in the blasted muck piles.