Controlled blasting for long term stability of pit-walls

Abstract Controlled blasting techniques were used to control over-breaks and to aid in the stability of the remaining rock mass at Rampura Agucha open-pit mine in India. The mine is a lead zinc mine producing 5.95 mtpa of ore and has recently started its underground part, which is slated to produce 4.5 mtpa of ore in near future. The mine is currently working at 260 m depth, and is designed to reach a depth of 372 m. During blasting, back break was the main concern as despite of carrying out pre-splitting; the benches experienced back breaks adversely affecting the stability of the remaining walls. Normal production blast consists of detonation of 6–8 rows involving 140–200 holes in a blast round. A master plan of the pre-split holes position at spacing of 1.2 m was prepared. The available explosive was in the cartridge diameter of 25 mm which provided decoupling ratio of 1:3.6. Each bench of footwall and of all stages of hang wall is pre-splitted to minimize damage to the rock mass. Pre-split holes of about 700,000 m are being drilled annually to get desired pit slopes. In the experimental trials the mouths of the pre-split holes were left without explosives from 0.8 to 2.7 m. In the latter stage the inclined holes of 115 mm at 80°, 70° and 60° were experimented. The pre-split holes drilled at 1.2 m spacing with 60° inclination on footwall and 70° on hangwall yielded desired results.

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