Optimization of powder factor, fragmentation and oversized boulders through subsystem studies in an opencast coal mine

The massive deposit of medium-grained, white-colored sandstone of about 20 m thick, is located immediately above the coal seam in Quarry No. 2, resulted lesser yield due to lower powder factor (m3/kg) and over-sized boulder formations, specifically from the stemming zones at Chotia Opencast Coal Mine of M/s Prakash Industries Limited, which was operating at a depth of about 30 to 40 m with an average bench height of 5.5 m. The criticality of the problem led to the rectification of the blast design parameters through incorporation of pilot holes and pocket charges, decked charges, air-decking, evolution of static energy distributions, and fragment data analysis for establishing optimized design patterns with available machinery. Several test blasts along with on-site testing of explosive quality, rebound hardness tests of overlying strata, and rearrangements of firing patterns through surface delay connections were considered for adopting the best-suitable blast pattern for the mine. Generalized and perceptible inferences were made to apply the results in other mines with similar kinds of problems.