STUDY OF BLAST FRAGMENTATION AND ITS IMPACT ON SHOVEL EFFICIENCY IN SURFACE COAL MINING

Mining Engineering

Blast fragmentation is one of the most consequential upstream processes in surface coal mining operations, exerting a profound and direct influence on the performance of loading equipment, particularly hydraulic and rope shovels. Inadequate fragmentation—characterized by oversized boulders, irregular muck pile profiles, and excessive fines—significantly degrades shovel productivity by increasing dig time per pass, elevating cycle time, inducing mechanical stress on dipper teeth and structural components, and increasing the frequency of unplanned maintenance stoppages. Conversely, optimally fragmented rock enables shovels to operate near their rated bucket fill factors, thereby maximizing tonne-per-hour output and minimizing unit cost of excavation. Despite the well-established qualitative relationship between fragmentation quality and equipment performance, quantitative field-validated data linking specific fragmentation indices to shovel efficiency metrics remain limited in the Indian surface coal mining literature. This paper addresses this gap by presenting a comprehensive study that combines field measurements, image-based fragmentation analysis, and shovel cycle time observation at three operating opencast coal mines in India. The study quantifies the relationship between the mean fragment size (x50) and the 80th percentile fragment size (x80), as determined by digital image analysis using WipFrag software, and key shovel efficiency indicators including bucket fill factor (BFF), digging cycle time (DCT), shovel utilization (SU), and effective production rate (EPR). A multi-variable regression model is developed to predict shovel productivity as a function of fragmentation parameters and operational variables. The findings reveal that a reduction in mean fragment size from 45 cm to 22 cm correlates with an improvement in bucket fill factor from 68% to 91%, a reduction in digging cycle time by 31%, and an increase in effective production rate by approximately 38%. The study further examines the role of blast design parameters—burden, spacing, powder factor, delay timing, and explosive energy—in governing fragmentation outcomes. Optimization recommendations are presented for blast designs that maximize shovel efficiency under varying geotechnical conditions. The results provide actionable guidance for mine planners and blasting engineers seeking to improve the overall productivity of the loading system through controlled blast design.

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