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Overbreak?the removal of rock beyond the intended excavation profile?represents one of the most persistent challenges in underground mining. While frequently overlooked as a secondary effect of blasting, overbreak significantly influences ground stability, development efficiency, and project economics. This study presents a comprehensive, field-based analysis of overbreak in development headings at a large underground metal mine in Rajasthan, India. Data were collected over five months using total-station surveys, blast performance records, and ground support documentation. Excavation profiles were analyzed with AutoCAD and Geovia SURPAC to quantify deviations from design, while statistical methods were employed to establish relationships between blasting parameters and overbreak. Results revealed an average overbreak of 7.68?ross all monitored rounds. Correlation analysis identified three key parameter driving overbreak: final cup density in perimeter holes. To address these issues, a modified perimeter-control blasting strategy was developed, featuring decoupled charges. The findings highlight that overbreak should not be accepted as inevitable but recognized as a controllable engineering parameter. With targeted adjustments in blasting design and execution, significant improvements can be achieved in safety, efficiency, and cost optimization. This research thus contributes both practical strategies for industry and empirical insights for advancing controlled blasting practices in underground metal mining.
Mining has historically sustained industrial growth by supplying essential raw materials (Hartman & Mutmansky, 2002). While open-pit methods dominate shallow deposits, underground mining becomes indispensable at depths beyond 300 m or where surface disturbance must be minimized (Brady & Brown, 2006). Globally, underground methods enable access to deeper, often higher-grade ores while reducing land-use conflict compared to surface operations (Hustrulid & Bullock, 2001). In India, depletion of near-surface deposits has increased reliance on underground mining (DGMS, 2020). Among available excavation methods, drill-and-blast remains the most widely applied for hard rock, owing to its flexibility, relatively low capital demand compared with tunnel boring machines, and adaptability to varied geometries (Singh, 2018). However, blast energy is difficult to control. Detonations generate stress waves and gas pressures that propagate beyond intended contours, creating three distinct zones: overbreak, or excavation outside design boundaries; damaged rock, with reduced strength; and disturbed zones, characterized by minor stress adjustments (Ibarra et al., 1996; Saiang & Nordlund, 2007). Overbreak is the most visible and operationally disruptive of these.
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Malti Thanvi*
Corresponding author
M. Tech Scholar, Department of Mining Engineering, College of Technology and Engineering, Udaipur, India
Malti Thanvi*, Analysis of Overbreak in Development Headings of An Underground Metal Mine, Int. J. Sci. R. Tech., 2025, 2 (9), 284-296. https://doi.org/10.5281/zenodo.17212499
Malti Thanvi**
10.5281/zenodo.17212499