Analysis of Overbreak in Development Headings of An Underground Metal Mine

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% across 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.