Optimising rock fragmentation and reducing blasting impacts in open-pit mines through stemming modification

Stemming length is a critical parameter in surface blasting, directly affecting explosive energy confinement, flyrock generation, fragmentation quality, and operational safety. However, conventional stemming design methods are mainly based on fixed relationships with hole depth, burden, or blasthole diameter and do not adequately consider variations in confinement caused by blasthole depth, rock properties, and row position. This study introduces a deterministic stemming design approach based on extensive field investigations conducted at two large open-pit metal mines. The proposed formulation determines stemming length based on burden, blasthole depth, rock density, and blasthole row number, enabling adaptation to variable confinement conditions within multi-row blast patterns. The performance of the new formula was evaluated under full-scale production blasting and compared with conventional stemming methods. Field results showed that optimised stemming reduced flyrock distance (up to 38%), powder factor (18–35%), and drilling and blasting costs (approximately 20%), while improving fragmentation uniformity and operational efficiency. Airblast measurements also indicated consistent reductions despite lower explosive consumption, while the effect on ground vibration could not be directly quantified because peak particle velocity was not measured. The successful application at two geologically distinct mining sites demonstrates the practical applicability and consistent performance of the new formula as a simple and physically based tool for improving blast safety, environmental performance, and cost efficiency in large-scale open-pit mining.