Optimization of Flyrock and Ground Vibrations in Blast Design: A Case Study from the Balangero Mine in Italy

Abstract

This study investigates the optimization of flyrock and blast-induced ground vibrations in open-pit blasting operations through numerical simulation using O-Pitblast software. The reference site is the Balangero mine, located in the Lanzo Valleys (Piedmont, Italy), historically one of the most significant European deposits of serpentinite and asbestiform fibers. The explosive configuration consists of CHE-ANFO EXTRA cartridges (90x500 mm) as column charge, APB 1350 pentolite boosters, and Rock Star 25/50 delay detonators in compliance with Italian regulations prohibiting the use of bulk explosives. Three rectangular blast patterns were evaluated by varying hole spacing and number of holes per row, keeping constant the number of rows, the burden, and inter-hole (75 ms) and inter-row (1 s) delays, while varying spacing and the number of holes per row. Ground vibrations were assessed through an attenuation law with the following parameters: k = 1500, α = 0.6, β = −1.2, (90% confidence level), without exceeding the Peak Particle Velocity (PPV) threshold of 15 mm/s at any surrounding structures. Flyrock clearance zones remained within 24 m for personnel and 16 m for equipment, well below regulatory limits. The result of this study highlights that detonation timing, particularly inter-row delay, is the critical variable in simultaneously controlling flyrock projection and seismic wave propagation.