A new approach in blast vibration analysis and prediction at iron ore mines

Uncertainties in vibration analysis from blasts can be attributed to the problem of determining the actual amount of explosive detonating within a specific time interval, and the number of holes effectively contributing to the resulting particle velocity. This paper describes the results of a systematic study carried out to investigate these effects at iron ore mines in India. It involved a total of over 42 blasts, employing one-, two-and three-hole calibration studies, and regular production blasts. In the latter, the bench height varied from 6 m to 14 m, and boreholes loaded with ANFO and Emulsion explosives were 100 mm and 160 mm in diameter. The in-the-hole velocity of detonation of explosives was monitored. Six tri-axial vibration sensors were located on ground surface along a linear array from 25 m to 1.54 km from the blast sites, to investigate the changes in amplitude, frequency, and duration with distance. Responses of various structures (including one-and two-story homes) to blast vibration were taken to investigate the impact of blast wave frequencies on vibration level on the structures. The study compares single-hole blast signatures with multi-hole ones, and provides guidelines on determining the 'effective' charge-weight in vibration analysis of such blasts. Optimum delay intervals between two detonations have been recommended to control vibrations and their impact on the structures. (C) 2005 Institute of Materials, Minerals and Mining and Australasian Institute of Mining and Metallurgy. Published by Maney on behalf of the Institutes.