Abstract:

Shifting blast vibration at highwalls of an open pit mine can reduce blast vibration damage to the highwall and increase the highwall stability. A successful project for shifting blast vibration frequency at highwalls was conducted at an open pit metal mine in Mexico.

The blast monitoring collected useful data for the site rock characterization – vibration (stress) attenuation versus scaled distance; site resonant frequency, ground p-wave velocity, and rock fragmentation measured from typical blasts. Using the multiple seed waveforms that are encoded with the site frequency response characteristics, the multiple seed waveform (MSW) modeling accurately predicts the dominant frequency at highwalls from a blast design. Blast design scenarios are modeled for blast vibration PPV and dominant frequency.

With parameters from the signature hole blast vibration and fragmentation measurement, the MBF and MSW models are established for the site. The models can be used to explore benefits from various blast design scenarios.

The delay timing in terms of lower PPV and higher dominant frequencies for the pits are recommended - by 10 Hz from 16 Hz to 26 Hz at a hard rock pit with the recommended timing of 40 ms – 120 ms echelon and by 5 Hz from 18 Hz to 23 Hz echelon at another relatively soft rock pit with the recommended timing 45ms – 135ms echelon.

The MBF modeling indicates the timing change from the base case to the improved case would not cause any significant fragmentation change.

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Remi Proulx