Estimating, appraising and establishing blast exclusion zone at Huni pit - A case study

The issue of accidental flyrock has the tendency to develop safety concerns for commuters around the main public road as mining progressed from 960 ​m reduced level (RL) to 912 ​m RL at Huni pit in Ghana. An evaluation was carried out using empirical models and an artificial neural network to assess and determine the safest blast exclusion zone. The calculations showed that the flyrock could travel a maximum of 220 ​m and 277.45 ​m horizontally for blast hole diameters of 115 ​mm and 127 ​mm, respectively, with the same stemming length of 2.0 ​m. The distances to the public road are much farther than these projected maximum horizontal distances. An artificial neural network (ANN) was also employed to predict the flyrock distance and it was found that the ANN model has the best root mean squared error (RMSE) value of 0.0012 and the highest coefficient of determination (R²) value of 0.99 for the flyrock throw prediction. Hence, the blast exclusion zone has been reduced to 500 ​m all around the pit from the pit crest satisfying the recommendation suggested by the Minerals Commission of Ghana. With the new blast exclusion zone, travelling from Damang through Akyempim to Twifo Praso, Takoradi, Cape Coast, and Accra during blasting times is no longer a bother.