Drilling rate prediction of an open pit mine using the rock mass drillability index

• Penetration rate prediction is necessary for cost estimation and project planning.
• Drillability depends on rock properties, machine specifications, and operational parameters.
• Intact rock properties and structural parameters of rock mass have strong effect on drilling rate.
• A new penetration rate model is defined and compared with previous models from literature.
• Model includes intact rock and rock mass properties; provides good estimation of penetration rate.

Besides intact rock properties, structural parameters of rock mass have strong effect on drilling rate. In this research, 11 different zones of an open pit iron mine were studied precisely to classify the area based on rock drillability point of view. Laboratory tests were conducted on the rock samples to determine strength parameters. Geological mapping of the rock facies was carried out and rock mass structural parameters as joint inclination, spacing, aperture and filling were recorded along with net drilling times of drill holes. Using these data, an empirical relation was developed to predict drilling rate (DR) using the rock mass drillability index (RDi) and also a relation that can predict uniaxial compressive strength (UCS) of rocks in terms of Schmidt hammer rebound values at this mine. In conclusion, all 66 zones of the mine area were classified according to the RDi. It was observed that RDi can reasonably predict drilling rate of rock masses. A new penetration rate model is defined based on the measured data and then compared with previous model of penetration rate from literature. Since the new model which involves not only intact rock mechanical properties but also structural properties of rock masses could attain better predictions in relation to the previous model.