In open pit mining drilling, like the other stages of mining, has a close relationship with the rock mass. The drilling process and its results are affected by various parameters of the rock material and rock mass. The effects of rock materials have been emphasized in various studies, however a lack of perfect knowledge of rock mass structural parameters may lead to unpredictable results. This paper presents a new classification system for specifying Rockmass Drillability index (RDi). For this purpose, six parameters of rock mass, including texture and grain size, hardness, uniaxial compressive strength (UCS), joint spacing, joint filling (aperture) and joint dip, have been investigated by physical modelling and rated. In this system, for each rock mass a rating from 7 to 100 is assigned. A higher rating represents a good-quality rock mass from the view point of drilling. Finally, considering the RDi rating, the drilling rate may be predicted at one of five modes; slow, slow-medium, medium, medium-fast and fast.


In open pit mining, drilling, as the initial stage of the exploitation operations, has a significant role in the other stages of exploitation. Considering high operating costs and expensive machinery, a full recognition of the parameters involved in drilling, and an effort to optimize exploitation methods, is necessary. Finally, effective drilling result in effective blasting, the desired fragmentation and the effective control of operating costs. Drilling, like the other exploitation stages, has a direct and close relation to the rock mass; this would be affected by the characteristics of the rock material as well as the rock mass. Therefore, recognition of the drilling environment and in situ rock mass properties would be a great help in choosing the type of drilling system, the number of drilling rigs and the mine production rate.

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