A reliable estimate of the drilling rate is essential in a successful drill and blast planning and mine production. Owing to this importance, numerous empirical equations of the drilling rate using the rock mass properties and the machine parameters have been proposed. However, these existing equations cannot be used in all site conditions. Hence, this paper aims to develop an empirical model for drilling rate estimation in hard rock mining. The data used for this study were collected from an underground mine located in Selibi-Phikwe, Botswana and included in-situ drilling rate, drilling machine specification and rock mass properties. Nonlinear regression model was used to derive the drill rate model. The result indicates high correlation between the estimated and the actual drill rates. In addition, it was found that the uniaxial compressive strength of the rock, the angle between the rock mass discontinuity planes and the drilling direction are the parameters impacting the drill rate the most. Also, the presence of quartz in the rock indicated good predictability of the drill rates.
Drilling is a very critical operation in exploration and production processes [1]. Rock drilling is performed by a number of techniques ranging from rotary – percussive in very hard rock, rotary or crushing drilling in medium hard rock and soft rock types. For drilling blast-holes in hard rock, the rotary percussive drilling is a standard in underground mining and tunneling providing maximum performance under most circumstances [2, 3]. In underground mining context, if not optional, the drilling rate dictates the mine productivity rate as it affects all subsequent operational units [4]. Therefore, an accurate estimation of drilling rates is critical for proper planning of mine development and rock excavation projects.
The drilling rate is also one of the most important parameters in drilling economics due to its crucial role in minimizing drilling operational costs. Drilling rate can be defined as the depth of penetration achieved per unit time for a given type of rock, drill bit diameter and air or water pressure. In mining, the term drillability is used to describe the influence of a number of parameters on the drilling rate and wear of the drilling tool [5]. The drilling rate of rock varies with a number of factors, some of which are controllable and some uncontrollable including: rock type, physical and mechanical properties of rock, orientation foliation, discontinuities, mineral composition, and type of drilling machine, thrust force, rotation, bit type, flushing, drilling method, experience of the operator and maintenance of the drilling machine.
