Development of a correlation between rotary drill performance and controlled blasting powder factors

Despite the availability of established, sophisticated methods for planning and designing stable slopes in rock, comparatively little attention is usually paid to the problems of carrying out the excavation. Blasting should be carefully planned to obtain optimum fragmentation as well as steep, stable pit walls for a minimum stripping ratio. The principal difficulty facing a blast designer is the lack of prior information about the many critical blasting characteristics of the rock mass. The common practice of trial-and-error blasting will eventually lead to a suitable design, but this must be repeated time after time in variable geology. This frequently results in many blast damaged slopes with decreased stability and increased safety hazards. For this research project, an extensive study was undertaken to develop a concise background knowledge on state-of-the-art blasting technology. A field research program at Afton Mine examined the relationship between characteristic rock mass features and blast performance for application in optimal blasting design. Due to the complex inter-relationships of the many rock mass properties, the development of a comprehensive rock blasting model is not feasible. A practical approach to the problem was achieved by classifying each rock type with a single Rock Quality Index value which can be obtained from monitoring the performance of a rotary blasthole drill. A series of controlled blasting tests revealed a strong correlation between the Rock Quality Index and Powder Factor values over a broad range of geological conditions. The correlation was found to be sufficiently reliable to enable the prediction of optimum Powder Factors for perimeter blasts in previously untested rock types. This Rock Quality Index and Powder Factor correlation provides a practical approach to solving the problems of site specific blasting design. Without the costs of additional equipment or specially trained personnel, the drilling can provide a continual supply of data, reflecting changes in the rock mass and permitting the selection of an economical Powder Factor. The ultimate goals of this simple correlation system are optimization of fragmentation, elimination of unacceptable blast damage, preservation of inherent rock strength, and maximization of slope stability.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat