An investigation to evaluate the relationship between rock quality index (RQI) and powder factor for surface mining

The determination of the blastability of the rock mass is a problem that faces blasting engineers on a daily basis. The costly trial and error approach may eventually lead to a suitable design, although constant variations in the rock mass properties presume that this approach is constantly in progress. Shortly after the publication, at UBC, of the Leighton report on the correlation between the Rock Quality Index (RQI) and the controlled powder factor defined at Afton Mine, this research project was established in order to determine the extent of such correlation. The Rock Quality Index is obtained from rotary blasthole drill performance data. Defined as a single numerical estimation of the rock mass properties, the RQI reflects variations in the rock quality. It is a simple and practical approach to blast design based on an empirical relationship. At Equity Silver, Lornex and Greenhills Mines, data were gathered and evaluated in order to confirm the relationship and determine the factors that influence or control its definition. It was found that many factors actually affect the determination of the relationship. They are easily divided in two categories, the factors related to the drilling mechanism or to the blasting process. The accuracy of the drilling data was of concern to Leighton and a drill performance recorder was used at two of the locations in order to obtain accurate data. This research project permits the conclusion that the basic idea of a correlation between Rock Quality Index and the rock mass blastability is right. The correlation is, at this time, site specific due to the difference in the RQI values obtained from various drilling equipment and also due to the specific blasting conditions. Since many variables are found to affect both the drilling and blasting mechanisms, basic guidelines are proposed in order to assure the success of further research on the Rock Quality Index. Optimum blasting is the key to improved slope stability, higher stripping ratio, high productivity and reduced maintenance cost. However, optimum blasting is achieved only with a well established rock mass characterization program.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat