An investigation into the effect of blast geometry on rock fragmentation

Abstract

S Reck fragmentation due to blasting is dependent on geomechanical, explosive and blast geometry parameters. A laboratory scale study was made to evaluate the effect of some blast geometry parameters (burden, spacing and bench height) on rock blasting. Experiments were divided into two groups-single hole tests to evaluate the effect of burden and bench height, and double hole tests to find out the effect of spacing and bench height. Optimum fragmentation burden was found to be 51 per cent of bench height. Significant increase in optimum breakage and fragmentation burdens vas observed with increase in the bench height. The rate of fall in fragmentation with increase in burden was greater in smaller benches because of increased stiffness of burden rock. Spacing to burden ratio of 3.0 to 4.0 gave optimum fragmentation. Fragmentation at less than optimum fragmentation burden even at a spacing to burden ratio of 5.0 was finer compared to the values obtained at optimum and greater than optimum fragmentation burdens for all spacing to burden ratios, suggesting smaller burdens even with larger spacings for finer fragmentation. Considerable improvement in fragmentation was achieved both qualitatively and quantitatively with increase in bench height. © 6th ISRM Congress 1987. All rights reserved.