Estimation of the powder factor in bench blasting from the Bond work index

Abstract

One of the most critical parameters in the determination of optimal blasting conditions is the powder factor. Accurate prediction of the powder factor reduces the costs incurred through trial-and-error blasting. Previous research to establish the initial powder factor has focused on relations between rock mass properties, blasting material and blasting geometry and has resulted in a number of empirical equations. A study has now been undertaken with the aim of developing a predictive method that is less dependent on local conditions. The basis of the method is the relationship between specific energy and particle size embodied in comminution theory. Application of the Bond work index should provide an enhancement of the previous approaches based on rock and explosive properties.The Bond work index was determined by use of the Bond mill for several different minerals and rocks at the sites being blasted and the results were compared with published values. The powder factor was determined locally by reference to similar bench blasting applications to the same minerals and rocks and the results were also compared with previous findings. Finally, a relationship between the Bond work index and the powder factor was established by the application of statistical and mathematical methods, taking into account the initial block sizes and product fragment sizes.