Predicting the extent of blast-induced damage in rock masses

We describe a new model for predicting the extent of blast-induced damage (BID) in rock masses. The model is based on Langefors' theory of rock blasting and the hypothesis that the maximum burden parameter defined by Langefors is a good indicator of BID. We have incorporated the effect of decreased internal energy of the gases as they expand to reach the walls of the borehole and then fitted the model to the available experimental data. Our model involves three easily obtainable parameters, namely, the energy loaded in the borehole, the coupling factor and the rock constant, and the mean gas isentropic expansion factor, which depends on the type of explosive used and on borehole and cartridge diameters. For this factor, we used approximate values independent of the type of explosive.The model indicates that there is a positive relationship between the internal energy of the explosive gases, once they have expanded inside the borehole, and the volume of damaged rock. This relationship is a function of the rock constant, a fundamental rock mass property that defines the maximum extent of damage under predefined charge conditions. The proposed model provides quite acceptable estimates of the fitted data, considering that just a single parameter is incorporated in the statistical procedure: the relationship between maximum burden and BID.

► Current models for predicting blast-induced damage are analysed.
► A model that is based on Langefors blasting theory is proposed.
► The model is developed and fitted with experimental data.
► Results and the goodness-of-fit of the model are discussed.
► Similarities and differences with other models are highlighted.