Development of a continuum damage model for blasting analysis

Abstract

This paper describes the development of a constitutive model for predicting rock damage due to explosive loading and the consequent fragment size distribution. The model is based on continuum mechanics and statistical fracture mechanics, assuming that the rock medium is an isotropic, continuous and homogeneous material with pre-existing micro cracks. Damage to the rock medium is defined as the probability of fracture at a given crack density which is obtained by integrating a crack density function over time. The minimum damage value at which the fragments may be formed is set by applying a micro crack coalescence criterion. Fragment size distribution is achieved by considering the equilibrium between kinetic energy and surface energy, with the changes in loading rate, material stiffness and damage taken into account. The simulation results are in accordance with the theory of explosive energy partitioning in rock medium and the damage zone, induced by the shock and stress waves, once established, remains stable. The model has been calibrated by field crater blasting and small scale bench blasting tests.