Modelling the effects of discontinuity orientation, continuity, and dip on the process of burden breakage in bench blasting

The objective of this paper is to introduce the development of a dynamic blasthole expansion model, which is coupled to the discontinuous deformation analysis (DDA) code of Shi (1988). The developed model considers the effects of blast geometry (blasthole shape, angle, and location), the physical properties of the intact rock and existing discontinuities, the distribution and orientation of pre-existing discontinuities, and the blasthole pressure on the processes of burden breakage, fragment throw and muckpile formation. The newly modified DDA code (DDA_BLAST) describes the expansion of the blasthole as a function of blast chamber volume and time. It is assumed in the code that the rock is already fragmented in-situ due to the intersection of pre-existing discontinuities and the passage of stress wave. Hence, the model only considers the gas pressurization phase of the blasting process. Moreover, the proposed model for the blasthole expansion assumes an adiabatic expansion of explosion products and variations in the explosion pressure upon expansion of the blast chamber are calculated from an equation of state. Accordingly, the newly modified DDA_BLAST code was used to simulate typical blasting problems in jointed media and delve into the mechanisms involved (in a macro scale) in the gas pressurization phase of the blasting process, burden breakage, and the effects of the discontinuity properties on the process of rock breakage by blasting.