Modelling of blasthole expansion and explosive gas pressurization in jointed media

Abstract

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 (Ph.D. Thesis, University of California at Berkely, Berkely, 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 blast chamber 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 blasthole expansion assumes an adiabatic expansion of explosion products and variations in explosion pressure upon expansion of blast chamber is calculated from an equation of state. Furthermore, a rigid-body damping algorithm, based on energy approach, was developed and implemented to the original DDA code. Accordingly, the newly modified DDA_BLAST code was employed 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 discontinuities on the process of burden breakage.