The objective of this paper is to investigate, in a simplified manner, the Process of rock blasting in discontinuous and blocky rock media. The developed code considers the effects of blast geometry (blasthole shape, angle, and location), the physical properties of the intact rock and existing discontinuities, and the blasthole pressure on the Processes of rock 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 media consists of a blocky rock mass which 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. The newly developed DDA_BLAST code was employed to simulate a typical bench blasting problem in jointed rock mass and delve into the mechanisms involved (in a macro scale) in the gas pressurization phase of the blasting Process.