INTRODUCTION
The computer code DMC ( Distinct Motion C_ode ) has been developed for modeling rock motion associated with rock blasting (Taylor and Preece 1989a&b). DMC was written to be computationally efficient by employing spherical elements and by vectorizing all of the code to provide more efficient operation on CRAY type computers. Several mechanisms have been added to DMC to aid the treatment of rock mass bulking during motion. One bulking mechanism, aspect ratio, is obtained by kinematically tieing spheres together. Another, rotation-induced-dilatation, is obtained by expanding the sphere radius as it rotates to simulate the interaction between corners and sides of cubes ( Preece and Taylor 1990 ). These two mechanisms, along with friction, allow a treatment of spherical element bulking that has not been possible before.
Confined volume blasting is usually difficult to control and predict because the material is expanding into a limited void space. An example of confined volume blasting is underground oil shale retort blasting. The example rock motion problem treated in this paper is the movement and subsequent bulking of material associated with the blasting of Retorts 7 and 8 by Occidental Oil Shale, Incorporated (OOSI). These retorts were rubblized in 1981 and processed in 1982. Both retorts were heavily instrumented and a large amount of data was obtained (Bickel 1984). The thermocouple data is of most interest here because it allows tracking of the burn front throughout the processing of the retort. The movement of the burn front gives an indication of the permeability field within the retort. The permeability field is a function of the porosity and the particle size within the retort bed. In this paper, the porosity field calculated using DMC will be compared with that observed in Retorts 7 and 8 through the movement of the burn front.
