Accurate computer prediction of the muck pile produced by a conventional blast requires modeling of the physics that occurs during the rock motion phase of a blast. The ability to predict the motion and the subsequent muck pile can have a significant economic impact on the mining industry. Some of the computer programs previously used to predict rock motion employed polygonal elements with comers and sides to model the rock (Cundall, 1971; Walton, 1982; Taylor, 1983). This approach allows the elements to bulk because of the corners and the aspect ratio. However, tracking the many interactions of the comers and sides of the elements is a computationally intensive process. Several other rock motion computer programs were developed that employed spherical elements, (Schamaun, 1984; Gorham-Bergeron et al, 1987) but they lacked correct bulking mechanisms or could not be vectorized for efficient execution on vector processing machines. A new spherical element code called DMC (Distinct Motion Code) (Taylor and Preece, 1989a, 1989b) has been developed this past year. DMC was designed and written to take advantage of super-computer vector processing capabilities. The efficiency has also been increased through the use of spherical elements, explicit time integration and a new contact search algorithm. When spherical elements were chosen for efficiency, some physically correct mechanisms for capturing the bulking behavior of the rock mass also had to he developed. This paper will treat several mechanisms that were developed to allow spherical elements to exhibit correct hulking behavior.