Publications

Geologic materials are often modeled with discrete spheres because the material is not continuous and discrete spherical models simplify the mathematics. Spherical element models have been created using assemblages of spheres with a specified particle size distribution or by assuming the particles are all the same size and making the assemblage a close-packed array of spheres. Both of these approaches yield a considerable amount of material dilatation upon movement. This has proven to be unsatisfactory for sedimentary rock formations that contain bedding planes where shear movement can occur with minimal dilatation of the interface. A new concept referred to as packing angle has been developed to allow the modeler to build arrays of spheres that are the same size but have the rows of spheres offset from each other. ne row offset is a function of the packing angle and allows the modeler to control the dilatation as rows of spheres experience relative horizontal motion.

Sandia National Laboratories and ICI Explosives USA have worked together since 1987 to develop computer modeling techniques for Rock Blasting. A result of this effort is the computer program DMC (Distinct Motion Code) which was developed for two-dimensional simulation of rock motion following a blast (Taylor and Preece, 1989 1992). This program has been used to study blasting-induced rock motion resulting from oil shale mining and has been coupled with a gas flow computation capability for better treatment of the explosive behavior. This past year it has been customized for simulations of bench blasting in coat mines and rock quarries (Preece and Knudsen, 1992b). The explicit descretized nature of DMC gives it an advantage over previous blast modeling programs because subtle differences, such as row delay timing, have an influence on the results. This paper will present a DMC study of the influence on percent cast of row delay timing in a typical coal mine bench blast.

The spherical element computer code DMC (Distinct Motion Code) used to model rock motion resulting from blasting has been enhanced to allow routine computer simulations of bench blasting. The enhancements required for bench blast simulation include: (1) modifying the gas flow portion of DMC, (2) adding a new explosive gas equation of state capability, (3) modifying the porosity calculation, and (4) accounting for blastwell spacing parallel to the face. A parametric study performed with DMC shows logical variation of the face velocity as burden, spacing, blastwell diameter and explosive type are varied. These additions represent a significant advance in the capability of DMC which will not only aid in understanding the physics involved in blasting but will also become a blast design tool. 8 refs., 7 figs., 1 tab.