Using blasting caps with electronic delay units, it has become possible to employ wave superposition in rock blasting. This paper presents computer simulations to investigate the hypothesis that fragmentation is improved in areas between blast holes where the tensile waves meet, overlap and interact. In this study, a numerical methodology using the code LS-DYNA was developed. LS-DYNA is a commercially available multi-purpose finite-element code, which is well suited to various types of dynamic modeling. Two different element formulations were used — Euler formulation in, and close to, the blast hole, and Lagrange formulation in the rock volume farther from the blast hole. The models used have a resolution (element size) of 50 mm and comprise approximately 20 million elements. Single and dual blast hole configurations have been studied, and a methodology to calculate possible fragmentation based on model interpretation was developed. The results showed that the amount of explosives and the blast hole spacing had the largest effect on fragmentation. The effect of varying delay times was small and local, implying that a significant increase in fragmentation should not be expected through wave superposition.
The primary purpose of all blasting is to fragment the rock into pieces of suitable dimensions for further handling. An improved fragmentation can result in reduced costs for both blasting and transportation of the blasted rock, improved environmental aspects, and reductions in energy consumption during crushing and grinding of the blasted rock, as well as improved metal recovery. Using blasting caps with electronic delay units, with delay times down to 1 ms, it has become possible to employ wave superposition in rock blasting. A hypothesis proposed by Rossmanith (2002) states that fragmentation is improved in areas between blast holes where the tensile waves meet, overlap and interact.
