Effects of Blasting on Damage of Impacted Rock
CIM Montreal 2003
Sean Gregerson, G Kunzel, M Pollanen, Charles Pelley, Stefan Kelebek,
A series of small scale tests have been conducted to evaluate the effect of micro-fracture development, imposed by blasting, on the material properties of the rock as well as its resistance to crushing and grinding. The uniaxial compressive strength, tensile strength, Poisson’s ratio, P-wave, S-wave velocity, point load test index, crushing and grinding work indices were evaluated for samples without any blasting load and for samples which had received a variety of blast loads ranging from a single impact with low strength detonating cord, to combination of impacts at different times and significant impacts with powder factors close to those used in practical blasts. It was shown that the rock mechanics parameters change even at low impacts, suggesting easier crushing of the rock. Damage values appear to be affected by timing as stress wave superposition affects the damage process. Fragmentation is achieved at higher impact levels while work index modification of the fragments is also observed when high powder factors are used, suggesting improvements in grinding. Analysis of micrographs shows the changes in fracture intensity as blasting load increases. Numerical modeling with the AutodynTM code enables visualization of the effects of stress waves and development of blasting guidelines. The work has suggested techniques to maximize damage and reduce grinding and crushing costs.