Summary
From a purely mechanical viewpoint, each explosive charge should produce a peak blasthole pressure (P b ) that just fails to crush (i.e. pulverise or plastically deform) the rock which surrounds it. WhereP b exceeds a critical value, some explosion energy is wasted in crushing an annular section of rock immediately around each charge. As a rock's dynamic compressive breaking strain decreases, so shouldP b (Hagan, 1977b).
This paper reviews information on, and anticipates the blasting performance of, bulk charges having effective densities which are as low as about 40% of that for ammonium nitrate fuel oil (ANFO). It also outlines the potential advantages of extending the reaction periods of charges, even to the extent that explosive reactions continue after the blasthole wall and stemming have started to move. The paper then proceeds to define situations in which the use of such lower-pressure charges is likely to result in greatest reductions in mining costs. Some methods of applying bulk charges having effective densities in the 0.3–0.8 g cm−3 range and/or lower reaction rates are suggested.
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Hagan, T.N., Gibson, I.M. Lower blasthole pressures: a means of reducing costs when blasting rocks of low to moderate strength. International Journal of Mining and Geological Engineering 6, 1–13 (1988). https://doi.org/10.1007/BF00881023
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DOI: https://doi.org/10.1007/BF00881023