Energy components in rock blasting

Abstract

Ten production blasts and one single-hole confined blast have been monitored in two quarries in order to assess the measurable forms of energy in which the energy delivered by the explosive is transformed in rock blasting. The seismic field from seismographs readings, the initial velocity of the blasted rock face obtained from high-speed video camera records, and the fragment size distributions from image analysis of the muckpile material are used to determine the seismic wave energy, the kinetic energy and the fracture energy, respectively, transferred in the blasting process. The blasting data and the methods of calculation of the energy terms from those are described in detail. Heat of explosion and useful work to 100 MPa have been used as descriptions of the energy of explosives. The maximum total energy measured accounts for not more than 26% of the available explosive energy if this is rated as the heat of explosion, though lower figures are usually obtained. The values measured for each of the energy components range from 2% to 6% of the total energy available for the fragmentation energy, 1–3% for the seismic energy and 3–21% for the kinetic energy. For the confined shothole, the seismic energy was 9% of the heat of explosion. The uncertainty of the calculated energies is analyzed from the variability of the measured data. Particularly important influential parameters are the treatment of the fines tail of the fragment size distribution in the determination of the fragmentation energy, and the use of P or S wave velocity values, and whether these are determined from in situ or from laboratory measurements, in the calculation of the seismic energy.