Measurement of shock pressure and shock-wave attenuation near a blast hole in rock

The objective of this study was to investigate granite responses to blasting. The focus was on the pressure and attenuation of shock waves in granite. Tests are reported on ten cylinders subjected to explosions from central pressed trinitrotoluene (TNT) charges with approximate density of 1.6 g/cm(3). Three cylinders had dimensions empty set 150 mm x 200 mm; seven, empty set 240 mm x 300 mm. Specimens had concentric holes drilled from both ends: one 20-mm hole to position the explosive charge and one 50-mm hole to insert a granite plug equipped with Manganin gauges, which were applied to monitor the pressures of the shock waves. The configuration of the gauges was analyzed before testing to investigate how precisely they could measure shock waves in the granite. One or two gauges were used in each cylinder at distances of 7, 15, 22 or 35 mm from the explosive charge in the cylinder axis. At detonation of the charge, the measured peak pressure values ranged from 15.9-4.4 GPa depending on distance from the explosive, with pressure rise times of similar to 0.5 mu s. In one specimen, deflagration occurred, resulting in a low peak pressure of 1.35 GPa 11 mm from the explosive and a 16-mu s pressure rise time. For specimens with two gauges, shock-wave velocities were found to depend strongly on the distance from the explosive. Fitting a curve to the experimental data, an exponential relation for the shock-wave peak pressure and its attenuation was obtained, expressing pressure (GPa) as a function of increasing distance (mm) from the explosive: p = 19.4 exp(-0.04x). The findings, especially regarding the damping term, may for instance be useful for verification of numerical models for blasting simulation.