ABSTRACT
Demands on blast design for the minimisation of damage are becoming more severe. In order to achieve control, the assessment of damage is vital. This paper discusses a technique which involves monitoring the pressure in sealed boreholes behind blast limits. The experimental technique is presented along with results from two sets of experiments. Underpressures ranging from -39 to -78kPa at one burden, 0 to -36kPa at two burdens and 0 to -20kPa at three burdens were recorded behind a series of bench blasts. After comparison with borehole video records and correlation with the dimensions of newly-formed cracks, the underpressures were attributed to the new volume created by the cracks. No evidence of penetration by high pressure gases was found, leading to the conclusion that the cracks were stress induced. Conversely, for the situation of fully confined crater blasts in a different rock type, peak overpressures in the range 5 to 280kPa were recorded at distances between 62 and 8 blasthole diameters. In this situation, gases were able to penetrate to the monitoring locations. Several conclusions are drawn from the work, most notably that the technique is a valuable aid to determining both the mechanisms and extents of blast-induced damage from different blast designs or in different rock types.
