Determining blast damage envelope through vibration model and validation using seismic imaging

Abstract

Blast induced rock damage has been related to peak particle velocity (PPV) by many researchers. Some researchers have estimated threshold values of PPV for rock damage by using the Holmberg–Persson near field formula (modified in this paper) and by extrapolation. In this paper, we propose a mathematical formula for assessing the extent of the damage zone by extending the formula proposed by Holmberg and Persson (1979) for the near field vibration approximation. This model gives the damage envelope when plotted in space (x,y). To test the acceptability of the proposed model, a crater blast experiment has been carried out in a surface mining bench with 1 m long and 32 mm diameter drill holes. The holes were loaded with 250 g (0·4 m) of explosive. Vibrations were monitored close to the blast site to establish the vibration predictor. The blast site was seismically imaged before and after the blast. The seismic images (pre- and post-blast) were analysed to determine the extent of rock damage and the damage envelope was computed using the proposed model. It was found that the damage envelopes obtained from the proposed model and from seismic imaging are in close agreement and it can thus be inferred that the proposed PPV based model is a valid means of determining the damage zone. In addition, the damage zones predicted from seismic images were 2–30 times larger than the physically measured crater volumes. Seismic imaging has thus been found suitable for determining the damage extent with reasonable accuracy.