Enhancing rock fragmentation in dragline bench blasts using near-field ground vibration dynamics and advanced blast design

Abstract

Fragmentation of desired size in large scale open cast blasting operations is a challenge often met with limited success. Literature review on fragmentation mechanics and modelling provided a comprehensive understanding on influencing parameters affecting the mean fragment size. Scientific methods of investigation such as scaled in-situ face mapping, seismic refraction tomography and in-hole continuous velocity of detonation measurement were carried out to generate necessary data. Impedance ratio, average inter-row delay and dynamic Poisson's ratio were found to influence the mean fragment size as the key affecting parameters. A multiple linear regression model was developed to predict mean fragment size relating the key variables. Near-field vibration signatures were used to identify the role of reflection breakage mechanism, using reflection breakage index (RBI). Near-field peak vector sum was observed with mean fragment size and consequently the optimum charge configuration was determined. Using the developed fragmentation model, an effective row to row delay of 14–18 ms/m of effective burden and maximum charge per delay of 1000 kg was found to be optimum to achieve the desired mean fragment size in the range 43–57 cm. This was in addition to reduction in near-field vibrations, superior bench slope conditions and negligible backbreak. The modifications were simulated in JKSimblast to observe the delay contours. Implementation of suggested blast design yielded a 12–15% increase in dragline productivity apart from appreciably reducing the dragline breakdowns.