Monitoring ground vibrations for predicting overbreak threshold levels in underground drivages

Abstract

Rapid development in underground drivages is the need of the hour to reduce the gestation period of mining and tunnelling projects. Despite the introduction of modern rock cutting machines, namely, tunnel boring machines, road headers, continuous miners etc., blasting still is the common excavation technique owing to its adaptability in wide ranging geo-mining conditions. Faster drivage rates are possible with the longer blast holes drilled by multi-boom drill rigs and wide range and type of delays available now-a-days. Since longer pulls are associated with high concentration of explosives they often cause overbreak due to excessive ground vibrations. Overbreak increases the overall drivage cost due to extra support and mucking required. Most of the existing controlled blasting techniques, namely, line drilling, pre-splitting, smooth blasting, micro-sequential contour blasting etc., need additional drilling and sophisticated delays and thus become costly to adopt in day toIn this paper, a brief discussion on the previous research conducted on the near-field vibration estimation models and threshold levels of PPV for rock damage is provided initially. Subsequently, both the near and far-field vibrations monitored in underground drivages of a Chromite mine and the threshold level of PPV for overbreak estimated from them are compared.