Blasting Technique for faster Drivage - A case study

Tunnelling is an important activity in mining and civil projects. Faster and cost effective tunneling is essential to avoid cost and time overruns of a project. Poor tunneling rates in India can be attributed, among a host of factors, to the poor blast performance due to inappropriate design of blast parameters with scant regard to geo-mining conditions as observed in the inclines of Tandsi project of Western Coalfields Ltd. The resulting low pull, high overbreaks, ground control problems, misfires, need of secondary blasting for grading, damage to support installations due to excessive throw of rock fragments and high defuming time were collectively responsible for a low rate of drivage (15 m/month) at the cost of Rs. 50,000 per metre. In an effort for improvement, the controllable and parly-controllable parameters were modified considering the geo-mining conditions like weak and irregular rock masses, moderately large D-shaped opening, inclination, mechanized drilling and loading facility, transportation arrangements and steel arch support for very poor rock mass conditions. The modified blast practice included parallel cut with large diameter empty holes, smooth blasting technique, larger diameter cartridge of low strength explosive, blasting the round in two phases and series-parallel connection. The rate of drivage consequently improved to 33 m/month and the cost of excavation was brought down to Rs. 39,000/m. Based on the experience at Tandsi, some guidelines have been suggested for optimum selection of blast parameters in a given set of geo-mining conditions