Ramulu, M. and Raina, A.K. and Sinha, A.
(2011)
New blasting techniques for productivity enhancement in underground coal mines.
Journal of Mines, Metals & Fuels, 59 (3&4).
pp. 76-82.
ISSN 0022-2755
Abstract
The pace of developments in underground blasting technology is insignificant in contrast to developments in opencast blasting. Blasting practices in underground mine s has limited flexibility due to many safety criteria, statutory and field constraints. This has narrowed the scope of major modifications in the solid blasting design vis-à-vis the efficiency and yield per round. However, it is high time to balance the opencast and underground mine production, in view of the exhausting reserves in shallow depth and socio-environmental problems due to opencast mining. With this back-drop, Central Institute of Mining & Fuel Research (CIMFR), Regional Centre, Nagpur developed two new underground blasting techniques with simple modifications in explosive loading patterns. They are: (i) in-hole delay solid blasting technique was in-hole delay solid blasting technique by inserting multiple delay detonators in cut holes to improve the solid blasting efficiency. The conventionally available resources are used in this technique without violating the statutory guidelines. The trial blast results indicated improvements in all the parameters like pull, yield per round, powder factor and detonator factor. The overall improvement in pull per round was 49% with 1.5m deep rounds and 40% with 1.8m deep rounds. The technique also resulted in reduction of ground vibration intensity by 32-37%.
Another blasting method developed was bottom hole decking technique by inserting air-deck at the bottom of the blast holes. In this technique a spacer is to be placed at the bottom of the hole and remaining portion of the hole is conventionally charged. The length of spacer is equal to 10-12% of depth of blasthole.
A wooden spacer or any antistatic plastic pipe can also be used for decking. The technique was also applied in both soft and medium hard coal formations while exploiting the thin coal seams. The trial blast results indicated improvements in pull, yield per round and powder factor. The overall progress/pull per round observed was 36% with 1.5m deep rounds and it was up to 22%was 1.8m deep rounds with the powder factor (ton/kg) improvement up to 70%. The technique was also result in reduction of ground vibrations by 20-26%. The experimental results also reveal that the in-hole delay solid blasting and bottom hole decking techniques are suitable for relatively harder and softer formations respectively for improving blasting productivity
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