Blasting plays a crucial role in every mining operation. Explosives malfunction due to shock waves is a serious concern for successful blasting results. Malfunction can range from sympathetic detonation to desensitisation and modification of firing times of conventional pyrotechnic detonators. This project sought to establish practical guidelines for the users of electronic detonators in small diameter blastholes in hard and medium strength rock. Specifically, the project sought to find the maximum deck length between explosive charges that will allow an explosive malfunction by either premature detonation or desensitisation of an electronic detonator.
Two series of validation blasts were performed in soft ground in dry blastholes to test the effectiveness of time-domain reflectometry, ground vibration and conventional video as measurement techniques. It was found that time-domain reflectometry was a reliable and accurate method. Two series of follow-up experimental blasts were conducted in hard, dry and hard, wet rock. The dry rock test pattern drilled was a 1.5m x 1.5m square pattern with 36 holes up to 2m deep. Of the 36 holes drilled, 33 holes were loaded with deck lengths varying between 0.6m and 1.0m. The dry test was completely successful in terms of method and the functioning of the acceptor charges. However, the wet rock test produced inconclusive results.
In general, the experimental results suggest a reduction in minimum deck lengths between small charges in dry, small diameter holes from 1.5m to 0.6m is acceptable for the conditions assessed. Good quality aggregate should be used for the decking material.