The effects of different explosive types on blast results when using small diameter holes are presented, Detonation behaviour is shown to vary widely between the four explosive types in common use, ascribed to the particle sizes of the explosive constituents, Variation in detonation behaviour causes different explosive types to interact with the rock in distinctly different manners, thereby affecting the amount of energy partitioned into shock and heave.
Throuqh extensive experimental investigations it has been found that, relative to dynamite, the greater shock Imparted to the rock by emulsion explosives gives finer fragmentation but also Increased back damage, The comparatively lower heave energy of emulsions causes less immediate overbreak but also reduces the ability to break out the burden. Other explosives with detonation behaviour between emulsion and dynamite give Intermediate blast results.
Considerably more than half the value of South Africa's annual mineral production relies on blasting with small diameter holes (<50 mm). At present, four different types of explosives are used in underground mining and tunnelling. Explosive type plays a major role In controlling Important blast results such as the degree of rock fragmentation, the success of break-out at the toe of the hole(socket length), the overbreak distance at the excavation perimeter, and the intensity and extent of damage to surrounding rock. These blast results impact strongly on the productivity, costs and therefore on the profitability of the mining or excavation operation.
Over the past decade watergel (slurry) and emulsion explosives have replaced the traditional dynamite and ANFO explosives in a large segment of the small diameter market and this trend will undoubtedly continue. The detonation behaviour of these new explosives is greatly different from that of traditional explosives and thus blasting results have also changed markedly. This is particularly true for small diameter holes where the variation In performance between explosive types is greatest. There is often confusion about why the various exploslves break differently, and also about the best ways In Which to apply the different explosives.
The control of blasting to achieve desired results has been restricted by limited understanding of explosive/rock interactions, and by the absence of experimental measurements which relate blasting Variables to important blasting results. As part of the research programme at COMRO extensive work has been carried out to characterize the blasting process in gold mines. Considerable progress has been made recently In understanding and controlling blasting and blasting. Detailed experiments were conducted to establish relationships between blasting variables and important blasting results. This work established that there are pronounced breakage differences between explosive types. In order to identify the mechanisms responsible for breakage differences, several aspects of explosive/rock interaction were quantified by the application of new experimental techniques which enable detailed measurement and study of rock response to explosive loads. A new research tool was developed which permitted for the first time a separation of breakage effects due to shock and gas penetration. This has provided important new insight into the mechanisms of rock breakage
