Blasting Improvements by Using Most Active Rock Variations on Blast.

摘要

Rock mass variations have a huge influence on explosives efficiency and on blasting results. Numerous blasting improvements could be gained by taking into account rock mass and its variations. However, extracted rock mass is generally considered as statistically homogenous. The development of a panel of pre-blast survey procedures that every blaster can use, consists in the realization of a process integrated into every day work: for example as well as toe burden or blast hole depth, discontinuities spacing or the weathering expanse have to enter in rule book, if it provides blasting efficiency and security improvements. The first step is to determine influences of every rock mass characteristics on blast. Texture, density or type of porosity imply a particular mechanical behavior, but rock discontinuities have an essential influence on decomposition and work of explosives: sedimentary structures, chemical weathering, fractures and their varied filling, strike and dip, may have contrasting effects on blasting. Next step consist in an estimation of local variations of given rock mass characteristics: it means to make an exhaustive collection of acting discontinuities to understand their relative importance in blasting. The exploited rock is then considered as a variable object. The previous survey procedure allows a better understanding of the system "pre-blast variations of rock mass characteristics / explosives chemical decomposition / blast results". So, blocks structure in the muck-pile and back-breaks are observed to define a hierarchy between different discontinuities influences on blast efficiency: the purpose is to relate the existence of variations among some rock mass characteristics and differences in blasting results (post-blast face geometry, muck-pile rock size...). Blocks in the muck-pile show indices of the cause of their formation: cuts along joints, alterations areas or "pure" fractures directly due to explosive and characterized by fractographic features. Post-blast face survey provides an evaluation of explosives energy dissipation: wasted (blast malfunction), through solely gases action or through a combination of shock waves and gases action. In 2002, this procedure has been used during an optimization program of a stone production on quarry: this Experimental Design based on Statistical process control required to find out the most active rock mass parameters on blast efficiency. This example shows how this rock analysis allows adapting blasting parameters, knowing origin of blast dysfunctions due to rock mass heterogeneities. This methodology already enables to predict blasting malfunctions as poor face movement, poor fragmentation and explosive desensitizing.