AIR-DECKED BLASTING TECHNIQUES - SOME COLLABORATIVE EXPERIMENTS

A laboratory and theoretical study of air-decks has been carried out t o assess the effect of the size and location of air-decks on fragmenta tion. The degree of fragmentation was found to depend on both factors. As the size of the air-deck increases the degree of fragmentation is reduced relative to a full-column charge; however, the reduction is re latively small until a critical size is exceeded. The critical size de pends on the strength and structure of the surrounding material. A cri tical air-deck length of 30-35% of the original explosive column was d etermined for the model materials that were used in the study. A theor etical explanation of the results that is based on pressure decay rate relationships was derived. The location of the air-deck also influenc es fragmentation. Owing to the interaction and oscillation of the two shock fronts from the top and bottom charges mid-column air-decks prod uce better fragmentation for the same air-deck length and explosive lo ading as top-column or bottom-column air-decks.