ABSTRACT
Fragmentation measurements have been used to relate fragmentation with the delay time used in the blast pattern. Medium scale experiments using accurate detonators with firing times within few microseconds of the timing of the design have been used to control fragmentation which has been measured using high speed photography and image analysis of the resultant muckpiles. Limitations are discussed and demonstrated using distinct element modelling of muckpile formation. It is demonstrated that surface observation of the blast or the muckpile can affect the results. Fragment development has also been modelled numerically and compared to the measurement to identify the mechanisms of fragmentation by blasting. It is indicated that fragmentation is optimized at a certain delay time which allows full development of damage zones by previous detonations. The delay time is site specific, dependent on explosives loading, blast geometry and rock material. Influence of delay on fragmentation makes dynamic assessment of fragmentation necessary for blast optimization.
