Effective pre-splitting is a key feature of wall control blasting. Most
mining operations use historical designs or rules-of-thumb for designing
pre-split blasts. If productivity and safety benefits are to be gained, these
methods need to be improved in order to accurately predict pre-split
performance. This will become more pertinent as overburden depths
increase, placing more demands on the pre-split operation. A classical qualitative quasi-static description of pre-splitting (Kutter
and Fairhurst, 1968) is presented and it is shown to give some useful
insights into the pre-splitting process. In particular, it is clear that the time
interval between the initiation of adjacent pre-split holes is a very
important factor. In terms of this analysis, it is shown that current
techniques which employ detonating cord as the surface initiation system
are not optimal. A static quantitative model for pre-split design which has been widely
reported is then discussed and its simplifying assumptions and their
implications are examined. It is shown that several of the assumptions
may be reasonably justified in the light of real pre-split results. It is
concluded that the model should yield conservative designs. For this
model, the key calculation of the blasthole pressure that is needed to
determine the required explosive charge is highlighted. Popular methods
employed in the literature for describing the expansion of real detonation
products are shown to be inappropriate and an alternative method using
the non-ideal detonation code, CPeX, is proposed.