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Rietspruit, South Afa~ica Throw Blasting Throw Blasting, or Controlled Trajectory Blasting, has been attempted all over tha world. The success of these opera- tions and whither the combination of presplitting and throw blasting has even been tried elsewhere is unknown to the authors. Explosive energ}' has to be applied to the overburden in order to fragment it sufficiently for digging purposes. Strip minine engineers hose sought a means to harness this ex- plosive energy to do additional work in moving the over- burden to some desired position, in this case the previous cut. Draglincs arc by far the major capital cost in strip mining. It is normal practice to select draglines to match the cm•is- aged maximum tonnage of the mine. Olsen producing mores are presented from selling additional coal due to stripping constraints. Additional stripping capacity which may be gained from throw blasting would be oC benefit to mines lolling in this category. Also [he additional capacity gain may be used on other operations such as spoilpile levelling or parting remotal. Alternatively, with the use of throw blasting relatively smaller draglines (or Icwer) could be used when starting a nc+v v'enturc. Rietspruit, it should be noted, has not increased its powder factor in order to use throw blasting. The hard sandstone requires the high powder factors in use. The utilization of throw blasting tcchniyucs arwc as a di- rect result of obscnrd ground movement due to the Cact [hat the highwall had been presplit. This previously presplit highwall, due to its competent nature, has no baucr of semi-broken rock to inhibit movement of the first lint of holes. This results in the most favourable conditions for initiating throw blasting. The development of the inlill blasting tcchniyucs. like the presplit, +sere based on experimentation, details of which arc beyond [he scope of this report. For site sake of com- pleteness, the development of this system is included in the Appendix. Results of Throw Blasting The following sketch represents the optimum result of e.x pcrimentation to date for throw blasting. ~~ ,. ems' "7Y ~ .~ i p7 ..>-. 'i7' `4~' 4r~ ,~ 1• vertical highwall section at Rietspruit. Ettect of DepthJWidth Ratio on °lo Blast-over Percentage blast-over is defined as the volumetric pcrccn- tagc of blasted material which is moved by blasting opera- tions, beyond the coal edge. The Appendix describes the effect of the detonating sc- yuencc on blast-over results, (or constant burden, spacing and powder factor. At Rietspruit the depth of overburden varies considerably, and variations in percentage blast-over hose been noted. If a constant strip width is maintained. then instinctively increased blast-over may be expected with increasing depth. In order to normalize results obsen•ed. depth; width ratio is used to show these results, since mi- norstrip width variations do occur. About the Aufhan: K. L. "Poppy",tkUunald is Nrnrral manaKrr n/ Hirts- pruif Opera'aaf Srrumes /r'fy/ L(d. whrail uprruaa Hiehprun mini. 4Vu3'nc R. Smith is ptannmK manaKCr (or Hiefsprwl. and Ur. IV. A. "lidf"Gwby, h(naunr: runa'u(fanL is manager u( i(tninP Hrwurrra f'/IPlnrl'rlnK Lfd.. Omm~a. Canada. About the Paper. Thr frxt has Arrn rdin'd ~u inr7udr only drr srrfmn of (he Paper dra(inq wrd~ Iwoarmn afnPpup; uprru(ium'. TAr rmnp(e4• Pm prr rnoy be uhfarnrd by untinN A. L..llrUona(d at Hirtsprmt. SI ~R F..."r „i~iC~ E14 FIG, 4. Section through Blast, ~0° Tie-up.