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Dragline Operations ' ngle and Multiple Seam spruit, South Africa The Rietsprui[ structure consisu o(a gentle syncline in the south and a corresponding anticline to the north with both plunging to the north east. The seams sub-outcrop against the unconsolidated cover or terminate against the felsite floor. The ven• thin No. 3 seam has little commercial significance. Presplitting The main reason Cor introducing presplitting was for de- watering purposes, in order to introduce dry mix explo- sives, as opposed to slurry explosives. The method, economics and resulting advantages are de- scribed elsewhere.' For the sake of completeness a brief description oC the method of presplitting is included. Method of Presplitting The desired presplit line is~surveyed in. Holes are marked out at dm" inten•als in the overburden above No. 4 scam ~d 6m inten•alsin the more competent midburdcn above o. 2 scam. Hotcs arc drilled to the top ul coal using a •Whne, P.E. and McDonald, K. L.. 'Controlletl 8lastmg in a Double Seam Opencast Coal Operahon." 'These tlimensions ale sometimes reduced m less competent ground. 250mm overburden drill. Generally 300m are presplit per blast, the length of the presplit is dictated by scheduling constraints. A single charge of 60kg of sl_t,rr}• is located at the bottom of the hole. No tamping (stemming) is used. All holes are detonated simultancousl}•, using denotating cord. Presplit Results A complete record oC results is documented elsewhere.' Pertinent to the paper is the (act that presplitting results in a competent, straight, vertical highwall. This enables accu- rate control of [he burden oC [he first row of holes (closes[ to the highwall) of the infill blast holes. Experience has shown that [he control oC this burden is a prime requisite o(success(ul throw blasting. II II ~ II II p 0 p II II ti II II II 11 II II II U ul ._12m FIG. 2. Section before Presplitting. E13 VOID ~ VOID General Manager McDonald s«addfes the presplit separation which he reels is a prerequisite to a competent vertical highwall and successful throw blasting, FIG. 3. Section after Presplitting.