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<br />• <br />• <br />Rietspruit, South Africa <br />Referring to Figure 6, it will be appreciated that the 20m <br />step in the highwall is necessary (or tailswing when the <br />dragline digs the mid burden key cut. (See step (our.) It u•as <br />realized that if this 20m bench could be "stretched" to ap- <br />proximately SSm, then the overburden could be blasted <br />into the power trough crca[cd by the midburdcn. <br />Comparing the previous two sets oC sketches it can be seen <br />that additional overburden had to be moved at some stage <br />in order to stretch the ?Om tailswing on midburdcn to the <br />desired Sim. Spoil diagrams were drawn to ensure that <br />spoiling room was available to achieve this end. <br />Accordingly, the next mining cycle was carried out, with <br />the additional overburden being moved to achieve the de- <br />sired geometry. <br />Advantages resulting from the New Double <br />Seam Dragline Operation <br />1. Effective Increase in Pit Length -The Throw Blast <br />system of dragline operation electively doubles the pit <br />length because both the \o. 3 and No. 2 scams are being <br />exposed simultaneousl}'. This allows corresponding larger <br />in-pit im~entories to be carried. <br />A BUCYRUS-ERIE 15i4W is used to build an in-pit bench <br />from which it uncovers No. d seam. <br />2. Blending of Seams -The Throw Blast system of <br />draglinc operation allows both scams to be mined simul- <br />taneously thereby ensuring a consistent quality of raw coal <br />feed to the plant. <br />3. Simplification of Coaling Operation - Whcn using <br />the Throw Blast system of draglinc operation, the draglinc <br />can spoil [he blasted No. 4 seam coal onto the blasted :\'o. <br />? scam coal which enhances blending and reduces shovel <br />moves. In the case of other mines, where a double seam <br />mining operation exists over the entire pit leneth, access <br />for the coaling of the upper seam presents a problem. Ac- <br />cess for coaling operation is usually gained from lou•wall <br />intermediate elevation ramps to the upper seam. These <br />ramps result in additional dragline rehandle. The Throw <br />Blast system of dragline operation could soh•c the problem <br />of access to the upper scam as this coal can be dumped <br />onto the lower seam (by dragline, shovel or dozer) and <br />subsequently be mined together with the lower seam. <br />4. Increased Spoilpile Stability -The blast-over results <br />in competent hard rock forming the base of the final spoil- <br />pile. as opposed to a mixture of subsoil and weathered <br />rock which formed the base when using conventional <br />Double Seam methods. The material now forming the toe <br />E18 <br />