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c. <br />~ .t. <br />~' <br />.~. <br />vo <br />Three BUCYRUS-ERIE'S t95-B electric mining shovels load coal at Reitspruil. The mine also employs three <br />BUCYRUS-ERIE~9 i570-W walking draglines antl live A5-R rotary blast Hole drills. <br />of i~~~ ,~I ~~. f: ~. I~r1~it•r.K~. ~qa OfP'~~ <br />100 <br /> <br />Q <br />W <br />O <br />N <br />Q <br />J <br />ra <br /> <br />90 <br /> <br />80 <br /> <br />70 <br /> <br />60 "` <br /> <br />50 A j <br /> <br />40 c, ., X- <br /> <br />_ <br />31 <br />,,. _ <br />- s <br />3 <br />0 <br />t0 <br /> <br /> <br /> t <br />to <br /> <br />0 0.1 0.2 0.3 0.4 0.5;0.6 0.7 0.8 0.9 1.0 <br />~ ~ ~ ~r D/W <br />-~ /I I 1 <br />FIG. 5. Graph showing Relationship between .. <br />Percentage Blast-over and Depth/Width Ratio. <br />n` '" , <br />-/`' <br />ragline Applications Using Throw Blasting <br />is a well knowdfact that the chop-down mode of dragline <br />application is relatively inctlicicnt (ca 60~•r,) compared [o <br />conven[ional dragline applications which use a key cut. If <br />_ ,, ~ ~-- - <br /> <br />%~ . <br />any advantage is to be gained from blast-over, then one of <br />the following two alternatives must be pursued: <br />a) Aim to blast-over a quantity cyuivalent to the swell the <br />material undergoes (due to blasting) so as to maintain the <br />same surface elevation. This will ensure minimum pad <br />preparation Cor the dragline, whilst still using the corrven- <br />tionul key cut systems of dragline opcrauon. (Sec Appen- <br />dix 60° Tic-up.) <br />b) Aim to blast-over a quantity large enough to more than <br />compensate Cor the chop~own mode of operation and de- <br />velop new dragline applications using, where nccessar}•, the <br />chop-down mode of operatton. <br />The Development of the Application of <br />Throw Blasting to a Double Seam Operation <br />On observing the displacement of the overburden, it was <br />realircd that if a chop-down operation could be eliminated. <br />or lessened, then the throw blasting could be of trcmcn- <br />dous benefit. In order to understand the development of the <br />application to a double seam operation, it is necessary to <br />understand the double seam system of mining employed <br />bcforc the observed throw blasting phenomenon. <br />Double Seam Dragline Operation without <br />Throw Blasting <br />Titc following sketches dcpic[ the mining scyucncc bcforc <br />throw blasting was applied and is referred to as Conven- <br />tional Double Seam Operation. <br /> <br />. ., E15 <br />