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Productivity Improvements Using Controlled Blasting in Opencast Coal Operation of r ~ ~_J By: K. L. McDonald, W. K. Smith, Dr- W. A. Crosby Abstract The dragline operation of most coal producers represents the major cost of mining opencast coal. Improvemen[s in dragline productivity can have a dramatic effect on overall mining operation. At Rie[spruit, controlled blasting techniques have been suc- cessfully introduced which increase mint productivity by throwing a portion of the overburden material such that it need not be dug by the dragline. This step also breaks-up the overburden better, improving the ease with which the dragline bucke[ enters [he bank. Two blasting techniques have been combined. A novel pre- split blasting technique is used to produce a vertical high- wall which is in turn used in the burden control of the main overburden throw blas[ technique. The resulting blast profile has reyuircd a completely new approach be designed (or the dragline operation. A number of other benefits have also been experienced using these techniques which include blast hole de+rarering, impru ved .rgjer,r, mu! lover coal /asses. This paper presents a description of the intro- duction of this new mining method with a discussion of the results achieved to date. Location Rietsprun is situated in the Witbank coal field. I IS kilome- ters cast of Johannesburg. South Africa's largest city. Al- most 50 percen[ of the countr}•'s annual coal output is mined in the area. The area has swell-developed industrial infrastructure and [here are several large power s[ations lo- cated in [he region. The mine property has a surface area of 3951 hectares, of which ?800 hectares are underlain b_v coal. The mean elevation oC the mine is 1551 metres above sea level. The topograph}• is gently undulating and is drained by ttvo s[reams, the Rie[spruit and the Steenkoolspruit. The climate is moderate and typical oC the eastern Highveld. A seven kilometres railsvav line has been constructed to link Rietsprun to the main Richards Bay line. Business Rietsprun is a joint venture between Transvaal Consoli- dated Land and Exploration Company (TCL) -the min- ing finance member of the Barlow Rand Group -and Shell, South Arica, a company of the Royal-Dutch group. Rictspruit is administered and managed by Rand Mines, a sister compan}' to TCL. Rand Mines is the mining arm of Barlow Rand. Coal transportation and marketing is the re- sponsibility of Shell. sURF.tCE .V WER The mint is an opencast strip minc..411 the coal produced is exported via Richards Bay, some 500 kilometres to the south east. Scale of Operation Some 40 million cubic metres of overburden hatr to be excavated in order to mine approximately 9.0 million tons of rau• coal per annum. In the month of March, 1980, over I,I million tons of coal acre mined. Geology The coal measures in the Wnbank region arc of Permian age and belong to the Middle Ecca formation. This forma- tion is part of the Karoo system, a scdimentar}• sequence developed after a period ofglaciation. Five coal seams are contained within the Middle Ecca beds, numbered in ascending order. METRES 13 12- SSEAY ]S 12 , . uv~n sEAY 26-7 ~LOWEA SEAY n 6.E 1 ~ SEAN s.o = t to L SEAM T nwrE rEL51TE E12 F1G. 1. An oltl BUCYRUSS shovel graces the front entrance to Rietsprurt mme. South Atrica.