Coal Age

DEC 2018

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20 December 2018 blasting Blast Casting Optimization by anthony konya, dr. calvin j. konya and dr. paul worsey Blast casting is the process of fragment- ing overburden material and moving it into the spoils pile using explosive energy with the main goal to minimize material handling. Blast casting design is focused simply on the throw and movement of the material rather than the fragmentation of rock in classi- cal rock blasting. Due in part to three main reasons: 1. This is waste material and does not need to meet specific sizing re- quirements for crushing; 2. The equipment for overburden re- moval is quite large and can easily handle large boulders; and 3. The rock being blasted is typically shales and siltstones, which break easily. The explosive energy used in the casting process replaces part of the work of the excavator by placing between 30% and 70% of the material blasted to its final resting location rather than the 5% to 10% typical in traditional overburden shots. Typically, an operation would like to see more than 50% of the material blasted to be cast into its final resting location, and in most operations that is an achievable goal. This is represented in Figure 1, as Zone 1, which shows the material blasted in its final resting location, requiring no to minimal material handling. Most operations limit blast cast- ing goals to that which falls into Zone 1; however, reducing material handling for the rest of the muckpile is also im- portant. Zone 2 will be described as the area of the muckpile that has been dis- placed from the bench, but is not in its final resting location. Material in Zone 2 requires less handling the material that has not been displaced from the original bench location, as in Zone 3. Depending on the pit width, material left in Zone 3 can significantly increase the overbur- den handling time. Therefore, after the material in Zone 1 is maximized, the ma- terial transferred from Zone 3 to Zone 2 is a secondary goal. If a mass balance is considered, where the post-blast muck pile present is distributed between Zone 1, 2 and 3; the goals of cast blasting are then: 1. Maximize volume of rock in Zone 1 (above 50% up to 70% in most cas- es); and 2. Minimize the volume of rock in Zone 3. The achievement of these goals and the optimization of a blast cast- ing operation can lead to large savings for a company, by either increasing the efficiency or reducing the necessary workload of the excavator and replac- ing it with explosive energy. This gives three unique scenarios for a mining company to consider when analyzing drill-and-blast costs in relation to exca- Figure 2—Zone 2 showing material moved from its location, but requiring some handling to position into final location (adapted from Shrihari, Worsey, Chiapetta). Figure 1—Zone 1 showing material blasted to its final resting location (adapted from Shrihari, Worsey, Chiapetta). Designs can be optimized to suit market and site specific needs

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