DRILL & BLAST
fi lling the holes with some type of T
raditional approaches to extracting material from the earth have nearly always involved drilling holes in the ground,
explosive and blasting the ground to fracture it suffi ciently enough to dig. T is does not always produce the desired result and is considered one of the more expensive processes in a mine, especially in coal mines. Some mines place little emphasis on generating an effi cient drill and blast process, which can cause downstream complications. Several diff erent areas contribute to blasting ineffi ciencies. Irregular hole placement can cause poor fragmentation that results in diffi cult digging for the loading equipment. Inaccurate depths can result in uneven benches. Holes that are over-drilled into the coal seam result in dilution of material into the coal. A misunderstanding of how hard the ground is can lead to a poor choice of explosive product for a particular blast. Many varying and unique
approaches have been explored to improve this process while trying to reduce costs. Approaching this just for drill and blast alone yields some advantages. However, more frequently a broader strategy such as the ‘Mine to Mill’ approach used for hard rock mines is required to improve effi ciencies across the mine as a whole. Hexagon Mining looks at the entire mining process to identify areas where technology can be applied to improve coal production. T e drill and blast process is one area where considerable benefi ts can be gained.
Design accuracy Firstly, the design of the pit should be examined. How the material is to be moved and what equipment moves it, needs to be understood. A strip mine operation may utilise throw or cast blasts where the blast moves the material into the adjacent strip. T is means the dragline or digging equipment does not have to move the material. T e more effi ciently
this is performed, the less the digging machine has to dig and the faster the production equipment can recover the coal.
Coal seams vary in shape, size, angle and location. It’s diffi cult to dig to a coal seam that is on a steep angle. T e coal horizon in this case may be too steep a grade for digging equipment to position itself correctly. Furthermore, coal seams that are near vertical provide additional challenges, as the seam will need to be exposed from the side. In all these cases, the design of the pit and consideration of how the equipment will extract the coal is a must. T e design of the blast and hence the drill pattern is an important step in this process. Simulation of the blast before it happens has become more common recently. Changes in drillhole placement and blast timing can be performed before the drilling operator drills the holes. T is approach allows for design changes before a single hole is drilled. If a high-precision guidance solution, such as Leica J2drill, is used to drill the holes, as-drilled data can feed into blasting simulators to adjust the blast design further before a shot is fi red. T is compensates for any variation in the drill operations performed to the original plan. However, varying the loading design at this stage is not best practice and generally not required. T e use of a high-precision guidance system to achieve accurate hole placement and accurate depth in the fi rst place, is the ultimate solution.
Accurate positioning Once a pattern is designed, it is transferred to the guidance system either via a wireless radio system or manually on-board the machine. T e operator is then presented with a virtual pattern on their display. Using a positioning
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