Engineering & Mining Journal

AUG 2017

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Page 37 of 99

BLASTING 36 E&MJ • AUGUST 2017 The burn cut, otherwise known as a par- allel hole cut, is one of the most com- monly used underground blasting meth- ods because it can be used in drifts of all sizes and dimensions. The burn cut has also been tested in almost all rock types and can effectively break weak or strong rocks, depending on the design. In a burn cut round, five different classifications of holes exist that work together to create a round, which pulls effectively, leaves a good contour and is cost-effective. The first of these holes is the relief holes (red box in Figure one) and are not loaded with explosives. These holes act as a relief point for the surrounding rock to break to, and they are normally larger in diameter, with both the diameter and the length of the hole controlling the total face advance of the round. The second type of hole is the cut hole (green box in Figure one) and these holes are loaded with explosives and closely spaced to the relief holes. These are also the first holes to fire in a round and smash and eject the rock between them and the relief holes. Depending on the round, mul- tiple layers of cut holes may exist, which will continue increasing the relief in the round. These holes tend to be discussed as "overloaded" because they have much more explosives in them than needed to break a very small amount of rock. The third type of hole is the production hole (yellow box in Figure one) and these holes are those that are now properly loaded for the amount of rock that they will break. By the time the production holes start to fire, all the cut holes should be fired and a large enough cut should be opened for pro- duction holes to break to. One critical thing to consider before deciding to switch to the production holes is: Will the open cut cre- ated be able to handle the total volume of material created by the production holes? If a hole fires and, after swelling, the extra vol- ume of material is larger than the open cut, then the round will freeze and the remain- der of the round will not break as intended. The fourth type of hole is the lifter hole (not pictured) and is drilled on the floor and loaded with explosives to break a smooth line along the bottom of the floor. These are typically closely spaced and fired after the production holes with simi- lar mechanics to a trim shot, but are nor- mally heavily loaded to maintain grade. The fifth type of hole is the Contour Holes (not pictured), which are drilled Modern Burn Cut Design By Anthony Konya, Dr. Calvin J. Konya and Dr. Paul Worsey Figure 1 — Burn round hole types (taken underground at S&T Experimental mine).

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