WALL CONTROL BLASTING TECHNIQUES -----------------------------------------------------
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thereby reducing the cost. Thus the cost of small diameter presplitting will not always exceed the cost incurred using large diameters as is sometimes believed. Each situation should be assessed according to the factors discussed above and the best option selected. Shooting the Presplit Line - The presplit line may be shot with the final production blast or before the final shot is laid out in the field. Both approaches are workable. When the presplit line is detonated with the final blast it should be initiated approximately 100 milliseconds before the final wall blast. In delayed blasts care should be taken that the presplit line does not precede the detonation of the adjacent buffer row holes by too great a time. A delay may need to be introduced into the presplit line periodically in order to avoid the possible disruption of nearby buffer holes from the detonating presplit holes. However, as many holes as possible should be shot instantaneously taking into account the lead time and any vibration control requirements, because this yields a better defined presplit. If the final wall shot is quite narrow the presplit row should be detonated with the final blast. Detonating the presplit holes in advance may lead to the mass of rock sliding off the wall, leaving very poorly fragmented material to be cleaned up. Following figure is an example of a final wall blast incorporating two production rows, a buffer row and the presplit holes angled at 80 degrees. This example is for an iron ore mine in competent rock.
Active Highwall Pre-splitting in Dragline Operations - The pre-splitting technique has also been used to control the successive highwalls in a blast casting operation. The standard method involves drilling large diameter holes on the designed highwall location and loading these with a concentrated charge of explosive in or near the bottom of the borehole. Active highwall pre-splitting has two advantages. First, it allows a very regular highwall to be produced. Therefore, front row burdens on the next casting shot can be well controlled for
Author: Partha Das Sharma, (B.Tech-Hons., Mining Engg.), E.mail: sharmapd1@gmail.com, Website: http://miningandblasting.wordpress.com/ Page 12