August 21, 2017

Check twice, blast once: The importance of blasthole monitoring

Senior Mining Engineer at AEL Mining Services
Senior Mining Engineer at AEL Mining Services

Measure twice and cut once’ is an old adage that every person who works with their hands has heard countless times, usually dispensed by their mentor as they learn the ins and outs of their craft. The learnings behind this phrase are to avoid having to duplicate your efforts, save time and eliminate any possibility of error in your results.

In the world of mining operations – where every cubic millimetre of ore and every second of uptime counts – this is especially true. However, some operations are failing to meet their potential by allowing poorly drilled blastholes to force them into duplicating blasts unnecessarily and ultimately hampering production in the long run. It is crucial that mines measure twice, and blast once.

Blasthole surveying is a key part of blast planning and blast optimisation. These two processes are vital in ensuring that every blast goes off without a hitch, that the optimal amount and type of explosives are used and that the right results are achieved.

When drilling blastholes, there are a number of technical and geological factors that can lead to an undesirable drilling pattern. From a technical aspect, excessive drilling and the use of worn out drill bits can lead to errors in blasthole structures while rock types and ground water can lead to drilling deviations.

Deviations lead to poor blast results, low productivity, safety risks and environmental impacts.

Blasthole surveying can identify drilling deviations as well as burden lengths and drilling depths. This is crucial to operations because a small burden length can result in too much rock being blasted from the bench face while too long a length results in the explosive energy coming back up the blasthole.

Using Boretrak™ equipment, for example, operations can check these factors as well as calculate drilling deviation from the design at fixed intervals. Boretrak™ comprises a control display unit (CDU) logger, a rack of rods, a probe and a gyroscope or gravity sensors. All of this equipment feeds into an interface which can represent the status of a drillhole, removing all guesswork from blast planning.

Other equipment which is crucial in checking drillholes is borehole calliper logs, which comprise a tripod with a probe on a pulley which is lowered into the hole. The probe is equipped with arms that can open out on command to measure the average diameter and average variance of the drillhole. In an ideal world, the hole should resemble a cylindrical tube – with smooth walls and an equal diameter throughout. In reality, however, there are often deviations. By measuring these deviations with the probe, blasting teams can determine the optimal amount and type of explosives that each unique hole requires or if the hole needs slight drilling adjustments.

A well planned and successfully executed blast has several benefits. It can deliver operation-specific fragmentation levels that results in improved productivity and removing the need for secondary blasts. This is because the correct level of fragmentation reduces the levels of loading and hauling, and optimises plant operations by making processes such as crushing more efficient.

A successful blast also improves safety because it reduces the amount of flyrock, while its environmental benefits include meeting airblast and ground vibration limits.

While the information that surveying provides is crucial, it is what operations do with it that really counts. Through thorough measurement and analysis, operations can take corrective actions to reduce downtime and unnecessary secondary blasts. By ‘measuring twice and blasting once’, mines can reap the financial and operational rewards of thorough planning and measurement.

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