Drill and Blast: Don’t discredit the Drill

Drill and Blast as a group is generally measured by the blast outcome. More often than not, the blast crew rather than the entire drill and blast process is held accountable for the blast outcome. Unfortunately, this is a common misunderstanding from those who are not intimately associated with the process and do not place value on the parameters which effect blast outcomes. These are:

  • Drill Selection and capability;
  • Bench preparation;
  • Drill, loading and initiation design;
  • Drilling and Loading accuracy (QA/QC).

Do you have the right tools for the job?

It is easy to make budget cuts in order to reduce drill and blast operating costs. In many cases, this will substitute blast quality for cost saving or production uplift – which in the long run will most likely increase the operating cost of the downstream processes i.e load and haul.

In the drilling world, the most common cost cutting initiative is increasing the drill hole diameter to maintain the same operating powder factor and reduce drill meters – this is highly attractive as it offers both a cost saving as well as a productivity uplift. Unfortunately, there is rarely consideration of the bench height distribution across the mine site when making this decision. As a result:

  • the stiffness ratio reduces (ratio of bench height to burden);
  • energy distribution reduces (because the patterns have been spaced out to maintain budget powder factor) and;
  • the stemming ratio increases (ratio of stemming to hole length).

You have the right tool, but is it sharp?

Slight modifications to production drills can see significant productivity improvement. For this reason, you need to understand the capabilities of your drill and the geology you are planning to drill. From a mechanical point of view, the key focus is generally on: Drill bit selection, flutes, rods, dust deflectors, curtain configuration, pull down pressures, torque ratios, compressor strength, etc. For anyone who is not seeing optimal results, engage your local drill representatives in collaboration with your drillers to see what improvement suggestions they might have.

Knowing the geological strata being drilled will save you hours of time being wasted. Make sure you log the strata being drilled and keep a record of the best performing drill bits. Maintaining this site knowledge will save your crews a lot of trial and error time and enable you to hit the ground running the next time you are back in that area.

Is your workbench sturdy?

Bench preparation is a key component in achieving consistent hole distribution and loading. Having consistent hole distribution will improve drill productivity by reducing manoeuvring and changes to mast angle, and blast crew productivity by simplifying the loading and initiation designs. Even with perfect execution, inconsistent distribution can result in pockets of poor fragmentation in the blast profile.

Where you can, maintain a hard floor. Drilling through fill material is slow and hard to collar. Depending on the amount of fill, most holes will suffer from some sort of backfill as a result. In addition to this, stemming confinement is much harder to achieve and cavitation can occur in-hole resulting in loss of explosive product.

Fill material can also become a significant hazard! If material was to collapse on a non-el downline, there is potential for misfire through snap, slap and shoot. Or if water saturation in the material was to occur, it can very easily slump – nobody wants to see a drill or bomb truck on its side because bench prep wasn’t completed correctly.

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