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Chapter 6: Drilling
November 1, 2007 By: Pit and Quarry Staff Pit & QuarryWhen considering drilling in a quarry environment, it is important to analyze not the present needs of the operation, but also the growth path the site will take in succeeding years.
Drilling is one of the critical elements in the drilling and blasting process. A blasthole is merely a cylindrical vehicle designed and strategically situated to hold and contain an explosive charge so that it can be detonated in the most efficient and optimum manner possible. No blasting system will be truly effective if the hole is poorly placed; i.e. excessive burden and spacing, sized incorrectly for desired results, insufficient in depth etc.
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The drilling phase is the most expensive in the drilling and blasting portion of production, requiring a sizable investment and upkeep. The impact of improper drilling can be felt throughout the remainder of the production cycle, such as excavating and hauling, crushing, screening and so on.
The purpose here is to concentrate on some of the factors that should be considered when evaluating and selecting drilling equipment for a mining project. The primary focus is on surface operations, rather than underground.
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Selection of hole diameter
The first step in the process is to determine what hole size or diameter is most befitting the application, bearing in mind that this could change over time as the operation grows and matures. This is probably the most important single factor since it will in large part determine the size, quantity and type drill or drills that will be needed.
Here are some (but not necessarily all) of the factors involved to determine the optimum drill capability:
- Required production.
- Terrain.
- Material characteristics.
- Type and size of excavating and hauling equipment.
- Proximity to vibration-sensitive areas.
- Bench or "lift" height.
- Explosives type and size.
All items should be examined and considered before making a final decision.
Required production
If intended annual production is one million tons, to choose a medium-sized rotary drill rig that is capable of drilling a 7-7/8-in. (200 mm) diameter hole and producing 3 to 5 million tons per year on a single-shift operation would be excessive.
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Conversely, an installation that requires 5 million tons or more per year might consider using something other than a crawler-mounted drifter drill capable of drilling only up to a 4-in. (102 mm) hole, as a large number of drills would be required. It may be, however, that with all other things being considered, such as improved blast fragmentation, this might still be the better overall choice.
Also to be considered, is the possibility of selectivity – where hole size may have to be reduced to effectively define the ore area or address a vibration issue. Another need here might be for a more maneuverable drill rig for difficult terrain or a truck-mounted unit, able to move more rapidly from one selected area to another, thereby reducing non-productive drilling time.
Terrain
The larger the hole diameter, generally the larger the drilling platform. Big drills, even those mounted on tracks are more limited in their ability to traverse adverse landscapes than smaller machines.
If you are into a pioneering phase, then you should definitely pursue a study of the gradability and "traversability" of various drill units. As the operation matures and will gradate into a smoother series of benches, the constraints will be altered. Therefore, initially it might be wise to choose a smaller hole diameter and a smaller drill(s) until such time as the development proceeds to the point where larger holes and larger drill rigs can be utilized.
If the initial development portion is of insufficient duration to justify purchasing the lighter, smaller drills, then rentals or contract drilling could be considered for the interim, then purchasing the larger rigs when full-blown production is achieved.
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