Size , Nature of Rock, Competence, Jointing and site Sensitivity determines Number of holes, Charge weight.
The number of holes, the drilling pattern per rock, burdens and spacing used, and drilling depth, is fundamental to the rock breaking process in civil engineering and mining. Basically a hole or holes are drilled into the rock, which are then charged, effectively stemmed and initiated electrically using a shot firer. Large volumes of expanding gases (one litre by volume per gram of propellant) are produced in a split second, pressurize the rock which splits/shatters in tensile, thus alleviating the pressure to atmosphere; the process then stops., which is benign. The drilling pattern and choice of charge weights is based upon the objectives desired:
- particle size
- sensitivity of the surroundings
- fly rock control
Particle Size
If less than 50cms particles are required, burdens and spacing must conform, but you must examine the natural jointing in the rock if applicable, because rocks will break at the joints, which are weak lines.
Sensitivity Of The Surrounding
If the rocks are next to the highway, or a village, or sensitive installations, the drilling pattern and the charge weights selected per cartridge in the drilled hole must be balanced; if the cartridge is heavily weighted and the burden too small, it will fly; if the cartridge weight is light and the burden too big, it will not break, perhaps create a few cracks. The balanced approach requires understanding through experience how different rock types break.
Fly Rock Control
Nonex non-explosive, non-detonating technology does not cause structural damage due shock wave and vibrations, but it can cause fly rock, which however is 100% controllable, by drill pattern design and additionally when very sensitive by effective covering methodology. Each application type requires different method statements, which are detailed per application. Suffice it to say that boulder breaking is the easiest of all applications; the rock is unconfined on all planes, and breaks effortlessly, broken rock moving without cover +- 10 metres on initiation, that is when using Nonex cartridges, all other variables being balanced.