Drilling and Blasting
Explosives
ANFO is cheap and safe but degrades in water and is low density; emulsions and heavy ANFO are water-resistant and more energetic. Know density, velocity of detonation (VOD), relative weight and bulk strength, and critical diameter. Select by hole condition: dry holes take ANFO or heavy ANFO; wet holes need emulsion or pumped heavy ANFO. Electronic detonators give the best timing accuracy; shock tube and detonating cord are cheaper alternatives.
Blast design
Burden and spacing scale with hole diameter. A common rule of thumb is burden (m) ≈ 25–35 × hole diameter (m), roughly 3 m for a 100 mm hole, with spacing ≈ 1.0–1.3 × burden. Add subdrill (about 0.2–0.3 × burden), stemming (about 0.7–1.0 × burden) and a powder factor expressed in kg/bcm or kg/t. Fragmentation models such as Kuz–Ram show that raising powder factor fines the muck, at the cost of higher cost and vibration.
Vibration and control
Peak particle velocity falls as scaled distance SD = D/√W increases. Pre-split and trim blasts protect final walls; accurate delays reduce misfires and overbreak.
Traps
- Mixing kg/t and kg/bcm - the unit changes the number by the rock density.
- Assuming higher VOD always means better fragmentation; coupling and energy partition matter.
- Overlooking water, freezing and dead-pressing, which ruin ANFO performance.
- Quoting a PPV figure without distance and charge weight.
Worked example
A 102 mm hole on a 5 m bench, burden 3.0 m, spacing 3.5 m, carries 31 kg of ANFO at 0.8 g/cm³. Volume per hole = 3.0 × 3.5 × 5 = 52.5 bcm, so powder factor = 31/52.5 ≈ 0.6 kg/bcm.