Start the new week with a blast! Have a great week everyone! Stay Safe.
These rules provide a first estimate in the absence of any better data.
→ Blasthole diameter in mm ≤ 15 x Bench height (BH) in metres
→ Bench height (BH) in metres ≥ (Blasthole diameter (D) in mm)/15
→ Burden (B) = (25 to 40) x (D)
→ Spacing (S) = 1.15 x B (This gives an equilateral pattern)
→ Subdrill = (3 to 15) x D
→ Charge length (C) ≥ 20 D
→ Stemming ≥ 20 x D or (0.7 – 1.2) x B
→ Burden stiffness ratio = BH/B : 2 to 3.5 good fragmentation
→ Stemming material size = D/10 to D/20
o (Angular material with minimum fines)
Presplit blasting
→ Spacing = Hole diameter x 12
→ Burden = 0.5 x production blast burden (B)
→ Uncharged length at top = 10 x D
→ Powder factor = 0.5kg per square metre of face
→ Do not stem holes.
→ Fire all holes on the same delay, or in groups of ≥ 5 holes
Smooth blasting→ Spacing = 15 x Hole diameter (hard rock)
→ 20 x Hole diameter (soft rock)
→ Burden = 1.25 x Spacing
→ Fire as many holes as possible on one delay.
→ Stem holes.
Powder factors – Typical powder factors used in mass blasts
→ Rock type – PF (kg/m3)
→ Hard 0.7 – 0.8 (kg/m3)
→ Medium 0.4 – 0.5 (kg/m3)
→ Soft 0.25 – 0.35 (kg/m3)
→ Very Soft 0.15 – 0.25 (kg/m3)
Typical powder factors used in presplit and smooth blasting
→ Rock type – PF (kg/m3)
→Hard 0.6 – 0.9 (kg/m3)
→Medium 0.4 – 0.5 (kg/m3)
→ Soft 0.2 – 0.3 (kg/m3)
Source: Blasting and Explosives Quick Reference Guide – Dyno Nobel
