How to Design a Basic Blast Pattern
Every production blast pattern on Earth reduces to five dimensions — burden, spacing, stemming, subdrill, and hole diameter — plus timing. Here's the first-principles method for a starting design, the way it's taught and the way it's field-tuned. (Design guidance for study; live shots belong to licensed blasters and site-specific rules.)
01Start from the hole diameter
Diameter is chosen by bench height and production rate, and everything scales from it. Classic starting rule: burden ≈ 24–30 × hole diameter for typical products and rock — a 6½" hole suggests roughly a 13–16 ft burden. Stiffer rock and lighter powder push toward the low end.
02Check bench stiffness
Bench height ÷ burden should sit around 2.5–4. Below ~2 the bench is 'stiff' — poor movement, toe problems, flyrock risk from confinement. A 40-ft bench with a 14-ft burden gives 2.9: healthy. If it comes out stiff, shrink the burden or the diameter, not your standards.
03Set spacing off the burden
Spacing = 1.15–1.4 × burden for staggered patterns with good timing (14-ft burden → 16–19 ft spacing). Square, instantaneous-row patterns run closer to 1.0–1.15. Staggered equilateral patterns distribute energy best and are the default unless geology argues.
04Stem to hold, subdrill to floor
Stemming ≈ 0.7–1.0 × burden of angular crushed stone (never drill cuttings if you can help it) — short stemming rifles energy skyward as flyrock and airblast; long stemming leaves cap rock on top. Subdrill ≈ 0.2–0.3 × burden below grade to break the floor flat; skip it and you'll meet the toe on every dig cycle for a month.
05Time it to move
Rows need somewhere to go: front rows fire first, and inter-row delays (commonly ~2–4 ms per foot of burden as a starting heuristic) give each row time to move before the next one shoots into it. Electronic detonators buy precision, vibration control, and fragmentation that non-electric shock tube approximates on a good day.
06Compute PF and pressure-check the design
Run the powder factor against the rock class target (0.8–1.6 lb/CY across most surface work). Then walk the design with the seismograph map, the flyrock radius, the face profile survey, and the drill logs — burdens measured off a laser-profiled face, because the face the driller drilled and the face the designer drew are rarely the same face.
Blast Master in the Sim Yard lets you feel exactly these tradeoffs — including what short stemming does to your afternoon.
Rather learn it by playing?
The Sim Yard has nine free browser games built on real mining problems — blasting, hauling, crushing, and more.
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