Big Dog Mining

Surface Bench Blast Pattern

Burden, spacing, stemming, subdrill and explosive per hole from your hole diameter and bench height. Two published methods, worked side by side, because where they disagree is worth knowing before you drill 200 holes.
Surface bench blasting only: vertical holes to a free face. Underground ring, drift and stope rounds work differently and are not what this calculates.
Once you have a pattern, Surface Blasthole Drill Productivity tells you what it costs to drill it.

Step 1: The hole and the bench

Everything downstream scales off these two numbers.

Units ?

Source equations are imperial. Metric is converted.

Blasthole diameter ?in

Drilled diameter, not the bit size you meant to use.

Bench height ?ft

Floor to crest. Hole depth is deeper by the subdrill.

Drill pattern ?

Sets the spacing-to-burden ratio.

Rock being blasted ?

Fills the bank density below. Override it for your own rock.

Bank density auto ?lb/yd³

Weight in the ground, before the shot.

Step 2: The explosive

Choosing a product fills in density, detonation velocity and energy.

Product ?

Density auto ?g/cc

As loaded in the hole.

Explosive energy class auto ?

For the Ash burden ratio. Our suggestion, not the book's.

Rock hardness ?

Pairs with energy class to set the Ash burden ratio.

Powder factor ?

The design target. Pick your ground or enter your own.

Powder factor value auto ?lb/yd³

Explosive per unit volume of rock broken.

burden

spacing

explosive per hole

Step	Value	Where it comes from

Bench section: one hole, to scale

Plan view: the pattern

Commercial explosive characteristics

Type	Grade	Density, g/cc	Detonation velocity, ft/s	Energy, RBS	Water resistance

SME Mining Reference Handbook, 2nd ed., p. 279. RBS is relative bulk strength with ANFO as 100. Water resistance matters more than the energy figure on a wet hole: ANFO has none at all.

Ash burden ratios, K_b

Explosive energy	Soft rock	Average	Hard rock

SME Mining Reference Handbook, 2nd ed., Table 11.2, p. 281, after Ash 1963. Burden is then K_b × hole diameter ÷ 12. The same table appears identically in the 1st edition on p. 207, which is a useful independent check on the transcription.

Published powder factors

Source	Condition	lb/yd³

Materials not in the handbooks. Rock salt appears nowhere in any of the 22 references behind these tools: not in Table 10.4-1, not in the Caterpillar weight-of-materials table, and nowhere in the full text. Its row is kept separately, shown under its own heading in the picker, and labelled on screen every time it is used. Bank density 2.16 t/m³ is the density of pure NaCl, the figure used for Avery Island domal salt (Oak Ridge, Thermal Properties of Rock Salt); swell 1.49 is the 49% Church (1981) gives for well-blasted rock, via the NRC report Bulking Factor of Rock for Underground Openings. Potash and trona are deliberately absent: the same treatment needs a source per material, and inventing two more rows to round out a list is how a table stops being trustworthy.

Worth saying plainly: salt is mined underground, room and pillar, not from a surface bench. That is very likely why no bench-blasting table carries it. The row is here for its density if you want tonnage, but the pattern this page works out is a surface pattern, and an underground round is a different calculation.

General surface blasting and the seismic-velocity table: SME Mining Reference Handbook, 2nd ed., pp. 284-285. Surface coal and surface metal mines: SME Mining Reference Handbook, 1st ed., p. 209.

These are first approximations. The source says so in as many words: the empirical methods here give a starting pattern that needs adjustment to meet field conditions. Structure, water, free faces, timing and what the last shot actually did all move these numbers, and none of that is in the equations. Shoot it, look at the muck pile and the back, and adjust.

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Terms of use and disclaimer

Estimating aid only. This calculator is an educational tool. It is not an engineering design and it is not a substitute for the judgment of a competent or qualified person.

No warranty. It is provided "as is", without warranty of any kind, express or implied, including any implied warranty of merchantability or fitness for a particular purpose. Equations and constants are cited to their published sources above, but transcription, implementation and the values you enter can all be wrong. Verify every result against the cited source and against your own site conditions before it informs a decision.

Not a statutory document. Nothing produced here is a ground control plan, ventilation plan, blast design, haul road design or hoist design. Those must be prepared, signed and approved under the regulations that apply to your operation. Compliance with MSHA, or with your own jurisdiction's mining regulations, is the operator's responsibility and remains so.

Assumption of risk. You use this tool entirely at your own risk. Mining is hazardous, and errors in ground support, ventilation, blasting or haulage can cause serious injury or death.

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