Blast Drill Pattern Calculator

Summary

Enter hole diameter, bench height, rock and explosive properties to estimate burden, spacing, charge mass, broken-rock volume, and powder factor.

How it works

1. Enter the blast hole diameter (mm) and select the rock type to set the empirical burden ratio (Kb).
2. Choose an explosive product to set relative weight strength (RWS) and a representative bulk density.
3. Set the rock density used to convert broken volume into tonnes.
4. The calculator derives the burden (B) using the empirically validated ratio B = Kb × d, where Kb ≈ 25–40 depending on rock conditions.
5. Spacing is set at 1.0–1.15 × burden for square/staggered patterns; subdrill is typically 0.3 × burden.
6. Stemming is calculated as 0.7 × burden; total hole depth = bench height + subdrill.
7. Review charge mass and powder factors, then validate all assumptions against site trials and the product technical data sheet.

Use cases

• Designing initial drill patterns for a new open-pit bench.
• Verifying that a contractor-supplied pattern matches rock conditions.
• Scaling patterns when switching to a larger or smaller drill rig.
• Estimating explosive quantity per hole and per blast block.
• Training junior blasting engineers on pattern geometry fundamentals.
• Comparing square versus staggered grid layouts for the same bench.

Frequently Asked Questions