FREE TOOL
First-pass pattern from hole diameter
A starting pattern from the hole diameter, using the ratios most texts quote. Adjust the ratios to what your ground has taught you; the panel updates as you type.
Calculator
This tool needs JavaScript. Your browser has it switched off, so the result panel will not update.
How it works and what it assumes
Burden scales with hole diameter because the energy a hole can deliver scales with the charge diameter. The 25 to 35 diameter range is a rule of thumb from decades of production blasting; dense rock, light explosives and a need for fine fragmentation push it to the low end.
Spacing is set from burden, stemming is set so the top of the charge is deep enough to be confined, and subdrill carries the breakage below the design floor. Hole length is bench height plus subdrill; charge length is hole length minus stemming.
Every one of these is a first estimate. Jointing, water, bench geometry, the explosive, the timing and the result you need all move the numbers. Treat the panel as the start of a design conversation, not its end.
Read the explanation
Pattern rules of thumb, and when they fail
Where the burden-in-diameters and spacing-to-burden ratios come from, and the situations that break them.
Read about Pattern rules of thumb, and when they fail
Want this fitted to your site?
The free tool is the lite version. The full version uses your products, your ground and your reporting.