# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DbFEL6FABuU
- **Gondola URL:** https://gondola.cc/posts/68267167-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/031cbcfb5c.jpg
- **Posted:** 2026-07-22T02:56:24.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Those neat rows of holes on a mine bench are the entire engineering problem. The explosive is the cheap part.

Each hole is drilled into a bench typically 10 to 15 m high, at diameters from 150 mm up to 311 mm on the larger rotary rigs. The geometry comes down to two numbers:

- Burden: distance from the hole to the nearest free face, usually 25 to 35 hole diameters
- Spacing: distance between holes along a row, commonly 1.1 to 1.4 times the burden

Holes are drilled slightly past the intended floor level. That subdrill, roughly 0.3 of the burden, stops the blast leaving a hard toe that shovels and dozers have to fight afterwards.

The top third is not explosive at all. It is stemming, angular crushed rock rammed into the collar to stop detonation gases venting straight up the hole. Vent it and you get flyrock, airblast and wasted energy instead of broken rock.

Then the mechanism itself. ANFO detonates at roughly 3,200 to 4,500 m/s, pressurising the hole into the gigapascal range. A compressive shock races out through the rock and reflects off the free face as a tensile wave, and rock is around ten times weaker in tension than in compression, so it tears itself apart from the face inward. High pressure gas follows behind, wedging those fresh cracks open and heaving the mass forward into a loose, diggable pile.

Nothing fires together. Delays of a few milliseconds between holes and tens of milliseconds between rows mean each charge detonates into a face its neighbour created moments earlier. Electronic detonators hold timing to under a millisecond, letting engineers deliberately smear the ground vibration across time so no single frequency builds up under nearby structures.

A blast is not an explosion. It is a scheduled sequence of very small ones.

#stemantics #miningengineering #blasting #rockmechanics #geotechnical

## Stats

- **Views:** 94,052
- **Likes:** 1,175
- **Shares:** 0
- **Comments:** 8

## Tags

geotechnical, rockmechanics, blasting, miningengineering, stemantics

---
Copyright (c) Gondola