# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdXIl_vScvr
- **Gondola URL:** https://gondola.cc/posts/70577844-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/d58f572794.jpg
- **Posted:** 2026-09-16T20:29:57.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A trench blast is the most confined work in commercial blasting. A production bench has a free face standing open in front of it. A trench has only the ground surface above, so the rock has almost nowhere to go, and every kilogramme of explosive is asked to do considerably more work.

That confinement dictates the entire design.

- Powder factor climbs to roughly 1.5 to 3.0 kg per cubic metre, against 0.3 to 0.6 on an open bench
- Hole diameters stay small, generally 32 to 76 mm, with burden and spacing frequently under a metre
- Subdrilling of about 0.3 times the burden carries the break below grade so the floor lifts flat rather than humped
- A stemming column of angular crushed aggregate, roughly one burden in length, confines the gas long enough for it to work

Sequencing matters more than charge mass. Detonation drives a compressive wave through the rock at 3,000 to 6,000 m/s. That wave reflects off the free surface and returns in tension, and rock fails in tension at roughly a tenth of its compressive strength. Millisecond delays between holes, typically 8 to 25 ms, let each hole open the relief the next one needs while holding the charge weight per delay low.

Vibration is the constraint that governs everything near structures. Ground motion is predicted through the scaled distance relationship formalised by Devine, in which peak particle velocity decays with distance divided by the square root of charge weight per delay. Siskind and colleagues at the US Bureau of Mines established the modern frequency dependent limits in RI 8507 in 1980, placing the residential threshold near 12.7 mm/s at low frequency.

Flyrock is handled mechanically rather than mathematically. Mats of woven wire rope or shredded tyre are laid across the pattern, weighted with soil, and the shot fired beneath them.

Confinement is not the obstacle in a trench blast. It is the variable the whole design is written around.

#stemantics #blasting #rockmechanics #civilengineering #geotechnical

## Stats

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## Tags

geotechnical, rockmechanics, blasting, civilengineering, stemantics

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