Re: blasting smallish tunnels in hard rock

On 06/01/2024 21:17, Richard Smith wrote:
[...]

I was in a pub in Camborne with a lot of ex (and some current) tin
miners.  Who were explaining thing like "You just stick a stick of
dynamite to it with a lump of clay and it does a job" and "No, we
couldn't use gelignite in South Crofty - too hot - the rock was at
about 80degrees - it would have gone off by itself before we finished
loading it" (that would be an "ooops") - and the sort of things kindly
Cornish ex-miners will explain over a few pints of beer.

Talking of small diameter brisant explosives for small-scale mining, how about PETN detcord?
While usually loaded at 10 g/m for transmitting trunkline shocks and directly initiating the more sensitive charges, it is also available in up to 100 g/m loading, which is about 1/2" diameter, and possibly more. It can be used up to 70C plus - one manufacturer says 107C is okay.
Not going to give you a huge face loading, but you could use fairly close-spaced 1/2" holes?
Just an idea, I have no practical experience of this, but sometimes you see detcord advertised for "pre-splitting", whatever that means.
Don't know about cost either, but I think a 50m roll of 100 or 150 g/m should be a few £100's - and will last a long time. And it can be detonated directly by standard 10g/m detcord, simple and providing a saving on detonators, though you may need delays.
You didn't say whether the tunnel is through soft rock or granite?
Peter Fairbrother