"millisecond-timed detonators" set me going - idea that it is possible to blast when there are buildings up above at the surface (at the surface the maximum effect is the power of one charge is timed milliseconds apart - yet at the blast location the effect for the tunneling is the sum of all blasts).
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As I understood it, the blasts are timed 0.1-0.5 Sec apart to let the rock fragments exit the central opening at 40-70 m/Sec, and the charges are large enough to fragment the rock but not so large they pulverize and pack it against the opposite wall.
I'll tread carefully - especially as I see how far I have to go and all the practical ahead of me - having just one 1.5m-deep blast-sized hole in granite to my portfolio so far...
Yes - groups timed about 0.1-0.5sec apart - broadly representing radial rings of charges.
However, in those rings there will be charges on the same "timing" and if you need to avoid the crockery on the mantlepieces in houses above bouncing you do have to have a subsequence milliseconds apart.
I am told that in Camborne/Pool/Redruth in the mining times up 'til the 1990's, even though the workings were by then hundreds of metres deep crockery rattling was just the familiar thing... Thousands worked in mining and many times that worked in something related to or supporting by mining and that was life there. The blasts were at an expected time, one infers from the following... They blasted just after the end of the day-shift - all but the blasters left, the charges were detonated and everyone left the mine while the ventilation cleared the fumes. ie. by the arrival of the night-shift of the trammers, who moved the ore to the shafts, where it was finer-crushed and loaded into skips hoisted to the surface.
Digressing into other detail:
I need to check this, but I think the stopers wrote on the "cousin jack chutes" the number of wagons-full they wanted taking away from under the working ends of the stopes, so that just the right amount of "head-height" room was left for them to continue next day shift. Given the blasted mineral takes up more volume than it occupied as solid mineral forming the lode - hence needing to create space to continue. Then the trammers could make up a full load in their train with any amount from the "cousin jack chutes" back where the stope was already cleared to full height below the next higher level. I think that nightly how-many-wagons is the writing you see on cousin jack chutes see in video of abandoned-mine explorers.
I'll tread carefully - especially as I see how far I have to go and all the practical ahead of me - having just one 1.5m-deep blast-sized hole in granite to my portfolio so far...
Yes - groups timed about 0.1-0.5sec apart - broadly representing radial rings of charges.
However, in those rings there will be charges on the same "timing" and if you need to avoid the crockery on the mantlepieces in houses above bouncing you do have to have a subsequence milliseconds apart.
I am told that in Camborne/Pool/Redruth in the mining times up 'til the 1990's, even though the workings were by then hundreds of metres deep crockery rattling was just the familiar thing... Thousands worked in mining and many times that worked in something related to or supporting by mining and that was life there. The blasts were at an expected time, one infers from the following... They blasted just after the end of the day-shift - all but the blasters left, the charges were detonated and everyone left the mine while the ventilation cleared the fumes. ie. by the arrival of the night-shift of the trammers, who moved the ore to the shafts, where it was finer-crushed and loaded into skips hoisted to the surface.
Digressing into other detail:
I need to check this, but I think the stopers wrote on the "cousin jack chutes" the number of wagons-full they wanted taking away from under the working ends of the stopes, so that just the right amount of "head-height" room was left for them to continue next day shift. Given the blasted mineral takes up more volume than it occupied as solid mineral forming the lode - hence needing to create space to continue. Then the trammers could make up a full load in their train with any amount from the "cousin jack chutes" back where the stope was already cleared to full height below the next higher level. I think that nightly how-many-wagons is the writing you see on cousin jack chutes see in video of abandoned-mine explorers.
I've got plenty more to find out about...
---------------------------- You've gone far past welding.
A few years back there was some granite blasting within about 50m of my house. They planted a seismograph next to the foundation to record the shock intensity and fired much smaller shots than later and further away. That was my only exposure to blasting practice. I caught most of the shots on video just in case.
There was no central hole and they fired all the charges simultaneously as far as I could tell. The blasts left deep pits filled with fairly large boulders under the blasting mats, which didn't move much. After they left a neighbor collected all the scrap metal and gave me a 3" drill bit with round black (carbide?) buttons. The granite here is somewhat fractured and contains many finer grained dikes.
I've seen explosives in use twice as an adolescent/teen . A guy was using half-sticks of dynamite to bust up the foundation wall of an old electric train station across the road from my childhood home . He would park a front loader in front of each charge to catch any debris from coming across the street towards the houses . The other time U&I Sugar blasted a large limestone* formation up on the mountainside above town . A large chunk of hillside jumped , and a few seconds later the shock wave hit . We were leaning against the side of a house , felt the whole house move . * The limestone was processed into lime , used in the beet sugar refining process .
I am told that in Camborne/Pool/Redruth in the mining times up 'til the 1990's, even though the workings were by then hundreds of metres deep crockery rattling was just the familiar thing...
----------------------------- This is perhaps too technical,
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it contains this: "Completely dry rocks display negligible attenuation." meaning the energy loss from blast to house may be only the geometric 1/r^2, by the inverse square law.
Thanks everyone for the amazing depth and knowledge of help you provided on this topic. While visiting family in Australia
the neighbour had worked in a gold mine in Aus. and explained some realities I was unsure about
That sent me looking / searching online and I found
As presented in
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"Thanks - Mt. Baker Mining and Metals "Opening My Gold Mine!" series" All explained there. Link to the "YouTube" "channel" where the 17 videos are. Which tell an amazing story.
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?
Is all granite. No killas (Cornish name for metamorphised sedimentary rock). Up on top of Carn Brea, hence entirely granite.
What the granite looks like can be seen in my webpage on boulder-splitting
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split sections...
I have seen vids for using these about 1/4inch cartridges to split rock in USA. Apparently won't do much if not confined, so have dispensation to be purchased without presenting explosives licence.
Thanks for detcord idea. You couldn't drill deeply at 1/2inch (clearance at 14mm)... At the 32mm of traditional Cornish drilling, could get 2m to 3m (?) - (I managed 1.5m in a few minutes).
Ah - I see - way to cheaply practice - do it in miniature - make little cubby-holes for storing tools in in the side of passageways, etc.
My instinct says one problem - with 14mm drill at longer lengths you can get, could not get water to flow down flutes to where cutting happening. Turn drillings into a harmless slurry, but also keep the drilling-tip cool doing a lot of work in this hard granite. You will be knowing - the drill-bits used in the likes of the Cornish Holman rock-drill and the American Gardner rock-drill (?) have a hole down the middle for the continuous supply of water which the rock-drill supplies.
What the granite looks like can be seen in my webpage on boulder-splitting
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split sections...
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Congratulations on your successful innovation that leaps a major hurdle.
When the corded hammer drill proved useless on granite I was lucky enough to be given the big Makita (to fix) which drills 1/2" (13mm) holes into granite adequately, and my jobs are close enough to the house to not need cordless tools for the harder slogging in granite or 1" holes in oak.
I didn't know there was an application for a close quarters masonry drill. I've used right angle drills only between house studs and under cars. The contractor bought the Makita and a long 1-1/4" bit for plumbing and wiring holes through concrete foundations. It takes spline drive bits which are becoming rare, he replaced it with SDS Plus. SDS = Steck-Dreh-Sitz, Insert-Turn-Seat.
I was thinking more like, for a person width and height tunnel, say 3x9 shots at 8" spacing, with 50cm deep holes with 40cm of 100g/m high loading detcord and 10cm stemming, connected by some low loading detcord.
Or possibly better, 15cm hldc, 10cm stemming, 15cm hldc, 10cm stemming, with a low loading detcord going past both hldc charges. Or even
8-8-8-8-8-10, if you can bear to do that.
Either no delays and only one detonator, or say divide it into four sections and use maybe three delay detonators.
That kind of cautious blasting, if it would work on the rock (it should be about right, but no guarantees), should not make too big a disturbance with aboveground at 20m. It might even be unnoticeable, even though it's a kilo of PETN.
For a hobby program.
As the tunnel isn't going to be very long - how long? one, a few, ten meters? - it shouldn't take too many shots.
Not that cheaply though; but a 50m roll of high loading detcord will get you maybe 5 to 8 shots. The low loading detcord will probably come in a much longer roll, and cost a little less.
Say £100 per shot, or a little more at 60cm of tunnel per shot.
PLEASE NOTE: I AM NOT AN EXPERT ON ROCK BLASTING
I didn't know that, specifically, though I do use through-fluid cooled drill bits from time to time. I don't know much about mining.
But I was only thinking of half a meter deep. That will still give you some rock to cart away between shots.
And if you can drill some larger diameter unfilled holes as well, so much the better. If the rock is only a few meters thick, you might drill through on the first try with a larger longer drill.
Don't know what the laws are Over There , but here in Arkansas ... I have several part-containers of Pyrodex that I've picked up here and there . Mostly yard sale stuff . My neighbor has some stumps . One in particular is right in the middle of where he wants his driveway . The plan is to drill it 1 1/2 inches and about 12-14" deep . Load about 2 ounces of Pyrodex R-S with a small charge of BP on top to ensure ignition and pack the hole with clay . We'll use cannon fuse to initiate the festivities . The objective is to split the stump into pieces he can drag out with his front-loader .
I'd like to hear how that goes. I may or may not have some knowledge of BP being easy to make firecrackers with, and Pyrodex in the same packaging becoming spinners or rockets instead of going pop.
We are blessed here with an abundance of clay ... I was talking with a guy that has some experience with this and he suggested clay as an ideal tamping medium . There's a large flat rock right next to the stump that I might lay on top too .
I like your thinking Peter. How to practice at manageable cost. That's the crucial point. Don't know what would happen. Would be interesting to find-out.
Black powder can be had - you are allowed to own muzzle-loaders here in the UK. With licencing yes; but "doable".
Whether a larger amount in the kg's could be had that way...
Black powder is used by stone masons because it will split rock without any shattering. It is on sale in bulk - but sure you would need a licence for that.
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