Merddinemrys spotted these massive bore hole at Croes y Ddwy Afon slate mine.

I presume they date from the 1980s when the mine was being untopped rather than when it was worked as an underground operation. But why the bore holes? Woudl they have been sampling for something or is it a method of quarrying the slate?

Photograph:

🔗Croes-y-Ddwy-Afon-Slate-Mine-User-Album-Image-005[linkphoto]Croes-y-Ddwy-Afon-Slate-Mine-User-Album-Image-005[/linkphoto][/link]

---

They use drill rigs these days and bench the ground out.
It's all about tonnages.

I think they are drilled in about 4M apart for the length of the bench and 2 -3 rows deep (depends on how much they want out in one go). Big excavators are used to fill big dumpers (50 tonners). Good stone go to the sheds for splitting, bad stones/muck go over the side of the tips.

---

Im sure this is the quarry where i saw photo's of explorers boating accross the flooded pit and into an adit. Or am i mistaken?

Quite possible, although it will have been a total waste of time!

Im sure this is the quarry where i saw photo's of explorers boating accross the flooded pit and into an adit. Or am i mistaken?

Although it would have saved getting orange feet and legs :lol:

---

I'm quite proud of my tan thank you! Contemplating lying in it next time!

There's a lot of massive bore holes like this one at Burlington Quarry in Cumbria, I think they are pretty modern.

---

What diameter are the bore holes in the picture?
They remind me of old but extant bore holes at Penrhyn.

I can't remember but would guess in the region of 3-4 inches. Give or take a yard Lol.

Nationwide had a track driven drilling rig powered by a large Cummins engined compressor. The compressor was run low on oil which did a lot of damage to the engine as you can imagine. Slate was extracted mostly from the now water filled pit. There was a collapse in the addit so they had to pump the water out with a sykes pump.
The mine was reopened by a group of men that had been on strike at Gloddfa approx 1987. Was then run by Nationwide slate who also worked Foelgron accross the road. Foelgron was worked for slate as well as sand and gravel. They also worked Cwmorthin. It was they that untopped the upper part of Cwm. They worked day and night at both quarries, but closed down about 1992. On closure every building at all 3 quarries were leveled by order of the Nat. park authority. Groes as it was called had a modern steel mill. It had a modern weighbridge of which the concrete foundations remain.

---

Those seem like the drill rig holes we use at llechwedd 104mm/4" for untopping the waste rock above the pillars. what's seen here are the half-barrels left after blasting!

---

There are of course some super examples of "smooth blasting" shot holes in the A55 cutting on Rhuallt hill.

---

Might be an attempt to "pre-split" - lightly loaded charges fired simultaneously crack the rock along the line of the holes - creating an easily managed face - when conditions allow, rather than leaving the jagged unmanageable face typically associated with production blasting

---

Yep that's it - I should have said "contour" not "smooth" :confused: , which is the same thing as pre split.
Nice though isn't it?

---

Back in the old days at Burlington they drilled these long holes then used a wire threaded through the hole to slowly cut the rock out. The wire was treated to a steady application of sand slip as an abrasive.

The remains of the weighted counterbalance rigs and huge piles of rusting wire are still dotted around the site.

---

Back in '93 (old days?) saw marble being extracted in that fashion in Guangdong (PRC)

---