I don't know if anyone has asked this before, but I was thinking about the geological aspect of bolting in slate mines, e.g. the bolting of traverses, abseils, etc. Was interested to know if anyone has placed bolts into the igneous whinstone in Cwmorthin or other slate mines in the area, and if so what the differences are between bolting an igneous rock of that nature, in comparison to slate. As a general rule, would it be harder to insert the bolts, safer, less safe, less of an issue with de-lamination of rock layers, not much difference etc.? I would be interested to know, from a geological perspective. but as with most things geological I expect it's hard to generalise!

What would the bolts which have been driven into the ceiling be going into? the “hard” above the vein?

I recall a project somewhere, where bolts where being tested but I can't remember if this was just in slate or included other rocks

On a related topic, when looking around the Cwmorthin tips I found some chunks of darkish grey rock, with an attractive compact feel, containing many small roundish or oblong white phenocrists, the matrix being smooth and not visibly crystalline – obviously igneous. Would like to find out what this is although I would describe it as a nice, if not overly dramatic example of a porphyry.

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Could be a micro gabbro or dolerite. Think there are some basic (and felsite) intrusions to the north,

Robin

shame can't post a photo :(
So if it's a dolerite, it might be related to the whinstone I mentioned above. Maybe it's the result of blasting through a whinstone dyke.
I thought it was quite nice stuff, some of the crystals catch the light and the feel is smooth almost a bit waxy. There was bits of it dumped beside the path at the top of the hill on the way up to the lake level adit. Most of it was dumped between the path and the stream, but don't particularly remember it from elsewhere. Wonder where in the mountain it came from, if it did.

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That banded white and black stuff in the opencast at Cwmorthin - "chert" it used to be called - is tough as hell though is prone at the same time to brittle fracture. But I figure you'd destroy several drill-bits just trying to get a bolt placement made - it is hard as old nails!

Amazing to think that what is basically compact volcanic ash intermixed with mud can get like that - the silica content is probably the main reason.

I have seen examples from deeper strata which are almost completely white/light grey but also hard and brittle looking with an almost metallic sheen I think this is a kind of volcanic tuff ("chert") anyway

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Having read the title I now have a Country and Western song running through my head ??

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Amazing to think that what is basically compact volcanic ash intermixed with mud can get like that - the silica content is probably the main reason.

I have seen examples from deeper strata which are almost completely white/light grey but also hard and brittle looking with an almost metallic sheen I think this is a kind of volcanic tuff ("chert") anyway

It's quite widespread - it is in Cwt y Bugail too, along with a much darker crystal tuff. All grouped within the Moelwyn/Rhiw-bach Volcanics, which were erupted before the more extensive Snowdon Volcanic Group.

If I remember I think Miles Moulding did some research into bolting slate a few years back, maybe worthwhile contacting him.

But the general rule is you can drill through the layers, but not into the layers, and instead of using compression bolts use resin anchors.

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Yes, bolting across / through the layers with resin anchors is the way to go. Bolting into the end grain of the layers risks delaminating and them pulling out.

The 'old men' bolting the bridge supports used inverted plug & feathers technique ie. expansion - the more you pull, the stronger the fix until either the hanger pull rod failed or the slate delaminated...

The quarrymens' worst enemies were these 'hards' either the whinstones or quartz. In Cwm a couple of weeks ago and was looking at some of the rock in various chambers - in a couple of chambers there were lots of thin stringy quartz veins in the walls which must have been a real problem causing massive delaminations as they worked underneath them. Walking in the intervening tunnels there were small delaminations in the walls / roof. Slaughterhouse springs to mind...

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Bolt testing...

I think this is the report referred to:

http://www.train4underground.co.uk/bolts-in-slate-testing-project/ 

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Having read the title I now have a Country and Western song running through my head ??

"Like a Whinestone Cowboy
Widing out on a horse
In a star-spangled wodeo."


....by Gwen Campbell? :lol:

Groan...... ::)

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Having read the title I now have a Country and Western song running through my head ??

"Like a Whinestone Cowboy
Widing out on a horse
In a star-spangled wodeo."


....by Gwen Campbell? :lol:

Groan...... ::)

Oh dear thought for a moment it would be a hard rock band. ideally performing in Cwmorthin ;D;D;D

Will follow up the reference on the slate bolting project 🙂

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Yes, bolting across / through the layers with resin anchors is the way to go. Bolting into the end grain of the layers risks delaminating and them pulling out.

The 'old men' bolting the bridge supports used inverted plug & feathers technique ie. expansion - the more you pull, the stronger the fix until either the hanger pull rod failed or the slate delaminated...

The quarrymens' worst enemies were these 'hards' either the whinstones or quartz. In Cwm a couple of weeks ago and was looking at some of the rock in various chambers - in a couple of chambers there were lots of thin stringy quartz veins in the walls which must have been a real problem causing massive delaminations as they worked underneath them. Walking in the intervening tunnels there were small delaminations in the walls / roof. Slaughterhouse springs to mind...

That was my thought when we first started looking at anchors in slate, but as it turns out anchors placed into the cleavage plane and those into the pillaring plane performed equally.

The big problem with slate (as with all other mines) is trying to find a big lump of solid rock to place the anchors into given the whole lot has been blasted...

Having read the title I now have a Country and Western song running through my head ??

"Like a Whinestone Cowboy
Widing out on a horse
In a star-spangled wodeo."


....by Gwen Campbell? :lol:

Groan...... ::)

:lol::lol: Do you have the earworm now?

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