Many thanks, Vanoord, for the info. If the rumbles appear to have been "just rumbles", any idea what they actually were?
When we were in Rhosydd last week and standing near the end of the no. 9 adit, we heard a distinct rumbling noise. For a moment I was a little apprehensive, until I remembered hearing military jets going over the area earlier in the afternoon and then deceided with a little relief, it was the noise of one of these being channeled down the adit to where we were. (I like going underground to avoid intrustive outside noises like that! 😠 )

Anyway, keeping in mind the sounds in Cwmorthin were heard apparently when there was very bad weather conditions, could they have been something to do with that? Even so, I very much doubt any outside noises would penetrate this far into Cwmorthin. However, having said that, when we were in there on a very windy day last week, I was quite surprised how draughtly it was even down on Lefel Ffrench. So if the air was being channeled through, what about sounds from outside too, if they were loud enough, eg thunder, or is this very unlikely!. :-[

I am very well aware that sounds can be very different in the underground environment in comparison to more familiar sorroundings, eg the noises made by water. What about sudden gusts of wind being channeled down tunnels and through chambers, could that cause unexpected rumbles?

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I wouldn't have thought individual gusts would be noticeable underground (far from surface) due to the averaging effects of friction through the passages, and buffering by large chambers. I would have thought that air movement would have been through pressure differentials between various entrances, although with large chambers and parallel paths each with different pressure/temperatures, I'm sure airflow in Cwmorthin is a complex business.

Robin

In my humble, I don't find 8E that worrisome - there are a lot of places in the mine that are a lot more unstable. That said, it does have potential for blocks to detach from the roof without warning, so I would probably advise against sitting there for lunch or having a nap in there.

just out of interest, which chambers are more unstable than
8E, and are they on the beaten track so to speak?
Am I right in saying that the large chambers to the west of the BVI are generally in a more stable state than those in the east towards Oakeley? This is the general impression we got at least from the well trodden areas. If so, is the rock generally better in the west of the lower back vein, in comparison to other areas?

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just out of interest, which chambers are more unstable than
8E, and are they on the beaten track so to speak?
Am I right in saying that the large chambers to the west of the BVI are generally in a more stable state than those in the east towards Oakeley? This is the general impression we got at least from the well trodden areas. If so, is the rock generally better in the west of the lower back vein, in comparison to other areas?

There's not a lot in the usually-trodden areas that has as much potential for falls as 8E, mostly because 8E is a particularly wide chamber, hence the roof has less support than usual.

If you start crawling up chambers, it's remarkable how much debris you can find!

I guess a lot of this has to do with a several factors:
- the closer to the surface you get, the less stable the rock tends to be
- the untopping in the 80s has shaken things up a lot in the top end of the mine
- the workings above Lake Level are older, so have had longer to decay
- the collapses of the 1880s (1890s?) affected the upper workings
- iirc there seemed to have been more instances of pillar-robbing in the higher workings as they were abandoned

Conversely, some of the lower workings on the Oakeley side are particularly shattered because they intersect with the area of the drop fault and the rock they pass through has been affected by the movement.

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How much of the workings are actually accessible on the Oakeley side? I know much has been lost over the years to untopping and the lower levels are flooded, but apart from that, I was wondering if there is still alot to see on the Oakeley side, as in Cwmorthin.

On my recent trip, I was quite interested in seeing more of the Oakeley workings eg, the old show mine area, but that seemed to be off our maps, so we did'nt risk going any deeper into Oakeley, and instead went over the dams back into Cwmorthin.

Where do you get if you proceed further into Oakeley along DE at the base of the compressor chamber? and what is there to see apart from the show mine area? (I am aware of the so called "bridge of death" but understand this is off the beaten track to someone like me who lacks SRT training!)

I would very much like to see some maps of Oakeley, I am familliar with maps which show their workings which go under Cwmorthin and have detailed maps of the chamber 34 incline area. (Graham Isherwood's book) but apart from that I know very little about Oakeley as such.

Can't wait for the Oakeley volumes to be released! 🙂

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Patience!

I'll come back on this later today.

Grahami

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How much of the workings are actually accessible on the Oakeley side? I know much has been lost over the years to untopping and the lower levels are flooded, but apart from that, I was wondering if there is still alot to see on the Oakeley side, as in Cwmorthin.

On my recent trip, I was quite interested in seeing more of the Oakeley workings eg, the old show mine area, but that seemed to be off our maps, so we did'nt risk going any deeper into Oakeley, and instead went over the dams back into Cwmorthin.

Where do you get if you proceed further into Oakeley along DE at the base of the compressor chamber? and what is there to see apart from the show mine area? (I am aware of the so called "bridge of death" but understand this is off the beaten track to someone like me who lacks SRT training!)

I would very much like to see some maps of Oakeley, I am familliar with maps which show their workings which go under Cwmorthin and have detailed maps of the chamber 34 incline area. (Graham Isherwood's book) but apart from that I know very little about Oakeley as such.

Can't wait for the Oakeley volumes to be released! :)

What's possible and what's permissible are two different things!

The original route along DE was partially blocked by a collapse in Chamber 29 9 (?) which has further collapsed recently and should be avoided. There may be alternative ways round, although this would require ropes.

A huge amount of the Oakeley workings have been lost due to the untopping, including some of the more notable bits such as inclines and the arched parts.

That work has also caused a lot of falls in areas adjacent to the opencast workings and consequently entirely cut off access to other parts that have not necessarily been as badly affected.

Then there's the flooding: since the cessation of pumping, the lower floors are now completely flooded, perhaps 10 floors worth.

If you're after bridges, the lower part of the Old Vein has probably the highest concentration of surviving bridges in the north Wales slate industry and you can get down there from a couple of places.

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I was just thinking to say something similar! I can illustrate what WAS there - but what IS there and what's accessible is entirely a different matter.
Thanks Vanoord.

Grahami

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What's possible and what's permissible are two different things!

The original route along DE was partially blocked by a collapse in Chamber 29 9 (?) which has further collapsed recently and should be avoided. There may be alternative ways round, although this would require ropes.

What is the current state of the collapse? Which bit has come down more. Haven't been that way in a while.. :angel:

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Best if you PM Vanord on details :smartass:

Politiks & sensitive areas. 😉

Best if you PM Vanord on details :smartass:

Politiks & sensitive areas. ;)

Very true 🙂
And it's haunted...lol

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To clarify (I hope) Vanoord's reference to bridges is to the Cwmorthin Old Vein - not Oakeley. I know it's confusing - and for a variety of reasons. Most of Oakeley's many bridges are long gone (or under very deep water) only the odd one surviving.

Map to show extent of flooding under preparation.

Grahami

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To clarify (I hope) Vanoord's reference to bridges is to the Cwmorthin Old Vein - not Oakeley. I know it's confusing - and for a variety of reasons. Most of Oakeley's many bridges are long gone (or under very deep water) only the odd one surviving.

Map to show extent of flooding under preparation.

Grahami

Sorry, yes indeed I was referring to the Cwmorthin Old Vein!

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OK - finally managed a couple of minutes free. Here is a work in progress showing the approximate extent of the Oakeley workings flooded since pumping ceased in 1968. The base plan is ca 1947-50 and was originally prepared when the Central Electricity Board was planning to dam Cwmorthin adn use it as part of a hydro scheme. The plan shows the high water level and part of the dam location.

Blue fill shows the flooding - it's only approximate as the level of water to the west was actually below G floor there.

The plan shows the Old Vein workings. Cwmorthin Back Vein is not shown, neither are the main Oakeley Back and North Vein workings (they were well above water level in any case) I'll add them in outline someday. The Oakeley New Vein is shown in outline only in red.

Don't mention inaccuracies - this not finished yet and I'll do a bit whenever I can, but I thought people ought to see it.

Obviously it is NOT any indication of what is there or accessible now. Historical use only.

Enjoy.
🔗Personal-Album-54-Image-68699[linkphoto]Personal-Album-54-Image-68699[/linkphoto][/link]


Grahami

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Many thanks for that Graham, very illustrative.

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Many thanks Graham. Was Oakeley Quarry's underground workings more extensive than Cwmorthin's, before large scale untopping took place? Is this the case even today if one includes the flooded chambers which, as I understand it, take the quarry levels down far deeper than anything in Cwmorthin.
I must admit I don't know that much about Oakeley in comparison to Cwmorthin and eagerly await your books!

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One thing, among others, I need to add to the map are the extents of the Cwmorthin Back Vein.

Regarding relative sizes extents etc. Oakeley always was greater than Cwmorthin. In the far past i.e. 1870s-80s before the great fall it was true also. The great fall led indirectly to the large scale untopping in that it brought the "tops" down and thus as was argued for many a year at the enquiry into the fall the fall contained either a lot of good slate from the broken walls which would pay for the uncovering OR so much worthless rubbish that the cost of clearing was significant!

Thomas Jones' great untopping plan of the 1890s foresaw the use of "mechanical contrivances" as well as additional inclines (which became Twr Babl and Ffridd). The great plan was not proceeded with. From then on as clearance progressed it became obvious that there was a limit to what could be cleared without further collapse. (The great fall continued on and off until 1912) Some clearance of the fall was done in chambers from underneath, in so far as that was possible, but by and large the lower open workings stayed much the same from the first world war up to the end of the old Oakeley comapny in 1968.

Work by the Ffestiniog Slate Group was concentrated at the eastern end of the open workings primarily to the north and east, where the old company had also been working. The Old vein is particularly thick here. This resulted in the gradual subsiding of the Old and New Bonc Siafft mills. The walls were cut using a mixture of traditional methods and wire sawing. McAlpines followed on this from the mid 1990s onwards, but to a larger extent cutting very much further to the north and indeed removing most of Bonc Siafft completely, it was the attempted extension of this to the west which ran into the unstable ground and ultimately brought things to a halt. They also extended their untoppings downwards by pumping the water up to the drain on G, clearing floors H and i at that end in the process. Other untopping work at the west end on the higher floors will have to wait another missive!

Cheers

Grahami

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Does anyone have any information/plans of the Oakeley back vein workings as I don't remember having seen any information about them. Are they cut off to furthur exploration?

On the subject of inaccessable areas, I remember seeing photos of unstable timbered areas of DE floor on the Oakeley side and remarks that alot of mine lies beyond shattered tunnels which pass through an unstable region (shale, I believe) between the new and old veins. I don't think that they have been explored to date, but I may be wrong.

Out of academic interest, does anyone have any old plans showing these lost areas?

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The 'lost' areas off DE are lost because they've collapsed very spectacularly!

Not sure how much work was carried out in the Back Vein at Oakeley, not a lot if I recall correctly?

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Vanoord, do you mean that the tunnels leading to the "lost areas" have completely collapsed cutting off whole areas which maybe in better condition?
That is what I understood up till now and have thus been interested in old plans which may show what lies beyond.

Have ground movements related to the proximity of the drop fault been at work or is it the fact that the tunnels just happen to penetrate a zone of bad rock in this area the main cause of the instability?

If i'ts just a band of unstable rock between the veins, it may indeed be possible that much better ground may lie beyond.
Please correct me if i've misunderstood! 🙂

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