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Mine Exploration Forum

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Author Wheal Harriett or Dolcoath
Dolcoathguy

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Joined: 21/05/2008
Location: Camborne, Cornwall

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Wheal Harriett or Dolcoath
Posted: 20/10/2012 18:31:21
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The depression in the old sump field which I have mentioned in the past, perhaps seems an inch deeper than last year, but it has been there for a few years.
It may just be a gentle subsidence, but better be safe than sorry...
Also today the local unit of the "Pengegon Parachute regiment" paid a visit to Dunkin's around 5pm today, deftly vaulting the fencing and exploring all inside for 2 mins, before coded whistles from their spotter mate as I came down the track opposite. So much for security, I think they need barbed wire!
I hung around to make sure they were not vandalising - they seemed more interested in exploring than damage.
Pics below of the suspect depression:



(click image to open full size image in new window)



(click image to open full size image in new window)








--

Is it safe to come out of the bunker yet?
IP: 89.242.54.17 Edited: 20/10/2012 18:47:32 by Dolcoathguy
stuey

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Joined: 15/08/2007

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Wheal Harriett or Dolcoath
Posted: 20/10/2012 18:41:37
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As promised. A KDC "plug"
IP: 46.208.75.221
Trewillan

Joined: 21/02/2012

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 00:19:45
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stuey wrote:



As promised. A KDC "plug"


The references to "wire mesh" worry me.

This is not and never has been the way to specify reinforced concrete!
IP: 87.113.227.129
Roy Morton

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Joined: 09/10/2007
Location: Redruth Cornwall

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 00:58:43
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I think they probably mean 150mm weld mesh and maybe not chicken wire....maybe Laugh

--

'Bid me discourse, I will enchant thine ear'
IP: 86.152.102.158
stuey

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 01:11:22
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The Carnon caps will be around long after humans are extinct.

They are very well done, in the same manner that the operation minecap jobs are not well done.
IP: 87.115.164.174
Trewillan

Joined: 21/02/2012

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 01:15:56
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Roy Morton wrote:

I think they probably mean 150mm weld mesh and maybe not chicken wire....maybe Laugh


Exactly, "probably" isn't good enough. And you know what thought did.

Standard mesh is 200mm centres isn't it? With a choice of wire diameter up to 10 mm? Which is unlikely to be adequate for a shaft cap.

Worrying to see something like that commited to print, it does appear to be a reproduction from a "proper" publication.
IP: 87.113.227.129
stuey

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 01:52:14
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Despite the mesh, whatever it may be, the caps are utterly bombproof and nothing is getting through them, ever.

The CAU report of New Shaft of wheal buller is enough to motivate any team of mine explorers to "dig under the cap" however, it would take proper machinery and time. They are really overkill. I read that after the first pour, it was common practice to use 3x the shorter dimension of the shaft in thickness. So, you are dealing with a proper plug.

Whilst they buggered up some epic trips and some unexplored history, they really did it properly.

IP: 87.115.164.174
derrickman

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 02:43:23
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I wouldn't make too much comment on rc concrete design as it isn't my speciality, but the function of the reinforcement in a concrete structure is to mitigate tension cracks.

A conical plug is only in tension across the unsupported face and given that the actual loads are not large - being mainly the a function of the diameter of the shaft and the self-weight of the plug - there is no need for a major reinforcement. The sides of the excavation serve as a constraint in themselves

--

''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.
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stuey

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 08:30:54
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When you talk about the underside being under tension, it's sat on Roy's mega mesh, which in turn is sat on 25mm or so many-ply which in turn is sat on mega RSJs.

Technically, it might be under tension, but it's not anything which would crack or even chemically change over hundreds of years.



There is a picture of an "operation minecap" plug which has been removed to replace with a proper one. You can see the conical sides and the lack of thickness, as well as the flat surface which was sat on the decking.

Back to the Dolcoath hole, I think they will be requiring either a big Cornish hedge around the area, or doing something very spectacular, expensive and complicated!
IP: 87.115.164.174
pengegon pixie

Joined: 18/10/2012

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 08:45:09
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Friend of mine tells me the Reinforcement Fabric was actually B1131. IP: 86.129.228.174
lozz

Joined: 03/08/2012
Location: Cornwall

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 10:48:14
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I wonder if the total costs incured in making safe/landscaping old workings have equalled or surpassed the profits made from these old mines......

Lozz.
IP: 109.152.79.200
Knocker

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 11:27:35
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B1131!!! That is serious mesh (12mm Bar) for no good reason.
I Very much doubt the RSJ's put in 25 years ago offer much in the way of structural integrity now (Their prime purpose was shuttering, with the cap designed to be self supporting upon failure of the shutter - hence the mesh at the base).

Stuey I expect KDCs guide is a rip of a NCB capping guide somewhere.
IP: 90.221.39.40
pengegon pixie

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 12:34:53
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Yes, first pour reinforced concrete 500-600mm was designed to hold the second pour main concrete plug, thickness depended on size of shaft. IP: 86.129.228.174
somersetminer

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Joined: 19/05/2012
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Wheal Harriett or Dolcoath
Posted: 21/10/2012 12:46:53
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Knocker wrote:

B1131!!! That is serious mesh (12mm Bar) for no good reason.


I suspect the reason is 'why entertain doubt', 1131 is the same as foundation reinforcing, Devoran (who I'm sure will be supplying the steel) are knocking this out all the time, all the load calculations are done for it, they can just bang in the cages, do the pouring and job done. and unlike the 80's jobs it will outlast all of us
IP: 90.217.81.219
agricola

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Joined: 28/10/2007
Location: In a book

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 13:10:38
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Its nice to know that Pirate FM are upto date with the news, as they mentioned this morning about the goings on in Dolcoath Avenue, only a week after it started !

On the subject of caps, I hope this cap is going to be strong as the E/W link road is planned to go over it, from the plans that I have seen, although I expect thats all changed ! Shocked

Does anyone on here know what the equivalent of making a mountain out of a mole hill is when applied to mine shafts is ?



--

If it can't be grown it has to be mined.
IP: 86.150.142.219 Edited: 21/10/2012 13:13:07 by agricola
Knocker

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 14:25:03
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A Sinkhole? IP: 90.221.39.40
Knocker

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 14:35:54
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I did hear the Pirate FM one this morning, had to laugh, what was it had to close down half a cornish housing estate? I assumed at first it was somewhere else or Dolcoath road had perhaps disappeared overnight! IP: 90.221.39.40
derrickman

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Wheal Harriett or Dolcoath
Posted: 21/10/2012 17:30:36
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agricola wrote:

Its nice to know that Pirate FM are upto date with the news, as they mentioned this morning about the goings on in Dolcoath Avenue, only a week after it started !

On the subject of caps, I hope this cap is going to be strong as the E/W link road is planned to go over it, from the plans that I have seen, although I expect thats all changed ! Shocked

Does anyone on here know what the equivalent of making a mountain out of a mole hill is when applied to mine shafts is ?



I did some work years ago, grouting up old culverted streams in Central London ... there are grouted sections in the Godstone mines where they pass under the M25.

It's quite feasible provided it is properly approached. The main problem is usually to assess where the flows have actually gone...

--

''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.
IP: 213.172.74.154
Peter Burgess

Joined: 01/07/2008
Location: Merstham. Or is it Godstone ...... ?

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Wheal Harriett or Dolcoath
Posted: 22/10/2012 09:15:17
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Not Godstone, Merstham. None of the Godstone workings pass under any motorway.


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Hé ! Ki kapcsolva le a villanyt ?
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derrickman

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Wheal Harriett or Dolcoath
Posted: 22/10/2012 16:51:15
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I picked up a few scraps about this from colleagues. The names currently applied to the workings don't seem to have been used by the designers and contractors at the time, it would be quite usual for works like that to be defined by the name of the relevant motorway contract plus chainages and/or coordinates relative to that contract survey control, or simply as a generic name plus OS coordinates.

I'm told there is a paper about this somewhere but I have no idea where to look for it.

Combe Down was the same. Fox Hill was always called Fox Hill, as far as could be determined, but most of the names of the working sections ( Byfields, Stonehouse Lane ) were derived from local names which often post-dated the workings themselves.



--

''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.
IP: 86.30.241.199 Edited: 22/10/2012 16:52:28 by derrickman
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