From historical evidence of working in the soft sandstone at Alderley, I
deduced the following was achieved by hand drilling in the later 19th
century. The quote is from our website at
http://www.derbyscc.org.uk/alderley/mining_f.htm
"Some mining records exist which show that the mining was organised on the
Cornish principle of having teams or 'pares' that contracted for particular
sections of work. The work could be sinking or raising shafts, driving
levels or stoping out the ore deposits. From the data, we can, for example,
deduce that one pare (4, 5 or 6 men and boys) could drive two fathoms of
horizontal level in the sandstone in a week. Assuming six days work, this
means two feet a day which is roughly the distance removed on each round of
firing. It suggests that it took a working day to drill the eight or nine
shotholes required, charge and fire them and muck out the debris (the
following morning). As space is restricted at the face, this would mean
each shothole taking about an hour to drill. While two of the team would be
drilling, others would be removing and stacking waste, laying track,
extending ventilation lines and, in the case of the boys, fetching and
carrying, taking messages and operating ventilation fans."
I should add that typical shotholes are triangular, about 4 ft long with 2
ft of blackpowder. There is a photo (without scale) on the bottom of page
http://www.derbyscc.org.uk/alderley/mining_2a.htm.
Hope this helps. If anyone has a better idea of speed, albeit in sandstone
not granite, I would appreciate knowing.
Regards,
Nigel Dibben
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----- Original Message -----
From: "Tony Brooks" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, November 10, 2006 7:36 PM
Subject: Re: [MINING-HISTORY] Hand Drilling rates
> David Summers is correct in saying that you can get 'short' barrels of the
> holes at the end of a longer round.
>
> The giveaway that this was a relatively modern hole is the shattering
> that
> you will see around the bottom, or toe, of the hole. This only occurs
> with
> high explosives. Any hole charged with black powder will not exhibit this
> as balck powder, which does not strictly speaking detonate, breaks
> predominately by gas pressure. The mechanism of rock breaking with high
> explosive is fundamentally different. HE on detonation sets up a fracture
> pattern around the hole - these fractures are then 'levered' open by the
> following high pressure gas in the hole.
>
> Most holes are charged leaving an uncharged collar of something a little
> less than the burden on that hole. Thus say, for example, there is a
> burden
> of one foot then there will be an uncharged collar of something similar.
> With hand drilling it is going to be a balance between a longer hole and
> therefore preportionally more hole charged against the problems of
> drilling
> longer holes and the fact that long holes do not break so well.
>
> Tony Brooks
>
>
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