Dear Pat,
The true effectiveness of dynamite explosives was dependent to a large part
on how fast a hole could be drilled to put it in! Therefore the history of
drilling machines plays a significant role in the matter.
Granted dynamite expls. had a significant impact simply by their VOD over
blasting powder, but ground conditions and the expertise in their use again
plays a large part. Most serious books on Cornish mining will give you a good
idea as to the increase in ground breaking, but the main feature - always -
was the introduction of compressed air drilling machines (particularly in
driveage).
I feel, as a ballpark figure, a 30% increase was achieved with hand drilling,
and 70% by machine with driveage (average figures). Stoping is another matter
of course, but the numbers will be roughly similar.
I hope this might be of some use. Regards, Bernard
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