Re the school class visit to a "gravel pit" and the comment about
drilling without water "because the rock was limestone".
Most of Gibraltar is made of limestone and, certainly when I was
there in 1953 in Tunnelling Troop, Royal Engineers, all drilling
was done dry -- including that in a three hundred foot long
eight foot by eight foot heading. The full round of 20 to 24 holes
was put in using a Holman Silver Three drill, hand-held ( we
had one air-leg, but it was broken ). The "master driller", a lad
from Derbyshire, formerly a fluorspar mine worker, used to
emerge at the end of the shift looking like a snowman. The
story was that, being limestone, the dust was no problem.
Certainly, it didn't seem to bother him -- it was what he had
done at home in Derbyshire, anyway!
What puzzles me is that dry drilling in limestone, and the use
of a cone crusher, should be taking place in what is called a
"gravel pit". Was this not a limestone quarry, where the rock
was crushed and screened to produce aggregate?
I would associate the term "gravel pit" with the working of
a naturally occurring alluvial sand and gravel deposit where
there was no rock to drill or crush.
Tony Brewis
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