Civil Engineering Reference
In-Depth Information
Figure 7.1: The different building stones.
Quarry stone has been extracted since the early Middle Ages. The work has
been by pure muscle power, chisels, sledge hammers and pickaxes as late as the
twentieth century. The stone quarryman's work is one of the least modernized,
despite the introduction of explosives and saws, flame cutting tools and other
cutting machinery.
Extraction methods
Extraction methods for various types of stone vary slightly, but the main princi-
ples are as follows.
Reconnaissance
The rock is inspected and samples are taken and tested for damp absorption,
strength, etc. It is important to split the rock without cracking it or causing it to
crumble or disintegrate. Layered and slate-like rock is the least problematic, but
the distance between splits should not be too small. Rock of the same structure is
usually evaluated by its sound when hit by a hammer, and the splinters or angu-
lar forms which split off.
Stone used to go through two further tests - for water absorption and heat
resistance. The water test involves leaving the stone in water for several days,
and checking that it does not increase in weight. To test heat resistance the rock
is placed in glowing coals and must retain its form and structure when raked out
afterwards. A good roof slate passes both tests. Another condition is that it must
not form a white film on its surface when exposed to air and moisture.
Quarrying
The surface of the rock should be cleared of trees, loose stones, earth and all other
organic matter. Holes are drilled for the charges. Placement of these holes is
