La pedra en sec. Materials, eines i tècniques tradicionals a les illes ...

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* 5 5.15 THE WORK i
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MAKING AN UNDERGROUND
PASSAGE
Definition
To construct a walled gallery with
drystone masonry. It is generally associated
to water collection, putting torrents,
irrigation channels and drains
underground.
Description
The underground passages can be
built in two ways: open cast mining or
underground mining. Open cast
mining is used when the gallery is not
very deep and its drystone masonry
wall is then built. In the case of deeper
underground passages, if the ground
is hard then the whole of the gallery is
dug and then the wall built from the
inside to the outside; if the ground is
soft then digging and walling is done
by stretches. In underground passages
over a certain length shafts
approximately the same distance
apart are dug to allow material to be
removed from the gallery and stones
lowered down to it.
The galleries come in a great variety
of sizes in terms of the length, width
and depth of the underground passage,
this depending on the type of
space to be covered.
The sides of the gallery are walled vertically
or with a slight inclination
towards the interior of the shaft, filling
the gap between the wall and the
earth with rubble. The gallery is
usually covered with a beamed roof or
various types of vaults (semicircular,
etc.). The beds of drains and irrigation
channels are also usually paved with
stone.
In the case of open cast mining, the
roof is made from the outside and is
finally covered with rubble and earth
until it reaches the height of the land
around it. Vaults on galleries are
usually narrow and can be built
without the use of props, although it is
necessary to use sticks in some
cases to hold up the stones before
the vault is closed. Beams and fascines
are known to have been used as
props in wider mines.
Tools required
Pick, triangular hoe, two-handled
basket, stone hoe, small stone hammer,
large stone hammer, barrow,
crowbar, lever, large hammer, mass,
sticks.