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

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* * *: 6 6.1.1 DRYSTONE MASONRY STRUCTURES '
TERRACE WALL
OR RETAINING WALL
Description
Dry stone wall which holds in a section
of land.
Uses
Most of the terrace walls on the island
are used to create and hold in agricultural
land 'steps' (terraced fields)
although they have also been used to
hold up tracks and roads and areas of
land where snow is gathered.
Site
Farmland terrace walls are located on
slopes, in valley bottoms and on
plains with diverse morphologies (fluvial,
interfluve, karst, structural) which
have a common need to retain soil
and prevent it being lost to erosion.
Materials
Limestone is the most commonly
used type of rock in the island's terrace
walls, although they are also built
with pedra de blanquer (tanner's
stone), gypsum, sandstone, pedra
d'esmolar (grinding stone), pedra
avellanada (hazelnut stone), breccia,
compacted clays, etc.
Size
Farmland terrace walls have been
found from 3 to 242m long and between
0.5 and 6.9 m in height, and taIler
alongside roads.
Route
Terrace walls can follow a straight,
cUNed (concave or convex), winding
or angular route or be made up of different
stretches.
Basic construction features
Assentament (Seating): the first stones
laid in the trench.
Caixa (Box): space between the face
and the earth and which is filled with
rubble.
Talus or rost (Talus or slope): slant
built into the retaining wall's facing so
that it has greater resistance to the
materials it holds in.
Reblada (Rubble): small stones which
are placed behind a retaining wall's
facing or between it and the secondary
facing. It is there to improve drainage.
Paredat (Facing/Bond): set of stone
rows which make up the wall.
Coronament (Crown): method of topping
off the last row in the bond.
Accessory features
Sostreig 0 sostrada : stones laid after
the seating which are used to level off
the wall until it reaches a projection or
tree root which juts out above the
facing. Various types of arches and
lintels are used so that the wall can
continue to be built up with no risk of
collapse.
Capginya (Column): set of stones in
the facing which are laid in the form of
a pilaster and placed on top of each
other vertically, It seNes to separate
the original facing from a collapsed
and repaired section so that if with
time one part should collapse this will
not affect the rest of the wall.
Brao (Double facing): double wall
with an internal face separated from
the external one by rubble: the distance
between these two faces varies
and the top of the internal face may
even be exposed if the flat area
behind it is lower. It may extend up to
the entire height of the retaining wall
or just part of it. It increases the
strength of the wall, seNes to 'store'
excess stones and prevents agricultural
work from knocking down the
upper part.
Contrafort (Buttress): reinforcement
used in very high terrace walls; it does
this acting as a double wall which
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