Civil Engineering Reference
In-Depth Information
town planning. Accordingly proceedure was speeded up by recourse to angular
measurement, and the Romans developed instruments designed for purposes
of survey (Adam, chap. 1). h ese were principally the
groma
, an instrument for
observing and setting out right angles in the horizontal plane, which could be set
up at any desired point and aligned in any direction (Adam, p. 11, i gs 3, 4, 5).
And the
chorobate
, a level in the form of a long sighting bench provided with both
a water trough and a plumb bob for its horizontal adjustment (Adam, p. 18, i gs
16, 17; Vitruvius VIII, V). However neither of these instruments were in routine
use for setting out buildings.
Roman
survey-
ing
instru-
ments
15
16
B.
Principles of Setting Out
1.
Built Monuments
h e setting out on the ground to control the construction of any monumental
building project requires that basic lines and points must be marked in a per-
manent way outside the area to be covered by the building. If this is not done
then there is every likelihood that the marks set out will be destroyed, removed
or obscured before they have fuli lled their function by the building construction
they are designed to control—e.g. excavation for foundations will do away with
the line demarcating the upstanding wall faces. h us the setting out marks must
be made so that they remain available for immediate and convenient checking of
the building construction (at least until all the upstanding elements of the build-
ing have taken shape).
A simple exemplii cation of this requirement is the traditional modern practice of
setting out simple construction projects. Open work wooden frames (called sight-
ing rails) are set up at the angles and at the position of cross walls etc., arranged
a metre or two outside the further limits of the building. h ese devices stand well
above ground level and marks are made on the upper rails so that cords can be
stretched between opposite “sighting rails” to demarcate the various lines of the
building, i.e. faces or axes of the foundations, upstanding walls etc. Such in prin-
ciple is the mechanics of setting out lines of projected buildings.
Implicit in this system is the unwelcome fact that very little archaeological evi-
dence of it has ever been observed. h e marks are not designed to stand forever,
they are destroyed by later building etc.; and, in any event, it has never been a
part of excavation programs to investigate the area outside monumental buildings
to identify the setting out marks (cf Arnold, p. 11). In short this very important
subject has never been properly investigated archaeologically and little is known
about it.
Set-
ting out
control
markings
must
be out-
side the
building
limits
37
