geological conditions are evidently unsuitable for highway con- e a
struction. Areas, where geotechnical problems may play a deter-
mining influence upon the construction cost are also of interest.
The geological-geotechnical photointerpretation therefore is an
important aid in this design stage.
A summation of the delimitations of terrain areas that are comp-
licated from point of view of highway construction (see fig 1)
gives an indication of the location of possible terrain corri-
dors. ,
The result of the analysis of the terrain is generally shown
in the form of limited terrain corridors (see fig 1) within
which, a number of alternative centerlines are possible. The
horizontal alignments of the centerlines are shown in outline
on a simple map or sketch together with their preliminary longi-
tudinal terrain profiles.
Aerial photographs from flying heights between 3000 m and 5000 m o ©
are generally used for the photogrammetric study of the terrain. -
Photo interpretation studies of these photographs ordinarily give
a satisfactory survey of the loading capacity and other geologi-
cal-geotechnical parameters of the terrain from the road construc-
tion point of view.
The result of the photo interpretation studies is mainly presen-
ted in the form of geological sketches of maps based on a photo-
mosaic. In some countries the photo-interpretation is made by
geological-geotechnical specialists, but in other countries the
design engineers have received so much training and experiences
in aeological-geotechnical photointerpretation, that this work
is included in the design routine. Both systems have advantages.
One advantage of training the designer in photointerpretation is
the fact, that he himself in a very natural and simple way can
get more qualitative information from the photographs without
relyinc on other experts. This psychological effect is very im- eo -
portant.
In some countries, no adequate topographical maps exist let alone
geological ones. In these areas a full airphotointerpretation may
be very valuable for the choice of the route for a road and for
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