Geology Reference
In-Depth Information
development, which will avoid the need to level the instrument, which
can be dif
cult, especially in the underground mapping of tunnels.
Data are usually collected by systematic scan-line or window sur-
veys but these are tedious to carry out, seem to be routine to the
unknowledgeable, and therefore sometimes delegated to junior staff
who may be unable or reticent to exercise independent judgement on
what is or is not signi
cant. Such surveys can give a false impression of
rigorous characterisation, whilst the important element of geological
interpretation, best done in the
field, is lacking. Experienced engineer-
ing geologists with training in structural geology should be able to
assess the rock conditions by eye, both with respect to the geological
conditions and potential for instability in a slope, and therefore can
carry out a subjective survey (
Figure 4.18).
The recommended
approach for collection and interpretation of discontinuity data from
rock exposures is set out in
Box 4-7.
Figure 4.18
Distinction
between objective
surveys (line/
window) and
(from Hencher,
1987).
SYSTEMATIC
a
b
d
g
c
f
Window survey
e
Line survey
Data collected systematically for all discontinuities
intersected along line of survey or within window
a
SUBJECTIVE
b
g
d
c
f
e
Potential for wedge and planar failures identified in field
and data collected specifically for those adverse joints
