Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 371

Table 13.5 Nuclear logging

Method References Measured

parameters

Expected
information

Gamma ray log ISRM 1981,

ISRM 2006

natural emission of
gamma radiation
from the rock mass
surrounding the
borehole

clay and shale content of
sedimentary rocks, detection of
discontinuities in crystalline
rocks

Neutron-neutron log ISRM 1981,

ISRM 2006

response of the rock
mass surrounding
the borehole to
bombardment by
high-energy neutrons
(gamma radiation
or slowed-down
neutrons)

detection of fractured zones in
crystalline rocks, porosity of the
rock mass

Gamma-gamma log ISRM 1981,

ISRM 2006

response of the rock
mass surrounding
the borehole to
bombardment by
medium-energy
gamma rays (back
scattered gamma
radiation)

density of the rock mass

Table 13.6 Miscellaneous logging

Method Reference Measured

parameters

Expected
information

Caliber log ISRM 1981 average borehole

diameter

changes of lithology and
fracturing, borehole stability

Temperature log ISRM 1981 temperature of the

fluid within the
borehole

groundwater or gas flow into the
borehole

TV log ISRM 1981 intensity of the light

reflected from the
borehole wall

images of borehole walls
(Section 13.5.2)

Some geophysical logging methods are associated with considerable uncertainties that
may lead to misunderstandings and thus to misinterpretations of the results. From the
viewpoint of a civil engineer there is still a need for development with regard to the
engineering-like evaluation and representation of the results of geophysical logging.
Before one of these methods is applied, their capability should therefore be checked
with respect to their applicability to the rock formation to be investigated. In any case,
geophysical investigations must be complemented and calibrated by exploration results
obtained from drillings and other rock mass exposures.