Weathering and geotechnical characterization of Korean granites
The objectives of this research are twofold, namely
(1) to investigate the relationship between the weathering of
granite and factors such as climate, geological structure,
geomorphology, and age:
(2) to measure and interpret the geotechnical behaviour of the
Jurassic and Cretaceous granites in South Korea.
The thesis consists of four parts; Part I presents the
general description of the research objectives, location and
regional geology of the study area, and reviews of the weathering
of granite and the influence of weathering on the engineering
properties of granite. The research approach is outlined in Part
II and the nature of existing data and method of investigation
are also described. This is followed by a detailed description
of the study areas and sites. Part III analyses and discusses
the results obtained in the field and laboratory studies. In
Part IV, the integrated results from this research are summarised
with conclusions and recommendations.
Five granitic terrains (Seoul, Kwanak, Palgong, Eonyang and
Pusan) were selected for the study after careful evaluation of
Generally the weathering of these Korean granites is
dependent on the local geomorphology, extensive fracturing by
faults and joints, zones of alteration associated with hydrothermal
alteration/mineralisation, the presence of basic dykes and, on a
more local scale, minor faults. The overall weathering of Koreangranites is rather gradual, seldom showing a core stone
development. The weathering profile is also found to be much
deeper (extending down to 30 m ) in the medium grained Cretaceous
granites than in the coarse grained Jurassic granites (where it
extends to 20 m ).
Seismic refraction surveys were conducted across the top of
vertical exposures to determine the suitability of the technique
for identifying the depth of weathering at the respective
locations. The results showed that the boundaries of weathering
grades could be predicted to within 2 m of that identified
The existing criteria for the weathering description and
classification of granite as a rock material and of its mass is
based on the degree of rock discolouration, the presence or
absence of the original rock texture and the soil-rock ratio.
These criteria were examined critically when applied to the
Korean granite and were consequently amended to include
quantitative index values.
In order to understand the influence of weathering on the
geotechnical properties of Korean granite, an intensive programme
of laboratory and field tests was conducted on typical specimens
of each weathering grade, as follows:
C 1 ) six types of field index test: Schmidt hammer, point load
strength, hand penetrometer, tilt test and simple tests of
slaking and permeability.
C 2 ) nine types of laboratory index test: natural and saturated
moisture content, quick absorption, specific gravity, density,
consistency limits, particle size analysis, p - wave velocity andslake durability:
( 3 ) three types of engineering design test: unconfined compressive
strength, deformability and direct shear box. (Permeability was
not measured but existing information on its typical values for
Korean granite was collected and used).
From these tests it can be concluded that most of the index
values are very sensitive to change in weathering grade.
Engineering design tests indicate that the unconfined compressive
strength is significantly reduced and that the rock becomes
ductile with increasing weathering grade and saturation.