Geology Reference
In-Depth Information
soil mechanics cheese, overlying stainless steel rock which could never
fail. This certainly indicates a lack of engineering geological thinking
and may re
ect some fundamental problems with training and the
sometimes-unhealthy compartmentalisation of geotechnics into rock
mechanics and soil mechanics. This is not just a Korean problem. As
noted in
Chapter 4,
in many situations sites are forgiving in that an
incorrect model does not inevitably lead to disaster. The geotechnical
engineer proceeds in normal fashion, ignorant of the real geological
conditions, but gets away with it. Unfortunately, this was one of those
unforgiving sites in a seriously adverse geological situation and where
a super
cial and rather poor approach to ground investigation and
modelling proved inadequate.
Cheung Road, Hong Kong
One section of Ching Cheung Road in Hong Kong has been the focus
for a series of large and unusual landslides since it was
first built in
1963 to 1967.
Figure 4.6
shows the section of road and was used
earlier to illustrate the usefulness of aerial photographs at desk study
stage.
In 1972, two major landslides occurred on Ching Cheung Road.
The HK Government engaged consultants to study the two land-
slides, partly because they were unusual in that both occurred on dry
days. The smaller of the two landslides occurred four days after a
major rainstorm, the larger ten days after the rainstorm. The investiga-
tion concentrated on a theoretical consideration of the in
ltration and
storage characteristics of the ground, but no explanation could be
given for the delayed nature of the failures. The consultant designed
the slopes to be cut back, but during the remedial works it was noted
that one of the slopes was issuing water and that movements were
occurring. A pragmatic solution was recommended to install a series of
raking drains, and this seems to have been effective in stopping the
movements. The two slopes subsequently survived effectively for sev-
eral years without any major event. In 1982, another major delayed
failure occurred on this section of the road, away from the area that
had been cut back with raking drains in the 1970s. As part of the
investigation for that failure, the early photographs were found and
interpreted showing the pre-disposing poor condition of the hillside.
The delayed nature of the failure was explained conceptually through a
delayed rise in the main groundwater table (Hencher, 1983c; Hudson &
Hencher, 1984).
Following the 1983 failures, the section of Ching Cheung Road was
selected for investigation and upgrading, as necessary under the
Landslide Preventive Measures (LPM) programme. Several boreholes
were put down, analysis conducted and a programme of cutting back
