Geology Reference
In-Depth Information
The drillhole record D2 is provided courtesy of Gammon Construction
Ltd, HK, for a hole taken to 14.78m depth. Descriptions of soil and
rock are to GCO (1988).
As for the UK example, the hole commenced with an inspection pit
to 1.50m to check for services. After that, the hole was advanced by
rotary drilling using water
flush. PX casing with an outside diameter
(OD) of 140mmwas installed to 3.50m and then HX (OD 114mm) to
6.50m at the top of rockhead, fromwhich depth the hole was uncased.
To a depth of 8.50m, an intermittent sampling strategy was adopted,
with Mazier samples and SPT tests. To 5.70m, the rock is all described
as grade V, completely decomposed granite. At 5.70m there is a 0.8m
thick basalt stratum, completely decomposed to very stiff, slightly
sandy SILT (also grade V). The basalt was sampled in an SPT test,
which gave an N-value of 91 (in the UK the test would normally have
been terminated at 50 blows).
From 6.50m, the drilling was continued using a Craelius T2-101
double-tube core barrel with an outside diameter of 101mm and core
diameter of about 84mm. The rock recovered is all described as
moderately strong or strong, moderately (grade III) or slightly decom-
posed (grade II) granite. Recovery in the rock is generally good and
RQD high. There is some information about discontinuities, their
nature, closeness and orientations, but no real detail. If this drillhole
was for a slope stability assessment, then more information would be
required, especially regarding the dip direction of the joints. If it was
for a foundation design, then such information would probably not be
necessary. Water levels have been recorded each morning and evening
but these would have been affected by the drilling process and water
flush so little can be interpreted from these data. A piezometer was
installed at a depth of 6.30m (at the basalt horizon). No details are
given on this log but probably the piezometer would have been
installed in a sand/gravel pocket extending above the basalt into the
sandy decomposed granite.
D.2 Consultant
s borehole log, Australia
The drillhole record D3 is provided courtesy of Golder Associates
(GA)/Sinclair Knight Merz, Brisbane, and with acknowledgements to
the Department of Transport and Main Roads, Queensland, for per-
mission. Only the
'
first three of seven sheets are presented. Soil and
rocks are described according to Australian Standards (1993).
Shorthand descriptors and other terms are given in sheet D3 (terms).
GA are consulting engineers responsible for investigating the site
where this borehole has been put down. It is the site of a complex
landslide so cores have been logged not only by the GI contractor (not
