Geology Reference
In-Depth Information
outlined in
Figure 4.23.
Sample types are B (bulk or bag sample of the
arisings), E (environmental for contamination testing), W (water
sample) and D (small disturbed tub or jar sample, generally taken by
a split tube sampler in an SPT test). SPT results (N-values) are given in a
separate column (S5 and so on) and more details of the SPT tests are
given in a separate sheet. In this example no undisturbed samples were
taken. If they had been, they would have been reported as U (open
102 mm tube) or UT (thin-walled open drive sample) together with a
record of the number of blows taken to drive the sample (for general
information only, as the driving force from the hammer is not usually
standardised). The cable percussion driving was continued to a depth
of 8.30m, by which time the investigation had encountered weathered
Coal Measures mudstone (described as very stiff slightly sandy CLAY
with lithorelicts of the parent rock). An SPT was attempted in the
weathered rock but only penetrated 146mm (rather than 300mm)
for 50 blows of the hammer when the test was terminated, which is
standard practice in the UK. In the cable percussion section of hole,
water was encountered near the surface but then as casing was
installed the hole proceeded in the dry until the base of alluvium at
4.20m depth. Water rose in the borehole to 3.90m.
From 8.30m, the hole was advanced using rotary drilling using
water
flush with a diameter of 0.12m. Advance rates are given at the
bottom of page 1. The
first drilling run was only 0.5m, but after that
1.5m runs were adopted up to 18m when a 2m run was carried out.
Total core recovery (TCR) was not bad, generally over 80%, but from
10.50 to 12.00m 47% of core was lost (TCR = 53%). Solid Core
Recovery (SCR) is de
ned as percentage of core with full circumfer-
ence. RQD is percentage of core (on a drilling run basis
NOT rock
type) in full sticks of sound rock >100mm in length. Fracture index
(no. per metre) is also recorded. Note that core run lengths are not
consistent with geological changes
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no reason why they should be
unless the driller noted some sudden change in advance rate or loss of
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fluid perhaps, which might cause him to stop and extract the
drill string to investigate the cause. In the contractor
flushing
s own style of log,
he has chosen to split the description into general and detail columns,
which is helpful. Water was encountered in the rock at a depth of
11.10m and rose to 6.40m. When the hole was complete, a standpipe
piezometer was installed
'
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details of the installation are on the log.
Also noted is chiselling time
this is useful information for the designer
(perhaps if he is considering using driven piles) but is also a record for
payment purposes. As a comment, note that there is no attempt to
describe weathering state (the strength consequence is clearly recorded
so there is no need)
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this contrasts with the HK and Australian
examples presented later. Initials of the crew who carried out the
boring, who logged the materials and prepared the log and who
checked the whole report are given.
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