Appendix D Geotechnical report App · MCU18/0013

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penetration may not be practicable and the test is

discontinued at a reduced penetration.

In the case where full penetration is obtained with

successive blow counts for each 150 mm of, say 4, 6

and 7 blows, the record shows,

4,6,7 N=13

In a case where the test is discontinued short of full

penetration, say after 15 blows for the first 150 mm
and 30 blows for the next 40 mm, the record shows:

15, 30/40mm

The results of the test can be related empirically to the

engineering properties of the soil.

Occasionally, the drop hammer is used to drive 50mm

diameter thin walled sample tubes (U50) in clays. In

such circumstances, it is noted on the borehole logs.

A modification to the SPT test is where the same

driving system is used with a solid 60° tipped steel

cone of the same diameter as the SPT hollow sampler.
The solid cone can be continuously driven for some

distance in soft clays or loose sands, or may be used
where damage would otherwise occur to the SPT. The
results of this Solid SPT are shown as "N" on the
borehole logs, together with the number of blows per
450 mm penetration.
Cone Penetration Tests - Test Method - Cone
Penetration Tests (CPT) are carried out in accordance
with AS 1289 Test 6.5.1-1977, using an electrical
friction-cone penetrometer.
The test essentially comprises the measurement of
resistance to penetration of a cone of 35.7 mm
diameter pushed into the soil at a rate of 10-20 mm per
second by hydraulic force. The resistance to
penetration is recorded in terms of pressure on the end
area of the cone (cone resistance, Ge in MPa) and
friction on the side of the 435 mm long sleeve
immediately above the top of the cone (friction
resistance, f., in KPa). These forces are measured by
electrical transducers (strain gauges) within the cone
device. The ratio between friction resistance and cone
resistance is also calculated as a percentage, ie.-
Friction Ratio (FR) = eee ence a¢ GPa) clon Resistance fe (7-102
The friction ratio, FR, is generally low in sands (less
than 1% or 2%) and generally higher in clays (say 3%
or more). The interpretation of sandy clays, clayey
sands and material with a high silt content is more

difficult, but intermediate values (between 1% and 3%)
would be expected. Highly organic clays and peats
generally have a friction tatio in excess of 5%.

Static cone data is recorded in the field on disc for later
presentation using computer aided drafting.

The equipment can be operated from any conventional
drill rig. A total applied load in the range of 4 to 10
tonnes is required for practical purposes, although
lighter loads may be used. The cone penetrometers
are available with various capacities of cone resistance
ranging up to 100 MPa for general purpose
investigations, while a range of 0 to 10 MPa can be
used where more sensitive investigations of soft clay
are required.

The cone resistance value provides a continuous
measure of soil strength or density, and together with
the friction ratio, provide very useful indications of the
presence of narrow bands of geotechnically significant
layers such as thin, soft clay layers or lenses of sand
which might otherwise be missed using conventional
drilling methods.

The lithology of the encountered soils is interpreted
from static cone data and is generally presented on the
static cone log sheets.

It is important to note that the lithology is interpreted
information and is based on research by Schmertmann
(1970), Sanglerat (1972), Robinson and Campinalli
(1986), modified to suit local conditions as indicated by
borehole information and laboratory testing.

As soils generally change gradually it is sometimes
difficult to accurately describe depths of strata
changes, although greater accuracy is obtained with
the static cone compared with conventional drilling. In
addition, friction ratios decrease in accuracy with low
cone resistance values, and in desiccated soils. As a
result, some overlap and minor discrepancies may
exist between static cone and nearby borehole
information.

Portable Dynamic Cone Penetrometers - Portable
Dynamic Cone Penetrometer (DCP) tests are carried
out by driving a rod into the ground with a falling weight
hammer and measuring the blows for successive

400mm increments of penetration.

 

 

 

 

NOTEREP.SAM

SOIL SURVEYS ENGINEERING