Appendix D Geotechnical report App · MCU18/0013

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The DCP comprises a Cone of 20 mm diameter with
30 degree taper attached to steel rods of smaller
section.

The cone end is driven with a 9 kg hammer falling 510
mm (AS. 1289 Test 6.3.2). The test was developed
initially for pavement subgrade investigations, and
empirical correlations of the test results with California
Bearing Ratio have been published by various Road
‘authorities. The Company has developed their own
correlations with Standard Penetration tests and
Density Index tests in sands.

LOGS

The borehole or test pit logs presented herein are an
engineering and/or geological interpretation of the
subsurface conditions, and their reliability will depend
to some extent on the frequency of sampling and the
method of drilling or excavation. Ideally, continuous
undisturbed sampling or core drilling will enable the
most reliable assessment but is not always practicable
or possible to justify on economic grounds. In any
case, the boreholes or test pits represent only a very
small sample of the total subsurface conditions.

The attached explanatory notes define the terms and
symbols used in preparation of the logs.

Interpretation of the information shown on the logs,
and its application to design and construction, should
therefore take into account the spacing of boreholes or
test pits, the method of drilling or excavation, the
frequency of sampling and testing and the possibility of
other than “straight line” variations between the
boreholes or test pits. Subsurface conditions between
boreholes or test pits may vary significantly from
conditions encountered at the borehole or test pit
locations.

GROUNDWATER

Where groundwater levels are measured in boreholes,
there are several potential problems.

«Although groundwater may be present in lower

 

permeability soils, it may enter the hole slowly or
perhaps not at all during the time the hole is open.

+A localized perched water table may lead to an
erroneous indication of the true water table.

+Water table levels will vary from time to time with
seasons or recent weather changes and may not be
the same at the time of construction.

NOTEREP.SAM

~The use of water or mud as a drilling fluid will mask
any groundwater inflow. Water has to be bailed out of
the bore and mud must be washed out of the hole or
"reverted" if water observations are to be made.

More reliable measurements can be made by use of
standpipes which are read after stabilizing at periods
ranging from several days to perhaps weeks for low
permeability soils. Piezometers, sealed in a particular
stratum, may be advisable in low permeability soils or
where there may be interference from perched water
tables or surface water.

FILL

The presence of fill materials can often be determined
only by the inclusion of foreign objects (eg. bricks,
steel, etc.) or by distinctly unusual colour, texture or
fabric. Identification of the extent of fill materials will
also depend on investigation methods and frequency.
Where natural soils similar to those at the site are used
for fill, it may be difficult with limited testing and
sampling to reliably determine the extent of the fill.
The presence of fill materials is usually regarded with
caution as the possible variation in density, strength
and material type is much greater than with natural soil
deposits. Consequently, there is an increased risk of
adverse engineering characteristics or behaviour. If
the volume and quality of fill is important to a project,
then frequent test pit excavations are preferable to
boreholes.

LABORATORY TESTING

Laboratory testing is normally carried out in
accordance with Australian Standard 4289 "Methods of
Testing Soil for Engineering Purposes". Details of the
test procedure used are given on the individual report
forms and the attached explanatory notes summarize
important aspects of the Laboratory Test Procedures
adopted.

ENGINEERING REPORTS

Engineering reports are prepared by qualified

personnel and are based on the information obtained
tation

 

and on current engineering standards of interpre’
and analysis. Where the report has been prepared for
a specific design proposal the information and
interpretation may not be relevant if the design
proposal is changed. If this happens, the Company

 

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