Appendix B- Geotechnical Investigation

                                                       -4-

exist between static cone and nearby borehole                GROUNDWATER
information.                                                 Where groundwater levels are measured in boreholes,
Portable Dynamic Cone Penetrometers - Portable               there are several potential problems.
Dynamic Cone Penetrometer (DCP) tests are carried            wAlthough groundwater may be present in lower
out by driving a rod into the ground with a falling weight   permeability soils, it may enter the hole slowly or
hammer and measuring the blows for successive                perhaps not at all during the time the hole is open.
100mm increments of penetration.                             wA localized perched water table may lead to an
The DCP comprises a Cone of 20 mm diameter with              erroneous indication of the true water table.
30 degree taper attached to steel rods of smaller            wWater table levels will vary from time to time with
section.                                                     seasons or recent weather changes and may not be
The cone end is driven with a 9 kg hammer falling 510        the same at the time of construction.
mm (AS. 1289 Test 6.3.2). The test was developed             wThe use of water or mud as a drilling fluid will mask
initially for pavement subgrade investigations, and          any groundwater inflow. Water has to be bailed out of
empirical correlations of the test results with California   the bore and mud must be washed out of the hole or
Bearing Ratio have been published by various Road            "reverted" if water observations are to be made.
Authorities. The Company has developed their own
                                                             More reliable measurements can be made by use of
correlations with Standard Penetration tests and
                                                             standpipes which are read after stabilizing at periods
Density Index tests in sands.
                                                             ranging from several days to perhaps weeks for low
LOGS                                                         permeability soils. Piezometers, sealed in a particular
The borehole or test pit logs presented herein are an        stratum, may be advisable in low permeability soils or
engineering and/or geological interpretation of the          where there may be interference from perched water
subsurface conditions, and their reliability will depend     tables or surface water.
to some extent on the frequency of sampling and the          FILL
method of drilling or excavation. Ideally, continuous
                                                             The presence of fill materials can often be determined
undisturbed sampling or core drilling will enable the
                                                             only by the inclusion of foreign objects (eg. bricks,
most reliable assessment but is not always practicable
                                                             steel, etc.) or by distinctly unusual colour, texture or
or possible to justify on economic grounds.        In any
                                                             fabric. Identification of the extent of fill materials will
case, the boreholes or test pits represent only a very
                                                             also depend on investigation methods and frequency.
small sample of the total subsurface conditions.
                                                             Where natural soils similar to those at the site are used
The attached explanatory notes define the terms and          for fill, it may be difficult with limited testing and
symbols used in preparation of the logs.                     sampling to reliably determine the extent of the fill.
Interpretation of the information shown on the logs,         The presence of fill materials is usually regarded with
and its application to design and construction, should       caution as the possible variation in density, strength
therefore take into account the spacing of boreholes or      and material type is much greater than with natural soil
test pits, the method of drilling or excavation, the         deposits. Consequently, there is an increased risk of
frequency of sampling and testing and the possibility of     adverse engineering characteristics or behaviour.        If
other than "straight line" variations between the            the volume and quality of fill is important to a project,
boreholes or test pits. Subsurface conditions between        then frequent test pit excavations are preferable to
boreholes or test pits may vary significantly from           boreholes.
conditions encountered at the borehole or test pit
locations.




NOTES RELATING TO THIS REPORT - SEPT 2013                                        SOIL SURVEYS ENGINEERING