Geotech 95141.00.R.001

Introduction                                            •   A localised, perched water table may lead to
These notes have been provided to amplify DP's              an erroneous indication of the true water
report in regard to classification methods, field           table;
procedures and the comments section. Not all are        •   Water table levels will vary from time to time
necessarily relevant to all reports.                        with seasons or recent weather changes.
                                                            They may not be the same at the time of
DP's reports are based on information gained from           construction as are indicated in the report;
limited subsurface excavations and sampling,                and
supplemented by knowledge of local geology and          •   The use of water or mud as a drilling fluid will
experience.    For this reason, they must be                mask any groundwater inflow. Water has to
regarded as interpretive rather than factual                be blown out of the hole and drilling mud must
documents, limited to some extent by the scope of           first be washed out of the hole if water
information on which they rely.                             measurements are to be made.

                                                        More reliable measurements can be made by
Copyright                                               installing standpipes which are read at intervals
This report is the property of Douglas Partners Pty     over several days, or perhaps weeks for low
Ltd. The report may only be used for the purpose        permeability soils.    Piezometers, sealed in a
for which it was commissioned and in accordance         particular stratum, may be advisable in low
with the Conditions of Engagement for the               permeability soils or where there may be
commission supplied at the time of proposal.            interference from a perched water table.
Unauthorised use of this report in any form
whatsoever is prohibited.
                                                        Reports
                                                        The report has been prepared by qualified
Borehole and Test Pit Logs                              personnel, is based on the information obtained
The borehole and test pit logs presented in this        from field and laboratory testing, and has been
report are an engineering and/or geological             undertaken to current engineering standards of
interpretation of the subsurface conditions, and        interpretation and analysis. Where the report has
their reliability will depend to some extent on         been prepared for a specific design proposal, the
frequency of sampling and the method of drilling or     information and interpretation may not be relevant
excavation.       Ideally, continuous undisturbed       if the design proposal is changed. If this happens,
sampling or core drilling will provide the most         DP will be pleased to review the report and the
reliable assessment, but this is not always             sufficiency of the investigation work.
practicable or possible to justify on economic
grounds. In any case the boreholes and test pits        Every care is taken with the report as it relates to
represent only a very small sample of the total         interpretation of subsurface conditions, discussion
subsurface profile.                                     of geotechnical and environmental aspects, and
                                                        recommendations or suggestions for design and
Interpretation of the information and its application   construction.      However, DP cannot always
to design and construction should therefore take        anticipate or assume responsibility for:
into account the spacing of boreholes or pits, the      •    Unexpected variations in ground conditions.
frequency of sampling, and the possibility of other          The potential for this will depend partly on
than 'straight line' variations between the test             borehole or pit spacing and sampling
locations.                                                   frequency;
                                                        •    Changes in policy or interpretations of policy
                                                             by statutory authorities; or
                                                        •    The actions of contractors responding to
Groundwater
                                                             commercial pressures.
Where groundwater levels are measured in
                                                        If these occur, DP will be pleased to assist with
boreholes there are several potential problems,
                                                        investigations or advice to resolve the matter.
namely:
•   In low permeability soils groundwater may
    enter the hole very slowly or perhaps not at all
    during the time the hole is left open;




                                                                                                   July 2010