Attachment 2 - Geotechnical Stability Assessment

Logs                                                   for fill, it may be difficult to reliably determine
                                                       the extent of the fill.
The borehole or test pit logs are an
interpretation of the subsurface conditions, and       Laboratory Testing
their reliability will depend to some extent on
the frequency of sampling and the method of            Laboratory testing is carried out in general
drilling or excavation.                                accordance with Australian Standard 1289
                                                       ‘Methods of Testing Soil for Engineering
Interpretation of the information shown on the         Purposes’.
logs, and its application to design and
construction, should therefore take into               Site Anomalies
account the spacing of the boreholes or test
                                                       In the event that conditions encountered on
pits, the method of drilling or excavation, the
                                                       site during construction appear to vary from
frequency of sampling and testing and the
                                                       those which were expected from the
possibility of other than “straight line” variations
                                                       information contained in the report, the
between the boreholes or test pits. Subsurface
                                                       company requests that it immediately be
conditions between boreholes or test pits may
                                                       notified. Most problems are much more readily
vary significantly from conditions encountered
                                                       resolved when conditions are exposed than at
at the borehole or test pit locations.
                                                       some later stage.
Groundwater
                                                       Review of Design
Where groundwater levels are measured in
                                                       Where major civil or structural developments
boreholes, there  are   several potential
                                                       are proposed or where only a limited
problems:
                                                       investigation has been completed or where the
         Although      groundwater        may   be    geotechnical conditions/constraints are quite
          present, in low permeability soils it may    complex, it is prudent to have a design review.
          enter the hole slowly or perhaps not at
                                                       Site Inspection
          all during the time it is left open.
         A localised perched water table may
                                                       Pacific Geotech would be pleased to provide
          lead to an erroneous indication of the
                                                       engineering        inspection services   for
          true water table.
                                                       geotechnical aspects of work to which this
         Water table levels will vary from time to
                                                       report is related:
          time with seasons or recent weather
          changes and may not be the same at           Requirements could range from:
          the time of construction.
         The use of water or mud as a drilling           i.    a site visit to confirm that conditions
          fluid will mask any groundwater inflow.               exposed are no worse than those
          Water has to be flushed from the hole                 interpreted, to
          and drilling mud must be washed out            ii.    a visit to assist the contractor or other
          of the hole or ‘reverted’ chemically if               site personnel in identifying various
          water observations are to be made.                    soil/rock types such as appropriate
More reliable measurements can be made by                       footing or pier founding depths, or
installing standpipes from which ongoing                 iii.   full time engineering present on site.
monitoring can be undertaken.

Fill

The present of fill materials can often be
determined only by the inclusion of foreign
objects (e.g. 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