Geotechnical Investigation

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Settlement values are subjected to a variety of factors; however, a properly designed and constructed pile should
have a serviceability settlement between 1% and 2% of its’ diameter.


8.2       TEMPORARY BATTER SLOPES
It is understood that a basement is to be constructed as part of the proposed residential dwelling. Therefore, it is
likely that temporary batter slopes will be required, with personnel working at the base of the excavations.
Near vertical temporary excavations less than 1.5 m depth in dry clay soils are likely to be suitable for short term
footing construction, excavation and construction of a basement, or installations of underground services provided
there are no sensitive services or structures, or vehicular trafficked areas located close to the excavation crest.
All excavations greater than 1.5 m depth will need to be benched or battered for stability and prior to personnel
entering the excavation.
Suitable unsurcharged temporary and permanent dry batter slopes for excavations up to 3 m in height in in stiff or
stronger clay soils can be formed at a slope of 1H:1V (short term), however should be confirmed by a geotechnical
engineer at the time of excavation. Where groundwater seepage is encountered, batter slopes will need to be
considerably flatter.


8.3       ACID SULFATE SOILS
Acid sulfate soils (ASS) are coastal and near-coastal soils, sediments or other materials containing iron sulfides.
They are environmentally benign when left undisturbed in an aqueous, anoxic environment, but when exposed to
oxygen the iron sulfides break down, releasing sulfuric acid and soluble iron. Both substances have considerable
ability to degrade the natural and built environment, and the acid may additionally mobilise other pollutants (ie.
aluminium, lead, zinc) if present in the soil.
Previous experience and available guidelines indicate that ASS are normally restricted in extent to recent
(Holocene to Pleistocene age) soil horizons deposited in a saline environment below RL 5 m.
ASS includes actual acid sulfate soils (AASS) and potential acid sulfate soils (PASS). AASS and PASS are often
found within the same soil profile, with AASS generally overlying PASS. AASS are highly acidic resulting from the
oxidation of soil materials that contained sulfides. PASS are soils that contain iron sulfides or sulfidic materials,
which have not yet been oxidised.
Based on the QASSIT guidelines, the following criteria was adopted to determine the presence of acid sulfate soils:
•   pHf of less than 4 indicates oxidation of sulfides has probably occurred in the past, indicating the presence of
    actual acidity (AASS).
• pHf between 4 and 5.5 indicates the soils are acidic. This may be as a result of limited oxidation of sulfides, but
    may also be as a consequence of the presence of organic acids.
• pHf of greater than 5.5 indicates the soil has little or no actual acidity; however this can be common with PASS
    materials or marine-influenced samples.
The pHf test method does not detect acidity bound within sulfides; however the pHfox test gives an indication of any
potential acid release. Results of the pHfox are summarised as follows:
•   pHfox of less than 3, plus a pHfox reading at least one pH unit below pHf, plus a strong reaction with peroxide,
    strongly indicates the presence of PASS.
•   pHfox between 3 and 4 indicates the possibility of PASS material and a pHfox between 4 and 5 may indicate the
    presence of small amounts of sulfide or fine carbonates.
•   pHfox of greater than 5 indicates that PASS material is unlikely.

To provide confirmation of the above qualitative testing, quantitative analytical testing was carried out on selected
samples, generally with the greatest difference in pHf and pHfox readings and strongest reaction to peroxide using
the Chromium Suite method.




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