Reference Document - RAL25/0020 & OPW25/0194 (As Published)

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        CBRW = (DF x CBRF0.33 + (1-DF) x CBRS0.33)3

        where:       CBRW = weighted subgrade CBR (%)
                     DF = depth of fill (m)
                     CBRF = CBR of fill material (%)
                     CBRS = CBR of natural subgrade (%)

The satisfactory on-going performance of pavements is dependent on the subgrade not being
allowed to become excessively wet. To improve pavement life, it is essential that sufficient subsoil
drainage be installed in areas where there is potential for water to enter the subgrade, (ie.
adjacent to unsealed areas, table drains, landscaped areas etc).

6.9     Acid Sulfate Soils

        6.9.1    What are Acid Sulfate Soils?

Acid sulfate soils (ASS) are naturally occurring sediments and soils containing iron sulfides or
sulfidic materials, often located over extensive low-lying coastal areas, predominately below RL 5
AHD. These soils are generally found close to the natural ground surface, but may also be found
at depth within the soil profile.

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.

        6.9.2    Criteria for Evaluation of ASS

The criteria on which the results of screening tests (pH f and pHfox) were assessed as indicative of
possible AASS or PASS were based on the following:
•     pHf of less than 4 may indicate oxidation of sulfides has probably occurred in the past,
      indicating the presence of AASS. None of the samples tested returned a pH f value of less
      than 4.
•     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. Generally the
      samples tested returned pHf values of between 4.6 and 5.5.
•     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. Generally only the surficial
      samples tested from the bores returned pHf values equal or greater than 5.5.

The pHf test method does not detect acidity bound within sulfides, however the pH fox test gives
an indication of any potential acid release. Results of the pH fox 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. None of the sample tested returned
      pHfox values of less than 3.
•     pHfox between 3 and 4 indicates the possibility of PASS material and a pH fox between 4 and 5
      may indicate the presence of small amounts of sulfide or fine carbonates. All of the samples
      tested expect for one returned pHfox values of between 3 and 5.




Proposed Subdivision                                                                  237894.00.R.001.Rev0
12-14 Gympie Street, Tewantin                                                                October 2025