Appendix B - Geotechnical Assessment · OPW23/0179

 Project No. PG-10375                                                                                                 Page | 6
 June 2023
 Ref: PG-10375, 2023-06-09, LTR VER 1
 Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville




     •     The stripped surface should be proof rolled using a vibrating roller or a large
           vibrating plate compactor (say 300kg), to identify areas of weak surficial soils
           and to compact the upper level material.
     •     The “clean” sands on site will be suitable for re-use as structural fill, provided
           material is free of organic matter and deleterious material. The silty sand and
           clays may prove difficult to re-use and should be preferentially disposed of.
     •     Imported fill should be of fair to good quality with a minimum Soaked CBR value
           of 10%, a maximum Iss=1.0% and a maximum particle size of 75mm, or a clean
           sand.
     •     All filling should be undertaken in layer thicknesses of approximately 250mm (or
           as appropriate for the compaction equipment being used). Fill should be
           compacted to a minimum dry density ratio of 75% Density Index for non-
           cohesive fill (i.e. sand).
     •     Field density testing should be carried out to check the standard of
           compaction achieved and the placement moisture content. The frequency
           and extent of testing should be as per guidelines in AS.3798-2007.

8.0 EARTHQUAKE CONSIDERATIONS

The design should consider the effects of an earthquake on the founding soils, as
outlined in AS.1170.4-2007, Part 4.

Liquefaction occurs as a result of pore pressures increasing and reducing the effective
stress to zero with consequent loss of strength.

The likelihood of liquefaction for an earthquake can be related to sand density. For
an acceleration of 0.08g, the following assessments as shown in Table 2 have been
made.

TABLE 2                EARTHQUAKE/LIQUEFACTION POTENTIAL

                   Liquefaction Potential                                                    Density Index (%)
                                                                                                    <35
                            Very Likely
                                                                                           (very loose to loose)
                                                                                                  35 – 54
                                Likely
                                                                                             (medium dense)
                                                                                                    >64
                              Unlikely
                                                                                       (medium dense to very dense)

Testing results indicated that sands that are likely to undergo liquefaction extended
to depths in the order of 2.5m to 3.0m. These materials will require removal, or
recompaction, as part of the foundation improvement works and therefore all sands
likely to undergo liquefaction will be removed from site during construction.

Reference to Section 4.2 in AS1170.4-2007, it is recommended that a site classification
of “Class Ce – shallow soil site” be adopted, in accordance with the definitions
presented in “Section 4.2 – Class Definitions”.