Attachment 12 - Geotechnical Investigation Report

                               PROPOSED RETIREMENT DEVELOPMENT
                               MYALL STREET, COOROY

5.0       INVESTIGATION FINDINGS
5.1        Geology
The 1:100,000 scale Gympie Special Geological Map (Sheet 9445 & (part) 9545) indicates that the site is
underlain by “andesites and intrusives” of the late Traissic age Kulangor Member (pale blue stippled
shading); part of the North Arm Volcanics Group. The north of the site, in the vicinity of a mapped
watercourse, is noted to feature a covering of Quaternary age flood plain alluvium comprising “clay, silt, sand
[and] gravel.”
An extract from the relevant geological map is shown below in Text Figure 8.




                                            Alluvium




                                                                    Indicative site location




                                 Kulangor Member




Text Figure 8: Extract from Gympie Special Geology Map


5.2       Subsurface Conditions
Detailed descriptions of the subsurface conditions encountered in the boreholes are provided in the borehole
reports attached in Appendix A, along with definition sheets which describe terms and abbreviations used in
the report.
Boreholes encountered relatively consistent subsurface profiles which can be summarised as follows:

         Topsoil – brown, firm to stiff, high plasticity silty clays with organics and rootlets to around
          0.2 m BGL; overlying
         Residual Soils – mostly stiff, pale grey mottled red, high plasticity silty clays, becoming very stiff to
          hard below around 1 m BGL.
         Extremely Weathered (XW) Material/Weathered Rock – was only encountered in borehole BH13
          (south-west of the site) at 2.1 m BGL; with auger refusal being encountered at 2.3 m BGL.
          However, we note that while weathered rock was not encountered generally within the scope of the
          boreholes to 3 m BGL across the site, the presence of weathered rock cannot be discounted within
          the depth of the proposed cut earthworks (up to about 6.5 m BGL).

Possible alluvial deposits were also encountered in boreholes within the low-lying ground to the north-west,
and adjacent to the creek. These consisted of reworked stiff to very stiff residual clays, and medium dense
to dense clayey sands and gravels, to depths of about 3 m BGL, underlain by the abovementioned residual
soils.



17 May 2019
Report No. 19071-001-Rev0                                 6