20220109 - Geotech · OPW23/0182

                              PROPOSED RESIDENCE
                              21 MAHER TERRACE, SUNSHINE BEACH

4.4         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 on the reports. The subsurface conditions encountered in the boreholes are
summarised as follows:

         Existing Fill (presumably uncontrolled) – comprising loose clayey sand to depths between
          0.6 m and 0.8 m BGL; then
         Residual Soils – comprising mostly medium dense clayey sand and stiff to very stiff sandy/silty
          clay of medium to high plasticity to depths between 1.2 m and 2.5 m BGL (borehole BH2
          termination depth).
         Extremely Weathered (XW) Materials/Sandstone – very dense clayey sand tending towards very
          low strength sandstone was encountered beneath the residual soils in borehole BH1 to 4 m BGL.
          The XW materials were underlain by very low strength sandstone, with auger refusal on inferred
          low strength (or stronger) sandstone at 5.4 m BGL.

We have not sighted any certification documentation regarding the existing fill, and it is taken to be
‘uncontrolled’ material in accordance with the definitions given in AS 2870-2011 Residential Slabs and
Footings.

Laboratory testing of the sample tested from borehole BH2 (1.2 to 1.5 m BGL) indicated that the material
was a sandy clay of medium to high plasticity. The laboratory test certificate is presented in Appendix B
The standalone DCP test (DCP3) undertaken to the rear of the property indicated the following subsurface
conditions:

         Firm/loose materials to 0.6 m BGL; then
         Stiff/medium dense materials to 4.4 m BGL; overlying
         Very stiff/dense (or stronger) materials to the DCP termination depth at 5.7 m BGL.

Table 1 below, summarises the subsurface profile in each borehole.
Table 1: Summary of Subsurface Profiles
                                                                                           Weathered
   Borehole No.                Fill            Residual Soils           XW Materials
                                                                                           Sandstone

          BH1                0 – 0.8               0.8 – 1.2              1.2 – 4.0        4.0 – 5.4AR


          BH2                0 – 0.6              0.6 – 2.5HR                    NE             NE

Notes: 1.        Depths noted in m BGL at time of investigation (22 June 2021)
       2.        NE denotes not encountered
       3.        AR denotes borehole terminated due to auger refusal

       4.        HR denotes borehole terminated due to hand auger refusal



Detailed descriptions of the subsurface conditions encountered in the boreholes are provided in the borehole
reports attached in Appendix A

4.5         Groundwater
No signs of groundwater seepage (‘springs’) were observed during our walk-over. Groundwater was not
encountered in the boreholes at the time of investigation.

Groundwater conditions are expected to be reflective of prevailing weather conditions and seepage may
occur at shallower depths, and at locations not previously observed, particularly following periods of
prolonged or heavy rainfall.




16 July 2021
Report No. 21236-001-Rev0                                6