Compiled Reference Documents - OPW25/0053 (As Published)

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3. Field Work

3.1    Field Work Methods

The field work for this investigation was carried out on 24 June 2024, and comprised the drilling
of four bores (designated as Bores 4 to 8). The bore locations were set out with reference to site
features, with locations recorded afterwards using a hand-held GPS device. It is important to note
that Douglas is not a registered surveyor, hence the coordinates are considered to be
approximate. The approximate bore locations are indicated on Drawing 1 in Appendix B.

The bores were sampled using a portable Christie Soil Sampler driving a 50 mm steel sample tube
to refusal at between 1.5 m and 2.3 m depth. Dynamic cone penetrometer (DCP) and pocket
penetrometer (pp) testing was carried out to assess the relative density and strength consistency
of the subsurface conditions. On completion, the bores were observed for groundwater seepage
and then backfilled with spoil which was tamped into the holes.

The field work was undertaken by experienced geotechnical personnel who logged the bores,
collected samples for visual and tactile assessment and subsequent laboratory testing. Strata
identification was undertaken through observation of recovered samples. Field descriptions and
samples were checked by a geotechnical engineer, with the borehole logs corrected where
appropriate to reflect the available laboratory test results.

3.2    Field Work Results

The subsurface conditions encountered in the bores are described in detail on the borehole logs
in Appendix C, together with notes which define the classification methods and descriptive terms
used. The depths were measured below existing surface levels at the time of investigation.

In summary, the subsurface conditions encountered in the bores typically comprised localised fill
and clayey sand topsoil overlying residual silty sandy clay, which are further described below:
•     Fill: Relatively ‘stiff’ silty sandy clay fill and sandy gravel was encountered to 0.6 m depth in
      Bore 7.
•     Clayey Sand: Surficial clayey sand topsoil was encountered to between 0.2 m and 0.25 m
      depth in Bores 4 to 6.
•     Silty Sandy Clay: Underlying the fill in Bore 7 and the clayey sand topsoil in Bores 4 to 6, silty
      sandy clay was encountered in the bores. The strength consistency of the silty sandy clay was
      typically stiff, firm to stiff locally between 1.0 m and 1.6 m in Bore 5.

No groundwater seepage was observed in any of the bores at the time of drilling or prior to
backfilling. It should be noted however, that groundwater depths and ground moisture
conditions are affected by climatic conditions, soil permeability, drainage conditions and human
influence; and will therefore vary with time.


4. Laboratory Testing

Selected samples recovered from the bores were tested in the laboratory for engineering
properties of plasticity and particle size distribution for classification purposes. The results of this
testing are summarised in Table 1 with material test reports in Appendix D.




Proposed Retaining Wall                                                                222438.01.R.001.Rev0
10 Surfside Court, Sunshine Beach                                                             August 2024