RFI -Attachment 6 - Geotechnical Investigation Report CORE.pdf

Walsh Consulting Engineers




4.1           Review of Available Geological Mapping
To assist in understanding the site geotechnical conditions, a review of published geological mapping was
undertaken (refer Section 5.1). Landslide Hazard Maps are discussed in Section 7.1.

4.2           Fieldwork
Eight boreholes were drilled at the locations shown on the attached Figure 1. The fieldwork was carried out
on 25 August 2021.
Six boreholes (BH1 to BH6) were drilled using a 4WD-mounted auger rig, to depths ranging between 2 m
and 5 m BGL. Two boreholes (HA1 and HA2) were hand-augered to 1.9 m and 0.8 m BGL, respectively,
where vehicle access was not available.
Underground services at the proposed borehole locations were assessed prior to drilling, to position
boreholes away from underground services. This included a combination of ground-penetrating radar (GPR)
and electro-magnetic techniques.
Dynamic cone penetrometer (DCP) tests were carried out adjacent to/within the boreholes to assess soil
density.
The boreholes were drilled under the direction of a geotechnical engineer from Core, who logged subsurface
materials in accordance with Australian Standard AS 1726-2017 Geotechnical site investigations, directed
the field testing and sampling, and made groundwater observations during drilling. The boreholes were
backfilled on completion.
Borehole locations were recorded in the field using a handheld GPS unit and measured from site features
where possible. Ground surface elevations at borehole locations were inferred from available survey data.
Reports of Boreholes and explanatory notes are attached in Appendix A. Subsurface conditions are
discussed in Section 5.2.

4.3       Geotechnical Laboratory Testing
Selected soil samples were forwarded to a NATA-accredited laboratory for the following laboratory testing:
      ▪    Four-day soaked, single-point California Bearing Ratio (CBR) (3 No.)
      ▪    Particle size distribution (PSD) or Atterberg limits (2 No.)
      ▪    Emerson class number (1 No.)
      ▪    Aggressivity (1 No.).
Laboratory testing was conducted in accordance with the procedures described in Australian Standard
AS1289 Methods of testing soils for engineering purposes.
Test results are summarised in Table 1 below. Laboratory test certificates are attached in Appendix B.
Laboratory test results generally confirm the field soil classifications. Test results are discussed further in
Section 6.




J001390-001-R-Rev0                                   4