Reference Document - OPW25 0085 (AS Published)

3.           Aims & Method of investigation
The aim of this investigation is to provide guidance regarding general geotechnical matters, such as
earthworks requirements for building works, and to address slope stability issues and on-site wastewater
management. It is understood that this report will be submitted to Noosa Council (NC) in support of a
Development Application for Reconfiguration of a Lot. The investigation and report have therefore been
designed to address the requirements of the relevant NC codes and policies. It should be noted that this
slope stability assessment only covers geotechnical matters to address relevant parts of the NC Landslide
Hazard Overlay Code and does not consider any other requirements of the Code (e.g. site aesthetics,
scenic amenity etc.).


3.1          Fieldwork
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 19 December 2024
to visually assess any indicators of slope instability. The walk-over included assessment of soil and rock
outcrops, surface drainage conditions, topography, evidence of erosion, and vegetation
coverage/condition.
This was incorporated with a subsurface investigation, which comprised the excavation of twelve test pits
(designated TP1 to TP12). The test pits were undertaken using a 5.5 tonne excavator with a toothed
bucket and ripper attachments to depths between 2.3 m and 3.2 m below ground level (BGL), across the
likely new building areas and adjacent to the new road alignment.
In situ soil strength was assessed by conducting dynamic cone penetrometer (DCP) testing from the
ground surface adjacent to the test pits when coarse grained materials were encountered. Pocket
penetrometer (PP) testing was carried out on fine grain samples recovered from the test pits and within
test pit sidewalls, where safe to enter. Disturbed samples were recovered from select test pits.
The test pits were backfilled progressively on completion, with excavation spoil left slightly mounded at
the surface. Co-ordinates were obtained using a handheld GPS unit with a recorded accuracy of ±3 m.
Test pit reports, along with explanatory notes, are presented in Appendix A. Approximate test locations
are shown in Figure 1, attached at the end of this report.


3.2          Laboratory Testing
Select soil samples were dispatched to a NATA accredited laboratory for geotechnical testing.
Laboratory testing was undertaken in accordance with Australian Standard AS1289 Methods of Testing
Soils for Engineering Purposes and comprised:
    Two Atterberg Limits tests and particle size distribution (PSD) analyses for soil classification
     purposes; and
    One (1 No.) single point, four day soaked CBR test for pavement design parameters.
Laboratory test results are discussed in Section 4.6. The laboratory test certificates are attached in
Appendix B.




Geo-Environmental Investigation for Proposed Subdivision
7 February 2025 | 24386-001-Rev0                                                                             3