Slope Stability Analysis

                                                                                                         ABN 51 640 311 842
                                                                                                         arcosgroup.com.au
                                                                                        Sunshine Coast | Brisbane | Gold Coast




1         INTRODUCTION
Arcos Unit Group Pty Ltd (Arcos Group) was commissioned to undertake a slope stability analysis for the project at
the location described on the title page of this report.
This report outlines the results of the investigation and laboratory testing by Global Testing, analysis, and interpretive
reporting on the following items:
 Review of the existing slope stability hazards, their attributed risks and impacts of the proposed development in
  alignment with the practices set out within the Australian Geomechanics Society guidelines; and,
 Provide recommendations from a geotechnical context that will avoid or reduce any potential instability.
This report must be kept in entirety. The use of this document is exclusively undertaken in accordance with our terms
and conditions.

2         REGIONAL GEOLOGY
The site is in an area underlain by Eocene aged Pomona beds, which typically comprises “shale, sandstone,
conglomerate, basalt”.

3         EXISTING STABILITY RISK
Local authorities prepare mapping tools to aid in assessing potential slope stability requirements. The mapping tools
are a “high level” approach where the site specific investigations are specific to a particular site/allotment. It is
important to note that where a site specific investigation and slope stability assessment are undertaken, they take
precedence.
Reference to the available overlays for the area show that a portion of the site has been initially mapped as
“Moderate” in terms of landslide hazard.

4         GEOTECHNICAL INVESTIGATION
A geotechnical investigation was undertaken for the development by Global Testing in May 2025. The investigation
included the drilling and sampling of six bores to a maximum depth of 4.5 m. Dynamic cone penetrometer (DCP)
testing was undertaken in each bore to provide information on the strength consistency of the subsurface. The
detailed bore log sheets are attached; however, in summary, the subsurface conditions encountered in the bores
generally comprised surficial clayey sand underlain by sandy clay, inferred to be residual soil. The strength
consistency of the sandy clay is typically firm to stiff initially, grading very stiff to hard with depth. No groundwater
seepage was observed in the bores; however, it should be noted that groundwater is transient and can fluctuate with
seasonal changes and human influences (such as broken infrastructure).

5         WALKOVER ASSESSMENT
Geotechnical comments are based on the factual findings of the investigation, best practice, local experience,
published correlations; however, are fundamentally founded in opinion and this should be considered.
The site is located on the eastern flank of the Maple Street ridge. Topographically, the surface elevation at the site
falls in a easterly direction down to Myall Street. Slopes angles range between 5° and 10°. There are no obvious
signs of recent or previous instability at the site (such as disturbed ground, tension cracks or hummocks). A variety
of vegetation ranging from small shrubs to mature trees were observed. The mature trees were all observed to be
typically vertical with no misshapen or curved trunks. Misshapen or curved trunks are usually good indicators for
previous slope instability.



Sunshine Coast | Brisbane | Gold Coast