220241.01 - 70 Blanckensee Road, BLACK MOUNTAIN - SECONDARY DWELLING - Slope Stability Report · EXE23/0033

                                                                                                       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 geotechnical investigation for the project
at the location described on the title page of this report.
This report outlines the results of the investigation, laboratory 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 the Middle Triassic aged Kin Kin Beds Formation, which typically comprises
“Strongly cleaved and commonly kinked mudstone with thin siltstone laminae; minor volcanilithic sandstone”.

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 the site has been initially mapped as “Moderate” in terms of
landslide hazard.

4         GEOTECHNICAL INVESTIGATION
A site classification investigation was undertaken by Global Testing on 23 May 2023. The purpose of the investigation
was to inform the site classification and effluent design for the proposed secondary dwelling. The investigation
comprised the drilling and logging of 5 boreholes at the location of the proposed secondary dwelling and the proposed
effluent irrigation area (refer test location plan). The subsurface conditions encountered in the boreholes generally
comprised potentially uncontrolled clayey sand fill to approximately 0.5 m depth, overlying stiff or stronger sany and
silty clays to termination of the bores at 4 m depth

5         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.
A site assessment was undertaken by a graduate geotechnical engineer on 3 July 2023. The allotment is described
as Lot 1 on RP193199 and encompasses approximately 20 000 m2. The site has been proposed to be placed in a
relatively level and clear area near the existing dwelling. Surface levels across the allotment are intially level where
the secondary dwelling is proposed at approximately RL203 (based on Noosa Council Intramaps) before falling away
to the north at angles of approximately 10 – 15 degrees to approximately RL 153. No obvious signs of disturbed
ground, tension cracks or hummocks were noted in the vicinity of the proposed residence during the assessment. 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