Slope Stability Report - Site 3

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The referenced report encountered surficial topsoil and localised fill overlying residual sandy
and silty clays underlain by weathered sandstone inferred to be from the predicted geological
unit at the site. No groundwater seepage was observed in the investigation undertaken.

5.0 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.


An experienced geotechnical engineer undertook the walkover assessment on 15 December
2020. As part of the walkover assessment, 'spot' measures were taken of the slope angles and
observations pertaining the any obvious previous slope instability on the allotment and
immediately adjoining areas that were readily accessible at the time of the inspection was
undertaken. The surface levels on the site fall away to the west and east from the relatively flat
level building platform at relatively uniform grades. The eastern slope has a grade of
approximately 26°, with the western slope being around 32°. No obvious signs of disturbed
ground, tension cracks or hummocks were noted during the walkover 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. The photographs attached to
this report show the conditions of the site at the time of the inspection and assessment
undertaken.

6.0 AGS Assessment
Landslides are caused where a soil or rock mass has a decrease in strength, usually attributed
to groundwater, resulting in the material not being able to maintain its own self-weight
resulting in a slope failure.


The Australian Geomechanics Society (AGS) developed a set of tools and procedures for
assessing the stability of a slope. The tools and procedures presented with the AGS
documentation form the basis of the assessment undertaken herein and their documentation
is attached for reference.


The guidelines also identify that the regulator typically sets the standard for levels of tolerable
risk. AGS defines tolerable risk as “risks within a range that society can live with so as to secure
certain benefits. It is a range of risk regarded as non-negligible and needing to be kept under
review and reduced further if practicable”.

The guides suggest that areas of moderate or greater risk should not be developed unless a
rigorous remediation plan be implemented to reduce the area to a level of Acceptable Risk.
AGS defines acceptable risk as “risk which everyone affected is prepared to accept. Action to further

30 Nov 2020                                                               Geotechnical Investigation